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[GMCnet] Problem with isolator? [message #321627]

Fri, 04 August 2017 15:09

Arthur Mansfield

Messages: 290
Registered: April 2010

Karma: 0

Senior Member

I checking my system with the main battery disconnected. Plugged into out side power. The house battery reads 13.5 volts. The cable from the back reads the same. The 12 volt system reads 10 volts. The voltage to the from battery reads 10 volts. The isolator voltage from the isolator reads 10 volts.

What is wrong?

Art
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Re: [GMCnet] Problem with isolator? [message #321628 is a reply to message #321627]

Fri, 04 August 2017 15:45

RF_Burns

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

Karma: 3

Senior Member

Reading between the lines of your message.. I'm guessing the "Main" battery is the "Engine" or Chassis battery up front.

So you have the chassis battery disconnected and engine is not running. Shore power is plugged in so your power converter is working. All the 13.5volt readings are correct.

I think you are saying "why do I read 10 volts on the chassis side wiring with no battery". I suspect you have everything turned OFF and what you are seeing is leakage current through likely the isolator. Turn on a load, like the headlights and I suspect the chassis voltage will goto zero volts.

Your voltmeter take very little current. The large diodes in the isolator do have a tiny amount of leakage current through them.

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: [GMCnet] Problem with isolator? [message #321629 is a reply to message #321627]

Fri, 04 August 2017 15:50

Matt Colie

Messages: 8547
Registered: March 2007
Location: S.E. Michigan

Karma: 7

Senior Member

Arthur Mansfield wrote on Fri, 04 August 2017 16:09

I checking my system with the main battery disconnected. Plugged into out side power. The house battery reads 13.5 volts. The cable from the back reads the same. The 12 volt system reads 10 volts. The voltage to the from battery reads 10 volts. The isolator voltage from the isolator reads 10 volts.

What is wrong?

Art

Art,

Which are you calling the Main Battery?
If this is the main engine aka chassis battery and it is disconnected, then the engine systems should be at zero volts.

Without knowing the status of everything, the isolator looks just fine.
You are on shore power and the converter is maintaining the house battery as it should.
Your chassis battery is, however, toast......

The isolator, if it is stock, has three terminals.
The center is fed directly from the alternator. With the engine off, that should be zero..
One terminal is connected to the house bank and that should also report 13.5 while on shore power.
The other terminal is connected to that main engine battery (in the common parlance here, it is called the chassis battery). If that is reporting less than 11.8V, then that battery has been damaged and may not recover, but you should try to charger it with either a free standing charger on it or put a jumper with a light bulb in it across the two end terminals of the isolator.

At this time, I strongly suggest that you NOT put a short heavy wire jumper on the end terminals of the isolator as this could cause the house bank to dump a great deal of power into your dead engine battery.

Did you know that the converter was never intended to maintain the engine (chassis) battery?

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: [GMCnet] Problem with isolator? [message #321630 is a reply to message #321627]

Fri, 04 August 2017 15:50

k2gkk

Messages: 4452
Registered: November 2009

Karma: -8

Senior Member

Bad isolator or bad ground with the house battery.

D C "Mac" Macdonald
Amateur Radio K2GKK
Since 30 November '53
USAF and FAA, Retired
Member GMCMI & Classics
Oklahoma City, OK
"The Money Pit"
TZE166V101966
'76 ex-Palm Beach
k2gkk + hotmail dot com

________________________________
From: Gmclist on behalf of 1104agm
Sent: Friday, August 4, 2017 15:09
To: gmclist@list.gmcnet.org
Subject: [GMCnet] Problem with isolator?

I checking my system with the main battery disconnected. Plugged into out side power. The house battery reads 13.5 volts. The cable from the back reads the same. The 12 volt system reads 10 volts. The voltage to the from battery reads 10 volts. The isolator voltage from the isolator reads 10 volts.

What is wrong?

Art
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?

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Re: [GMCnet] Problem with isolator? [message #321633 is a reply to message #321629]

Fri, 04 August 2017 16:49

Arthur Mansfield

Messages: 290
Registered: April 2010

Karma: 0

Senior Member

Sorry The house battery is the one in the back. The front battery is is the engine battery. With the engine battery disconnected the voltage to the isolator reads what the rear battery reads. Both the other terminals read about 2 volts less than the input to the isolator from the rear battery. With the Engine battery hooked up the two that read less than than the house battery read the engine battery voltage. The engine is not running in any of these checks. When the engine is running the two terminals read 14.5 volts. The house battery still reads the voltage of the house battery.

If one terminal is supposed to be zero without the motor running then I have bad isolator.

Art

> On Aug 4, 2017, at 3:50 PM, Matt Colie wrote:
>
> Arthur Mansfield wrote on Fri, 04 August 2017 16:09
>> I checking my system with the main battery disconnected. Plugged into out side power. The house battery reads 13.5 volts. The cable from the
>> back reads the same. The 12 volt system reads 10 volts. The voltage to the from battery reads 10 volts. The isolator voltage from the isolator
>> reads 10 volts.
>>
>> What is wrong?
>>
>> Art
>
> Art,
>
> Which are you calling the Main Battery?
> If this is the main engine aka chassis battery and it is disconnected, then the engine systems should be at zero volts.
>
> Without knowing the status of everything, the isolator looks just fine.
> You are on shore power and the converter is maintaining the house battery as it should.
> Your chassis battery is, however, toast......
>
> The isolator, if it is stock, has three terminals.
> The center is fed directly from the alternator. With the engine off, that should be zero..
> One terminal is connected to the house bank and that should also report 13.5 while on shore power.
> The other terminal is connected to that main engine battery (in the common parlance here, it is called the chassis battery). If that is reporting
> less than 11.8V, then that battery has been damaged and may not recover, but you should try to charger it with either a free standing charger on it or
> put a jumper with a light bulb in it across the two end terminals of the isolator.
>
> At this time, I strongly suggest that you NOT put a short heavy wire jumper on the end terminals of the isolator as this could cause the house bank to
> dump a great deal of power into your dead engine battery.
>
> Did you know that the converter was never intended to maintain the engine (chassis) battery?
>
> Matt
> --
> Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
> Electronically Controlled Quiet Engine Cooling Fan
> OE Rear Drum Brakes with Applied Control Arms
> SE Michigan - Twixt A2 and Detroit
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

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Re: [GMCnet] Problem with isolator? [message #321637 is a reply to message #321627]

Fri, 04 August 2017 20:14

RF_Burns

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

Karma: 3

Senior Member

If the center terminal and the engine (front) battery terminal both read 14.5V with the engine running, then the isolator is faulty. From the center (alternator) terminal to the house and engine battery there should be a voltage drop of approx 0.7 volts, which is the forward voltage drop across a silicon diode. You should be able to test this with the isolator terminals disconnected. Check each outer terminals to the center terminal on the ohm or diode test scale on your multimeter with the leads in both directions. A good isolator should should read low ohms in one direction and open in the other.

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: [GMCnet] Problem with isolator? [message #321639 is a reply to message #321637]

Fri, 04 August 2017 22:33

Arthur Mansfield

Messages: 290
Registered: April 2010

Karma: 0

Senior Member

Thanks I was just starting to examine the wiring diagram. I was wondering what the drop should be across the diode. I do not know what I have. I started checking because I lost an alternator on each of my last trips.

Art
> On Aug 4, 2017, at 8:15 PM, Bruce Hislop wrote:
>
> If the center terminal and the engine (front) battery terminal both read 14.5V with the engine running, then the isolator is faulty. From the center
> (alternator) terminal to the house and engine battery there should be a voltage drop of approx 0.7 volts, which is the forward voltage drop across a
> silicon diode. You should be able to test this with the isolator terminals disconnected. Check each outer terminals to the center terminal on the ohm
> or diode test scale on your multimeter with the leads in both directions. A good isolator should should read low ohms in one direction and open in
> the other.
>
>
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
> Hubler 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
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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Re: [GMCnet] Problem with isolator? [message #321643 is a reply to message #321639]

Sat, 05 August 2017 08:00

Matt Colie

Messages: 8547
Registered: March 2007
Location: S.E. Michigan

Karma: 7

Senior Member

Arthur Mansfield wrote on Fri, 04 August 2017 23:33

Thanks I was just starting to examine the wiring diagram. I was wondering what the drop should be across the diode. I do not know what I have. I started checking because I lost an alternator on each of my last trips.

Art

Art,

It is unlikely that a bad isolator could take out an alternator, but a bad alternator can damage an isolator pretty easily.

Actually, I just realized that the above has a problem. The problem is with a defective aftermarket regulator. The alternator voltage regulator that is supposed to be used in our application is what is called "remote sensing". It adjusts its output based on input from the system that is downstream of the isolator. This compensated for the 0.6V drop in the isolator and other line losses. The OE version of this regulator is supposed to limit the alternator output to 18.0V max. I have not seen, but have heard of offshore parts that do not include this feature and allow the regulator to "run away" when the returned voltage signal is lost or way low of the mark. This could result in damage to lots of things.

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: [GMCnet] Problem with isolator? [message #321645 is a reply to message #321627]

Sat, 05 August 2017 08:32

JohnL455

Messages: 4447
Registered: October 2006
Location: Woodstock, IL

Karma: 12

Senior Member

Reading your first post ---you are trying to check the isolator by plugging in and reading battery voltage? Unless the unit has a bat to bat short fail mode (very odd) this is not how to test the isolator. Connect all the batteries, unplug from wall and run engine. Meter center terminal to ground and then each outer terminal to ground and report back with Voltages as xx.x or xx.xx resolution.

John Lebetski
Woodstock, IL
77 Eleganza II

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Re: [GMCnet] Problem with isolator? [message #321663 is a reply to message #321645]

Sat, 05 August 2017 17:32

Arthur Mansfield

Messages: 290
Registered: April 2010

Karma: 0

Senior Member

Motor running. House power off. Both batteries hooked up.

house battery 13.09 lower left terminal
engine battery 14.55 upper terminal
alternator 14.55 lower right terminal

Motor not running everything off
house battery 12.85
engine battery 12.42
alternator 12.42

Art
> On Aug 5, 2017, at 8:32 AM, John R. Lebetski wrote:
>
> Reading your first post ---you are trying to check the isolator by plugging in and reading battery voltage? Unless the unit has a bat to bat short
> fail mode (very odd) this is not how to test the isolator. Connect all the batteries, unplug from wall and run engine. Meter center terminal to
> ground and then each outer terminal to ground and report back with Voltages as xx.x or xx.xx resolution.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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Re: [GMCnet] Problem with isolator? [message #321665 is a reply to message #321627]

Sat, 05 August 2017 17:45

James Hupy

Messages: 6806
Registered: May 2010

Karma: -62

Senior Member

You should nor show any voltage at the center tap with the engine off and
the key in the off position, and the boost switch in the off position.
Unless, sumthin is hooked up incorrectly. That is supposed to be the output
from the alternator. It goes into the isolator, and out the upper and lower
taps. From there to charge the engine battery, and the house battery (s).
If anything else is hooked up there, it shouldn't be.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On Aug 5, 2017 3:33 PM, "1104agm" wrote:

Motor running. House power off. Both batteries hooked up.

house battery 13.09 lower left terminal
engine battery 14.55 upper terminal
alternator 14.55 lower right terminal

Motor not running everything off
house battery 12.85
engine battery 12.42
alternator 12.42

Art
> On Aug 5, 2017, at 8:32 AM, John R. Lebetski
wrote:
>
> Reading your first post ---you are trying to check the isolator by
plugging in and reading battery voltage? Unless the unit has a bat to bat
short
> fail mode (very odd) this is not how to test the isolator. Connect all
the batteries, unplug from wall and run engine. Meter center terminal to
> ground and then each outer terminal to ground and report back with
Voltages as xx.x or xx.xx resolution.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

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Re: [GMCnet] Problem with isolator? [message #321666 is a reply to message #321665]

Sat, 05 August 2017 17:49

Arthur Mansfield

Messages: 290
Registered: April 2010

Karma: 0

Senior Member

Thanks That is what I was thinking. Something is wrong and I guess that is why I am loosing alternators.

> On Aug 5, 2017, at 5:45 PM, James Hupy wrote:
>
> You should nor show any voltage at the center tap with the engine off and
> the key in the off position, and the boost switch in the off position.
> Unless, sumthin is hooked up incorrectly. That is supposed to be the output
> from the alternator. It goes into the isolator, and out the upper and lower
> taps. From there to charge the engine battery, and the house battery (s).
> If anything else is hooked up there, it shouldn't be.
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403
>
> On Aug 5, 2017 3:33 PM, "1104agm" wrote:
>
> Motor running. House power off. Both batteries hooked up.
>
> house battery 13.09 lower left terminal
> engine battery 14.55 upper terminal
> alternator 14.55 lower right terminal
>
> Motor not running everything off
> house battery 12.85
> engine battery 12.42
> alternator 12.42
>
> Art
>> On Aug 5, 2017, at 8:32 AM, John R. Lebetski
> wrote:
>>
>> Reading your first post ---you are trying to check the isolator by
> plugging in and reading battery voltage? Unless the unit has a bat to bat
> short
>> fail mode (very odd) this is not how to test the isolator. Connect all
> the batteries, unplug from wall and run engine. Meter center terminal to
>> ground and then each outer terminal to ground and report back with
> Voltages as xx.x or xx.xx resolution.
>> --
>> John Lebetski
>> Woodstock, IL
>> 77 Eleganza II
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> _______________________________________________
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Re: [GMCnet] Problem with isolator? [message #321668 is a reply to message #321665]

Sat, 05 August 2017 18:00

k2gkk

Messages: 4452
Registered: November 2009

Karma: -8

Senior Member

Admittedly I have little experience with these coaches, but manuals I have seen show the isolator mounted vertically.

Also, the voltages listed indicate to me that the isolator is shorted between the alternator and engine battery and that the "house" battery has received SOME charge but is likely defective with probably one shorted cell and the voltage drop across the diode between alternator and house battery is excessive (should be .65 to .75 Volts). Also, the engine battery is not apparently taking any charge.

D C "Mac" Macdonald
Amateur Radio K2GKK
Since 30 November '53
USAF and FAA, Retired
Member GMCMI & Classics
Oklahoma City, OK
"The Money Pit"
TZE166V101966
'76 ex-Palm Beach
k2gkk + hotmail dot com

________________________________
From: Gmclist on behalf of James Hupy
Sent: Saturday, August 5, 2017 17:45
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Problem with isolator?

You should nor show any voltage at the center tap with the engine off and
the key in the off position, and the boost switch in the off position.
Unless, sumthin is hooked up incorrectly. That is supposed to be the output
from the alternator. It goes into the isolator, and out the upper and lower
taps. From there to charge the engine battery, and the house battery (s).
If anything else is hooked up there, it shouldn't be.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On Aug 5, 2017 3:33 PM, "1104agm" wrote:

Motor running. House power off. Both batteries hooked up.

house battery 13.09 lower left terminal
engine battery 14.55 upper terminal
alternator 14.55 lower right terminal

Motor not running everything off
house battery 12.85
engine battery 12.42
alternator 12.42

Art
> On Aug 5, 2017, at 8:32 AM, John R. Lebetski
wrote:
>
> Reading your first post ---you are trying to check the isolator by
plugging in and reading battery voltage? Unless the unit has a bat to bat
short
> fail mode (very odd) this is not how to test the isolator. Connect all
the batteries, unplug from wall and run engine. Meter center terminal to
> ground and then each outer terminal to ground and report back with
Voltages as xx.x or xx.xx resolution.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
Gmclist Info Page - GMCnet
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Re: [GMCnet] Problem with isolator? [message #321669 is a reply to message #321627]

Sat, 05 August 2017 18:13

k2gkk

Messages: 4452
Registered: November 2009

Karma: -8

Senior Member

In other words, replace the isolator and BOTH batteries to start!

D C "Mac" Macdonald
Amateur Radio K2GKK
Since 30 November '53
USAF and FAA, Retired
Member GMCMI & Classics
Oklahoma City, OK
"The Money Pit"
TZE166V101966
'76 ex-Palm Beach
k2gkk + hotmail dot com

________________________________
From: Gmclist on behalf of D C _Mac_ Macdonald
Sent: Saturday, August 5, 2017 18:00
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Problem with isolator?

Admittedly I have little experience with these coaches, but manuals I have seen show the isolator mounted vertically.

Also, the voltages listed indicate to me that the isolator is shorted between the alternator and engine battery and that the "house" battery has received SOME charge but is likely defective with probably one shorted cell and the voltage drop across the diode between alternator and house battery is excessive (should be .65 to .75 Volts). Also, the engine battery is not apparently taking any charge.

D C "Mac" Macdonald
Amateur Radio K2GKK
Since 30 November '53
USAF and FAA, Retired
Member GMCMI & Classics
Oklahoma City, OK
"The Money Pit"
TZE166V101966
'76 ex-Palm Beach
k2gkk + hotmail dot com

________________________________
From: Gmclist on behalf of James Hupy
Sent: Saturday, August 5, 2017 17:45
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Problem with isolator?

You should nor show any voltage at the center tap with the engine off and
the key in the off position, and the boost switch in the off position.
Unless, sumthin is hooked up incorrectly. That is supposed to be the output
from the alternator. It goes into the isolator, and out the upper and lower
taps. From there to charge the engine battery, and the house battery (s).
If anything else is hooked up there, it shouldn't be.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On Aug 5, 2017 3:33 PM, "1104agm" wrote:

Motor running. House power off. Both batteries hooked up.

house battery 13.09 lower left terminal
engine battery 14.55 upper terminal
alternator 14.55 lower right terminal

Motor not running everything off
house battery 12.85
engine battery 12.42
alternator 12.42

Art
> On Aug 5, 2017, at 8:32 AM, John R. Lebetski
wrote:
>
> Reading your first post ---you are trying to check the isolator by
plugging in and reading battery voltage? Unless the unit has a bat to bat
short
> fail mode (very odd) this is not how to test the isolator. Connect all
the batteries, unplug from wall and run engine. Meter center terminal to
> ground and then each outer terminal to ground and report back with
Voltages as xx.x or xx.xx resolution.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II

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Re: [GMCnet] Problem with isolator? [message #321671 is a reply to message #321663]

Sat, 05 August 2017 18:21

Ken Henderson

Messages: 8726
Registered: March 2004
Location: Americus, GA

Karma: 9

Senior Member

Art,

Are you SURE about the information below?

house battery 13.09 lower left terminal
engine battery 14.55 upper terminal
alternator 14.55 lower right terminal

If the alternator is connected to an "outside" terminal rather than the
center terminal, as you indicate, then it cannot charge ANYTHING because
its output is blocked by the diode which only allows current to flow FROM
the center terminal -- NOT toward it. And if that's not bad enough, the
alternator is expecting feedback from the engine battery (which is now
completely isolated from the alternator) to tell the alternator when it's
providing enough voltage to that battery. The alternator, sitting there
fat, dumb, and happy, keeps getting the feedback from the engine battery
saying "my voltage is low, give me some more". And the alternator
complies, increasing its output to AT LEAST 18 VDC -- perhaps 28+ VDC if
the regulator doesn't have the 18 VDC internal limiter. Yes, that can
destroy an alternator without ever helping a battery at all.

Connect the alternator output to the CENTER terminal on the isolator, the
house battery to one of the outside terminals, and the chassis battery to
the other outside terminal. THEN check the voltage at each of the 3
terminals, without, and then with the engine running.

Without the engine running you should measure 0 VDC at the center terminal
and whatever each of the batteries is at the outer terminals. With the
engine running, you should read a voltage at the center terminal which is
approximately 0.7 VDC greater than what you read at the engine terminal.
What the voltages on the chassis (engine) and house batteries are will
depend upon their current state of charge. When they're fully charged, you
should read something on the order of 13.8 VDC on each of them and about
14.5 VDC on the alternator (center) terminal -- all dependent slightly on
numerous factors.

HTH,

Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc., etc.
www.gmcwipersetc.com

On Sat, Aug 5, 2017 at 6:32 PM, 1104agm wrote:

> Motor running. House power off. Both batteries hooked up.
>
> house battery 13.09 lower left terminal
> engine battery 14.55 upper terminal
> alternator 14.55 lower right terminal
>
> Motor not running everything off
> house battery 12.85
> engine battery 12.42
> alternator 12.42
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach

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Re: [GMCnet] Problem with isolator? [message #321672 is a reply to message #321627]

Sat, 05 August 2017 18:51

JohnL455

Messages: 4447
Registered: October 2006
Location: Woodstock, IL

Karma: 12

Senior Member

If you disconnect the batteries, then disconnect the isolator completely, you can do a go/no go Ohm test on the isolator. From center to outside you should have continuity one way and not the other when reversing the meter leads. Repeat for center to the other outer terminal. Should be same as first. Then fully charge both batteries slowly untill 100%. You can then load test them with a hand held tester (I prefer the digital type for instant pass/fail) rather than blindly replacing batteries that may be serviceable.

John Lebetski
Woodstock, IL
77 Eleganza II

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Re: [GMCnet] Problem with isolator? [message #321673 is a reply to message #321671]

Sat, 05 August 2017 19:25

Arthur Mansfield

Messages: 290
Registered: April 2010

Karma: 0

Senior Member

Sorry the added definition makes no sense. With everything disconnected and time for all stray voyages to be gone. The alternator and the engine battery are shorted which is what the voltages when indicate. The house battery to the alternator diode checked as it supposed to. I guess one diode is shorted. So I guess I need to replace the isolator?

Art
> On Aug 5, 2017, at 6:21 PM, Ken Henderson wrote:
>
> Art,
>
> Are you SURE about the information below?
>
> house battery 13.09 lower left terminal
> engine battery 14.55 upper terminal
> alternator 14.55 lower right terminal
>
> If the alternator is connected to an "outside" terminal rather than the
> center terminal, as you indicate, then it cannot charge ANYTHING because
> its output is blocked by the diode which only allows current to flow FROM
> the center terminal -- NOT toward it. And if that's not bad enough, the
> alternator is expecting feedback from the engine battery (which is now
> completely isolated from the alternator) to tell the alternator when it's
> providing enough voltage to that battery. The alternator, sitting there
> fat, dumb, and happy, keeps getting the feedback from the engine battery
> saying "my voltage is low, give me some more". And the alternator
> complies, increasing its output to AT LEAST 18 VDC -- perhaps 28+ VDC if
> the regulator doesn't have the 18 VDC internal limiter. Yes, that can
> destroy an alternator without ever helping a battery at all.
>
> Connect the alternator output to the CENTER terminal on the isolator, the
> house battery to one of the outside terminals, and the chassis battery to
> the other outside terminal. THEN check the voltage at each of the 3
> terminals, without, and then with the engine running.
>
> Without the engine running you should measure 0 VDC at the center terminal
> and whatever each of the batteries is at the outer terminals. With the
> engine running, you should read a voltage at the center terminal which is
> approximately 0.7 VDC greater than what you read at the engine terminal.
> What the voltages on the chassis (engine) and house batteries are will
> depend upon their current state of charge. When they're fully charged, you
> should read something on the order of 13.8 VDC on each of them and about
> 14.5 VDC on the alternator (center) terminal -- all dependent slightly on
> numerous factors.
>
> HTH,
>
> Ken H.
> Americus, GA
> '76 X-Birchaven w/Cad500/Howell EFI & EBL,
> Manny Brakes & 1-Ton, etc., etc., etc.
> www.gmcwipersetc.com
>
> On Sat, Aug 5, 2017 at 6:32 PM, 1104agm wrote:
>
>> Motor running. House power off. Both batteries hooked up.
>>
>> house battery 13.09 lower left terminal
>> engine battery 14.55 upper terminal
>> alternator 14.55 lower right terminal
>>
>> Motor not running everything off
>> house battery 12.85
>> engine battery 12.42
>> alternator 12.42
>>
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> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

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Re: [GMCnet] Problem with isolator? [message #321674 is a reply to message #321633]

Sat, 05 August 2017 20:34

Ken Burton

Messages: 10030
Registered: January 2004
Location: Hebron, Indiana

Karma: 10

Senior Member

Have you verified that the isolator is wired correctly as previously suggested by Ken H?

If you have it wired correctly and the boost solenoid is open, then you are correct. You have a shorted diode on the engine side and probably an open diode on the house side. If is unimportant at this point how the house side is behaving because you have to replace the isolator anyway to fix the engine side.

Replace the isolator.

Once you get the correct readings at the isolator (center terminal 14.7 - top and bottom terminals 14.0), you can charge up the batteries from the engine driven alternator and decide the health of the batteries. At this point it does not sound like the batteries are bad.

If the isolator is NOT wired correctly then nothing stated above applies.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

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Re: [GMCnet] Problem with isolator? [message #321766 is a reply to message #321627]

Mon, 07 August 2017 12:20

jhbridges

Messages: 8412
Registered: May 2011
Location: Braselton ga

Karma: -74

Senior Member

Art, you mention lower left, lower right and upper terminal, which indicates you don't have the original isolator in the original location. You may even have a four terminal isolater, which isn't correct for the GMC (although it can be made to work). Can you describe the isolater fitted to the coach?

--johnny

Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons. Braselton, Ga. I forgive them all, save those who hurt the dogs. They must answer to me in hell

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Re: [GMCnet] Problem with isolator? [message #321781 is a reply to message #321766]

Mon, 07 August 2017 18:54

Ken Burton

Messages: 10030
Registered: January 2004
Location: Hebron, Indiana

Karma: 10

Senior Member

Johnny Bridges wrote on Mon, 07 August 2017 12:20

Art, you mention lower left, lower right and upper terminal, which indicates you don't have the original isolator in the original location. You may even have a four terminal isolater, which isn't correct for the GMC (although it can be made to work). Can you describe the isolater fitted to the coach?

--johnny

Yes, that confused me too. I'm happy I'm not the only one.

Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

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