Lucas RF 95 voltage regulator modification.

[Ray White]

As I now have a 45 amp alternator with built in voltage regulation (Stealth Dynamater) I no longer need the RF 95 but I would still like to retain it in position and use the fuses and terminals as before.

Obviously the D and F terminals will become redundant... but can I still connect the input from the ammeter at terminal A ?

Would it be possible to avoid the field and shunt windings ( and contacts ) and still have an earth?

I don't want to destroy the instrument as I would like, if possible, to be able to still use it with a dynamo should the need arise.

[Steve Simmons]

I don't know much about wiring for alternators but you should be able to remove the guts of the RF95 and jump the connectors. You can also buy dummy regulators. Here's one I found in a quick web search:
https://www.autoelectricsupplies.co.uk/ ... tegory/169

[Ray White]

I don't know much about wiring for alternators but you should be able to remove the guts of the RF95 and jump the connectors. You can also buy dummy regulators. Here's one I found in a quick web search:
https://www.autoelectricsupplies.co.uk/ ... tegory/169

Steve. I had read that the RF95 could be used with an alternator like mine but I can't seem to find it now. The Dynamater fitting instructions show a complete bypass but if I could at least use the fused terminals it would save fitting another fuse box. I already have a plan to use a 4 way fuse box and several relays. I am not likely to fit a "dummy" voltage regulator but it is an option.

[stephen stierman]

I have installed new "guts" into one of these for TC2911 simply by soldering in new wires in lieu of using the metal lines that I just clipped away. You could certainly do the same with the fuses in the regulator. Just run your own circuits by looking at the wiring chart from what you have. There really is no reason to take power from the alternator as you can pull it from some of the other hot wires. Since the regulator function is not being used, just rewire it from the hot wires in the harness that you want to fuse.

[Ray White]

I have installed new "guts" into one of these for TC2911 simply by soldering in new wires in lieu of using the metal lines that I just clipped away. You could certainly do the same with the fuses in the regulator. Just run your own circuits by looking at the wiring chart from what you have. There really is no reason to take power from the alternator as you can pull it from some of the other hot wires. Since the regulator function is not being used, just rewire it from the hot wires in the harness that you want to fuse.

It seems that I have the choice to remove the windings completely or de solder the wires; neither options allow me to quickly switch the alternator for the dynamo in an emergency.

If I take 12 v from the ammeter to the decommissioned RF95 terminal A, where is ground?

[stephen stierman]

Well Ray, switching from one charging system to another in an emergency would be nice, but it is not something that is normally done and charging systems are not typically designed for such eventualities. I suppose if your alternator is of one wire design you could simply attach the hot wire to the starter or some other location to charge the battery. This would bypass the RF 95 in the charging function. You would have to get some juice to it to allow the fused circuits to work and if you looked at the wiring chart might be able to figure this out. However the idea gives me a large headache and eye strain so my suggestion would be a more simple solution.

[Ray White]

Stephen. I have made the decision to settle for a modified RF95 such as it no longer regulates the voltage but can be used as a four way fuse box. In order that the current is prevented from flowing through the coils I have de soldered them from their vertical stakes between which I have soldered a heavy wire. This enables the current to still flow through terminal A and the fuse . The coils are securely insulated and can be easily reinstated if required.

The terminals D and F remain vacant. However, there needs to be an external 12 volt supply link from terminal A to terminal A4 to similarly enable that fuse. The earth terminal is now redundant.

I was interested to read your suggestion of a "hot" wire. I have in fact done this with an Austin Seven. Many years ago, when I acquired "Trundles" my 1930 Austin Swallow, my Father in Law calculated the resistance requirement for a given length of insulated Nichrome wire and by passed the failed cut out system. For such a temporary solution it worked surprisingly well for several years.!!! It was important that the ignition never be left switched on without the engine running and the battery had to be disconnected when charging; other than that, it worked well on the rather feeble 6 volt Austin ...but I would not risk it with the 12 volt 45 amp alternator fitted to the MG.

[stephen stierman]

Ray, I have fitted one wire GM alternators to several British cars, my Mini for one to replace the generator and my Morgan when the Lucas failed. The particular GM unit that is used is quite easily obtainable, seems at every auto parts store and economically priced. I used the existing wiring harness and removed the regulators and just wrapped the proper wires together to take them out of the system, but these cars all had a separate fuse box.

[Kregg Hunsberger]

The RF95 regulator can be used for power distribution without any internal modification. The ground (earth E terminal) wires need to be removed. This leaves the buss floating at the supply side voltage. The Field (F terminal) wire also needs to be removed. The Alternator does not use the Field line. The supply current from the battery is through the ammeter, one of the regulator relay windings to the ignition switch, to the A1 terminal through the fuse to the A2 terminal. The D terminal is left unconnected. The A3 to A4 fuse is left in the normal configuration. I would recommend using a volt meter in place of the ammeter and connecting charge and sense lines of the alternator at the starter/Battery terminal.

[Duncan M]

When I rebuilt the original dynamo, I found that all that was wrong with it was the insulating paper between the field coils and case needed replacement.

[Ray White]

I am not very good with electrics but I a willing to lean if I can. One thing that concerned me was that by passing current through a winding in a different way than it was designed for may cause a build up of heat. That is why I bypassed it. The coils connections can easily be reinstated should a dynamo need to re fitted.

BTW...what is a floating buss ?

[Kregg Hunsberger]

In the configuration stated, the current through the coil winding is the same as the stock configuration supplying current to A terminal. By removing the connection to the E (earth) ground terminal, the voltage buss bar (the regulator frame) is no longer tied to the ground reference through the shunt windings of the solenoids. The current path to the F terminal is from the regulator frame through a resistor. There is no current in this path since this is no longer used to power the field windings of the Dynamo (generator), The regulator frame (what I called the buss) is floating since the D terminal from the Dynamo is also not connected (no voltage applied). In normal operation of the regulator, the frame is tied back to the battery through the cutout relay contact to the A terminal through the ammeter to the battery. When the Dynamo voltage is sufficient to pull in the cut out relay contact the regulator frame is tied to the battery as stated before and the current from the Dynamo charges the battery.

[Ray White]

Thank you for your advice, Kregg. I will not pretend to have grasped everything as you describe it but that is more to do with my failing intellect than anything else. I will study what you have written and with luck I shall learn from it.

Incidentally, the normally open contacts are open but the normally closed contacts (on the left) are not closed. Perhaps this is relevant?

[Kregg Hunsberger]

Ray, The relay on the left (unenergized) should make the connection between A (A1) terminals and the frame through the relay windings. The Relay on the right (unenergized) between the Field and the frame will be the resistor. That relay when energized shorts out the resistor. A good description of the regulator operation can be found on the TC Motoring Guild website at http://www.tcmotoringguild.org/techinfo/TClinic-62.pdf (Part 1) and http://www.tcmotoringguild.org/techinfo/TClinic-63.pdf (Part 2). I hope this is helpful.

If the right side relay is not making contact, the Dynamo cannot charge the battery. The relay contact in that case would need to be cleaned/adjusted.

[Kregg Hunsberger]

A correction to my last post. I got my relay functions reversed. The normally closed relay on the right shorts out the resistor in the unenergized state (opens to reduce charging at high voltage) and the relay on the right is the Dynamo cutout relay. Open when not charging (engine off) and when the Dynamo voltage is below battery voltage (hopefully). If not set correctly the Dynamo can act as an electric motor and drive the engine.

[Ray White]

Kregg. You should know that I have never driven this car since getting it; apart from the short distance from the trailer, up my drive and into the garage. I immediately began the re build which included removal of all the electrics that the p.o had incorrectly installed.

The contacts on the left should be normally closed at rest ... but on my voltage regulator it is slightly open. As I have an alternator (Dynamater) I shall not be using the regulator - therefore it's condition is somewhat academic, but I imagine the battery could not have been charging when I bought the car. Perhaps it might explain the seemingly new battery.?!?

[Kregg Hunsberger]

Ray, Given you are not using the regulator, the condition of the voltage regulating relay is a mute point since the Field terminal should not be connected to anything. If the system was intended to be functional, this condition would leave the series resistor in line with the voltage supplied to the field windings, reducing the output voltage of the Dynamo. This may have the effect of the cut out relay never having enough voltage to pull in the contact and never charging the battery. Given you are running an alternator, as I had said early in the posts, the Fuse blocks and distribution aspects of the regulator can still be used given the Earth (E terminal), Field (F terminal) and the Dynamo (D Terminal) wires are disconnected from the regulator. The Ignition warning light wire which originally connected to the D terminal should be connected to the alternator warning light wire. In both cases using the light with the Dynamo or alternator the voltage on both sides of the light is the "hot" potential when generating. When the system is not generating power the voltage from the ignition switch flows through the light through the charge system to ground.

Just out of interest, are you running a positive or negative ground? Since alternators are typically negative ground, you will need to make sure the fuel pump and some of the electronics will operate properly. Most of the electronics don't care, although it is something needed to be checked.

[Ray White]

Kregg. The TC is positive ground and I have a positive ground alternator ( a Dynamater ) with a relay that has a wire connecting terminals 30 and 86. The fuel pump and coil are set for positive ground as is the electronic distributor, fan and heater. To counter stray voltage spikes I am fitting relays with a diode. I hope they will also help protect the switches.