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Mon Jul 21, 2014 4:53 pm

I just bought (after many years of searching) a '74 bus. Most parts are brand new (engine, starter, brakes, etc.). On my drive home (I picked it up 5 hours from where I live), the lights got dimmer and dimmer. I had to push start it after getting gas. I've done many tests and am thinking (hoping?) it is just the voltage regulator.

Van details:
1974
2 litre engine
solid state voltage regulator

Tests:
The charging light initially never came on, but after some wiggling of the light it now works and is always on when the van is running

Battery: 12v with van off, 12v with van running (I recharged it with a battery charger after the trip home. The battery is brand new)

I tested the blue wire leaving the voltage regulator and going to the charging light with the van running and there was no voltage.

Since it is a solid state regulator, I couldn't do any of the other tests from the Ratwell page as they are for the mechanical version.

Is there anything else I am missing/should be testing? I think I'm hoping it is the regulator since it's a fairly cheap part and easy to switch.

Thanks for reading, hoping for some great feedback.

Dave.

Mon Jul 21, 2014 6:13 pm

Welcome,
Start by testing all 3 wires in the regulator harness for continuity, they can break inside the insulation where they meet the terminals and appear perfectly OK, also check that none of the terminals have pushed back out of the plug or are loose on the terminals.

Mon Jul 21, 2014 6:44 pm

Here is a little information. Good Luck

Pronunciation (Samba) English

Cleaning+Rodents+Hantavirus
Up in smoke... Bus fires... don't let it happen to you!
Volkswagen Type 2 Bus M-Plate Decoder
Bus VIN / Chassis Numbers
Type 2/Bus Owner's Manuals
Bus repair manuals
Bus parts manuals
Early Baywindow Bus Parts Book
Late Baywindow Bus Parts Fiche
Type 2 Wiring Diagrams
Model and Year Variations
Type 4: Secrets Revealed
Distributor Parts & Specifications
PARTS INTERCHANGE MANUAL
Youtube Videos

There is a ton of information located at the top of the Forum section.

Mon Jul 21, 2014 9:26 pm

For the alternator to charge, you need voltage on the DF terminal on the alternator no matter the kind of regulator. So as Busdaddy suggests and check the continuity of the wires in the harness and then see if the regulator is supplying the DF circuit with voltage or not.

No voltage on DF would mean a bad regulator, while voltage there with no output would imply a bad alternator.

You may have to rev the engine a bit to get the alternator to excite.

Tue Jul 22, 2014 2:24 pm

Ok,

I checked the harness, looks good, also rouble checked all the fuses, re tested the voltage regulator, now I get 5 volts at DF.

I also checked the nut of the alternator while the motor was running and it was magnetic, which I believe means it is working?

Maybe unrelated, but the orange/yellow brake light is now illuminated as well...

Tue Jul 22, 2014 5:36 pm

Here's what you're working with:

The quick test is to measure the voltage (1) across terminals Df and D- and (2) from terminal D+ to ground, while the engine is running at a fast idle. If there is voltage between Df and D- (a couple of volts) and not 12 to 14 volts at D+, then the alternator is suspect. If there is voltage from D+ to ground but no voltage across Df and D-, then the regulator is suspect (this assumes the ALT light on the dash is lit).

Check and report back.

p.s magnetic nut means nothing.

Mon Jul 28, 2014 5:19 pm

According to your tests, my alternator is the problem. Pulled it out today and will get it rebuilt.

Also found the brake light switch had a prong broken off which caused the brake warning light to be on.

Hopefully I will be back up and running next week.

Thanks everyone for all the help!

Mon Jul 28, 2014 5:27 pm

these things are to be expected. You will get it running the way you want it.

Word of caution. There are many threads here where the rebuild ends up with too long a post on the back that hits the metal cooling cover and shorts out the harness and other things. Double check the length of the post to be sure the backing plate clears. Use some modeling clay etc if you need to, to get the clearance.

Fri Aug 01, 2014 5:24 pm

Alright, my problems are not solved unfortunately....

Took the alternator in to be tested and it works fine (it was a place that specializes in rebuilding them.

So I reinstalled it, and re tested the voltage regulator, my results:

D+ to ground = 5v

DF to D- = 2v

I also checked the wires between the alternator and the voltage regulator and they are good.

I need to order a few things from bus depot, should I be ordering a voltage regulator as well?

Thanks!

Fri Aug 01, 2014 5:30 pm

Time for some indepth testing with it installed, read all of this: http://www.ratwell.com/technical/ChargingSystem.html

Fri Aug 01, 2014 8:07 pm

Quote: Took the alternator in to be tested and it works fine (it was a place that specializes in rebuilding them.

So I reinstalled it, and re tested the voltage regulator, my results:

D+ to ground = 5v

DF to D- = 2v

I also checked the wires between the alternator and the voltage regulator and they are good.

I need to order a few things from bus depot, should I be ordering a voltage regulator as well?
Those readings tell me the voltage regulator seems to be trying to work. With 2 volts from Df to D-, there should be enough rotor current to get the alternator going. The 5 volts from D+ to ground says the alternator is just barely working.

In general, voltage regulators seem to either work or not (especially the solid state models). Alternators, on the other hand, can mostly fail, but not completely, depending on how many diodes fail and how they fail (open or short). Thus, the verdict is unclear.

I'd take the alternator back in along with the regulator and harness, and have them tested as an assembly. For the test, make sure you add a ground wire from the alternator case to the regulator case, as it's not in the stock harness. When he tests it, you should get 14+ volts on both B+ and D+ to ground, and B+ should take a load.

The alternator has two sets of diodes (nine total: three for the D+ output, three for the B+ output, and three are shared between outputs). All must be good for the alternator to work.

By the way, did you check the tranny ground strap? It's part of the alternator circuit. As the bus starts (also using the tranny ground strap), it's probably OK, but can't hurt to check...

Fri Aug 01, 2014 9:12 pm

I think you did the right thing ordering the regulator. It's not producing enough voltage across the armature. They run about 5 to 7 volts across the armature not 2 volts.
D+ becomes part of that too (It still could be bad D+ diodes, the three little isolation diodes in the alternator)(hopefully the shop tested it using D+ so they know for sure the D+ didoes inside the alternator are good). Under normal operation D+ needs to be at a little over 14 volts but since one thing causes the other that causes the one thing well there you have it.

Sat Aug 02, 2014 9:23 pm

Ok, more info that might shed some light.....

My van is a '74 but has a 2.0L engine and the 70 amp alternator. While looking for a new regulator, I realized that the previous owner had installed this voltage regulator:

http://www.busdepot.com/043903803b

Which according to bus depot is not the correct regulator? Could this be as simple as the old owner bought the cheapest regulator and it isn't compatible with my van?

Sat Aug 02, 2014 10:32 pm

As it fits "68 through 71", it would seem to be for a generator, not an alternator. Actually, their listing is very confusing, reading it again.

From the picture, it seems to have a connector which plugs directly into the harness (alternator style), not individual wire connections (generator style).

One giveaway is that on generator regulators, the charge current passes through the regulator (two big red wires) to measure the current. Not so on alternators, as they are inherently current limiting, without help from the regulator, and connect directly to the battery (via the starter).

Sun Aug 03, 2014 8:57 am

Bus Depot application notes are generally not to be trusted. Just about everyone selling a regulator with a
reference part #043-903-803B indicates it is for alternators with ext. regulator, as 72-79 busses had.

Sun Aug 03, 2014 9:29 pm

It would be nice to see a photo of your Alternator. Basically there are two types of Alternator external Voltage Regulators, A Circuit and B Circuit. A Circuit regulators were used on the Bosch and B circuit on the Motorola Alternators. A circuit regulators regulate the current through the brushes and the armature on the ground side. B circuit on the D+ side. Part's Web-Sites aren't differentiating between the Bus and the Camper Alternators. Voltage Regulator. These regulators are likely just for the 55 amp alternators. RockAuto shows the 70 amp Alternator as a ACDelco unit.
ACDelco Voltage Regulator E685A.

Sun Aug 03, 2014 11:32 pm

And that's why the alternator rotor winding (unlike the previously used generators) is fully floating - either type will work. Electronic regulators are generally the 'A' type (rotor pulled low); mechanical regulators are generally the 'B' type (rotor pulled high). Alternator regulators aren't involved with alternator current output (aside from the ability to provide sufficient rotor current, and physical fit, if of the internal type). They strictly control output voltage.

Mon Aug 04, 2014 11:17 am

Noticed on the 73-79 Bus schematics under "Technical" above that the external regulators are drawn as mechanical devices! I just figured they were using an obsolete schematic symbol and they were really transistors by then. "telford dorr" interesting post you made above, Do you have any other info on the mechanical type Alternator Voltage Regs?

Mon Aug 04, 2014 3:14 pm

Haven't seen an external mechanical alternator regulator in ages. All seem to have been replaced over the years with the electronic type.

Not sure on what years mechanical regulators were used by the factory. I assume '72 or so, but not sure after that. Typically, the schematic shows the correct components as delivered by the factory, so mechanical regulators may have gone all the way to '79.

All internal types were electronic.