420A I think my alternator is bad

[Myjr]

The alternator is only charging at 12.5 with everything on and 13 four with everything turned off can somebody tell me exactly what size alternator I should get? Keep in mind I have a 6000 W amp stereo system that I run as well. should I buy a higher amp alternator?

 

[BLACK'98DSM]

From what I've seen your only 2 replacement options for alternators are 85A and 90A. The stock alternator is 90A.

You're using a 6000 watt amplifier? Must be a serious sound system. I would upgrade the battery size and see if that helps. I previously had an amplifier somewhere around 750 watt I believe and it would drain the stock battery size after a half hour or so and lights would dim with sub operation the whole time. I got a larger battery which I believe was 950 CCA and it performed much better. Any OEM style alternator will have no issue charging a larger battery if it's in good shape. I'm still using the stock alternator from '97. And have been through many large batteries and miles. I have a smaller than stock battery now so I bet the alternator will last forever.

With no accessories running my alternator charges at 14.0V. Which is on the slim side because of an underdrive pulley and 650 rpm idle. Revving I see a slight jump to 14.5V

13.5V seems like it may be getting weak, but is that with sound system on or off?

 

[Myjr]

Yes. That is with the power cable to the amp system disconnected and everything including AC turned off.

when we run the ac it gets lower... I think a standard 90 watt from autozone for 128 should do right?

napa claims they have a "new" one for 238 dollars but it has to be ordered.

the battery we are using is an optima red , 720 CCA , 910 CA , 90 minute reserve capacity.

Im not sure we can fit a battery bigger than that in this car...

 

[Myjr]

Well , we put an Newly remanufactured alternator in from oreillys and it gives the exact same results.

This time he only drove it for 6 or 7 miles and maybe 45 minutes to an hour before the battery died. New battery optima red.

Does anyone have any other sugestions?

 

[Dericsh]

Does the battery indicator on the dash work?

 

[Myjr]

I have been using a multimeter to test it. batter was charged at 12.6 before we ran it. Once started it was at 13.5 with nothing but the car running, after putting in the new alternator

 

[Dericsh]

Maybe this will help with some further troubleshooting.

https://www.dsmtuners.com/threads/2g-new-alternator-doesnt-charge.506601/#post-153611544

However, the resolution to that particular thread was the new aftermarket alternator was no good.

I’ve heard optima batteries aren’t what they used to be. Are we sure this battery is not faulty and capable of holding a charge?

 

[SixBolt_16G]

should I buy a higher amp alternator?

Yes.

6000 watts on a 90 amp alternator?

Im no car audio expert, but that sounds highly illogical.

I wouldve thought at least a 200+ amp alternator.

 

[BLACK'98DSM]

You probably won't have any luck finding a 420a alternator with a higher amperage rating than 90.

I had an idea though. Since the Chrysler 2.4L is so similar to the 420a, I started alternator shopping for a 90's Dodge Stratus. You can buy a 125 amp alternator for those and I bet it would fit on the 420a. You may also have to find a 2.4L mounting bracket but I'm unsure. The belt has a different number of grooves so a pulley swap for sure. The connectors may even be different but you'd really need the 2 alternators side by side to know exactly what needs to be done for the swap. You can definitely MAKE it fit though.

I may actually do some deeper digging into this myself as I've seen many people asking for 420a alternator upgrades and getting no answers. Sort of intrigued to see how I can find an upgrade for us. I'm sure the extra 35 amps is useful for aftermarket systems and such. A safe and effective way to do this would be great although 20-ish years late to the game.

 

[DirtMcGirt]

To the OP, keep in mind that Optima red tops are just starting batteries so they don’t have any deep cycle characteristics. With any significant electrical demand additions, a yellow top (or equivalent), is recommended. As others have pointed out a high amp alternator is also advisable. I run this 150A, that pops up on eBay from time to time, on my eclipse:

ECLIPSE, TALON, SEBRING, NEON HIGH OUTPUT LOAD BOSS ALTERNATOR 150 AMPS | eBay

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