Home » Public Forums » GMCnet » dual 12v house batteries -birchaven
| dual 12v house batteries -birchaven [message #269925] |
Sun, 18 January 2015 11:43  |
Joe Weir
Messages: 769
Registered: February 2013
Location: Columbia, SC
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Fellow travelers,
My birch has the 2nd house battery at the back under the closet, with a manual cut off in the bathroom under the medicine cabinet.
The batteries are weeks apart in age with the first one getting charged multiple times due to less than full readings, due to the, at the time, undiscovered dead house battery in the back.
I've read in the forum about the evils of having two 12v batteries in parallel, and wonder if I need to "fix" this arrangement, or let it be.
My worries are the long term battery health, 25' of 40 year old cable connecting the two, and the somewhat sketchy looking cut off switch in the bathroom.
I like the idea of having as much battery capacity as possible, but I know just enough about 12v systems to be dangerous.
Is there a recommended primer on rv 12v systems anyone has found handy. I realize there are a lot of EEs on the list who talk circuits faster than I can understand English, I'm talking about a reference for the less gifted.
Better yet, has anyone pondered this before and come up with an improvement in the design?
76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator, brakes, Sully airbags, fuel lines, seats, adult beverage center... those Coachmen guys were really thinking about us second hand owners by including that beverage center...
Columbia, SC.
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| Re: dual 12v house batteries -birchaven [message #269927 is a reply to message #269925] |
Sun, 18 January 2015 12:11  |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
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Joe Weir wrote on Sun, 18 January 2015 09:43Fellow travelers,
My birch has the 2nd house battery at the back under the closet, ...
... Better yet, has anyone pondered this before and come up with an improvement in the design?
Coachman wasn't that consistent it how they wired the Birches. There also could be changes made by PO's over the years. Keep this in mind while reading my response.
I have heard of (and seen one) early Birchavens with a separate dedicated generator starting battery accessed through the closet of the rear bath. It was discontinued sometime later in the production. Most likely due to dead battery due to non-use. (The same reason GM dropped this design with the other changes for MY1975.) While you could install a combiner to keep this gen-set starting battery charged, I'd just remove it.
My 1978 came with a house and chassis 12v, both up front on the curb side. The Onan is started through the circuit breaker and a long cable to the rear. As the Onan doesn't draw THAT much, it works fine. The changes I have made were installing a three battery tray from JimK and replacing the house battery with two 6 volt golf cart batteries. Works fine, lasts a long time...
Two 6v golf cart batteries should provide enough capacity for most users... unless you dry camp for several days, or have above normal power needs. You can use the space from the other rear battery for storage.
Also: Be sure to inspect the cable going to the rear, Coachman wasn't very thoughtful when they installed mine... running over some moving parts on the way back.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
[Updated on: Sun, 18 January 2015 12:23] Report message to a moderator |
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| Re: dual 12v house batteries -birchaven [message #269929 is a reply to message #269927] |
Sun, 18 January 2015 13:19 |
Joe Weir
Messages: 769
Registered: February 2013
Location: Columbia, SC
Karma: 7
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mike miller wrote on Sun, 18 January 2015 12:11... There also could be changes made by PO's over the years. Keep this in mind while reading my response.
I have heard of (and seen one) early Birchavens with a separate dedicated generator starting battery accessed through the closet of the rear bath. It was discontinued sometime later in the production. Most likely due to dead battery due to non-use. (The same reason GM dropped this design with the other changes for MY1975.) While you could install a combiner to keep this gen-set starting battery charged, I'd just remove it.
Also: Be sure to inspect the cable going to the rear, Coachman wasn't very thoughtful when they installed mine... running over some moving parts on the way back.
thanks mike. The PO did indeed to some rewiring. The rear battery charges off the front, but the overall wiring is done in such a way I'm not sure if it is the po or the original workmanship. The battery in the rear is connected to the front, and charges when the front is charging.
Reclaiming that space in the closet allows more room for an on an replacement, or maybe a spring loaded shore power reel to store the cord.
What kind of weight are you running up front?
76 Birchaven - "Wicked Mistress" - New engine, trans, alum radiator, brakes, Sully airbags, fuel lines, seats, adult beverage center... those Coachmen guys were really thinking about us second hand owners by including that beverage center...
Columbia, SC.
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| Re: [GMCnet] dual 12v house batteries -birchaven [message #270031 is a reply to message #269925] |
Mon, 19 January 2015 21:50 |
Rob
Messages: 651
Registered: November 2013
Location: Victoria, BC
Karma: 3
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My plan (likely this season) is to remove both of my 12V house batteries (1 in front and 1 in rear) and replace them with 2 Costco 6V golf-cart batteries, and mount them in the rear. Mine is a Royale (26') - so I have a fair bit of space behind the Onan. I'm not sure if a 23' has as much space in that location.
I'm planning to use a cabinet slide (rated for 210 lbs.) from Lee Valley as the base for the battery tray.
Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath
On 2015-01-18, at 9:43 AM, Joe Weir wrote:
> Fellow travelers,
>
> My birch has the 2nd house battery at the back under the closet, with a manual cut off in the bathroom under the medicine cabinet.
>
> The batteries are weeks apart in age with the first one getting charged multiple times due to less than full readings, due to the, at the time,
> undiscovered dead house battery in the back.
>
> I've read in the forum about the evils of having two 12v batteries in parallel, and wonder if I need to "fix" this arrangement, or let it be.
>
> My worries are the long term battery health, 25' of 40 year old cable connecting the two, and the somewhat sketchy looking cut off switch in the
> bathroom.
>
> I like the idea of having as much battery capacity as possible, but I know just enough about 12v systems to be dangerous.
>
> Is there a recommended primer on rv 12v systems anyone has found handy. I realize there are a lot of EEs on the list who talk circuits faster than I
> can understand English, I'm talking about a reference for the less gifted.
>
> Better yet, has anyone pondered this before and come up with an improvement in the design?
>
>
> --
> 76 Birchaven - New engine, trans, aluminum radiator, brakes, airbags, fuel lines, seats, upholstery, adult beverage center... those Coachmen guys were
> really thinking about us second hand owners...
> Columbia, SC.
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Rob -
Victoria, BC -
76 Royale - Rear Twins/Dry Bath
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| Re: [GMCnet] dual 12v house batteries -birchaven [message #270062 is a reply to message #270033] |
Tue, 20 January 2015 16:33 |
Rob
Messages: 651
Registered: November 2013
Location: Victoria, BC
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Thanks for that - I'll keep it in mind!
Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath
On 2015-01-19, at 8:21 PM, Billy Massey wrote:
> Remember that any carbon steel in the battery compartment will rust quickly
> and completely. If you can find stainless slides, they'll be worth it.
> bdub
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Rob -
Victoria, BC -
76 Royale - Rear Twins/Dry Bath
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| Re: dual 12v house batteries -birchaven [message #270064 is a reply to message #269925] |
Tue, 20 January 2015 17:49 |
mickey szilagyi
Messages: 273
Registered: January 2013
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If you plan to build a tray and use a cabinet slide have a look at the images below first. Applied and probably others sell this tray and it's built to fit behind the Onan in the original battery compartment. It is stainless steel. We installed it when we replaced our burned out Onan. It works great however the only disappointing thing is the fiberglass/plastic tray is just a bit too small for the batteries we put in it, two Duracell 6V golf cart batteries. We gound out the corners of the tray and the batteries fit. We told Jim K about the tray being too small and he indicated he'd contact the people that make the trays. Maybe they're made bigger now. We did a lot of research on golf cart batteries and found they are not all the exact same size. We found some that were even longer by 1/8 inch or more and that makes 1/4 inch more space needed. You won't get another 1/4 inch out of the tray we bought.
Here's the tray we bought: http://www.appliedgmc.com/prod.itml/icOid/767
Here's a few photos of our installation. If you do contact Applied we'd be interested if they ever made the tray longer. Not all 6V golf cart batteries will fit in it, period.
http://www.gmcmhphotos.com/photos/generac-primepact-50g-installation/p49765-stainless-steel-battery-tray.html
and
http://www.gmcmhphotos.com/photos/generac-primepact-50g-installation/p49770-batteries-installed.html
We also made new cables using 2/0 gauge welding wire soldering closed-end lugs on the ends. 2/0 might have been overkill but several members on this forum recommended it and we're not sorry we used it. Welding wire is extremely flexible and works great.
Good luck!
Mickey
1977 Kingsley, 403, Lansing, MI
[Updated on: Tue, 20 January 2015 17:57] Report message to a moderator |
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| Re: [GMCnet] dual 12v house batteries -birchaven [message #270072 is a reply to message #270031] |
Wed, 21 January 2015 09:49 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Rob wrote on Mon, 19 January 2015 22:50My plan (likely this season) is to remove both of my 12V house batteries (1 in front and 1 in rear) and replace them with 2 Costco 6V golf-cart batteries, and mount them in the rear. Mine is a Royale (26') - so I have a fair bit of space behind the Onan. I'm not sure if a 23' has as much space in that location.
I'm planning to use a cabinet slide (rated for 210 lbs.) from Lee Valley as the base for the battery tray.
Rob
Rob,
I don't know if you know, I have been around boats all my life and I did a lot of work on other people's boats before the depression killed that business. One thing I did learn very first hand is that lead/acid batteries do not like to be in parallel. Stories here could last several rounds of beer. More importantly and apart from the battery explosion problem is the simple fact(s) that:
A- All golf cart batteries are real deep cycle and will be much more tolerant of minor abuse and
B- The bank of series jars (battery cells) will evenly distribute the load (this is something that will not happen in parallel).
To eliminate any doubt, a GMC fit 23 has no accessible space aft of the APU (genset). The space can be accessed when the APU is out, so you can clean out the walnuts that the squirrel put in there, but it is a useless space and only open to the APU bay. If I ever figure out what to do about it, I will definitely post the topic.
In younger days, I sailed several long passages with men that had been on submarines in WWII. They knew a lot about how to treat batteries, they had to. I listened and absorbed about 30% by my best guess. The consistent warning was about trying to charge batteries in parallel to full density (that was always how they spoke of charge level).
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] dual 12v house batteries -birchaven [message #270088 is a reply to message #270072] |
Wed, 21 January 2015 17:22 |
Rob
Messages: 651
Registered: November 2013
Location: Victoria, BC
Karma: 3
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Senior Member |
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Yes - one of the main reasons why I wanted to remove my dual 12V batteries and replace them with dual 6V GC batteries was to eliminate the imbalance issue you were referring to.
I've never looked closely at a 23' - but I assumed there was very little space rear of the Onan.
Matt Colie wrote on Wed, 21 January 2015 07:49Rob wrote on Mon, 19 January 2015 22:50My plan (likely this season) is to remove both of my 12V house batteries (1 in front and 1 in rear) and replace them with 2 Costco 6V golf-cart batteries, and mount them in the rear. Mine is a Royale (26') - so I have a fair bit of space behind the Onan. I'm not sure if a 23' has as much space in that location.
I'm planning to use a cabinet slide (rated for 210 lbs.) from Lee Valley as the base for the battery tray.
Rob
Rob,
I don't know if you know, I have been around boats all my life and I did a lot of work on other people's boats before the depression killed that business. One thing I did learn very first hand is that lead/acid batteries do not like to be in parallel. Stories here could last several rounds of beer. More importantly and apart from the battery explosion problem is the simple fact(s) that:
A- All golf cart batteries are real deep cycle and will be much more tolerant of minor abuse and
B- The bank of series jars (battery cells) will evenly distribute the load (this is something that will not happen in parallel).
To eliminate any doubt, a GMC fit 23 has no accessible space aft of the APU (genset). The space can be accessed when the APU is out, so you can clean out the walnuts that the squirrel put in there, but it is a useless space and only open to the APU bay. If I ever figure out what to do about it, I will definitely post the topic.
In younger days, I sailed several long passages with men that had been on submarines in WWII. They knew a lot about how to treat batteries, they had to. I listened and absorbed about 30% by my best guess. The consistent warning was about trying to charge batteries in parallel to full density (that was always how they spoke of charge level).
Matt
Rob -
Victoria, BC -
76 Royale - Rear Twins/Dry Bath
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| Re: [GMCnet] dual 12v house batteries -birchaven [message #270148 is a reply to message #270112] |
Thu, 22 January 2015 11:43 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
Karma: 0
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Senior Member |
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ljdavick wrote on Wed, 21 January 2015 17:46Gary Bunzer's "Balance of Power" article from the January 2012 Family Motor Coaching magazine does an excellent job of detailing the issues with multiple batteries connected in parallel / series.
I am fairly sure I have seen that article or another like it. Yes, you _CAN_ run battery banks in parallel, if properly balanced in all aspects: age, size and cable lengths are just some of the considerations. Doing that with the battery banks at each end of the coach is a little problematic. Yes, it could be done, but 2 6v in one end is soooo... much easier!
The area aft of the Onan on both my Birchavens is used for shore power cable and is accessed through small "trap door" next to the Onan. You can also go in through the floor of the closet (rear bath) or under the street side of rear dinette. (side bath)
I assume this is where the "extra" battery is located in some Birchavens... mostly 1976's.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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