Coach batteries: 6v or 12v?

[CampYoey]

Sent: 8/19/2003

I am getting ready to add rechargeable batteries to the `79 Minnie Winnie. Right now there is an automotive battery in place. Last night while tinkering, the lights kept dimming whenever the water pump kicked on. I've read various options - six vs 12, parallel verses serial. Any personal experience with either?

Camp Yoey

[Ir_0008d1]

Sent: 8/19/2003

I had a 6v engine battery on my 21 year old motorbike, and sometimes it wouldn't even start the engine. Even when running on a full charge you couldn't use the lights or the indicators for very long. Everyone kept advising me to always buy a vehicle with a 12v battery. I had a new motorbike previous to that with a 12v engine battery, and as I recall I could run the lights as much as I want and I never had to recharge it. If the battery you're thinking of is a leisure battery, keep it in mind that there are few 6v electrical products. So you'll need two of them. But I'd go for a 12v heavy duty one if it will trickle charge off the engine.

[melyash]

Sent: 8/20/2003

If your doing any amount of dry camping (not hooked up to the 110V grid) then I would suggest running a pair of 6V batteries in series to run your Coach. They will give you slightly more capacity (5-10%) but more importantly they will handle the discharge/recharge cycles better and last longer. The thing to watch for, is the Physical dimensions of the batteries. I wanted to put 6V in my unit, but the compartment slide out tray had a wooden mounting tray in it which raised the batts just high enough that I was afraid they might short against the Compartment door frame as they slide back into the coach. With that sort of amperage involved, they could easlily "Weld themselves into position" in milliseconds, with the resulting fire, explosion, and other nastiness associated with grounding that much energy.

They would have been fine in the compartment themselves, with over an inch of clearance, but the door frame was my worry point.  Having said that, I will still go 6V some day, after I do a mod to the wood in the battery tray and lower the height a bit.

As you will see in other posts I am a true believer in the book "Managing 12 Volt Systems" by Harold Barre. This is available from Camping world, and also from Amazon. Buy it, Bore yourself silly by reading the first few chapters on theory and operation, then get into the Motorhome section and get a great idea of how your system should work.

Good Luck. Matt

[Collyn down-under]

Sent: 8/23/2003

Series/parallel connection is one of those topics bedeviled by campfire and website mythology.

At the RV level it really does not matter - the pros and cons are different for each - but more or less balance out.

Firstly though, for batteries of more or less equal size and condition the energy sortable is the same for either connection. It is simply not correct that one way stores more or less energy than the other.

The main argument against series connecting two 6 volt batteries to get twelve volts is that if one fails prematurely there will be an imbalance if there's now one new and one old one - in that the old one will limit the total charge sortable.

The main arguments against parallel connection is (a) that one battery may 'grab' more of the charge than the other (but whoever holds these views do not understand how batteries charge and (b) that if one battery develops a shorted cell the other will discharge into it with dire results. It is true that one will discharge into the other. It is nonsense to suggest consequently dire results because the discharge rate is determined by the remaining good cells.

My marginal preference is paralleling up to three batteries of the same type and age (amp/hour capacity does not matter, but if someone else marginally prefers series connection that's fine by me.

Personally I'd follow the advice of buying whatever fits best and connecting them accordingly.

Interesting though that one of the USA's best makers of
smart regulators etc comes out quite strongly in favor of the parallel approach.

There's a heap about this stuff in my book 'Motorhome Electrics' - but it may be more than you actually wanted to know!
Collyn down-under

[Myk-dK]

Sent: 8/25/2003

I'm a fan of the two 6 volters,  the reason being way more amp/hour capacity than two 12s in parallel.
myk

[Oz]

Sent: 2/20/2004

Very good reading on this in the resources section: "Smart RVing".

Basically, the author has run 3 set-ups over the years.

He found that 12v batteries were good, length of performance based on quality of battery and primarily on how well they are maintained (the maintenance is a must read!)

He then went with 6 volts.  He found they worked better and lasted longer because they are designed form equipment that runs off electric for extended times (like golf carts and fork lifts).  They have thicker plates and so hold the charge better (VERY basically speaking).

He then used 12v Gel batteries.  He has found that these have been by far the best.  He ran the same 6 batteries for ten years.  Very low maintenance, no "gassing".  Expensive to say the least but, well worth it.