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| [GMCnet] Introduction and question [message #306246] |
Wed, 31 August 2016 19:05  |
glwgmc
Messages: 1014
Registered: June 2004
Karma: 10
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Hi Perry,
Welcome to the group! You will find much to like and many new friends as you attend rallies and reach out to the GMC community.
We also have a Clasco that was done in 1994 as a retirement present for the then owner. We found it in an air conditioned warehouse building in Naples, FL, a few years ago with just 11,000 miles on the clock since the Clasco restoration. It joined our 78 Royale and we use both extensively. As a matter of fact, my wife posed an interesting question the other day. Why, she asked, do we have two cars when all our highway driving is done in one of the GMCs. We put about 10,000 to 20,000 miles a year on each of the GMCs but only about 5000 to 7500 miles on the cars!
Combiners and isolators do the same thing, but in very different ways. A combiner can best be described as a voltage controlled relay that closes (combines two battery banks) whenever a charge current is sensed. When the voltage drops even slightly between the two battery banks the relay opens and keeps one battery bank from drawing the other down. The isolator uses diodes to accomplish this same task. I am a fan of quality combiners as there is no voltage drop across the relay as there is across the diodes. If you have more than two battery banks, you can keep adding combiners so no matter what charge current is available (from shore power or your generator going through your converter/battery charger in the coach or from your alternator while driving) all your batteries will always be fully charged. I like brands like Blue Sea made in Bellingham, WA, and Victron made in Denmark. You will find them at marine supply places or from our GMC motorhome vendors.
To install a combiner all you need to do is connect one terminal to one battery bank, the other terminal to the second battery bank and ground the unit. The way your diagram is drawn the Perko switch shuts off the house battery and the generator battery but leaves the chassis battery always on. It also isolates those two batteries from ever seeing the alternator charge if you forget and leave it in the off position. It also isolates the chassis battery from seeing the converter/battery charger if you are plugged into shore power or are running your generator while that switch is off. Seems to me like too much chance for human error, leaving you with one or more dead batteries when you think they are being charged. I would simply install a combiner between your chassis battery and your house battery and another between the house battery and the generator battery and eliminate the Perko switch until you decide when and under what conditions you might want such a shut off switch.
The other observation I would make is why you have a separate generator battery. Most of us start the generator off of the house battery bank. The space to side of the generator is large enough to install one 4D or one 8D or two six volt deep cycle house batteries (which will give you 200 to 250 amp hours of capacity depending on which battery you select). Take a look at the presentation I gave some time ago called “Living Large in your GMC”. That talks all about the various configurations of batteries, combiners, isolators, inverters, converters, etc. It is available from my web site on the GMC page, or from the GMCWS.ORG web site. It may also be on the GMC49ers web site and/or the GMC Cascaders web site.
Enjoy and welcome!
Jerry
Jerry & Sharon Work
Kerby, OR
glwork@mac.com
http://jerrywork.com
78 Royale with most everything done to modernize a GMC mechanically
77/94 Clasco bone stock (now with FiTech EFI) and looks like it just left the Clasco facility
Both drive equally as well.
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Message: 3
Date: Wed, 31 Aug 2016 14:25:59 -0600
From: Perry Barber
To: gmclist@list.gmcnet.org
Subject: [GMCnet] Introduction and question
Message-ID:
Content-Type: text/plain; charset="utf-8"
Hello,
My wife Teri and I purchased a 1978 Royale this summer. It was Rudy and Grace Litke's coach for about 20 years. Rudy and Grace are now in Southport,
NC moving from Connecticut. They purchased the coach in 1996 right after the original owners the Buzzard's of New Mexico had it refurbished by Clasco.
We feel fortunate to have a the opportunity to enjoy it and make it ours.
My question has to do with installing a Combiner. Right now it has a Perko switch that as I understand it controls the battery connections, charging
and use. I am at a loss on how to proceed. I'm fairly handy but would welcome some direction to make sure I get it right.
http://www.gmcmhphotos.com/photos/data/6969/medium/Perko_1.jpg
http://www.gmcmhphotos.com/photos/data/6969/medium/Perko_2.jpg
http://www.gmcmhphotos.com/photos/data/6969/Perko_Settings.pdf
Thanks in advance.
Perry Barber
--
P. Barber
Raleigh, NC
1978 GMC Royale - 1995 Clasco Upgrade
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Jerry & Sharon Work
78 Royale
Kerby, OR
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| Re: [GMCnet] Introduction and question [message #306254 is a reply to message #306246] |
Wed, 31 August 2016 20:25  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Perry,
One comment in Jerry's write-up caught my eye:
"It also isolates those two batteries from ever seeing the alternator
charge if you forget and leave it in the off position."
That possibility is a recipe for disaster! If the GMC uses an alternator
with a "Remote Sense" (RS) terminal, meaning that the alternator's output
voltage is controlled by feedback from the battery to which it is
connected. If it's not connected to the battery to which the RS terminal
is connected, it will continue to increase its output voltage, trying to
bring the non-connected battery up to its correct voltage. Most
alternators (but not all) have an internal limit of 18 VDC -- that's TOO
MUCH for many items in the coach to withstand without damage, and operation
at that voltage for even a short time will probably damage the alternator
itself seriously.
IF the RS terminal has been connected directly to the output of the
alternator, this problem does not exist, but the diagram in your 3rd
reference does not show an RS generator, so there's no way to even guess
whether your wiring is safe; the only safe guess is NO..
Which brings us to isolators: If you do re-install an isolator, be sure
the RS line is connected to the chassis battery. If it is, and remains,
connected directly to the alternator output, the batteries connected via
the isolator will ALWAYS be 0.6-0.7 VDC below full charge -- a significant
shortage. The reason is that the isolator's internal diodes impose that
voltage drop between the alternator and the batteries. The RS line tells
the alternator to increase its output voltage to compensate for that drop.
Another isolator fact: The common failure mode is for the chassis side
diode to become "open" (non-conducting). That returns the alternator to
the "recipe for disaster" discussed earlier.
One of the benefits of the combiner is, as Jerry mentioned, that it
eliminates the diodes' forward voltage drop (the dissipation of the heat
from that drop is why isolators have those big fins on them).
HTH,
Ken H.
On Wed, Aug 31, 2016 at 8:05 PM, Gerald Work wrote:
> Hi Perry,
>
> ...
> Combiners and isolators do the same thing, but in very different ways. A
> combiner can best be described as a voltage controlled relay that closes
> (combines two battery banks) whenever a charge current is sensed. When the
> voltage drops even slightly between the two battery banks the relay opens
> and keeps one battery bank from drawing the other down. The isolator uses
> diodes to accomplish this same task. I am a fan of quality combiners as
> there is no voltage drop across the relay as there is across the diodes.
...
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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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