Alternator output?

fras · Postby **fras** » February 9th, 2021, 9:27 am

On a vehicle with a 140 amp alternator, approximately how many amps would be available for audio at idle?
Vehicle is diesel btw!

Postby SR » February 13th, 2021, 6:47 am

altec · Postby **altec** » February 13th, 2021, 7:06 am

Depends on the current draw, which depends on how much electrical stuff you have running eg headlights. Electrician can measure that for you easy.

fras · Postby **fras** » February 16th, 2021, 3:42 pm

SR wrote:28

ur joking right?

fras · Postby **fras** » February 16th, 2021, 3:42 pm

altec wrote:Depends on the current draw, which depends on how much electrical stuff you have running eg headlights. Electrician can measure that for you easy.

ok cool

88sins · Postby **88sins** » February 16th, 2021, 5:16 pm

Depends on what you have adding load to the electrical system as altec mentioned. Lights, ac, even your radiator fans will draw and reduce the total power available to your amp. Get a clamp meter that can read DC amps, and check the power being delivered at the amp power input for a better idea of what's going on.

Also, for maximum power, you could have the run the amplifier power cable connected directly to the alternator, but that may cause a bit less power to get to your battery, engine and other accessories whiletl the systemis is playing on full blast. Not something I advise you do on your own or on a daily driver, but it can be done.

fras · Postby **fras** » February 19th, 2021, 9:41 am

88sins wrote:Depends on what you have adding load to the electrical system as altec mentioned. Lights, ac, even your radiator fans will draw and reduce the total power available to your amp. Get a clamp meter that can read DC amps, and check the power being delivered at the amp power input for a better idea of what's going on.

Also, for maximum power, you could have the run the amplifier power cable connected directly to the alternator, but that may cause a bit less power to get to your battery, engine and other accessories whiletl the systemis is playing on full blast. Not something I advise you do on your own or on a daily driver, but it can be done.

No lights or ac... Just audio in use! Also the fan is driven by the engine (clutch fan)

adnj · Postby **adnj** » February 19th, 2021, 3:22 pm

There is no simple answer on alternator output unless the alternator output curve is known. All things being equal, a lower maximum output current alternator may have a higher output at idle. Larger, heavier alternators produce more current at lower RPMs, also.

This chart shows alternator shaft speed versusus output. Most alternator pulley designs try to use sizes that are 2:1 to 3:1. Most OEM automotive design requirements leave about 10 amps of vehicle power for the Vehicle Navigation & Entertainment system - sometimes you may see up to about 30 amps.

Postby SR » February 20th, 2021, 6:46 pm

An oem alternator is designed to provide what the vehicles needs with a small reserve capacity. No oem manufacturer will put a alternator with a high reserve capacity as it will send the cost of the vehicle up. Aftermarket alternators are designed to provide high amperage to run aftermarket accessories such as sound systems etc.
This is why your lights dip at night when the bass kicks in as the alternator cannot provide the additional current and the battery cannot provide it quickly enough plus when under load the battery itself also becomes another load for the alternator