Small (under 20kw) backup gensets

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kcbooboo
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Re: Small (under 20kw) backup gensets

Post by kcbooboo » Tue Jan 05, 2016 2:45 pm

Yup, obviously a bad flasher! I can only wonder how well this unit would run on an AM station where the load is changing at a much greater rate with modulation.

As promised, a follow-up to the site visit one generator company did this morning. There were several flaws in his logic and his apparent knowledge of some of the setback regulations. He added up the total maximum load possible based on the electric panel and decided I needed a 20kw genset. One big load is the clothes dryer, which will shut off if there's a power failure. Another is the stove; the oven will shut off if there's a power failure but the stove-top burners will continue to run. Now I'd never have any (much less all of the burners) on and not be home, so I could easily shut them off when on generator. The other big load was the A/C compressor which runs fine on the existing unit. The total actual load is probably only a few kw at any one time, so a 12kw genset is more than adequate and has run fine in both attended and unattended uses. So he proposed some load shed relays to turn the dryer and stove off when there isn't enough power. Neither of us knows if the Kohler genset can utilize load shed relays without a Kohler xfer switch. Then he determined that the #6 wire currently carrying power from the genset would be too small for a 14kw genset, until I pointed out that the genset is derated to 12kw on natural gas. Someone else later pointed out that if I did manage to overload the generator, the 50A breaker inside it would just trip, so it protects itself from an overload. Then he wanted to pull a full permit just to replace the genset, which I consider to be a repair; I did pull a permit 14 years ago when I first installed the Onan but there was never a load analysis done. So basically this guy was trying to sell me a whole lot more than I needed or wanted. I've got another company coming in Thursday for hopefully a much more realistic discussion.

Bob M.

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Re: Small (under 20kw) backup gensets

Post by ka4koe » Wed Jan 06, 2016 2:24 pm

Generac does not have a good reputation in the construction industry. I never specify them. Never have. Never will.

Philip

kcbooboo
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Re: Small (under 20kw) backup gensets

Post by kcbooboo » Wed Jan 06, 2016 5:40 pm

I've probably heard more bad things about Generac than Kohler, but that could be because there are more Generac units in service than Kohler. However Kohler has been making lawnmower engines for a very long time so they should have gotten it right by now. Of course I said the same thing about Onan but I was wrong on that one. Unlike Zenith, the quality just never went in before or after the name went on.

I also don't think Generac gensets can work with my existing GE/Zenith/Onan xfer switch that uses two-wire start control and does all the switching logic. I know Kohler can use that type.

Bob M.

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Re: Small (under 20kw) backup gensets

Post by kkiddkkidd » Wed Jan 06, 2016 6:30 pm

kcbooboo wrote:I also don't think Generac gensets can work with my existing GE/Zenith/Onan xfer switch that uses two-wire start control and does all the switching logic. I know Kohler can use that type. Bob M.
The Generac xfer function is oddly split between the xfer switch AND the generator. A typical xfer switch can probably be made to work with the Generac but it is not just a simple switch closure from the switch to start/run the generator.

I don't recall the exact wiring but the first of the HomeDepot generators that we installed, I prewired for a typical 2-wire start/run and had to go back and pull more wire due to the voltage sample required by the generator.
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Re: Small (under 20kw) backup gensets

Post by kcbooboo » Thu Jan 07, 2016 7:34 am

Kohler uses a twisted pair data line to communicate between the genset and xfer switch, doing away with the two-wire start. Low-voltage power comes from the genset on another pair. This allows for a loaded genset-controlled exercise cycle. In those setups that just use two-wire start, the genset can't tell the xfer switch to transfer, so a loaded exercise has to be initiated by the xfer switch. From what I've read, the loaded exercise involves an actual power outage rather than just a switchover, which seems rather odd.

One small Generac installation has what appears to be a very dumb xfer switch; the genset does everything and sends signals back to the xfer switch to tell it to switch.

The previous setup was a 1960s vintage 6kw Onan with a much simpler setup. Two mechanically interlocked contactors had coils that were fed by commercial power and the generator. When commercial power failed, that coil released but its contacts remained closed. The genset was told to start. Once it did, its voltage built up and that energized the other coil, transferring building power to the generator. When commercial power was restored, its coil would attempt to pull in but didn't have enough strength to do the job. The genset was told to shut off, and as it slowed down, its output voltage would reduce. Once it got to about 20V (and who knows how many Hz), that coil would get weak enough that the commercial power coil could over-power it and cause the contactors to switch building power back to commercial. So the entire building would suffer a major brownout and essentially lose all useful power until the contactors could switch back. Crude but effective.

Bob M.

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Re: Small (under 20kw) backup gensets

Post by kkiddkkidd » Thu Jan 07, 2016 8:32 am

kcbooboo wrote:Crude but effective.
Crude but dangerous would be more like it... It seems like every time I have a genset shut down unexpectedly, I have damage on the powered circuits. UPS's seem to be particularly unhappy with an unspooling generator.
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Re: Small (under 20kw) backup gensets

Post by kcbooboo » Thu Jan 07, 2016 1:19 pm

It got the job done and the equipment managed to survive. Of course for most of its life there was no UPS or need for one. Older equipment just rode through it or powered down then right back up again. Computers with hard drives ended that luxury and we all know how much of an improvement digital is!

Bob M.

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Re: Small (under 20kw) backup gensets

Post by NECRAT » Thu Jan 07, 2016 4:15 pm

Our transmitter gen-set XFer switch will open on low voltage / lost leg from the Generator. It will stay in the off position until the next stable power comes available, then switch to it within 2-5 seconds.
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Re: Small (under 20kw) backup gensets

Post by ChuckG » Thu Jan 07, 2016 9:02 pm

kcbooboo wrote: So the entire building would suffer a major brownout and essentially lose all useful power until the contactors could switch back. Crude but effective.
I lost a console and 4 UPS' that way. Not fun. I added 2-one minute delay relays. Now the Xfer switch kicks back one minute after commercial power is restored (relay #1 opens the generator coil lead causing the contactors to switch) and #2 shuts the generator down 1 minute after that. less than $30 in parts.
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kcbooboo
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Re: Small (under 20kw) backup gensets

Post by kcbooboo » Fri Jan 08, 2016 4:52 am

Luckily that old Onan genset and xfer switch are history, replaced by a more modern Generac system. So far it's functioned fine.

I had a second salesman visit my house yesterday. He and I were on the same page this time, although he was surprised at all the problems I've had with the Cummins/Onan, since he sells a lot of those. Hopefully his quote will be more in line with my limit.

Bob M.

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Re: Small (under 20kw) backup gensets

Post by kcbooboo » Thu Apr 14, 2016 12:36 pm

I ended up with a Kohler 14RESA genset. I kept my existing GE/Zenith/Onan xfer switch. Kohler units are compatible with the two-wire start used by the xfer switch.

The electrician arrived just after 7am on the install date. I disconnected the charger that was inside the xfer switch, then he disconnected the Onan RS12000 genset. At 9am a truck arrived with the new genset and concrete pad. The two guys built up a base of two layers of cinder blocks, slid the pad on top, then slid the genset onto that. Just as they finished the plumber arrived at 11am and the electrician went out to buy wiring supplies. The plumber finished at 1pm; he only had to run pipes outside the house. The electrician came back at 1pm and the genset was started and powering the house by 3pm. They still had to come back two weeks later to install the 120V carburetor heater and do the startup registration, but by then the unit had already been tested and is now doing a 20 minute exercise every Saturday at noon. It's putting out 120.1VAC at 60.0 Hz; can't complain about that. Now all I need is a power failure.

The Onan was picked up a few days after it was removed, along with all the new and used parts that I still had lying around plus a CD of manuals. I understand the new owner will be converting the unit to propane.

I received two quotes for maintenance contracts, in the $650 range. One included consumables, like oil, filters, and spark plugs; the other did not, but I added $60 for those to the price to make the comparison easier. In the end I decided to do the maintenance myself, at least for 2016 and 2017. I will likely call in a Kohler tech in 2018 as a "service call" and have him check the items that I don't know about. That will still be less than half the price of the maintenance contract.

I was surprised that genset maintenance contracts are quite a bit different than my old oil burner maintenance contracts, which covered annual cleanings and replacement of the oil filter, burner nozzle, and electrodes, and also emergency "no heat" calls. The genset plans cover two visits a year and nothing else. I'd be surprised if it takes 15 minutes of time for a small unit like I have. It would make sense on a 100kw or larger diesel set, where there's so much more to check, but not for me with a limited income. Since I maintained the Onan and all my lawn and garden equipment myself, I can certainly change oil, filters, and spark plugs as required, check for leaks and loose hardware, proper operation, etc.

I hope this unit lives long and prospers. May the (electromotive) force be with it.

Bob M.

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Re: Small (under 20kw) backup gensets

Post by RodeoJack » Fri Apr 15, 2016 5:37 am

Interesting to read everyone's experiences with the different brands.

I've never specced a Generac at a commercial location, but I take care of a few, and have had no problems, so long as the load is easily within the generator's range. No AMs though. All of mine have Onans, and they seem to work well. I know of 4 others that take care of STL and WISP sites. Those also seem to be doing a good job.

6 years ago, I (had) installed a Generac 20kW at my parents' place. I use load shedding to drop out the dryer and oven, and prioritize the top burners vs the hot water tank. Their electric heat has a 4-stage sequencer for the heat coils. I put in a contactor that drops the furnace to 50% by disconnecting 2 of the coils. The system has worked well, only requiring a battery and the occasional tuneup kits I elect to put in during the "off season".

But.... it's probably like everything else in this business. Ford VS Chevy VS Ampliphase.

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Re: Small (under 20kw) backup gensets

Post by kcbooboo » Fri Apr 15, 2016 11:26 am

One company wanted me to install a 20kw genset plus load shedding because I have an electric clothes dryer, an electric range, and an electric A/C compressor. Two of those three will shut off and not come back on if the power fails. I think if the entire circuit breaker panel amperage was added up, it would exceed the 100A service I have in my house. So when the quote came in and the first of four digits was 9, I told the guy to stop right there. A friend had a genset installed by the same company and they ended up with a similarly over-rated and over-priced job. They had two A/C compressors and everything else was gas and they still had to use load shedding for the compressors.

When I first installed my Onan in 2002 I tried loading it down. I had the A/C, dryer, and the burners on the stove all running and still only drew 40A out of 50 allowable.

If you do your homework and know what you need and can get by without, you can make a decent purchase and get a system that will do exactly what you need.

Bob M.

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