Home » Public Forums » GMCnet » Flat battery today ...alternator? (help!)
Flat battery today ...alternator? [message #370471] |
Sat, 10 September 2022 19:56 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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Managed to get the engine started using the dual battery switch .. then put a meter on the solenoid positive and ground ...meter read 10.8v ...revved up the engine, no difference in reading ...kept engine going for a few minutes and battery meter voltage slowly started to decrease. With headlights on voltage dropped further.
Took battery out, put it on charge for about 15 mins, came up/recovered normally.
I diagnosed this as an alternator problem, could it be anything else?
TIA
Larry
Larry - Victoria BC -
1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
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Re: Flat battery today ...alternator? [message #370472 is a reply to message #370471] |
Sat, 10 September 2022 21:10 |
JohnL455
Messages: 4447 Registered: October 2006 Location: Woodstock, IL
Karma: 12
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Alternator or isolator or connections.
Running, meter center terminal of isolator which is alt output. Should be 14.8 or so or .7 above desired system voltage.
I guarantee your batteries are not fully charged after 15 mins. It would take several hours with a 10A and days with a trickle.
John Lebetski
Woodstock, IL
77 Eleganza II
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Re: Flat battery today ...alternator? [message #370473 is a reply to message #370472] |
Sat, 10 September 2022 23:32 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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No, it wasn't fully charged or anything, just started to come up when we put the charger on it to see if it would TAKE a charge.
Going to load test it tomorrow. House batteries are fully charged so I let them be.
I have a cutoff switch in the chassis battery circuit which is off most of the time; I only turn it on if I'm going to run the engine.
I'll get the alternator checked tomorrow morning and if both it and the battery are OK I'll look at the isolator - Thanks!
Larry
Larry - Victoria BC -
1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
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Re: Flat battery today ...alternator? [message #370475 is a reply to message #370473] |
Sun, 11 September 2022 07:19 |
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Matt Colie
Messages: 8547 Registered: March 2007 Location: S.E. Michigan
Karma: 7
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Larry,
Yes, your charging system has failed, but don't go buying parts before finishing the diagnosis.
You have a meter? If no, go get one.
Measure the battery voltage.
Fire the engine. Measure again.
Measure between the center of the isolator and the plate. Should be 14+ with the engine running. Less than that check alternator connections.
Engine Off. Headlights on.
Measure between the battery + and the terminal on the boost contactor. Same as the battery?
Same for the battery - and the aluminum ground plate where things are mounted. Same? Ok connections are good.
Engine off.
If you were good to there, pop the wires off the islator and set the meter to resistance. May be marked as Ω.
Check between the center and both others one way and then reverse the test leads and do it again. If you don't get a difference one way and not the other, things are good.
Isolator failures are rare, but do happen.
Good luck Be sure to tell us what you find.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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Re: Flat battery today ...alternator? [message #370476 is a reply to message #370475] |
Sun, 11 September 2022 08:35 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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Matt - I have an appointment this (Sunday) morning at my alternator re-builder's place: the owner is making a special trip into town to open up his place for me. I'm bringing the battery and alternator into him for testing. Before I got any advice here I assumed the alternator had developed a problem so I removed it.
I hadn't had any charging issues like this before and because the positive lead to the battery from the solenoid didn't show more than 10 or 11v with the engine running I made that analysis. Now I see the isolator is where I should have placed my meter. Oh well, I can do that when I get back out to the coach and reassemble everything (if the alternator tests good)
Thinking about the role of the isolator and the fact that my battery was down so much after behaving normally just last week, am I right thinking a failed isolator could have allowed my house batteries to draw down the chassis battery?
Larry
Matt Colie wrote on Sun, 11 September 2022 05:19Larry,
Yes, your charging system has failed, but don't go buying parts before finishing the diagnosis.
You have a meter? If no, go get one.
Measure the battery voltage.
Fire the engine. Measure again.
Measure between the center of the isolator and the plate. Should be 14+ with the engine running. Less than that check alternator connections.
Engine Off. Headlights on.
Measure between the battery + and the terminal on the boost contactor. Same as the battery?
Same for the battery - and the aluminum ground plate where things are mounted. Same? Ok connections are good.
Engine off.
If you were good to there, pop the wires off the islator and set the meter to resistance. May be marked as Ω.
Check between the center and both others one way and then reverse the test leads and do it again. If you don't get a difference one way and not the other, things are good.
Isolator failures are rare, but do happen.
Good luck Be sure to tell us what you find.
Matt
Larry - Victoria BC -
1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
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Re: Flat battery today ...alternator? [message #370479 is a reply to message #370477] |
Sun, 11 September 2022 10:41 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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Thanks guys, advice heeded. will report back later on when I get home.
Larry
Larry - Victoria BC -
1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
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Re: Flat battery today ...alternator? [message #370480 is a reply to message #370471] |
Sun, 11 September 2022 20:43 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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The alternator tested good but the battery failed the load test. Battery is 4 yrs old BTW. When I got back to the coach I put the battery on charge again and got it up to about 12.5 after about an hour or so.
After reinstalling the alternator and battery, the coach started right up. I ran the engine for about 10 mins then turned on the headlights and blower for about a minute then shut the engine down. I should mention I have a chassis battery cutoff switch that I switch off whenever the engine isn't needed. I shut it off after engine shutdown.
After about 1/2 hour, I switched the battery on again via the cutoff switch and tried starting the engine. No go.
I installed another known good battery and went for a test run, about 5 miles or so, Dash A/C and blower on max. Stopped and restarted several times and coach behaved normally.
When I first discovered the non-cranking issue, the battery, which had been performing normally had been disconnected via the cutoff switch for about a week prior - so no chance of a parasitic draw pulling it down. I guess it just gave up suddenly?
Anyway, thinking a new battery is in the cards.
One thing I didn't understand. When I put the meter on the center tap of the isolator I got about 15+ volts or so and also when I put the meter on the house battery side of the solenoid I got over 14v too but when I metered the solenoid tap on the chassis side, the most I saw was 11+v and this was with the fully charged known-to-be-good battery. Is that normal if the chassis battery is fully charged?
Larry
Larry - Victoria BC -
1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
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Re: Flat battery today ...alternator? [message #370481 is a reply to message #370475] |
Sun, 11 September 2022 21:48 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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Matt, I wasn't able to do the test on the isolator as the terminals were so rusty I couldn't budge them and didn't want them to snap, they felt like they might.
..also not EXACTLY sure what you are saying here: "If you don't get a difference one way and not the other, things are good."
Could re-phrase that please?
thanks
Larry
Matt Colie wrote on Sun, 11 September 2022 05:19
If you were good to there, pop the wires off the islator and set the meter to resistance. May be marked as Ω.
Check between the center and both others one way and then reverse the test leads and do it again. If you don't get a difference one way and not the other, things are good.
Isolator failures are rare, but do happen.
Matt
Larry - Victoria BC -
1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
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Re: Flat battery today ...alternator? [message #370482 is a reply to message #370471] |
Mon, 12 September 2022 07:49 |
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RF_Burns
Messages: 2277 Registered: June 2008 Location: S. Ontario, Canada
Karma: 3
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Larry,
An Isolator allows current to flow from the center post (Alternator) to the outer posts (Chassis and House batteries). It blocks current from flowing from the battery terminals to the alternator or to each other. Therefore the house loads cannot discharge the chassis battery, but the alternator can charge both batteries.
Since you see ~15 volts at the center post (alternator) but less than 12 volts on the chassis side, that indicates to me that the Isolator is faulty. The battery terminals should be about 0.7 volts lower than the alternator terminal with the engine running. That's the only test you really need to indicate a good/bad isolator.
Isolators are widely available, I'd suggest Princess Automotive or Canadian Tire for us Canadians. Get one rated at at least 90 Amps, 120 or 150 amp models give you some more robustness.
The center terminal is generally the Alternator. It doesn't matter which battery connects to the other two terminals.
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC. 1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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Re: Flat battery today ...alternator? [message #370483 is a reply to message #370482] |
Mon, 12 September 2022 10:05 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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Hey thanks Bruce - Makes sense. I knew the isolator wasn't a "smart" device so couldn't figure out why it could be "regulating" the supply to the chassis battery. At the moment Canadian tire doesn't stock any but Princess Auto is carrying a 90 amp model ..that one looks physically identical to what's on board right now so I'll pick one up this morning.
Thanks again
Larry
RF_Burns wrote on Mon, 12 September 2022 05:49Larry,
An Isolator allows current to flow from the center post (Alternator) to the outer posts (Chassis and House batteries). It blocks current from flowing from the battery terminals to the alternator or to each other. Therefore the house loads cannot discharge the chassis battery, but the alternator can charge both batteries.
Since you see ~15 volts at the center post (alternator) but less than 12 volts on the chassis side, that indicates to me that the Isolator is faulty. The battery terminals should be about 0.7 volts lower than the alternator terminal with the engine running. That's the only test you really need to indicate a good/bad isolator.
Isolators are widely available, I'd suggest Princess Automotive or Canadian Tire for us Canadians. Get one rated at at least 90 Amps, 120 or 150 amp models give you some more robustness.
The center terminal is generally the Alternator. It doesn't matter which battery connects to the other two terminals.
Larry - Victoria BC -
1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
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Re: Flat battery today ...alternator? [message #370484 is a reply to message #370471] |
Mon, 12 September 2022 11:00 |
JohnL455
Messages: 4447 Registered: October 2006 Location: Woodstock, IL
Karma: 12
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Possible scenario. Your failed battery may have taken out one diode in your isolator. The battery fail you experienced is typical with today’s batteries. My take is in the old days they would gradually start to crank slower over a period of time. Today the end of life curve is dramatic.
John Lebetski
Woodstock, IL
77 Eleganza II
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Re: Flat battery today ...alternator? [message #370485 is a reply to message #370484] |
Mon, 12 September 2022 11:46 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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John, my experience is that the old batteries gradually lost their oomf but yes indeed these new ones fail suddenly... what's up with that? lol
Larry
JohnL455 wrote on Mon, 12 September 2022 09:00Possible scenario. Your failed battery may have taken out one diode in your isolator. The battery fail you experienced is typical with today’s batteries. My take is in the old days they would gradually start to crank slower over a period of time. Today the end of life curve is dramatic.
Larry - Victoria BC -
1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
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Re: Flat battery today ...alternator? [message #370488 is a reply to message #370471] |
Mon, 12 September 2022 17:44 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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Fitted a new Princess Auto isolator, now I have charging to both house and chassis batteries.
Replaced old chassis battery with a new 800cca unit. All good now! Thanks for all the help guys
Larry
Larry - Victoria BC -
1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
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Re: Flat battery today ...alternator? [message #370490 is a reply to message #370489] |
Mon, 12 September 2022 22:57 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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I didn't see the combiner, I'll have another look in a sec ...I got the blue aluminum fin unit. A bit larger physically than the one I took out but still fit in the space above the shut-off switch I installed last year. Mounted it using 2 of the existing holes and 2 self-tappers for the lower mounts to the aluminum plate. I never plug in to shore power so no real advantage to charge from the converter -unless I run the genny I guess?
With the temps being what they are this summer I'm running the dash a/c fan on max when I'm traveling -thankfully my dash A/C blows ice cubes even though it's an R134A conversion
Larry
RF_Burns wrote on Mon, 12 September 2022 20:37Did you get the isolator that has the aluminum fins? or the one in the plastic case. The plastic case unit is a combiner. It connects the batteries together when it detects that either battery is getting a charge voltage, either from the alternator or the house power converter. Nothing wrong with the combiner, but you do lose the higher voltage from the alternator which is used on high-speed fan to give you more air flow from the dash heater-A/C unit.
Larry - Victoria BC -
1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
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Re: Flat battery today ...alternator? [message #370491 is a reply to message #370471] |
Mon, 12 September 2022 23:10 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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Bruce - On second thoughts I did see the plastic one but didn't really know what it was or how it was hooked up etc, so passed on it. It seemed a bit pricey too at $80, so I checked on eBay and I saw hundreds of these sold under different "brands".
Large price range but some as low as CAD$17 ..of course they're probably all made in the same factory.
https://www.ebay.ca/itm/115520865663
cheers
Larry
Larry - Victoria BC -
1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses
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