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TR2/3/3A Amp Gauge-erratic reading after alternator conversion
- Thread starter Redoakboo
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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.
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
Luke Skywalker
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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
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
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
Jedi Warrior
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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
Graham
charleyf
Luke Skywalker
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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
charleyf
Luke Skywalker
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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
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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
Luke Skywalker
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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
The shunt is the curvy white wire in the photo.
Charley
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charleyf
Luke Skywalker
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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
Charley
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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.