# My UPS is charging my 75AH Car battery



## Jism (Nov 23, 2019)

Yes,

The battery of my car died today. I dont have a clue why but everything was dead as shit. I am lucky that the battery of the car is in the trunk and not the hood, since the key only unlocks the trunk. I removed it, attached it onto my UPS and it's slowly charging right now.






I think the charging current is around 700mah, it's a 650VA UPS. All i need is like 10Amps put into the battery for the car to start again (and let the alternator do the rest). But does the charging just stop at a certain voltage ? Or a certain current? Or will it continue untill it runs into oblivion?

I will polish the connectors afterwards with a metal brush, to make sure the contact are properly. I prefer having it fully charged and the light is currently blinking indicating it's charging. But i think it will stop at a certain voltage, correct?


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## R-T-B (Nov 23, 2019)

I don't imagine that dainty UPS battery is going to do much for you.

Ever consider investing in like, a AC car battery charger?

Anyways no, if you direct wired it, it won't "stop".  The voltages will just eventually meet in the middle between both cells, somewhere.  It might be just enough, but I doubt it.

EDIT:  Oof, I am not a good reader. You are using the UPS charging circuit!

It will push the battery up to whatever the UPS bus voltage is.  That COULD be dangerously high for your battery.  I'd take it off if it goes over 13.5v or so.


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## Jism (Nov 23, 2019)

The UPS battery is still inside the casing, just detached from it's mains. It's a 7A 13.8V or so.

So it's charing based on voltage and not current.


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## R-T-B (Nov 23, 2019)

Jism said:


> The UPS battery is still inside the casing, just detached from it's mains. It's a 7A 13.8V or so.
> 
> So it's charing based on voltage and not current.



Realized that lol.  Thought I had to be understanding something wrong and whatya know, was right!


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## hojnikb (Nov 23, 2019)

R-T-B said:


> I don't imagine that dainty UPS battery is going to do much for you.
> 
> Ever consider investing in like, a AC car battery charger?
> 
> ...



Lead acid batteries are usually charged to 14,4V (thats the cutoff voltage). So no, charging over 13,5v won't blow up the battery. Pb is pretty tolerant to overcharging (much more than li-ion for example) but obviously you'd want some control over how much you charge.

In OPs case, it's going to be fine. I wouldn't leave this setup for days, but a 15-20h charge will be fine.
But since the battery is flat, it's certainly on it's way out. Starter type batteries _really_ dont like to get fully discharged.
Charge the battery and get a new one.


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## R-T-B (Nov 23, 2019)

hojnikb said:


> So no, charging over 13,5v won't blow up the battery.



Nope, but I figured the other common UPS bus voltage over that (24V) would.  The cutoff was somewhat arbitrary, really.


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## Jism (Nov 23, 2019)

Car battery can sustain even up to 14.5V. Happens when you drive a car as well. The alternater is constantly switching in between various RPM's thus varying voltages. A charging controller inside the car or alternator makes sure the voltage is evened out for that matter. Some folks even charge their 12V battery with a 24V charger. It's possible, but just dont leave it on there too long.

I was just wondering if the 700mah (it takes longer, days even) was capable of Fully charging the 75AH thats marked on the battery. If i directly hook up the wire from and to the extra UPS battery the wires really get hot, i suspect that one battery is charging up the other and current is flowing through those wires like crazy.


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## R-T-B (Nov 23, 2019)

Jism said:


> If i directly hook up the wire from and to the extra UPS battery the wires really get hot, i suspect that one battery is charging up the other and current is flowing through those wires like crazy.



Yeah that I would not recomend at all.

What you are doing is safe, if very slow.


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## sam_86314 (Nov 23, 2019)

Just gonna throw this in...

I think some lead acid batteries (particularly non-sealed ones like car batteries) release hydrogen when charging. Could be a potential fire hazard if charging indoors?


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## Jism (Nov 23, 2019)

At 700mah? I doubt it.

There's a indicated build into the battery, supposed to lit green when it's charged. But it's all black meaning the battery is dead. If i turn on the UPS it refuses to even power ON when you pull the cord with no load lol. That voltage must be awefully low then.


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## newtekie1 (Nov 24, 2019)

Jism said:


> I am lucky that the battery of the car is in the trunk and not the hood, since the key only unlocks the trunk.



I'd be willing to bet there is a key hole hidden somewhere that unlocks the drivers door and would then let you open the hood.  It might not even be near the door.  The Corvette that I had put the key hole in the little overhang over the back license plate.



Jism said:


> and let the alternator do the rest



This is extremely hard on the alternator.  It is not recommended to charge a battery with an alternator, they are built to top off the battery a little and keep it charged, not charge a pretty well dead battery.


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## Jism (Nov 24, 2019)

So what do i do then? Keep the thing hooked to the UPS for at least 20 hours? 

No there's no secret hatch or so. It's a cabrio with a locked roof that could only be opened from either inside (trunk) using a special tool or electronically when your inside the car. The key fits into the door but it wont do anything (i.e unlock). It only unlocks the trunk where the battery is sitting at.


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## newtekie1 (Nov 24, 2019)

Jism said:


> So what do i do then? Keep the thing hooked to the UPS for at least 20 hours?



I mean, at the rate it is charging now, to get 10Ah in it, you're looking at 14+ hours anyway.

I mean, you gotta do what you gotta do. And I'd be lying if I said I've never jumped my car with a dead battery and let the alternator charge the battery from dead.  I'm just letting you, and anyone else reading, know it is bad for the alternator. So it might be time to invest in a proper battery charger.


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## Jism (Nov 24, 2019)

Since the wires got hot when i attached the UPS's internal battery, is'nt the same happening when the battery is getting charged slowly? Or is it a one way direction where current flows in and not out?


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## Zareek (Nov 24, 2019)

That is a creative way to charge your car battery. I would have just grabbed a $10 float charger from Harbor Freight myself...


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## newtekie1 (Nov 24, 2019)

Jism said:


> Since the wires got hot when i attached the UPS's internal battery, is'nt the same happening when the battery is getting charged slowly? Or is it a one way direction where current flows in and not out?



The wires got hot because when you connect two batteries that are very different voltage, they try to equalize.  So the UPS battery that was probably at 13v+ was just dumping current into the car battery that was likely a lot lower(probably below 10v).  Because there was no current limiting device in the circuit, the UPS battery was transferring energy at the maximum current it could provide, which is going to get the wires pretty darn hot.

On the other hand, the UPS had a current limiter to charge the battery a lot slower so the wires don't get hot.



Zareek said:


> That is a creative way to charge your car battery. I would have just grabbed a $10 float charger from Harbor Freight myself...



The $10 float charger from Harbor Freight might actually charge the battery slower than the UPS. The UPS is probably charging at 700 mAh, the $10 charger from HF charges at 500 mAh.


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## Jism (Nov 24, 2019)

Zareek said:


> That is a creative way to charge your car battery. I would have just grabbed a $10 float charger from Harbor Freight myself...



Haha. It is the most easiest way of charging any battery in the first place. But it was "late" and everything here is as good as closed, knowing i might need the car tomorrow.  A UPS is technically nothing more then a inverter / battery charger with a simple 7A battery put into it's housing. They are good for short power interrupts, depending on load it could run 220V for 5 up to 60 minutes.

But yes. It's not the brightest thing but it works! 



newtekie1 said:


> On the other hand, the UPS had a current limiter to charge the battery a lot slower so the wires don't get hot.



So lets say, i leave the thing for 48 ~ 72 hours on the UPS, woud'nt the battery at some point have more current then the 7A battery? And will it even continue to charge untill the thing is full or at least holds its own capacity again? Or is it fairly simple, the wires wont be running into issues since the incoming current is nothing more then 0.7A?


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## Bones (Nov 24, 2019)

newtekie1 said:


> I mean, at the rate it is charging now, to get 10Ah in it, you're looking at 14+ hours anyway.
> 
> I mean, you gotta do what you gotta do. And I'd be lying if I said I've never jumped my car with a dead battery and let the alternator charge the battery from dead.  I'm just letting you, and anyone else reading, know it is bad for the alternator. So it might be time to invest in a proper battery charger.



+1 to this.

It's not great for an alternator to charge one from flatout dead but it can be done.
A battery charger would be MUCH better to use if at all possible.
Man, I miss the days of having a generator in a vehicle - That WILL charge a battery from dead without issue and do it quickly too if the battery is good.

Anytime you have a wet cell battery, charging will generate this gas period. It's a nautral by-product of the charging process along with the battery getting warm/hot.

To clarify - A battery being warm while charging is normal and expected. 
If it's to the point you really can't leave you hands on it to pick it up or just leave them on it period, then it's a hot battery.

Noted a post above about hitting a 12v battery with 24v's, that isn't too smart either because it generates excessive hydrogen gas and the battery itself will get HOT from the extra voltage, possibly causing the battery to ignite the gas and make it blow.

I do know since it gets hotter the electrolyte inside /evaporates/boils off and could leave you with a "Dry" battery.

Another thing is excessive amperage, not voltage used in charging - That too can boil off electrolyte and cook one good.
Accidentally did that to my bike battery this past spring using a 10 amp charge rate instead of the slower 2 amp rate - I forgot to change the charge rate when I hooked it up and cooked it but good in about 2-3 hours from being dead.

If you ever see a battery that's swollen it's probrably due to overcharging, those could also blow if trying to charge it and usually are low on electrolyte too.

Now.... If it's just _slightly_ swollen it's probrably OK to top off the electrolyte level if possible and try a low amperage charge. If the battery gets really hot during the charging process it's resisting the charging and is bad - Replace it and make sure your alternator isn't overcharging the battery or you'll be replacing that one too before long.  In any case if a battery gets really hot while charging it's probrably bad, would be best to replace it.

If a battery is already hot *NEVER* connect anything to it for charging/jumping off or disconnect anything from it either, best to simply leave it until it cools then deal with it.

In my time of working on equipment in the field such as forklifts, bobcats, skid-steer loaders and such these are things I learned just by having to work with such issues.


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## Jism (Nov 24, 2019)

In a very young era in my life, i used to work with electric scooters for older people. This is kind where i got my experience with battery's from. From small ones to big industrial ones, the tech behind it is pretty cool. Apart from that, i just wondered what would happen with the wires or UPS in the first place if the battery would be charged to it's full (75AH) extend. Its proberly not going to happen since the thing would be already at the right voltage on only 1/3rd of it's current charge. but enough to start the car, head for a longer distance and charge it while it drives.

I still have no clue on why it died completely. It was just a very low voltage (9V) which makes me think i either left the radio on or something else is pulling current from the battery while not in use. Or the battery is just near to dead, that's also a possibility since there's no DATE/YEAR markings on the battery itself. Battery's for cars usually go in between 3 to 5 years. Esp in colder days (which it is now) they start lacking power.





A few hours later, there's sufficient voltage in now on which the UPS operates when i pull the mains. So it's charging. There's no heat coming off the UPS. It's a slightly warm transformer but nothing special. But for those curious on charging battery's, hell even with a PSU from a computer you could technically charge a battery up to whatever it supplies in amps on the 12V line. You need a small bridge to tweak up the voltage (13.8V instead of 12V) and its good to go.


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## delshay (Nov 24, 2019)

Has anyone here ever replaced their car battery with supercapacitor? If you have how well does it work?. I do believe you can buy them as a drop-in replacement.


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## Jism (Nov 24, 2019)

Capacitor loses their charge way faster then a car battery does.


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## delshay (Nov 24, 2019)

Jism said:


> Capacitor loses their charge way faster then a car battery does.



Just seen Grog6 posting about car battery replacement as a capacitor here https://www.techpowerup.com/forums/...ie-in-a-few-months.261350/page-2#post-4158437


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## moproblems99 (Nov 24, 2019)

Jism said:


> Car battery can sustain even up to 14.5V. Happens when you drive a car as well. The alternater is constantly switching in between various RPM's thus varying voltages. A charging controller inside the car or alternator makes sure the voltage is evened out for that matter. Some folks even charge their 12V battery with a 24V charger. It's possible, but just dont leave it on there too long.
> 
> I was just wondering if the 700mah (it takes longer, days even) was capable of Fully charging the 75AH thats marked on the battery. If i directly hook up the wire from and to the extra UPS battery the wires really get hot, i suspect that one battery is charging up the other and current is flowing through those wires like crazy.



Car batteries can sustain about to 15V on a fast bulk charge.  Many alternators put out 14.7 or above.  I also hate to brake it to you, but you are not likely starting your car with a 10AMP charge.  Your battery likely holds between 75-90A of usable juice.  You'll likely need to get 20 or more.

EDIT:  700ma is going to take forever to charge where you need it.  Likely well into the next day.


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## arbiter (Nov 24, 2019)

Zareek said:


> That is a creative way to charge your car battery. I would have just grabbed a $10 float charger from Harbor Freight myself...





newtekie1 said:


> The $10 float charger from Harbor Freight might actually charge the battery slower than the UPS. The UPS is probably charging at 700 mAh, the $10 charger from HF charges at 500 mAh.


Depending on state of charge in the battery at the start it might NOT even charge it at all and report you need a new battery. That is an issue now days with chargers that are sold these days. It relies on a computer chip to test the battery and if there is pretty much 0 volts showing it won't even try. Its nice to have an older charger laying around for those kinda days to least give a charge to the battery. I have that happen not long ago where someone left key in the "run" positon on my tractor and battery was 100% dead. Float charger wouldn't even try to charge it til i used non-computer one to give it a charge for 10-15min.



moproblems99 said:


> Car batteries can sustain about to 15V on a fast bulk charge.  Many alternators put out 14.7 or above.  I also hate to brake it to you, but you are not likely starting your car with a 10AMP charge.  Your battery likely holds between 75-90A of usable juice.  You'll likely need to get 20 or more.
> EDIT:  700ma is going to take forever to charge where you need it.  Likely well into the next day.


Depending on size of engine a car starter can draw if i remember right 100+amp's. Had battery test in a little sunfire with a 2.2liter engine and that is what their test detected when it started.


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## Jism (Nov 24, 2019)

The battery has 75AH for long term and 680A+ or so for CCA (Cold-crank-amps)

So even if it would have just 10A of current, the CCA would be around 100A which should be sufficient for a quick start. The thing does'nt take forever, it pretty much starts instant from my experience. If i would charge it for at least 24 hours it should be around 50 to 70% depending on this sheet:



			How to calculate the charge time of a car battery | Calculators
		



Car battery capacityCar battery voltage (measured)Selected amperage car chargerCharge time of a car battery75 AhAbove 12,40 V1A30 hour
I have'nt measured if it is or was 700mah, i just suspected that but it could be one amp as well on 12~13V. I do not have a multimeter around, if i could measure it i would know the definitive answer to that. But i suspect it's close to that number. Technically i could even hook it up to a PSU and start charging with that. My Antec 750W provides a 100A on 4 combined rails, it would last less then an hour or so to fully charge it at just 12V.


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## moproblems99 (Nov 24, 2019)

Jism said:


> The battery has 75AH for long term and 680A+ or so for CCA (Cold-crank-amps)
> 
> So even if it would have just 10A of current, the CCA would be around 100A which should be sufficient for a quick start. The thing does'nt take forever, it pretty much starts instant from my experience. If i would charge it for at least 24 hours it should be around 50 to 70% depending on this sheet:



Unfortunately, the rest of the electronics need to run in addition to cranking the engine.  A 20% charged battery just isn't going to be able to do all that.  Even if you get lucky and it fires right off.



Jism said:


> I have'nt measured if it is or was 700mah, i just suspected that but it could be one amp as well on 12~13V. I do not have a multimeter around, if i could measure it i would know the definitive answer to that. But i suspect it's close to that number. Technically i could even hook it up to a PSU and start charging with that. My Antec 750W provides a 100A on 4 combined rails, it would last less then an hour or so to fully charge it at just 12V.



You will blow your battery up if you try to charge it with 100A.  If your battery is only 75AH then your battery can probably "store" 50-60 amps.  You are likely going to need a good 20-25A inside that battery to start.  You'll be looking at a solid 25+ hour charging time to get there.  Additionally, driving your car around with mostly discharged battery is not good for your charging system.  Contrary to popular belief, vehicle charging systems are not designed to charge mostly discharged batteries.  They are designed to maintain batteries and top them up while the vehicle operates.


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## Jism (Nov 24, 2019)

"On combined rails" which means each rail only puts out 25A, not 100A unless you start hooking these wires up together. Calm lol. I'm not putting my PSU to that battery. Right now it's doing very well the UPS seems to run a slight load now on the battery which means it came from dead to having some current. I'll leave it up the night going and i expect a green indicator in the morning or so.

Yes i understand that dynamo's arent designed for charging or being pushed at constant full load (requirement). I think it was a 120A Dynamo or so but maybe that thing had it's best time, i dont know,. Lets see where it ends tomorrow morning and if it's a success i hope to not put it back again.

Maintaince free battery's usually have their filling holes under the plastic labeling right? Pouring in some distilled water in esp. winter periods doesnt hurt i think.


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## hat (Nov 24, 2019)

I guess that works in a pinch, but it's best to have the right tool for the job. I recently charged a dead ass battery with one of these:






						1.5 Amp Battery Maintainer | STANLEY
					

The 1.5 amp battery charger and maintainer is perfect for charging 6 volt and 12 volt batteries. You can use it to charge the batteries of RVs, motorcycles, lawn mowers, ATVs, boats or jet skis, ...




					www.stanleytools.com
				




In hindsight, I wish I would have spent a few bucks on a slightly bigger charger (even though these aren't typically used to charge batteries, but rather to maintain them... but they most certainly can be used to charge). But I got what I got and it works when I need it.


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## eidairaman1 (Nov 24, 2019)

newtekie1 said:


> I'd be willing to bet there is a key hole hidden somewhere that unlocks the drivers door and would then let you open the hood.  It might not even be near the door.  The Corvette that I had put the key hole in the little overhang over the back license plate.
> 
> 
> 
> This is extremely hard on the alternator.  It is not recommended to charge a battery with an alternator, they are built to top off the battery a little and keep it charged, not charge a pretty well dead battery.



Jump starting allows the alternator to charge it.


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## newtekie1 (Nov 24, 2019)

delshay said:


> Has anyone here ever replaced their car battery with supercapacitor? If you have how well does it work?. I do believe you can buy them as a drop-in replacement.





Jism said:


> Capacitor loses their charge way faster then a car battery does.



I remember seeing someone on youtube that did this.  He started with 6 sueprcaps that were about the size of his original battery when combined, then went to much smaller caps.  They worked great for his car when it was driven daily.  He even let it sit over the weekend, and by monday the voltage had dropped to 10v, but because of how capacitors work they were still able to start the car.

I think he later added a Lithium Ion battery to it though so he could leave the car sitting for over a week without the battery draining, or leave the car off with the radio running or whatever.

The other advantage was the supercaps charge up extremely fast. So even if they went dead, connecting even a basic low amp float charger would charge them up enough to start the car in just a few minutes and a normal 10A battery charger would charge them in seconds.



moproblems99 said:


> Unfortunately, the rest of the electronics need to run in addition to cranking the engine. A 20% charged battery just isn't going to be able to do all that. Even if you get lucky and it fires right off.



Most cars turn off a good majority of the electronics when you turn the key to the start position.



arbiter said:


> Depending on state of charge in the battery at the start it might NOT even charge it at all and report you need a new battery. That is an issue now days with chargers that are sold these days. It relies on a computer chip to test the battery and if there is pretty much 0 volts showing it won't even try. Its nice to have an older charger laying around for those kinda days to least give a charge to the battery. I have that happen not long ago where someone left key in the "run" positon on my tractor and battery was 100% dead. Float charger wouldn't even try to charge it til i used non-computer one to give it a charge for 10-15min.



The $10 float charger that HF sells isn't that sophisticated. It's basically a 15v 500 mA wall-wart with battery connectors on it.  No computers in this bad boy.  And before anyone freaks out about it being 15v, most of the storage chargers are 14.7v, and by the time you consider the loss to resistance in the tiny wires HF uses and across the battery and the little LED indicator light the voltage actually does drop to about 14.7v.



eidairaman1 said:


> Jump starting allows the alternator to charge it.



Of course it does, but that doesn't mean it's good for the alternator.  I mean, we've all done it.  And doing it every once in a while isn't likely going to kill the alternator prematurely.  But if you're one of those people that just refused to replace that bad battery, and is jumping your car like once a week because its going dead all the time, expect to be replacing your alternator soon.

I have one of these in each of my cars, and one in the garage. This just sit charging constantly and work quite well to jump start cars. I've used them on my own cars as well as saving a few other stranded people.


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## Bones (Nov 24, 2019)

moproblems99 said:


> Car batteries can sustain about to 15V on a fast bulk charge.  Many alternators put out 14.7 or above.  I also hate to brake it to you, but you are not likely starting your car with a 10AMP charge.  Your battery likely holds between 75-90A of usable juice.  You'll likely need to get 20 or more.
> 
> EDIT:  700ma is going to take forever to charge where you need it.  Likely well into the next day.



Any alternator putting out above 14.5v's to a standard automotive battery is overcharging it. They can tolerate voltage above that for a short period of time but the rule for a 12v system is 14.5v, the limit you'd want to see it go to before the regulator kicks in.
I mean if it's maybe .2 volts or so above it's still fine but there is a limit to how much is just that and 14.5v's is about right to base it on as a standard.

I will also say the above based on what is a standard equipped starting system is right but in how it is, it's also a factor. You can for example use a larger lead cable than stock with a smaller battery in CCA and have it start the engine normally without any ill-effect.

In fact this is how I solved a problem with my car eating starters.
Changed out the positive cable from battery to starter with an oversized cable and not only did it stop cooking starters but I could then use a smaller battery too.

The car had a Ford 460 bored .030 over making it a 466 CID engine and after the cable swap I could literally start it with a 450 CCA battery. It spun over faster than before too with the standard cable using an 1100 CCA battery to crank it with.
From that point onward I never had another starter cook on me.

If you ever run into a problem with staters going bad/cooking and struggling to turn the engine over, replace the starter cable from battery to starter and get as large of a cable as possible - And be sure you replace the ground lead from the battery in the same way too.


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## newtekie1 (Nov 24, 2019)

Bones said:


> Any alternator putting out above 14.5v's to a standard automotive battery is overcharging it. They can tolerate voltage above that for a short period of time but the rule for a 12v system is 14.5v, the limit you'd want to see it go to before the regulator kicks in.



Above 14.5v is not overcharging.  It's normal for an alternator to be between 14 and 15v.  And most maintenance/storage battery chargers will charge at 14.7v.


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## Jism (Nov 24, 2019)

Bones said:


> If you ever run into a problem with staters going bad/cooking and struggling to turn the engine over, replace the starter cable from battery to starter and get as large of a cable as possible - And be sure you replace the ground lead from the battery in the same way too.



I figured that out once on my RS4 B5 500HP. The grounded cable that went from the battery to the chassis suffered from corrosion on the connectors. Imagine that up to 90 amps has to flow through that wire alone. Once we replaced the wire and attached another one directly to the engine block itself any of the elecitrical issues the thing had dissapeared completely. I'm sure it helped performance as well by a small factor. Factory's usually put the basics but dont take the cars age with it over time and what once was good might be today half of what it was before.

Attached the car battery on the car again, everything worked out of the box without a dimming light anywhere. Charged very well. The culprit was the left on radio that was sipping energy for over 3 days.


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## Bones (Nov 24, 2019)

newtekie1 said:


> Above 14.5v is not overcharging.  It's normal for an alternator to be between 14 and 15v.  And most maintenance/storage battery chargers will charge at 14.7v.


I'm sorry but I must disagree to an extent.
Yes you will see _spikes_ that can go up to 15v's with the system being under a load such as with headlights and all else going but a flatout _sustained_ voltage rate of around 15v's no matter what will cook one slowly.
Not every system will regulate the same, thats why I said 14.5v was a standard. Note I did say it can be above that a little and still be fine as long as the battery wasn't showing any signs of trouble so there is leeway but 14.5 sustained without a load (Battery charging only - No lights, AC or other stuff in use) was the standard we used.


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## Jism (Nov 24, 2019)

In order for a correct charge the charging voltage has to be higher then the battery is rated for.

You can charge at lets say 12V onto a 12V battery but charging with 13.8V is better and consumes less time.

It really suprises me that the battery was as good as full after 20 hours left for charging. Car started instant.


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## Bones (Nov 24, 2019)

Jism said:


> *In order for a correct charge the charging voltage has to be higher then the battery is rated for*.
> 
> You can charge at lets say 12V onto a 12V battery but charging with 13.8V is better and consumes less time.
> 
> It really suprises me that the battery was as good as full after 20 hours left for charging. Car started instant.



Thats something we can all agree on. 

Good to hear the UPS did the trick for you but you really need a proper charger for that purpose.


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## newtekie1 (Nov 24, 2019)

Bones said:


> I'm sorry but I must disagree to an extent.
> Yes you will see _spikes_ that can go up to 15v's with the system being under a load such as with headlights and all else going but a flatout _sustained_ voltage rate of around 15v's no matter what will cook one slowly.
> Not every system will regulate the same, thats why I said 14.5v was a standard. Note I did say it can be above that a little and still be fine as long as the battery wasn't showing any signs of trouble so there is leeway but 14.5 sustained without a load (Battery charging only - No lights, AC or other stuff in use) was the standard we used.



I didn't say 15v sustained, but it is normal these days to see an alternator to output up to 15v for short times.  Especially with modern alternators that are computer controlled.  Charging for short periods at 15v will actually extend the life of the battery, it de-sulfates the battery. It's not going to cook the battery, it will cause the electrolyte to boil off over time, but even that will take quite a long time to happen at only 15v.

But you're claim was an alternator putting out over 14.5v was overcharging the battery, and that is just not true, and that's my point.  Even at 14.7v, it is not overcharging or causing any harm to the battery.  I'd say 14.8v or more for long periods of time would be overcharging the battery but even going over that for short periods of time is not just OK, but actually normal in modern cars.


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## Grog6 (Nov 24, 2019)

moproblems99 said:


> ...
> You will blow your battery up if you try to charge it with 100A.  If your battery is only 75AH then your battery can probably "store" 50-60 amps.  You are likely going to need a good 20-25A inside that battery to start.  You'll be looking at a solid 25+ hour charging time to get there.  Additionally, driving your car around with mostly discharged battery is not good for your charging system.  Contrary to popular belief, vehicle charging systems are not designed to charge mostly discharged batteries.  They are designed to maintain batteries and top them up while the vehicle operates.



This is the real issue with a partially charged battery. 

An alternator is designed to supply a bunch of current, IF the system tries to draw it.

My cars have 130A alternators, if you try to charge a dead battery with them, they will boil it, boiling acid out all over the engine and front of the car; and even worse if you're driving when it happens.

You need to measure the voltage of the battery, with the charger off, and all loads disconnected.
After some charging is should at least be 2.2V/cell or 13.2V.

You will likely find that one or more cells are bad, making the voltage lower than the 13.2V nominal voltage.
That's called a "Dead Cell", and is the way 99% of batteries die.
A cell is at least 2V, so if your battery after charging is barely reaching 12V, it's probably got a dead cell, and won't start your car.

A battery with a dead cell usually won't pass much current, so even if you get it to take a charge, it might just barely start your car.

You also need to open the caps, and fill the cells inside to the full line with Distilled Water. NOT tap water. 

They will pry off with a screwdriver, if it's not a gel cell.

You will probably find one cell much emptier than the others, this will be the bad cell.
Full it full, and charge it overnight; the charger in a UPS is meant for gel cells, so it won't hurt your battery.

I've used car batteries with UPS's before, just running 10awg cables out of the case. 
The UPS usually overheats and shuts down after an hour or so, but some of them don't mind at all.

I'll bet the battery is going to have a dead cell, unless you left the lights on, and found it before it was completely dead.
The battery voltage is the key to knowing if it's coming back.

A fully charged battery will measure almost 14V; 12V is a dead battery. Nominal charge, not full, not empty will be close to 13.2V.

Here's a good primer on batteries:





						Lead-based Batteries Information – Battery University
					

Learn about the differences within the lead acid battery family; the sealed lead acid (SLA), also known as gel cell, and the valve-regulated lead acid (VRLA).



					batteryuniversity.com
				




To the guy that keeps bringing up capacitors: you only get one shot to try to start your car with a cap, then all the charge is gone, along with the other problems.
If it's a motorcycle you can push to start, it's not as much of a problem, and saves a bunch or weight.



newtekie1 said:


> I didn't say 15v sustained, but it is normal these days to see an alternator to output up to 15v for short times.  Especially with modern alternators that are computer controlled.  Charging for short periods at 15v will actually extend the life of the battery, it de-sulfates the battery. It's not going to cook the battery, it will cause the electrolyte to boil off over time, but even that will take quite a long time to happen at only 15v.
> 
> But you're claim was an alternator putting out over 14.5v was overcharging the battery, and that is just not true, and that's my point.  Even at 14.7v, it is not overcharging or causing any harm to the battery.  I'd say 14.8v or more for long periods of time would be overcharging the battery but even going over that for short periods of time is not just OK, but actually normal in modern cars.



If your alternator is putting out that much voltage, and it's over ~60F outside, it's overcharging, and will boil your battery.
13.8 is low rate charging, and 14.4 is high rate charging, for 77F or 25C.

To high of a charging rate just turns the water to hydrogen, and boils the electrolyte.


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## Jism (Nov 24, 2019)

Bones said:


> Thats something we can all agree on.
> 
> Good to hear the UPS did the trick for you but you really need a proper charger for that purpose.



Yeah i know and i realise that. But i normally dont have or need a additional car battery charger in the first place. A good battery / car / alternator can hold the setup for at least 3 years even in the winters. So there's no real need (the winter here in portugal is around 0 degrees and not -10 to -20 in holland sometimes) for a external charger keeping the battery fit.

I could have asked for a jumpstart, required me to drive a good amount to have the battery at least at acceptable levels, or be smart and practical and just wind the car battery onto a UPS which is technically a slow charger and does the job as well. This was caused by myself by leaving on the radio. Apparently it sipped power together with the amplifier for the subwoofer build into the car and do that for 3 days and it's gone. It explained the super low voltage upon testing.

So for anybody looking for a quick charger, pretty much almost anything supplying DC 12V ~ 14V does the trick. Depending on amperage it charges with it varies from a few hours to even a few days for a full charge. I left it on for 20 hours which would be perhaps half of it's power rating. Not even sure, but it started without a glitch.


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## newtekie1 (Nov 24, 2019)

Jism said:


> Yeah i know and i realise that. But i normally dont have or need a additional car battery charger in the first place. A good battery / car / alternator can hold the setup for at least 3 years even in the winters. So there's no real need (the winter here in portugal is around 0 degrees and not -10 to -20 in holland sometimes) for a external charger keeping the battery fit.
> 
> I could have asked for a jumpstart, required me to drive a good amount to have the battery at least at acceptable levels, or be smart and practical and just wind the car battery onto a UPS which is technically a slow charger and does the job as well. This was caused by myself by leaving on the radio. Apparently it sipped power together with the amplifier for the subwoofer build into the car and do that for 3 days and it's gone. It explained the super low voltage upon testing.
> 
> So for anybody looking for a quick charger, pretty much almost anything supplying DC 12V ~ 14V does the trick. Depending on amperage it charges with it varies from a few hours to even a few days for a full charge. I left it on for 20 hours which would be perhaps half of it's power rating. Not even sure, but it started without a glitch.



Alternatively, grab a cheap Lithium-Ion booster pack that you can use to jump start your car with.  They are about $35 here in the States these days, plus they usually have USB outputs so you can charge your phone with them and such.  They're really handy.



Grog6 said:


> If your alternator is putting out that much voltage, and it's over ~60F outside, it's overcharging, and will boil your battery.
> 13.8 is low rate charging, and 14.4 is high rate charging, for 77F or 25C.
> 
> To high of a charging rate just turns the water to hydrogen, and boils the electrolyte.



It's funny how people just repeat what I said.  Yes, it is boiling the electrolyte, but it is doing it extremely slowly.  And like I said, winter float chargers tend to output 14.7v, and I've left batteries connected to them for a solid 4 months straight in a heated garage and had no noticeable loss of electrolyte.

I'll say it one more time, and then I'm done.  My point was that the statement that anything over 14.5v is overcharging is wrong.  The fact is up to 14.7v is acceptable and not considered overcharging.  And modern computer controlled alternators will charge at 15v for short periods of time to de-sulfate the battery.  Yes, it boils electrolyte, but not that fast.


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## moproblems99 (Nov 24, 2019)

newtekie1 said:


> Most cars turn off a good majority of the electronics when you turn the key to the start position.



Well, you still need, the injectors, the fuel pump, ignition coils, most of the modules.  It's many of the high current devices.



Bones said:


> Any alternator putting out above 14.5v's to a standard automotive battery is overcharging it. They can tolerate voltage above that for a short period of time but the rule for a 12v system is 14.5v, the limit you'd want to see it go to before the regulator kicks in.
> I mean if it's maybe .2 volts or so above it's still fine but there is a limit to how much is just that and 14.5v's is about right to base it on as a standard.



There are many different states of battery charge each with different voltage and amperage requirements.  Some stages are low voltage while some are high voltage.  Some are low amperage and some are high amperage.  Smart charges manage all of this for optimum charges.  Smart chargers will charge at more than 14.5V and it isn't overcharging.

Source:  My 7 years as an ASE master certified technician.


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## Jism (Nov 24, 2019)

Those things only put high load when you put it to work for a 100%, not idling or normal city driving.


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## moproblems99 (Nov 24, 2019)

Jism said:


> Those things only put high load when you put it to work for a 100%, not idling or normal city driving.



?


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## Jism (Nov 24, 2019)

> Well, you still need, the injectors, the fuel pump, ignition coils, most of the modules. It's many of the high current devices.



You make it sound like these parts are on constant max duty cycle (and thus consuming max load) which is'nt really true.










Here's my older RS4 B5 with ~ 500HP. The battery light blinked when going full power. It was'nt a power problem related to alternator or battery, but the charge controller which slowly got toast on the alternator itself. In normal use this woud'nt appear. Performance was'nt affected either, the weird behaviour of the charge controller just caused a notice on dash.


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## Bones (Nov 24, 2019)

moproblems99 said:


> Well, you still need, the injectors, the fuel pump, ignition coils, most of the modules.  It's many of the high current devices.
> 
> 
> 
> ...



You made a good point which to an extent validates what I said.

I was going by the standard I was taught in shop where I was working and have to agree there are different standards between places and the like. It's true what I was working on was more of the industrial/heavy equipment side of it instead of the automotive side but I've done auto too before - Not as much as you but I've been there before.

A smart charger can do that because (If I'm not mistaken here ) it uses a "Pulse" type of charging rather than a continuous DC feed of power to the battery. Now, I could be wrong about the ones for auto but that's what we had for those industrial batteries.
Had those in the shop and warehouse for charging the really big batteries for forklifts (24, 36 and 48 volt) and they did charge those up quickly, used a higher voltage as you said but because it was a pulse type of charge it didn't hurt them at all.

Had done such for over 20 years in the field and shop myself, never had any complaints over what I did concerning all that.

Just shows there are different standards out there and with all this proves just that as how it is.
As long as the battery is getting charged, nothing is getting damaged or destroyed on the process it works.

I'll also say I don't know everything either and still learning because if I did know it all, I would be in serious trouble.


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## moproblems99 (Nov 24, 2019)

Bones said:


> You made a good point which to an extent validates what I said.
> 
> I was going by the standard I was taught in shop where I was working and have to agree there are different standards between places and the like. It's true what I was working on was more of the industrial/heavy equipment side of it instead of the automotive side but I've done auto too before - Not as much as you but I've been there before.
> 
> ...



Newtekie hit on why the over 15V charging happens which is to attempt to reverse any sulfation that has happend from typical undercharged batteries but it happens at very low amperage (less than .5A).  Bulk charging is done at lower voltages (about 13.5V) and higher amperage.  The last  10% of charge or so works at an elevated voltage and reduced voltage.  Then the desulfation routine kicks in.

In theory, everyone is right.  15V is on the high end but it will still work.  Alternators usually top out in the 14.7 or 14.8 range.



Jism said:


> You make it sound like these parts are on constant max duty cycle (and thus consuming max load) which is'nt really true.



I didn't imply they are on constant duty cycle but these still draw lots of juice.  Specifically fuel pumps as many are not variable speed and do run full duty cycle.  However, you also have to take into account the context of the situation.  Trying to start a car on a 20% charge.  Any extra power use is a problem.


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## Bones (Nov 24, 2019)

moproblems99 said:


> Newtekie hit on why the over 15V charging happens which is to attempt to reverse any sulfation that has happend from typical undercharged batteries but it happens at very low amperage (less than .5A).  Bulk charging is done at lower voltages (about 13.5V) and higher amperage.  The last  10% of charge or so works at an elevated voltage and reduced voltage.  Then the desulfation routine kicks in.
> 
> In theory, everyone is right.  15V is on the high end but it will still work.  Alternators usually top out in the 14.7 or 14.8 range.
> 
> ...



I can see Newtekie's point being plausible related to desulfication, it definitely helps with that potential issue. Where they normally top out as a norm is about what I was getting at, 14.5v's was the standard we used for a regular auto type battery _without a load_, no headlights, AC or other things in use when charging was checked. For an auto 15v's with such in use is plausible, no doubt if checked with all that going on, if the charging voltage _stays_ there all the time or even higher is when it's a potential problem.

Between all of us we've seen "Wet" looking batteries that got hot and started seeping at the top, bulging.... You know what I mean. That happens too with industrial batteries and we kept an eye out for such going on because when one of those decides to go "Boom", it's not pretty and we've had a few do it before. The steel encased batteries didn't bulge, they just got really wet on top and that was a sign the battery wasn't so healthy anymore or maybe a charger wasn't acting right.
I know a regular auto battery can literally blow the hood open on a vehicle when it goes - I've seen it before and undoubtedly you have too.


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## moproblems99 (Nov 24, 2019)

Bones said:


> I can see Newtekie's point being plausible related to desulfication, it definitely helps with that potential issue. Where they normally top out as a norm is about what I was getting at, 14.5v's was the standard we used for a regular auto type battery _without a load_, no headlights, AC or other things in use when charging was checked. For an auto 15v's with such in use is plausible, no doubt if checked with all that going on, if the charging voltage _stays_ there all the time or even higher is when it's a potential problem.
> 
> Between all of us we've seen "Wet" looking batteries that got hot and started seeping at the top, bulging.... You know what I mean. That happens too with industrial batteries and we kept an eye out for such going on because when one of those decides to go "Boom", it's not pretty and we've had a few do it before. The steel encased batteries didn't bulge, they just got really wet on top and that was a sign the battery wasn't so healthy anymore or maybe a charger wasn't acting right.
> I know a regular auto battery can literally blow the hood open on a vehicle when it goes - I've seen it before and undoubtedly you have too.



Definitely not pretty or fun to be around.  Overvolting and overamping can both do that.


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## Bones (Nov 24, 2019)

Reminds me of the time we had one blow that was to the fire pump in the DC. 
Had two 24v banks of two deep cycle diesel batteries (Main and backup banks) going to a Caterpillar 3208 V8 diesel engine and it was all inside of a small cinder block building for that purpose. One day I went out to start the pump for a test and saw one had for some reason blown up and **it was everywhere.

Those were on a maintenance charger to keep them hot at all times and is also a regulation to have it in use but if a battery has a problem it can make it get hot and well.... You know. That's also why there was a plexiglass barrier in place between them and where you'd be to start the engine - They could blow right when you'd hit the switch to start the pump and with that incident it had been knocked over on it's side. 
Glad I wasn't there when it did.


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## Grog6 (Nov 25, 2019)

There's a lot of info in the link I posted.






						Charging Information For Lead Acid Batteries – Battery University
					

Review various Lead Acid charging methods and examine why some systems work better than others. Find also simple guidelines for charging Lead Acid batteries.



					batteryuniversity.com
				




I've been doing this for a long time, and my car batteries usually last 10 years or so by doing things like this.

Also, a car charging circuit in most cases is a simple 2 stage device, high rate (14.4) or float. (13.8)

The only exception I've found is the 200A Mitsubishi alternator in later Crown Vic police cars; they're controlled by the car eec over canbus.

Some expensive chargers use pulse charging methods that supposedly desulfate the plates; I know of no cases where that worked on a bad battery, however.



> The correct setting of the charge voltage limit is critical and ranges from 2.30V to 2.45V per cell. Setting the voltage threshold is a compromise and battery experts refer to this as “dancing on the head of a pin.” On one hand, the battery wants to be fully charged to get maximum capacity and avoid sulfation on the negative plate; on the other hand, over-saturation by not switching to float charge causes grid corrosion on the positive plate. This also leads to gassing and water-loss.
> 
> Temperature changes the voltage and this makes “dancing on the head of a pin” more difficult. A warmer ambient requires a slightly lower voltage threshold and a colder temperature prefers a higher setting. Chargers exposed to temperature fluctuations include temperature sensors to adjust the charge voltage for optimum charge efficiency. (See BU-410: Charging at High and Low Temperatures )
> 
> The charge temperature coefficient of a lead acid cell is –3mV/°C. Establishing 25°C (77°F) as the midpoint, the charge voltage should be reduced by 3mV per cell for every degree above 25°C and increased by 3mV per cell for every degree below 25°C. If this is not possible, it is better to choose a lower voltage for safety reasons. Table 2 compares the advantages and limitations of various peak voltage settings.


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## Jism (Nov 25, 2019)

In a car you dont have a fixed variabel, but a constant switching and dynamic one, pretty much dictated by the engine's current RPM and / or current load onto the battery/alternator. It's just not a ideal situation. I live with a battery usually lasts 3 to 5 years, depending on brand and / or usage. After that replace it with a 75 euro costing one incl. installation and good to go.

Edit: So glad i have a UPS in the first place. Power outtage of exactly a second. It jumped in and prevented from losing my work! TV and all other equipment flew out.


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## ShrimpBrime (Nov 25, 2019)

Jism said:


> In a car you dont have a fixed variabel, but a constant switching and dynamic one, pretty much dictated by the engine's current RPM and / or current load onto the battery/alternator. It's just not a ideal situation. I live with a battery usually lasts 3 to 5 years, depending on brand and / or usage. After that replace it with a 75 euro costing one incl. installation and good to go.
> 
> Edit: So glad i have a UPS in the first place. Power outtage of exactly a second. It jumped in and prevented from losing my work! TV and all other equipment flew out.



I did want to give my 2 cents here. May hurt feelings.
But you know what???
One of the dumbest things you could do is charge a car battery inside the home. Dont be offended, just Dont do that please.
Automotive batteries are dangerous period.

The altenator charges the battery and runs all system components period. The battery is to simply start the vehicle and nothing more. Should always be at a full charge.

Battery has un told amount of battery life. Not a single person here can predict if a battery is going bad in 1 year or 10, so bragging that your battery lasted 5 years means nothing.

The rpm of the altenator means nothing above usually 1200 rpm. The altenator may create more voltage but the output regulator controls that current so revving your engine really fast during a jump start is pointless.

But yea, charge the car battery not inside the home. Please. People can be seriously injured.


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## TheoneandonlyMrK (Nov 25, 2019)

ShrimpBrime said:


> I did want to give my 2 cents here. May hurt feelings.
> But you know what???
> One of the dumbest things you could do is charge a car battery inside the home. Dont be offended, just Dont do that please.
> Automotive batteries are dangerous period.
> ...


I agree ,car batteries and I would say tyres are a danger no one realises, they blow up bad.


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## Jism (Nov 25, 2019)

Guys i am very aware that charging car batterys releases gasses, thats why i set it in a place where 2 windows where open.

I cant pull a powercord from 20 meters through the car like that. It was a quick and dirty sollution.


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## ShrimpBrime (Nov 25, 2019)

Jism said:


> Guys i am very aware that charging car batterys releases gasses, thats why i set it in a place where 2 windows where open.
> 
> I cant pull a powercord from 20 meters through the car like that. It was a quick and dirty sollution.



It's the explosion part you'd be worried most about. Might be rare to you, but I've seen it happen on a 10amp charger.
Seen my old boss get it in the eyes. You wanna know how hard it is to help a guy screaming and running in circles is?? Well, you don't want to find out trust me.

But you did what you had to do, but if possible, find some one to just jump start the car. Once the car is running, the alternator will charge the battery, just let it idle for an hour and you'll be good to go.


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