Help me find a PSU(s)?

Zii · Apr 6, 2018

This link will show you the components of my build, and the PSU wattage estimate.

I have a 1200w PSU, but sadly it only has four 6+2 pin connectors. I will have 3 graphics cards in this build, so I need at least six of those GPU connectors, two for each card. It'll leave one of my cards in the dust :[

I ordered the blackhawk ultra case from Rosewill, as it allows for 2 PSUs. Was thinking I could buy another 500w PSU and use it at the bottom exclusively for the 3 graphics cards (assuming I can find one with at least 6 of those GPU power connectors) [strike]or is it better to buy a 300w PSU and use it for just that one GPU that the other 1200w can't handle? Can't figure this out. Bonus if the PSU has red LED's![/strike]

Edit to above: just found a brand new EVGA 450w in my closet. Can I make this work with a 650w I have laying around, or does it have to be used with the 1200w? JSYK the 650w only has two 6-pins. I have a ton of molex to 8-pin, and dual-molex to 8-pin. Are those safe? Should I use the single molex or dual-molex to 8/6pin adapters?

But I don't know much about dual PSU setups. Is there some kind of plug I can buy that bridges the two connectors on the 2nd power supply's 24-pin so it will always be on?

I don't want to fry my system because I'm unfamiliar with PSU's in general.

If it matters, the 3 cards will always be on, and usually under 80% load rendering something.
7950: two 6-pins
7950: one 6-pin + one 8-pin
270X: two 6-pins

madmatt30 · Apr 6, 2018

You can split a 6+2 pin into 2x6 pin with the use of adapters perfectly safely.

If that 1200w psu you currently own is good quality you dont need to replace anything.

Albrett · Apr 6, 2018

One very powerful PSU would be optimal. Some of the 1500 watt ones have about 8 8-pin connectors, though I don't have any specific recommendations.

You could get multiple PSUs, though the only situation where this would be advisable would be if you had a specific mining board, as many of them have 3 24-pin connectors on the motherboard.

You can get cheap adapters for 2 PSUs, though there's certainly more risk involved than other options. If you're wanting the cheapest possible solution, however, it might be worthwhile. Here's a few examples of the adapters: https://www.ebay.com/itm/2x-24-Pin-Dual-PSU-Power-Adapter-Cable-Connector-Cord-for-ATX-Motherboards/332426577323?hash=item4d662b05ab:g:znwAAOSwbF1Z8c5l

https://www.ebay.com/itm/Power-Supply-Adapter-Connector-Dual-Triple-Relay-Adapter-Link-Multiple-add-2PSU/122824223909?hash=item1c98e4eca5:g

qQAAOSwfVhZ5EqN

Or you could get some molex/8-pin to 6-pin adapters.

Zii · Apr 6, 2018

madmatt30 :

Oh, so you mean I can use a single 6-pin to split it into two 6-pins? This would still supply enough power to the card even at full load? Is this better than using a molex or two, and adapting it to a 6-pin?

Zii · Apr 6, 2018

Albrett :

I'll pick one of those up! The molex adapters are totally safe then?

What's the best way to split the power? Should the 450w be used to power the mobo, drives, CPU, and fans? Or should I use the 450w to power the cards only? Do I have enough power left over from the 450w to power other peripherals, or is this a bad idea? I read somewhere about different voltages between the PSU's causing shorts or something not ideal like that.

madmatt30 · Apr 6, 2018

Zii :

no , thats not what I mean

ATX & PCI Express specs dictate that a 6+2 pin (8 pin) cable is capable of supplying 150w of 12v power.
A 6 pin Pcvi express is capable of 75w of 12v power - half as much.

You can therefore buy a 6+2 pin to twin 6+2 (as long as you only use the 6 pins of the adapter cable) without compromising the psu or the cable itself.

So

6+2 pin from psu - to twin 6+2 pin adapter cable - Plugged to 7950 that requires 2 x 6 pins
6+2 pin from psu - to twin 6+2 pin adapter cable - Plugged to 270x that requires 2 x 6 pins

Use the remaining 6+2 pins that come from the psu to power the 7950 that requires 6+8 pin.

That keeps you within the specs of that single 1200w psu that you own.

4x 6+2 pins means that its geared up to supply 600w of power (4x 150w) to gpu's through its 4 connectors.

A 7950 pulls 180w max,a 270x pulls 12-130w

So total draw with all 3 cards 100% stressed is under 500w.

Within specs.

This all hinges on what model psu that 1200w actually is ?

The quality of the unit itself would dictate whether Id be happy doing the above over anything else.

Dont use molex adapters for gpu's, thats a fools game, they are not geared up for particularly high current & there is no isolation between the pins inside the block connector.

Zii · Apr 6, 2018

madmatt30 :

I see! So basically an 8-pin to two 6-pins is safe.

Here's a picture of the 450w, if I'm reading this correctly it has two of the 6+2 pins.

So this leaves me at my last questions;
Since the 1200w is modular and I can't find the 6-pin connectors... I'll need to buy a 2nd PSU anyways.

Want to make sure I get this right.
1) I have the 450w, so how much should the other PSU be rated at?
2) Should I use the 450w for the CPU/mobo/HDD's etc. and second PSU for all 3 GPU's
or
use the 450w for one GPU, and 2nd PSU for everything else + the 2nd 3rd GPU's?
*already bought that 24pin cable linker thingy
*have a few 8-pin to dual-6-pins if needed

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Help me find a PSU(s)?

Zii

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