HP 65W laptop charger vs HP 135W SFF desktop Power brick?

[rockit00]

I have a pair of older HP 14" laptops. I use them on occasion of power outages and bi-monthly Windows 10 updates. I have been using the OEM 65W charger to keep them charged. I have a 135W power brick from a decommissioned HP SFF desktop PC. The 65W charger fits both laptops and the 135W fits both laptops also. I haven't plugged the 135W power brick into the wall socket while connected to the laptops yet. I never leave A/C chargers plugged in and unattended overnight. 65W-19.5v DC - 3.33A versus 135W-19.5v DC - 6.9A. Is this safe for a laptop charger?

 

[Harlow]

65W-19.5v DC - 3.33A versus 135W-19.5v DC - 6.9A. Is this safe for a laptop charger?

Both chargers output 19.5V (which is good) and presumably have exactly the same DC plug that fits in the laptop. If so, I would be quite happy to try the 135W PSU. The laptop should only draw the current required to meet charging rate, as set by the laptop designer for the internal battery.

The charge rate for batteries is known as the C-rate:
https://batteryuniversity.com/article/bu-402-what-is-c-rate

If the laptop is designed to work from a nominal 3.33A charger, when you connect a charger capable of supplying 6.9A, I would not expect the current drawn to rise significantly above 3.33A. The laptop designer should have optimized the charge rate to work with the "standard" 3.33A charger and set the input current limit accordingly (somewhere below 3.33A).

There is a slight chance the laptop will draw a current somewhere between 3.33A and 6.9A when connected to the 135W charger, if HP offered a choice of several different PSUs for the same laptop, e.g. 65W, 100W and 135W. Some people prefer to carry a lightweight charger in their laptop bag, so HP may have offered a choice of PSUs with different capacities and weights.

If you want to check the actual charge rate of both chargers, download a copy of BatMon and install it on the laptop. The app starts with Windows and you can use it to measure the charge rate when the charger is connected, or the battery discharge rate when the charger is unplugged. If you notice a big difference in the charge rate between the two chargers, or the battery gets hot when charging, don't use the 135W charger. The "risk" is yours. If in doubt, contact the manufacturer.

https://www.passmark.com/products/batmon/

Battery charging at 33210mW (= 33.21W):-

Battery discharge at 18000mW (= 18.00W):-

 

[Waldorf]

@rockit00
if the plug is the same (layout, as in =/-) and fits, your fine to use it, and probably will warm up less, as your not "maxing" what the brick can do.

@Harlow
if the 135w gets hot, the 65w would get hot too.
c-rates on laptops and the like are set by mfg, and short of some high end gaming laptops or units using multiple PD usb-c ports, wont change how fast they charge.

just because PD based charging can increase power draw to charge faster, doesnt mean regular power bricks do.

 

[Harlow]

if the 135w gets hot, the 65w would get hot too.

A 135W PSU will probably be twice the physical size of a 65W PSU. Since it can output double the power, a 135W PSU should have bigger internal heatsinks and greater thermal mass. If the laptop pulls the same power from a 135W supply as it does from a 65W PSU, i.e no more than 65W, I would expect the bigger 135W PSU to run cooler to the touch than the smaller 65W PSU at the same power output. This is based on my time as an electronics engineer designing PSUs for MILSPEC and AeroSpace applications.

c-rates on laptops and the like are set by mfg, and short of some high end gaming laptops or units using multiple PD usb-c ports, wont change how fast they charge.

Exactly what I was thinking, i.e. the laptop should continue to draw 65W max when connected to a 135W PSU.

 

[Waldorf]

@Harlow
how does my statement contradict that?
if the 135w would have gotten hot, short of being defective, the 65w would get hot too.

 

[ShrimpBrime]

I have a pair of older HP 14" laptops. I use them on occasion of power outages and bi-monthly Windows 10 updates. I have been using the OEM 65W charger to keep them charged. I have a 135W power brick from a decommissioned HP SFF desktop PC. The 65W charger fits both laptops and the 135W fits both laptops also. I haven't plugged the 135W power brick into the wall socket while connected to the laptops yet. I never leave A/C chargers plugged in and unattended overnight. 65W-19.5v DC - 3.33A versus 135W-19.5v DC - 6.9A. Is this safe for a laptop charger?

Plenty safe. The laptop will only draw what it needs and or capable of. If the laptop is rated at only 65w, that's all it'll use for operation while charging the battery.

HFGL!

 

[Harlow]

how does my statement contradict that?
if the 135w would have gotten hot, short of being defective, the 65w would get hot too.

I didn't actually say anything about either charger getting hot in my original posting.

or the battery gets hot when charging

My only reference about something getting hot was the battery, not the chargers.

if the 135w gets hot, the 65w would get hot too.

This was the first time anyone mentioned the chargers getting hot.

As I mentioned after the subject of charger temperature cropped up, if the laptop draws the same amount of power from both chargers, I'd expect the 65W charger to get hotter than the 135W charger, due to the larger thermal mass of the bigger charger. Anyway, it's not worth worrying about further, so I'll stop there. Let's just choose to differ.

 

[Waldorf]

never stated such. my response was about you explaining in detail, what i already said (if the bigger one got hot, the smaller one would be too).

all chargers are designed for the unit it comes with, dont need to install or monitor anything, or look at charging rates etc, to figure this out.
worked 2 decades with it/hw to know this to be the case, without doing a single time, what you recommended.

its fine for ppl that are familiar with it or want it explained how it works, but why overcomplicate stuff/answer in such detail, while not really answering the actual question with clear yes/no.

 

[rockit00]

Thanks to all! BatMon is a great app that I had not heard of. I used the power brick on both laptops without any noticeable heating issues with the batteries or charger. The laptops appear to charge a bit faster with the brick than with the laptop charger. It is nice to have options.