Electrical problems

[elclem1]

Hi all Just been running my LHD 69 TR6 engine for the first time. The amp gauge reads maximum deflection + once the engine has started. then reduces a little to about 3/4+ and there it stays. when the electric fan cuts in it goes up then comes down when it stops. I have changed batteries alternators and gauges to no avail. what could be the problem please?

[Mike C]

I assume that as you have a CC you are not feeding a fuel pump through the ammeter.

 

I have had similar problems in the past when the alternator developed a faulty voltage regulator , but you have changed alternators - you might have got 2 defective ones - check the alternator charging voltage is below about 14.5 V @ 3000 RPM . Regulators are cheap and easy to replace. This might help-

 

https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=32&cad=rja&uact=8&ved=0ahUKEwj4-o2MncbaAhWBu7wKHVPxCro4HhAWCCwwAQ&url=http%3A%2F%2Fvintage.mitchell1.com%2FPClubData%2Fchassis%2Felis73%2FV2I733026.pdf&usg=AOvVaw1eq8Ws1RKcVIApxew7YvRS

[RobH]

As Mike suggests - its possible that your ammeter is wrongly connected so that the fuel pump the cooling fan and other loads are connected to the battery side of the gauge - (it must be like that if the fan causes a positive reading). That means that any current taken by those circuits reads as a positive 'charge' on the meter because it flows from the alternator, through the ammeter to the load. Those connections should be on the alternator side of the ammeter for it to read correctly.

[elclem1]

Great will try that

[elclem1]

Ok I put another good amp meter from the alternator output to the battery +ve and it replicated the reading on the dash fitted one. as far as I can see I have fitted the fuel pump direct from the battery and still have the high +ve on the amp gauges. Battery voltage is 13.7 volts. I have another TR6 that has the correct readings and tomorrow I will change over the alternators but I am not holding out much hope. any other suggestions. when you say battery side of the amp gauge what exactly do you mean? on the back of the amp meter I have a brown wire that goes to the starter motor and hence +ve side of battery I have a brown and white wire from the alternator that goes to the back of the amp meter and a small one from the same terminal to the ignition switch looking at the back of the amp gauge I have brown on the right and the two brown and whites on the left is this correct.?

[RobH]

Its exactly BECAUSE the fuel pump is connected direct to the battery that you see this. The alternator is feeding current through the ammeter to the fuel pump as well as to the battery so the ammeter shows the sum of both currents. If you don't want it to do that then the pump (and the cooling fan) should be connected to the alternator output (your brown/white wire), not to the battery. Then the alternator current goes directly to the pump and fan without flowing through the ammeter to give the continuous high reading.

 

The ammeter will show a high initial discharge with just the ignition on, as the pump will be drawing current from the battery through the ammeter. When the engine is started, the alternator takes over and the pump current ceases to flow through the ammeter which will then just show the battery charging current.

[elclem1]

SORTED!!! many thanks for the help and advice I think I was being a duffer.