[T3] Voltage Regulator

[Jim Adney]

On 1 Nov 2010 at 21:45, Tim Keohane wrote:

> I charged the battery @ 10 amps for 24 hours, then 2 amps for 3 days.  
> 4 hours after removing the charger these are the results:
> Battery charge 		13.5 volts

That was actually quite hard on the battery. You put more than 240 
amp-hours into a 45 amp-hour battery. The result has to be lots of 
hydrolyzed water and probably some battery plate damage. (Plate 
damage occurs when hydrolization occurs inside the sintered plates, 
causing them to flake off bits of plate material.)  

> @ 2500 RPM  No Load
> Battery 				14.5 volts
> Gen.			        14.5 volts  10.5 Amps
> Battery circuit  		1.6 Amps
> Fuse Panel circuit        8.5 Amps

This seems pretty normal. I'm surprised that the V at the generator 
isn't a bit higher than the V at the battery, but the low voltage 
drop was probably due to the low current. Still, from the numbers 
below, I would have expected ~0.4 V difference.

Note that the current out of the generator = the sum of the currents 
out of the VR. As it should be.

> @ 2500 Low Beams ( 2x 55 watts)
> Battery				14.5 volts	
> Gen.				15.2  volts   20.5-21.5 amps
> Battery circuit                1.5 - 2.5 amps
> Fuse panel circuit         19.3 amps

Again, this is pretty normal. At the same voltage the battery is 
taking about the same current, while the excess is going to the 2 
headlights via the fuse panel, and the currents in and out of the VR 
sum the same.

> The generator light only comes on when I turn the key to start. Once 
> started it goes out, and does not indicate when the generator is 
> insufficient to maintain the battery @ 12.5 volts or higher. I can 
> visualize the generator light remaining out if it V R is receiving 
> ample current regardless of the circuit out except when the battery 
> goes down during use. I would also think more amperage would flow to 
> the battery to maintain it. 

I'm guessing that you're expecting more out of your idiot light than 
it can actually deliver. It's exactly the same as any other 
automotive charging system idiot light and they are not a perfect 
system.  They only tell you when there is a difference between the 
generator output voltage and the battery voltage. When they both go 
down together the light does not light.

> My first impression is everything here seems within parameters, but  
> the battery dies then the car without an indication. When a fresh  
> battery is installed the car starts and runs without a hic-up.  I have  
> not checked the strength of the battery. I guess I'll have to replace  
> the bulbs with something requiring a little less.

I think you're on the right track. The electrical system on our cars 
cannot support those lights for extended drives. If you drove with 
those headlights for no more than a half hour at a time, followed by 
several hours of no headlights, they would probably be fine. You just 
need to give the charging system and battery a chance to recover. 
Note that nothing much happens at idle; the generator needs decent 
rpms to put out its rated current. 2500 rpm was a good choice for 
your tests.  

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