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brewvan
Samba Member
Joined: March 21, 2025
Posts: 26
Location: Loomis california
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 Posted: Thu Jun 12, 2025 8:20 pm Post subject: Battery not charging but alternator puts out good voltage |
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| Hey my battery isn't charging... my alternator is putting out 13.5-13.8V. When I test the battery not running after a charge its at 13.2v but when its running its at 12.8 and falling. The voltage at the terminals isn't matching the alternator. Any ideas? |
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syncrodoka
Samba Member
Joined: December 27, 2005
Posts: 12288
Location: Santa Cruz, CA
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| Posted: Thu Jun 12, 2025 8:27 pm Post subject: Re: Battery not charging but alternator puts out good voltage |
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| Grounds |
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jimf909
Samba Member
Joined: April 03, 2014
Posts: 8159
Location: WA/ID
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| Posted: Thu Jun 12, 2025 9:55 pm Post subject: Re: Battery not charging but alternator puts out good voltage |
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| brewvan wrote: |
| Hey my battery isn't charging... my alternator is putting out 13.5-13.8V. When I test the battery not running after a charge its at 13.2v but when its running its at 12.8 and falling. The voltage at the terminals isn't matching the alternator. Any ideas? |
So you're measuring 13.5 - 13.8 volts at the alternator and 12.8 at the battery?
Somewhere between the alternator and the battery there are connection(s) or wires that are not passing the current to the battery. All connections and wires are suspect. Connections corrode and wires are wear items that fail as well.
#1 - clean until shiny the battery terminals and clamps AND the battery ground strap to the body. Ensure that the clamps are tight.
#2 - keep going from there.
Extra credit: do voltage drop tests to diagnose the circuit.
_________________
- Jim
| Butcher wrote: |
| This is the main fault with DIY'ers, they get together on these forums and pat themselves on their backs spreading bad information. |
Guilty as charged.
Current: 1990 Westy Camper - Bostig RG4, 2wd, manual trans w/Peloquin, NAHT high-top, 280 ah LFP battery, 160 watts solar, Flash Silver, seam rust, bondo, etc., etc.
Past: 1985 Westy Camper - 1.9 wbx, 2wd, manual trans, Merian Brown, (sold after 17 years to Northwesty who converted it to a Syncro). |
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latelogan
Samba Member
Joined: July 13, 2023
Posts: 61
Location: Parksville british columbia canada
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| Posted: Thu Jun 12, 2025 10:40 pm Post subject: Re: Battery not charging but alternator puts out good voltage |
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all the above.... and ditto grounds...
When you are measuring at the alternator what are you using as ground? Its possible that the ground connections through the van not great.
I had a hot fuse to the fridge the other day because it wasnt seated correctly! (the one behind the driver seat) I measured it at 0.45 Volts!! (reseating fixed it)
Check and renew the ground from the engine through to the frame (at the transmission) or if there are others to the block and then the one in the battery compartment.
And when you have the battery out, you could take it to a FLAPS and get them to charge and test it.
_________________
1991 Westy stock 2.1 auto transmission
1978 Westy (Sold)
1971 Westy (Sold) |
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brewvan
Samba Member
Joined: March 21, 2025
Posts: 26
Location: Loomis california
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| Posted: Fri Jun 13, 2025 12:26 am Post subject: Re: Battery not charging but alternator puts out good voltage |
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| grounds seem like a good start. Ive been using the body of the alternator as the ground. for testing the battery ive been using the ground on the battery and the ground terminal on the battery |
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jlrftype7
Samba Member
Joined: July 24, 2018
Posts: 4514
Location: Chicago
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| Posted: Fri Jun 13, 2025 6:59 am Post subject: Re: Battery not charging but alternator puts out good voltage |
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To clarify- yours is an '86 Westy, right?
If you aren't experiencing any starting issues with the Starter Motor, your Engine to Body Ground is probably working- doesn't mean it doesn't need attention or changing the cable to a new one that runs from the body grounding point to under the lower starter mounting point... but..
While we're in the same area... how rigid is the main positive battery cable at the starter itself, esp the last 6-8 inches of cable as it attaches to the starter motor. It it's fairly rock hard, it's probably loaded with corrosion in the strands from years of service if it's the original cable.
A voltage drop test as noted above ^^^ is quick and easy.
As a final FYI, our cable on our '84 was losing at least 1 volt between the Altn. and the battery due to corrosion internally.
I replaced the cable with a larger gauge version. Lots of threads on replacing the cable here on Samba.
_________________
'68 Westy- my first VW and vehicle/Bus- long gone.- sold it to a traveling Swiss couple....
'67 Type 3 Fastback, my 2nd car- gone
'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto |
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Sodo
Samba Member
Joined: July 06, 2007
Posts: 10615
Location: Western WA
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| Posted: Fri Jun 13, 2025 9:17 am Post subject: Re: Battery not charging but alternator puts out good voltage |
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| latelogan wrote: |
| When you are measuring at the alternator what are you using as ground? Its possible that the ground connections through the van not great. |
Grounds are the likely suspect for 2025, the ~40th anniversary.
Because most people think there's nothing that can go wrong with grounds.
The positive cable is often suspected first, even though its direct, and pure copper.
Considered MORE suspect than the ground,
which is a haphazard,
outdoor daisy-chain of multiple connections
of dissimilar metals,
un-inspected for 40 years.
Some folks REPLACE their positive cables, at great effort and expense.
If replaced without testing it properly, that can be a big waste of time & money to end up with something perhaps not as good a the OG cable.
Anyone who's having thoughts of replacing a positive cable should study-up on the "voltage drop test".
In 5 minutes, with a volt-meter, you can confirm whether this new cable is necessary (or, hopefully, NOT necessary).
But thats (mostly) a different subject.
===== back to strange battery charging behavior =========
Measuring at the alternator, what voltage to do find at these 3 locations:
With engine running, hi beams, wipers and defrost fans, everything you can turn on high. Use as much electricity as you can.
1) Test voltage between 12v+ terminal (the m8 STUD in the center of the 13mm nut)
to the Alternator case
2) Test voltage between 12v+ terminal (the STUD)
to the cylinder head
3) Test voltage between 12v+ terminal (the stud)
to somewhere shiny on the steel van chassis in the engine bay.
Attach a jump-start cable ( cleanly ! ) to the battery negative and positive.
Extend it to the engine compartment.
This is sorta like having the battery in the engine compartment.
Be very careful with that HOT 12v+ clamp! Think of it "like FIRE!"
4) Test voltage between 12v+ terminal (the stud)
to the negative jumper clamp.
5) Test voltage between the alternator caase
to the negative jumper clamp ---->should be 0.0 to to 0.2v)
6) Test voltage between 12v+ terminal (the stud)
to the positive jumper clamp ---->should be 0.0 to to 0.2v)
These tests will help to identify where the problem is.
They (should) suggest where to zero in.
_________________
'90 Westy EJ25, NEW oil rings (!) 2Peloquins, 3knobs, SyncroShop pressure-oiled pinion-bearing & GT mainshaft, filtered, cooled gearbox.
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered original gearbox
....KTMs, GasGas, SPOT mtb |
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Wildthings
Samba Member
Joined: March 13, 2005
Posts: 52271
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| Posted: Fri Jun 13, 2025 3:51 pm Post subject: Re: Battery not charging but alternator puts out good voltage |
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| What year is your Vanagon, that can make a big difference here. |
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