[OT] Generator testing

[Frank DiPrete]

Ben Scott wrote:
>   Bruce accidentally sent this off-list, but said I could forward it
> here for benefit of all...
> 
>   Thanks again, Bruce, for the good info!

Thank you for the forward

> 
> ---------- Forwarded message ----------
> From: Bruce Dawson <jbd at codemeta.com>
> Date: Wed, Sep 9, 2009 at 10:14 PM
> Subject: Re: [OT] Generator testing
> To: Ben Scott <dragonhawk at gmail.com>
> 
> Ben Scott wrote:
>>   I know many UPSes don't like the output from some generators, for
>> example -- they stay on battery (which runs down and then drops the
>> load).
> 
> My experience has been this is because the UPS doesn't like the phase
> output of the generator. This can usually be resolved by using a
> generator that has sine wave output. Another (probably easier to find)
> solution is to use a generator that has a 220 socket. Some of the better
> UPSs don't like the phases output by "single-coil" generators, and
> getting a generator with a 220 socket tends to generate a better waveform.
> 
> Note that you don't have to use the 220 receptacle, just find a
> generator that has the capability.
> 
> Keep in mind that generators will tend to raise or drop voltage whenever
> the load changes, however, all of our UPSs (mostly APC) tend to cope
> with that. They'll beep until the generator is able to come back up to
> speed. If the generator doesn't come up to speed, then you're probably
> loading it beyond its capacity - or have a really cheap one that doesn't
> auto-throttle according to the load (or have a governor controlled
> throttle).
> 
> --Bruce


I have a generac/siemens 13kva generator wired through a transfer switch 
to my 150A service. What Bruce states above is the case with this setup. 
The generator puts out slightly less that 110 volts at 58Hz at the low 
point and when put under heavier load comes closer to 60hz, 110.

I can hear the rpm's of the generator fluctuating when this happens.
Load increases, voltage drops slightly, governor increases the throttle.
This is normal and expected behavior from the generator.

When I had the system installed I was informed that I would have to 
select UPS units that can condition power within a window of 
voltage/power/frequency input.

I am using an APC smart ups on my rack that can deal with this quite 
well with minimal switching from battery to outlet.

The good news is that the generator comes up in 20 seconds so the UPS 
capacity does not have to be hours, but minutes of run time for the load 
to deal with the 20 seconds of down time before the transfer switch 
changes the power source from utility to generator; and the few seconds 
of fluctuation out of the UPS's input tolerance that happens during run 
time.

I had a few cheapo UPS units that have zero input tolerance and can be 
used as door stops.

The ice storm last winter was a 5 day "test".




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