Is it bad to run computers on modified sine wave 24/7?

[Red Squirrel]

For a while I've been wanting to upgrade my UPS setup to a proper 48v dual conversion setup with pure sine inverters, but reality is that stuff is hard to find, and is expensive.

So I'm thinking of just running everything off a 12v inverter and then powering it by a 13.5v power supply and putting a battery in the middle. Considering the first stage of a computer PSU is to rectify into DC anyway, I can't see it being an issue, but would it? Heck, could I run them right off DC? Then I can skip the inverter altogether and only need a boost converter to bring about 170vdc into the PDUs. If I end up designing my own power supplies I'd probably do a 48v system, but if I buy I'll buy 12v. It's easier to find 12v stuff.

My ideal setup would be telecom grade rectifiers and inverters, but can't find anywhere that really sells that stuff other than used on Ebay.

 

[JoeBleed]

everything i've read says most computer power supplies don't care about modified sign wave due to the conversion process. So as long as your inverter is of decent quality, it should be fine. You mention putting a battery in the middle, be careful with over charging. I think early, cheap UPS units used to be modified/square sign wave. I think.

Also, unless your power is crappy to start with(noise/fuz in the wave), Online ups unites aren't necessary usually. Odds of a cheap inverter failing and causing you downtime is more likely than a decent standard ups with AVR. Oh, i've researched online UPSs a little while ago, many to most units from APC, Tripplite, and Eaton offer a power saving mode which basiclly turns it into a standard switchable unit. I'm trying to remember if my EAton unit was defaulted in this mode or not. But then again, it wasn't new when i got it.

 

[HutchinsonJC]

I think early, cheap UPS units used to be modified/square sign wave. I think.

**Many** UPS are a modified/squared off wave (don't read that as me saying it's a fully squared wave). And these UPS are HORRIBLE for induction motors. In many cases the motor will run very inefficiently (hot), or while under load it's possible it will not run at all. The motors can also end up running with a lot of noise.

Some electronics can actually run better, more efficiently, on squared off sine wave, but most devices will be designed to work with a proper sine wave anyway, because that's what is coming out of the wall... basically everywhere.

If the UPS is not marketed in some way to tell you that it generates a proper sine wave, then it almost assuredly does not as it's more costly to make a UPS generate a decent sine wave, which means that if it did, they'd market/advertise it to you some how.


"Is it bad to run computers on modified sine wave 24/7?"

For a while I've been wanting to upgrade my UPS setup

UPS shouldn't be outputting anything but sine while the power is active. It's when you lose power that the UPS kicks on generating a modified or a sine wave from the battery in the UPS. So when you say 24/7, it shouldn't be getting 24/7 squared waves from any UPS.

Personally, I recommend a proper sine wave UPS just because it makes the UPS available to any type of electronics to be plugged into it, but most computer power supplies will probably deal with a modified sine wave without too much of a hiccup.

 

[Red Squirrel]

UPS shouldn't be outputting anything but sine while the power is active. It's when you lose power that the UPS kicks on generating a modified or a sine wave from the battery in the UPS. So when you say 24/7, it shouldn't be getting 24/7 squared waves from any UPS.

Hence my question, since my proposed setup would mean the computers are always running on inverter. Similar to how the telcos do it, though with telcos a lot of the equipment is designed to run straight off the DC bus but there is stuff on inverter too (they use pure sine though). The idea is to not have a delay between switching to battery. I've seen that cause issues at random. I think it really depends on how unlucky you get, like if the power outage strikes right when the sine wave is at 0 volts, the PSU is already discharging it's capacitors at that point, then the delay for the relay to kick on and the inverter to start supplying power adds to the lack of power and then the PSU dies. Basically it misses part of an AC cycle during the transfer. Now if the power outage hits when the AC sine wave is high it's less of an issue as the capacitors can carry over the load while the UPS transfers to battery. At least that's my theory. I've turned my breakers on and off many times and I'd say 90% of the time the UPSes all transfer on time, but once in a while they don't, especially if the power outage is dirty. Like slowly turning off the breaker and letting it arc. Or a tree falling on a line and it does not quite cut the power cleanly etc.

Though the more I think about it, I think I will just wait for now. I do have the UPS for my workstation and mining rig that needs a new battery which is what got me thinking about this since it seems I just changed those batteries a few years ago, and now I already have to do it again. Flooded cells, which is what you'd use for a setup like this, don't need to be changed so often. Pricing out inverters and PSUs and really this temporary setup would end up costing me like $600 so I'm better off just spending more on a proper pure sine setup in the future once I can figure out a way to source the equipment I need, or learn how to design my own converters. I can get pure sine inverters off solar stores, it's the rectifiers that are harder to find but those would be simpler to design.

 

[HutchinsonJC]

If the electronics on a 12v modified sine wave inverter are anything like they are for most modified sine wave UPS, it'll have probably close to 470v peak voltage... which long term use will most likely burn something up on a typical computer power supply.

Some UPS manufactures have had techs or engineers reply by email about this 470v deal a few times that I've seen; that's where I'm getting this 470v from (the rms is obviously much lower). The bulk capacitor (qty x1 400v or qty x2 200v) of a pc power supply doesn't like that 470 volts, though.

I guess in the end, it's really going to heavily depends on how the folks behind the inverter do their stepped wave. I'd sooner get a pure sine inverter and not have to worry about it.

 

[HutchinsonJC]

Looking some stuff, allow me to correct my above because I mis-remembered the capacitor setups on pc power supplies.

If your power supply uses active power factor correction you'll have a single 450v capacitor and the 470v peaks will be pretty minimal problem, but still, a long term use or setup, might shorten life of the capacitor.

In a non active power factor correction power supply, where you have a switch to click from 120 to 240v (red switch, usually)... you have generally two 200v capacitors and in the 120v mode, you only get one 200v capacitor (the other sits idle). In that situation the 470v peaks are way beyond spec for the capacitor.

 

[Red Squirrel]

Actually yeah you're right a lot of them might greatly overshoot so you end up with spikes. I'd have to put one on a scope and see but that would require to buy before to be able to test it. Not like they advertise the wave form.

Think for now I'll just go ahead and replace the existing gel cells in the existing UPS, then stick to the plan of doing the proper 48v pure sine setup. When I do that setup I can just have it power everything instead of having a bunch of smaller UPSes. I do have a 12v inverter-charger setup that runs on flooded acid batteries but I don't want to put too much stuff on there, it's only 750w. The nice thing with flooded acid is they are cheaper per amp hour, and also have a longer life time. You can get 25+ years out of them if you take good care of them. I'm not as religious about it as I should be (ex: monitoring cell temperatures, midpoint voltage etc) so I might get more like 10 years but still better than gel cells.

 

[Ken g6]

Heck, could I run them right off DC?

Anybody mentioned a "picopsu" yet?

https://www.amazon.com/Mini-Box-picoPSU-160-XT-Power-Mini-ITX-Supply/dp/B005TWE6B8

 

[Red Squirrel]

Anybody mentioned a "picopsu" yet?

https://www.amazon.com/Mini-Box-picoPSU-160-XT-Power-Mini-ITX-Supply/dp/B005TWE6B8

Yeah heard of those actually. Would work for smaller machines, not sure about big servers or even a full blown workstation though.

I wish 48v ATX and server PSUs were more common. You'd think they would be as they would probably be popular in data centres. No reason those can't be setup like telcos. They do make them but they are much harder to find.

 

[Modular]

It sounds like this may be what you're looking for:

https://www.newegg.com/Product/Product.aspx?Item=N82E16842107133

I've been running this one for my home theater setup for about a 2 years. It's a double-online, pure sine wave UPS. It's got plenty of backup time as well and the price is amazing for what you get. I got mine from Amazon for $299 so it might be worth waiting to see if the price comes down again. I don't see it on Amazon at the moment though.

Edit: the fan it comes with is absolutely, hilariously loud. I replaced mine with a Noctua NF-A8 ULN and the temperature is the exact same, but I can't hear it running at all. That's my only major complaint about this UPS. Navigating the menu is also a little cumbersome, but not a big deal as once you have it setup how you want, you really don't need to use the menu again.

I also like to see how many watts my system is drawing, or what the line voltage has fallen to while under heavy loads - you can see these things by navigating to them through the menu, but you can't make them static on the display at all times. It will time out and revert back to just saying "Online Mode" or something like that. I'd much rather that I could leave it on the wattage I'm drawing and have it stay there. A minor complaint. It doesn't effect day to day usage at all.

Hope that this helps!

 

[thecoolnessrune]

Yeah heard of those actually. Would work for smaller machines, not sure about big servers or even a full blown workstation though.

I wish 48v ATX and server PSUs were more common. You'd think they would be as they would probably be popular in data centres. No reason those can't be setup like telcos. They do make them but they are much harder to find.

Telco equipment is expensive. Expensive heavy iron gear is also available with LVDC and HVDC. Cisco UCS Blade Chassis for instance can be ordered with 48-60 VDC and 200-380 HVDC Power Supplies. Many Dell servers have similar power supply options. One caveat aside from sourcing the power supplies is the power distribution module (PDM) or Power Plane (it goes by a could different names in the industry) when you have redundant Power Supplies. Sometimes swapping a server over to DC Power Supplies mandates that the PDM or PP gets swapped out as well. The Technical Manual for the server should specify it. You can can search for your equipment and see if there was a DC option for it.

Telcos use DC because they had to. Telco Racks are not nearly as dense as modern computer racks. You had relays and a bunch of other Analog era stuff where AC would pose large challenges to minimizing noise, interference, and solenoid chatter. Those issues are becoming far less prevalent nowadays but when you have all that historical equipment to service, the standard carries on.

To carry DC to the Rack in a large datacenter you'd need to use HVDC designs with step-downs, and while there's lots of AC Power Supplies that do 120 or 240 (and the 3-phase in-betweens), there's little DC equipment that will handle 48V Telco DC along with 300V HVDC. You also can't get low voltage without active components unlike tapping a leg to neutral on a 3-Phase source.

These aren't unsolvable hurdles, but just like the Telco industry is "stuck" in 48V due to ancient standards, the Datacenter industry is "stuck" in 208V 3-phase power. The difference is 3 phase is very flexible, with 120V able to take a leg to neutral, and everything else taking a phase to phase. If you need lots of power, you install 3 Phase Power Supplies, and if you really need high power you skip the distribution PDU in the facility and take 480V 3 Phase directly. You can again, do all this with DC, but you're going to need active components that increase cost. There's simply a lot of factors in why DC isn't in common use.

 

[Red Squirrel]

Hmm yeah I guess 48vdc would not work well in a data centre. We have around 1,600 amps at 54vdc being drawn from our power plant and I imagine that is a very small number in the data centre world. And yeah telco equipment is not cheap, probably why I can't really find it. There are plenty of sites that "sell" it, but they don't actually... sell it to anyone. You have to be a company with the right contacts and a procurement dept etc. When a site does not show the price of something or make it available to buy, it means you can't afford it.

So yeah think I will probably end up sticking to my original plan of building my own 48v setup. I should start small scale, maybe I will build a square wave UPS as a project. I might even look at CSA/ETL certification depending how far I go. That would allow me to sell the units.

I may still experiment with a ~1kw inverter and 13.5v psu to build a crude dual conversion UPS for machines that arn't as important but still don't want plugged right into mains though, like my mining rig. If the peaks are two high I could always swap the capacitors in the computer PSU for higher voltage rated ones or see if I can filter those peaks out with some kind of snubber circuit. For now I'll probably just replace the gel cells in the existing UPS for those machines though, just hate spending money on stuff that does not last. I just changed those not that long ago. At least with flooded acid batteries they last longer. You CAN connect those to a regular UPS but I don't like how they charge so hard, I've clocked voltage as high as 15 volts on some units. It's probably why the gel cells don't last tbh. If you float them at 2.25v per cell they are probably fine. But with flooded at least you can add water.

 

[Red Squirrel]

Ordered a 1500 va UPS for the mining rig, That should at least tie me over till I can get a proper high capacity 48v setup going that can just do everything.