 Battery charging without ALT light, What’s going on? |
|
|
|
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG.
This site is not affiliated with Porsche in any way. Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners. |
|
|
| VaccaRabite |
 Sep 30 2026, 02:06 PM
Post
#1
|
|
En Garde!  Group: Admin Posts: 13,921 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region 
 |
A friend of mine had his battery pop in his 914. Battery acid everywhere. We got it running last weekend after a year of sitting.
Of note, the alternator light never turns on. BUT, the car is charging the battery at 13.9 volts. How is this possible? My guess is that he has a damaged or failing diode in the alternator, but I thought the battery COULD not charge without the alternator light turning on. So I’m confused. Thanks Zach |
   |
 
|
  |
Replies(1 - 7)
| Artfrombama |
Sep 30 2026, 03:38 PM
Post
#2
|
|
Artfrombama Group: Members Posts: 485 Joined: 21-January 24 From: One of the chosen few Member No.: 27,870 Region Association: South East States
|
If you have an old battery that never fully charges, the alternator will continue to try to charge resulting in gassing and the potential to explode.
|
|
|
|
| VaccaRabite |
Sep 30 2026, 04:41 PM
Post
#3
|
|
En Garde! Group: Admin Posts: 13,921 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region
|
Battery didn’t explode persey. But it did spray acid over the engine bay and was on its way to exploding.
Battery has been replaced. As have all the affected wires and switches. So now the car is running and driving and charging. But the alternator light never turns on. And this does not make a lick of sense to me. Zach |
|
|
|
| SirAndy |
Sep 30 2026, 04:45 PM
Post
#4
|
|
Resident German Group: Admin Posts: 42,530 Joined: 21-January 03 From: Oakland, Kalifornia Member No.: 179 Region Association: Northern California |
Wait, i'm confused. The alternator light is supposed to be off when the car is running.
Are you saying it doesn't come on with the key on but the engine off? Does he even have a bulb in there? Did anyone bypass the light? I have seen so much hacked wiring in 914s. (IMG:style_emoticons/default/idea.gif) |
|
|
|
| 930cabman |
Sep 30 2026, 04:51 PM
Post
#5
|
|
Advanced Member Group: Members Posts: 4,851 Joined: 12-November 20 From: Buffalo Member No.: 24,877 Region Association: North East States
|
Please clarify, how/why would a battery pop or spray acid? This one is new to me.
being very overcharged? |
|
|
|
| VaccaRabite |
Sep 30 2026, 05:02 PM
Post
#6
|
|
En Garde! Group: Admin Posts: 13,921 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region
|
Not my car and I’m currently 100ish miles from it.
I’m not clear on why the battery popped, but I suspect overcharging. On key in, the alternator light does NOT turn on. It stays off throughout startup and driving. By everything I know this means the car should not be able to charge, but measuring across the terminals at idle he’s making 13.9 volts. When the car is off it settles at 12.6 volts. Zach |
|
|
|
| VaccaRabite |
Sep 30 2026, 05:05 PM
Post
#7
|
|
En Garde! Group: Admin Posts: 13,921 Joined: 15-December 03 From: Dallastown, PA Member No.: 1,435 Region Association: MidAtlantic Region
|
QUOTE(SirAndy @ Sep 30 2026, 06:45 PM)  Wait, i'm confused. The alternator light is supposed to be off when the car is running. Are you saying it doesn't come on with the key on but the engine off? Does he even have a bulb in there? Did anyone bypass the light? I have seen so much hacked wiring in 914s. (IMG:style_emoticons/default/idea.gif) Correct. The light never turn on. He replaced the light with another bulb today and it remains off. None of the bulbs on this car are LED. The light used to come on normally as far as I know. I’ve driven the car and that’s something I would have noticed. But the alt is getting field from somewhere I guess. Just not the right place. Zach |
|
|
|
| porschetub |
Sep 30 2026, 11:34 PM
Post
#8
|
|
914 Guru Group: Members Posts: 5,179 Joined: 25-July 15 From: New Zealand Member No.: 18,995 Region Association: None |
QUOTE(VaccaRabite @ Oct 1 2026, 12:05 PM) QUOTE(SirAndy @ Sep 30 2026, 06:45 PM) Wait, i'm confused. The alternator light is supposed to be off when the car is running. Are you saying it doesn't come on with the key on but the engine off? Does he even have a bulb in there? Did anyone bypass the light? I have seen so much hacked wiring in 914s. (IMG:style_emoticons/default/idea.gif) Correct. The light never turn on. He replaced the light with another bulb today and it remains off. None of the bulbs on this car are LED. The light used to come on normally as far as I know. I’ve driven the car and that’s something I would have noticed. But the alt is getting field from somewhere I guess. Just not the right place. Zach Wow that is weird ,without the lamp working there is no excitation for the alternator , the load the lamp has is enough to trigger that due to current used ,as you mentioned it could be sourcing load from elsewhere ? strange one hopefully Spoke will pop in ? |
 |
|
|
9 User(s) are reading this topic (9 Guests and 0 Anonymous Users)
0 Members:
|
Lo-Fi Version | Time is now: 30th September 2026 - 11:49 PM |
Invision Power Board
v9.1.4 © 2026 IPS, Inc.