Discuss Generator + UPS Woes in the Electrical Forum area at ElectriciansForums.net

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gdi2k

Greetings,

I'm in the Philippines and have an office full of PCs that need to run with as little interruption as possible. Power is pretty reliable here in general, but we have rotational blackouts for an hour a day at the moment due to a regional shortage caused by damage from the typhoon in November.

We have a generator, and each PC has a UPS backup battery. The idea is that when the grid switches off, all equipment is powered by UPS until the generator comes online. But when it does, most of the UPS devices don't accept the generator's power output (they all synchronously click back and forth between line and battery) and continue to discharge until they shutdown. At that stage we bypass the UPS devices until grid power returns, then we have to switch everything back again. It's a pain.

We've had the generator looked at a few times, apparently it's doing its job correctly and according to spec; it's voltage and frequency is spot on. It is not overloaded (not even to 50%).

The UPS people (APC) tell me to reduce the sensitivity setting on the UPSs, but it doesn't make a difference.

What we've got:
  • Generator is a 5000W portable unit, specs linked here.
  • A range of UPS devices, from cheap "fire hazard" grade, to more respectable (or at least expensive) APC units.

Ironically, it seems that the cheaper the UPS, the more tolerant it is to accepting power from the generator.

I am looking for help as to how I can solve this. I have read of power line conditioners - is this what I need?

Any advice greatly appreciated!
 
The switch-mode power supply that the UPS's and PC's will use are an ugly load for the generator to deal with.

Have you tried adding a simple resistive dummy-load to the generator such a halogen flood or even an oil heater?
 
The switch-mode power supply that the UPS's and PC's will use are an ugly load for the generator to deal with.

Have you tried adding a simple resistive dummy-load to the generator such a halogen flood or even an oil heater?

Thanks for this, I will try to find something suitable. At the moment it is powering all the UPS devices, a few strip lights and not much else.

I will report back...
 
Have looked at your gen spec. It is a very small generator. Is it an inverter output device or a proper rotating machine?

I have had to deal with generator / ups interaction in mission critical national infrastructure settings on several occasions. A large restive load, as suggested will probably help. Even a constant rotating one such as a dummy motor is likely to be of benefit.

I am also a bit confused by your statement of an 'office full of PCs'. That generator won't power many PCs. I had to read your first post a couple of times to ensure you didn't mean 5000kW, but check on your machine spec confirms 5kW. This is probably only good for a handful of PCs, partly due to the dirty load. Just bear in mind that if the gen is an inverter output one, it will be a dirty power supply as well.
 
How is the generator connected into your system, I hope not just through a plug and socket? Also, does this generator have an AVR (automatic voltage regulator) If it doesn't, then you could well have UPS acceptance problems.
 

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