Small (under 20kw) backup gensets

Doesn't fit in a category? It does now.
User avatar
Shane
Posts: 764
Joined: Fri Feb 01, 2008 12:08 am
Location: Omaha
Contact:

Re: Small (under 20kw) backup gensets

Post by Shane » Wed Dec 30, 2015 1:49 pm

Thanks to all for their comments. I've just heard more bad things about Generac than other brands, which might be because there are more of them installed.
Could be. I had never considered that. Also, my minimal experience with Generacs has been ok. Sometimes getting UPSs to stop complaining just requires adjusting the UPS to not be so persnickety.

Until a few years ago, I had a Class C motor home with an Onan 4kw generator in it. Never needed to do it but since I was able to keep it parked at my house, if I had needed emergency power, that's where it would have come from. Downside was 110 only, no 220. I no longer have the motor home but haven't yet come to a full realization that, "no you DON'T have backup power at home anymore!"

A former radio group with stations here in Omaha had a big Class A they would take out on remotes and such. On their studio building was a connection to hook the motor home's generator to the mission critical stuff in the studios. I thought that was kind of silly until I realized it was rather clever.

On the subject of automatic exercising: all well and good except for one thing. We had some "failed to start" indications last winter. After fixing the problem, the service tech recommended that if the weather was going to be real cold - say, not above 20 and possibly below zero at night - to disable the automatic exerciser feature and just do manually exercising during the day when the temps were warmer. He had seen problems be caused by generator testing in unusually cold weather, when it could have been postponed.

I'm still waiting for some seriously colder forecasts before shutting it off. It tested successfully last night, but 14 days from now might be another story. BTW, the studio generator is labeled Coleman but I suspect someone else manufactures it. Anyone know who the mfg. might be for Coleman generators?
Mike Shane, CBRE
---Omaha---

kcbooboo
Posts: 450
Joined: Sat Dec 10, 2011 4:53 pm
Location: East of the Mississippi

Re: Small (under 20kw) backup gensets

Post by kcbooboo » Thu Dec 31, 2015 7:23 am

Coincidentally, the power could fail when the weather is poor, requiring the genset to start and run, just as if you were trying to exercise it. I have never activated the automatic exerciser; I prefer to do it myself so I know if it works or fails. I too would delay the test by a day if the weather would be warmer or dryer.

Kohler offers a carb heater for their units, mainly to prevent cold damp air from freezing the throttle plate. Onan didn't have one nor apparently need one. I never considered a battery heater but I was told they will bake the battery and cause very short life. Other than when the battery goes dead, that's never been a problem for me. I replace it every 3 years and avoid finding a dead battery, which almost always never happens when exercising the unit.

My Onan was somehow set to run at 60.49 Hz. Most UPSes don't care but some do and naturally I had one of those. A 15 minute phone call to the mfgr and lots of button presses desensitized the unit, but many are very picky, overly picky in my mind, especially the true on-line UPSes that regenerate the power 100% of the time. Why they should care what the quality of the incoming power is, is beyond me. The only time it might matter is if the UPS has to shut down because of dead batteries and switch the loads back to commercial power, and I can live with a change in frequency at that point, but it shouldn't fail to operate when running on a genset, especially at an AM station where the load is continuously and rapidly varying.

Bob M.

User avatar
KPJL FM
Posts: 564
Joined: Fri Nov 16, 2007 9:28 am
Location: planet Earth, 3rd rock from sun

Re: Small (under 20kw) backup gensets

Post by KPJL FM » Thu Dec 31, 2015 9:19 am

basically it elevates the genset 1-2 feet off the ground, so you don't have to shovel the snow away ...

more like 4 - 6 feet around these parts :D
Trim to fit, paint to match, tune for minimum smoke.

User avatar
kkiddkkidd
Posts: 550
Joined: Mon Dec 03, 2007 11:13 am
Location: Lawrenceburg, TN

Re: Small (under 20kw) backup gensets

Post by kkiddkkidd » Thu Dec 31, 2015 10:10 am

One thing to keep in mind when installing a propane (and possibly NG) genset, is that you shouldn't rely on the regulator to keep up with the instantaneous fuel requirements. Some of the manufacturers tell you this up front and others (Generac) tell you after you have a running problem.

I installed a 14kw HomeDepot Generac at a site and had the propane supplier (who is also a Generac dealer) do the gas plumbing. It ran great for several months and then started running a little rough and shortly quit running at all. A different propane service guy came back and was very unhappy that his installer had just hooked the regulator directly to the gas input flex hose. He added about 10 or 12ft of 1in iron pipe between the regulator output and genset input and it now runs like a top. The volume of the pipe acts like a reservoir and allows the regulator to react to the average fuel needs of the engine and not have to snap open and closed every time the engine takes a huff. Generac had just sent it's dealers a service bulletin on the subject before we had this unit plumbed. The additional pipe simply makes a 5ft U-shape along the TX building wall from the regulator and back to the flex generator input hose. The service guy had no explanation for why it originally worked OK and then quit but said that he had seen the same thing several times before. The regulator tested OK and is still in service.

Before the additional pipe was added, the regulator made bad noises and vibrated like a cheap motel bed when the engine was running but is almost totally silent and still now.

A lot of the local propane dealers around here also work on various generator brands.
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

kcbooboo
Posts: 450
Joined: Sat Dec 10, 2011 4:53 pm
Location: East of the Mississippi

Re: Small (under 20kw) backup gensets

Post by kcbooboo » Thu Dec 31, 2015 12:40 pm

Luckily mine is running on natural gas. There's about 30-40 ft of 1 inch flexible gas line between the 11" regulator at the meter outside the house, and the gas inlet of the genset. Still have 11" of static gas pressure there. Lots of variation while the engine is cranking though but once it starts (if it starts) everything seems to be nice and stable, with 4" coming out of the genset's regulator.

The Kohler blurbs say they'll run on 3.5-11" of pressure. The Onan really wanted 11" but ran surprisingly well on 6" when I first installed it, as that's all I had available for the first few years. At one point Generac wanted 11" as well but it seems that they all changed their specs due to the rapid surge of home standby generator installations where 6" is the normal pressure.

I can understand how a longer gas line would almost act as an inductor, smoothing out the pulsing demand from the genset. It also depends somewhat on the design of the regulator and how fast it can respond to changes. The regulator Onan used on my genset is basically an open pipe with some sort of gate that blocks some of the opening when the pressure builds up. This means it's wide-open when the genset starts up, giving it a big blast of gas, but once things start moving, the regulator kicks in and reduces the pressure somehow. I've seen other valves where the gas flow is blocked most of the time and opens more as the pressure is reduced. Not sure which is better or can respond faster.

Bob M.

kcbooboo
Posts: 450
Joined: Sat Dec 10, 2011 4:53 pm
Location: East of the Mississippi

Re: Small (under 20kw) backup gensets

Post by kcbooboo » Thu Dec 31, 2015 12:46 pm

"basically it elevates the genset 1-2 feet off the ground, so you don't have to shovel the snow away ..."

If you have seen such an elevated installation could you take a photo and post it? I'd like to see how they construct it.

We rarely get that much snow but I never had to worry about it with the Onan since it's air intake is up at the very top of one end. Kohler does it differently, hence the elevated platform technique.

We had at least 30 inches of snow a few years ago. I stepped out into it and it came up all the way to my crotch, and I hadn't actaully touched the blacktop yet. Took several minutes to cut a path to my shed, then clear the snow from in front of the doors, then another 45 minutes to get about 60 feet down the driveway. The snowblower was just about making a tunnel under the snow. On the sidewalks where the town plows had pushed some snow, it was taller than the output chute. The genset was essentially buried. Luckily I didn't need it.

Bob M.

grich
Posts: 307
Joined: Fri Sep 02, 2011 11:19 am
Location: MP89.5, Mason City Subdivision

Re: Small (under 20kw) backup gensets

Post by grich » Thu Dec 31, 2015 3:40 pm

Shane wrote:
On the subject of automatic exercising: all well and good except for one thing. We had some "failed to start" indications last winter. After fixing the problem, the service tech recommended that if the weather was going to be real cold - say, not above 20 and possibly below zero at night - to disable the automatic exerciser feature and just do manually exercising during the day when the temps were warmer. He had seen problems be caused by generator testing in unusually cold weather, when it could have been postponed.

I'm still waiting for some seriously colder forecasts before shutting it off. It tested successfully last night, but 14 days from now might be another story. BTW, the studio generator is labeled Coleman but I suspect someone else manufactures it. Anyone know who the mfg. might be for Coleman generators?
I've never worked at a site that had their genny exercise at night. Ours all run during the day when we can hear and see them run. Do you do that to appease the staff at your place, or to appease the neighbors? :D

User avatar
Dale H. Cook
Posts: 770
Joined: Thu Dec 20, 2007 9:08 am
Location: Roanoke/Lynchburg, VA
Contact:

Re: Small (under 20kw) backup gensets

Post by Dale H. Cook » Thu Dec 31, 2015 4:33 pm

kcbooboo wrote:My Onan was somehow set to run at 60.49 Hz.
Decades ago, pre-Onan, I worked for a station with a vintage Cummins genset. The Cummins tech did an annual inspection and PM every fall before the mountain got cold and snowy. He set the frequency with his Fluke 8060A with the genset running under load, and none of my standby power units (none of them were true UPS units) ever complained.
Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html

kcbooboo
Posts: 450
Joined: Sat Dec 10, 2011 4:53 pm
Location: East of the Mississippi

Re: Small (under 20kw) backup gensets

Post by kcbooboo » Thu Dec 31, 2015 5:43 pm

The Onan unit used a speed controller made by Synchro-Start. The speed was not adjustable unless you had a laptop, their software, and an interface cable, none of which were available to anyone but the Onan factory. So 60.49 is what I had to live with for the last 14 years. 1/2 second per minute doesn't sound like much but let it run for an hour and things are quite far ahead, mainly analog clocks.

The Kohler units seem to be adjustable from the control panel or a laptop, both voltage and frequency. If it's an installer option I'll connect my Fluke 189 DMM and they'll adjust it until I'm happy.

Being present during exercising is one reason I never activated the scheduler. You have no idea it didn't work unless you do it yourself.

Happy New Year to all.

Bob M.

User avatar
Shane
Posts: 764
Joined: Fri Feb 01, 2008 12:08 am
Location: Omaha
Contact:

Re: Small (under 20kw) backup gensets

Post by Shane » Fri Jan 01, 2016 11:16 pm

I agree, being present is better. I just don't know how often it would actually get done if it had to be done manually.

The fact it tests every other Tuesday night (5:35pm standard time; 6:35pm daylight at the moment) is merely because that's when someone pushed the button to start the timer last. I am usually still hanging around at that time but I don't always hear it or remember to check before it stops.

However, the switchgear/exerciser displays a very obvious flashing code for us to see the next morning. It gives codes for several different types of failures. One time it gave us a code we hadn't seen before. It turned out it was putting out 56V!

I have used the same service guy since 1980-something. He also sold us the two generators we have at my current employer (Studio + one tx site). (Of our other two stations, one has a big Onan outside which exercises weekly unattended and has a service contract with the local Cummins people.) It's strange he never mentioned that cold weather testing thing in all that time, but that could be because only this one generator of those I've been associated with or responsible for is outdoors not counting the big Onan.

I don't think the neighbors care although new people have been known to be frightened by it (!), so I may change the time on it so its in a warmer part of the day.

Great discussion. This is not an area of great expertise for me, so I've learned something from everyone here. Thanx. And Happy 2016!
Mike Shane, CBRE
---Omaha---

User avatar
Shane
Posts: 764
Joined: Fri Feb 01, 2008 12:08 am
Location: Omaha
Contact:

Re: Small (under 20kw) backup gensets

Post by Shane » Fri Jan 01, 2016 11:36 pm

Thought this might be interesting, too. When I worked for KFAB, the transmitter has (still has but a newer one now) a 250kw in an anteroom not outside but in a mostly unheated inside area. It had a circulating pump to keep the oil warm. Rarely did that beast have trouble starting. Again an unattended site, but during my time when it kicked on it lit up a status channel on the remote control and sounded a non critical alarm/reminder deal.

That thing was capable of keeping one 50kW transmitter on the air, and the other one operating into a dummy load if that was ever needed. These weren't DX 50s but a 317C3 (sure do miss that one!) and an RCA Ampliphase BTA-50H1, I think.

Sorry for the drift.
Mike Shane, CBRE
---Omaha---

kcbooboo
Posts: 450
Joined: Sat Dec 10, 2011 4:53 pm
Location: East of the Mississippi

Re: Small (under 20kw) backup gensets

Post by kcbooboo » Sat Jan 02, 2016 5:53 am

Some gensets have a water heater that circulates by convection. That heater is actually rather hot (100F). To be fair, the genset engine is a big V8 and it provides nearly 75kw for an FM station, but surprisingly the output voltage regulation is horrible; the TX output power will vary by over 5% as the tower lights flash on and off. It drives the TX's automatic power control crazy.

I've seen silicone heating pads that can get attached to the crankcase of smaller engines, but if you use synthetic oil rated for 5w30, or 10w30, oil thickness usually isn't a problem. At least it hasn't been a problem in my little Onan. Having said that, my snowblower with a 10hp Tecumseh engine and normal 5w30 oil is nearly impossible to start with the recoil starter when the temp is below 10F. You can pull the handle and the engind will turn, but as soon as the rope stops moving, so does the engine. Luckily it has a 120VAC starter motor and that works great.

Some engines seem to need a carb heater; others do not. I'll get one on the new Kohler. It seems they're worried about condensation forming inside the throttle body and freezing the throttle plate, but mainly when the engine isn't running.

Bob M.

User avatar
Shane
Posts: 764
Joined: Fri Feb 01, 2008 12:08 am
Location: Omaha
Contact:

Re: Small (under 20kw) backup gensets

Post by Shane » Mon Jan 04, 2016 9:22 pm

That 75kWer may have a defective governor. The old studio generator at KFAB was supposed to be able to support the whole building but if the A/C was running it would slow down to where the Simplex clock system would get all out of whack.

<the Simplexes were designed with special individual synchronous motors that expected about 58 Hz. So they would run a little ahead til the second hand reached :30, then stop and wait for a pulse from the master.>

With the generator running slow like that we had to shut down the A/C so the clocks would stay on time. Some years later the tech found and replaced the defective governor and we had no more regulation problems after that!

And to think of all the sweat we wasted!
Mike Shane, CBRE
---Omaha---

kcbooboo
Posts: 450
Joined: Sat Dec 10, 2011 4:53 pm
Location: East of the Mississippi

Re: Small (under 20kw) backup gensets

Post by kcbooboo » Tue Jan 05, 2016 5:30 am

I have no idea if the big genset has an electronic or mechanical governor. I also don't know how sophisticated its voltage regulator is. Apparently the tower lights draw a considerable amount of current, and I don't know if it's distributed across all three phases or just running on one or two. Only two of the four light levels blink, so how much power can they be? I don't know if the unit was new or used when it was installed probably 15 years ago. Doesn't matter; it's not my problem. If this genset fails to start, there's a second brand new 60kw unit and xfer switch in series with it.

Woke up to a lovely 6F temp this morning. I think our high Monday was in the low 20s. Quite a shock considering how warm it was just prior to Christmas.

Bob M.

User avatar
kkiddkkidd
Posts: 550
Joined: Mon Dec 03, 2007 11:13 am
Location: Lawrenceburg, TN

Re: Small (under 20kw) backup gensets

Post by kkiddkkidd » Tue Jan 05, 2016 8:17 am

kcbooboo wrote:I have no idea if the big genset has an electronic or mechanical governor. I also don't know how sophisticated its voltage regulator is. Apparently the tower lights draw a considerable amount of current, and I don't know if it's distributed across all three phases or just running on one or two.
I had a 125kw Cat genset that the tower lights drove nuts even though it was running well under max output. It wasn't the load but the surging load. I could jump out the flasher and it settled down instantly but the flash rate set up a "resonance" that caused the genset to start surging badly. I could manually hold the governor/throttle control rod and make it settle down and it would immediately start surging again when I stopped "buffering" it. The entire light load was on one phase.

The local Cat dealer said that they could replace the governor and fix it but I recall the cost being $5k+. I eventually installed a relay to bypass the flasher while on emergency power and was moving to build an alternating load when the group sold to the large broke conglomerate and they (typically) side lined the project (and eventually myself...).

They had another smaller, newer Cat generator at another site with about double the flash load that you could just barely hear the genset tone change with flash. I believe that it's load was spread across 2 phases.
--
Kevin C. Kidd CSRE/AMD
WD4RAT
AM Ground Systems Company
http://www.amgroundsystems.com
KK Broadcast Engineering
http://www.kkbc.com

Post Reply