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Old 11-26-2012, 02:41 PM   #104
Beastly Adventurer
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Joined: Aug 2006
Location: Carnation, WA USA
Oddometer: 1,345
I'm finding that this discussion is being repeated on a lot of threads across the ADVRider spectrum, from dirt bikes to street tourers. Manufacturers are implementing new technology faster than we are educating ourselves on how that technolgoy works, how we need to properly use it, and the consequences of new failure modes.

FI bikes have ECU's that require not only current but a consistent voltage for the ECU. This is why you can't just "jump it and go" with a depleted battery. The stator may provide enough power for the fuel pump, but without the minimum charge on the battry (or capacitor), the resulting voltage fluctuactions trip the ECU to failure mode and it shuts off to protect itself. To avoid these failure modes, either a battery or a capacitor will do, but the battery has to be in good condition (e.g. not recently totally discharged) and a properly sized capacitor needs to be fully charged.

With all accessories off (e.g. headlight), 9V is the minimum, but 12V is better, with the capacitor or battery providing the "depth" to produce a stable (non-fluctuating) current for the ECU. (This means that the kick-starter also needs some "depth" or "buffer" from an electrical reservoir to provide stable current to start the bike.)

One of the best discussions I've seen to date regarding the electrical requirements in somewhere in the middle of the WR250 Megathread. Bigger batteries and stronger alternators help avoid similar situations in modern automobiles, but the weight penalties for motorcycles result in compromises in the electrical system designs.

The aftermarket won't pick-up on the emergency starter concept due to the liability of "hurting" the ECU.

Spend some time reading other threads and see what has already been done before messing around with your bike. Google is your friend.

Lithium-Ion batteries are lighter than lead-acid batteries, but they seem to have less stable current properties when stressed. Also, voltage in lead-acid batteries drops off slowly with inadequate charging; Li-Ion drops like a step function. Lots of folks are using Li-Ion to save weight; some few have had problems. Others are carrying small Li-ion battery packs as backups for their lead-acid primary batteries when riding the far reaches of beyond. Still others are wiring-in capacitors to augment their factory electrical systems.

The bottom line - protect your bike's battery. With FI bikes, get in the habit of turning them off with the key ALL the time (assuming your bike has one). If you have to use the Kill Switch, get in the habit then turning off the key. Most of us don't use this procedure enough to make it a habit, but with FI / ECU sophistication come new REQUIREMENTS that need new riding habits.
1990 Honda NT-650 Hawk-GT

Never doubt that a small group of thoughtful, committed citizens can change the world;
indeed, it's the only thing that ever has. - Margaret Mead

Gryphon12 screwed with this post 11-26-2012 at 02:49 PM
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