Ashford, almost any amp should have an input power rating somewhere,
although you may have to look inside the manual to find it. Otherwise,
there are just too many uncertainties to get a meaningful number just by
looking at output ratings.
However if you must, find the output rating in RMS watts (not peak or
'music' or anything like that; you may have to look in the manual for this
number too), divide by 12 volts, then _divide_ by about .4 (60% lost to
heat). For your 100 watt example, that's about 21 amps. Keep in mind
though that this is a maximum, you wouldn't expect it to draw this much all
the time. Minimum is probably only a few amps.
ISTR the Bosch/Fiesta alternator was rated 55 amps. However I suspect this
is a much more conservative rating than the rather optimistic 42 amps of the
Lucas.
'Normal' headlights draw about 5 amps each, the heater blower is probably
close to that.
Randall
> -----Original Message-----
>
> I've got the stock alternator or my 70 TR6. I'm thinking of upgrading
> the stereo to add an external amp to my CD player, however, I'm a bit
> worried that with my stock setup it's not such a good idea. I also lack
> almost all skills related to electrical so I'm turning to those my DC
> inclined. I was given this example and would like to know if this is a
> good rule of thumb?
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