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Old 12-30-2012, 03:35 AM   #15
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OK so you made me get up and get out the manual fior the genset.

Onan QD Diesel
7.5 KW
Model HDKAJ

Page 8 of the manual:

" For top performance and engine life let the engine warm up for two minutes before connecting appliances."

Page 9 of the manual:

Disconnect large appliances and let the genset run for two minutes then press the switch to stop the genset.

Onan does in fact tell the owner not to start the genset under load. In fact they tell the owner to let the genset to run for two minutes before loading the genset. Especially in cold weather.

They also say loading the genset is the responsibility of the owner (page 9).

On page 10 they say connection to utility power is the responsibility of the owner. Along with a caution that interconnection must never be made.

And here is the safety warning:

"Interconnecting the genset and the public utility (or any other power source) can lead to the electrocution of personnel working on the utility lines, damage to equiptment and fire. An approved switching device must be used to prevent interconnections."

End of manual quote.

The least expensive approved switching device is the plug on the end of the power cord used to plug into the power source. There is no way you can plug that one plug into the utility and the genset recepticle at the same time. It also requires the transfer of all hot legs and the ground and neutral.

If you have an on board transfer system this gets more complcated along with more expense both for the original installation and the repair if you transfer the load.

So yes Onan warns of damage to the genset along with other expensive equiptment if the owner does not start the genset without load or shuts it down without load.

So you can comply with the instructions the genset has breakers to disconnect the load before starting the genset. And those same breakers will disconnect the load before shuting down the genset.

The basic needs are supplied by Onan. You might rather have a remote way to disconnect rather than standing in the rain operating genset breakers but that is your choice, all it takes is money and some who knows how to do it.
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Old 12-30-2012, 11:46 AM   #16
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The autogenset system on mine does let it warm up before engaging the transfer switch. Since the AC circuits are offline that means the air conditioners would be too. The generator comes on line and shortly after that the charger kicks in, then one AC usually starts before the other by a minute or two. If you have the refer on automatic and the hot water heater on those will come online quickly and most likely before the air conditioners. I am satisfied mine will load up safely. As for shut down. Unfortunately I don't think mine will shed the loads before shutting off. Something I will check on for future reference.
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Old 12-30-2012, 03:08 PM   #17
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It is not good for the generator or the loads to allow auto connection or disconnect when the gen set is started or shut down.

There are several reasons.
Most gen sets have a time delay before the transfer switch closes on start up to allow the voltage and frequency to stablize before loading can begin. It is expected that connecting loads are at a minimun during connection to limit the current on the tranfer switch and allow the generator to pick up the loads. A small gen set (all MH gen sets are small) has several % of sppeed droop so the voltage and frecuency will need to stablized between each connected loading. Large loads should be connected one at a time with a delay between each loading. I do not think that any MH has a auto load sequencer installed for the gen set. They are usually reserved for large industrial facilities or power plants. Remenber starting current is close to 5 times running current for the first 5 cycles. The speed droop on a MH gen set can be as much as 10% as well, so loading currents, frecuency and voltage can varry to the extent that eupipment damage can occur. This may be the equipment being loaded or the gen sets voltage regulator.

Shuting down the generator while it is still connected has even more potential for equipment danage than connecting to many loads at once. The reasons are many, I will give a few.
The gen set voltage regulator will try to maintain voltage for a few cycles but can't keep up. While doing so the current flows increase. This is one of the primary causes for voltage regulator failure.

Loaded equipment will see voltage drop and thus draw more current, they will alos see frequency drop which can cause damanage in all kinds of strange ways.

Very little equipment have frequency or voltage protections circuits and if they do why challenge tem?

So the simple answer is manually load and unload the circuits when placing the generator online or offline. I would suggest that you do this for the inverter as well. It has different load parameters but some of the same issues.

The land line power will handle about any thing your transfer switch can handle but you sill have the high current draw for the first 5 cycles.
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Old 12-30-2012, 07:36 PM   #18
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Been reading and analyzing this thread. I then check my Onan manual. I don't think the generator is loaded when it is being shutdown. Depressing the stop switch removes 12VDC from the control board. The control board provides power to the ignition system, fuel pump and excitation for the field. The generator is not self-excited. If the field excitation is removed, voltage immediately goes to 0VAC, all loads are shed, the ATS is de-energized allowing to to go the shore power position. Don't know about everybody's coach, but on loss of power my A/C units go into a lock-out condition for 20+ seconds after power is restored, and my microwave stops and doesn't automatically re-start. These are the largest loads. I think any Dryer or washer, I don't have them, would also stop and have to manually re-started. My converter comes on line when power is restored but does not go into a loading sequence for several seconds, I think it has to sense what is going on in the DC system for it to do its thing. So the only loads I know that are immediate are the TVs, Hot water heater and the refeer. The refeer drops to gas mode and takes several seconds to transfer back to AC mode. So the largest load is the Water heater (1000 W). I think the ats can easily handle that load during a transfer either way. My ats is a break before make in both directions. 1/2 a second is a lifetime in the AC system. If the ats was a 50 milli-second ABT maybe load shedding would be a problem, but the ats would then be sized according. JM2...
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Old 12-30-2012, 08:12 PM   #19
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Unless the generator has an output breaker and it has been opened or the transfer switch that transfer back to shore power is already in that position, it is still connected to the buss during the shut down.

you said If the field excitation is removed, voltage immediately goes to 0VAC, all loads are shed, the ATS is de-energized allowing to to go the shore power position.

Nothing happens in any electrical system immediately. It happens over a few frenguency cycles. That brief peiod of time is where something happens and euipment damage can occur. You may be ok for 1000 times and then on 1001 it get you.

It is your equipment so operate it as you like. I have connected 2000 MW (Megawatt) loads with no problem and then had equipment damage occur on much smaller loads. The motorhome is just a smaller distribution system. Power Plant operators are trained to minimize that loads on connection and dis-connection of a generator when possible. Murphy is a live and well in any electrical distribution system thus hope for the best and ask your self "what is the worst thing that cvan happen" whenever you operate your system.
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Old 12-30-2012, 08:22 PM   #20
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On a motor home with a working automatic transfer switch starting the generator "With a load on" is impossible.

WhY (you ask) (Or at least you should ask) is this so?

Well, the genrator starts, it sends voltage to the Auto transfer switch which is, Technically, a load but so small it truthfully does not matter.. 30 seconds (to 2 minutes) later the ATS says. OK Lets Rock it and Roll and transfers the loads to the genrator, but by now the Generator is up and running.

Shutdown is another matter

AND DO NOT HOT SWITCH But that I mean do not start the generator while connected to shore power and big loads present.. This will nto (generally) bother the generator (It may trip a circuit breaker) but it can seriously FRY the transfer switch.

Same on shutdown, The major danger is to the transfer switch.

So kill big loads .. personally I suggest both starting and stopping, easier to remember that way.
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Old 12-30-2012, 08:46 PM   #21
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rsha,

Operated similar equipment as you for 43+ years. Most commercial power generators are seperately excited during start-up but are self excited during operation. My units had a sizable load on the generator from self-excitation and house loads prior to syncing to the grid. Suspect you worked in the nuclear industry where your generators were base loaded vice load following like your Rv generator. Can't really compare the two due to type of application. Nice try. JM2...
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Old 12-30-2012, 09:11 PM   #22
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Teddy

Base load or load follow has nothing to do with this thread. You are free to operate your equipment as you see fit, i was just trying to post advice on safe operation of equipment. You have guess correctly in that I spent 43 years operating various power plants, 2 fluidized bed coal and 3 nuclear and 6 yrs in the Navy operating ship engineering equip, 1 DDG, 1 SSBM and 1 nuclear prototype. When posting on this site the range of readers varies from $M MHs to camper trailers with a plugin generator. Some will have protection built in and some don't. Good safe operating advice will work with or without installed protective equipment.
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Old 12-31-2012, 08:04 AM   #23
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Genset Starting with Load

Wow, perpetuated a lot of discussion. Thanks again for inputs, I learned a lot---well more than I needed, actually. I think the bottom line is HAVE NO LOAD DURING STARTING OR STOPPING IS ALWAYS A SAFE, EQUIPMENT PRESERVING WAY TO GO! Thanks again. Grzly03, 40' Overland, Temecula, CA.
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