Alternator - 37 Amps enough?

Alternator - 37 Amps enough?


Missing-Presumed Wheeling
Lifetime Supporter
Plumas Lake, CA, USA
1974 CJ5 ~ Fresh built AMC 360 - SM420 - D20 - D30F with upgraded 30 spline shafts and knuckles & D44R - 4.27 Gears - ARB Lockers F/R - All chrome molly axles - on 33's - YJ 4" Lift Spring Conversion
Getting a new alt tonight, but while looking at the specs, it's showing 37 amp. output... Ultima 01-0174 - Alternator | O'Reilly Auto Parts

So while i am sure this was enough for the basic accessories on the Jeep from the factory, I have:

Aftermarket stereo
Warn M8000 Winch
Brighter Headlights (I assume aftermarket, there when got them)
12v power supply / cigar lighter

And plan on the off road KC daylighters at one point or another, as well as possibly (way down the road) some e-lockers...

Now i know all these things are not drawing always at the same time, but say I'm running my stereo, heater, cb, headlights all at once while driving, how can i tell how much of that 37 amps is being used and therefore if the battery is getting a charge from extra or draining from over usage? Need to know if I should turn stereo and heater off while I need to winch myself out etc.

Just bought a Red top Ultima, and things aren't cheap. Want to know whats going on before draining and killing this thing on a snow run or something...:cool:

Do I need to find the individual amp drain of each item? Is there a easy load test for overall apms being used? :rolleyes:

Should I get a higher output alt? Will this one be sufficient?

Thanks all,:notworthy:
~ JR
That 37 amp rating will be it's max output and will only occur at higher rpm's. You probably wont get much over 10 amps at idle. An easy way to gauge how effective your alternator is would be to watch a volt gauge. If your volts drop below 12.5 volts with the engine running, then your battery is being drained by the devices. The alternator is no longer keeping up with them.

Going to a 50 amp alternator would be helpful but anything over that may be too much for your wiring. The large wire between the alternator and the battery must be able to handle the amps put out by the alternator. If it gets hot, it is too small.

Small amp gauges that you hold over or clamp over the battery cable are available. You could use them to measure the drain while you use your stereo, winch etc. You'll need to do it with the engine off or you won't get a true reading because you will have 2 power sources. The battery and the alternator.
I think I've decided to go with this one instead... NAPA AUTO PARTS

Mostly because I have remembered I also switched to MSD Streetfire ignition with the DUI Distributor and spark plugs gaped at .050... Meaning (I assume) my ignition system is drawing quite a bit more than the original did. :cool:

Thank You Jeff (I assume Jeff) for the info too. I greatly appreciate it. I will make sure to keep a feel out on that wire to see if it needs replacement. :notworthy:

Now for the dropping below 12.5 volts... I have the gauge that shows zero in the middle with numbers going both ways... I will take a pic tonight, as I am unsure, but i think it is an AMP gauge... And although I am sure it is basic, I have never fully understood how they work, and how to read them.

I need to do some further investigation and reading up on this... But I am assuming they are different and serve different purposes than the Volt gauge...

I do have a volt-meter that measures a number of different electrical things... Is this something I could measure with? at the battery etc?

Sorry, I know this is basic stuff... I am not as good with Gauges and electrical current draws and flows as I will be soon ;)

~ JR
Heres a good site with alot of good info on altenators, Pirate4x4.Com - The largest off roading and 4x4 website in the world. also here is a good site for 12 volt basics Pirate4x4.Com - The largest off roading and 4x4 website in the world. I personaly think that a 50 amp altenator is good for running all your acc. except the winch Bustadave had a good point in a simalur thread the winch can pull up to 400amps and no altenator will keep up with that high output or not. Run your winch a little at a time to allow your battery to charge and cool your winch down,or you can set up a dual battery. I have a factory altenator and I have a winch and have used it alot by pulling a while and letting the battery recharge I also have a 1000 cold cranking amp battery. I personaly think a high output altenator is a waste of money, I'm sure some out there are going poop poop on this statement. Just my .02
Thats a good link 1986cj7 gave ya, there's also a part two on alternators.
I'm a fan of 100 amper's myself, they usually don't cost much more.
A 10 ga wire from the alt. is a must though.

Jeep-CJ Donation Drive

Help support by making a donation.

Help support by making a donation.
This donation drive ends in
Top Bottom
AdBlock Detected

I get it, I'm a Jeep owner and ad-block detectors kinda stink but ads are needed on this site. This is a CJ site, all the ads are set for autos (some times others get through.) I cannot make them just for Jeeps but I try.

Please allow ads as they help keep this site running by offsetting the costs of software and server fees.
Clicking on No Thanks will temporarily disable this message.
I've Disabled AdBlock    No Thanks