# 2 PSU in one rig - questions



## dami2504 (Mar 20, 2021)

Hello
I'm currently running a mining rig with 8 GPU.
1. My Biostar TB250-BTC Pro can handle to 12 graphic cards. Atm my psu is 1650 W and power usage of rig from the wall is +- 1200W.
I would like to connect 2nd PSU and another 4 cards to my rig. Does it metter how powerfull the 2nd PSU will be? I mean for example if i can connect 1) 1650 W PSU and 2) 1000 W PSU in one rig? Or i have to buy 2nd 1650W for safety usage?
2) My second question is about connection beetwen 2 PSU. I know that i have to use add2psu but I would like to ask how safety split GPUs/risers/motherboard/cpu/fans between my 2 PSU. Woult it be nice?
1650W PSU: 8 GPUs/risers/moterboard/cpu/fans
2nd PSU (for example 750W): 4GPUs/risers


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## trog100 (Mar 20, 2021)

i think its okay to have two different size psus.. mine are two 850 watt units.. you do need a connector to make sure both supplies come on together..

its year or three back since i built mine so i am a bit rusty on the detail..


trog


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## dami2504 (Mar 20, 2021)

And is it okay to connect them like i said in my post?
1650W PSU: 8 GPUs/risers/moterboard/cpu/fans
2nd PSU (for example 750W): 4GPUs/risers

Or should i keep all risers and motherboard on 1 psu (I read this somewhere)?


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## Zach_01 (Mar 20, 2021)

You can mix any wattage PSUs in any rig as long as you load them accordingly. Keep in mind that the GPUs draw a significant amount of power through riser cards. So you need to distribute them too.
It’s better to measure power separately for both PSUs for you to know what load each have.
If the additional 4 GPUs are the same with previous 8 then a 1000W second PSU will be enough.

I would connect all new 4GPUs and their riser cards to a second 1000W. It should load it less than 600W and that’s ok. Again if the 4new GPUs are the same with old ones.

Yes you can connect the new 4 risers’s power to old PSU and GPU connectors to the new one so you might be able to get away with a smaller one, like 850W but consider that it’s better not load the old one more than the 1200W that already has.
1200W out of 1650W is about 70% load depending the PSU’s efficiency. It’s better not to give it more load for its longevity.

And like @trog100 said you need a special cable to connect the 2 PSUs for them to start together.


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## dami2504 (Mar 20, 2021)

Yes 4 new GPU's will be the same as old ones. After underclock/undervolt hiveos shows +- 110W per card. Thank your for your answers. I will keep in mind your advices.


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