Topic: Too dangerous to draw more than 1200w on Corsair 1200 PSU? (Read 2871 times)

WTF is going on with the 180-190V brownout though?

OK, my shelf rig uses a different approach to mackminer's, and he's pulling 8.7 GH/s against my 7.4 GH/s (according to arsbitcoin, oddly enough we're both using the same pool unless there are two mackminers...) but I have ONE cable running into my triple-board triple-PSU rig.

My PSUs are cheap, for all the usual reasons. Quality manufacturers, but anything over 1000W gets really expensive really quickly. So Shelf 1 runs two Cooler Master Silent Pros (1000W, 800W) and a Corsair 850W unit. None of the three PSUs individually pull more from the wall than their rated output, and since the inefficiency is on the conversion side, 10% inefficiency means the safe rated 1000W pull from the biggest PSU would pull 1,111W from the wall. That'd be OK. But none of the rigs do.

All three go into one power cable, which has the UK equivalent of a Kill-A-Watt stuck on the end. When ArsBitcoin isn't being DDoS'd, and the shelf rig can kick arse, that 'kill-a-watt-alike' shows between 2200 and 2300W.

Given the room has a single dual-socket outlet, each rated at max 13A at nominal 240V, I'm not 100% comfortable about the current draw on those cables. There's a 13A extension cord (20M) between the socket and the rig too!!! Yes, the cable gets mildly warm, but not as hot as when I tried to run the same sort of rig on a 10A home-made extension cable - the wire was too hot to touch and the female socket nearly caught fire. I'm using solid-conductor ring-main stuff now...

But even with the idiotic 10A extension, the smoking sockets and the floppy, melting wires... the voltage NEVER dropped lower than 220V. You'd expect a pretty hefty voltage drop from the resistance of the under-spec extension cable and the heating of the wire causing further resistance. But it wasn't much.


Mack... if your supply is showing 180-190V on a 240V main then either your 'kill-a-watt' is fucked or you need to get the circuit the miners are on looked at. Especially when you're investing in quality kit and 8 kW air conditioning units. Yes, the best quality PSUs are probably the only things that can cope with brownouts like that, but what happens when the input voltage drops? Well, the input current draw is increased to provide the same power. The PSU may be built to ramp up the amperage from your '240V' supply which has suddenly dropped to 180V... but that's the voltage dropped by a quarter. Hence to maintain the same power, the PSU will draw 4/3 more amps of current (sorry if maths is duff but I'm a bit wasted).

Going back to my situation, with around 10A steady on a 13A mains line, I'm in the safe zone. If my 240V supply dropped to 180V, then the PSUs would pull 10 * 4 / 3 = 13.333A. Hopefully the fuse in the extension cord would pop and 'boom' my miners would stop. Hopefully the PSUs would cope with a sudden loss of power and not fuck up all my GPUs.

But 13.3A on a domestic circuit is above spec. If you're really seeing 180V input and you're doing the same sort of thing as me, then you're either popping fuses every time it happens, or your kill-a-watt is fecked, or you're reading it wrong. That sort of voltage brownout would make your PSUs work like bastards to deliver the power your rigs are pulling. Fuck knows if the air-con could even cope with a voltage drop like that.

Where are you reading those figures from? I've got cheap (£10) Maplin own-brand 'kill-a-watt' devices and I've not had a duff one. I'm seriously taking the piss with the electrical setup in my 200 yr old UK house (the consumer unit still has Bakelite fuses with hand-coiled wire in them, for example) and I've built my own ring main for the office... I'm eating a LOT of power and *some* cables are getting warm. But I've *never* seen 180V at the outlet. The only time I have problems is when the knackered battery in my UPS decides to try to kill my Mac Pro and all the big screens - even a random spike like *that* doesn't affect the miner rigs - every one on a surge protector and kill-a-watt, either a power strip version or an individual socket.


OK, I've had enough booze, TL;DR - when your volts go down, a regulated PSU will pull more amps. If you're currently (hehehe) pulling 10A on a domestic main, and your voltage drops from 240 to 180, then you WILL either blow a fuse, trip a breaker, blow a PSU, blow an entire rig, or set fire to something. You've got me worried now - I'm checking the voltage on all my kill-a-watts. 

Yes, but the 1200W DC rating is the addition of loads on the 12v, 5v and 3.3v rails. You will basically only be drawing power from the 12v rails.  To be sure, check the maximum specced load on the 12v rails (in watt or ampere, its always written on the side).

Then again, for an el cheapo 350W PSU, this might make a big difference as up to half of that  "350W" might only be delivered on the 5v and 3.3v, but a decent 1200W is probably all about 12v anyway, Id be shocked if it was specced for less than 90 amp (1080W DC)

That's really good to know. Just to clarify the max is 1200 dc.

Would I be correct to assume that a good PSU would have a cutoff aswell as opposed to letting itself blow up.

That's really good to know. Just to clarify the max is 1200 dc.

It makes sense because I assume the PSU can cope with dissipating extra ac anyway?

Would I be correct to assume that a good PSU would have a cutoff aswell as opposed to letting itself blow up.

This.  1220W AC at the wall @ 85% efficiency is 1037W DC.  The powersupply is rate to provide 100% of rated load (1200W) continuously. 

You are fine.

Are you drawing 1220w at the wall? Keep in mind the ratings are for power delivered to the PC at 12v (and some at 5 and 3.3v). Power supplies are not 100% efficient, assuming 85% efficiency if you deliver the rated 1200W to the PC, it will by pulling  1411W at the wall without exceeding its specs.

If you want real peace of mind then a UPS with pure sine wave output is what you want, good stable power to the box at all times using one of them.

Not really useless, but at the very least it gives you a peace of the mind .  Dealing with power companies can be tedious and pain in the neck.

Maybe you want to get a surge protector or something while waiting for your power company reply, such variance is not common.

I really hope that my PSU's don't get damaged with this variance. Can't cope with more downtime and putting more money in.

I measured (with good equipment) anything between 150 and 270 V in a timeframe of about 3 weeks. I was curious why my equipment froze at random, UPS-es made strange noise (and one died) and so on. After that I decided not to measure anymore...

The electricity mains in my country has a variance of +/-7%.  It is impossible to get 180-190V

lol that's made up on the spot b.s.  
but whatever