I've used a number of things over the years.
Insulation does a *lot* to reduce the power needed for heating/cooling.
If you have 1" of styrafoam on all sides of your batteries, and you
drive your EV every day, you probably won't need heaters. The waste heat
produced by battery resistance during driving and charging should be
sufficient to keep them warm.
If you live in a hot climate, you may actually have to COOL them.
Battery life is greatly reduced by high temperatures.
1. Plastic signboard with nichrome resistance wire threaded through the
"tunnels". No good. I got hot spots that melted the plastic in some
areas, and didn't provide enough heat in others.
2. Commercial battery heating "blanket", intended to wrap around an
ICE's 12v starting battery. They produce lots of heat, since they have
negligible insulation. A single 100w battery blanket was enough to heat
an entire battery box with six golf cart batteries and 1" of styrafoam
insulation. The blanket was flat, and stood on edge between the rows of
batteries (3 batteries, blanket between them, 3 batteries). This worked
pretty well with no thermostat (I just plugged it in when the battery
got cold, not plugged in when they were warm).
3. Electric blanket, taken apart, with the resistance wire spread out
around the battery box. The wire in modern electric blankets is actually
a 2-conductor cable, with a carbon loaded material between them to act
as a resistor. It automatically regulates its temperature at around
60-90 deg.F. Soil heating wire, and home floor heating wire have the
same construction.
This worked well, but you have to be *very* careful not to bend it
sharply or pinch it (like having a battery sit directly on it). If you
do, it will fail!
4. Nichrome resistance wire from an old electric blanket or battery
heating pad: The single wire can produce hot spots, so I removed it from
its packaging, and glued it to a sheet of aluminum the size of the floor
of my battery box. Use high-temperature silicone rubber; the type used
for sealing furnace ducts and flue pipes.
This worked, but was messy and lumpy. I installed them aluminum side up,
with a 1/2" thick sheet of styrafoam underneath it to act as a pad and
prevent pinching the wire anywhere. Over time, battery acid (these were
lead-acid flooded batteries) attacked the aluminum, though the heater
still worked.
5. My most recent design used nichrome heating wire from a battery
heating pad. I stuck it to an aluminum sheet with double-sided carpet
tape, then put the whole thing in a polyethylene bag (2 sheets,
heat-sealed at the edges). Then I potted it with a 2-part silicone
rubber compound that would set even without air inside the bag (I used
Dow Corning Sylgard 170). I mixed it, dumped it in the bag, and then
sandwiched it between two pieces of carpet padding and piled old
batteries on top to squeeze out the excess. That gave me an encapsulated
waterproof acid-proof heating pad to put in the bottom of my battery boxes.
--
Teaching children to program goes against the grain of modern education.
Just imagine the chaos if they learned to think logically, plan, create,
implement, test, and execute!
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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