new post, continue with charging issues to engine battery

[brian1]

on my battery isolater, the top post leads to the positive on firewall to battery , then to battery,
middle post leads to wiring harness which i assume leads it back to alternator, the bottom post feeds towards to the big red cable that i think feeds the rear battery, same cable which used to have insulation issues.

after charging battery for a short bit i connect it back up. then measure, from battery ground to all 3 terminals i have voltage. little low on battery post but it was not on charge very long.

i use boost switch to start, then measure again. also all measured against battery ground. the middle one which i think is alternator has close to 19 vdc on it (bad regulator?) the top one, battery positive is still a little below the 12vdc.
the bottom one is also at the 19 vdc, which i assume is feeding voltage to rear battery.

couple questions,
is regulator external to alternator or internal,
why would the lead to rear battery read the 19 vdc if it had not had a chance to over charge yet, all input appreciated, i assume this isolator is wired properly , or atleast i have not changed it.
thanks bgk
--
brian
asheboro, nc
75 eleganza 2 74 build
118k miles and counting,
DOG HOUSE

 

[george rudawsky]

The center contact should be the feed from the alternator - obviously if it's reading 19 volts, the voltage regulator is not doing it's job (internal to the alternator). The isolator can only feed voltage in one direction from the center terminal to the outer ones, and those should always read a bit lower voltage than the center terminal.

Since yours are reading different voltages on the two legs, I wonder if the isolator is going bad as well. They are not terribly expensive and are easy to swap out, so if yours is original, I'd consider getting a new one. I would also take the alternator in to have it checked and rebuilt if needed.

If you think of the GMC electrical systems as three separate systems (engine 12 volt, coach 12 volt, and coach 120 volt), the troubleshooing becomes a bit easier.
--
George Rudawsky
Chicago, IL
75 Palm Beach

 

[Ken H.]

Brian,

The diode to your chassis battery is bad -- i.e., the isolator is shot. The
low voltage on that battery's isolator terminal is the first clue -- it's
not being charged. The second clue is the 19 VDC on the other two terminals
-- the alternator has a "voltage sense" lead connected to the chassis
battery and depends upon that to tell it when it's reached the appropriate
charging voltage. The the diode failed, the alternator is trying to bring
that 12 VDC up to about 14.2 VDC; but, no matter how hard it tries, the
voltage sense lead still says 12 VDC. The 19 VDC is an internal limit of
the alternator's internal regulator.

You need to replace the isolator with a good one or, preferably (IMHO), a
combiner.

You can test my theory by connecting a jumper wire between the top two
terminals on the isolator. The alternaor voltage should drop to 13.8-14.2
VDC and stay there, charging the chassis battery. The house battery will
also be charged, but to about 0.7 VDC less, because of the isolator diode to
which it's still connected.

That "...big red cable that i think feeds the rear battery, same cable which
used to have insulation issues" very likely STILL has insulation issues. I
presume you put shield of some sort, or lots of electrical tape, on the
visible section of the cable. The likely problem is that the cable runs
through the living area of the coach THROUGH the left (driver's side) wall.
There have been numerous reports of that cable's deteriorated insulation
allowing shorts to the aluminum ribs through which it runs. Some fires have
started there -- usually catastrophic.

If mine was as bad as you made yours sound, I'd waste no time checking the
condition inside the wall, or disconnect it and bypass it with a
well-shielded parallel cable along the frame.

JWID.

Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com

>
>
> on my battery isolater, the top post leads to the positive on firewall to
> battery , then to battery,
> middle post leads to wiring harness which i assume leads it back to
> alternator, the bottom post feeds towards to the big red cable that i think
> feeds the rear battery, same cable which used to have insulation issues.
>
> after charging battery for a short bit i connect it back up. then measure,
> from battery ground to all 3 terminals i have voltage. little low on battery
> post but it was not on charge very long.
>
> i use boost switch to start, then measure again. also all measured against
> battery ground. the middle one which i think is alternator has close to 19
> vdc on it (bad regulator?) the top one, battery positive is still a little
> below the 12vdc.
> the bottom one is also at the 19 vdc, which i assume is feeding voltage to
> rear battery.
>
> couple questions,
> is regulator external to alternator or internal,
> why would the lead to rear battery read the 19 vdc if it had not had a
> chance to over charge yet, all input appreciated, i assume this isolator is
> wired properly , or atleast i have not changed it.
> thanks bgk
> --
> brian
> asheboro, nc
> 75 eleganza 2 74 build
> 118k miles and counting,
> DOG HOUSE
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>

 

[brian1]

Ken
i ran that big troublesome cable thru a plastic pipe i had in garage, old style black plactic water hose. rubber tape on ends hoping to keep moisture out of it. the insulation was not off, just cracked very bad, and discolored to almost white. i am not sure how to check it inside walls, which are finished .
running a new one i hope to be a winter project,

i assume this isolator is an over the counter part form napa?
also, assuming my coach wiring is original, if i disconnect the big wire to the rear, besides alternator not charging that battery, would there be any other ill effects. i assume when plugged into 120vac or genny running that coach battery would still get charged, do i loose the boost for starting?
thanks bgk
--
brian
asheboro, nc
75 eleganza 2 74 build
118k miles and counting,
DOG HOUSE

 

[Ken H.]

If you disconnect the deteriorated cable at the front, it will still be
connected to the house battery and the converter in the rear and thus still
may constitute a hazard -- and NO boost. You need to either pull the
interior wall panel to examine the cable and ensure it's not a hazard; or,
you need to replace it, IMHO.

Yes, you can buy an isolator at many auto parts stores, most RV dealers, or
via the internet. A LOT of us prefer a combiner, which allows either the
alternator or the converter to charge both battery banks, unlike the
isolator which does not allow the converter to charge the chassis (engine)
battery. www.yandina.com is the place to go to buy a C100 combiner for not
much more than an isolator.

Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com

>
>
> Ken
> i ran that big troublesome cable thru a plastic pipe i had in garage, old
> style black plactic water hose. rubber tape on ends hoping to keep moisture
> out of it. the insulation was not off, just cracked very bad, and discolored
> to almost white. i am not sure how to check it inside walls, which are
> finished .
> running a new one i hope to be a winter project,
>
> i assume this isolator is an over the counter part form napa?
> also, assuming my coach wiring is original, if i disconnect the big wire to
> the rear, besides alternator not charging that battery, would there be any
> other ill effects. i assume when plugged into 120vac or genny running that
> coach battery would still get charged, do i loose the boost for starting?
> thanks bgk
> --
>

 

[brian1]

ken
sorry to be so troublesome,
where in the back could i disconnect this "bad" cable. i am thinking if all i loose is boost, then i can disconnect it at both ends, run isolator output that used to go to house battery to my engine battery, this would allow me to confurm isolator and alternator, at camp site in a couple weeks i will be plugged in so house battery keeps charge. i can take my battery charger with me to jump off coach battery in a pinch, and wife does not get to remind me that i just bought and installed a microwave in coach. complete with 15 amp breaker and circuit, which should drive charger if it turned out my engine battery was done.
over winter i can hide cost of combiner, cable to rear, as i do step and other things
thanks again
brian
--
brian
asheboro, nc
75 eleganza 2 74 build
118k miles and counting,
DOG HOUSE

 

[Ken H.]

Brian,

I have an entirely different configuration than you (or anyone else), and I
don't even know what coach model you have, so someone may need to correct
this: Go to your converter, which I presume is about half way back in the
living area on the left side. There should be two large wires going into
it, hopefully red and black. Follow the red one to an isolated stud on the
big aluminum longitudinal member (the beltline on the outside), similar to
the one below the isolator on the firewall. There's probably a large wire
leading to the rear (to the Onan) and the large wire from the front that you
want to disconnect.

If you find that and get it loose at both ends, I suggest you use a
multimeter to check the supposedly loose wire to make darned sure it really
is. Tape up both ends to be sure nothing and no one connects it to
anything.

With that accomplished, if your wiring is all standard, you should have
isolated the chassis and coach 12 VDC systems. You no longer have any use
for the isolator, good or bad. Just use it as a junction block by moving
the top wire (which you've said goes to the chassis battery) to the center
terminal of the isolator, to which the alternator is connected. Now you
won't have the 0.7 VDC drop across the isolator diode, the voltage sense
line to the alternator will again control its output voltage and you should
be in good shape -- once you get a battery charger or jumper wire on that
chassis battery so you can start without the boost switch.

Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com

>
>
> ken
> sorry to be so troublesome,
> where in the back could i disconnect this "bad" cable. i am thinking if all
> i loose is boost, then i can disconnect it at both ends, run isolator output
> that used to go to house battery to my engine battery, this would allow me
> to confurm isolator and alternator, at camp site in a couple weeks i will be
> plugged in so house battery keeps charge. i can take my battery charger with
> me to jump off coach battery in a pinch, and wife does not get to remind me
> that i just bought and installed a microwave in coach. complete with 15 amp
> breaker and circuit, which should drive charger if it turned out my engine
> battery was done.
> over winter i can hide cost of combiner, cable to rear, as i do step and
> other things
> thanks again
> brian
> --
> brian
> asheboro, nc
> 75 eleganza 2 74 build
> 118k miles and counting,
> DOG HOUSE
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>

 

[Ken B]

On the isolator, move the engine side wire to the center terminal of the isolator. This will get you around the possibly defective diode in the isolator and allow you to check the charging voltage again. If the diode is indeed bad the engine side will act and charge as normal. The house side will also slowly charge as it will see 13.3 volts instead of the nominal 14.0 volts.

Once you have proven that is your problem you can replace the isolator or buy a combiner. You could also drive it this way for a while.


--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

 

[brian1]

confurmed bad diode, after switching the 2 wires at isolator my alternator ready much better, it dropped from 199 to 15, and as it ran approx 15 minuntes it dropped to slightly over 14. all read with cheep meter to chassic ground,
i also saw that isolator actually dropped it close to a full volt , i am not sure if i can get combinner in before my trip next week, but it is cooming soon, after i told wife i needed an 100 plus alternator, it was easy to sell her on the 60 combinner after alternator was confurmed good.

this site is great, before i bought my coach , with this site i felt i could keep one on the road, now after buying, i know i can, thanks to all,
brian
--
brian
asheboro, nc
75 eleganza 2 74 build
118k miles and counting,
DOG HOUSE

 

[thomas phipps]

If you live near a Northern Tool outlet, not Harbor Freight, they have a combiner on sale (according to net ad) for $30. It will do the trick.
Combiner from Yandia will also do the trick.
Or, as Mr Elf shows, use both.

Tom Phipps,
needs a 3 battery isolator.

 

[Ken B]

> confurmed bad diode, after switching the 2 wires at isolator my alternator ready much better, it dropped from 199 to 15, and as it ran approx 15 minuntes it dropped to slightly over 14. all read with cheep meter to chassic ground,
> i also saw that isolator actually dropped it close to a full volt , i am not sure if i can get combinner in before my trip next week, but it is cooming soon, after i told wife i needed an 100 plus alternator, it was easy to sell her on the 60 combinner after alternator was confurmed good.
>
> this site is great, before i bought my coach , with this site i felt i could keep one on the road, now after buying, i know i can, thanks to all,
> brian


If yo moved the wire as I stated in my previous posting,You can drive it the way it is for a long time. You just will not fully charge the house batteries from the engine driven alternator. If you are going to plug into shore power when stopped then the house batteries will fully charge there. This way you can go on your trip and replace the isolator with a new one or with a combiner at your convenience when you return.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

 

[brian1]

ken
last question as i think this thru, i understand i can move engine battery connection to alternator connection to bypass this bad diode, i assume if i did that and did not stay plugged in say in drive way at house, would the coach battery pull down engine battery? to which the 2 would keep at an equal state? i ask this because thru all this hot weather i have been leaving my vent fan on but at highest temp, trying to just move a little air at temp extremes, i noticed that fan would be good for approx 3 weeks or so. is it bad to leave fan on like this? it sure has been hot
thanks again
brian
--
brian
asheboro, nc
75 eleganza 2 74 build
118k miles and counting,
DOG HOUSE

 

[Gene Fisher]

why not just put in a combiner?

gene

>
>
> ken
> last question as i think this thru, i understand i can move engine battery connection to alternator connection to bypass this bad diode, i assume if i did that and did not stay plugged in say in drive way at house, would the coach battery pull down engine battery? to which the 2 would keep at an equal state? i ask this because thru all this hot weather i have been leaving my vent fan on but at highest temp, trying to just move a little air at temp extremes, i noticed that fan would be good for approx 3 weeks or so. is it bad to leave fan on like this? it sure has been hot
> thanks again
> brian
> --
> brian
> asheboro, nc
> 75 eleganza 2 74 build
> 118k miles and counting,
> DOG HOUSE
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>

--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and -------
http://bdub.net/gmcmotorhome.info/
Alternator Protection Cable
http://bdub.net/gmcmotorhome.info/APC.html

 

[Matt Colie]

> ken
> last question as i think this thru, i understand i can move engine battery connection to alternator connection to bypass this bad diode, i assume if i did that and did not stay plugged in say in drive way at house, would the coach battery pull down engine battery? to which the 2 would keep at an equal state? i ask this because thru all this hot weather i have been leaving my vent fan on but at highest temp, trying to just move a little air at temp extremes, i noticed that fan would be good for approx 3 weeks or so. is it bad to leave fan on like this? it sure has been hot
> thanks again
> brian

OK Brian,

If you did as KenB suggested, the house(coach) battery cannot deplete the engine(chassis) battery. The only problem is that the engine alternator will not be able to fully charge the house battery as it is limiting its output based on the engine battery.

To you other question - Yes, it is not good for either the house battery or the fan. If you can get enough cord to supply the converter, the house battery problem is covered. The other is just running hours on the fan that probably does have a limited life (most things do).

Matt
--
Matt & Mary Colie
'73 Glacier 23 Chaumiere (say show-me-air) Just about as stock as you will find
SE Michigan - Twixt A2 and Detroit

 

[Ken H.]

Brian,

Most of your questions about isolators can be answered from one
fundamental fact: Current can flow FROM the alternator terminal;
never TO it.

Ken H.

>
>
> ken
> last question as i think this thru, i understand i can move engine battery connection to alternator connection to bypass this bad diode, i assume if i did that and did not stay plugged in say in drive way at house, would the coach battery pull down engine battery? to which the 2 would keep at an equal state? i ask this because thru all this hot weather i have been leaving my vent fan on but at highest temp, trying to just move a little air at temp extremes, i noticed that fan would be good for approx 3 weeks or so. is it bad to leave fan on like this? it sure has been hot
> thanks again
> brian
> --
> brian
> asheboro, nc
> 75 eleganza 2 74 build
> 118k miles and counting,
> DOG HOUSE
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>

 

[Ken B]

> ken
> last question as i think this thru, i understand i can move engine battery connection to alternator connection to bypass this bad diode, i assume if i did that and did not stay plugged in say in drive way at house, would the coach battery pull down engine battery? to which the 2 would keep at an equal state? i ask this because thru all this hot weather i have been leaving my vent fan on but at highest temp, trying to just move a little air at temp extremes, i noticed that fan would be good for approx 3 weeks or so. is it bad to leave fan on like this? it sure has been hot
> thanks again
> brian

No,
The coach battery is still isolated by it's diode in the isolator and the coach battery has no effect on the engine battery.

I was just trying to give you a solution so you could use your coach for a while until you buy and receive a replacement isolator or combiner.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana