Max vehicle alternator current

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Max vehicle alternator current

Post by geojoe1 » Fri Oct 06, 2006 6:21 am

Ok those of you that read and helped with the last post 'to fuse or not to fuse' know that I am working on a DC to DC converter. I am boosting the battery voltage from a running car. My converter will be drawing 70 + amps. How much current can a vehicle alternator produce? I don't want to drain my battery and fry my alternator. Anyone have experience with high power car stereos. I suppose these would pose the same concerns.

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Post by dyarker » Fri Oct 06, 2006 6:39 am

Depends on the car. Small cars with 1.4 Liter engines might have a 45 Amp alternator. A full size Detroit beast with largest V-8 option, air conditioning, and trailer towing package might have a 100 Amp alternator.

Luckily music only draws max current a low percentage of the time. Just don't forget to leave enough current for ignition system, headlights, wind shield wipers, etc, hee hee

Do not tell us which state you live in, we'll know when you start testing that audio system :cool:
Dale Y

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Post by Chris Smith » Fri Oct 06, 2006 8:38 am

Alternators and batteries are self regulating.

The alternator will only produce its maximum amount of current, and then it will stay warm to hot and then start to harm the alternator gradually after continued and sustained time of maximum draw because your stretching the alternator and running it extremely hot. This may take years to break down the alternator and its parts unless you really force the current to its maximum at 24/7.

All alternator in their serial number or description plates have the amperage stamped or stenciled on them. This number might simply use the digits of 55A, 100A etc or even just the digits alone.

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Post by dacflyer » Fri Oct 06, 2006 9:50 am

seen some emergency fleet vehiches have 300 to 500 amps..
i am sure you might can find any size you want so long as it does not stall the engine, or bogg it down too much..and also if it fits in the car :P

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Post by haklesup » Fri Oct 06, 2006 4:02 pm

Is that 70A continuous or 70A peak (and for how long).

If its just a peak demand, the battery will supply short bursts of several hunderd Amps for up to minutes no problem especially if it is a fresh heavy duty battery.

As for the Alternator, you need to go to the parts store (or a website) and find out what the replacement part numbers are from the counter. Look also for heavy duty replacement parts. Then go home with the numbers and look up the specs on the Alternator. At I am seeing 60A, 80A and 100A alternator options in the same size package.

You may need to upgrade to a heavy duty alternator and regulator (if not built into the alternator). Really, it depends on your car model and how the charging system is arranged.

Does the car have an ammeter on the dashboard, keep an eye on it. You can also install your own from aftermarket parts off the shelf in an auto parts store.

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Post by jollyrgr » Mon Oct 09, 2006 3:07 pm

I believe the alternator in my Suburban is a 120A version. They sell several different versions ranging from 100A to 124A depending on the parts store you get them from. You can get a Duralast 105 amp model from Auto Zone for $80 plus $30 core charge (unless you have a junk alternator lying around). It is part number DL1345-6-7. Hopefully this works: ... ONE%7C%7EB
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Post by Bern » Sun Oct 15, 2006 9:22 pm

A few months ago, I had a project where I was pulling heavy current from the electrical system, and was concerned about alternator capabilities. I asked several different auto mechanics, and alternator rebuild houses, and basically was told the same story. The ratings on an alternator are peak and for short periods of time. If you plan on continuous loading, plan on 60% to 80% being a safe load. If you use an alternator off a heavy duty truck, that percentage goes ups quite a bit.

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