Posted by The Older Gentleman on May 8, 2007, 1:27 pm
> >> It was surprising to see how much an alternator could load a motor
> >> down.
Which is why production racers have been known to "accidentally"
disconnect the alternator on some bikes, to get another horsepower or
two.
> >
> >Yes, I've seen that.
> >BTW it is the reason why so many bicyclists in The
> >Netherlands drive without a light. That tiny generator on their
> >front wheel loads their knees too much.
>
> Humans are about 1/10 th HP, IOW 75 watts ( except Henry and
> Thumper, of course ). That doesn't leave a whole lot to drive a light
> bulb whilst moving your ass down the road.
Heh.
--
BMW K1100LT 750SS CB400F CD250 Z650 SL125
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....
Posted by Rick Cortese on May 8, 2007, 3:18 pm
oldgeezer wrote:
> Albrecht via MotorcycleKB.com schreef:
> <snip>
>
>>There is an old wives tale that never seems to die. The tellers of OWT's say
>>that if you hook the
>>jumper cables from a fully charged car battery to a discharged motorcycle
>>battery, the car battery will quickly charge up the motorcycle battery
>>because it has so much more "juice" available.
>>
>>In truth, a fully charged car battery at rest may only be putting out about
>>12.8 volts.
>>
>>If the motorcycle battery is discharged down to 12 volts, the difference is
>>only 0.8 volts. It would take
>>about 20 hours to charge up a 16 ampere hour motorcycle battery from a car
>>battery.
>>
>>You could slow charge the motorcycle battery faster using a car charger on
>>the 2 to 3 amp setting.
>
>
> Your message that it takes longer than you'd expect is correct.... It
> does.
> But the arithmetic you use is incorrect.
>
> You are talking about two different things. Voltage (V) and capacity:
> Ampere*hours (Ah).
>
> The amount of Amps flowing into the 'empty' battery depends on two
> things:
> The voltage difference (your 0.8V) and the resistance of the circuit
> (jumper cables,
> plus internal resistance of the dead battery, plus the internal
> resistance of the car battery).
I do it myself, all the time, but...
I think one thing to caution the original poster about is the amount of
current a truck battery can deliver.
Whenever someone says they are going to jump something with a car
battery, including another car, I just automatically say to myself "Oh,
you mean you are going to hook up a 500 Amp charger to you dead
vehicle." I know all things are not equal, a battery charger typically
puts out much higher voltage then a fully charged lead/acid battery.
Since the problem started with leaving his lights on I think we can
assume the battery may be down to zero volts. This would shift your
calculations a bit towards the high side of safe. As one poster pointed
out, don't start the truck or its alternator will be putting out maybe
100 amps worth of ~15V DC which would shift the calculations even more
in favor of cooking the battery.
Rick
Posted by The Older Gentleman on May 8, 2007, 4:01 pm
> I think one thing to caution the original poster about is the amount of
> current a truck battery can deliver.
A poster on ukrm, a couple of years ago, had a flat battery on his
airhead BMW, and got a jump-start from a truck.
He mentioned that the bike started instantly, and then the rest of us
howled: "Christ! Trucks have 24v electrics!!!"
It must have been like one of those scenes in ER.
CLEAR! ZZzzzzaaappp!
Amazingly, the only thing it fried was the quartz clock.
--
BMW K1100LT 750SS CB400F CD250 Z650 SL125
GAGARPHOF#30 GHPOTHUF#1 BOTAFOT#60 ANORAK#06 YTC#3
BOF#30 WUSS#5 The bells, the bells.....
Posted by oldgeezer on May 8, 2007, 6:51 pm
The Older Gentleman schreef:
> A poster on ukrm, a couple of years ago, had a flat battery on his
> airhead BMW, and got a jump-start from a truck.
> He mentioned that the bike started instantly, and then the rest of us
> howled: "Christ! Trucks have 24v electrics!!!"
And the truck driver had to push his truck all the way home. ;-)
Rob.
Posted by Mike W. on May 7, 2007, 7:18 pm
On 7 May 2007 13:56:39 -0700, dzaremba@gmail.com wrote:
>If so, is the procedure any different than that for jump starting a
>dead car battery?
Your voltage regulation gear on the bike is sized to take care of the
excess electrons created by it's on-board charging system. If you use a
larger vehicle to jump it like a car, do NOT start the vehicle. Now your VR
has to sink all those many more electrons produced by the larger charging
system on the car. If you just use the battery, you should be fine as
should your VR since the battery isn't at a voltage that's high enough to
cause regulation. Good luck.
Mike
--
Mike W.
96 XR400
99 KZ1000P
70 CT70
71 KG 100 (Hodaka-powered)
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> >> down.