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900w 32A PSU blew fuse on 2 x 280x's. Checked single rail but still..

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December 17, 2013 12:27:05 PM

Yea.

It was one of those sonic-cracking, sparks flying, arm-reflex-over-face moments.

All I was doing was a routine install of a 2nd 280x using a PCI-e 1x - 16x riser. The problem occurred when they both finally began to mine. In the first 10 seconds of mining, my PSU's fuse blew (so it seems so far) and a sharp blue spark went flying out of the double-cased box, accompanied with a loud cracking and shards of what I'm guessing now is glass.

Here's the setup. System was fine with Sapphire 280x @ 755kh/s:

CPU: E4400 2Ghz 800FSB http://ark.intel.com/products/29753/Intel-Core2-Duo-Pro...
Heatsink: Zalman Copper heatsink and fan (12v DC 2.65A)
Motherboard: P5E-VM-HDMI: https://www.asus.com/Motherboards/P5EVM_HDMI#specificat...
RAM: 2Gb Dual Channel DDR2 800 Transcend 5-5-5
HDD: Seagate Sata2 160Gb HDD

Cards:

Sapphire R9 280x Vapor-X 2x8pin: http://www.sapphiretech.com/presentation/product/produc...

on riser, new card:

Gigabyte R9 280x GV-R928XOC-3GD: http://www.gigabyte.co.nz/products/product-page.aspx?pi...

PSU: 900w Apower AK series: http://www.ebay.com/itm/A-Power-AK900-900W-Watt-ATX-Com...

As I understand it, the "dual volt rails" are not actually multi-rails like most PSUs claim, therefore I worked to the assumption that (after deducting in testing using a multimeter) it was actually the same 32A rail.

However, 32A on 12V1 and/or 12V2 should be more than enough to cover 2 x 12.5A cards, assuming this figure is indeed correct.? I cannot recall where I read that. I also however do not know the Amps required by the motherboard, and I had a series of fans loaded onto the motherboard and chassis:

0.24A - 80mm fan
0.68A - 80mm fan
0.17A - 80mm fan, that seemed to go WAY faster attached directly to the 12v (and not the MB) so thought I'd tried this out.
0.18A - 120mm fan
0.16A - 120mm fan

If one adds the fans and Zalman CPU fan this = 4.08A, assuming that the middle fan there is operating at 0.17A only.

So my questions are:

Why might this have blown a fuse in a brand new PSU (worked for 1 week @ 750kh/s)?
How much headroom in Amps should I leave for this motherboard, and motherboards in general?
Would one presume that other parts would be fried and if so, which ones specifically?
I would hate to have to open the cover of 2 brand new $350 cards (1 week old).
December 17, 2013 12:33:40 PM

Noone wants to answer this as the bitcoin miners are the reason the 280xs have been out of stock for a month :p 
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December 17, 2013 12:40:16 PM

axfalcon said:
Yea.

It was one of those sonic-cracking, sparks flying, arm-reflex-over-face moments.

All I was doing was a routine install of a 2nd 280x using a PCI-e 1x - 16x riser. The problem occurred when they both finally began to mine. In the first 10 seconds of mining, my PSU's fuse blew (so it seems so far) and a sharp blue spark went flying out of the double-cased box, accompanied with a loud cracking and shards of what I'm guessing now is glass.

Here's the setup. System was fine with Sapphire 280x @ 755kh/s:

CPU: E4400 2Ghz 800FSB http://ark.intel.com/products/29753/Intel-Core2-Duo-Pro...
Heatsink: Zalman Copper heatsink and fan (12v DC 2.65A)
Motherboard: P5E-VM-HDMI: https://www.asus.com/Motherboards/P5EVM_HDMI#specificat...
RAM: 2Gb Dual Channel DDR2 800 Transcend 5-5-5
HDD: Seagate Sata2 160Gb HDD

Cards:

Sapphire R9 280x Vapor-X 2x8pin: http://www.sapphiretech.com/presentation/product/produc...

on riser, new card:

Gigabyte R9 280x GV-R928XOC-3GD: http://www.gigabyte.co.nz/products/product-page.aspx?pi...

PSU: 900w Apower AK series: http://www.ebay.com/itm/A-Power-AK900-900W-Watt-ATX-Com...

As I understand it, the "dual volt rails" are not actually multi-rails like most PSUs claim, therefore I worked to the assumption that (after deducting in testing using a multimeter) it was actually the same 32A rail.

However, 32A on 12V1 and/or 12V2 should be more than enough to cover 2 x 12.5A cards, assuming this figure is indeed correct.? I cannot recall where I read that. I also however do not know the Amps required by the motherboard, and I had a series of fans loaded onto the motherboard and chassis:

0.24A - 80mm fan
0.68A - 80mm fan
0.17A - 80mm fan, that seemed to go WAY faster attached directly to the 12v (and not the MB) so thought I'd tried this out.
0.18A - 120mm fan
0.16A - 120mm fan

If one adds the fans and Zalman CPU fan this = 4.08A, assuming that the middle fan there is operating at 0.17A only.

So my questions are:

Why might this have blown a fuse in a brand new PSU (worked for 1 week @ 750kh/s)?
How much headroom in Amps should I leave for this motherboard, and motherboards in general?
Would one presume that other parts would be fried and if so, which ones specifically?
I would hate to have to open the cover of 2 brand new $350 cards (1 week old).


I don't normally say this, but you've managed to make pretty much every single mistake possible.

First, you purchased a cheap-shit $60 PSU. What did you honestly expect? Good 1,000+ watt PSUs retail for over $250 for a reason, they use high quality components and have sufficient headroom for overloading.

Second, you used a PCIe riser. NEVER use PCIe risers for GPUs. GPUs can draw 75 watts from the motherboard, 75 watts from a 6 pin connector, and 150 watts from an 8 pin connector. The PCIe 16x slots are rated to deliver 75 watts, the 1x slots are not. Each 280x draws upwards of 250 watts under mining conditions. If it can't draw 75 watts from the motherboard, it must draw all 250 watts from the PCIe connectors which together are rated to deliver 225 watts (75 watts on the 6 pin + 150 watts on the 8 pin). Since the GV-R928XOC-3GD is heavily overclocked it will draw closer to 300 watts.

Third, you threw all of this into an ancient system that was not designed for such rough use. That motherboard is old. It may be capable of driving two behemoth GPUs, but that does not mean that it will do so continuously. Furthermore, the components are going to be old and worn out. I would not be surprised if you have leaking caps on there, certainly not after pushing it so hard.
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December 17, 2013 12:41:53 PM

But I mine Litecoin lol :p . Well was attempting to anyway. And yes, tell me about it. Although I did have to pull myself away from keeping it in my system when I bought it (the first one).
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December 17, 2013 12:44:13 PM

280X draws about 260W for scrypt mining. When OCed even more. This gives about 22A per card. Knowing cheap PSUs, their usual rail distribution is one for CPU and MB, second for everything else. This is why it blew up.

I don't really understand people mining on cheap PSUs like yours. For a mining rig you want the best PSU there is. Single rail, platinum efficiency. Then you can sleep soundly. Your electric bill is lower, your rig is safe. I'm mining myself, I did plenty of rigs for friends, believe me, PSU is the most important part of mining rig.

EDIT:
Don't believe in this crap about risers and old mainboards causing problems.
My 24/7 rigs on old amd 780x motherboards run four 290x on risers each and no problems.
No problem on older 6950 rigs too (6 cards per board).
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December 17, 2013 1:00:59 PM

Bejusek said:
280X draws about 260W for scrypt mining. When OCed even more. This gives about 22A per card. Knowing cheap PSUs, their usual rail distribution is one for CPU and MB, second for everything else. This is why it blew up.

I don't really understand people mining on cheap PSUs like yours. For a mining rig you want the best PSU there is. Single rail, platinum efficiency. Then you can sleep soundly. Your electric bill is lower, your rig is safe. I'm mining myself, I did plenty of rigs for friends, believe me, PSU is the most important part of mining rig.

EDIT:
Don't believe in this crap about risers and old mainboards causing problems.
My 24/7 rigs on old amd 780x motherboards run four 290x on risers each and no problems.
No problem on older 6950 rigs too (6 cards per board).


Yes I thought the youtube videos of old boards with 4+ cards looked a little counter-arguing although he/she's got a point about having a good board. The caps are those new types btw, sleeveless (or whatever they're called).

I didn't know the brand was cheap btw as we don't get that brand here in NZ. The price of 1000w (can't get a decent 900w for less than 1000w price) is well over $390 at their cheapest. This one was $100 and brand new. I figured, 2 x 375w cards (max) would be fine in it, given 32A.

So basically I was drawing roughly 44A out of a 32A rail?

And the fuse type, it says: 5F one end, and F8L250v the other end. Will an F6L250v work if I replace it and keep the PSU on some other non-intensive system?
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December 17, 2013 1:35:15 PM

PCIe 1x does not support 75w? Does this mean powered risers only because, I suspected they were only required after 2 or 3 cards were added.
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December 17, 2013 2:05:28 PM

Yes it does support 75W. PCI-E provides power on first few pins (before key notch).
Two usecases for risers:
To move cards away from motherboard to give them more air to cool. There are 16x-16x risers as well as 8x-16x 4x-16x 1x-16x and all combinations.
To use x16 cards in smaller slots (usually x1).

Recently I saw risers with integrated molex plugs to provide more power for GPU. Haven't tried that.

As for the fuse. 8A 250V fuse should not blow up because of one of the PSU rails overload. I suspect that there might be something else wrong with the PSU.
8A at 250V gives max 2000W of power. Replacing it with 6A (1500W) should be enough. Even with maximal theoretical load of 900W at 80% efficiency your PSU shouldn't draw more than 1125W from the wall.
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December 17, 2013 2:26:12 PM

Might there be a multimeter PSU checklist somewhere?
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December 17, 2013 2:53:26 PM

I don't think so. Each PSU is internally different. Some components operate at very high voltage, which is dangerous. I don't recommend experimenting unless you know exactly what you are doing.

Try replacing the fuse. Hopefully it won't blow up again and fry half of your hardware. However, I recommend to get rid of this PSU and use a quality product.
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December 17, 2013 3:02:47 PM

Oh I'll be sure to get rid of that PSU alright. Brand new out of box blow-out must be called the "AK Series" because they give good explosions for AK47 target practice.

Thanks a bunch :) 
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December 17, 2013 3:08:42 PM

Bejusek said:
Yes it does support 75W. PCI-E provides power on first few pins (before key notch).
Two usecases for risers:
To move cards away from motherboard to give them more air to cool. There are 16x-16x risers as well as 8x-16x 4x-16x 1x-16x and all combinations.
To use x16 cards in smaller slots (usually x1).

Recently I saw risers with integrated molex plugs to provide more power for GPU. Haven't tried that.

As for the fuse. 8A 250V fuse should not blow up because of one of the PSU rails overload. I suspect that there might be something else wrong with the PSU.
8A at 250V gives max 2000W of power. Replacing it with 6A (1500W) should be enough. Even with maximal theoretical load of 900W at 80% efficiency your PSU shouldn't draw more than 1125W from the wall.


PCI-SIG very clearly states in the PCIe electomechanical specification that 1x cards are limited to an initial power draw of 10 watts and only up to 25 watts under reconfiguration. Only 16x cards in a 16x slot are allowed to draw 75 watts. Most boards can deliver 75 watts to a 16x card connected via a riser but this is in breach of specification. It may work on some boards, but it is not "supported" and can cause problems.
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