What to do with these two power supplies?

[COLT601]

So I built up my first mining rig and didn't research thoroughly enough. I bought two Corsair 750w power supplies for $80 bucks each. They only have two 8 pin slots each to connect to GPU's and if I were to run a Y splitter i'd be afraid of a fire. So right now I can only run 4 AMD RX 580s. I ordered two EVGA 1000w power supplies which will be here on the 14th. I have 7 GPU's total and my motherboard will support 8.

Any ideas what I should do with these two Corsair units?  Are there any ultra cheap motherboards that are actually available that'll support 4 GPU's? I could build a 2nd rig smaller rig that only runs 4 cards.

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[Tonnec]

You can run more than 1 psu on the same system, use an Adaptor splitter Cable Connector
so you can use both psu.

[burntmytoast]

You can split as long as it is one riser and one card per pcie cable

[COLT601]

You can split as long as it is one riser and one card per pcie cable

Are you sure about that??

There are only two 8 pin slots on each power supply. I would have to run two 8 pin Y adapters to get four GPU's per power supply.

[COLT601]

You can run more than 1 psu on the same system, use an Adaptor splitter Cable Connector
so you can use both psu.

I have both power supplies running on one system right now

[nc50lc]

If you have enough molex/sata connectors, you can use a molex to 8pin adapter/converter to each rail.
Make sure to use only one rail per GPU and a good quality adapter.
However four (4) 185W GPU is a bit of an overload for a 750W PSU.

You can go for 3 RX580 for each PSU.

[COLT601]

If you have enough molex/sata connectors, you can use a molex to 8pin adapter/converter to each rail.
Make sure to use only one rail per GPU and a good quality adapter.
However four (4) 185W GPU is a bit an overload for a 750W PSU.

You can go for 3 RX580 for each PSU.

I did order a sata 6 pin to PCIE dual 6+6/2 pin cable (my cards take both 6 and 8 pin connectors to run)

Once I had the cable plugged in to the SATA port on the PSU and tried to power on the mining rig, that power supply and anything I had connected to it would turn on for 1/2 a second and then immediately shut off

[djn053]

If you have enough molex/sata connectors, you can use a molex to 8pin adapter/converter to each rail.
Make sure to use only one rail per GPU and a good quality adapter.
However four (4) 185W GPU is a bit an overload for a 750W PSU.

You can go for 3 RX580 for each PSU.

I did order a sata 6 pin to PCIE dual 6+6/2 pin cable (my cards take both 6 and 8 pin connectors to run)

Once I had the cable plugged in to the SATA port on the PSU and tried to power on the mining rig, that power supply and anything I had connected to it would turn on for 1/2 a second and then immediately shut off

one sata cable power is not enough  to run，only can startup，not mining！！

[nc50lc]

That depends on your powersupply.
Some PSU has a dedicated 12v Rail for the GPU Power connectors allocated with 80% of the max power of the unit, leaving about 100-150W for other components.
If your PSU is one of those, that might be the reason.

Better wait for those EVGA 1000W PSU.