Getting Wired

Text: Robert Smith • Photography: Robert Smith

Mom knew there was a problem when the ceiling fell in. A sharp winter frost had frozen and ruptured a water pipe in the loft above our under-heated English house, and when the thaw came, there was water everywhere. It was 1943, and Dad was otherwise occupied in the Royal Air Force. But when he returned from duty, he determined to avoid similar problems in the future. Parsimonious but enterprising, he insulated the exposed pipes, but also wrapped a single, fine nichrome wire through the insulation. Hooked up to a suitable electrical supply, the nichrome wire heated up, keeping the pipes warm. The same principle is at work in your electric vest...

I'm not suggesting you make your own heated clothing: my dad's experiment worked fine in the attic, but pipe insulation wrapped with bare wire wouldn't cut it on the road. A number of companies can supply heated clothing - Gerbing, Aerostich, BMW and many others - and a trip to your local bike store, or a quick survey of internet outlets will provide more than enough in the way of choices.

How it works
Though construction details vary, almost all heated clothing works on the same principle; that is, through the electrical heating of a nichrome wire embedded in the fabric. Nichrome, an alloy of 80 percent nickel and 20 percent chromium, has very high electrical resistance for a metal, so applying a suitable voltage to a length of nichrome wire will cause it to heat up. Knowing the applied voltage (nominally 12 volts for most motorcycles) and the amount of heat needed (the desired temperature increase) allows the clothing designer to specify the length and thickness of wire required. The thinner and/or shorter the wire, the more it will heat up, and vice versa.

Nichrome has another useful property: Its coefficient of electrical resistance is effectively independent of temperature, at least in the range we're interested in. So the electrical resistance (and therefore power consumption in watts) of an item of heated clothing will stay more or less the same regardless of how hot it gets.

Heated garments are usually constructed from fabrics that are embedded with nichrome wires. The wires connect to provide the appropriate electrical resistance, heating the garment, and terminate in a pair of wires that connect to your motorcycle's electrical system.

How to choose
Following the principle that keeping your body core warm is critical in warding off hypothermia, a heated vest is an obvious choice, and it's easily the most commonly worn heated winter wear. Choosing one is mostly a matter of materials, construction, styling - and watts. All other things being equal, the more watts, the warmer the vest will get - though there are other considerations. For example, Gerbing's heated vest liner is rated at 55 watts, the Aerostich Kanetsu vest at 45 watts, and the BMW heated vest at 42 watts. Fit is also important. The vest should be worn close to the body for best results, but with at least one layer underneath. You probably don't want to have to wash the vest too often.

How to install
On motorcycles with an external power outlet, installing an electric vest is pretty straightforward; if it has the right connector, you just plug it in. Aerostich heated gear, for example, is available with BMW/Triumph PAC-012, cigar lighter type, or SAE connectors. But there is another consideration: Does your motorcycle's electrical system have enough spare capacity?

Most modern bikes will cope with the extra load okay, as long as you haven't added too many other power-consuming accessories. Older motorcycles may be more of a problem. How can you tell?

First, you need to know the output of your bike's alternator. For example, my Triumph Sprint ST has a 300-watt unit. I have twin 60-watt headlights, a 6-watt pilot light, twin 6-watt taillights and two 2-watt panel lights. Allowing 50 watts for the ignition system and computer, that's a total of 192 watts. Adding a 55-watt electric vest would make it 247 watts, still OK. But I have heated grips as well, which typically draw around 30 watts, so a total of 277 watts. If I apply the brakes (2 x 21-watt brake lights), I'm up to 319 watts, which means I'm exceeding the alternator output and drawing down my battery. Not good.

Of course, I don't ride round with the brakes on, so most of the time I'm still under the alternator output. But if I wanted to fit a set of accessory driving lights, or add heated pant liners or socks, I'd be well over. Few things suck more than a flat battery on a cold night. That's why BMW's new R1200GS Adventure has an 800-watt alternator.

Don't know the power draw of your electric vest? You can calculate it with a multimeter. Switch the multimeter to the "ohms" scale, and hook the probes to the connector on the vest. Note the reading. From Ohm's Law, W=V2/R, where W=watts, V=volts and R=resistance in ohms. So the power draw in watts for a 12-volt system is 144/resistance. If your meter measures 3 ohms, the power draw is 48 watts.

What if your electrical system will cope with the power draw, but there's no power outlet? Aerostich also sells fused direct-to-battery connectors: or you can make your own hookup - but it must be properly fused. Even worse than a flat battery is an electrical fire!

I found a neat gizmo in an auto supply store that replaces the main fuse in my fusebox and has a fused power outlet built in. I wired this to an SAE quick-disconnect I bought at Radio Shack, and I use it both to supply power to my electric vest and for trickle-charging my battery. Total cost: less than $ 5. You must use some kind of quick-disconnect: Many's the time I've gotten off my bike without realizing I'm still plugged in!

In summary: heated clothing can make the difference between a miserable (and potentially dangerous) ride and a pleasant one. And it can extend your riding season by a couple of months in winter. What's not to like?