TBerk,

well I have to agree and disagree with you on one point! (hows that for a
Canadian response!)

I agree that the alternator output will drop when a load is applied but...

My alternator states a nominal output of 14V, I measured 14.1 or
thereabouts. With a 450W load, (2X100W headlights plus one 250W aux light)
the voltage only dropped to 13.8 - 13.9. All measurements done at the
battery, which is in the engine compartment in my van.

BTW, the two previously mentioned  loads are on separate supplies, 2 X 8
guage wires, the headlights using 2 40 amp relays (one for lows, one for
highs) and the aux light has a single 70 amp relay.

on 27/6/01 2:20 PM, T Berk at tberk@mindspring.com wrote:

> Good point Alister, just wanted to add-
>
> When calculating the output it is best not assume 14 volts, there is
> voltage drop and other reasons why you hardly ever actually _see_ 14.5 volts.
>
> Even so, if you calculate out (12v*90A)*.667 = 720.36 watts. Still a bunch.
>
> The other thing to consider is it takes mechanical energy to 'generate'
> the electricity. This means you will loose more HP to the Alt the higher
> amperage you choose.
>
> I also think if you RELAY all those lights and make the travel of
> electrons efficient around the car you will be fine with the 90A unit.
>
> hth,
> TBerk
>
>
> Alistair Bell wrote:
>>
>> A couple more points...
>>
>> Alternator output is listed on the alternator, for example my 90A Bosch has
>> this bit of code: N1-> 14V 34/90, which translates to 14 volts at 3400 rpm
>> (alternator speed, faster than crankshaft speed due to pulley size), and 90
>> Amps.
>>
>> But it is commonly assumed (i love that phrase) that maximum continious
>> alternator output is at best only 2/3 of their max rating.
>>
>> So with that in mind:
>>
>> - Dave C. will have 460W of light producing apparatus up front
>> - A 90 A alternator will continiously produce 0.667(90A*14W) = 840W
>>
>> Leaving 380W "spare"!
>>
>> (the 55A alternator will be able to produce 0.667(55A*14V) = 514W)
>>
>> Also remember that this doesn't take into consideration losses due to wiring
>> resistance etc.
>>
>> BTW Dave C., my alternator is currently (!) handling a 450W light load with
>> no
>> problems, don't have the killer stereo though.
>>
>> Alistair
>>