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Old 03-01-2012, 09:58 AM   #1
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Using two generators at same time?

We use a Honda 2000 generator for basic electric power when boondocking but it will not run the microwave.
I have been shutting the Honda off to use the house mounted generator but wonder if this is needed.
Does anyone know if there would be a problem running both for a short period of time?
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Old 03-01-2012, 10:06 AM   #2
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Don't do it. There a few gens that are made tto link together but they are conected electronicly so the 60 hrz is in sink. If you try to hook up gens that are not made to run together they will work against each other and burn things up-------- so don't do it
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Old 03-01-2012, 10:07 AM   #3
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There are two factors to consider when paralleling 2 or more AC generators - synchronization and load sharing.

Synchronization - if you put the output of 2 AC generators on the same bus bars and the generators are not PRECISELY in phase (i.e., synchronized), you can severely damage both generators as well as potentially any loads downstream of them.

Load sharing - if 2 or more AC generators are running in parallel, there has to be some control system algorithm to tell which generator(s) to take any load swings - increases or reductions in load. Each generator cannot try to respond independently ignoring the other generator(s) running in parallel, or havoc can result.

The above is why Honda has the paralleling cable for its EU2000i generators - to allow them to "talk" to each other so that their outputs (even though generated by inverters) are synchronized and the load sharing is taken care of.

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Old 03-01-2012, 10:39 AM   #4
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I agree with autofish. However one way to tell if it is even possible is to start each generator(not connected to each other) and measure the voltage between the live leg of one generator to the live leg of the other generator. If the voltage is zero you may be in luck. The other issue to overcome is to synchronize frequency. You may want to check out this website for more information.
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Old 03-01-2012, 11:50 AM   #5
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The way I read his post is I don't think he is trying to hook them up together but asking if it would hurt to run the house generator at the same time the portable Honda generator is running. Wouldn't this be like running the generator when plugged into shore power? Is there an automatic transfer switch and if so which source would be dominant?
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Old 03-01-2012, 12:06 PM   #6
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If the built in genset is properly wired to a transfer switch and the portable genset is connected by the rig's umbilical, then starting up the built in may cause the transfer switch to supply rig power from the built in rather than the portable. I say 'may' because it depends upon how the transfer switch is wired - they usually have a preferred power source they'll use of both potential power sources are live at the same time.

The only way to tell whether the transfer switch defaults to umbilical or genset is to see which provides the power to the relay in the switch and how the relay contacts are wired. It may be documented in your RV manual as well. You can also just run a test to determine how it works.

The Honda 2000i (and others in its inverter line) will syncronize their output with any AC present on their load lines within a reasonable range. That is what allows them to be paralleled up for greater output. You might be able to parallel a Honda 2000i with an alien genset and get away with it but that is risky because the alien genset may well run outside of the tolerances of the Honda and it won't be able to synchronize properly.

The question is why you are running a portable genset when you have a built in ready to hand. Noise? Fuel efficiency? -- do be aware that a portable genset needs to be placed well away from the rig as a CO precaution and other such safety measures taken.
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Old 03-01-2012, 12:36 PM   #7
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Normally the transfer switch is normally closed to the generator side and electrically switched when shore power is detected.
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Old 03-01-2012, 12:51 PM   #8
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I assume you have a motor home..... The "House" generator is something like an Onan or a Genrac. Wired to the house system via an automatic transfer switch.

Well, I have news, bad news and good news.

First the news: If your motor home has an automatic transfer switch, then about 30 seconds AFTER you start the house generator it will "Transfer" over. Disconnecting the honda completly, No danger to either generator.

Now the bad news.. It is recommended you kill all loads, before the transfer happens. or kill power THEN transfer, the inductive "kick" when it transfers has been known to FRY a Relay or two in the ATS.

Now the Great (Good) news: If you pick up a 2nd Honda 2000, and a Honda parallal kit, They play real nice with each other.. I do not recommend trying it with a different make of generator, but two Honda EU-2000i's play real nice together, They even make one called a "Companion" I believer it has a 30 amp outlet.
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Old 03-02-2012, 02:39 PM   #9
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Thanks for the answers it is about what I thought, best to turn off the little genny.
My wife forgets it is on and just fires up the big one to microwave something.
We like to dry camp, usually it is when off road riding with our toys.
The little genny is quite and cheap to run plus the maintenance on it is simple.
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