The Delicious Smell of Burning Fingers

Yesterday I completed the power pack for the handle grips. Today I gave it a bit of a bench test. One of my assertions in the design was that I did not need the 12V buck converter, that the ~11V – ~15.5V output of the 4S battery post BMS was sufficiently close to the 12V Lead Acid + Alternator these were designed for (which would normally have a charging voltage of about 13.8V).

Lets see, let them run for half hour, whip out the FLIR. Hmm. 140C. That’s normal for your hands, right?

Now, the handlegrips have a 3-position switch (OFF/LOW/HIGH). I suspect that the High puts 2 coils in parallel, and Low puts them in series. But I’m not sure, it might be just 1 coil versus 2 coils.

The multi-meter suggests that HIGH is 5.9 Ohms, and LOW is 7.1 Ohms. Hmm. So its not as simple as that.

Unloaded, full charge, the output from my pack is 16.3V. Measured at the load (so post drop in wire) we see 16.0V on LO, and 15.9V on HIGH.

Doing a little math, on the LO (7.1Ohm) setting, we are drawing 36W. On the HI setting we are drawing 43W.

OK, so its more or less inline with what I was thinking. Once these are installed on steel handlebars there is a lot of heat sinking, that loss plus the colder outdoor plus the wind will probably drop these to 60C or so, and, with my gloves on, no burning. Or so I predict.

What do you think?

I predict the following

View Results

Loading ... Loading …






4 Responses to “The Delicious Smell of Burning Fingers”

  1. Jayme Snyder

    My second best friend in the whole wide world was showing me the heated usb charged wirelessly controlled insoles he received for Christmas…
    He was mentioning the opposite problem, the controller pack goes up past 60*C but thankfully the insoles don’t actually get that hot.
    I was just mortified about the idea of having a LiPo pack under feet intending to pedal through slushy salty guck.
    You could stick a resettable thermal fuse inline in the handle bar similar to what’s commonly found in a microwave oven, furnace, dryer etc.
    The right value fuse will have a modulating effect that can stop them from overheating in your garage.

    1. db

      i cannot imagine a universe where I would want my feed surounded by something i couldn’t get off quickly, on top of something with a lipo pack in it getting compressed and moved around. It sounds like a recipe for learning to tap dance rapidly.

  2. Mike Shrake

    How many minutes do you predict these will operate on hi or low before they stop working?

    1. db

      so far, on high, its run for more than 2 hours w/o catching fire, failing, etc. There’s a bit of a plasticy/rubbery/china electronics smell tho!

      when on the bike, at ~ -5C external, w/ my gloves on, i cannot keep my hands on it on high, so that is out.
      On low, its acceptable but warm through the gloves.

      I think its just nichrome wire in there, no active electronics.

      I’m considering putting a PWM on it tho to modulate the power a bit.

Leave a Reply

Your email address will not be published. Required fields are marked *