What Size Alternator Do I Need?

[William from NOLA]

What Size Alternator Do I Need?
by CarGodz/ Michael


This is a question that seems to be arising more and more these days with the addition of larger (more powerful) amplifiers.

1)First you will need to look at the amplifier(s) themselves and their fuse values (total).
2)Next you will be required to know the amperage rating of your stock alternator

Most typical stock alternators use a value of 70-80%, meaning that the vehicles maximum load is 70-80% used under vehicle usage.
Now we take the alternators amperage rating and multiply an average of 75% (you may use 80% if you wish to allow yourself an added protection of power). Now take that number and add the total fuse values of the amplifier(s) and the final figure will be how much power you will require from an alternator.

Side Note #1: The addition of added aftermarket items that will require power will increase your amperage load and you should judge accordingly. Items such as Video Monitors, On Board Gaming Systems, DVD Players, Lighting, ETC. may not require a huge amount of power alone, but added with together or with an aftermarket audio system may have a larger load than expected. If you are planning (or even thinking about) the additional items afore mentioned then you may wish to just add the total calculated fuse value(s) to the stock 100% value of the alternator.

Side Note #2: If you are currently only adding a single amp for subwoofer(s) and are planning (or even thinking about) the additional amplifier(s) for highs, midrange, components, etc. then please estimate the amount of power required and add to the total fuse value(s) to save yourself the headache, time, and money of having to upgrade your alternator again in the future.

Examples:
Example #1
Adding a single amplifier with (2) 40 amp fuses
Stock alternator rated at 90amps
Fuse values total = 80 amps
90 x 75% = 67.5 (always round up) = 68
68 + 80 = 148
So therefore you will require an alternator with a minimum rating of 150 amps

Example #2
Adding a single amplifier with (2) 40 amp fuses
Stock alternator rated at 105 amps
Fuse values total = 80 amps
105 x nothing as we will (or do) add for additional items (let’s just say Monitor, DVD, HID lighting, & a couple neons)
80 + 105 = 185
So therefore you will require an alternator with a minimum rating of 185 amps

Example #3
Adding multiple amplifiers with (2) 40 amp fuses (amp #1) and (2) 25 amp fuses (amp #2)
Stock alternator rated at 120 amps
Fuse values total = 130 amps
120 x 75% = 90
130 + 90 = 220
So therefore you will require an alternator with a minimum rating of 220 amps

Side Note #3: While other electrical components of your vehicle may help such as the Big 3, Upgraded or Additional Batteries, (Capacitors not suggested) these are not a direct replacement for creating power and are only to assist in transferring and storing power and are Not and should Not be used as a substitute.

Thanks and above all when dealing with electricity of any sort, think smart and safe for yourself and your equipment
CarGodz/ Michael