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Generac and frequency control

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Posted by Nate on August 1, 2007, 12:52 pm
 
There are a few other posts about this but I'm going to chime in
also.

We just installed a Generac 16KW generator at our office to supply our
server room, network backbone, phone system, and supporting air
conditioning.  First test after installation showed that every APC UPS
would NOT accept the power from the generator... this is pretty much
all of the gear that we are trying to protect.  Frequency checks on
the generator indicate that it's low... around 57 to 58 Hz (no means
to adjust it).  Called Generac and was told this is a known issue and
that this generator won't maintain 60 Hz until it's loaded to the
upper end of it's capacity (we're currently running about 55% load).
I'm pretty surprised that Generac is selling a product like this and
apparently it's only an issue in their V-twin engine models.  I've
worked in the electrical generation/distribution field and I've never
heard of anything like this before.  Even my cheap house and camper
generators maintain frequency throughout their load range.

One additional note on the UPS units.  We noticed that the Tripp Lites
do accept the power because their frequency tolerance is twice that of
the APC line.  Also, the larger rack mount APCs do have a sensitivity
adjustment which, when adjusted fully, will accept the low freq
power.  End result is that we're looking at replacing all our smaller
UPS units or working in additional load to the generator.


Posted by danny burstein on August 1, 2007, 1:00 pm
 

[snip]


Just a comment about the UPSes. If you're going
to undertake replacement, see if you can move
the UPS boxes _outside_ the air conditioned server
room area.

Reason: They typically add another 10 percent (very
rough figure...) in electrical demand due to their
inefficiencies. So a 2 kw load becomes a 2.2 one, adding
to the heat in the room, and thus the needed air conditioning.

(They'll pull X amount weather loaded or not, and
then a small percentage of the throughput that'll
vary with the load).


--
_____________________________________________________
Knowledge may be power, but communications is the key
             dannyb@panix.com
[to foil spammers, my address has been double rot-13 encoded]

Posted by philkryder on August 2, 2007, 7:17 am
 
It sounds like he has more than adequate capacity to deal with the 10%
overload.
And moving the AC load from the UPSs may just make it more difficult
to deal with.



Posted by Pete C. on August 1, 2007, 1:36 pm
 Nate wrote:

That's one of the risks you take when trying to cheap out and use a
consumer line home backup generator in a commercial setting. Purchase
the correct commercial rated generator from Generac (or Kohler, or Onan,
or Cat or Detroit, etc.) which will have a "real" governor and you won't
have any problems. Bottom line - select the correct product for the
application.

Pete C.

Posted by Pete C. on August 1, 2007, 1:41 pm
 "Pete C." wrote:

Additionally, you should also be using commercial grade UPSes which have
adjustable set points. The frequency set points should be set for the
45-65 Hz range which pretty much anything you have there should be rated
to accept.

Pete C.

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