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Old 10-16-2012, 03:09 PM   #23
Twilight Error
Going nowhere slowly
 
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Joined: May 2002
Location: The Submarine Mines
Oddometer: 22,549
Quote:
Originally Posted by Twilight Error View Post
Hmmmmm....

I've been following the various LiIon battery threads with mild interest. I don't think the technology is ready for prime-time here in the Northeastern winter, where the temperatures don't often reach freezing and can sometimes dip below zero at night. I ride year-round (unless the roads are icy), so cold starting is a concern.

That said, my background in building LiIon batteries for spacecraft might be useful to those folks who want to use these batteries.
Space is a very unforgiving environment with some pretty extreme low temperatures (very dependent on the particular orbit). A battery failure will render your million-dollar spacecraft a million-dollar bit of space debris. Batteries are taken quite seriously and lots of work goes into making sure they work when they need to.

Every battery that left my shop had a common design feature: A heating element connected to directly to the battery through a thermostat. The heater was a simple resistive-film type unit, stuck to the Aluminum case with an appropriate adhesive. When the thermostat closed, the heater warmed up and kept the battery within its operating range - simple and reliable.
Why not do something similar with these batteries? We have pretty easy access to resistive heating elements - adhesive grip heaters aren't very different than the heaters I used to install. Depending on the surface of the battery case, you can probably stick the heaters directly to the battery. If you've got surface features like ribs or ridges, a thin Aluminum plate could be glued to the surface with a thermally conductive epoxy and the heaters stuck to that. Wire the heaters to the battery through a toggle switch. When you've got to warm the battery, simply flip the switch for a minute or two and then start the bike.
Okay, this is good until you forget to turn the heaters off and cook your battery.

So we modify the circuit a bit: a SPST latching relay is our friend here. For those who don't know the difference between a relay and a latching relay, a regular relay flips to its "normal" position when the coil current is removed. A latching relay stays in position until another signal is sent to the coil (internally reversing polarity) to flip the contacts to the other position. Any momentary pushbutton or toggle switch will actuate the latching relay to the closed position, sending current to the heaters. A 12v source present *after* the bike is running is needed to disengage the heaters. On my 1150, I'd use the blue testlead coming off the alternator - that only shows 12v when the alternator is spinning.
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