My newly acquired 500F runs nicely and everything works, but the battery was going completely dead in minutes.

After some investigating with a multimeter, I found there was no resistance at all between the positive and negative battery leads

My attention was drawn to the suspiciously shiny and new regulator. And, after opening it up, I'm surprised the car operated normally. The fuse is blown and has shorted against the adjacent pin, there's a lot of melted plastic inside and one of the gaps has bridged itself.

The corrosion inside the case suggests that water has got in (due to the rubber backing being damaged?) but I wanted to check some things with you all before I put a new one in:

1. is there likely to be any other cause for the regulator dying that I should check first? There's a chance that this one died because it got wet, but the original one may have been replaced for another reason.

2. Are there any faults (such as melted wires) I should look for that could have been caused by running the car with this failed unit in place? Everything seems fine.

Thanks for your help.

Hi
Just to be clear, your 500 does have a generator fitted, not an alternator?
The item on the underside of the regulator is a resistor, not a fuse. The one damaged is the field shunt which will only overheat if the voltage is too high. Despite the paint job and label I'd suspect that the regulator is either faulty or possibly 6V unit.
A new regulator is the first thing to get but you need to check the voltage as ou start te car first time and switch off the ignition immediately if the voltge goes above 14.5V.

Robert G8RPI.

g8rpi said:

Hi
Just to be clear, your 500 does have a generator fitted, not an alternator?
The item on the underside of the regulator is a resistor, not a fuse. The one damaged is the field shunt which will only overheat if the voltage is too high. Despite the paint job and label I'd suspect that the regulator is either faulty or possibly 6V unit.
A new regulator is the first thing to get but you need to check the voltage as ou start te car first time and switch off the ignition immediately if the voltge goes above 14.5V.

Robert G8RPI.

Click to expand...

Yes, I have a generator.

The more I look at this regulator, the more I think you are right. Someone has messed around with it.

When I find a new one, I'll be sure to test the volts.

Thanks.

Check what is the generator output voltage, it might also damaged and produce more than 12 volts (14.5) If that's the case you must overhaul your generator.

g8rpi said:

Hi
Just to be clear, your 500 does have a generator fitted, not an alternator?
The item on the underside of the regulator is a resistor, not a fuse. The one damaged is the field shunt which will only overheat if the voltage is too high. Despite the paint job and label I'd suspect that the regulator is either faulty or possibly 6V unit.
A new regulator is the first thing to get but you need to check the voltage as ou start te car first time and switch off the ignition immediately if the voltge goes above 14.5V.

Robert G8RPI.

Click to expand...

Hi Robert,

Just curious as to what faults could cause the voltage to go above 14.5v if a new (and hopefully correctly-functioning out-of-the-box!) regulator is fitted?

Al.

Hi,
A short circuit between the field terminal and ground will cause this. The generator is self exciting. The regulator works by either shorting the field directly to ground or via a resistor (the damged one in this case) to ground.
A shorted turn or turns in the field could also cause the damage as it would result in excessive field current. More current means more voltage. It does look like a dodgy "new" regulator though.

Robert G8RPI.

Personally I'd just replace with an electronic one. i know it doesn't look original but it will work accurately and repeatedly. People have modified the cover to fit over them if you want to disguise it a little.

I' be happy to build an electronic one into a old case if anyone want's to give it a try.

Robert G8RPI

Make sure that the generator and battery grounds are clean and tight. Make sure the positive cable ends at both battery and generator are clean and tight.
There is a ground cable that is supposed to go from the generator to the chassis, make sure that is there. Often it is missing.
Correct charging rate, as measured at the battery with the engine running at 2000 rpm, is anywhere from 13.5 to 14.6 volts depending on the state of charge of the battery. Check each battery cell with a specific gravity tester. If you find a dead or very low cell, the battery is bad.
Replace the voltage regulator with a solid state unit. The point type are ultimately unreliable and old school. The solid state ones are actually cheaper.
John

Thanks for the help everybody. :slayer:

A new regulator and the voltage looks to be fine, at revs and with/without everything turned on.

I'll put overhauling the generator and checking all the connections up on the list, however. In case the regulator is having to work harder than it should.