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Thread: Onan Generator

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    Onan Generator

    Still trying to understand how all of this works. I have a 2021 349M. It has a Onan generator. 3 questions.
    1. Why does the rv manual say to connect to shore power before starting the generator?
    2. The rv manual says to turn off main power before starting the onan?
    3. There are 2 AC switch’s next to the start stop button. I don’t understand when these should be on-off?

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    Long Hauler D2Reid's Avatar
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    Reading 1 and 2 it looks like exactly the opposite instructions. So taking a wild guess I would say that connecting to shore power before starting the generator would be to charge your batteries to full. The Onan needs about 11.7 volts on the battery to start, I would have to look the 11.7v up to make sure that is correct, it's just what I remember off the top of my head. But 12+v would be better.

    Then, Turning the main power off before starting the Onan is a guaranteed way of not having a conflict between the two. Most RV's with built in generators have an automatic switch that keeps the conflict form happening. It senses when power is produced by the generator and switches to that side, effectively turning off the main power before applying the generator power. But maybe yours does not have that switch, in which case it would be really important not to apply generator power while main power is on.

    AC switches, I assume you mean air conditioner, or are they alternating current. Hmmm! I am going with air conditioner. Air conditioners (A/C) have a huge power surge when they first come on and start up the A/C compressors. Mostly it's ok to leave them on when applying power, but I don't like to. That great big surge on two A/C units going through the line causes stress on the breakers and the rest of the electrical system. They are designed to take it, but I think it's better if you turn the A/C units off, then turn them back on one at a time. This reduces the stress on the system and ensures a better start up on the A/C unit extending it's life.

    I hope that helps some. Safe Travels!
    Dallas
    2017 Momentum 376TH, 2019 Ford F450, Dual Rear Wheel, 4x4, diesel.
    2015 Harley-Davidson Street, XG750

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    Quote Originally Posted by D2Reid View Post
    Reading 1 and 2 it looks like exactly the opposite instructions. So taking a wild guess I would say that connecting to shore power before starting the generator would be to charge your batteries to full. The Onan needs about 11.7 volts on the battery to start, I would have to look the 11.7v up to make sure that is correct, it's just what I remember off the top of my head. But 12+v would be better.

    Then, Turning the main power off before starting the Onan is a guaranteed way of not having a conflict between the two. Most RV's with built in generators have an automatic switch that keeps the conflict form happening. It senses when power is produced by the generator and switches to that side, effectively turning off the main power before applying the generator power. But maybe yours does not have that switch, in which case it would be really important not to apply generator power while main power is on.

    AC switches, I assume you mean air conditioner, or are they alternating current. Hmmm! I am going with air conditioner. Air conditioners (A/C) have a huge power surge when they first come on and start up the A/C compressors. Mostly it's ok to leave them on when applying power, but I don't like to. That great big surge on two A/C units going through the line causes stress on the breakers and the rest of the electrical system. They are designed to take it, but I think it's better if you turn the A/C units off, then turn them back on one at a time. This reduces the stress on the system and ensures a better start up on the A/C unit extending it's life.

    I hope that helps some. Safe Travels!
    I believe another reason to turn the power switch off is to make sure there is no load on the generator when starting it. It eases the startup process.
    Bob (retired) & Vicki
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    Quote Originally Posted by RVneautral View Post
    Still trying to understand how all of this works. I have a 2021 349M. It has a Onan generator. 3 questions.
    1. Why does the rv manual say to connect to shore power before starting the generator?
    2. The rv manual says to turn off main power before starting the onan?
    3. There are 2 AC switch’s next to the start stop button. I don’t understand when these should be on-off?
    For #3

    Those switches are your 30 amp breakers. 30 amps for leg 1 and 30 amps for leg 2. Those WILL trip before the main breaker panel when overloaded, FYI. Those should always be on unless you want to disconnect power or they trip.

    As far as for # 1 & 2... ignore them both. You have an automatic transfer switch that does the thinking for you. If not hooked up to shore power it will draw off battery only, if hooked up to shore power think of it like jumping another car with your engine running (except shore power vs alternator). IIRC, the transfer switch will prioritize generator over short power and kick over to generator after its initial checks. It will not allow both to distribute power simultaneously.

    Hope that helps.

    Newly full timing in our 2021 Momentum 395MS-R with our tow pig being a 2021 F-450 KR

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    Long Hauler D2Reid's Avatar
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    Quote Originally Posted by A.Texas.Yankee View Post
    For #3
    Those switches are your 30 amp breakers.
    Funny how when you read someone else take on something you suddenly realize an assumption you made is incorrect. I had envisioned @neautral starting the generator from the control panel inside, like mine, not from the generator itself. Then with your post, duh, breaker switches.

    Thanks for the clarfificaton.
    Dallas
    2017 Momentum 376TH, 2019 Ford F450, Dual Rear Wheel, 4x4, diesel.
    2015 Harley-Davidson Street, XG750

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    Long Hauler D2Reid's Avatar
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    Quote Originally Posted by A.Texas.Yankee View Post
    For #3
    Those switches are your 30 amp breakers.
    Funny how when you read someone else take on something you suddenly realize an assumption you made is incorrect. I had envisioned @neautral starting the generator from the control panel inside, like mine, not from the generator itself. Then with your post, duh, breaker switches.

    Thanks for the clarification.
    Dallas
    2017 Momentum 376TH, 2019 Ford F450, Dual Rear Wheel, 4x4, diesel.
    2015 Harley-Davidson Street, XG750

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    Quote Originally Posted by D2Reid View Post
    Funny how when you read someone else take on something you suddenly realize an assumption you made is incorrect. I had envisioned @neautral starting the generator from the control panel inside, like mine, not from the generator itself. Then with your post, duh, breaker switches.

    Thanks for the clarfificaton.
    You are very correct. I just happened to have recently tripped a breaker so it was fresh in my mind.

    Newly full timing in our 2021 Momentum 395MS-R with our tow pig being a 2021 F-450 KR

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    Site Sponsor JCR GD's Avatar
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    These have been answered but I'll sum up

    1. Maybe a typo? 9 times out of 10 there is no shore power when needing to start the gen. (ie dis-connect)
    2. Probably to ensure no load.
    3. Breakers-always on.
    Jim (& Sharon)
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    Long Hauler offtohavasu's Avatar
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    There isn't a load on the generator when it starts. There's a time delay on the transfer switch before it engages power from the generator.
    Curtis, Christine, Cole, and Charlotte

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    Quote Originally Posted by offtohavasu View Post
    There isn't a load on the generator when it starts. There's a time delay on the transfer switch before it engages power from the generator.
    But most generators, if not all, say to turn off all power sources before starting the generator. I have two generators, several years different in age, and they both say it. Of course one installed in an RV from the manufacturer may be different.
    Bob (retired) & Vicki
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    2019 Reflection 31MB
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