Lead Acid and Cold Weather

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GregsGarage
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Postby GregsGarage » Mon Oct 27, 2008 1:12 pm

Probably more to due with a warm battery delivering more power than a cold battery, so a warm battery will appear to have a higher state of charge. A battery produces current through a chemical reaction, heat will speed up any chemical reation. I suspect that running the battery at high temp will greatly shorten its life.
Greg Fordyce

Daewoo Matiz
http://www.evalbum.com/4191

JonSpence
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Postby JonSpence » Mon Oct 27, 2008 1:37 pm

I'm not sure that constantly running a PbA battery at a higher temperature will shorten it's life. Though a quick google implies that excessive temperatures will.
However a PbA battery that has been drained is at more risk of freezing, which can be terminal.
The same google remarked that discharge is a endothermic reaction, ie consumes heat.

By the way, I thought that padheaters recommended a 60W heater for each battery, not a 1KW heater. Other battery heaters seem to be in the 60-80W range.

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retepsnikrep
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Postby retepsnikrep » Mon Oct 27, 2008 3:57 pm

I've been through this a few times with a selection of EV's and I had a heated battery compartment for my last two EV which used lead acid and then early lithium.

Any EV should really have the cells in a weatherproof box in one secure location if possible, this should be pretty high on the design criteria from day 1 of any planned conversion IMO. If you have decent "Kingspan" insulated weatherproof box your don't need huge amounts of power to heat the batteries, certainly not 60W per battery.

The system you implement should be capabale of heating or cooling as reqd as all cells have an optimum temp, I aimed at 20-25C with lead and 25-30C with early lithium.

If you look at the pics in this link you will see I used a huge area for battery storage but I was able to keep the temp of that well controlled and power consumed max was about 80W for the entire thing using a disssembled old electric blanket and a habistat vivarium temp controller.

Even in sub zero temps batteries could be kept at my target levels without huge increase in power consumption.

http://www.solarvan.co.uk/ac1.htm

Shows clearly 'Kingspan' cell sandwhich

http://www.solarvan.co.uk/habistatpulse.pdf

Also when I was using lead acid I had this box which had kingspan underneath and an electric blanket under the cells. When needed during coldest periods I could also lower a kingspan cover/box over the whole unit, snug as a bug in a rug.

www.solarvan.co.uk/pbbox.jpg

Basically insulated boxes fitted with thermostatically controlled electric blankets/cooling fans is the solution IMHO.

And just found a photo of my first lithium insulated box here

www.solarvan.co.uk/oldlithiumbox.jpg

It would be a simple Picaxe project to make temp controller with relay or mosfet outputs to control a battery heating/cooling system. An 08M picaxe consumes a miniscule amount of power as well, and you could even have a 16x2 fancy lcd temp display if you wanted.

Bare project estimate <£10 + lcd £15.00

That could be a useful community project with someone perhaps knocking out a pcb :wink: I'm not volunteering at present :shock: too busy.
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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MB
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Postby MB » Thu Oct 30, 2008 1:40 pm

The G-Wiz has a battery heater that uses a very low wattage - I can't remember off the top of my head exactly what the wattage is but I'll check at the weekend when I have my car in bits again.

It runs off the 240v power supply but it works really well. As I keep my car on charge when it's not in use, this suits me absolutely fine.
My new book is out: The 2011 Electric Car Guide is available from Amazon and all good bookshops.


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