Alternator question

[Jimmy9190]

I have a similar post about my battery and alternator on here, but am making this post to see what you guys all think. This is sort of a different question.

To make a long story a little longer-

I had a 600 CCA Auto Craft Silver battery in my truck, 2 days ago it went bad and I replaced it with a Duralast Gold which is 750 CCA. Autozone does not stock the red top Duralast battery for my truck. I could have ordered one I guess but I needed a good battery right then. Anyway, the Duralast Gold is a very strong, great quality battery and is doing fine so far.

The original battery for my truck was probably 550 or maybe 600 CCA. The Auto Craft one that failed was not quite 3 years old, date of manufacture was Nov. 2007 and I bought it in January 2008. Now I have a stronger battery but am using the original stock 117 amp alternator. There is an upgraded 136 amp alterator option for my truck, and I just wonder, does the new stronger battery need the 136 amp alternator to keep it charged better? I wonder if a 10 year old 117 amp alternator will have problems keeping this new battery charged. It's the original alternator, and my truck has 135,000 miles on it now. It's a 2001 Dodge Dakota with a 3.9 V6 and a 5-speed manual.

I think it would be smart to just go ahead and replace the old 117 amp alternator with the 136 amp version. Seems to me it would be a good improvement and a smart way to avoid more battery troubles later on. A reman 117 amp alternator is $129.00 at Advance or Autozone. With the LC123 40% off discount code from Advance I can get a reman 136 amp alternator for about $149.00. Either one should fit and bolt right back in place on my engine.

What do you all think?

Thanks for any ideas here.

 

[xxch4osxx]

Id go for the 136amp alternator, but thats just me.

 

[firefighter]

The alternator will only put out what it needs to so having the higher amps will be a moot point, Now if you were towing and had a ton of lights on your vehicle or trailer, and a bunch of other electronic gizmos, or were a police car with all there electronics that would be a differant story. I think you should be fine with what you got.

 

[Garak]

I'd say either is fine. As was pointed out, the alternator is only going to put out what it needs. If you have a need for a bigger alternator, go for it. If the $20 difference doesn't matter, might as well go for it, too.

If you want to save $20, go with the original specification.

 

[J. A. Rizzo]

The capacity of your battery has nothing to do with the output required from your alternator. What counts is the load. If you had lots of accessories like heated seats and headlights and foglights and an AC inverter and the rear defogger all going at once, you would need a bigger alternator to keep up with the demand. Upgrading your alternator for the sole reason that you have a higher capacity battery doesn't hold water. The alternator only puts out what is needed to meet demand. A higher capacity battery doesn't put any higher demand on the system, so upgrading the alternator won't make any difference. If there is a problem with the output from the alternator, the charge system malfunction light will come on or you'll have other indications, like a squealing bearing or dim lights, etc. I would leave the alternator as is. If it ain't broke...

 

[Jimmy9190]

Good. You guys saved me $150.00. Thanks for the replies and info. No I don't have a lot of extras on the truck, just a mild stereo system with one small amplifier and a Viper alarm. I use Night Hawk 9007 headlights but other than that everything else is stock. The truck doesn't even have power locks or windows.

In my other post I put up my ideas about the battery and was thinking of replacing the stock alternator, just as a precaution due to its age and mileage, plus the charging voltage seemed a bit low, 13.6 at the battery, engine idling with the bright lights and AC off, and also 13.6 idling with the AC and lights on. Increasing RPM does not increase the volts from the alternator.

I had Autozone test the alternator with a hand-held load tester, it said the alternator was good. I was thinking the "if it ain't broke" thing too, but I just wonder if it wouldn't be good insurance to replace the alternator now before it fails on me going to work one morning?

 

[The_Jeff]

Most dodges have external regulators, probably in the PCM for you. If it wants to do 13.6 volts and you aren't getting any trouble lights, that's what you're going to get new alt or old.

There's a battery temp sensor (!) that reduces charge when the battery/underhood area is warm. Try again with a stone cold truck; I bet you get over 14 volts.

 

[firefighter]

Originally Posted By: eljefino
Most dodges have external regulators, probably in the PCM for you. If it wants to do 13.6 volts and you aren't getting any trouble lights, that's what you're going to get new alt or old.

There's a battery temp sensor (!) that reduces charge when the battery/underhood area is warm. Try again with a stone cold truck; I bet you get over 14 volts.


I will second that a fair amount of cars are computer controlled alternators, some even shut them off at times to save fuel. The days of diagnosing alternators with a voltmeter are comming to an end, the days of using a scan tool are just beginnig

 

[Jimmy9190]

Thanks for the idea, I checked it again about 30 minutes ago. It is about 85 to 90 degrees outside and the truck has been sitting overnight. It had 12.65 volts with the engine off, 13.65 volts with the engine idling and 13.67 with the AC and high beams on. I can check it again when it finally does cool off here, sometime in late October we will have temps in the upper 60's to low 70's in the first few hours of the morning. I'll see what kind of voltage I get then.

I know the voltage regulator is an internal part of the PCM on my truck. I agree the alternator is only going to put out a set voltage according to the voltage regulator and PCM. I shouldn't obsess about it and will just leave well enough alone until I have reason to replace the alternator. Some alternators last 100K to 150K, some last longer than that, and some don't last as long as others. I just hope if and when mine goes it's not on the side of a dark road in the rain in the boonies I drive through every day commuting back and forth to work.

This is the fourth battery my truck has needed. Batteries, especially cheaper quality batteries like OEM and cheap parts store batteries don't last a long time in the heat here. I guess they don't last long in the cold up north and in Canada either. I was concerned about the strain that 3 bad batteries had put on my factory alternator but it seems all is well for now and I will leave it alone unless and until it fails.

Thanks for the help here. Sorry to bring up such a ridiculous and OCD post.

 

[caravanmike]

on all of the chrysler jeep products i own have battery temp sensors. i know this was mentioned above, but my 99 jeep cherokee with a 117amp denso alt puts out 13.54 volts all summer long! (with no problems) once when i started it this winter, when it was 2 below zero (car parked outside) i was getting 15 volts for the first ten miles to work! once the battery warmed up i was back down below 14 volts!

one of the advantages to this system is batteries last forever as long, as they are not discharged in their lifetime and as long as their was not a manufactures defect when battery was purchased. i have one battery in this system that lasted 10years (sears diehard). mike

 

[Jimmy9190]

Thanks for the info. On the Dodge forum some guys there said they never got over 13.6 volts at idle either. Dodge probably designed the PCM that way. The system in my girlfriend's Honda Accord is charging 14.25 volts at idle, which is what got me to thinking about the alternator. I think her car just has a higher output alternator because there is a lot more electrical accessories and components on her car. Plus Honda has those puny little lawnmower-sized batteries so the car probably needs a stronger electrical system to keep everything running.

I am going to leave well enough alone on my alternator until it gives me a good reason to replace it. I went through this same scenario not long ago, wondering if I should replace my water pump due to it being original with 135,000 miles on the truck. I decided to leave the water pump alone too. I think there will be enough advance warning signs if either one starts having problems.

 

[mechtech2]

I always like a bigger battery.
It would be very rare to have a battery need constant charging [enough to warrant a bigger alternator].
There would have to be unusual circumstances.