How to pick a new alternator

[ladz]

How do you size a alternator the right way? and should the regulator be changed too? total amp draw

[Leadfoot]

well it all depend on the application and rpm of the engine. also how many accessories you have.

for the most part heres a quick brake down.

if you got a dual batterie set up and say a trailer I would go with a 80amp or 100amp alt.

if you got a single batterie set up and not to many accessories you can get away with a 40amp. alternator but you would be better of with a 60 amp or better.

as for the voltage regulator for the $15 ta $20 it not a bad idea to replace it to. specially if you see rust all over it. (if you aren't using an internal or single wire alt)

[bluef250]

Your alternator needs to be sized for the load. At a minimum take the sum of the amps of all the things that draw current that you have added - higher powered headlights, sound system amps, electric pumps, electric fans - then add 50 amps and you have an estimate of the size alternator you need. For mine 60 watt headlights - 10 amps and electric fan - 40 amps - would give 50 extra amps plus the 50 amps existing load, and the minimum size alternator would be about 100 amp. This is not an exact calculation. A 100 amp alternator working at 50 amps (50%) will be less stressed (and work longer) than a 50 amp alternator working full out (100%). When you upgrade you need to consider the power connection from the alternator to the battery. The OEM design is made to provide some cushion (like a shock absorber) between the battery and the alternator. So probably not a good idea to connect the alternator directly to battery. Also remember to provide a fuse, circuit breaker, or fusible link on the power feed in case the new alternator goes bad. This wire must also be sized for the alternator output. The 100 amp alternator needs about a 6 gauge wire. http://www.powerstream.com/Wire_Size.htm A larger wire size - 4 awg - would not hurt. The regulator tells the alternator to make power or not to make power and how much. Most of the newer alternators have and an internal regulator so the existing OEM unit is not needed.

[QC]

The life expectancy of an alternator that is putting out 100% of its rated capacity is about 30 seconds. The main reason that car makers went to 80-100 amp alternators is that at an idle a 100 amp alt. puts out about 20 amps, but a 40 amp alt. only puts out 5-10 amps. The output is directly related to RPM, so idleing in traffic with the air on and the radio blasting the bigger alt. might have a chance to keep up. When the alt. can't keep up the battery supplies the difference, so the reserve capacity of the battery is also important.