| [GMCnet] 3 battery isolator [message #337743] |
Tue, 09 October 2018 19:30 |
powwerjon
Messages: 849
Registered: March 2013
Karma: -2
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Senior Member |
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Dean,
You Need to download the following from bdub s website.
http://www.bdub.net/manuals/avion.pdf
Your comments are incorrect and not how the 12 VDC system works. You should have 2 batteries ( interior batteries )in the back and 2 in the front. The forward most battery is the chassis battery and the one just behind it is the front interior battery and is internal to the 12 VDC system.
You should read Page 5, para 5 called 12-volt system. It goes onto page 6 the entire first column. The Avion is a different animal on how it is wired. Look at the picture at the bottom of page 6 first column. You will see that the front and rear batteries are tied together on the lower part of diagram. You only need what came with the coach which was a standard 2 battery isolator. You should also look at page in the back reference area marked “12 Volt Wiring Diagram for 26’ Avion Interior. One side of the isolator charges the interior batteries and the other side charges the chassis battery.
The wiring diagram show that from the factory they had two 12 volt batteries in the rear (main battery supply) wired in parallel which is NOT the best of installation set up for battery longevity. I currently use two 6 VDC batteries in the back wired in series. The two gold cart batteries have been proven to be the best installation for the GMC motorhome. As I finish the coach rebuild, I will also change the front single 12VDC interior battery to two 6 VDC golf cart batteries and a good chassis battery. The two 6 VDC golf cart batteries and the single chassis battery will fit in the front area. I have done several installation in that configuration.
The 73 and 74 interior battery layout is different than the Avion which was produced only in 1975. The 73 & 74 had both the coach and chassis batteries in the right front. The battery in the back was for starting the Onan and was charged by the Onan. The 75 GMC produced coach had the more conventional layout with the chassis battery in the front and the coach battery in the back and that is what was produced in that config until the end of production.
You should review the wiring diagrams for the 75 and later GM built coaches tool They are available on the Bdub website.
J.R. Wright
GMC Great Laker MHC
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 GMC Buskirk 30’ Stretch
75 GMC Avion (Under Reconstruction)
Michigan
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