considerations when making a diy controller for heated motorcycle gear - Page 1
Forum section: electronics / projects

author: KTP
author_rank: Frequent Contributor
timestamp: November 13, 2011, 01:52:18 pm
content: We just purchased some Gerbing heated gear for riding our WR250Rs in the late fall when it is brrr cold in the winter.I was considering making my own digital controller for the jacket and gloves because I didn't particularly like the $99 Gerbing controller with two pots. I figure it is probably just a 555/mosfet circuit inside, and didn't look very rugged or waterproof. I would prefer a digitally adjustable heat controller with a membrane keypad on the handlebar. I already happen to have several 4 key membrane keypads with 3M stickyback.The jacket draws 7.6 amps at 12V and the gloves draw 2.2 amps (pair) at 12V.I was thinking of something simple, like a MSP430 PWM'ing a pair of low RDS-on mosfets with a gate driver circuit to quickly charge the large gate capacitance. I don't have a lot of experience with heating controllers though, and would like opinions on things I may need to consider. The biggest problem may be the inductance of all of that wire in the jacket with the 7.6 amps flowing through the wiring and the di/dt from the fast switching. Should I worry much about accidentally creating a loop antenna system? I wonder if Gerbing's supposed 555 circuit has any problems or underwent CE testing...

author: Rufus
author_rank: Super Contributor
timestamp: November 13, 2011, 03:55:15 pm
content: Quote from: KTP on November 13, 2011, 01:52:18 pmThe thermal time constant of your heaters is going to be measured in seconds. You could PWM at a fraction of a Hz so losses from slow switching are irrelevant. A heavy pulsing load on the bike electrics might be an issue.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: November 13, 2011, 04:00:13 pm
content: First and most important thing to consider is fail to safety. ANY fault should switch off the system other wise you could end up very toasty.

author: Zyvek
author_rank: Regular Contributor
timestamp: November 13, 2011, 10:03:56 pm
content: You might find this of interest:http://www.warmnsafe.com/Circuit_Analysis.pdfI have one of their products for heated grips, and I've been thinking about making my own for a heated vest as well.

author: KTP
author_rank: Frequent Contributor
timestamp: November 13, 2011, 10:51:57 pm
content: Thanks Zyvek! It looks like they are just using comparitors as a simple oscillators. I would guess one for the base frequency and one to modulate it. Nowadays a microcontroller would be a smaller part count. I may calculate from the schematic and component values what base frequency they are using for the PWM.What I didn't want to do by accident is PWM at a high frequency (so no audible buzz) and create an unwanted transmitter from the loops of wire in the jacket on some harmonic of the PWM base frequency. Perhaps I am just being paranoid, but the other suggest of just doing low HZ on/off to control the heat sounds good too. There are times I want full power to the jacket and gloves, and they can handle full on without burning up or burning the user. The motorcycle has a 350 watt alternator, so all good there too. Sounds as simple as an MSP430 flipping a medium size TO220 mosfet on/off at a few HZ would fit the bill nicely. The only downside would be a slight inefficiency at low heat cycles due to higher peak currents in the wire from the battery causing higher I^2 R losses vs a much higher PWM frequency at the same duty cycle (the wire inductance would cause the shorter/faster pulses to be much less peak current and thus have lower losses in the non-jacket wiring....if I have thought this through correctly).

author: Zyvek
author_rank: Regular Contributor
timestamp: November 15, 2011, 12:39:51 am
content: One thing I've always wanted to address was offsetting the current going to the throttle grip vs the clutch grip, since the bar end on the clutch side soaks up heat it's not a warm as the throttle side. PWM I'm hoping will help on my smaller bikes that don't have a lot of spare amps left over....