TR2/3/3A Converting to Negative Ground.......

[karls59tr]

My generator died again.....200 mile trip...I left the electric fan on by accident(toggle switch) with headlights on as well...I guess that plus the heat did it....was going 70 all the way and the red light came on.
I'm thinking of converting to an alternator but I don't see any links on how to convert to Neg ground?

 

[malbaby]

You may find this link interesting.............................https://www.tr-register.com.au/Files/technical/narrowbelt.htm
I have done the full conversion on my car.

 

[Geo Hahn]

My generator died again.....200 mile trip...I left the electric fan on by accident(toggle switch) with headlights on as well...

That doesn't sound like a formula for sudden generator death - do you know what failed?

I'm sure there are advantages and good reasons for converting to alternators but I never have, preferring the simplicity and originality of the dynamo.

As for converting to negative ground - that is pretty simple and can be done while you are still using a generator. In your case polarity of the fan would probably need changing, the alternator would read backwards unless you swap the connections and the radio (if any) would have to be considered. All that and you should 'flash' the generator just to be gentle and proper.

 

[TR3driver]

Also best to swap the low tension wires on the coil. Doesn't make a big difference, but might as well keep the right spark polarity.

Any added electronics (like electronic ignition or a radio) will need attention (or even replacement) as well.

My guess would be that the control box was set just a little bit "hot", which allowed the generator to try to keep up with the headlights and radiator fan. One of the conundrums of auto generators is that they will easily put out enough current to overheat themselves, if not limited by the regulator. They can't "boil over", but the overheating will ruin the winding insulation and melt the solder on the commutator, leading to the dread red light. I went through that dance many times "back when" before I learned that protecting the generator is more important than keeping the battery charged.

Or, since the TR3 control box actually limits the sum of current and voltage (rather than either one by itself), it may be that just running with the system voltage way low (caused by the excess load) allowed the generator to put out too much current. I haven't experimented with that, but it seems like a real possibility given how the box works.

 

[karls59tr]

Thanks for the info guys. I'm going to convert to the alternator...if the generator tests good I'll use it om my 4A if I ever get around to it.

 

[Frank_D]

I have had ongoing charging issues over the last year. Had my C39 generator and two control boxes bench tested and set up by a reputable British Vehicle Electric tech over the winter. Re-installed the original Lucas control box and generator in the spring and all seemed good for about 2500 miles. Then I got the dim red light curse and not so good ammeter and voltmeter readings. Swapped control boxes to my after market back up. That helped but only for a while.

Last Friday I installed the Triumph Rescue alternator kit. My 59 TR3A was already negative ground. Install went very well and the voltmeter sits at 14 volts even at 900 RPM idle. However, my headlight relay system for the halogens is fed from the battery post on the solenoid. I am thinking I should move that feed to a power source like the horn feed to take it out of the ammeter circuit. With my current set up, the voltmeter drops to 12.5 V when headlights are on and the ammeter is well into the negative. Any comments on this last consideration? Thanks.

Frank D........ near Toronto Go Blue Jays

 

[TR3driver]

However, my headlight relay system for the halogens is fed from the battery post on the solenoid. I am thinking I should move that feed to a power source like the horn feed to take it out of the ammeter circuit.

The original horn feed is still on the battery side of the ammeter. Better IMO would be to tie the headlight feed into the same junction as the alternator output.

With my current set up, the voltmeter drops to 12.5 V when headlights are on and the ammeter is well into the negative. Any comments on this last consideration? Thanks.

I am a bit puzzled, you said the headlight feed was tied to the battery. That should mean the ammeter never reads discharge for the headlights. Sounds like possibly you are mistaken about how they are connected.

Other than that, it sounds normal to me. Even alternators have reduced output at lower rpm, some more than others. Possible solutions include using a smaller alternator pulley (so it spins faster, but check that it doesn't turn too fast with the engine at redline); or getting an aftermarket alternator that has been modified for better output at idle (Lestek used to offer these, I'm sure others do as well).

Or, just accept it as normal. That was the original design after all, the car runs off the battery when the generator/alternator can't keep up. I ran that way for many years with my previous TR3A and it's 60 amp Ford alternator.

Possibly everyone knows this, but I'll mention just in case. The TR2 through earlier TR3A used a C39 generator rated at 19 amps. Later TR3A through TR4A used a C40 rated at 22 amps. Slightly larger physically, but mounts to the same points. The control box was modified slightly as well, and Lucas warned against using mis-matched components.

 

[Frank_D]

Thanks Randal for the insight. My feed for the headlight relay is at the output for the alternator which is the battery post of the solenoid. I guess I am just looking for what my new normal is and if you view waht I have described as "normal" that is good enough for me. I have retained the control box but it is virtually empty and only there as a place to connect the leads for the ignition lamp and to connect the brown/blue and brown/white leads. At a glance it looks normal. Here is an image of that part of the shelf. Thanks again for the feedback.

 

[TR3driver]

If you have the output of the alternator connected directly to the battery, then the ammeter is never going to indicate correctly. Any load connected to the other side is going to register as a discharge, even when the alternator is charging the battery.

That is the way some instructions say to do it, since the stock ammeter cannot handle the full output of the alternator. But what I chose to do instead was to install a shunt at the ammeter, to approximately double it's capacity (to 60 amps). That way, although the value indicated was half of the true value, I could still glance at it to see if the battery was being charged or discharged, a little or a lot.

Here's a shot of the shunt (taken as I was dismantling the car)

 

[charleyf]

Randall,
I would guess that the size and length of the shunt wire matter here. Can you tell us the wire size and length?
Charley

 

[TR3driver]

The shunt I came up with was 3.5" of 16 AWG copper. That worked with 3 different TR3/3A ammeters that I checked, but not with the TR6 ammeter that a friend checked for me. Since I don't know that all TR3/3A ammeters are the same, you should probably check yours.

 

[Frank_D]

Thanks for the shunt details Randall. As to my situation with the new alternator, here is a quick update which should conclude concerns. This morning after a few days at rest the battery was sitting at 12.8 volts. Startup was instant as usual and after a few minutes I brought her to normal idle. I checked voltage (digital voltmeter) across the battery and it was at 14.4; good. Then I put on headlights, blower fan, wipers and driving lamps. The voltage across the battery was at 14.3; also good. The installed voltmeter sitting under the dash was reading 12.5 at that point so the issue is the voltmeter.... sort of. I shut off all accessories and measured the voltage across the voltmeter terminals and it read 13.4, same as the installed voltmeter. I have that voltmeter connected to the white wire side of the ignition switch. Not sure why there is a difference of 14.3 at the battery and 12.5 at the voltmeter but all I really care about is that the battery is getting its charging from the alternator. I guess I could change the source of feed for the voltmeter but I would want it switched so not sure where to go with that. I am OK at this point. Thanks again to all who contribute.

Frank D.......

 

[TR3driver]

I have that voltmeter connected to the white wire side of the ignition switch. Not sure why there is a difference of 14.3 at the battery and 12.5 at the voltmeter

Similar to the results I saw with the factory voltmeter on my Stag, once I had recalibrated the voltmeter itself. The "problem" was that there was simply that much voltage drop through all the wiring and ignition switch, when the various loads were on. No single bad connection (except maybe the contacts inside the ignition switch), just a little bit at each and every junction.

Part of the reason I still prefer an ammeter.

To make the voltmeter work better, I'd set up a relay just for it, with the coil controlled by the white (or better yet green) circuit; and get power from as close to the battery as possible (brown circuit).