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1967 Tr4a Ammeter


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Hi,

Some time ago I replaced the dynamo with a 65 amp ammeter.

Following advice I replaced the  +/-30amp ammeter with a +/- 60amp unit and wired as the instruction that came with the alternator from Revington.

The ammeter never shows any positive charge but only a very small negative discharge.

I wonder what is going on and why I changed the ammeter?

Should the wiring be different to show both charge and discharge?

Regards

David

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I bet the alternator output is wired to the wrong side of the ammeter.

And you did not really have to change to a 60A one.

Bob

Edited by Lebro
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Well perhaps if you told us how yours was wired David we might be able to see what was wrong. Have you a diagram?

At a guess the alternator output is connected direct to the battery and not via the ammeter.

If you turn the headlights on without the engine running do you see an appropriate discharge - about 10A?

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Thanks David. If the car is wired up as per those instructions the ammeter should certainly be reading OK. I guess you will already have double-checked the connections including the new shorting links on the control box.

What does the ignition warning light do?   Does it behave normally?

That slight discharge you mention is probably the ignition circuit  - if the engine has stopped with the points closed the coil will draw a couple of amps when the ignition is turned on. It would be interesting to know whether the headlight load is registered properly though.  If not it might indicate a problem with the ammeter though being such a simple instrument that is unlikely. Turning the headlights on with the engine off should show a discharge of about 10Amps. If you then start the engine, that discharge should  disappear because the alternator will supply the current instead of the battery. 

If that is OK the next check would be to see whether the ammeter works in both directions. You can do that by swapping over the connections on the ammeter and repeating the test, in which case it should show a 10A charge. 

Alternatively, if you still have the old 30A meter you could try connecting that up and see if the indications are the same. 

I assume the battery is actually getting charged properly when you are running.  

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Having looked at the above modified wiring diagram for TR4a, I notice that headlights, cooling fan, radio, & cigar lighter are wire direct to battery, so they will not show as a discharge on the ammeter.   With engine running using any of those would tend to show as a charge on the ammeter, as the alternator is both charging the battery through the ammeter (correctly), & supplying current for the above items through it.

Does not explain you not seeing any charge registered.

Bob.

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+1

You are right Bob. I had misinterpreted how the lighting relays were shown and in fact the ammeter only feeds the relay coils - so the load test I mentioned above won't indicate as I expected.  

David it would be a good idea to move the feed point for the lighting relays and your auxilliary fuse box (those new red and brown wires) from the starter solenoid to the 'A' terminal on the control box. That way you should see discharges registered properly on the ammeter.

As the wiring stands, with the engine running and the headlights on there will be a 10Amp CHARGE shown on the ammeter. With the engine off the ammeter will not register the lights nor any substantial load as a discharge, other than the horns. 

If the meter shows nothing I suspect either the new ammeter isn't working or the alternator isn't giving any output. 

 

 

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