Lead Acid - the choices

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Delinquent
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Lead Acid - the choices

Postby Delinquent » Wed Sep 03, 2008 6:23 pm

In my continuing research before stumping up for the Mev Pocket, I started looking at batteries today. Lead Acid will be the route forward in the short term, so was merrily looking at the various Ah car batteries for given sizes, when a colleague asked why I was using car batteries. "lead acid, cheap" says I...

but am I going the right route with "car" batteries - is it better to have more numerous, smaller packs (say motorcycle gel packs) and going for a series AND parallel wire up to achieve the same Ah or cost per KW are car packs going to do the business, just not in such a readily placeable solution? Was looking for around 40-50Ah @72v which does lend itself nicely to car ones!

bobc
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Postby bobc » Wed Sep 03, 2008 7:45 pm

Car batteries are designed to provide high currents for a short time for starting cars - as a power source for an EV they ain't so good because they can't take the deep cycling. However there are UPS, caravan and golf cart lead acids around which are much better, you just can't get 'em from Halfords.
I was intending to use a contact of my brother's in Rochdale who deals in these things, but I'm no expert & reckon I have a steep & potentially expensive learning curve ahead when my car conversion hits the road!
I do know that our greenpower school racing cars COMPLETELY flatten the car batteries in a race & they seem to do 4 or 5 races without a detectable (which would be 5% or so) drop in capacity. They are being discharged at a 2hr rate (i.e. somewhat slower than an road EV).
I believe that a suitable lead acid set, if it's not regularly discharged below, say 30%, should do several hundred cycles before starting to wimp out, maybe even a thousand.
The (very expensive) lithium cells will do thousands of cycles at much deeper discharges, and weigh a LOT less for the same energy capacity.

Delinquent
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Joined: Fri Feb 01, 2008 4:45 pm
Location: Southampton

Postby Delinquent » Wed Sep 03, 2008 8:05 pm

thanks bob, you have confirmed one of my fears, but then also maybe answered them too.

My EV will be used for very short runs only (6 miles per day total) the only reason I was looking for the higher capacity was a: for those occasional "jaunts" and b: because getting it to the charging point would be more involved than just pulling up each night. If however it were going to extend battery life considerably then it would be worthwhile.

The biggest downside to the car batteries is size - not due to lack of it, but due to "packaging" them. Double the number at half the size would be eminently more packable within the preferred structure design.

JonSpence
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Re: Lead Acid - the choices

Postby JonSpence » Thu Sep 04, 2008 7:25 am

I could be wrong but my understanding is that some of the active material in Pb(lead) starter batteries is replaced with material that conducts electricity better. Or to put it another way, they are optimised for short (very short) periods of high discharge rather than for maximum total discharge capacity.

I've little or no practical experience but have been following the subject for many years.

Some years ago I came upon this company.
http://www.batterymegastore.co.uk/cgi-b ... mmerce.cgi

I can't comment upon how good they are, but the price, capacity and size info of Pb batteries that they sell might be useful to you.

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EVguru
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Postby EVguru » Thu Sep 04, 2008 8:58 am

Modern starter batteries are not designed to be discharged more than about 15% on a regular basis. Leaving you lights on just a handful of times can damage the battery to the point that starting becomes marginal.

Leisure batteries are a much better choice, but I'd still treat them as a consumable item, maybe getting a year or so out of them. I used to buy them through the local independent motor factor, who was signed up to the http://www.a1motorstores.co.uk/ consortium. At one point I was getting 110Ah batteries for less than £40 each including vat.
Paul

http://www.compton.vispa.com/scirocco/
http://www.morini-mania.co.uk
http://www.compton.vispa.com/the_named

Delinquent
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Location: Southampton

Postby Delinquent » Thu Sep 04, 2008 9:16 am

Cheers guys, confirmation enough for me.

Paul, when you say leisure batteries, I assume you mean golf cart type packs? I've just phoned a place associated with that linked company, requested batteries suitable for leisure applications and got a resounding "huh?" :lol: Will have to try some more. £40 for 110Ah is superb, hopefully the lower Ah ones will still be below that! (wishful thinking probably)

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EVguru
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Postby EVguru » Thu Sep 04, 2008 9:25 am

Caravan batteries.
Paul

http://www.compton.vispa.com/scirocco/
http://www.morini-mania.co.uk
http://www.compton.vispa.com/the_named

Delinquent
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Joined: Fri Feb 01, 2008 4:45 pm
Location: Southampton

Postby Delinquent » Thu Sep 04, 2008 9:27 am

ahhh - will try again, cheers :)

Had a good look around that battery megastore, some interesting packs on there, but price isn't keen on a lot of them!

JonSpence
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Postby JonSpence » Thu Sep 04, 2008 9:46 am

Delinquent wrote:Cheers guys, confirmation enough for me.

Paul, when you say leisure batteries, I assume you mean golf cart type packs?


Usually it's taken to mean Caravan batteries, or in some cases light boat batteries. Semi deep cycle, but with expectations of some high current usage. I myself would include golf "cart" or mobility scooter types in this group, though they are really semi-traction batteries.

Golf cart batteries describes batteries for golf carts, just as fork lift and submarine batteries describe what they are used for.
More useful descriptions are.

Starting,
Leisure, Semi-traction.
Traction,
Deep cycle,

However like anything, the terms tend to be used more by those with some idea of what they are talking about.

Delinquent
Posts: 43
Joined: Fri Feb 01, 2008 4:45 pm
Location: Southampton

Postby Delinquent » Thu Sep 04, 2008 9:48 am

JonSpence wrote:However like anything, the terms tend to be used more by those with some idea of what they are talking about.


:lol: which definitely wouldn't include me. Only battery powered applications I've ever played with (other than cars) before have been NiCd NiMh or LiPo, so the lead acid is all a bit confusing. Getting there though with your guys help :)


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