Re: Battery Heating Idea

[Eric Jelinski <jelinski@idirect.com>]

Not sure if this message got sent out as I never saw it come back....
somebody wrote.....
>+20 during the drive.  Moral of the story - have to do more work on 
>sealing the front battery compartment, hopefully before it gets cold 
>here.  
snip
>It has been a very mild winter here so far, haven't gotten my winter 
>coat out of the closet yet.

I've been thinking and experimenting with this issue for over 4 years and
here's my crude conclusions...
Battery temperature depends on a lot of things like:
- ambient temperature,
- wind,
- how well the battery compartment is sealed,
- how well insulated,
- how batteries are spaced in the compartment,
- whether battery compartment is inside the cabin or outside the cabin,
- quantity and temperature of air blown across battery to remove hydrogen,
- how deeply discharged,
- charge management upon recharge,
- age of batteries, internal resistance/charge acceptance,
- type of battery (internal resistance),
- discharge current,  I2R,
- charge current,  I2R also,
- whether charging or equalizing,
In terms of ev batteries, the first priority is the battery charging
algorithm along with temperature compensationa and the protective limits to
prevent both overcharging and a temperature excursion.
With the current technology of just using heating elements the battery
temperature will float up or down (usually up) based on the above list of
items that affect the battery temmperature.
Around where I am, on the 44 parallel, in the great lakes region, the
ambient temperature can vary from 30 deg C in summer to 0 C (for an average
winter), but oops there it went to -20 for about a week this January., and
it will jump around between 0 and -20 for February, and then jump bewteen
15 to 30 in the summer.   What temperature do we want our batteries to be
at, and how do we maintain that ideal battery temperature of  +25 deg C
(most of the test point data for batteriey performance)?
The ideal method of battery temperature would be a device that heats when
they get cold and cools the batteries when they get hot.... but that (a
heat pump) is way too expensive and elaborate.  So.... what do I recommend:
- make your insulation easily removeable ,
- use the battery blankets sparingly,  you may not need any battery heaters,
- ventilate adequately,
- use temperature compensation on the chargers,
- use separate chargers for each battery compartment.  This might mean
having a 36 volt charger for the 6pack up front and eg. a 72 volt for the
rear part of the pack... or go to something like the Guest Chargepro's.
- di/dv shut off,  if you can get your hands on a reasonable priced control.
- a timer that does an ultimate shutoff of the charging. You read the
e-meter, do a bit of math and set the timer.
- drive your ev everyday more or less the same distance helps smooth the
battery temperature.
Sorry for being long winded, but I think necessary to discuss in detail to
sort out this problem.  What works for one may not work for the next guy
and it depends on a lot of things.
regards,   
Eric Jelinski
Durham Electric Wheels
# 2 Waverley Road
Bowmanville, Ontario, Canada, L1C 1k7
phone  905-623-6653   fax 905-623-7530
e-mail  jelinski@idirect.com

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