Re: [DML] Alternator upgrade troubles
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Re: [DML] Alternator upgrade troubles



There are several reasons why it doesn't make sense to increase the
size of an alternator in a car above a certain point. The belt that
drives it, the current carrying capacity of the wires, the capacity of
the battery, and the calculated load, just to name a few. Another
problem is that alternators are an "on or off" type of device. They
cannot modulate in response to load. A 180 amp alternator cannot
generate that kind of power at idle so it has a "set point" where it
won't charge until a certain RPM. Generally the lower the output the
lower the RPM that it can start charging. It is also a function of
load by the way of the voltage on the system. Think of the alternator
and the battery as complementary power sources. They work differently
but complement each other and need to be balanced to each other. An
electrical system is a SYSTEM and you cannot make radical changes by
swapping out one part without considering the system as a whole.
Unless you are running huge loads there is no need to oversize the
alternator. In theory the purpose of an alternator is to recharge the
battery after the starting cycle and to handle "base loads". The
battery is there to help with short, peak loads, like at idle with the
lights and the A/C on at a stop light for a short period of time.
Putting a smaller pulley on "fools" the alternator into thinking the
motor is running faster than it really is. It also has less surface
for the belt to grab so it could slip and you overspeed the alternator
which can cause premature failure. BTW a bigger alternator will also
generate more heat which reduces the current carrying capacity of the
wiring. Everything is a balance of trade-offs. Bigger is not always
better.
David Teitelbaum
vin 10757



--- In dmcnews@xxxxxxxxxxxxxxx, "Ryan Wright" <ryanpwright@...> wrote:
>
> Thanks Rob & others for your replies. This issue has been resolved
(see below).
> 
> 1. Why 180 amp? I had two concerns in wanting to upgade. The first was
> voltage drop at idle - the stock Motorola left my headlights dim at
> idle. The second concern was to provide power for a higher output
> stereo install.
> 








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