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Home » GMC » GMCnet » Isolater vs Alternator (My experience)
Isolater vs Alternator [message #326603] Fri, 01 December 2017 16:21 Go to next message
Ernest Dankert is currently offline  Ernest Dankert   United States
Messages: 97
Registered: May 2007
Location: Ogden, New York
Karma: 1
Member
I replaced my 80A alternator with a 100A with dual belt pulley.
In getting the transmission replaced the coach was unplugged and static
for 1.5 months 450 miles from home. During the return trip the 2x12V
house batteries fully loaded the alternator (supposition to fit the fact)
and the 100A alternator toasted the isolater. I know the exact moment as
the dash blower was on high and the blower hit warp drive 9+. Blue smoke
came from the dash and nasty electrical stench. (We were in wall to wall
traffic and could not pull off.) Bypassed the isolater at a pull off so
we had power.

Replaced the house batteries with a 4D deep cycle, replaced the blower motor/fan
assembly, tossed the isolater and now rely on combiner. The blower hi speed gets
its power straight off the alternator tap to the isolater. When the isolater failed
due to overload the sense circuit maxed the alternator.


1977 Eleganza II
Ogden NY
Re: Isolater vs Alternator [message #326626 is a reply to message #326603] Fri, 01 December 2017 23:12 Go to previous messageGo to next message
Ken Burton is currently offline  Ken Burton   United States
Messages: 8368
Registered: January 2004
Location: Hebron, Indiana
Karma: 31
Senior Member

Your problem was the unplugged alternator. By unplugging it, the alternator lost it's reference voltage and went to maximum which was 18.5 volts or more depending on the regulator version built in the alternator. You are lucky if all you lost was the isolator. The same thing would have happened if you had a combiner installed. The excess voltage and associated current caused by the disconnected alternator sense line had to go somewhere. Usually it is the battery(s) that most of absorb it until they boil dry. Then the voltage goes even higher.

I had that happen on an airplane that I was flying one time. It boiled the battery dry and then took out the radios and several position lights. I ended up shutting down the alternator in flight and flying home a couple hundred miles in the dark without anything electric working. Aircraft engines do not use any alternator / battery electric to run. They have dual magneto ignition systems.



Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
Re: [GMCnet] Isolater vs Alternator [message #326628 is a reply to message #326626] Sat, 02 December 2017 04:10 Go to previous messageGo to next message
johnd01 is currently offline  johnd01   United States
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Registered: July 2017
Location: Sacrameot
Karma: 0
Senior Member
Sounds like the isolator to the chassis battery opened which increased the
alt. output and cooked the house batteries. If the house battery load had
been the problem the other side of the isolator would have opened and the
house battery would have been saved.
Looks like you we should oversize the isolator. We should be able to build
our own isolators from diodes.
Correct me if I am wrong but I think we could use half of a full wave
bridge like:
https://www.amazon.com/Baomain-Bridge-Rectifier-MDQ-100A-Module/dp/B01JIKSHCA/ref=pd_sim_328_3?_encoding=UTF8&psc=1&refRID=AS5H1C1VNSSMRHE2WHZ Z
or
https://www.amazon.com/Baomain-Bridge-Rectifier-MDQ-200A-Module/dp/B01JILFZCO/ref=pd_bxgy_328_2?_encoding=UTF8&psc=1&refRID=7VY1G9T5A8A558NREZ JJ


On Fri, Dec 1, 2017 at 9:12 PM, Ken Burton wrote:

> Your problem was the unplugged alternator. By unplugging it, the
> alternator lost it's reference voltage and went to maximum which was 18.5
> volts or
> more depending on the regulator version built in the alternator. You are
> lucky if all you lost was the isolator. The same thing would have happened
> if you had a combiner installed. The excess voltage and associated current
> caused by the disconnected alternator sense line had to go somewhere.
> Usually it is the battery(s) that most of absorb it until they boil dry.
> Then the voltage goes even higher.
>
> I had that happen on an airplane that I was flying one time. It boiled
> the battery dry and then took out the radios and several position lights. I
> ended up shutting down the alternator in flight and flying home a couple
> hundred miles in the dark without anything electric working. Aircraft
> engines do not use any alternator / battery electric to run. They have
> dual magneto ignition systems.
>
>
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
> _______________________________________________
> GMCnet mailing list
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>



--

*John Phillips*
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Johnd01 John Phillips Avion A2600 TZE064V101164 Rancho Cordova, CA (Sacramento)
Re: Isolater vs Alternator [message #326629 is a reply to message #326626] Sat, 02 December 2017 06:54 Go to previous messageGo to next message
Tom Lins is currently offline  Tom Lins   United States
Messages: 134
Registered: February 2004
Location: Elkton, FL
Karma: 0
Senior Member
Ken Burton wrote on Sat, 02 December 2017 00:12
Your problem was the unplugged alternator. By unplugging it, the alternator lost it's reference voltage and went to maximum which was 18.5 volts or more depending on the regulator version built in the alternator. You are lucky if all you lost was the isolator. The same thing would have happened if you had a combiner installed. The excess voltage and associated current caused by the disconnected alternator sense line had to go somewhere. Usually it is the battery(s) that most of absorb it until they boil dry. Then the voltage goes even higher.

I had that happen on an airplane that I was flying one time. It boiled the battery dry and then took out the radios and several position lights. I ended up shutting down the alternator in flight and flying home a couple hundred miles in the dark without anything electric working. Aircraft engines do not use any alternator / battery electric to run. They have dual magneto ignition systems.



The question that comes to my mind is there a way to protect against the sense circuit failure?
Or is vigilance your best defense?


Tom Lins
Elkton, FL
77 GM Rear Twin
Re: [GMCnet] Isolater vs Alternator [message #326630 is a reply to message #326628] Sat, 02 December 2017 06:51 Go to previous messageGo to next message
Ken Henderson is currently offline  Ken Henderson   United States
Messages: 7318
Registered: March 2004
Location: Americus, GA
Karma: 41
Senior Member
John,

That would certainly work if you use the two ac terminals as the two
battery terminals and the (-) terminal for the alternator input. That
would provide the necessary isolation of the batteries. At the (+)
terminal would appear the highest of the House and Chassis battery
voltages, less about 0.7 VDC. For those using electric windshield wipers,
that could be used as the +12 VDC supply, providing a speed reduction of
about 5%, which many would like. Or it could be used for any accessory for
which constant supply from either battery was desired (radio?).

The BIG question is whether the bridge, despite its rating, would survive
for very long. Certainly it should be mounted to the aluminum plate, or,
preferably, a finned heat sink, with thermal paste. I would NOT use the
100A version. Since they're designed for ac rectification, the average
current through each pair of diodes is only 1/2 of the bridge's rating.
Longevity may still be an issue.

Without knowing the internal construction of the bridge, it's difficult to
evaluate its probable longevity, but I suspect it's not as robust as the
isolators. Those have two diodes with their metal cases bonded to a common
aluminum plate to which the alternator input is connected; the other ends
of the diodes connect to the batteries. That assembly is potted with an
epoxy for environmental protection. I've never yet seen nor heard of a
shorted isolator. They predominantly fail by becoming open. I've cut,
broken, ground away the epoxy on a couple of failed ones and found the
"failed" diode (still good) separated from the aluminum plate. My theory
is that the different thermal coefficients of expansion of the diodes,
aluminum, and epoxy stresses the diode-plate junction, causing it to
eventually fail. Isolators are designed for the continually varying
current and environmental conditions to which we subject them, yet they
eventually fail -- too frequently.

I suspect that the subject bridges are intended for use in primarily
constant loads and may be more likely to fail in our application.

Thus, I prefer a robust combiner, which totally eliminates it as the cause
of the loss of feedback condition which causes runaway alternators. I have
had 2 of the Yandina C100 combiners fail. After one replacement under
warranty, the second time I upgraded (with warranty credit) to the C135,
which has given no trouble for 5+ years. It should be remembered that
Anna-Marie Foster, Yandina, inventor of the combiner, originally rated the
C-100 at 50A. Competitors offering almost identical units with 100A
ratings forced her to change her specification -- with no design change. I
consider the original 50A rating more appropriate.

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

On Sat, Dec 2, 2017 at 5:10 AM, John Phillips
wrote:

> Sounds like the isolator to the chassis battery opened which increased the
> alt. output and cooked the house batteries. If the house battery load had
> been the problem the other side of the isolator would have opened and the
> house battery would have been saved.
> Looks like you we should oversize the isolator. We should be able to build
> our own isolators from diodes.
> Correct me if I am wrong but I think we could use half of a full wave
> bridge like:
> https://www.amazon.com/Baomain-Bridge-Rectifier-MDQ-
> 100A-Module/dp/B01JIKSHCA/ref=pd_sim_328_3?_encoding=UTF8&psc=1&refRID=
> AS5H1C1VNSSMRHE2WHZZ
> or
> https://www.amazon.com/Baomain-Bridge-Rectifier-MDQ-
> 200A-Module/dp/B01JILFZCO/ref=pd_bxgy_328_2?_encoding=UTF8&psc=1&refRID=
> 7VY1G9T5A8A558NREZJJ
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
Re: [GMCnet] Isolater vs Alternator [message #326632 is a reply to message #326629] Sat, 02 December 2017 07:10 Go to previous messageGo to next message
Ken Henderson is currently offline  Ken Henderson   United States
Messages: 7318
Registered: March 2004
Location: Americus, GA
Karma: 41
Senior Member
Tom,

WIth the installation of a combiner, the chassis battery is always
connected to the voltage sense line to the alternator, thus eliminating one
of the two most common causes of sense circuit failure. The second, much
less common, failure, the connection at the alternator, can only be managed
by rare preventative maintenance: Disconnect and examine the connector,
replacing it if corroded or weak, and applying some contact
cleaner/lubricant, such as CRC 2-26. Gene Fisher's APC (Alternator
Protection Cable) offers new, good quality, connectors so its installation
should help, despite the addition of one more pair (Pins 1 & 2) of
connections. The Nichrome wire protection is not the only benefit of the
APC! :-)

Ken H.

​PS: Tom, I just noticed your signature block: "Elkton, FL". When did
you move? Or are you playing Snowbird? Will we get to see you at the
​January GMCSS/GMCDL rally in St. Augustine? KH


On Sat, Dec 2, 2017 at 7:54 AM, Tom Lins wrote:

>
> The question that comes to my mind is there a way to protect against the
> sense circuit failure?
> Or is vigilance your best defense?
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
Re: Isolater vs Alternator [message #326633 is a reply to message #326626] Sat, 02 December 2017 07:44 Go to previous messageGo to next message
Matt Colie is currently offline  Matt Colie   United States
Messages: 6465
Registered: March 2007
Location: S.E. Michigan
Karma: 32
Senior Member
Ken Burton wrote on Sat, 02 December 2017 00:12
<snip>
I had that happen on an airplane that I was flying one time. It boiled the battery dry and then took out the radios and several position lights. I ended up shutting down the alternator in flight and flying home a couple hundred miles in the dark without anything electric working. Aircraft engines do not use any alternator / battery electric to run. They have dual magneto ignition systems.

That is WHY aircraft have dual magnetos.

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
Re: Isolater vs Alternator [message #326640 is a reply to message #326629] Sat, 02 December 2017 10:57 Go to previous messageGo to next message
Ken Burton is currently offline  Ken Burton   United States
Messages: 8368
Registered: January 2004
Location: Hebron, Indiana
Karma: 31
Senior Member

Some alternator regulators have a limit built in to them. I think it is set around 18 volts. On my airplane after I fixed the damage and replaced the external regulator, I added a crowbar circuit that fires an SCR and trips the field circuit breaker at around 15 volts. That shuts down the alternator. This would not work on a GMC because the regulator is internal to the alternator.

On a GMC I have often thought of adding 2 diodes in series giving a 1.3 or 1.4 volt drop. The diodes could go between output and the sense line input. Also 2 resistors could be used between the output and ground. Then tap the junction of the two and attach it to the sense line. The values could be 9 to 1 or 15 to 1 for a 10% to 15% voltage cap.

On the loose sense connection at the alternator. On mine the connection that was loose was actually on the added APC female terminal. So I am suggesting that even if you have an APC attached, that connection needs to be checked to be sure it is very very tight. That APC was on there for many years before the connection failed. I really felt stupid when I found it, because Colonel Ken had already twice run be back and forth to AZ for a replacement alternator.

When this problem popped up, I noticed it on my $2.00 volt meter while driving. I was able to manage the over voltage while driving buy adding load. I turned on the headlights and ran the heater fan at various speeds to keep the output at a reasonable voltage level. When I arrived at the rally a couple of days later I erroneously replaced the alternator under warranty and eventually found the loose sense connection. Without that meter I would not have been able to accomplish this.


Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
Re: [GMCnet] Isolater vs Alternator [message #326641 is a reply to message #326632] Sat, 02 December 2017 11:21 Go to previous messageGo to next message
emerystora is currently offline  emerystora   United States
Messages: 4193
Registered: January 2004
Karma: 9
Senior Member
But Ken —

Even with an isolator "the chassis battery is always connected to the voltage sense line to the alternator”.

I would think that if you have a combiner then the voltage sense line is connected to both the chassis battery and the house battery which would then “hide” a weak chassis battery from the alternator.
Am I not correct on this?

Emery Stora
77 Kingsley
Frederick, CO

> On Dec 2, 2017, at 6:10 AM, Ken Henderson wrote:
>
> Tom,
>
> WIth the installation of a combiner, the chassis battery is always
> connected to the voltage sense line to the alternator, thus eliminating one
> of the two most common causes of sense circuit failure. The second, much
> less common, failure, the connection at the alternator, can only be managed
> by rare preventative maintenance: Disconnect and examine the connector,
> replacing it if corroded or weak, and applying some contact
> cleaner/lubricant, such as CRC 2-26. Gene Fisher's APC (Alternator
> Protection Cable) offers new, good quality, connectors so its installation
> should help, despite the addition of one more pair (Pins 1 & 2) of
> connections. The Nichrome wire protection is not the only benefit of the
> APC! :-)
>
> Ken H.
>
> ​PS: Tom, I just noticed your signature block: "Elkton, FL". When did
> you move? Or are you playing Snowbird? Will we get to see you at the
> ​January GMCSS/GMCDL rally in St. Augustine? KH
>
>
> On Sat, Dec 2, 2017 at 7:54 AM, Tom Lins wrote:
>
>>
>> The question that comes to my mind is there a way to protect against the
>> sense circuit failure?
>> Or is vigilance your best defense?
>> --
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org


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Re: [GMCnet] Isolater vs Alternator [message #326645 is a reply to message #326641] Sat, 02 December 2017 11:48 Go to previous messageGo to next message
Ken Henderson is currently offline  Ken Henderson   United States
Messages: 7318
Registered: March 2004
Location: Americus, GA
Karma: 41
Senior Member
Emery,

Wben installing the combiner, the chassis battery should be connected
directly to the sense wire. Since the combiner only closes when it senses
charge-capable voltage (~13.8 VDC), the sense line would not be connected
to the house battery if the alternator was too weak to achieve that
voltage. So, no, the combiner would not "hide" a weak chassis battery.

Can't necessarily say the same about a house battery though: There is a
condition in which the combiner could be detrimental: A defective house
battery could pull the alternator below charge voltage while the combiner
was closed, even with the sense line attempting to hold the voltage up.
The combiner would drop out after a preset delay (30 sec., IIRC). With the
excess load removed, the alternator would again achieve charge voltage,
closing the combiner, and again attempting to charge the weak battery. So,
the combiner could conceivable subject the alternator to cyclic full
loading and even over-stress.

Seems like there ain't nuthin' perfect!

Ken H.

On Sat, Dec 2, 2017 at 12:21 PM, Emery Stora wrote:

> But Ken —
>
> Even with an isolator "the chassis battery is always connected to the
> voltage sense line to the alternator”.
>
> I would think that if you have a combiner then the voltage sense line is
> connected to both the chassis battery and the house battery which would
> then “hide” a weak chassis battery from the alternator.
> Am I not correct on this?
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
Re: [GMCnet] Isolater vs Alternator [message #326646 is a reply to message #326632] Sat, 02 December 2017 11:59 Go to previous messageGo to next message
Richard Denney is currently offline  Richard Denney   United States
Messages: 612
Registered: April 2010
Karma: 2
Senior Member
Most passenger cars used one-wire alternators, where the output voltage is
sensed internally. We used to convert Delco three-wire alternators to
one-wire alternators by wiring the field-sense wire to the exciter wire
(which is connected to the battery). I built a rally car out of a Toyota
Corolla back in the day, and the three sets of driving lights were too much
for the 40-amp Toyota alternator. I replaced it with a Delcotron modified
to tie the sense wire to the exciter wire right at the plug.

With a combiner, I don't see why we couldn't do that now--no isolator diode
drop requiring compensation. That would reduce the failure point to the
plug itself.

Rick "thinking out loud" Denney

On Sat, Dec 2, 2017 at 8:11 AM Ken Henderson wrote:

> Tom,
>
> WIth the installation of a combiner, the chassis battery is always
> connected to the voltage sense line to the alternator, thus eliminating one
> of the two most common causes of sense circuit failure. The second, much
> less common, failure, the connection at the alternator, can only be managed
> by rare preventative maintenance: Disconnect and examine the connector,
> replacing it if corroded or weak, and applying some contact
> cleaner/lubricant, such as CRC 2-26. Gene Fisher's APC (Alternator
> Protection Cable) offers new, good quality, connectors so its installation
> should help, despite the addition of one more pair (Pins 1 & 2) of
> connections. The Nichrome wire protection is not the only benefit of the
> APC! :-)
>
> Ken H.
>
> ​PS: Tom, I just noticed your signature block: "Elkton, FL". When did
> you move? Or are you playing Snowbird? Will we get to see you at the
> ​January GMCSS/GMCDL rally in St. Augustine? KH
>
>
> On Sat, Dec 2, 2017 at 7:54 AM, Tom Lins wrote:
>
>>
>> The question that comes to my mind is there a way to protect against the
>> sense circuit failure?
>> Or is vigilance your best defense?
>> --
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Rick Denney
73 x-Glacier 230 "Jaws"
Off-list email to rick at rickdenney dot com
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Re: Isolater vs Alternator [message #326647 is a reply to message #326626] Sat, 02 December 2017 12:19 Go to previous messageGo to next message
Ernest Dankert is currently offline  Ernest Dankert   United States
Messages: 97
Registered: May 2007
Location: Ogden, New York
Karma: 1
Member
The isolater failed; dropping the sense circuit. The alternator ran away, leaving the dash blower as the only load on high. When I stopped I moved the alternator output direct to battery on the isolater giving the alternator load and sense.

1977 Eleganza II
Ogden NY
Re: [GMCnet] Isolater vs Alternator [message #326648 is a reply to message #326645] Sat, 02 December 2017 12:14 Go to previous messageGo to next message
James Hupy is currently offline  James Hupy   United States
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Registered: May 2010
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Senior Member
K.I.S.S. is a principle that guides a philosophical mindset. Mine in
particular. While combiners may the best thing since sliced bread, they
still complicate an otherwise anvil simple system. Not much to an
alternator, a trio of conductors, and an diode isolator. Darn thing either
works, or not. Combiners, with their combinations of wires that MUST NEVER
be shortened, along with led lights that sometimes are steady, sometimes
blinking like Rudolph's nose, sometimes not at all, are a bit like
redundant components that only create more questions of their own. I will
stick with what I know.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On Dec 2, 2017 9:50 AM, "Ken Henderson" wrote:

> Emery,
>
> Wben installing the combiner, the chassis battery should be connected
> directly to the sense wire. Since the combiner only closes when it senses
> charge-capable voltage (~13.8 VDC), the sense line would not be connected
> to the house battery if the alternator was too weak to achieve that
> voltage. So, no, the combiner would not "hide" a weak chassis battery.
>
> Can't necessarily say the same about a house battery though: There is a
> condition in which the combiner could be detrimental: A defective house
> battery could pull the alternator below charge voltage while the combiner
> was closed, even with the sense line attempting to hold the voltage up.
> The combiner would drop out after a preset delay (30 sec., IIRC). With the
> excess load removed, the alternator would again achieve charge voltage,
> closing the combiner, and again attempting to charge the weak battery. So,
> the combiner could conceivable subject the alternator to cyclic full
> loading and even over-stress.
>
> Seems like there ain't nuthin' perfect!
>
> Ken H.
>
> On Sat, Dec 2, 2017 at 12:21 PM, Emery Stora wrote:
>
>> But Ken —
>>
>> Even with an isolator "the chassis battery is always connected to the
>> voltage sense line to the alternator”.
>>
>> I would think that if you have a combiner then the voltage sense line is
>> connected to both the chassis battery and the house battery which would
>> then “hide” a weak chassis battery from the alternator.
>> Am I not correct on this?
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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Re: [GMCnet] Isolater vs Alternator [message #326652 is a reply to message #326647] Sat, 02 December 2017 13:39 Go to previous messageGo to next message
Emery Stora is currently offline  Emery Stora   United States
Messages: 675
Registered: January 2011
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Senior Member
The sense wire to the alternator does not connect to the isolator. It goes to the engine battery through the wiring harness. If the isolator failed it shouldn’t drop the sense circuit. When your isolator failed it didn’t allow the alternator to direct the right voltage to the engine battery which caused the sense wire to the alternator to increase the voltage from the voltage regulator.

When you moved the alternator output direct to the battery it then gave proper voltage to the battery and the sense wire that told the alternator voltage regulator to drop the voltage to the normal amount.

The alternator wire you moved doesn’t include the sense wire — just the alternator charging output.

Emery Stora
77 Kingsley
Frederick, CO



> On Dec 2, 2017, at 11:20 AM, Ernest Dankert wrote:
>
> The isolater failed; dropping the sense circuit. The alternator ran away, leaving the dash blower as the only load on high. When I stopped I moved
> the alternator output direct to battery on the isolater giving the alternator load and sense.
> --
> 1977 Eleganza II
> Ogden NY
>
> _______________________________________________
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Re: Isolater vs Alternator [message #326659 is a reply to message #326603] Sat, 02 December 2017 21:02 Go to previous messageGo to next message
JohnL455 is currently offline  JohnL455   United States
Messages: 2994
Registered: October 2006
Location: Woodstock, IL
Karma: 16
Senior Member
Sense wire on the engine battery terminal of the isolator -- is the engine battery as Emery said. Someone above asked how to prevent the problem. Don't run a 100A alternator into an 80A old isolator. I would want at least a 150A. They are not expensive. I run the Yandina combiner across the 2 battery systems at the isolator. Works great an don't have to think sbout it.
I see one other "problem" with ditching the isolator. A bad alternator cannot draw down batteries if the isolator is in place as current can't flow that way.


John Lebetski
Woodstock, IL
77 Eleganza II
Re: Isolater vs Alternator [message #326660 is a reply to message #326659] Sat, 02 December 2017 21:28 Go to previous messageGo to next message
Ken Burton is currently offline  Ken Burton   United States
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Registered: January 2004
Location: Hebron, Indiana
Karma: 31
Senior Member

Wow. Doom and gloom on isolators.

My OEM isolator and my 100 amp dual pulley alternator have co-existed for 13 years. I put a lot of load on them as I seldom plug in anywhere when I travel. So during the day my alternator and isolator have to recover the discharged golf cart batteries.

I have been involved with the replacement of 3 combiners and 1 isolator on GMCs. None of which were on my coach. The isolator that broke was rusted so badly that I twisted off a stud trying to loosen the rusted nut. Had I left it alone and not tried to clean the connections it probably would still be running today. I have the bad isolator and someday I'll open it up to see if the stud can be replaced. It was and is still good electrically. That is more than I can say about the three bad combiners I worked on. Two of the bad combiners were on Dan's coach. He ended up carrying a spare in case it failed again.


Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
Re: [GMCnet] Isolater vs Alternator [message #326671 is a reply to message #326630] Sun, 03 December 2017 08:25 Go to previous messageGo to next message
USAussie is currently offline  USAussie   United States
Messages: 15496
Registered: July 2007
Location: Sydney, Australia
Karma: 42
Senior Member
Ken,

It appears that Yandina no longer makes the C-135:

http://www.yandina.com/

Keeping in mind that I am electrically challenged would the C-160 be the one to order?

Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808



-----Original Message-----
From: Gmclist [mailto:gmclist-bounces-AT-list-DOT-gmcnet-DOT-org] On Behalf Of Ken Henderson
Sent: Saturday, December 2, 2017 6:52 AM
To: GMC Mail List
Subject: Re: [GMCnet] Isolater vs Alternator

John,

That would certainly work if you use the two ac terminals as the two
battery terminals and the (-) terminal for the alternator input. That
would provide the necessary isolation of the batteries. At the (+)
terminal would appear the highest of the House and Chassis battery
voltages, less about 0.7 VDC. For those using electric windshield wipers,
that could be used as the +12 VDC supply, providing a speed reduction of
about 5%, which many would like. Or it could be used for any accessory for
which constant supply from either battery was desired (radio?).

The BIG question is whether the bridge, despite its rating, would survive
for very long. Certainly it should be mounted to the aluminum plate, or,
preferably, a finned heat sink, with thermal paste. I would NOT use the
100A version. Since they're designed for ac rectification, the average
current through each pair of diodes is only 1/2 of the bridge's rating.
Longevity may still be an issue.

Without knowing the internal construction of the bridge, it's difficult to
evaluate its probable longevity, but I suspect it's not as robust as the
isolators. Those have two diodes with their metal cases bonded to a common
aluminum plate to which the alternator input is connected; the other ends
of the diodes connect to the batteries. That assembly is potted with an
epoxy for environmental protection. I've never yet seen nor heard of a
shorted isolator. They predominantly fail by becoming open. I've cut,
broken, ground away the epoxy on a couple of failed ones and found the
"failed" diode (still good) separated from the aluminum plate. My theory
is that the different thermal coefficients of expansion of the diodes,
aluminum, and epoxy stresses the diode-plate junction, causing it to
eventually fail. Isolators are designed for the continually varying
current and environmental conditions to which we subject them, yet they
eventually fail -- too frequently.

I suspect that the subject bridges are intended for use in primarily
constant loads and may be more likely to fail in our application.

Thus, I prefer a robust combiner, which totally eliminates it as the cause
of the loss of feedback condition which causes runaway alternators. I have
had 2 of the Yandina C100 combiners fail. After one replacement under
warranty, the second time I upgraded (with warranty credit) to the C135,
which has given no trouble for 5+ years. It should be remembered that
Anna-Marie Foster, Yandina, inventor of the combiner, originally rated the
C-100 at 50A. Competitors offering almost identical units with 100A
ratings forced her to change her specification -- with no design change. I
consider the original 50A rating more appropriate.

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

On Sat, Dec 2, 2017 at 5:10 AM, John Phillips
wrote:

> Sounds like the isolator to the chassis battery opened which increased the
> alt. output and cooked the house batteries. If the house battery load had
> been the problem the other side of the isolator would have opened and the
> house battery would have been saved.
> Looks like you we should oversize the isolator. We should be able to build
> our own isolators from diodes.
> Correct me if I am wrong but I think we could use half of a full wave
> bridge like:
> https://www.amazon.com/Baomain-Bridge-Rectifier-MDQ-
> 100A-Module/dp/B01JIKSHCA/ref=pd_sim_328_3?_encoding=UTF8&psc=1&refRID=
> AS5H1C1VNSSMRHE2WHZZ
> or
> https://www.amazon.com/Baomain-Bridge-Rectifier-MDQ-
> 200A-Module/dp/B01JILFZCO/ref=pd_bxgy_328_2?_encoding=UTF8&psc=1&refRID=
> 7VY1G9T5A8A558NREZJJ
>
>
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Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426
Re: [GMCnet] Isolater vs Alternator [message #326672 is a reply to message #326671] Sun, 03 December 2017 08:56 Go to previous messageGo to next message
Ken Henderson is currently offline  Ken Henderson   United States
Messages: 7318
Registered: March 2004
Location: Americus, GA
Karma: 41
Senior Member
Yes. IIRC, the C-160 uses a large external solenoid relay rather than the
internal one in my C-135.

Ken H.


On Sun, Dec 3, 2017 at 9:25 AM, Rob Mueller wrote:

> Ken,
>
> It appears that Yandina no longer makes the C-135:
>
> http://www.yandina.com/
>
> Keeping in mind that I am electrically challenged would the C-160 be the
> one to order?
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
Re: Isolater vs Alternator [message #326673 is a reply to message #326660] Sun, 03 December 2017 09:01 Go to previous messageGo to next message
Matt Colie is currently offline  Matt Colie   United States
Messages: 6465
Registered: March 2007
Location: S.E. Michigan
Karma: 32
Senior Member
I don't know about all the other versions, but I have a 73 that has some traits that lead me to believe it was a strange build. The alternator is supposed to be 80amp. The machine in that place now (I did not replace it, but it has been serviced) still looks like the 80amp version. But, things have probably been changed.

We were having alternator belt trouble early on. It was so bad that I regularly put on two belts and tied one back because on a '73 the fan blade and the A/C belt both have to come off to get the new belt in where it needs to be. It was not alignment and I could still but a belt with the right back width. But I was not yet on the forum. This went on for too long because I always though I had a fix in. When I was trying to figure out why I was losing belts (yes Gene, they were at specified tension) whenever we dry camped, I finally put my Hall Probe on the alternator cable one morning. I was really expecting to see that the charge profile was wrong (too high a current for too long). Well, even though the machine is supposed to limit at 80, after the cold start and during the time at high idle, that Hall probe, and Fluke 87 set told me that they were witnessing 96 Amperes....

Before you say that can't happen, remember that when this coach was built it was supposed to have an E5000 91R (Grp.27 side terminal) house battery in the right front. That is a roughly 80AH battery. It was at that end of a piece of #10SAE (not AWG) wire. That battery was a 4D when I got the coach and the #10SAE is now #8 (maybe 6) AWG. This makes for a condition that is very different than when what the pictures and old numbers would allow.

That was when I hunted up a dual sheave for that service. Yes, the power steering sheave can slip when very wet, but it is very manageable when it does.

While doing all the boat work I did before the depression shut us down, I was both informed by suppliers and gained some first hand experience (at my own cost) that a 100 Ampere load on a 12V nominal machine is about all any single V-belt can do for very long at all. There are available marine service machine and regulator sets that can be programed to limit the output current. I have installed these, but the cost is a serious issue. They are great for sailboats where upgrading the installed alternator drive is impractical.

Now, what really surprises me, and I am not complaining, is that it seems that the isolator has never been replaced and still functions as it should. I did replace a very few isolators, but I also replaced more than an few Yandina Combiners. Those were both the 50 and 100 size. The contacts would cease to make a solid an dependable connection. Those are the little ones that come with wire leads that you are not supposed to shorten because just like the #10 battery wires in a GMC, those are a current limiter. The larger version Yandinas all have lugs. I saw those very rarely and never had to replace one.

We now have a dual sheave and a pair of GC2s and I put a PD9260 up front to get the house charged when I have to do it with the APU.

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
Re: [GMCnet] Isolater vs Alternator [message #326674 is a reply to message #326672] Sun, 03 December 2017 09:01 Go to previous messageGo to previous message
USAussie is currently offline  USAussie   United States
Messages: 15496
Registered: July 2007
Location: Sydney, Australia
Karma: 42
Senior Member
Ken,

I clicked on the C-160 and this link opened:

http://www.yandina.com/c160Info.htm

It doesn't say anything about a large external relay?

Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808


-----Original Message-----
From: Gmclist [mailto:gmclist-bounces-AT-list-DOT-gmcnet-DOT-org] On Behalf Of Ken Henderson
Sent: Sunday, December 3, 2017 8:57 AM
To: GMC Mail List
Subject: Re: [GMCnet] Isolater vs Alternator

Yes. IIRC, the C-160 uses a large external solenoid relay rather than the internal one in my C-135.

Ken H.



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Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426
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