[T3] A Tale Of Two Regulators

[Jim Adney]

On 24 Apr 2014 at 11:24, Chris Sheridan wrote:

> My Daily Driver is again experiencing electrical issues. You may remember I
> replaced the battery, regulator, belt, generator brushes about a year ago,
> and the generator itself about 2 years ago.
> 
> Over the last month or so I noticed the lights dimming at idle. When I rev
> the motor or begin driving the headlight brightness increases, when I stop
> at a stop sign the lights get very dim.
> 
> Also the battery began to no longer hold a charge. - slowly became
> difficult to start over a few weeks.

It's a little hard to explain all this in an email, but I'll try.

This is called a 12 V system, but it's really a 14 V system with a 12 
V battery. The generator's voltage output capability is proprotional 
to its rpm. When the engine is idling, the generator isn't doing 
anything, so you're just running off the 12 V battery. When you speed 
up, the generator is able to put out more than 12 V, so the generator 
takes over the load, and also puts charge back in the battery, so it 
will be topped up the next time the engine slows down.

The voltage regulator keeps the generator from putting out more than 
14.4 V, because more than that is hard on the battery, and also hard 
on any other electrical parts in your car.

If you've been driving long enough to fully charge the battery, it 
will have enough energy to hold the voltage up to 14 V at idle, for a 
short time, but the load that the car puts on the battery when the 
generator isn't charging will rather quickly pull the battery voltage 
down to ~12.6 V. The voltage will drop more slowly after that, but a 
decent battery will be able to hold the voltage above 12 V for a long 
time.

So, it's normal for the voltage to drop at idle and go up when 
driving. Normally, however, this drop will be gradual and not 
particularly noticable in the headlights.

> I brought the battery in for testing and was told it was shot. I had it
> replaced last week and it began to start brightly again, but then I noticed
> it started to start harder again after a few days, and the light dimming
> was still there.

Your old battery might have been shot, or it might have just been 
discharged. From your other symptoms, I'm guessing the latter. The 
question is, "Why isn't it getting charged?" Check the wire that runs 
from your VR to the battery. Make sure it is in good condition and 
making a good connection on both ends.

As Chad suggested, it's also possible that there's some unexpected 
current drain that is discharging your battery while the car is 
parked. Strictly speaking, this would not be called a short; it's 
just an unexpected load or drain. You can look for this as others 
have suggested, but in my experience, such problems are always due to 
non-factory equipment installed later in the car's life. The most 
common culprit is an aftermarket stereo with a digital display.

If you have one of these radios, the display should go OFF when you 
turn off the key. It it doesn't, that means that it is wired wrong, 
so that some part of it is on all the time and is draining your 
battery while the car is parked, even if you have the radio turned 
off. Such radios have two 12 V input leads: One that should be hot 
all the time, to maintain the radio's memory, and one that goes off 
with the key, to shut down the parts of the radio that take 
significant power. It's common for people to wire these both to be 
hot all the time so that they can play the radio while they're 
parked, but that "advantage" leads to the disadvantage of battery 
discharge.  

> I then ordered a new regulator from my FLAPS - it was an aftermarket exact
> replica of a 1970 bus regulator - more square and boxy than the typical
> bosch t3 regulator. - the computer insisted this was the right part for the
> 1970 t3 even though I questioned the Type 2 part number (211) - I replaced
> it into my car and began driving it and started smelling burnt wiring after
> about a block, so I parked it again.

The VR for a '70 Beetle, Bus, and Type 3 are all the same. If it has 
markings that say 14 V, 30 A, then it is correct. If it says 35 A, 
then it is the unique one for a '71 Bus and is wrong for your car.

All of these OE style regulators have a large resistor on the 
underside. That resistor has oil on it, left from the manufacturing 
process, when new. Once put in service, the oil burns off, putting 
out a bit of smoke. If that's all this is, then it's not a problem. 
If you actually have a wire that's getting hot, then you have a bad 
VR, or something is shorted or wired wrong.

> What gives. Can I use the older style regulator on a FI T3? What is causing
> my lights to change intensity based on my engine rpm?

The older style should be fine, as long as it's wired right and it's 
not the wires that are getting hot. My experience with aftermarket 
VRs, however, is that they tend to be of poor quality and don't last 
long. I have genuine Bosch 30-019s here if you can't find one 
locally.

The fact that your lights brighten up when the engine speeds up tells 
us that there is nothing wrong with your generator. So that's not the 
source of your problem.

-- 
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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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