TR4/4A Exasperating experience with voltage regulators

[Sarastro]

This is a description of my trials while trying to get a working voltage regulator, in the hope that my experience might help others. It's a long story, but I'll try to keep it brief. The full story can be found here: http://tr4a.nonlintec.com/electrics/#voltageregulator .

When I restored my TR4A, I installed a new Lucas voltage regulator. Some time later, I noticed that it didn't seem to be working right. I took off the top off and immediately noticed that the cutout relay wasn't closing. So, I removed the unit, checked it in my electronics lab, and realized quickly that it wasn't even close to being adjusted right. I readjusted it in the lab and then tweaked it on the car. It was much better, but still not right--I suspect that the temperature compensation was wrong, and I just couldn't do much to fix that.

I am an experienced electrogeek, so I considered making my own regulator, but decided against it--just didn't want to spend the time and energy. I bought and installed a solid-state regulator, also from Lucas, from British Parts Northwest. It lasted about six hours. I called BPNW, and they quickly sent me a new one. I was still concerned, as the fabrication quality was abysmal, and previous experience didn't give me much confidence. The cluelessness of the design, in which transistors are mounted on a heat dissipator, but then the dissipator is enclosed inside the regulator box, didn't help.

My solution was to use a Bosch regulator designed for VWs. They are also used by the early-Porsche guys, and they work fine there. Only problem is that the Porsche/VW field coil is energized by grounding the field terminal, while the Lucas one requires applying the generator output to the field terminal. Not really a problem, at least for me--an electronic switch allowed the regulator to be used with a Lucas generator. The whole contraption is shown below:

The aluminum box on the right houses the switch. The Bosch regulator is a little weird, in that the generator output voltage is present on the housing, so you have to be careful working under the hood with the engine running. Full details of the circuit, if you are interested, are given in the link, above.

The good news is that this regulator works really well. After starting the car, the charge current is about 10 amps, dropping to zero in a minute or so. The ammeter stays at zero for any load that the generator can handle, indicating precise charge regulation. I know, it looks awful, but its good performance should maximize battery life, and with batteries going for about $200 today, that's important. And, after all, it's under the hood, where few people will notice it.

 

[DrEntropy]

Nicely done, Steve. Though surprising you haven't made the switch to an alternator as well. I did that to the MGB and also added relays to absorb initial load on switches for lights, horn and an electric pusher fan. Made the car a lot more "trustworthy" IMHO.

 

[Sarastro]

Ironically, I had the Bosch regulator because I removed it from my Porsche 912 after converting to an alternator. But for the TR, I just decided (for now, at least) to keep it stock. I've often felt that a car without a lot of additional electronics should be OK with the generator, but only if the voltage regulator is improved. This was, in part, an experiment to see if that was true, and I think now that it is.

 

[DrEntropy]

Ironically, I had the Bosch regulator because I removed it from my Porsche 912 after converting to an alternator. But for the TR, I just decided (for now, at least) to keep it stock. I've often felt that a car without a lot of additional electronics should be OK with the generator, but only if the voltage regulator is improved. This was, in part, an experiment to see if that was true, and I think now that it is.

Makes sense. The MGB was converted because I'd put halogen driving lights up front along with same in the headlamps, added aluminum radiator and the fan, along with some air horns. Just seemed prudent to change to the alternator and add the relays.