UPS That Doesn't Play Well When Running On the Generator

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sparkyrick

Senior Member
Location
Appleton, Wi
I learned something new today. A new customer that we are doing a second floor build-out of unused space was going to have us re-feed their UPS because they said it wasn't on their generator. I looked into it and the entire building is actually on the generator (277/480V, 800A), how they didn't know that is beyond me. But the real kicker is when the building goes to generator, the 100A, 120/208V UPS will not connect to the generator power and shuts down after about 15 minutes when the batteries are depleted. Both the Gen-set and the UPS are well known brands too. A quick search reveals that this is a common issue with UPS systems and generators.

I guess I have to find the exact model of the UPS and see if the settings can be changed to accept generator power that fluctuates slightly. Anyone else have this issue before?
 
Long ago, in a city far away.... does the generator have a mechanical or electronic governor? I've found that with the line current waveform* from the battery charger of many, especially older, UPSs, a mechanical gov will get hopelessly confused. I've also found that some UPSs are very frequency sensitive when phase-locking the inverter to the bypass. Is there a static bypass feed from the gen to the UPS? Try running the UPS with that disconnected and let the inverter use it's internal frequency clock.

*asymmetric, probably lagging, not linear, etc

Edit- Hmm, scratch the bypass idea unless it's also fed from the generator. I'd still look at the governor and freq stability.
 
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ceb58

Senior Member
Location
Raeford, NC
I have a few UPS's that didn't like to play with the generators. The UPS's has a terminal board on back where you could put a jumper wire in to expand the parameters which on a few wasn't enough. But I did do some searching and found with the right service password I could open up the Hz parameter to accept the generators fluctuation.
 

sparkyrick

Senior Member
Location
Appleton, Wi
I have a few UPS's that didn't like to play with the generators. The UPS's has a terminal board on back where you could put a jumper wire in to expand the parameters which on a few wasn't enough. But I did do some searching and found with the right service password I could open up the Hz parameter to accept the generators fluctuation.

I'll recommend that to the customer. I'm betting when the TS switches to EM power, the generators voltage and frequency sag slightly when the load connects. The UPS is probably seeing that sag and not connecting to the generator power.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Dirty power. I've seen that problem frequently. UPSs look at the input power and when they see fluctuations and crap from the generator they switch to battery to keep it from getting to the load. That's exactly what they are supposed to do. If you have one which you are able to play with to make it less "sensitive" you are only fooling yourself. Hell, just unplug it and connect the computer directly.

The right answer is to get a better UPS, one which always runs on battery and only uses the commercial power to keep the batteries charged. Then there is the option of a better generator too.

-Hal
 

tom baker

First Chief Moderator
Staff member
I have seen this on a Best Ferrups UPS when running on a generator, it was not happy that the generator was .5 hz slow, so it kicked in. Solution was to use software to adjust the frequency tolerance of the UPS.
I would call the UPS tech support line, they have experience with this and can assist.
I did find out the the newer UPSs (such as Eaton Powerware 9000 series) don't have this issue.
 

ceb58

Senior Member
Location
Raeford, NC
Dirty power. I've seen that problem frequently. UPSs look at the input power and when they see fluctuations and crap from the generator they switch to battery to keep it from getting to the load. That's exactly what they are supposed to do. If you have one which you are able to play with to make it less "sensitive" you are only fooling yourself. Hell, just unplug it and connect the computer directly.

The right answer is to get a better UPS, one which always runs on battery and only uses the commercial power to keep the batteries charged. Then there is the option of a better generator too.

-Hal

I don't see it as fooling any one and I think the Eaton 9170+ is a very good unit for the application but When the UPS comes set with only a 1 Hz +/- tolerance then it is asking a lot out of any generator. But I have found that most of the communication site I have that have a small load on the generator has the most deviation in Hz. I have buildings with a total load of about 9 Kw with a 40 Kw generator. With that small of a percentage of a load it is hard for the electronic governors to lock in and keep the Hz in a low tolerance but if I adjust them to run with a 3 Hz +/- then they are happy with the generator.
 

sparkyrick

Senior Member
Location
Appleton, Wi
Dirty power. I've seen that problem frequently. UPSs look at the input power and when they see fluctuations and crap from the generator they switch to battery to keep it from getting to the load. That's exactly what they are supposed to do. If you have one which you are able to play with to make it less "sensitive" you are only fooling yourself. Hell, just unplug it and connect the computer directly.

The right answer is to get a better UPS, one which always runs on battery and only uses the commercial power to keep the batteries charged. Then there is the option of a better generator too.

-Hal

It is an older UPS system that feeds a 42 space panel, not a simple desk model. The gen-set is is a Cummins Power Generation and is only a few years old. I think it's a 550KVA unit, but I'd have to double check. Given that the UPS is an older system, perhaps a replacement double conversion system would be the best route. But I will contact the manufacture and see how tight the frequency tolerances are right now and see if widening the band is an option.
 
Dirty power??? Isn't the whole point of a UPS to isolate the load from line disturbances? A UPS that simply kicks over to battery&inverter and doesn't keep charging the batteries, isn't worth much IMHO. Always supply the load and always keep the batteries charged as long as there's some input power.

So-
Does the genset have a mechanical or an electronic governor? Probably mech. if it's not actually holding speed/freq. (Has this been verified?)

Is the existing UPS line-interactive or double conversion? ("older" UPSs were double conversion because that's all there was, I'm thinking 30 years ago, not 10) A real double conversion system shouldn't care about input freq (unless it's used as freq/phase reference for the inverter).

Is there a static bypass and is it fed from the ATS? Sounds like it would be from the initial post. (Try running the UPS from genset w/o the static bypass line powered.)
 

sparkyrick

Senior Member
Location
Appleton, Wi
Dirty power??? Isn't the whole point of a UPS to isolate the load from line disturbances? A UPS that simply kicks over to battery&inverter and doesn't keep charging the batteries, isn't worth much IMHO. Always supply the load and always keep the batteries charged as long as there's some input power.

So-
Does the genset have a mechanical or an electronic governor? Probably mech. if it's not actually holding speed/freq. (Has this been verified?)

Is the existing UPS line-interactive or double conversion? ("older" UPSs were double conversion because that's all there was, I'm thinking 30 years ago, not 10) A real double conversion system shouldn't care about input freq (unless it's used as freq/phase reference for the inverter).

Is there a static bypass and is it fed from the ATS? Sounds like it would be from the initial post. (Try running the UPS from genset w/o the static bypass line powered.)

There's only one feeder supplying the UPS, so I'm guessing so static bypass line powered. What exactly does the static bypass do anyway?
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
I have a few UPS's that didn't like to play with the generators. The UPS's has a terminal board on back where you could put a jumper wire in to expand the parameters which on a few wasn't enough. But I did do some searching and found with the right service password I could open up the Hz parameter to accept the generators fluctuation.

We have had the opposite problem. Generator doesn't like the UPS.
Once some load was added to the UPS everything was fine.
 
There's only one feeder supplying the UPS, so I'm guessing so static bypass line powered. What exactly does the static bypass do anyway?

It's usually an internal electronic switch in the output line of the UPS, fed by both the inverter and (usually) an external power input, that allows you to power the load without running the inverter. Used in case of inverter faults but can also be triggered if the batteries run down and the bypass line has power. If there is a bypass feed, it's often used as the freq/phase reference for the inverter.

Check to see if the UPS has a "bypass" feature. In your case with only one feeder, I think we're back to things like freq sensitivity of the UPS control system and genset stability.

And I'll second what qcroanoke said, sometimes it's the genset that doesn't like the UPS. More load on the UPS can help, but also sometimes more (3-phase balanced) load on the genset can help.
 

ceb58

Senior Member
Location
Raeford, NC
We have had the opposite problem. Generator doesn't like the UPS.
Once some load was added to the UPS everything was fine.

That is true Mike but think of it this way. You added load to the UPS so in turn you have added load to the generator which in turn helps settle the electronic governor down. In one of our older metal buildings we had only the radio equipment with no UPS. The generator would not settle down and kept hunting. We wound up installing 5 Kw heat strips on a relay. They would come on when the generator ran and would keep the generator running at a steady speed.
 

Fulthrotl

~Autocorrect is My Worst Enema.~
The right answer is to get a better UPS, one which always runs on battery
and only uses the commercial power to keep the batteries charged.
-Hal

if i were looking for something like that, can you recommend
any manufacturers?

i'd love to get a 2KVA unit for personal use that works that way,
but that's a separate issue, as i suspect nothing on the market
that small works that way.
 

iwire

Moderator
Staff member
Location
Massachusetts
if i were looking for something like that, can you recommend
any manufacturers?

i'd love to get a 2KVA unit for personal use that works that way,
but that's a separate issue, as i suspect nothing on the market
that small works that way.

It's called a double conversion UPS. Here is a 1kva http://www.amazon.com/1000Va-On-Line-Double-Conversion-Critical-Network/dp/B00180HW6G

<snark>They are more expensive and over the top for personal use. In other words you will love to get one and tell us about it.:D<snark>
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
A customer of mine bought an inverter style generator from Northern Tool to run his boiler for floor heat. He was worried about the surges of a standard generator affecting the electronics. Pretty impressive. RPM of gen came up as load came up. His had the ability to parallel with a 2nd generator of the same style/brand. Small & and about twice the price.
 

sparkyrick

Senior Member
Location
Appleton, Wi
A customer of mine bought an inverter style generator from Northern Tool to run his boiler for floor heat. He was worried about the surges of a standard generator affecting the electronics. Pretty impressive. RPM of gen came up as load came up. His had the ability to parallel with a 2nd generator of the same style/brand. Small & and about twice the price.

My Honda EU2000i does the same thing. I think they were the first manufacture to offer inverter generators and then the copycats started. LOVE my little Hondy genny.
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
That is true Mike but think of it this way. You added load to the UPS so in turn you have added load to the generator which in turn helps settle the electronic governor down. In one of our older metal buildings we had only the radio equipment with no UPS. The generator would not settle down and kept hunting. We wound up installing 5 Kw heat strips on a relay. They would come on when the generator ran and would keep the generator running at a steady speed.

Not really Curtis,
I went to Pennsylvania to check one doing this and even with the heat running and all other loads on the genset everything was fine, until the UPS came on line then the genset went nuts, RPM's were up and down. As soon as I plugged in1500 watts of heat into the ups supplied outlets everything was fine.
Not sure why.
 

ceb58

Senior Member
Location
Raeford, NC
Not really Curtis,
I went to Pennsylvania to check one doing this and even with the heat running and all other loads on the genset everything was fine, until the UPS came on line then the genset went nuts, RPM's were up and down. As soon as I plugged in1500 watts of heat into the ups supplied outlets everything was fine.
Not sure why.
Well, I do remember one that was in one of the larger buildings. It had a small load on it and it made the generator hunt. We wound up removing 2 modules dropping the Kw rating down to 12Kw.
 
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