Battery or Alternator trouble?

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Dan Walters

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I'm having trouble figuring out what's going on.  I went out to start my 4K Onan generator on my 1998 Allegro and it wouldn't start from the generator control panel.  So I started the engine, which started fine and then tried it from the switch on the dash and the generator started just fine.  I thought the battery might be low so I let it and the engine run while I took care of some maintenance issues inside.  After a while, I noticed that the alternator guage on the dash was in the red on the low end.  The engine ran long enough that it should have charged the batteries, so I shut it off.  As soon as I shut off the engine, the generator died.  I tried to restart the engine and everything was dead.  During this whole process, I made sure the DC power switch was off.  This sounds to me like either a battery or alternator problem or both.  Any thoughts?

Dan
 

Jeff

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Dan:

It sounds like you have a bad chassis battery or a bad connection, I would check out the connections first and then the battery.
 

Dan Walters

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Jeff,

Thanks for the input.  I did check the connections and everything looks good on that front.  I'm thinking, like you, that I have a dead chasis battery.  I'm going to take both of them out and get them checked.  Thanks again.

Dan
 

John From Detroit

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I sense a typo.  The batteries that have gone south are the HOUSE batteries, not the chassis battery

When you ran the engine a solonoid switch was engaged, this parralled the house and chassis (engine) batteries, the house batteries being shorted took down the engine battery but not before the generator was started.

I am assuming the dash guage is a voltmeter, not an ammeter.

Some rigs are now equiped with a "Smart" power control center for 12vdc, these will lock the chassis and house batteries together till the voltage drops to a set point, at which point they seperate them so you can still fire up the main engine (or the generator depending on which ran dead)
 

Dan Walters

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John,

You are right.  I should have said the house batteries.  The chassis battery charged up with the battery charger and started the engine without any problem but it went dead after I had everything running for a while.  I suspect that one or both of the house batteries are bad.  Thanks for the input.

Dan
 

Shayne

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Dan  you should replace both batteries if you need too.  They should always be replaced in set of 2, 3, 4, or whatever amount you have.  Use deep cell golf cart batteries.  Good Luck
 

Dan Walters

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Shayne,

Thanks for the tips.  I can use all the advice I can get.  The chassis battery looks like a regular automotive type side post battery.  Should I get a special battery to replace it with?

Dan
 

Shayne

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I always buy the heaviest deepest cycle I can buy  Usually a 7 yr  24mo free replacement  as I just did on the Regular battery  I replaced the 4 - 6 volt batteries last August as I did the Reg. However last week the Regular Battery decided to go South so it had to be replaced.  Stuff happens.  Good Luck
 

Gary RV_Wizard

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The chassis battery looks like a regular automotive type side post battery.  Should I get a special battery to replace it with?
No - there is nothing "special" about the chasiss battery - it's a regular car/truck type "starting" battery, not a deep cycle or marine type.
 

Jeff

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Dan Walters said:
Gary,

Thanks.  I guess that I will want one with high cranking amps rather than deep cycle to turn over the big motor better.

Dan

Dan:

Perhaps I missed something, I thought you said after shutting off  the motorhome engine everything went dead. If that means you could not restart the motorhome then the chassis battery (or alternator) could be bad. Next, if your house lights, pump, etc are still working then the coach (house) batteries may be OK, if not they need to be replaced as well.

John:

On two of our earlier coaches the gen started off the chassis batteries and then charged the coach batteries, probably to keep the starting loads off the deep cycles.
 

Dan Walters

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Jeff,

That's right.  When I turned off the ignition, the generator died as well.  Then, the engine would not re-start, the generator would not re-start and none of the 12 volt systems (lights, etc.) would come on either.  It was like all three batteries were drained.  I don't know if a dead house battery can drain the chassis battery or not, but it started initially and then would not start after running for a while.  It looks like all of the batteries are several years old and I will probably end up replacing all three.  Thanks again.

Dan
 

John From Detroit

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Jeff and Dan, the problem is with the HOUSE batteries, they appear to be sorted out, When he first started the engine and the charging solonoid closed he was able to start the generator, but then the shorted house batteries took down the engine batteries (at least that is my guess)

High cranking amps are NOT a good thing for house batteries, high amp-hour capacity is a good thing, AGM batteries have this feature BUT, and this is a big but, they need special charging and if your rig is not programmable, don't

NOTE: possibility is that the house batteries are not shorted, just that dead, since they hold a lot more enegery than the chassis battery, they can run that far down.

Remove house batteries, take to battery store and have a test done, odds are they will fail but if they don't, the test is usually free, or low cost if not, and you have eliminated the most likely problem,,, Gets harder after that.

Meanwhile, hook a charger to the chassis battery to re-charge it so you can start the rig
 

Karl

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Dan,

Sounds like you have more than one problem. The alternator gauge in the red would indicate a defective alternator or slipping belt (check tension). If alternator diodes were open, that would result in low or no output; if shorted, low or no output AND a possible drain on the chassis battery. Could also be a defective voltage regulator; some alternators have them built right into them. Running the engine without recharging the chassis battery would result in your not being able to restart the engine.

Some rigs will have a pushbutton (Aux Start) on the dash which will operate a solenoid to parallel the house and chassis batteries in the event you inadvertently drain one or the other. This would allow you to start either the genset from the chassis battery, or start the main engine from the house batteries. I can't think of any rigs where the house batteries and chassis battery are wired together purposely. Perhaps the solenoid contacts have welded themselves together. Check with an ohmmeter.


The genset quitting when you shut off the engine doesn't make any sense at all. A genset, once started, provides its' own running and ignition voltage, and is completely separate from the engine circuits. Check your gas tank fuel level. If it's below about 1/8th full, the genset will stop automatically to leave you with (hopefully) enough gas to get you to a gas station.
 

John From Detroit

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One posiblity is a blown 12vdc converter, the genset does not provide 12vdc in most cases, it relies on teh converter (As I have found out by testing) if the house batteries are totally dead, I mean, like five volts, then it will take time for the genset to build up enough voltage in those batteries for the generator igintion system and shutting off the main engine (thus seperating the genset from the mains battery) will cause it to stall.

Page two of this is that if the dash alternator/battery guage is a VOLTMETER it may also be registering a totaly dead HOUSE battery.

Still, I do suggest the entire system be checked,,, Starting with the batteries
 

Jeff

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Dan:

I guess the proof will be in the pudding. ;)

Please let us know what you find.
 

Dan Walters

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Bellville, Texas
Jeff, John, Karl,

Thanks to all of you for you input.  I've learned a lot from everything you all have told me.  I did take all three of the batteries out today and took them to be tested.  It seems that ALL THREE batteries are bad.  The chassis battery had a dead cell.  This was the oldest battery of the three.  The other two house batteries were also bad, but were only 1 1/2 years old and still under warranty.  The dealer is replacing them tomorrow, so I will be able to test all three new batteries together.  I did install the new chassis battery by itself late this evening and the motor started and the ampmeter on the dash shows that the alternator is charging.  We'll see what happens when I get the other two batteries installed.  I'll let you know how it turns out.  Thanks again to all of you for your input and advice.

Dan
 

John From Detroit

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Karl said:
Generators don't require 12 volts to run. The ignition is provided by a magneto.

Depends on the generator,  Some have Magneto systems, some solid state high enegery, some breaker point and some..... ELECTRIC FUEL PUMPS
 

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