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Checking Alternator

January 05, 2015, 03:53:20 pm

Started the coach today for final check before heading to Florida and the alternator is not charging. I read an earlier post and checked the two small wires. Both are hot when switch is on, only one when switch is off. I checked the alternator voltage at the isolator and it is reading 6 volts. Are there other tests I  can do before removing the alternator. In the past it would read 12 volts when first started but when the rpms were raised, it would go between 13 and 14 volts. I have a spare alternator but I want to be sure that this one has died before replacing it. Thanks for any help you can give me.
Jerry

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Re: Checking Alternator

Reply #1 – January 05, 2015, 04:16:40 pm

Read voltage at each of the isolator terminals and let us know.

Verify that the small sense wire from isolator to alternator is there, with clean and tight connections.

Brett

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Re: Checking Alternator

Reply #2 – January 05, 2015, 04:45:19 pm

Brett,
the voltages are as follows: Battery one - 13.4 volts,  Battery two - 12.5 volts. Sensing wire is there and now freshly cleaned. It is connected to the Battery two terminal. No voltage on it when disconnected. I assume it gets it's voltage from the battery terminal. Correct?

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Reply #3 – January 05, 2015, 05:09:03 pm

Correct, the sense wire senses voltage on the chassis battery terminal of the isolator and sends that voltage to the alternator.

So, what are the readings at the isolator terminals (B+ from alternator) as well as the terminals for house and chassis battery with the engine running at high idle (say, 1100 RPM or so)?

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Re: Checking Alternator

Reply #4 – January 05, 2015, 05:27:35 pm

Brett,
Readings are Battery one 13.5 volts, Battery two 12.5 volts and alternator voltage started at 7 volts and fell  to 3.5 volts.
Jerry

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Re: Checking Alternator

Reply #5 – January 05, 2015, 05:28:34 pm

This was at approx. 1250 rpms

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Re: Checking Alternator

Reply #6 – January 05, 2015, 05:44:44 pm

Yup, alternator is the likely suspect.


If you want to troubleshoot yourself and it is a Hehr Powerline: Untitled Document

You could also contact them for the name of your nearest Hehr dealer who can likely rebuild it:

4616 Fairlane Avenue
Fort Worth, TX 76119
Phone: 817-535-0284
Fax: 817-531-2755
Email: sales@hdpsi.com

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Re: Checking Alternator

Reply #7 – January 05, 2015, 05:50:32 pm

Well I'll try the spare tomorrow..Thanks

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Re: Checking Alternator

Reply #8 – January 06, 2015, 10:07:31 am

If the coach has been setting up for a good while the brushes may be hung up.
Using a rubber mallet give the alternator a couple good whacks and check again.  You never know.
Gary B

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Re: Checking Alternator

Reply #9 – January 06, 2015, 02:09:24 pm

Thank you Gary for the suggestion. I was changing out the alternator when you send it, so I didn't get to try it.
Good news is I had a spare and it is is installed and charging just fine.
Thank you Brett for the trouble checking guide.
You guys are great..
Jerry

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Re: Checking Alternator

Reply #10 – January 06, 2015, 04:11:58 pm

Jerry, that will be $25 for the Technical help, so please send chq to Brett??
He he
JohnH

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Re: Checking Alternator

Reply #11 – January 06, 2015, 05:58:09 pm

John,
It sure saved me more than that. Wished I could have tried the hammer trick. I used to have to do that on our Lincoln starter.
Off to Florida and warm weather.
Jerry

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