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[GMCnet] Replacement Isolator [message #98864]

Tue, 07 September 2010 16:19

Jim White[1]

Messages: 144
Registered: September 2008

Karma: 0

Senior Member

Seems like my isolator is frozen shut on both circuits and is passing
current to the rear battery cables (with the combiner disconnected).

The GMC MI Parts Book shows three models:

Sure Power (70 Amps), (95 Amps) and (120 Amps).

Which do I need for a 1975 GB with 30 amp camp ground service?

I can rebuild an engine but know nothing about DC electricity.

Thanks-

Jim "Doc" White
75 GMC Stretch (with new big ass Mac Dash and GPS radio)

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Re: [GMCnet] Replacement Isolator [message #98865 is a reply to message #98864]

Tue, 07 September 2010 16:32

RF_Burns

Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada

Karma: 3

Senior Member

I'd get the 120Amp. Your alternator is likely rated at 80Amps so you could get the 95, but if the 120 is not much more money, then get it.

The rating of the AC house service does not have any bearing on the battery isolator, only the alternator current goes through the isolator.

You don't need to buy one from GM, its just 2 power diodes. I got my last one at the local electronic surplus store for under $50.00.

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

[Updated on: Tue, 07 September 2010 17:09]

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Re: [GMCnet] Replacement Isolator [message #98870 is a reply to message #98865]

Tue, 07 September 2010 16:57

WD0AFQ

Messages: 7111
Registered: November 2004
Location: Dexter, Mo.

Karma: 207

Senior Member

And I ain't even got one of those.
Dan

3 In Stainless Exhaust Headers One Ton All Discs/Reaction Arm 355 FD/Quad Bag/Alum Radiator Manny Tran/New eng. Holley EFI/10 Tire Air Monitoring System Solarized Coach/Upgraded Windows Satelite TV/On Demand Hot Water/3Way Refer

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Re: [GMCnet] Replacement Isolator [message #98871 is a reply to message #98864]

Tue, 07 September 2010 16:57

C Boyd

Messages: 2629
Registered: April 2006

Karma: 18

Senior Member

Jim White[1

wrote on Tue, 07 September 2010 17:19] Seems like my isolator is frozen shut on both circuits and is passing
current to the rear battery cables (with the combiner disconnected).

The GMC MI Parts Book shows three models:

Sure Power (70 Amps), (95 Amps) and (120 Amps).

Which do I need for a 1975 GB with 30 amp camp ground service?

I can rebuild an engine but know nothing about DC electricity.

Thanks-

Jim "Doc" White
75 GMC Stretch (with new big ass Mac Dash and GPS radio)

Hi Jim: O`Reillys has a 95 amp for $29.99.... 120 amp is $79.99
http://www.oreillyauto.com/site/c/search.oap?keyword=battery+isolater

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C. Boyd
76 Crestmont
East Tennessee

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Re: [GMCnet] Replacement Isolator [message #98874 is a reply to message #98864]

Tue, 07 September 2010 17:23

Hardie Johnson

Messages: 483
Registered: January 2004
Location: Raleigh NC

Karma: 0

Senior Member

Jim White1 wrote on Tue, 07 September 2010 17:19

Seems like my isolator is frozen shut on both circuits and is passing current to the rear battery cables (with the combiner disconnected). <> Which do I need for a 1975 GB with 30 amp camp ground service?
<>

If you have a (Yandina) combiner you do not need the isolator at all. It replaces that function of isolating and combining the two circuits. Don't disconnect the combiner, remove the isolator. If you feel you must have it, take it to a real electronics shop and have them replace the diodes. Should be about $10.00

Hardie Johnson "Crashj"
1973 26 foot Glacier, White Thing
Raleigh NC

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Re: [GMCnet] Replacement Isolator [message #98883 is a reply to message #98870]

Tue, 07 September 2010 18:44

bill schurman

Messages: 97
Registered: February 2004

Karma: 0

Member

Dan.

Without an isolator how do you just wire only a combiner ? Why not both as I have ? Without this how is the high speed blower wired ?

Bill

William S. Schurman
P.O. 773325
Steamboat Springs, CO at the foot of Rabbit Ears Pass
970-846-4212

> To: gmclist@temp.gmcnet.org
> From: gregg_dan@hotmail.com
> Date: Tue, 7 Sep 2010 16:57:01 -0500
> Subject: Re: [GMCnet] Replacement Isolator
>
>
>
> And I ain't even got one of those.
> Dan
> --
> Dan & Teri Gregg
>
> http://danandteri.blogspot.com/
>
>
>
>
> _______________________________________________
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Re: [GMCnet] Replacement Isolator [message #98938 is a reply to message #98864]

Wed, 08 September 2010 07:48

RF_Burns

Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada

Karma: 3

Senior Member

The isolator is likely a potted construction, in other words the diodes are immersed in a type of epoxy. I didn't even bother to try to fix mine and I'm in electronics!

To bypass the isolator if you have a combiner, and your isolator is not shorted between the two battery terminals. Move the wire from the center isolator post (this is the alternator output wire) and connect it to the engine battery post of the isolator. Now the alternator will charge the engine battery directly. Then connect one combiner wire to the same post that you just moved the alternator wire to, and the other positive combiner wire to the opposite isolator post (this will be the connection to the house battery) And of course connect the combiner ground wire to ground. Now your isolator is just a handy terminal block.

If you were using your alternator terminal as a higher voltage source, or engine running indicator, it will now be at engine battery voltage.

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Re: [GMCnet] Replacement Isolator [message #98941 is a reply to message #98938]

Wed, 08 September 2010 08:15

WD0AFQ

Messages: 7111
Registered: November 2004
Location: Dexter, Mo.

Karma: 207

Senior Member

There you go Bill. My assistant, Bruce, just answered your question. Notice I refer all simple questions to my helpers. Laughing

Hope to see lots of yall in 2 weeks.
Dan

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Re: [GMCnet] Replacement Isolator [message #98950 is a reply to message #98938]

Wed, 08 September 2010 08:44

Mr ERFisher

Messages: 7117
Registered: August 2005

Karma: 2

Senior Member

>
>
> To bypass the isolator if you have a combiner, and your isolator is not
> shorted between the two battery terminals.
>

YES, this works ,

but

you will no longer have these functions
http://www.gmcmhphotos.com/photos/showphoto.php?photo=26982&title=engine-running-functions&cat=4944

gene

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