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?