There are a few other posts about this but I'm going to chime in
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.
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
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).
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
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
Well, that's just a "feature" than cuts back power when there isn't much
load. Most generators that size have that "feature." The idea is to save
fuel while keeping the generator ready to take on full load.
Basically, you buy a generator without this "feature."
There are cheap generators and expensive generators. A 16 KW would be at
the high end of "home" generators because it's big enough to handle most
heat pumps (with the strip heaters disconnected), the water heater, the
stove, etc. without excessive "power management."
Well, for some applications, this "power down" feature is useful.
It's not whether it's "commercial" but whether it can handle the job.
The "Generac 16KW" should be enough to narrow it down to the Generac
residential automatic backup generators as seen at Depot / Lowe's and
similar. The Generac commercial grade line starts at 18KW and goes
rapidly up from there.
Agree it doesn't make sense and is contrary to any basic mechanical
governor generator I've dealt with.
The governor could be adjusted, but that's not where the problem lies as
57 Hz is perfectly acceptable to any piece of server, network, phone or
A/C equipment built in the last couple decades.
Right, the commercial / industrial generators have the "Isochronous
Close, the problem is in both the UPS and generator selection. They're
trying to support a commercial operation with consumer components, both
a consumer residential generator and mostly consumer UPSes as well.
Given the wide input voltage and frequency tolerance of most every
server, network and phone product of any recent vintage, the first step
is to get the UPS set points adjusted to more reasonable limits,
replacing the little consumer UPSes with no adjustability. Next on the
list after getting the UPS issue under control is to test and see just
how far out of spec things go when the A/C compressor(s) switch on and
The OP indicated they're loading the generator to about 55% load, but
without a breakdown of how much of that is the constant load from the
electronics vs. the variable load from the A/C and if they just used the
listed running load of the A/C or if they accounted for the starting
load, we don't know how undersized the generator is.
Probably, but then I'm not going to go looking and guessing just to give free
Umm, seems to me Google started out with "consumer" equipment. The equipment's
tagging ("consumer" or otherwise) has nothing to do with the problem. Since I
presume that this guy doesn't want to change out all his UPSs or change the
and is looking for a low cost solution, I point at the problematic UPSs.
The lowest cost solution is simply to adjust the governor such that the frequency
spread of the generator falls within the acceptance range of the UPSs. As you
not much else other than line-operated clocks give much of a damn about
At the same time I would be trimming the generator frequency I'd be looking at
offending UPS to figure out how to broaden its acceptance range. There may be an
internal pot or DIP switches or something else that sets the range. I'd spend a
little time figuring that out before I'd start spending money to change out
equipment. If I were incapable of figuring that out then I'd spend a little
a technician who could before I spent a LOT of money on equipment changeouts.
BTW, it doesn't take electronics to make a full PID governor. Woodward, among
others, has made a full PID self-contained hydraulic/mechanical governor for
Rare to find one on a generator below about 100KVA.
John De Armond
See my website for my current email address
The governor is electronic and, as stated in the original post,
Generac admits it's a known issue with this governor and the V-twin
engine. I spent half my career in power generation, have operated
large scale turbine generators, motor generators, and have been to
Fort Collins CO for Woodward governor training. You really should
stop talking down to people who you know nothing about (your previous
Several points here. Not sure why you keep assuming all the APCs are
consumer grade but you don't seem to pay attention much. As stated in
the OP, several of these are rack mount units (several thousand
dollars each). FYI, even the smaller ones are several hundred dollar
units that are on small loads such as firewalls, switches, routers,
etc. None of the APCs tolerated this frequency. The APC rep knew
immediately what the issue was and, by default, pretty much all APCs
are set for a 5% (3Hz) tolerance. Again, as stated in the OP, you can
adjust these beyond that. Also, how in the world is the generator
undersized? If you'd read the OP, it's well oversized. It's running
55% load and we may have to ADD load per Generac to get the frequency
where it needs to be.
Danny thanks for your respectful and attempted helpful input. The
rest of you guys, the problem IS the generator (the manufacturer
admits it for crying out loud) and it was installed by a licensed
electrician who has installed many small gen sets.
I'm not going to respond further to some of the ridiculous crap that I
know will follow but please feel free to continue putting forth
incorrect conclusions based on assumptions that are coming from who
FYI, there's not a single question in the OP... it was just a warning
to anyone who was thinking about purchasing one of these.
Pete, get a life. You spend way too much time on Usenet.
a bit more
Thanks for the warning.
My first thought when I saw the original post was
"?I wonder if that's an electronic governor unit?"
I'm a bit surprised that you feel that the 57-58hz to be a generator
I thought perhaps the generator drops below 57hz momentarily when
something like an AC unit kicks in.
But your description sounds like the all the APC units fail to accept
the Generator feed even under steady 55% load.
At the Generac site,
This 16kw model
a spec sheet
the CONTROLS tab shows 60hz +- 5%.
If you really are getting 57-58hz, why don't you feel it is an APC
I suppose alternatively, APC might say it was a problem in choosing a
generator with too wide a tolerance or too low initial set point.
If it were only one or two UPSs, I'd think it was a tolerance stack
issue - but for all of them to not accept 57-58hz when the APCs say
that they have a 5% tolerance, seems like they (APC) should accept
some of the responsibility.
Is there any hope of Generac offering a mechanical governor option? Or
Or alternatively, obtaining an electronic module with a 62 hz set
I wonder if anyone makes a separate adjustable electronic governor
Well then, Nate, ole buddy, if you're the expert then why are you here asking for
help? (True, you didn't explicitly say "help me" but one would presume you
just saying "look at me, what a dumbass mistake I made" with your post.) I wasn't
talking down to you then but I sure am now. Frankly, you struck me as someone
over his head but I decided to try to help nonetheless. After all, I've made a
of money following behind guys like you. Why not give some back?
BTW, I would be impressed with your apparent training and experience - if any had
If I may point out a few things. You did NOT mention in your original post that
generator has an electronic governor. In fact, you made no mention of a
all. As far as "Generac admitting..." I take that with a grain of salt until
information is given. Who at Generac? The dealer's parts changer? Some
tech support dude at some call center who was sweeping floors last week?
Which brings up the next point. You STILL haven't bothered to tell us which
you're dealing with. Presuming that it is this one:
and downloading the 16KW manual, I see that the manual specifies the frequency
of this generator over its entire load range. Had you read this manual and read
APC manuals, that the two were incompatible out of the boxes would have been
I should point out that if your reported numbers are correct - "around 57 to 58
then your unit is operating out of spec (reading the manual really does help).
You mentioned that your "RV generator" holds tighter frequency than this one.
indicated to me that you didn't have a clue, as the RV line of Generacs behave
like the corresponding non-inverter generators from Onan. NONE hold tight
control. I have a LOT of experience in that area. I also have a Generac
RV generator mounted on a cart sitting in my basement that I use for standby
I've completely characterized that unit and tuned the governor as tightly as I
and it STILL sags with load, as one would expect for proportional-only control.
your training and experience (sic) you should know better.
Now that you're a self-proclaimed expert, I have to join others and ask what
expert bozo are you to specify a consumer-grade generator before confirming the
compatibility of the generator and your loads. As I mentioned above, sufficient
information to determine the incompatibility of the generator and APS boxes is
literature. Confirming compatibility before buying hardware is pretty basic
engineering. Oh wait, I forgot. You're a tech. I have to agree with the
your company should have hired a competent engineer to design this system.
I have no problem with the consumer-grade generator per se. A properly selected
would probably do the job. I have to say "probably" because at this point I have
little idea what loads actually exist, given your amateurish and incomplete
presentation. That selection process involved work that was obviously over your
and now your company is going to pay the price. I wonder how long it'll take
boss to figure out that you're flailing around trying to cover your ass?
Since you're the expert AND a smart-ass, I'm going to sit on my thumbs and let
wallow in the mess you made. After reading the manual (did you bother to do
the solution is fairly obvious but I'm going to keep that to myself - at least
someone is paying my fee.
John De Armond
See my website for my current email address
This is not some sort of "econo throttle" feature, that is only found on
small portable generators, not fixed standby ones, and the generators
that do have it throttle down well below the few percent that 57Hz vs.
60Hz equates to.
As noted elsewhere, the commercial standby generators are quite a bit
different from the residential standby generators, the change from a
basic mechanical governor to an much more sophisticated one being a
I didn't say that the small variation in frequency was the cause of the
problem. There will be a much larger variation in frequency seen when
the OP's A/C kicks on which will be an additional problem. The
residential standby generator he is using (as noted the Generac
commercial start at 18k) won't hold frequency anywhere near as well as
the commercial line which have superior governors.
a bit more
The Generac residential standby generators don't even have a
specification given for frequency regulation, so your 57Hz certainly
falls within what can reasonably be expected of the unit.
If you spent half your career in power generation as you say, then you
should know that you can't expect a rock solid 60Hz from a small
consumer grade generator.
Every small APC unit I have ever seen is indeed consumer grade. Even
some of their rack mount units are still consumer grade in a spiffy
chassis (think Hummer2). APC does make commercial grade units, but from
the information you have provided it's fairly apparent that the
installation in question has grown in drips and drabs, with a bunch of
little consumer grade UPSes instead of a couple large commercial grade
Price does not equal quality. As I noted, some of APCs rack mount units
are still consumer grade in a spiffy case.
The very fact that you have all these separate small UPSes shows the
necessity of a full facility review and upgrade.
Have you noticed that the 57Hz you indicate the generator supplying
falls within this 5% / 3Hz tolerance?
Again, you haven't told us if that 55% load accounts for the starting
draw from the A/C, and what proportion of that 55% load represents
static load vs. dynamic. As for "getting the frequency where it needs to
be", the 5% low you're getting is within reasonable expectations for
such a generator and also appears to meet the published specifications
for those generators since they don't appear to even have a claimed
frequency regulation tolerance. They do specify +/- 2% voltage
regulation implying that the lack of a frequency regulation rating isn't
The problem is your expectation of the generator, not the generator. The
manufacturer indicated the 5% low frequency is known on that unit, but
given the lack of a stated frequency regulation tolerance, it is not a
problem or a defect.
I guess you never looked at the manufacturers specifications for the
generator or you would know where the claims are from.
People purchasing that generator for it's intended purpose -
"Residential Standby" - are unlikely to have any issues. You are simply
expecting your Chevy to perform like a Ferrari.
Yes, I do. It's one of the few things I can do while waiting impatiently
for the corporate bureaucracy at work to grind through it's absurd
overhead so that I can actually get some work done. It's no wonder this
country is on the fast track down the tidy bowl swirl...
BTW, the UPSes and generators in our facilities are redundant, 480V 3ph
and total in the MW range so I have some familiarity with the subject.
With the fully digital electronic governor, there is no reason that this
line of residential generators couldn't hold the long term frequency tolerance to
within a fraction of a cycle and transient tolerance to a cycle or two. Generac
could have implemented a full PID governor, even included feedforward
if they desired. Whether they did remains to be seen.
I can say that the electronic governor on my Generac Impact RV inverter generator
works fairly well. It doesn't need tight RPM control since it's variable speed.
impresses me is the good transient response. There is zero frequency shift and
almost no voltage sag even when my RV's AC kicks on - representing a significant
portion of the full load rating of the genny.
John De Armond
See my website for my current email address