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 > Question about Onan Generator

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Chum lee

Albuquerque, NM

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Posted: 02/09/20 02:27pm Link  |  Quote  |  Print  |  Notify Moderator

Many RV's have an "AUX BAT" or auxiliary battery switch somewhere on the dash. The purpose of this switch is to temporarily connect the house batteries to the chassis battery(s). When you press this momentary contact switch, provided there is adequate voltage/current available somewhere in the system to operate the relay, you now have the benefit of ALL the system batteries linked together for the purpose of starting the coach engine, or the generator. Often this is enough "juice" to get you out of a jamb.

As others have said, the generator will automatically charge the house batteries through the battery charger built into the converter when running, but generally, it will not charge the chassis battery unless the "AUX BAT" switch is pressed. (not recommended for long term charging)

That said, I often hook up a separate 12 volt (automotive type) battery charger to one of the house 120 Volt outlets to top off the chassis battery if/when the generator is running.

When you start the chassis engine, generally, a few seconds after starting, you will hear another relay engage which now connects the chassis and house batteries together so that you can charge all the batteries while underway using the main engine alternator. (it takes a long time/drive to do this if the house batteries are low)

Chum lee

MrWizard

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Posted: 02/09/20 04:00pm Link  |  Quote  |  Print  |  Notify Moderator

wopachop wrote:

I was cycling my onan5500 a couple days ago. Store my batteries in the garage.

Pulled out battery to start the genny. Ran for about 55mins. Genny still running I disconnected the negative cable and it died instantly.

Also had my 12v disconnect switch turned off.

Made me wonder the dealio. If the disconnect switch was turned on, would the converter then power the fuel pump?

Will have to test that next month. The fuel bowl was filled with gas so I guess it wasnt a fuel pump issue but instead a "making spark" issue?


If the disconnect was in use with the Onan running !
You were powering the generator directly from the battery with out charging it from the converter
When you removed the negative cable you removed 12v control, spark, and fuel pump
And left your battery in a partially discharged state


Radiate The Happy
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Dusty R

Charlotte Michigan 48813

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Posted: 02/09/20 04:42pm Link  |  Quote  |  Print  |  Notify Moderator

If it was just the fuel pump that lost power, the generator engine would continue to run until the carb bowl ran empty.

Dusty

wopachop

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Posted: 02/09/20 06:03pm Link  |  Quote  |  Print  |  Notify Moderator

DrewE wrote:



In general, there's little reason to ever have the disconnect switch disconnected that I can work out; the main one is perhaps when doing maintenance on the wiring or batteries.
For me it's when on shore power and dont like my wfco doing the charging/maintaining.

I had thought the battery was just to start the genny. That was fun to learn.

Just did a quick test on my 5500.
Prime button pulled 1.2amps
Starting was over 100a.
Running it pulled 2.5a and steadily dropped to 1.54a where it seemed to hold.

maillemaker

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Posted: 02/10/20 12:04pm Link  |  Quote  |  Print  |  Notify Moderator

Quote:

As others have said, the generator will automatically charge the house batteries through the battery charger built into the converter when running, but generally, it will not charge the chassis battery unless the "AUX BAT" switch is pressed. (not recommended for long term charging)


My MOM switch is powered by the house batteries, but AUX BAT is powered by the engine battery so the key must be in RUN for the batteries to be ganged.

This is so you cannot permanently gang the house batteries to the engine batteries while the engine is off - otherwise you could accidentally drain both your house and engine batteries and be stuck.

My Onan 4BGE will also shut down if the engine battery is disconnected (mine starts from the engine battery). But while running the inverter charges the house batteries.

Strange that it would actually run off of the engine battery but not charge it. I did not know that.

Steve


1990 Winnebago Warrior. "She may not look like much but she's got it where it counts!"



mchero

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Posted: 02/10/20 04:43pm Link  |  Quote  |  Print  |  Notify Moderator

My 93 Pace Arrow Diesel had a 3 cylinder Kubota generator that had a small alternator.


Robert McHenry
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drsteve

Michigan

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Posted: 02/11/20 09:23am Link  |  Quote  |  Print  |  Notify Moderator

Son of Norway wrote:

The battery supplies the energy needed to run the generator, right? So, while the generator is running, does it send a 12-volt DC current back to the battery to keep it charged, or does the generator just continue to drain the battery until the battery no longer has enough voltage to keep it running?



No. The battery supplies the energy needed to start the generator, not to run it. Once the generator is running, there is no drain on the battery.


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Chum lee

Albuquerque, NM

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Posted: 02/11/20 02:39pm Link  |  Quote  |  Print  |  Notify Moderator

mchero wrote:

My 93 Pace Arrow Diesel had a 3 cylinder Kubota generator that had a small alternator.


In addition to being used in RV's, some generators are designed to work as "stand alone" power supplies. IF/when that is the case, the manufacturer generally provides some way of recharging the starting battery if an electric start is provided. It's not necessary if your stand alone genny uses a pull start as its sole means of starting. Many motorcycles use an alternator, which also functions as a starter to save weight

Chum lee

DrewE

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Posted: 02/11/20 03:27pm Link  |  Quote  |  Print  |  Notify Moderator

drsteve wrote:

Son of Norway wrote:

The battery supplies the energy needed to run the generator, right? So, while the generator is running, does it send a 12-volt DC current back to the battery to keep it charged, or does the generator just continue to drain the battery until the battery no longer has enough voltage to keep it running?



No. The battery supplies the energy needed to start the generator, not to run it. Once the generator is running, there is no drain on the battery.


Built-in RV generators do typically need 12V power when running, not just when starting. If the generator is getting that power from a battery that is not being otherwise recharged, it will be a drain on that battery. Generally things are set up to the converter, powered by the generator, is powering the 12V system including the generator's control electronics and also charging the battery, but without that the generator very definitely will be draining a battery in most RVs. (The 12V power is needed for the generator's fuel pump, control electronics, etc.)

There are of course different designs of generators, and I'm sure there probably are some RV installations that do not require external 12V power once running, as well as some that have a 12V charge circuit built into the generator. To my knowledge, they're distinctly in the minority; most are set up as described above.





bounder39zman

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Posted: 02/11/20 07:48pm Link  |  Quote  |  Print  |  Notify Moderator

the Emerald III had a small (1 amp) charging system, using a stator winding labeled the "B" winding. this winding operated the electric choke heater on older models, and provided enough 12v, using a resistor and diode on control board for fuel pump and ignition system, and controls. Newer (last 20 years or so) generators relied on RV converter to keep batteries from discharging. Commercial versions all have 12v charging systems. BTW...NEVER a good idea to disconnect battery from generator when running. Like a car alternator, you risk shocking and damaging control board components.

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