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Old 12-28-2012, 09:08 PM   #1
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Genset Starting with Load

I am relatively new Class A owner, and have a '98 Overland 40, with Onan 7.5. I also have a houseboat, and the electrical system is nearly identical. The houseboat has a Westerbeke 15k genset. Westerbeke says it will damage the genset if it is started or shutdown with the load on. I have searched both the Overland owner's manual and the Onan manual, and neither mentions this possibility. It seems logical to me that if they expect you to start the generator with the load off, there would be a convenient way to turn load on and off at the drivers console. There isn't, so ........ Anyone have any inputs? Thanks, Grzly03, Dick.
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Old 12-28-2012, 09:22 PM   #2
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Start and shut down with no load. Run for several minutes without load on start up and shutdown. You gen will love you and you won't be blowing expensive control boards.
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Old 12-28-2012, 09:29 PM   #3
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Amen !
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Old 12-28-2012, 09:30 PM   #4
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Welcome to the forum.

General practice is to try to have minimal loads on when switching from one power source to another to avoid slamming the relays involved in the change over. I believe it's the transfer switch but got that confused once and got chastised so I'll leave the specifics to the experts.

No, there's no way in most rigs to shut down the load (Air Conditioner for example) from the cockpit.

Good luck.

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Old 12-29-2012, 03:24 AM   #5
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I have a 7.5 Onan QD. In the manual it tells the owner to let the genset stablize before putting a load on the genset.

One of the first things I have noticed about the MH industry is that it seems this taken care of when I go outside and un-plug the power cord from the genset recepticle. So, here is what they expect; Either sit in the drivers seat, open the front access panel, or stand in the kitchen; start the genset; go outside and shut off the main breaker; plug in the power cord; turn on the main breaker. To shut down; go outside; shut off the main breaker; unplug the cord from the genset, go back inside and shut down the genset.

So, what do I do? Leave the cord pluged into the genset and start the genset with load applied. What I do is full of potential problems the first of which was the display of the microwave did not like this. $75.00 just for the part.

Here is what I did, next to the genset power connection I installed a small electricial box, In that box there is a contactor (large relay) also a timed delay timer. The contactor breaks the two 120vac lines to the genset recepticle that the MH cord is pluged into. The delay relay is controling the coil of the contactor. current draw is less than a night light. The control voltage for the contactor is sourced from the genset. Granted when I start the genset the electronic delay timer is on the genset output it draws about the same as a LED. The delay timer is a "delay on make" so as the genset starts the timer starts its count down, 90 seconds (1 and 1/2 minutes) later it turns on the contactor.

The result is that the genset will start with only the delay timer connected and 1 1/2 minutes later it connects the coach to the genset. As soon as the voltage drops below the accepticle output it removes the coach from the genset.

Now I just start up the genset at any start station. The bother is that I have to wait for a minute and a half to reheat the cup of coffee.

To protect the genset and the coach it now takes me twice as long to heat up a cup of coffee.
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Old 12-29-2012, 06:49 AM   #6
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Transfering electrical loads

I recently traded a 02 Monaco that had a 10.0 kw Onan in it. The manual discussed running the genset at no load for a while before shutdown, but not much about Transfering the load. This past summer I pulled into a campground in Kansas when it was 100deg with both air conditioners running and plugged in to the post....no power. I checked everything and told the manager it was the pedestal. Three sites later I discovered it was not the shore power. I was able to park but had to go to a remote area and run the generator all night. It had run for 48 hrs continuously across the scorching Midwest. Turns out I blew the power transfer switch. Those relays do not like Transfering with 30-50 amps on them. My new RV says turn everything off when Transfering. I guess that makes more sense than dropping $500 to replace a transfer switch in the heat of summer!
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Old 12-29-2012, 08:24 AM   #7
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Wink How I do it!

I never start or stop the generator under load. Mine seems to have a delay at startup before the power is applied to the rv so this has not been a problem. Whenever I shut down I turn things off to reduce the load as much as possible, wait about 1 minute and then shut the gen set off.
The main power relay on mine did blow the second year I owned the rv. Mine has an electrical circuit that delays the generator power input at startup as I mentioned. This type of relay normally has an over lock to ensure they don't try to activate if a second power source is detected. When I first purchased the rv I had no idea of how the shore/generator power was set up. At one time I tried to transfer from one power source to the other without stopping one first and then starting the other. The double input burned up the switch. When I finally had a good look at the set up I found that only one side of the power relay had an overlock!
I reinstalled a new switch in the same way the manufacturer had done it, but now I ensure to always disconnect one power source before connecting the other and no load during this operation.
Two minutes without power can't be that bad!
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Old 12-29-2012, 08:29 AM   #8
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Not only is starting or stopping the generator with a load bad for the generator, it is bad on the driven equipment. During starting and stopping, the frequency and voltage take wide swings which ca kill certain users. It is really easy to shut off the loads, A/C, microwave, TV, etc and let the set run with minimal load for a couple of minutes.

Think how you would feel if you were tucked into a nice cozy warm bed and some one cane up, booted you out of bed and dropped a 100# pack on you back and were told to take of running up hill...RIGHT NOW.

Ken

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Old 12-29-2012, 08:47 AM   #9
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Quote:
Originally Posted by Grzly03 View Post
I am relatively new Class A owner, and have a '98 Overland 40, with Onan 7.5. I also have a houseboat, and the electrical system is nearly identical. The houseboat has a Westerbeke 15k genset. Westerbeke says it will damage the genset if it is started or shutdown with the load on. I have searched both the Overland owner's manual and the Onan manual, and neither mentions this possibility. It seems logical to me that if they expect you to start the generator with the load off, there would be a convenient way to turn load on and off at the drivers console. There isn't, so ........ Anyone have any inputs? Thanks, Grzly03, Dick.
I don't know about damaging the genset, but starting and stopping the generator under a high electrical load will certainly damage the transfer switch. High load will cause the contacts to arc and burn. Sometimes the contacts will get hot enough to fuse. Burned contacts also have high resistance which can cause overheating and possibly start a fire.
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Old 12-29-2012, 10:19 AM   #10
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Genset Starting with Load

Thanks for all the inputs, confirming the principle. In the houseboat, all the controls, breakers, genset starting/stopping functions are on the electrical panel at the helm. At some time in the future a mod to the MH might be in order. Grzly03, Dick.
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Old 12-29-2012, 10:43 AM   #11
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Wouldn't an EMS delay the load while the genny spun up?
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Old 12-29-2012, 11:03 AM   #12
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Wouldn't an EMS delay the load while the genny spun up?
Mine does on startup but can still put a very heavy load on quickly if I left the AC's in the run position.

I agree with all about letting it warm up a couple of minutes before adding loads and especially cooling down for just a couple of minutes at idle. At idle they draw lots of air and cool quickly.

Here are a couple of paragraphs out of my manual.
Attached Files
File Type: pdf Pre start.pdf (133.1 KB, 33 views)
File Type: pdf Stopping.pdf (42.5 KB, 27 views)
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Old 12-29-2012, 11:13 PM   #13
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What happens with the "auto-start" gennies?
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Old 12-30-2012, 02:59 AM   #14
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Most likely start under load.

Transfer relays generally are rated for the connected load. None of them are likely to be rated to transfer connected load. The difference?

It all has to do with the mass of the power contacts of the relays. If they are closed they are in the normal rating position. They must carry the rated load without overheating and burning out.

If you try to transfer the rated load then arcing takes place (arc welding) This arcing under load will cause the surface of the contacts to burn and in time the entire contact area can burn.

My genset is rated at 30 amps per leg. When I picked a contactor to delay loading the genset on start up I picked one rated at 100 amps per leg. I live in the MH during the summer without grid power. This contactor has been transfering load for two summers now and shows no sign of overheating. But in time it will need replacement. If it fails to soon I will pick the next replacement with a larger rating. Even so, in time it will fail and require a replacement set of contacts or a new contactor.

About the only device that the average owner can get to transfer a load is a breaker. That is why your 50 amp service in a MH has a main breaker rated at 50 amps. Even so if you turn it on and off enough you will visit the hardware store for a new one. Repacement is the nature of transfering a load.
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