DIAGRAM: Starter & alternator circuit “The Voltage Drop Test"

[Sodo]

Tryna keep vans off the flatbeds......

If you have a little understanding of electricity, or friends who do, here's a diagram for your Samba Vanagon files.

Here's a how-to to qualify the high-power legs of your Vanagon circuit. These are responsible for starter cranking speed, battery charging speed, headlight brightness, radiator fan speed.

The diagram shows six locations to measure voltages.
The tools required are a volt meter, and a 100 amp load tester.
The load tester is sold as a battery tester, and they cost only about $30.

1) Load-test the battery. 100Amps is not a definitive qualifier. You really want to test it with about 325 amps. But if it struggles with 100A, perhaps your battery is the problem.

Negative legs of the circuit are much easier and safer to measure voltages.
For tests 2 thru 6 you may need a helper to push the 100A button (for 5 seconds) while you read the "voltage drops".

2) Measure the voltage drop between the battery post and the steel van chassis. It's common to have losses here. 0.25v is acceptable. Maybe even towards 0.5v. If you find 1.0v your starter is slowing. My van has 0.07v drop here.

3) Measure the voltage drop between the chassis (somewhere shiny) and a starter mounting bolt. It's common to have losses here. 0.25v is acceptable. Maybe even towards 0.5v. If you find 1.0v, your starter is slowing. If you find 2 volts it's really slow, and the electricity is ruining your internal drivetrain parts. Delete that VW ground and replace it with a 4g cable from the starter mounting bolt directly to the chassis.

4) You have to be very careful measuring positive posts. Measure the voltage drop between the battery POSITIVE post and the starter positive post. This is not particularly easy. You can use jumper-cables to extend your multimeter leads. 0.25v is acceptable.

5) Measure the voltage drop between the starter positive post and the alternator positive post. This is not particularly easy. You can use jumper-cables to extend your multimeter leads. 0.25v is acceptable.

6) Measure the voltage drop between the alternater case and the van chassis. Your van may have an engine ground, and some of the grounding may come from the faraway transmission ground. 0.25v is acceptable.

The connections degrade over time, especially the five corrodable connections between the starter and the transaxle forward ground..
As they corrode, the starter slows, headlights dim,
it won't re-start at the gas station....
.....flatbed rides loom large in your future.
These are difficult to maintain or renew. Best to bypass all of them with a “$20 mod”

You may be inclined to purchase a new starter that's perhaps not required (yet!).
TEST the circuit FIRST.
The new starter may behave the same as the old one if your degraded circuit is the actual problem.
Sometimes just unbolting and rebolting your starter is all that's needed to renew the starter's electrical connection and restore starter operation. But there are other connections that may need to be restored as well.

The connections across the engine to the alternator is another daisy-chain of corrodable materials.
For that reason it's best to add a direct ground from the starter case to the chassis,
AND
add a direct ground from the starter mounting bolt to the chassis.
See this Diagram regarding grounds modification: https://www.thesamba.com/vw/gallery/pix/2534409.jpg
A couple $20 ground cables may be the cheapest and most effective mod you can do.
_________________


'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

[crazyvwvanman]

I see some issues with your Rev A diagram and the location of the Load Tester negative lead position.

If you don't have a DC clamp meter you should get one, making sure it does DC amps with the clamp.
Then use it to verify that the assumed amount of amps are flowing where you think they are.

Mark

[E1]

Deleted.
_________________
If ever twice as rich, we’re gettin’ a double-wide
’84 “Westfailure”/2.1 Digijet/5.43 Ring & Pinion/Peloquin/D-rated BFG KO2s

AI has spoken to further illiteracy, to steal, to cheat, and to replace humans
The caveman’s first question to the headhunter: “Hey, you got any coffee?”

[Wildthings]

Losing 0.07V on your positive cable between the battery and the starter is very acceptable, while losing 0.4 volts on your ground circuit at only 100 amps seems quite high to me.

[Sodo]

[bobhill8]

Thanks for doing this. I appreciate all these sorts of tutorials and save them on paper in my van.
_________________
1986 Westy
1971 Squareback

[Sodo]

[fxr]

[Sodo]

[fxr]

[Wildthings]

[Sodo]

[Sodo]

[1988M5]

All of this loaded testing is good stuff, but while you're at it and have all the tools out, check other high-power consumers. Defroster, HVAC fan, headlights, radiator fan, ECT..
The more testing you do, the better and faster you will become.

BK
_________________
1991 tin top GL
2002 Winnebago Vista. VW VR6 24V Eurovan front clip powered class C 21' RV.
Some BMWs.

[Sodo]

[crazyvwvanman]

I don't really have time for this today but I'll steal a few minutes.
Yes, the voltage drop test is valuable, with some fine print reserved.

The DC Clamp Meter seems an almost essential addition.
I bought one recommended here by someone, Amazon.

I have 2 of the HF Load Testers, a 2 year old one and a 2 day old one, exact same model number.
The older one read 89 amps connected at the battery posts of my 87.
The new one read 95 amps there, back and forth multiple tries with each.

Maybe more time tomorrow.

Mark

[crazyvwvanman]

After I compared the different readings from my 2 HF Battery Load Testers, I wanted more data.
I took them inside where I had a new spare 100ah LiFePo4 battery waiting for a project.
First I tested it with my 2 year old one, reading the amps from my DC Clamp Meter.
This time it read 94 amps, not 89 like with my starter battery in my Westy.

Next tested with the new Load Tester just purchased, which gave 95 amps previously.
The DC Clamp Meter display jumped around before suddenly showing amps dropping to 0, while sounds came from the new Load Tester along with some flashes of sparks inside it near the load-on switch I was pushing on.
So I re-seated the cables and tried again, same results.
I was sure I had fried something but no.
The old one still worked with the LiFePo4 and the new one still worked back outside on my van starter battery.

What happened? I'm not sure.
One guess is that the BMS in the LiFePo4 objected to the new unit's 100+ Load Tester amp draw, even as brief as it must have been.

Clearly the HF so called 100amp Battery Load Tester isn't a precise and calibrated device.
Also it isn't meant to test LiFePo4.

I'm going to have to think about this more.

Mark

[jimf909]

[Sodo]

If that 2nd tester is not consistent with a 12.6v start-battery either.... I'd look for a bad connection (?). It could be repairable in a fraction of the time it takes to drive to Harbor Freight. I can't imagine what could go wrong in such a simple machine.
The good/bad scale is of course depicts a 12.6v battery not 13.3v.

Incidentally if you had a significantly deteriorated ground path with 0.8 volts of "drops",
a 13.3v start battery should crank the engine as fast as a "perfect" system.
Those little Lithium "pocket jump starters" may confuse diagnosis if you don't consider their higher beginning voltage.

anyway back to the Voltage drop test....
the Load Tester's contribution to the test ....
It's easier, quieter and more repeatable than using the vehicle starter load.
And you can load specific legs of the circuit ( if they're discrete legs ).
_________________


'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

[crazyvwvanman]

I agree, for what they are built to do for only $20 I'm satisfied.
Now though we are using them in a different way so variations in their performance may be more significant.
Does it make sense to compare voltage drop measurements down to the 1/1000 volt when the test setups can vary so much just in the Load Tester?

I'm planning to get another one today for this project, since I'm going to HF anyway.
I want to build a test box using 2 of them with matched performance, in part so I can do more tests in a shorter time without burning them out.

Mark