Noob PSU question

ChrisbtrChrisbtr Member Posts: 3
I decided to start mining a few weeks ago and its been a lot of fun. Definitely found a new hobby. Here is my Q. I have a 750 watt evga PSU powering 4 red dragon rx 570s. When I have 3 plugged in everything is fine and they get 23-24 mhs with blockchain drivers installed. But if I plug in the 4th then the system doesnt want to boot up properly and for example doesn't recognise any device plugged into the USB ports. But with 3 all is well. Do you think my psu is too low and the likely problem? Thanks!!

Comments

  • MrN1ce9uyMrN1ce9uy Member Posts: 190 ✭✭
    What kind of motherboard do you have? Have you configured any BIOS settings?
  • TaltonTalton Member Posts: 25
    RX 570s draw about 120w each at a guess, maybe more if you've not undervolted or underclocked the core.

    The average PC, meaning just the mobo, cpu, whatever else is plugged in will do about 90w.

    Brining you upto about 570w, so your PSU should be fine, you may want to get a electric meter for your plug so you can see how much it's actually using.

    As MrN1ce9uy said, there's likely something in your motherboard bios that needs switching over.

  • chaffychaffy Member Posts: 36
    I'm running 5 RX570s on a Biostart TB-250 board with no mods, getting 21+ mh/s per card, and it draws 900w at the wall. Take 100w for the board, cpu, ram, risers, etc... gives me 160w per card. If you're drawing the same power per card, that fourth card puts you at 740w. This all just an educated guess using 100w for all hardware except the cards themselves. I don't think your PSU can handle the fourth card.
  • ChrisbtrChrisbtr Member Posts: 3
    My mb is asus z270-p and havent edited bios. I will check on a power meter to find exactly what I'm pulling.
  • kurthunkkurthunk Member Posts: 17
    This isn't a problem with your psu. At boot all the video cards are at idle power consumption which a fraction of their load. You would only run into an issue if you got them all mining.

    It is probably a pcie lane issue if your USB ports are failing to work. Try reducing your pcie speeds from Gen3 to Gen2 in your BIOS to free up more lanes.
  • Ericjh801Ericjh801 Utah, USAMember Posts: 370 ✭✭
    I agree that it's not a PSU issue. Your video cards do not full draw at bootup, only when you start mining, so the 750 shouldn't cause an issue with booting and I think you would be fine mining on it also (I run 4 580's on a 750 with no issues). I would check your bios settings, also try using the 4th card and swapping it with another in the 3 card set to see if it works with 3 total. If so, then try another PCIE port, riser, etc. Good luck!
  • ChrisbtrChrisbtr Member Posts: 3
    I appreciate the replies. I tried switching out the risers and gpu and no matter what it will boot with 3 plugged in and it won't as soon as I add a fourth. I disabled things like onboard lan, lights, sound but still the same problem. I haven't tried going from gen3 to gen2 pci because I can't figure out how to do that. I've searched around a lot and can't find much useful info on that process. If anyone has any more insights that would be awesome. Thanks
  • NicodemusNicodemus Member Posts: 29
    Dude, you are just pulling too much out of your 750w power supply, as stated by @chaffy. If you do the undervolt, it would probably still draw too much of your 750w power supply.

    But here it goes another thought... You'll probably be running your rig 24/7. These desktop power supplies are not supposed to be working at full cappacity 24/7. They are just not meant to do that. So, you HAVE to count on using "just" 80% of the advertised capacity.

    Now some math... If you have a 750w, 80% of draw would be 600w. That's the magic number to 4 RX5** gpus with undervolt (which seems you haven't done yet). So, in your case, I'd first understand how to mod bios and do the undervolt (click here to se a very nice tutorial). Then you'll probably have cards drawing 120w each. Thinking about 200w of draw for other components (cpu, memory, mobo, etc), you'd need a power supply providing 680w. This is provided by a 850w power supply, not 750w.

    Now, another math... If you can't do the underclock for some weird reason, you'd be drawing something beteen 150/160w for each card. Let's use 160 do do the math. 160x4 = 640w. Plus 200 for other components, you'd be looking at 840w, or a 1100/1200w power supply.

    So... take your time, go to that tutorial, do the bios mod and overclocking/undervolting. Measure power draw. Sell yout 750w, grab a new 850w. That's it.
  • Ericjh801Ericjh801 Utah, USAMember Posts: 370 ✭✭
    Gen1/2/3 settings should be in the same menu that says "Mining enabled" I thought. I have the BTC-250+ (8 GPU setup). I wouldn't think changing that mattered as far as it booting up and seeing them. I left mine all on auto when I was setting it up and it was fine.

    Are you on the latest bios? Did you try resetting BIOS to factory after doing that?
  • eforiuseforius Member Posts: 17
    Find the bios settings for your mobo and if using windows UEFI install
  • bthitmanbthitman Member Posts: 5
    I'm curious how you are physically connecting 4 cards to this PSU! The EVGA 750s that I have come with 3 cables, with 2 8-pin (6+2) connectors each.

    Using both 8-pin connectors on a single cable to power one card = 3 cards powered from the PSU. (assuming that your cards have the 8-pin AND the 6-pin power connectors)

    Or are you running just 8-pin power to the cards?

    Or do the cards only have one 8-pin power requirement? (and not the extra 6-pin that are seen on some cards)

    If the last statement is true, and you are trying to use the 750 to power 4 cards AND the mobo, then you are probably tapped out in terms of PSU power...
  • MiningRigBuilderMiningRigBuilder Member Posts: 5
    No need to guess on the power consumption. See this mining rig builder
  • Ericjh801Ericjh801 Utah, USAMember Posts: 370 ✭✭
    He's right, don't guess, or use a website to figure it out. Buy a killawatt and measure it at the wall. Or a metered PDU. The best the most accurate thing you can do.
  • peshetomanpeshetoman Member Posts: 78
    I bet is a mix of issues here :) first of all a 750 power supply has at most 3 PCI 12v lines. I bet he is also using a few sata to 6(8) pin converters, putting 2 much pressure on the sata lines. For 4 GPUs best is to use 1kW PSU. you have enough PCI lines, you have the required cables and most importantly you have stability. 750W can power most up to 3 cards and it is at limit. Even if you undervolt and etc the power supply wont handle it properly due to its limits and a PSU protection will kick in. Just get a second supply at 350W, paperclip it(or get a 2PSU adapter) and plug the 4th card in it...
  • Ericjh801Ericjh801 Utah, USAMember Posts: 370 ✭✭
    That's not necessarily true. I'm running dual 750W PSU's with 8 RX 580 cards and i'm under the power limit and have NO issues with any of the rigs (4 setup with dual 750's, one with dual 800's). Currently pulling approximately 1150w per setup so definitely under the 1500w max limit.

    Also some of the 750W PSU's i'm using have 4 PCIE individual cables, but one of them only has 2 that I daisy chained and they are working without an issue also. I agree, I wouldn't use SATA to PCIE to power video cards. I do use them to power the PCIE risers without issues.

    He never did answer previous questions so I guess we wait.

    I bet is a mix of issues here :) first of all a 750 power supply has at most 3 PCI 12v lines. I bet he is also using a few sata to 6(8) pin converters, putting 2 much pressure on the sata lines. For 4 GPUs best is to use 1kW PSU. you have enough PCI lines, you have the required cables and most importantly you have stability. 750W can power most up to 3 cards and it is at limit. Even if you undervolt and etc the power supply wont handle it properly due to its limits and a PSU protection will kick in. Just get a second supply at 350W, paperclip it(or get a 2PSU adapter) and plug the 4th card in it...

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