Z-Cred Heated Jumper

What you need:

• 2 metres transparent polypipe tubing or similar (£0.88 @ B&Q)
  for ponds, home brew, etc about 5mm diameter
• 2 metres of resistive (constantan) wire (about £5 for 10m at Maplins)
  special wire that gets hot with electricity
• 1 old sweatshirt
• needle and thread
• solder and iron
• zip ties
• electric cable and socket assembly

My jumper used 2 metres of resistive wire (9.4 ohms total) which gives about 20 watts at the 14 volts the alternator puts out to charge the battery. Don't use less than 2 metres of wire (~10 ohms) or it will get too hot and melt the polypipe! On a cold night's ride from london to oxford in mid jan it worked fine and you wouldn't want it any hotter. The longer the wire you use, the cooler it will get.

Instructions:

1. Cut 2 metres of resistive wire and 1.95 metres of polypipe. Thread the wire through the polypipe. It helps to hold the polypipe with your toes and thread the straightened wire in vertically. After about 1.5 metres you will need to swing the pipe around your head to get it to thread in the rest of the way (mind the missus).

2. With the bits of wire exposed, solder the ends of the normal electric cable to it (this is the wire that will run to the bike's battery - any flexible mains cable is good).
3. Push the soldered joints into the polypipe so everything is insulated.
4. bring the two ends of the polypipe together, fold the electric cable over and zip tie them together. This means that if the cable is yanked there is no pull on the soldered joints, just on the cable sheaf and polypipe. Try not to make it too bulky here as it may feel uncomfy later.

5. Turn your sweatshirt inside out and tape the assembly in place as in the final picture. Remember to choose which side you want the electric cable to emerge from carefully as it swaps over when you turn the sweatshirt the right way round. Stitch the zip-tied bit securely in place and then stitch around the polypipe (not through it).
6. All you need to do now is fasten some kind of socket to your bike's battery and some kind of plug to the end of the electric cable. I used a pc power wire and the socket from the back of an old pc as they were handy, but anything will do. If you choose a shaver plug or similar, be careful that you arrange things so that nobody will plug it into the mains and blow themselves up! Similarly be careful of having exposed metal prongs on the socket side as the bike's battery will happily cause serious mischief too, if shorted out!
7. Finished! You can now enjoy toasty riding for a tiny fraction of the cost of a commercial heated waistcoat :o)

This is the jumper inside out, apologies for the quality but you get the idea!

Extra stuff:

§ Safety conscious types may like to add a switch and a fuse of some sort. I'd suggest a 2 amp fuse and inline fuse holder from Maplins (probably about £2).

§ The poly pipe serves two purposes. Firstly it insulates the resistive wire and secondly it gives it a tough rigidish structure as the resistive wire fatigues quite quickly if bent back and forth or too sharply.

§ If you want to make it cooler, make it longer. If you make it shorter than 2 metres or less than ~10 ohms you will burn yourself.

§ If you want to make it hotter then add a second run of 2 metres and join it in parallel (side by side, not one after the other).

Feel free to make/suggest your own improvements to these ideas. I've made heated grips using this resistive wire (and heated insoles to prove a point) and they work fine. Let me know if you come up with something else or send me a picture if you make one. I will be trialling mine properly at the 2006 Dragon Rally :o)

phill jackson

phillipdj@yahoo.co.uk

EXTRA NOTE - NOVEMBER 2006

After using the jumper at the 2006 Dragon Rally I decided that the jumper needs two runs of wire in parallel as I suggested in the extra stuff. If you do this and have a fuse you will need to double the rating of the fuse. This doesn't make the temperature higher, but gives more heat.