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Battery heating
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This subject has often cropped up as an aside to other threads so I thought I'd start a new thread to find out what other peoples' views are on the subject.
SEC's spec sheet shows that a battery at 50c should deliver about 15% more energy than one at 20c which in turn is about 10% up on a battery at 10c, real world tests seem to give a wide variation of results ranging from much less of a temperture effect than that stated by SEC to considerably more. It's also widely accepted that heating batteries, and in particular fully discharging them whilst heating, will drastically shorten their useful life.
My view is that battery heating should be banned, this would be quite difficult to police but as a start simply insisting that all batteries in quarantine must be placed on the ground with no boxes, wrappings, etc, allowed would be a good start. I'm not saying prevent teams from keeping their batteries a bit above ambient on a very cold morning but anything to keep the playing field as level as possible would be better and would help improve the sustainability of Greenpower by teams not needing to replace batteries every season. -
then we would get into teams comlaining about having to remove their batteries form fittings they use on their cars. although it would definitely make moving aroung in quarintine easier and prevent a breach of the 'batteries must be carried singally' ruling
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T2.9 only seems to ban heating whilst batteries are in boxes or trolleys, presumably that's to prevent heating in quarantine.
The batteries we're using now contain very little acid compared to a flooded lead acid battery so the thermal capacity of them is low and they cool down quite quickly, my suggestion of no boxes or coverings in quarantine would mean even if they were heated to 50c prior to quarantine they'd be down close to ambient by the time the first battery change is due. -
Lead's specific thermal capacity is only 3% that of water, so if an AGM battery is approximately 12% acid (water) by weight the lead will only account for about 15-20% of the overall thermal capacity.
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I also think that battery heating should be banned mainly from a green and a levelling of speeds basis, although I don't think the issue is so bad with the new batteries as the gain is less. Keeping all of them on the ground for a couple of hours will level them off a bit (not sure how much) but probably won't stop teams heating them if there is a reasonable amount of heat left in them and you would have to ban insulating wraps. Instead an infrared thermometer could be used in quarantine to restrict batteries to <= 25 degrees with something like a (degreesC - 15) minute penalty if above, would require someone to spend some time doing this though. Random temperatures would add some more variation on a race to race basis.<br />
When we were looking at battery heating and insulation with the Yuassa's, I was astounded to see that water has over 30x the thermal capacity of lead .... -
I have a slightly iffy practice battery here so will do an experiment to see how quickly heat is lost from an unwrapped battery. The same battery showed an increase of 20% over unheated when tested a few weeks ago (probably why it's now a bit suspect!) so the advantage is still significant.
My feeling is that the majority of experienced teams do some degree of warming and a few are actively heating to 40c -50c or more. Everyone knows it's bad for the batteries and is turning them into expensive doorstops very quickly, but as long as heating is allowed nobody wants to blink first and give their rivals an advantage. As Terry says, a ban is good from a green standpoint and good for racing, I'd also add that it's good for your bank balance!
Maybe policing needn't be too difficult, a quick check as cars go onto the grid, under temperature go on the grid over temperature sit in the pit lane for 10 minutes. Similarly with quarantine, not allowed to leave if over temperature.
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We only saw about 10% improvement in our tests (above 18 degrees), although we are heating to less than 37 degrees. I would guess ours end up being between 25 and 30 during a race with the lower heat capacity and so the actual gain would be less than this. SEC do recommend below 40 degrees. We did take a couple up above 40degrees when a thermostat was set wrong, and there was a noticeable fizzing from them ... Note that the bats do improve by over 17% over their first 4 or so cycles, could that be some of your 20% ?.
I agree with the bank balance bit as well :) -
The battery I tested had been fairly well used, certainly more than four cycles, but the temperature was 50-55c so that would explain the higher output.
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Hold on! These new batteries are a bit iffy in my opinion and other comments made to me personally and on the blog following the final bear me out on this......they are not reliable, despite following manufacturers recommendations and we suffered from this! We don't heat the batteries up and they are put on their final charge in ambient temperature of about 20C. After that when loaded onto the van they are kept under a 12volt heated blanket. Once we arrive at the race location, they are placed in an insulated box to deter the early morning chill factor. Why would anyone want to insist that the batteries should be placed on a hard cold floor during quarantine? Come on, it's hard enough making these batteries last for their intended 1H 20m without adding more compromises. Just because some teams can't be bothered to make the effort to make an insulated box, why should the teams that do be penalised?
CC -
600? The spec sheet claims a little under 300 cycles for 12MRT batteries at 100% discharge, but there is no stated definition of what would be regarded as end of life performance; it might be as high as 80% of original capacity it could be as low as 50%. Battery life will also be drastically shortened by overdischarge, we have a pair that have gone down to 18v on a couple of occasions and are now maybe 5% down on our other batteries. I'll be happy if we get 30 cycles, that would still be a lot more than the Yuasa's but if they're heated to significantly above ambient I doubt they'd last more than 10 cycles.
My suggestion to ban heating wouldn't affect guarding against a cold night/morning, if you put a battery at 20c into quarantine at midday I can't see why it would cool down when ambient is likely to be in the range 18-25c, but it would prevent your rivals who have heated theirs to 40 or 50c having an advantage as theirs would certainly cool down.
A very rough and ready test gave the following. Battery at 41c cooled to 29c after 1 hour, 23c @ 2 hrs, 20c @ 3 hrs and 18c @ 4 hrs, that was in a shed at 12c. -
Point taken, although you may well find that an 18-25C a bit optimistic for a Final in October. We were lucky this year bit I seem to remember that for four years on the trot (from 2005) we had a frost on the morning of the Final. We didn't go in 2010 so I don't know what it was like.
CC -
Agreed, 18-25c would be pushing it for October, not exactly guaranteed for Alford in June either!
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I'd support the ending of battery heating if it makes the batteries last longer. Lead and acid are nasty enough without having to recycle more than necessary. It doesn't seem all that green to me to deliberately shorten the battery life for a gain, although 15% is attractive. and I can see why people do it.
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We had a test session today in fairly extreme conditions and I can confirm SEC's spec sheet which says the capacity at 0c will be 80% of the capacity at 20c! Our batteries had been in the trailer overnight so were slightly below freezing and even after the snow stopped it didn't get much warmer. Luckily the track we use is right next to the sea so was clear of snow.
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We intend to ensure our batteries are kept warm this season, by keeping them warm overnight before an early start, keeping them in insulated boxes in transit and in quarantine plus using an electric blanket during transit. I agree it's hard enough without the added cold battery issues. Doubt if we can keep them above 20 degrees though. Not sure caretakers cabin which is our only overnight storage possibility for the batteries ever reaches 20degrees, maybe we will have to buy him a fan heater and time switch. Keeping the batteries warm before an early start is our main problem.
Ashley -
Further to my previous message we have just tested our 12V electric blanket, not exactly capeable of heating anything, so no danger of heating the batteries in transit, it will probably prevent them from cooling down. I cannot see how without a big investment you could safely heat the batteries to 30 - 40 degrees then transport them, however, if your car is fully developed you may have the time to devote to battery heating.
