Date: Sat, 31 Oct 1998 13:09:05 GMT
From: (Eric Graudins)
Subject: BMW: DIY Heated Handgrips. (Longish)

LO presidents.
This is similar to what I posted on an Oz motorcycle newsgroup a while ago. It may be relevant to those who are heading towards winter, unlike us down here in Oz who are getting ready for the barbecue season. It is submitted in the spirit of Pirsig, who also can't see the sense is spending a couple of hundred dollars when a couple will do.

A significant development from the Oz Deep South LoTech Motorcycle Research Labs.

Its starting to get cold here in Tassie. In a cuppla weeks its going to be bloody cold. And my hands are going to get icy cold, because some mongrel decided that he needed my Spidi winter gauntlets more than I did. This morally bankrupt cretin knocked them off out of my helmet which I had left dangling on the rear indicator of the mighty Chicken Wing. Probably had a spot of gardening to do. (This wouldn't happen now - I can whack them into one of the wonderful glove boxes on the RT ! )

I rode home that night with my mind filled with many thoughts:

1.) The hearty discussion that would take place if I ever found the aforesaid mongrel

2.) How I had looked at other people riding without gloves, and thought what dickheads they were, and pondered the fact that I was doing exactly the same thing

3.) Thought about getting some of those wonderful heated handgrips, so that I could use my lighter gloves all year round. - Nah - they are more expensive that another pair of gloves. Then, EUREKA!!! The light globes went off in my head - (or was it a speed camera - It wasn't- its been 3 weeks now, and no ticket.)

4.) I realised that heated handgrips are just a bit of resistance wire connected to the battery, and wound round the handgrips and coated with rubber. For this they charge over nearly $200.00

Upon checking the trusty Dick Smith catalog, (and no, I wasn't still riding at this stage) I found that item W-3200 is 4 metres of Cuprothal resistance wire with a resistance of 6 ohms per metre. For this they charge $1.20.

2 metres of this wound round each handgrip would give about 12 watts of heat. After application of the she'll be right rule, and a couple of stubbies (13oz bottles of beer) , I was confident that this was exactly the right amount of heating required. Total current drain should be about 2 amps.

To cut a long story short - it worked beautifully with the resistances connected in parallel across the battery. However, It's a bit too warm. I've got to turn it off after about 5 minutes. (see! you can't always rely on the she'll be right rule)

I then added a 5 ohm 10watt resistor in series with the aforementioned resistance wires. The temperature was now beautiful.

I then added a switch to bypass the resistor for those tiimes that it is really cold, and you need the extra heat in the grips.

I drilled a hole into the handlebars near the headstem so that I could run the wiring through the handlebars, and out the ends. This was to solve the problem of connection to the heating element on the twistgrip. (Yeah, I know I've weakened the bars, and I know that someone an engineering degree will come back at me with detailed discussions of stress risers, and calculations proving that the handlebars now have less strength than a wet tissue. I've applied the partly discredited "she'll be right" rule again, and decided that the risk is acceptable. Anyway, it's been working on the CX for nearly 2 years now)

My handgrips are the black foamy touring ones, with a chrome knob on the end. The soft foam allows the resistance wire to be wound tightly around the grips. It digs into the foam, and does not slide laterally across the grip.

I used twin core wire running through the handlebars. I removed the chrome cap on each handgrip. The power wires were fed through a hole drilled near the headstem, and out each end of the bars. I ran twin core wire with +ve and -ve, rather than trying to find an earth for the heating element on the handgrip. I ran the +ve wire under the foam, so that it came out on the inner side of the handgrip. One end of the resistance wire was tied in a rolling hitch and wound in a spiral around the handgrip, at a spacing of about 6mm. 2 metres of wire will reach the entire width of the handgrip, where it was again hitched I soldered the first couple of turns together so it would not unroll, and also soldered the power leads to each end of the resistance wire. I glued the chrome end tips back on with silastic.

P.S. don't forget to put on some kind of switch, and a 5 amp fuse.

DISCLAIMER: This information pure fantasy of course. I would never suggest that anyone ever actually put it into practice, and deprive motorcycle accessory manufacturers of much needed revenue. Things like this are far too complex for the average person to undertake without professional assistance. Your bike could explode, catch fire, go rusty, or all three. I only thought of it because my brain has been burned out by the harsh rays of the sun caused by the huge hole in the ozone layer directly above us. Have pity on me.

Eric Graudins
Tasmania, Australia.
K100RT CX500 Ulysses #12359 (Oz Old Farts Bike Club)
AND on the 8th day, the lord said "OK Murphy, you can take over now"