A good reason to keep your Isolator

[RF_Burns]

Seems a lot of people want to remove the Isolator when they install a combiner. Here is a good reason why you should keep the Isolator and install
the combiner across it.

A couple of days ago when I started the Murray, the GEN light stayed ON. Checked the DigiPanel and it showed only 12V. So I got out the voltmeter and
checked the alternator voltage at the Isolator and it was near zero volts. My alternator was 11 years old, so I guess it had a good run.

I pulled the alternator and opened it up. The problem was clear, the jumper strap at the output stud was burnt off inside. The plastic insulating
washer was burnt off inside and badly melted on the outside. I cleaned up the stud, replaced the insulating washers and replaced the jumper strap.
Checked the bearings and brushes, everything else looked ok. Re-installed and we were back in business with a working alternator.

It was clear that the alternator output stud was likely (or would have) shorted to the case of the alternator. If I didn't have the Isolator, the
battery current would have flowed back through the #10 alternator wire causing lots of current, smoke and maybe flames. Its what us electronic types
call I Norton.

So you may want to keep your Isolator for just another layer of protection. The 0.7 volt drop across the Isolator that some say limit the battery
charging is a red herring. The alternator uses a remote voltage sensing wire which is connected to the battery. The alternator's internal regulator
uses feed-back from this wire and automatically raises its output voltage to compensate for any voltage loss.

Just my 2 cents!

--
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

 

[6cuda6]

Thanks for the tip and explination Bruce.....sounds like the best of both worlds...charge batteries and protect them.
--
Rich Mondor,

Brockville, ON

77 Hughes 2600

 

[Chazzer]

Bruce,

Are you running a 80 or 100 amp alternator? Single pulley or two?.

Inquiring minds....would like to know...
--
Jim Owens,

78 Royale,

Out skirts of Kitchener, Ontario

 

[jim kanomata1]

Bruce,
Great to know that some of you out there still have the skill and energy to
take things apart and evaluate them.
Thank you for your valuable feedback.

On Sat, Sep 7, 2019 at 6:35 AM tonka6cuda6--- via Gmclist <

> Thanks for the tip and explination Bruce.....sounds like the best of both
> worlds...charge batteries and protect them.
> --
> Rich Mondor,
>
> Brockville, ON
>
> 77 Hughes 2600
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502

 

[RF_Burns]

Jim,
Its a 100Amp Delco 15SI series that the PO had installed at Bormann's as part of the sale (old one was toast).

I had Bormann's also install a dual pulley and belts shortly after I bought it. I've been running the same belts now for 11 years with no issues. I
do have a spare set with the same part numbers, but my 11 year old belts look more rugged than the new spares!
--
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

 

[Chazzer]

Cool...

I've been contemplating upgrading to a 100 amp with the dual pulley myself and keeping the current as a road back up.
--
Jim Owens,

78 Royale,

Out skirts of Kitchener, Ontario

 

[Matt Colie]

> Cool...
>
> I've been contemplating upgrading to a 100 amp with the dual pulley myself and keeping the current as a road back up.

Jim,

Hang on before you go that expense.
Borrow an ammeter and get the house bank way down and watch the charging current right after start up. Your 27SI is at least an 80 amp number, but
bet it never gets close. A 100 amp won't do any better. The problem is the almost 30' (10m) of #10SAE (not AWG) wire to the house bank. The
alternator will limit its output voltage by what it sees in the cab, so 14.4 is all you will have up front. The resistance to the rear is the charge
killer.

Our coach had a similar problem the other way. The PD9140 in the back could never get near 40. I ended up adding a PD9260 at the passenger's right
ankle to get by the lead length issue. It worked.

From both technical advise and personal experience, 100 amp is over the limit of a single belt. This can be a long story at an table at Mansfield.

I had the opposite problem.
My coach has the house bank in the left front. My 27SI was supposed to limit at 80amp. Well, GM never counted on a pair of GC2 (T105) just a few
feet away. I could not keep a belt when we dry camped. I finally went to double. Then I put in a Bogart Trimetic and watched as it climbed to 92 on
a cold start at after a multi-day dry camp. That was just the house bank!! In a later test with a Bell current probe an a Fluke 87 (we are talking
about the good stuff here) I saw 98+ for a short time in the power lead out of the alternator.

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

 

[Chazzer]

Great info Matt!

I was kicking around the idea as I mentioned. I actually don't have any serious alt problems currently. I did notice that I was having some
intermittent squealing climbing the hills of NY and the Berkshires in Mass though, this past August. It was baking hot outside with the newer Sanden
(last year) working over time trying to keep us cool. Heading straight into the super hot mid day sun it was 34 degrees Celsius out side, that Sanden
definitely had a task on hand. So did the alt it seemed to appear.



Perhaps I should look into adding the double pullet to my current alt. I had also been thinking of having a road spare on board.
--
Jim Owens,

78 Royale,

Out skirts of Kitchener, Ontario

 

[6cuda6]

> > Cool...
> >
> > I've been contemplating upgrading to a 100 amp with the dual pulley myself and keeping the current as a road back up.
>
> Jim,
>
> Hang on before you go that expense.
> Borrow an ammeter and get the house bank way down and watch the charging current right after start up. Your 27SI is at least an 80 amp number,
> but bet it never gets close. A 100 amp won't do any better. The problem is the almost 30' (10m) of #10SAE (not AWG) wire to the house bank. The
> alternator will limit its output voltage by what it sees in the cab, so 14.4 is all you will have up front. The resistance to the rear is the
> charge killer.
>
> Our coach had a similar problem the other way. The PD9140 in the back could never get near 40. I ended up adding a PD9260 at the passenger's
> right ankle to get by the lead length issue. It worked.
>
> From both technical advise and personal experience, 100 amp is over the limit of a single belt. This can be a long story at an table at
> Mansfield.
>
> I had the opposite problem.
> My coach has the house bank in the left front. My 27SI was supposed to limit at 80amp. Well, GM never counted on a pair of GC2 (T105) just a few
> feet away. I could not keep a belt when we dry camped. I finally went to double. Then I put in a Bogart Trimetic and watched as it climbed to 92
> on a cold start at after a multi-day dry camp. That was just the house bank!! In a later test with a Bell current probe an a Fluke 87 (we are
> talking about the good stuff here) I saw 98+ for a short time in the power lead out of the alternator.
>
> Matt

So Matt, if you were to rewire for your encountered problem what gauge would you have guestimated? I think im going to run into something similar here
as my converter is on the left side of the coach, between the kitchen and the closet (so about 20 feet down the left side) and the house battery is in
the right front of the engine compartment.

Im going to replace the converter in a couple weeks and if pulling wire is needed, nows the time.

--
Rich Mondor,

Brockville, ON

77 Hughes 2600

 

[john r. lebetski]

Good info. Not only that, a slower charge rate is better for the batteries. Bigger not always better.
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[richard h staples]

Bruce,
I agree completely with you. A "combiner" isn't going to charge your batteries any faster unless there's a problem in the system. Besides, I like
the other thing my "dual voltage" system allows: higher voltage to the A/C fan in high position, 16+ volts to my refrigerator "12V" heating element
which runs only when the engine runs, and an easy way to trigger my electric fuel pump "safety" cutoff relay which shuts off the pump when the engine
(alternator) stops.

BTW, I don't know about others, but the schematic for my coach shows a "0" gauge wire from the front (auxiliary battery switch) to the living area
junction block (in the utility cabinet with the buzz box), and then a "1" gauge wire to the rear auxiliary battery switch where the house battery
cable connects. Only a short (~ 1 or 2 foot) length of 10 gauge from the isolator to the front aux. bat. switch.

My .02,
Rick Staples
--
Rick Staples, '75 Eleganza, Johnstown, CO

"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien

 

[6cuda6]

> BTW, I don't know about others, but the schematic for my coach shows a "0" gauge wire from the front (auxiliary battery switch) to the living area
> junction block (in the utility cabinet with the buzz box), and then a "1" gauge wire to the rear auxiliary battery switch where the house battery
> cable connects. Only a short (~ 1 or 2 foot) length of 10 gauge from the isolator to the front aux. bat. switch.
>
> My .02,
> Rick Staples

I wish i had yhe original schematics for our Hughes then i'd see the gauge size....at it stands i can only visual compare and read what other have.

--
Rich Mondor,

Brockville, ON

77 Hughes 2600

 

[Matt Colie]

> > > Cool...
> > >
> > > I've been contemplating upgrading to a 100 amp with the dual pulley myself and keeping the current as a road back up.
> >
> > Jim,
> >
> > Hang on before you go that expense.
> > Borrow an ammeter and get the house bank way down and watch the charging current right after start up. Your 27SI is at least an 80 amp
> > number, but bet it never gets close. A 100 amp won't do any better. The problem is the almost 30' (10m) of #10SAE (not AWG) wire to the house
> > bank. The alternator will limit its output voltage by what it sees in the cab, so 14.4 is all you will have up front. The resistance to the rear
> > is the charge killer.
> >
> > Our coach had a similar problem the other way. The PD9140 in the back could never get near 40. I ended up adding a PD9260 at the passenger's
> > right ankle to get by the lead length issue. It worked.
> >
> > From both technical advise and personal experience, 100 amp is over the limit of a single belt. This can be a long story at an table at
> > Mansfield.
> >
> > I had the opposite problem.
> > My coach has the house bank in the left front. My 27SI was supposed to limit at 80amp. Well, GM never counted on a pair of GC2 (T105) just a
> > few feet away. I could not keep a belt when we dry camped. I finally went to double. Then I put in a Bogart Trimetic and watched as it climbed
> > to 92 on a cold start at after a multi-day dry camp. That was just the house bank!! In a later test with a Bell current probe an a Fluke 87 (we
> > are talking about the good stuff here) I saw 98+ for a short time in the power lead out of the alternator.
> >
> > Matt
>
> So Matt, if you were to rewire for your encountered problem what gauge would you have guestimated? I think im going to run into something similar
> here as my converter is on the left side of the coach, between the kitchen and the closet (so about 20 feet down the left side) and the house
> battery is in the right front of the engine compartment.
>
> Im going to replace the converter in a couple weeks and if pulling wire is needed, nows the time.

Rich,

In your case this will only be between the converter and the house bank. That was my case too, and I kept running the numbers up and decided that the
equal loss for both sides (I lost just a little less charge voltage on the ground side as I did the hot) that the arrangement as existed was not
salvageable. That is why the new converter in the front. (Installation was a serious PITA as a new 120V line also had to be run.) I could simple
not do a double run of 1/0 without tearing into the coach. That is what it would have taken.

In your case, I would do what I sometimes do when confronted with such an issue. I go to the suppliers and total the prices for all the options
(spreadsheets are handy) and decide how much the gain in copper is worth. I can remember two suppliers, and I am pretty sure that there was a third.

http://www.genuinedealz.com
http://www.delcity.net

Yes, everything is a compromise.

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

 

[johnny]

Along these lines, I have to wonder a bit. While checking the belt alignment, I noticed an interesting 'wobble' on the return side of the alternator
belt. Makes me wonder whether we might benefit from a newer alternator with a clutch fitted. While the V-belt handles the wobble without a lot of
problems, I suspect it would quickly take the outer ridges off a serpentine belt. I note pretty much all the bew cars are fitted with clutch
alternators, I suspect this is why. Compared to the 60s rides, the electric load is grossly larger now and if there are three or four ulses a second
to the field, the result without the clutch would be very noticeable.

--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

 

[6cuda6]

> Along these lines, I have to wonder a bit. While checking the belt alignment, I noticed an interesting 'wobble' on the return side of the
> alternator belt. Makes me wonder whether we might benefit from a newer alternator with a clutch fitted. While the V-belt handles the wobble
> without a lot of problems, I suspect it would quickly take the outer ridges off a serpentine belt. I note pretty much all the new cars are fitted
> with clutch alternators, I suspect this is why. Compared to the 60s rides, the electric load is grossly larger now and if there are three or four
> ulses a second to the field, the result without the clutch would be very noticeable.
>
> --johnny

Clutch alternator is because the alternator stops to abruptly when shut off so the serpentine belt squeals....clutch prevents that.

--
Rich Mondor,

Brockville, ON

77 Hughes 2600

 

[johnny]

MOre importantly the clutch removes the jerks. I suspect they are the reason in a higher (100 amp +) alternator. Belt tension will keep the
alternator spinning, and when you shut the ignition off, the excitation to the alternator goes away. Thus it provides only the friction load which is
minuscule by comparison. If you have a belt squeal on shutdown, you've some other problem.

--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