Home » Public Forums » GMCnet » How to parallel house batteries? (With Ken Burton's recent issue in mind)
| How to parallel house batteries? [message #182462] |
Thu, 30 August 2012 19:14  |
zhagrieb
Messages: 676
Registered: August 2009
Location: Portland Oregon
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Thinking of Ken's problem paralleling 2 12v batteries, what is a safe way to parallel two pair of golf cart batteries?
Glenn
Glenn Giere, Portland OR, K7GAG
'73 "Moby the Motorhome" 26'
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| Re: [GMCnet] How to parallel house batteries? [message #182478 is a reply to message #182462] |
Thu, 30 August 2012 19:59  |
powerjon
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Registered: January 2004
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Glenn,
There is no way to permanently connect two sets of batteries in
parallel. No two or more batteries are exactly the same. The
batteries will self discharge and the batteries state of charge will
be reduced. That said you can do a parallel battery setup if you
connect them with a relay setup that disconnects one set from the
other. They need to be charge separately. It is like the boost
switch that we have on our coaches.
JR Wright
On Aug 30, 2012, at 8:14 PM, Glenn Gyre wrote:
>
>
> Thinking of Ken's problem paralleling 2 12v batteries, what is a
> safe way to parallel two pair of golf cart batteries?
>
> Glenn
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: How to parallel house batteries? [message #182485 is a reply to message #182462] |
Thu, 30 August 2012 20:25 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
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There are multiple schools of thought on this subject. I'm not nearly as excited about the effects of minor differences between batteries as some others, and prefer to deal with that minor demon rather than the complexity of having to run your generator twice as long to charge the battery banks separately, or to have a complex charging / switching system that introduces difficulties of its own. I had a couple paralleled 12V batteries (incorrectly wired by the PO), and it wasn't a big deal to trace down the unusual battery drain (just disconnected the two, took a couple readings, replaced the bad battery, and I'm done). YMMV.
There's a very good article on the subject called 'Balance of Power' that as in the Family Motor Coaching magazine. Perhaps you can look it up or have someone send you a copy.
In the article (which is quite comprehensive, IMHO), the author suggests that the best approach is to use "Y cables" to connect to the positive and negative terminals of the 6-volt battery pairs (effectively eliminating any discharge/charge discrepancy due to the cable resistance). He also acknowledges that simply connecting the negative feed at one end of the battery stack, and the positive feed at the other will provide good results (rather than just taking both negative and positive feeds off the nearest battery pair, which can tax the nearest pair considerably more because of the added cable and connector resistance associated with the farthest pair).
Just as a reference, solar power systems often have many series / parallel batches of 6 volt lead acid cells. This does complicate troubleshooting a bit when it comes to identifying an individual bad battery, but it's still quite possible to make this much more complex arrangement work just fine. Is it theoretically perfect? Nope, but it's the best you're going to do on a system that can't survive on a couple 6V batteries, and is used in countless installations around the world (including a few I've worked on).
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: [GMCnet] How to parallel house batteries? [message #182491 is a reply to message #182478] |
Thu, 30 August 2012 20:48 |
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mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
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While JR is technically correct, people have been paralleling batteries for years. There ARE issues and with this and you'll have better results if you try and avoid it...
The banks do NOT need to be charged separately. The only time you REALLY need to try and isolate the banks is when left in a steady state... no charge, no load. That is the only time the small differences of a MATCHED set of batteries will cause any problems. (Unmatched banks are another story...) One of the keys is to ensure the cable lengths and number of connections to each bank is as close to equal as possible. (Each bank should "look" the same electrically from each end... for load and charging.) Another method is the use of combiners to connect the batteries when being charged but disconnect the before they discharge each other. This method does not require matched batteries, but each bank should be loaded separately. (Not an issue if the banks have different uses... like house and starting.) But if you NEED large amounts of power, paralleling might be the only real choice. Some... maybe many... just live with the reduced life span of batteries configured in parallel.
OBTW: You are talking about MORE than one BANK of two 6 volt golf cart batteries aren't you? (Two 6 volt batteries connected in serial is effectively ONE 12 volt battery "bank.")
| powerjon wrote on Thu, 30 August 2012 17:59 |
Glenn,
There is no way to permanently connect two sets of batteries in
parallel. No two or more batteries are exactly the same. The
batteries will self discharge and the batteries state of charge will be reduced. That said you can do a parallel battery setup if you connect them with a relay setup that disconnects one set from the other. They need to be charge separately. It is like the boost switch that we have on our coaches.
On Aug 30, 2012, at 8:14 PM, Glenn Gyre wrote:
> Thinking of Ken's problem paralleling 2 12v batteries, what is a
> safe way to parallel two pair of golf cart batteries?
|
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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| Re: [GMCnet] How to parallel house batteries? [message #182528 is a reply to message #182505] |
Fri, 31 August 2012 00:25 |
mickeysss
Messages: 1476
Registered: January 2012
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just for the hell of it be careful - this stuff can cause problems.
if you parallel two 6 volt golf cart batteries, you get 6 volts out to main, that has to be done in series to get 12 volts out to the main.
2 / 12 volt batteries only parallel means positive to positive and negative to vegative then out as 12 volts. to main system,
series means positive to negative with 2 / 6 volt batteries then out as positive and negative giving 12 volts to main system.
mickey :-)
be careful this is invisible stuff and needs scientific info first.
don't trust what i say recheck it.
On Aug 30, 2012, at 7:46 PM, Larry Davick wrote:
> And the answer to Glen's question is in that article in the FMCA Magazine.
>
> Larry Davick
>
> On Aug 30, 2012, at 5:14 PM, Glenn Giere <glenngiere@gmail.com> wrote:
>
>>
>>
>> Thinking of Ken's problem paralleling 2 12v batteries, what is a safe way to parallel two pair of golf cart batteries?
>>
>> Glenn
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| Re: [GMCnet] How to parallel house batteries? [message #182531 is a reply to message #182528] |
Fri, 31 August 2012 01:35 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Here is my approach
1. Do do it.
2. If you feel you must do it, keep the paralleled batteries separated when not under charge and when under charge use something to limit the current flow between them. I would figure out the maximum amount of current that would flow while under charge and install a fuse at 125% or 150% of that value. It could also be a circuit breaker but not an automatic reset one.
In my case I was using two 18 amp-hour batteries to tun a small refrigerator. (The refrigerator draws 4 amps so I have an 8 amp fuse inline with it.
I figured at 10 amp fuse should do for charging so there is a10 amp fuse between them. If it blows under normal operation, I'll up it to 15 amps.
I definitely will not parallel coach batteries. There is too much stored power there. We were parked near to Roger Black at the last Amana Colonies rally when one of his parallel house batteries exploded at 2 or 3AM. Even Roger heard it with no hearing aids.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: How to parallel house batteries? [message #182565 is a reply to message #182558] |
Fri, 31 August 2012 09:23 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
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| Matt Colie wrote on Fri, 31 August 2012 08:44 |
| Glenn Giere wrote on Thu, 30 August 2012 20:14 |
Thinking of Ken's problem paralleling 2 12v batteries, what is a safe way to parallel two pair of golf cart batteries?
Glenn
|
Glenn,
Yes there is, but it requires that the paralleling include massive fuses. Fuses like an AMG175 and holders are available at many car parts stores.
There are two problems with paralleling lead acid batteries.
One is problems if one of the two strings has a failure. This often results in explosions, acid spills and fires. That is what the fuse is for.
The other is that without seriously involved technology and a lot of arm waving, your two-string bank will not have a usable capacity of string * 2. This is because the internal resistance of the batteries varies with EVERYTHING (except the Federal Funds Rate). Even batteries side by each will be different enough to make things not be optimal.
I (used to) do this sort of thing all the time for long passage cruisers. Imagine dry camping 300 miles from land.
Matt
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Matt, it is my contention that the fuse size should be only slightly larger than the maximum expected charge rate or maximum expected discharge rate which is ever is larger.
In the original setup in the GMC the rear or house batteries are protected by a 50 amp CB. This means they never expected to exceed that rate EXCEPT in the boost mode. In the seldom used boost mode they wired a jumper around the CB. That jumper is actually a high current relay/solenoid.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: How to parallel house batteries? [message #182583 is a reply to message #182565] |
Fri, 31 August 2012 10:54 |
zhagrieb
Messages: 676
Registered: August 2009
Location: Portland Oregon
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Thanks all for the good info. You've sufficiently "scared" me. If I go this route I think a switch between banks is in order.
Glenn
Glenn Giere, Portland OR, K7GAG
'73 "Moby the Motorhome" 26'
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| Re: How to parallel house batteries? [message #182586 is a reply to message #182462] |
Fri, 31 August 2012 11:35 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
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A battery can fail at any time. It can have different failure modes. The shorted cell mode means you are trying to pump 14 charging volts into a 10v batt. Gets hot. Goes boom sometimes. Internal loose connection causes boom sometimes too.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: How to parallel house batteries? [message #182590 is a reply to message #182462] |
Fri, 31 August 2012 12:06 |
bwevers
Messages: 597
Registered: October 2010
Location: San Jose
Karma: 5
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I have 2 x 6 volt golf cart batteries in series in the front.
And 1 x 12 volt house battery in the rear.
They are both on the same bus. They are charged by
a Progressive Dynamics Charge wizard, which I keep
plugged in when not using the MoHo.
I check the water level in the batteries every few months.
It's been working this way for 5 years.
If the rear battery somehow shorts internally, there
is a circuit breaker back there to limit the current.
What else can go wrong?
Regards,
Bill
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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