TR2/3/3A Amp Gauge-erratic reading after alternator conversion

[Redoakboo]

I have done a alternator conversion on my 54 TR-2 that I am restoring. I am now getting a erratic reading in the negative side of the gauge. Is there a wiring change I need to make to clear this up?

 

[karls59tr]

There are ways to correct that but I just installed a period correct looking voltmeter.

 

[Hamish Racing]

Have you converted to neg earth
And changed the wiring in the regulator. ?

 

[Redoakboo]

Yes, I have neg ground and the Dummy Regulator installed. The engine starts right up and runs fine but, the amp meter fluctuates between 0 and -15.

Dick

 

[Redoakboo]

Yes, I have neg ground and the Dummy Regulator installed. The engine starts right up and runs fine but, the amp meter fluctuates between 0 and -15.

Dick

I have seen some posts on the installation of a shunt on the back of the amp gauge. What does that do, an where is it installed?

 

[Sarastro]

A shunt is used to change the ammeter's range. It won't affect what you are seeing.

By a "dummy regulator" you mean just a box with no innards, right? If there still is some stuff in the box, it could cause what you are seeing. Looking at Hamish's photos, I would leave the field (F) terminal disconnected, not grounded (E terminal). That could cause what you are seeing.

What kind of alternator are you using? Does it have an "S" (sense) terminal? If so, that should be connected to some point in the electrical system.

Do you have another ammeter you can try? It's possible that the ammeter just coincidentally started sticking right now.

In the end, you might just have a bad connection somewhere.

 

[charleyf]

I will pass on some advice given by Randall Young. The alternator is negative ground. So if your car was set up for positive ground you will need to reverse the leads on the amp gauge. Second the amp gauge is set for 30 amps. Your alternator output is about 60. To accommodate the increased amps a shunt is needed . I can get you the measurements of the shunt if you want to go that way.
I have 2 TR4s with alternators and went with a voltmeter in place of the amp gauge. The voltmeters are available cheap, like at Harbor Freight. They are 2" just like the amp gauge. To hook it up you just need to find a green wire behind the dash.
Charley

 

[Redoakboo]

A shunt is used to change the ammeter's range. It won't affect what you are seeing.

By a "dummy regulator" you mean just a box with no innards, right? If there still is some stuff in the box, it could cause what you are seeing. Looking at Hamish's photos, I would leave the field (F) terminal disconnected, not grounded (E terminal). That could cause what you are seeing.

What kind of alternator are you using? Does it have an "S" (sense) terminal? If so, that should be connected to some point in the electrical system.

Do you have another ammeter you can try? It's possible that the ammeter just coincidentally started sticking right now.

In the end, you might just have a bad connection somewhere.

I have the C40 Style neg ground alternator that looks just like the old generator. I bought it from British parts Northwest along with the NCB100XB Dummy Regulator. It has the diode setup inside. Both came with wiring diagrams for setup.

 

[Graham H]

Yes, you need to reverse the leads on the amp gauge and that should fix it. Generally what happens after you start the engine is the amp gauge will show +15 to 20 amps but only for a short time just until the battery regains the charge then drop back to +1 or 2 amps.

Graham

 

[Redoakboo]

Yes, you need to reverse the leads on the amp gauge and that should fix it. Generally what happens after you start the engine is the amp gauge will show +15 to 20 amps but only for a short time just until the battery regains the charge then drop back to +1 or 2 amps.

Graham

Mine is showing -15amps, not +15 amps?

Dick

 

[charleyf]

To correct the negative reading on the ampmeter you need to switch the leads on the back of the ampmeter. This has been stated in my previous message as well as from Graham. This requires that you access the back of the amp gauge and remove and switch the connections from one spade to the other. You are now running the direct current ( DC) in the opposite direction with the negative ground.
Charley

 

[Redoakboo]

To correct the negative reading on the ampmeter you need to switch the leads on the back of the ampmeter. This has been stated in my previous message as well as from Graham. This requires that you access the back of the amp gauge and remove and switch the connections from one spade to the other. You are now running the direct current ( DC) in the opposite direction with the negative ground.
Charley

Charley,

I'm looking at a digital pic i took of the back of the dash. I assume the two wires to swap are the heavy brown ones? Dick

 

[charleyf]

Charley,

I'm looking at a digital pic i took of the back of the dash. I assume the two wires to swap are the heavy brown ones? Dick

Yes those are the wires. Just switch the spade they are located on.
Before you do this disconnect the battery of the car. Those wires are hot all the time.
Charley

 

[Redoakboo]

Thanks, will try tomorrow.

Dick

 

[Sarastro]

Switching the wires will make it read in the right direction, but won't change its erratic nature, unless the problem is the ammeter needle sticking on the (-) side of the meter. But Charley raises a valid question: is it continuously erratic or just for a minute or so after starting? If the latter, it may well be normal.

 

[charleyf]

Just for the record and in case somebody else is interested. I looked up my notes on what Randall Young recommended for the shunt wire. It is 3.5" long using a 16 awg copper wire. I have set up my amp meter with a shunt but am still a few weeks away from starting the car for the first time.
The shunt is the curvy white wire in the photo.
Charley

 

[Redoakboo]

Switching the wires will make it read in the right direction, but won't change its erratic nature, unless the problem is the ammeter needle sticking on the (-) side of the meter. But Charley raises a valid question: is it continuously erratic or just for a minute or so after starting? If the latter, it may well be normal.

Just for the record and in case somebody else is interested. I looked up my notes on what Randall Young recommended for the shunt wire. It is 3.5" long using a 16 awg copper wire. I have set up my amp meter with a shunt but am still a few weeks away from starting the car for the first time.
The shunt is the curvy white wire in the photo.
Charley

Is the shunt wire run from the two large brown wire connectors? Dick

 

[TFB]

The shunt is a jumper from one ammeter terminal to the other.

Does the ammeter read negative with the lights on and the engine not ruing?
Tom

 

[charleyf]

Below is a picture of the back side of an amp gauge. Note at the right in the picture are the two large spades for the brown wires. Pointing to the left are two smaller spades. These can be used for the shunt if you choose to use one. Note this is from a TR4 so it has it's own light socket.
Charley

 

[Jim_Stevens]

Can you define “erratic”? I’ve got a similar setup, pos ground, with a shunt. On start up, ammeter reads high for 20-sec or so, while the battery is charging. Then for the first 10-min or so, I’ll see some spiking, irrespective of the load (like my OD). Then it goes away. Not concerned.