Why do the VEGAs on the PSU without the Mobo, use more power than when on mobo?

[ben8jam]

I have a 850W EVGA G3 and a 750 EVGA G3.

I have a Asrock connected to the 850W along with 3 VEGA 56.

On the 750W PSU I have two VEGA56.

When mining Cryptonight, the 850W psu reads 550W (the Mobo takes about 50-80W) which means the 3 Vega are only drawing about 150-160W.

But on the 750W psu it reads, 410W, which means those are running at 205W!

I can move the cards around between the mobos and the numbers stay exactly the same, so it's not a config or a card issue.

All running on risers. All identical cards. all identical settings.

What on earth would cause this?

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[Michael20]

on different load, psu have different efficiency

[adaseb]

I have a 850W EVGA G3 and a 750 EVGA G3.

I have a Asrock connected to the 850W along with 3 VEGA 56.

On the 750W PSU I have two VEGA56.

When mining Cryptonight, the 850W psu reads 550W (the Mobo takes about 50-80W) which means the 3 Vega are only drawing about 150-160W.

But on the 750W psu it reads, 410W, which means those are running at 205W!

I can move the cards around between the mobos and the numbers stay exactly the same, so it's not a config or a card issue.

All running on risers. All identical cards. all identical settings.

What on earth would cause this?

Your Mobo plus CPU most likely use about 30Watts and not 80Watts.

Also your efficiency varies depending on how much load you are pulling from the PSU. You pull too little or too much and your efficiency is worse.

If the PSU are identical then maybe one is older than the other and less efficient due to capacitors aging.

[Geraldo]

on different load, psu have different efficiency

Also your efficiency varies depending on how much load you are pulling from the PSU. You pull too little or too much and your efficiency is worse.

If the PSU are identical then maybe one is older than the other and less efficient due to capacitors aging.

Yeah, I agree with both people above. That's more like PSUs efficiency issue. Your EVGA G3 (80 PLUS Gold rated) with the efficiency - 90% in 115V nor  92% at 220V-240V (AC). How about the other one?  have you checked its efficiency?

So this is your rig scheme, you were powering your mobo using EVGA G3 (850Watt) plus three cards (VEGA), and the other two cards (VEGA) powered with 750Watt PSU (we don't know the type of this PSU). Is it right? And how about the Risers powering scheme? How do you measure the power that is being used? Using physical tools (Power meter) or through Software?