# UPS on a Generator



## MikeFL (Apr 16, 2016)

What % of that 12kW is your demand?


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## wiz1997 (Mar 30, 2021)

The UPS's at full load would be 9600, so around 80%.

Don't know if we are going to power or be able to power all four UPS's or the small AC unit in the server room.

Plant manager jumped the gun on me and ordered the generator.

Now I have to make it work.

I can work out the load issue, just wanted to see if there is something I need to do to clean up the generator power.


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## kb1jb1 (Nov 11, 2017)

Is it a portable generator or a standby permanent one? Portables generally do not have clean power as a permanently installed type.


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## gpop (May 14, 2018)

Had a Allen Bradley UPS which hated the generator but after adjustment it was fine. The other 50 to 100 UPS units i have installed all work fine with a generator. They might switch for a few seconds to battery power if the genny picks up a heavy load but that's basically why we installed them in the first place.


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## wiz1997 (Mar 30, 2021)

kb1jb1 said:


> Is it a portable generator or a standby permanent one? Portables generally do not have clean power as a permanently installed type.


Portable.

Which is why I am asking about something to clean up the power if needed.


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## splatz (May 23, 2015)

You can use a power conditioner to clean up the power from the generator. I haven't purchased any in a while but Sola was the most common brand in my area. They use a ferroresonant transformer and have a very good reputation for quality and for lasting, but they were not cheap. You'd probably be better off buying UPS's that tolerate your generator's output power. Looks like the prices are even higher now 

23-28-275-6 | SolaHD | Voltage Regulator (abbdrivesales.com)











You have to look at how tight the frequency range the generator will run and make sure the UPS will accept that frequency range without switching off AC supply and running off the batteries, but that's not all. If the generator is supplying a square sine wave or otherwise ragged power, the UPS may not accept it. The UPS may have an adjustment for this.

The better online / dual conversion UPS's generally handle dirty power better because they only use the supply to rectify and charge batteries, the batteries run the equipment through an inverter. The Ferrups, which used is still sold by Eaton, is known for handling all kinds of noisy, raggedy power, and for lasting forever. They build in a ferroresonant transformer like the Sola power conditioners use. You couldn't go wrong installing a single Ferrups sized to power all the PDUs in the racks in the data center or server room - no UPS in the racks. Eaton has other UPS's that are specifically rated for using with generator power though, and they prefer to sell their newer lines over the old Ferrups. They keep the Ferrups around because there are a lot of very loyal customers that won't accept anything else.

But your UPS's sound like they are much smaller. What is the VA rating of the UPS's? I've had good luck with Eaton 9PX and 9SX type UPS's since long before they were Eaton, those are online / dual conversion and last a long time. Eaton has different UPS selector pages, there's one for the smaller units and another for the bigger room sized to facility sized units. Their website is a bit mixed up from buying companies and changing things and never quite ironing things out over the years. If you can get someone decent on the phone, they have good people, it's just getting to them is a challenge.


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## Forge Boyz (Nov 7, 2014)

We did a server room with a 100KW Eaton UPS that was backed up with a customer supplied 100KW Generac generator. The UPS refused to accept the power from that generator and would run on batteries only when the power was out. The generator was a two pole unit and was apparently electrically "dirty". We replaced it with a Cummins and they have had no problems since.

Sent from my SM-G970U using Tapatalk


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## micromind (Aug 11, 2007)

splatz said:


> You can use a power conditioner to clean up the power from the generator. I haven't purchased any in a while but Sola was the most common brand in my area. They use a ferroresonant transformer and have a very good reputation for quality and for lasting, but they were not cheap. You'd probably be better off buying UPS's that tolerate your generator's output power. Looks like the prices are even higher now
> 
> 23-28-275-6 | SolaHD | Voltage Regulator (abbdrivesales.com)
> 
> ...


Nearly a million dollars for that power conditioner????????


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## paulengr (Oct 8, 2017)

1. Do not buy APC. That garbage goes on UPS for stupid reasons. It’s supposed to be double conversion.
2. If your generator is not that stable get a better one. Even the most garbage Generac comes with a digital AVR these days and they’re cheaper than the old analog ones. Industrial generators cost more for a reason. But let’s get right down to it. Your UPS should accept anything between -15% and +10%. That is what is known as STANDARD CONDITIONS. for normal operation. It should accept a wider range for short periods which is where the UPS is supposed to do its job. Look at CBEMA curves as the standard. Your AVR should keep the generator dips under 1% (if generator is sized correctly). If you need to adjust system voltage a little you can usually tweak it. Many can adjust response times too but usually the factory defaults are good enough. If you overtune it, it can give unstable output..The generator should come up to speed and energize the line in 30 seconds once it receives a run command. Now the reason for mentioning standard conditions is that APC does not follow those even though it’s part of NEC and UL. They can specify other conditions (and they do) but you’ve been warned.

So that being said a lot of welders and RV/portable gensets are pretty awful. But you shouldn’t be using those for your IT equipment. But plenty of sites get a huge 2 hour battery and a big welder.


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## splatz (May 23, 2015)

micromind said:


> Nearly a million dollars for that power conditioner????????


Well that's list :|


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## SWDweller (Dec 9, 2020)

Most generators produced below 20 kw are considered portables. Great for a camping trip or some saws on a construction site. Under 20kw generators typically are RPM driven and have not controls for voltage or HZ. 3600 rpm generator into a ups your asking for trouble, IMO. Who knows you may get lucky. Then there is a all of the neutral and grounding considerations which I will assume you worked out before you bought the equipment. 

Point of order you have 4 UPS's and two 120v circuits on the typical gen set. How are you planning on making that work? If you use the 50 amp circuit that may be available what fusing or over current devices have you purchased? 

How long do you have based on the current load will the UPS's last? 

Manual transfer, sure hope someone that is trained for this is on site 24-7-365.


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## joe-nwt (Mar 28, 2019)

Take the generator back and get an inverter style. Quit dickin'n around here, we're talkin' IT here for pete's sake!


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## paulengr (Oct 8, 2017)

joe-nwt said:


> Take the generator back and get an inverter style. Quit dickin'n around here, we're talkin' IT here for pete's sake!


Large generators aren’t inverters. Inverter generator a very noisy output that passes right through the rectifier onto your DC bus. Very, very bad idea.


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## Navyguy (Mar 15, 2010)

Isolation Transformer.

Cheers
John


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## joe-nwt (Mar 28, 2019)

paulengr said:


> Large generators aren’t inverters. Inverter generator a very noisy output that passes right through the rectifier onto your DC bus. Very, very bad idea.


Since the transferring will be done manually, and the UPSs are only 15% loaded, I bet this would serve him just fine.



https://powerequipment.honda.ca/generators/ultra-quiet-7000i-es


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## nrp3 (Jan 24, 2009)

Air cooled is one thing and 3600rpm units are the norm. I just say no to 3600 rpm liquid cooled units of any brand. Most companies have 1800 rpm units in a variety of KW sizes. I get the impression and or from limited schooling that capacitive loads from large UPS units could significantly drive up the size of the generator in relation to load. I have a couple of small three phase air cooled units that have done ok with small server rooms. IT guys are always around when we test the transfer switches and there hasn't been any screaming.


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## nrp3 (Jan 24, 2009)

Most of the units today aside from the smallest standby units are electronically governed. I try to avoid those anyway (mechanically governed).  Portables are mostly mechanically governed on the small side. That said, maintained, they don't do too bad, on a residence.


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## LGLS (Nov 10, 2007)

Navyguy said:


> Isolation Transformer.
> 
> Cheers
> John


An Iso will just duplicate the same waveform it's supplied with though... just no reference to ground.


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## splatz (May 23, 2015)

Here's some more real pricing for power conditioners.

The OP still hasn't indicated the VA rating of the UPS's that are at 15% load. Just because it has a 20A 120V supply doesn't mean the capacity of the UPS is the full capacity of the circuit. It is likely it's more than 120*15*.8 = 1440VA or the manufacturer would have used a 15A plug for a 15A circuit. It's probably less than 120*20*.8 = 1920VA so let's just say they are 2000VA UPS's. If they are loaded less than 15%, that's 2000*4*.15 VA or just 1200VA total load. That's not much and I'd carefully verify the load is really that the load is really that low before spending any money.

From the SolaHD spec sheet, there's a 2000VA unit that would work and leave you with some additional capacity

Catalog Pages: SolaHD™ CVS Hardwired Series Constant Voltage Transformers, February 2020 (ideadigitalasset.com)










The price for this at Allied (usually a bit high)










Four grand is not cheap but consider that's likely the cost of one server on one of those four UPS's and it doesn't seem so bad. Sure it's probably better to have the right UPS and the right generator but if this gives you the flexibility to make whatever combination you get stuck with work, it has a lot of value.


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## just the cowboy (Sep 4, 2013)

I'll let you know next week, I am starting up a Koehler 30 amp one that will feed (3) 700 watt UPS's at 25 % load each and I told the contractor it needs to do just that. 
I did try a Honda whisper and the ups did not come out of battery mode.
I tried the portable that was mounted to my truck same thing UPS would stay in battery 
Hooked it up to our light pole unit, UPS tripped GFI but it did run it on the non fine GFI receptacle.


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## LGLS (Nov 10, 2007)

If it has utility power, and gen backup, and a UPS... WHAT other than our missile defens and communications system could possibly be that dire important?!?!?!


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## JRaef (Mar 23, 2009)

The TYPE of UPS will make a huge difference. The best type to use in conjunction with a backup generator is a* double conversion on-line UPS*, which is of course the most expensive type. It is a rectifier / power conditioner on the front end that converts AC to DC, then the DC feeds a battery bank and the DC is inverted back into AC for the load. Because the batteries are always connected to the DC bus, there is no "transfer time" when the power source changes. More importantly here, the line interactive front end automatically adjusts to whatever is happening on the line side, but because it is also just rectifying to DC anyway, input frequency fluctuations from the generator are irrelevant.

Cheaper Off-Line UPS are the ones that give you headaches, because without the ability to ignore frequency fluctuations, they are forced to go onto batteries any time the line side source is not damned near perfect. Stay away from those for this kind of application.


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## just the cowboy (Sep 4, 2013)

LGLS said:


> If it has utility power, and gen backup, and a UPS... WHAT other than our missile defens and communications system could possibly be that dire important?!?!?!


Any server that is running a SCADA system. If my network has to do a restart the operators go blind to all remote site operations till the reboot of all software is complete. Same with PLC's for the system UPS holds PLC up till generator kick in.


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## splatz (May 23, 2015)

LGLS said:


> If it has utility power, and gen backup, and a UPS... WHAT other than our missile defens and communications system could possibly be that dire important?!?!?!





just the cowboy said:


> Any server that is running a SCADA system. If my network has to do a restart the operators go blind to all remote site operations till the reboot of all software is complete. Same with PLC's for the system UPS holds PLC up till generator kick in.


Besides the type of UPS - online or line interative - the two main specs on a UPS are the VA rating and the runtime. The runtime boils down to just a function of the amp-hours of the batter bank. With a generator, you don't need a lot of runtime. But you still have to cover your VA rating, so you can get past the blips before the generator powers up and the delay for it to sync up.


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## paulengr (Oct 8, 2017)

On larger systems it pays to look at high availability servers and redundant networks. So in this case you have two servers running identical VMs that constantly check with each other. In the event that you have a server failure the transition to the backup is a few milliseconds. Most people won’t even notice. Hardware wise each server should be on a separate UPS and have its own network switches also on a separate UPS. Similarly at the storage level having two SANs running is helpful.

In practice what I have found is there are always things you don’t expect that cause problems with any backup system. For instance in one installation there was already an isolated subpanel with all the emergency stuff in it. We just moved the critical servers and HVAC to the same subpanel. The first time the system operated is when we discovered all the battery powered exit signs and emergency lighting fed from that panel would not operate because the generator fooled them into staying turned off. But the good news according to the IT guy was that a fridge plugged into the only receptacle in the utility room stayed on so at least he could see to put his lunch away.

Another one was a 52 MW turbine that was set up for islanding. The first time it got “tested” is when they discovered the PLC running the cooling tower was on a noncritical line so the whole system was crippled and shut down 20 minutes into operation.


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## just the cowboy (Sep 4, 2013)

paulengr said:


> On larger systems it pays to look at high availability servers and redundant networks. So in this case you have two servers running identical VMs that constantly check with each other. In the event that you have a server failure the transition to the backup is a few milliseconds. Most people won’t even notice. Hardware wise each server should be on a separate UPS and have its own network switches also on a separate UPS. Similarly at the storage level having two SANs running is helpful.


You just described my system. With the exception of I have two redundant high availability servers systems running two applications, with two backup storage systems. They are located in separate locations, Veem does full cross backups. If I do lose a whole system to fire, ransomware, corruption or main machine failure I can just restore it to the other server and be back in operation again.


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## dvcochran (4 mo ago)

wiz1997 said:


> Company purchased a 12KW generator 120/240 to power 4 UPS backup systems for our servers.
> 
> I've done some research and found that a UPS may not function well on a generator.
> 
> ...


I am assuming it is not an inverter generator? 
A power conditioner like this could be used: Power Conditioners - Power Distribution - MSC Industrial Supply (mscdirect.com)


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