Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 12, 2025 ...

Troubleshooting the alternator

December 04, 2013, 06:59:48 pm

I refilled my batteries w/ distilled water and disconnected and charged each one separately. The last time my coach was started ( 3 months ago ) the alternator was charging perfectly. When I reconnected the batteries today, the amp gauge shows the alternator is not charging. I cannot figure out why. I have done this same procedure every December in preparation for our Florida trip. Could someone reply with a troubleshooting checklist? I have a spare, but do not want to change this one out w/o checking it?
Thanks for your help. 

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Re: Troubleshooting the alternator

Reply #1 – December 04, 2013, 07:11:18 pm

If, indeed, you have an ammeter vs a voltmeter, if the batteries were charged to OVER the voltage set by the alternator/regulator, it could show a discharge when first connected.

Would be very interested in the voltage of batteries before start up and also with the alternator online/engine running.

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Re: Troubleshooting the alternator

Reply #2 – December 04, 2013, 07:23:20 pm

Sorry, Brett, my bad. It is a voltmeter not an ammeter. Voltmeter reading just below 12V with engine running and Audit shows batteries at 11V. Should I check the coach batteries with a multimeter before starting?

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Re: Troubleshooting the alternator

Reply #3 – December 04, 2013, 08:52:01 pm

Jerry,

I would charge both battery banks from shore power/generator. Use the boost switch to charge chassis batteries.  Then recheck. 

Sure, you could have an alternator issue, a regulator issue, or a battery isolator issue, but completely discharged batteries will give very weird readings.  So, I would start by fully charging the batteries and likely having them load tested.  If good, then we can get into checking out the charging system.

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Re: Troubleshooting the alternator

Reply #4 – December 04, 2013, 10:13:35 pm

On my 98 u295 the alternator worked just fine, then about a week later started and was not charging. I took the alternator off and removed the voltage regulator and found that there was a brush hanging up. I cleaned the commutator rings and installed new brushes and reinstalled the voltage regulator and the alternator and all was good, so may be a very simple thing.

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Re: Troubleshooting the alternator

Reply #5 – December 05, 2013, 08:47:45 am

I replaced my alternator last spring thinking that it had gone bad. A small corroded wire was the problem with mine. It simply fell off the alternator.

I want to admit to you right now, that I am a Foretravel Wannabe and had this happen on my 5.9L Cummins in my current Itasca, so this may or may not be the case with yours:

My alternator is self-exciting, meaning that there is a short red 14-guage wire going from the positive terminal on the alternator to the regulator terminals at the bottom of the alternator.

It some installations, the regulator is fed via a fused connection that comes from the ignition. If that is the case, check to see if there is a bad fuse.

Hope this helps.

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Re: Troubleshooting the alternator

Reply #6 – December 05, 2013, 08:49:49 am

The dash voltmeter is at the end of a line of many, many electrical connections from the alternator.  So a low dash voltage could mean many things.  It could mean a bad alternator or bad battery with a shorted cell that sucks up all the power the alternator is putting out.  But from my experience (with the same age coach as yours) it's most likely an electrical connection somewhere in the system that built up some resistance while in storage - this includes the dash ignition solenoid.  As Brett suggested, it's difficult to diagnosis the system if the batteries don't have a good change, but since you were able to start the engine they (at least the chassis batteries) must be in decent shape.  BTW, did you have to use the boost switch?
I would (while engine is running) check with a digital voltmeter:
1.  Actual voltage of each battery - at the battery terminals (all batteries -  chassis and house)
    If less than 13 volts then measure voltage at the battery isolator.  Center terminal (from alternator) should be around 14+ volts.
    Other side terminals of isolator should match respective battery (house/chassis)
2. If batteries are 13+ plus then you have a bad connection somewhere between your batteries and the dash voltmeter.  Measure ignition solenoid voltage at both large terminals.  They should be very close to the same voltage. 
    How does this voltage compare with the reading on the dash gauge?  The voltage drop could be the wire connection to the dash gauge.  Many possibilities, your voltmeter is your main tool.

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Re: Troubleshooting the alternator

Reply #7 – December 05, 2013, 10:46:42 am

Hi John,

On my 2002 320 the low reading on the dash voltmeter turned out not to be alternator problems. I re-adjusted the calibration potentiometer inside the gauge to match the battery voltage. To do this you must remove the gauge from the dash in order to see the small hole in the case's threads. A jeweler's screwdriver works quite well.

Jim

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Re: Troubleshooting the alternator

Reply #8 – December 05, 2013, 10:50:05 am

If you notice your voltmeter go down while you're driving the first thing to do is flip the Audit monitor over to the tank levels to see if the voltage went down on the coach batteries at the same time. If the coach batteries still show normal voltage you know it's a problem that only exists in the chassis electrical system, so it can't be the alternator or voltage regulator. It could be the ignition solenoid under the dashboard. If the coach batteries and chassis batteries both show a low voltage reading while you're driving you probably have lost your alternator, voltage regulator, isolator, or something related to them. Don't drive any further than you have to before you fix it. Driving with the genset running and the boost solenoid closed won't supply enough DC power, especially if you're using the lights and wipers and defroster motor. The charger only supplies about 40-70 amps of power. Your alternator probably supplies about 160 amps by comparison.

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Re: Troubleshooting the alternator

Reply #9 – December 05, 2013, 11:47:39 am

Yes, as to whether you can drive with the generator and inverter/charger or converter supplying all the 12 VDC leads depends on what inverter/charger or converter you have as well as what 12 VDC electrical loads you are running.

The vast majority of newer coaches with their inverter/chargers ARE capable of going cross country with the generator powering the charger section of the inverter/charger and the boost switch keeping chassis batteries up.

Even lower output converters can keep up if you are not using lights, etc.

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Re: Troubleshooting the alternator

Reply #10 – December 05, 2013, 12:48:29 pm

First, thanks for everyone's input.
Here are my voltage readings:
Chassis battery ( less than a year old ) 12.3 volts
House batteries, separate and connected 12.2 volts
Dash voltmeter 11 volts.
With engine running - voltage is the same
Terminals on the alternator - Current sensing right terminals facing rear 12.2 volts
Ignition terminal small left facing rear - 11.2 volts
Output terminal .12 volts -- same at regulator ( center tap )
Voltage does not change when engine is running.
Sound like a bad alternator?

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Re: Troubleshooting the alternator

Reply #11 – December 05, 2013, 03:32:39 pm

Well, i just aired up my tires to prepare to get the old girl inspected and probably the alternator changed out.  I started her to pull off my pads and lo and behold the alternator is charging. Putting out 13.5 volts according to the dash voltmeter.
I guess when it figured out I had called in the experts, it figured it better start behaving.
With the voltage readings I was getting, the loose connection would have to be in the alternator, wouldn't it?
Thanks again for everyone's help.
Jerry



 

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Re: Troubleshooting the alternator

Reply #12 – December 05, 2013, 03:40:03 pm

Jerryetc, Alternator not charging could be as simple as not being activated til engine RPM increased.  Try again, start up, watch voltmeter, still low ? Then rev up, works OK ?
Gary B

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Re: Troubleshooting the alternator

Reply #13 – December 05, 2013, 04:50:43 pm

Thanks Gary. I had revved it up and even re-started. Nothing changed until this last re-start. Keeping my fingers crossed.
Jerry

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Re: Troubleshooting the alternator

Reply #14 – December 05, 2013, 08:07:24 pm

Maybe one of the brushes was stuck and it freed itself as the alternator warmed up?

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