Battery Not Charging - New Battery, New Alternator, Problem Persists (1 Viewer)

[MATT0404]

So I bought my 100 last year around this time. Service history showed recent alternator and battery replacement, which I thought was a good thing. I've put about 5k miles on it and have had a few experiences where the low battery voltage light comes on, then the VSC and ABS lights, then the beeping noise, then all the dash lights, then the nav display turns off, etc. I limped it home once, charged the battery up and all was well for a while.

Just recently I installed a USB charger and digital voltage gauge so I can monitor battery voltage more closely. I was on my way home one day and watched the battery voltage go from 13.6v down to under 7v. Around 9v I started pointing the rig to the auto parts store. As I was pulling it, the voltage was dipping under 7v and I suddenly lost fuel injection and she sputtered out, then surged to life long enough to get into the parking lot.

I bought a new battery to get me back home. As I was driving home, I noticed the voltage started at 14v and by the time I was home it was 13.8v. Drove it around town running errands the next day and noticed it would start off strong but gradually drop down to 12.9-13.2v in stop and go traffic. On the highway or 55mph+ roads it would charge back up to ~13.7v again. I started to suspect the alternator and noticed the new alternator was an AC Delco with a remanufactured for General Motors sticker on it. I decided to replace it with a new Denso reman.

I installed the new alternator last Saturday and the symptoms have not improved. It's not died on me again...yet, but it still starts off around 13.9v and will eventually drop down to 12.9-13.2v. It'll start to recharge at cruising speeds, but as soon as I'm in traffic (which is very light in rural PA) the voltage starts dropping. Immediately after installing the alternator, I started it up and just let it idle. It held voltage while the idle was high, but after 10 minutes, the voltage dropped from 13.9v to 13.2v. Am I wrong to assume it should be able to maintain 14v with a new alternator and battery?

Cliff notes:

• Bought 100 last year with recent alternator and battery replacement in the service history
• Two times now I've experienced low battery light, then VSC, then ABS, then beeping and full loss of electronics
• Installed digital voltage gauge and watched voltage drop from 13.6v to under 7v at which point I lost fuel injection
• Replaced battery and watched it suffer similar voltage drop
• Voltage pretty steady at cruising speed, but drops quickly in stop and go
• Checked and thoroughly cleaned all grounds
• Noticed replacement alternator was an AC Delco reman
• Replaced alternator with new Denso reman
• Issue not resolved

I'm not sure where to go from here. Suggestions?

 

[flintknapper]

Am I wrong to assume it should be able to maintain 14v with a new alternator and battery?



View attachment 2003207

Yes, wrong to assume it should 'always' be 14+ volts.

Depends on the health of your battery and what electrical load it is seeing.

Upon start up...mine will charge at 14.1-14.3 but over a period of a few minutes...drops down to 13.2-13.7 depending on load (at idle).

I would be concerned if you see less than that AND your battery discharges again to a degree that leaves you stranded.

 

[MATT0404]

Yes, wrong to assume it should 'always' be 14+ volts.

Depends on the health of your battery and what electrical load it is seeing.

Upon start up...mine will charge at 14.1-14.3 but over a period of a few minutes...drops down to 13.2-13.7 depending on load (at idle).

I would be concerned if you see less than that AND your battery discharges again to a degree that leaves you stranded.

View attachment 2003276

Ok, so not abnormal for it to drop to low 13s at times. Admittedly, I haven't driven it much since the new alternator. I'll give it a little more and observe behavior. Thanks!

 

[gil12]

It sounds like you have a short while running that is draining your voltage.

I've been wanting this induction dc meter:

CM610A 600A T-RMS AC/DC Clamp Meter

Amazing deals on this 600 A T-Rms Ac/Dc Clamp Meter at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

But am waiting for a problem like yours to justify the purchase! ☺

(In short, I'd start with fresh battery, run thru your circuits and see if the meter shows an unexpected increase in amps.)

Gil

 

[flintknapper]

Ok, so not abnormal for it to drop to low 13s at times. Admittedly, I haven't driven it much since the new alternator. I'll give it a little more and observe behavior. Thanks!

Correct. Entirely possible IF your battery is good and the load demand is small. That is the entire purpose of the voltage 'regulator' in your alternator. To ensure you don't over-charge your battery. Now...if the load demand is high (right after a start, lots of electric items on like lights, radio, window use, etc) then you should expect to see your alternator running at or above 14 volts but not more than 15 volts. Once the electrical load subsides and the battery recovers...then anything from 13.2v to 14.7v would be considered normal.

Also, check your multimeter for accuracy on another vehicle.

 

[flintknapper]

But am waiting for a problem like yours to justify the purchase! ☺

Haha....! Hoping for a problem in order to make a tool purchase. That's good.