Re: [ST] jump starts

[Neil Lindsey <neillindsey@xxxxxxx>]

Whoa gang,

I guess it's time for a basic electricity tutorial.

So what if motorcycle starter doesn't draw the same current as a car's
starter?  Brian, you are correct that that it won't likely drain the car's
battery if the car's engine is off, but who cares? ...... we were talking
about potential damage to the motorcycle  ---- can't see it!

Cranking current is delivered by the car battery (an electrical storage
device), not by the alternator.  The reserve current capability of any car
battery FAR exceeds the current delivering capability of that vehicle's
alternator/charging system.  That's why it takes time to re-charge a dead
battery.  A charger simply cannot deliver the amperage required (besides the
battery would overheat).

It is an electrical LOAD, such as the motorcycle starter, that DRAWS current
from the electrical source.  Current is not PUSHED into the load.  The
electrical resistance of the load determines how much current it draws, and
this does not change if the car's motor is running, nor will it change the
current drawn by any other electrical device on the motorcycle.

I thought about the fact that once both vehicles are running (assuming a
successful jump start) there are now TWO regulators involved (connected in
parallel), but I do not believe that this would cause a problem either.
Ultimately it is the voltage at the battery post that determines if the
regulators are going to want to charge the battery and they do this by
raising that voltage, which causes the battery to draw more current.  I
can't see how that charging voltage would hurt 'the other' regulator,
because current only flows OUT of a regulator, not the reverse.

Bottom line -- motorcycles are NOT any different than cars in this regard

Regards,
Neil

PS.  I'm not an EE either, but I have a Diploma in Electronics Technology,
not that it it should be required to understand the basic laws of
electricity

original message:

>>Date: Fri, 30 May 2003 00:24:13 -0500
>>From: "Brian D ." <brd@xxxxxxx>
>>Subject: Re: [ST] jump starts

>On Thu, May 29, 2003 at 09:18:53PM -0700, Blake Sobiloff wrote:
>> On Thursday, May 29, 2003, at 08:49  PM, Richard D'Amours wrote:
>> > as long as you jump start with the car
>> > engine off...you will be ok.
>>
>> OK, what's up with the "leave the car engine off" advice? I've never
>> had to jump-start a motorcycle, but have had the opportunity to
>> jump-start a few cars, with my car. I seem to recall that the "donor"
>> vehicle was supposed to remain running, the theory being that the
>> running vehicle's alternator would ensure that there was enough juice
>> supplied to handle the drain of both vehicles (i.e. you don't want to
>> kill the donor vehicle's battery, too!).
>>
>> What makes motorcycles different?

>First, a motorcycle starter doesn't need as many cranking amps to turn
>over the smaller motor.  This also means that jumping a bike won't risk
>draining the car's battery with the engine off.

>Second, car alternators put out high amperage.  The ST has a lot at 40A
>(IIRC), but cars can put out more than that and fry the bike's
>electrics.

>Laters,
>Brian<--not an EE by any stretch

>Euless, TX
>'97 VFR 750 (red, of course)
>'99 Sprint ST(black, RIP)



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