Monday, May 28, 2012

Advice on Taking Jumper Cables

I saw some advice for motorcycle travelling: "Take along a set of jumper cables".

The reason you need jumper cables, is in case the battery is discharged at some time during the trip. You could use the jumper cables (and a good battery) to get the motorcycle started again.

Years ago, motorcycles started more unpredictably, and we used to bump start (or push start) them, or use a kick start lever if equipped, or at times use jumper cables.  Today the batteries are better, and with fuel injection, the bikes seem to start every time, with only a few rotations.  So its tempting to ignore the possibility of no-start scenario while on a trip.

On this trip, the need for jumper cables is twice as likely with two bikes.  And we just happen to have a second bike to jumpstart from. Also, both bikes have batteries over 5 years old. Another reason we may end up with a weak battery is if we use them to charge our electronic devices.  Finally, while the Vulcan is hard to push start, with the Burgman it is simply impossible.  Of course neither bike has a kick start. With fuel injection, I'm not sure kick starting is even possible any more.

There are times you are most likely to need jumper cables.  One is when you go to start the bike in the morning, so in this case you will be in a campsite or at a motel.  Another is if you park your bike during the day, and leave the lights on.  Although you almost never need to recharge the battery on the side of the road, this can happen if your alternator has stopped working, and within a few hours your battery will gradually run down until the bike stops running.

You should check how accessible the batteries on each bike are.  On the Burgman 400, you need to open the glove compartment (no tools needed) and then use a large Phillips screwdriver to undo the battery cover.  Once that's off, the battery terminals are available for attaching clamps.  On the Vulcan, you need to remove the seat (key required), then the same large Phillips screwdriver to remove the two screws holding the tool tray, to access the battery.

If you are not successful with jumper cables, hopefully you did not botch the jump start so badly that both machines are now fried. If one bike is still good, use the same screwdriver to remove the cables from the bad battery, pull  it out and use the running machine to take it to be replaced or recharged.

Figure out a good place to store the jumper cables. We only need one set of cables, and I will use the Vulcan tool tray.  This tray is empty because I carry all the tools in  more convenient location where I don't have to remove the luggage to get at them. Car cables are simply too large and probably won't work, so I have a set of smaller cables that may or may not work, but at least they fit the space.  It makes sense to put the jumper cables in the underseat tool tray, because if we need them, we will also be needing to access the battery right below the tray.

While I was fiddling around in the garage, I discovered another SAE pigtail plug wiring harness for my motorcycle. It was brand new, the polarity was correct, and even better, it had a cover for the SAE plug so that it would not touch any metal bits, and keep it shiny and clean.  So I removed my old resoldered harness from my previous blog and replaced it with this new one.  That's the fourth new motorcycle part I needed, that I found around the house in the last two weeks, that I didn't even know I had.

Picture: From the Hell's Tunas Motorcycle Club picture gallery
Jump starting a bike, looks like a flashback to the seventies.


  1. I had the idea that just taking a spare battery might work well. If possible, something that would fit both bikes, possibly the gel type, "no acid spillage". I think the battery would not take more space than the jump cables. As for making a long road trip on five year old batteries, you're braver than me.

  2. You write, 'With fuel injection, I'm not sure kick starting is even possible any more.'

    Not only possible, but actually available on a number of current retro bikes.

    For example, Royal Enfield's current 'Classic' models have both EFI and a kicker ...

    Suzuki's TU250X is an oddball, in that the case has a provision for a kicker (even a cast-in label for it) but is shipped without a kicker installed. But perhaps the casting is simply a leftover from the old ST250 carburetor days.

    The problem is that, if the battery is so flat that it cannot power up the ignition and the fuel pump, kicking the bike to life may well be an insurmountable challenge ... LOL!

    Anyhow ... in the interests of conserving space and weight, it might be worthwhile to consider a shorter set of cables in a smaller gauge. Normally, jumper cables are used to draw starting current from the donor bike, currents can run in excess of 100 amps, so stiff heavy cables are the order of the day.

    Whereas what's actually required (especially for an EFI bike) is simply to bring the battery voltage for the lame bike up to where it can power up the pump and spin the engine for a couple of cycles.

    It'd be interesting to do the math to see what gauge would be needed if the cables were used only to support charging of the lame battery for five minutes, rather than actually feeding its starter motor ;-)

    1. Very interesting that they are making fuel injected bikes with kick starters.

      Well, I have not done the math, but 10 gauge cables seem to be used in commercial products for bikes, meaning there is probably some excess capacity there for starting Harleys and such. I went with 12 gauge, so that it would fit the tool kit. I suspect that I could get away with the smaller wire to start the Burgman if I let the weak battery charge off the jumper cable for about 10 minutes before pressing the starter. Hopefully only a few seconds will be enough to get the motor running.

    2. Oops, forgot to mention I went to Canadian tire and made up a set of custom jumper cables with 12 gauge wire and big copper "battery tester" clamps. It just fits the tool tray.

  3. You write, 'I ... made up a set of custom jumper cables with 12 gauge wire.'

    I couldn't find the specification in a quick search, but would guess that your Vulcan's alternator pumps out something in the order of 30-40 amps - not significantly more than the ampacity of 12 gauge wire ...

    And, although you'd risk softening the insulation by pumping starting current through those wires, the 'fusing current' for 12 gauge is well in excess of 200 amps. Just pack some vinyl electrician's tape to patch any damage ;-)