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Old 01-20-2025, 02:00 PM   #1
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Question 1999 Freightliner XC charging house batteries?

Are the house batteries supposed to be charged by the engine driven alternator while on the road? I'm seeing maybe 12.5 volts at the batteries with the engine running. Doesn't seem like enough.
Thanks!
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Old 01-20-2025, 02:07 PM   #2
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Yes, the alternator should be charging both chassis and house battery banks.
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Old 01-20-2025, 02:18 PM   #3
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Thanks Brett for the reply. I don't have my schematics with me...is the charging circuit protected with a fuse? Alternator is new and charges the chassis batteries nicely
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Old 01-20-2025, 02:40 PM   #4
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Freightliner doesn't supply the wiring and solenoids involved in charging the house batteries, from the alternator ; your coach builder did .

What make and model is your coach ?
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Old 01-20-2025, 02:45 PM   #5
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Some systems want to see the chassis batteries fully charged , from the alternator , before switching to charging both battery banks .

How long did you run the engine before testing the output to the coach battery bank ?
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Old 01-20-2025, 03:11 PM   #6
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1999 Winnebago Chieftain 36 diesel
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Old 01-20-2025, 03:12 PM   #7
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About 15min. Dash gage shows about 15V but not sure of accuracy of gage.
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Old 01-20-2025, 03:29 PM   #8
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does your coach have relay isolators, or diode isolators? If its diodes, you're dropping.75V on the way to the batteries. Hopefully your alternator has a sense wire that will bump the output voltage to compensate (if the wire is hooked up)
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Old 01-20-2025, 03:42 PM   #9
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If your really seeing 15 volts, that means you have the wrong alternator or a missing sense wire.

That can burn out the diode type isolator, if equiped.

Post pictures of the battery control compartment.
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Old 01-20-2025, 04:24 PM   #10
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An alternator typically delivers around 14 volts DC. I have 2 vehicles w/alternator readouts on them and one is always at 13.9 and the other at 14.2. Years ago I had a 2-yr old battery die and traced it to a bad alternator delivering less than 10 volts; the new alternator now reads 14.0 volts (vs the previous 13.9).

15 volts however seems high. So not only does it appear the alternator may have failed to the high side, but a protection circuit between the alternator and battery has done it's job to protect your batteries from a dangerous overcharge. Whether it is a solenoid, relay, or fuse is dependent on your chassis.

Alternatively, has any work been performed recently w/the chassis batteries? If so, maybe things weren't hooked back up correctly. Also ensure the cables on the alternator are bolted on tight or they're not damaged in any way.

Lastly, how old are your batteries? Old batteries cannot hold a charge as well as new ones. So if they're old, the 12.5 volts -- the low end of a charged battery -- may be telling you it's time to replace them. Fully charged batteries should read above 13.2 volts. Cold weather only exacerbates a battery's weakness ... Don't know what the temperature is where you're at, but I've given more battery boosts to stranded drivers more times in the Winter than Summer. I remember because helping folks in the bitter cold and knee-deep snow s**ks more!

Good luck
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Old 01-20-2025, 08:19 PM   #11
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I'm on the road and using a cheap VOM. I will buy a new digital one tomorrow so I can see what is really going on here.

Thanks for all the help!
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Old 01-20-2025, 08:19 PM   #12
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Quote:
Originally Posted by Panheadguy View Post
1999 Winnebago Chieftain 36 diesel
A look at the wiring info on the Winnebago site may provide some answers about the way the house battery charging system works.

http://www.winnebago.com/Files/Files...ram/Wiring.htm
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Old 01-24-2025, 03:11 PM   #13
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I looked. Info overload for me!
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Old 01-25-2025, 07:39 AM   #14
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If the battery's are truly charging at 15 volts you will have a heavy sulfur smell in the battery compartment. Dash gauges are close at best but not 100% accurate, cheap volt meter are about the same a decent quality is going to cost you but worth having or you can go into any automotive shop and usually they will test the system for free and test your batteries.
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