View Single Post
Old 01-13-2013, 12:43 PM   #2
Twilight Error
Going nowhere slowly
Twilight Error's Avatar
Joined: May 2002
Location: The Submarine Mines
Oddometer: 22,796
Originally Posted by Orangecicle View Post
Thinking of adding a 12 volt battery warmer to warm up the Shorai on cold starts. Below freezing starts are really difficult. Even turning on the key with all of the lights on and waiting 5 minutes does not seem to help. It takes three tries at a minimum, and sometimes many more. I thought that adding battery warmer would both warm the battery and act as a drain to help warm the battery thorugh use.

Here's the only battery warmer/blanket I can find that is DC powered:

Any thoughts?
I posted up an idea for a heater control circuit some time ago, possibly in The Garage. The basic idea is you'll want something that turns off when the bike is running, you don't want to overheat the battery if you can avoid it. You'll need:
Two momentary normal open switches, toggle or pushbutton - your choice. They'll be switching a relay coil (~120mA), so they doesn't need to be massive.
A latching relay. McMaster sells pn 1358t714, it will handle the heater draw nicely. McMaster also sells adhesive-backed silicone heaters in a variety of sizes, you may find one that will fit your battery better than the gate battery heater.
A switched power supply, this is driving a relay coil, so nearly anything thats alive with the key 'on' is acceptable.
A power supply that is only present when the regulator is alive. I'd tap into the diagnostic wire from the alternator if this was a BMW, perhaps KTM has something similar? In any case, it only has to drive a relay coil.

Connect the battery to one side of the switched circuit on the relay through a fuse, connect the heater to the other side and ground to the battery.

Connect the switched power lead to both momentary switches and from the other side of each momentary switch, connect to the relay coils. Ground the other side of the coils.

Connect the alive power directly to the other relay coil.

The starting sequence is this:
You get to the bike on a cold morning and put the key in the ignition, switch it to 'on'. Hit the momentary switch to actuate the relay and close the connection from the battery to the heater. The latching relay means the switch stays closed (and battery contunues to warm) until the other coil is energized to open the relay - no need to stand there and hold the switch, or remember to flip it back when the bike is started. Ideally, this happens when the motor is running and the heat circuit is no longer needed. If, for some reason, the bike does not start and you need to stop heating the battery, hit the other momentary switch (I'd bury it somewhere, under the seat perhaps, where it won't be confused with "on") to manually actuate the coil and open the heat circuit.
If you're all about the destination, take a fucking flight. - Frank Turner
Got brap, and twice as much fuel as you. - Akarob
Twilight Error is offline   Reply With Quote