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Flickering ammeter


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I have noticed the ammeter needle in my TR4a has started to flicker quite noticeably. It doesn't do this all the time, rather it happens every few seconds and flickers wildly from mid point down to the -ive end, then goes steady for another few seconds. Any ideas on cause and cure?.

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Those details are a bit sketchy, which makes diagnosis difficult Edmond (apologies if that is not actually your name)

 

Does it do it all the time when the ignition is switched on or only with the engine running ? Are you running an alternator or a dynamo? Have you made any recent changes to the electrical system or fitted extra equipment ? Does the running of the car seem affected ? If you have exrta equipment (eg spotlamps) is the circuit separately fused ? Do you have electronic ignition ?

 

An ammeter has a mechanical centre-zero so its unlikely to be a meter fault or a connection to it; something must be causing intermittent high discharge to cause the flicker. I would first look at the wiring run from the ammeter to the fuse box in case something is shorting to chassis. Since you do not mention blown fuses is it may not be after that point. If that looks OK then pull each fuse in turn to see if the fault stops. If it does not its probably in the ignition or charging circuits and could be a regulator fault.

 

Rob

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Rob - the car is converted to negative earth, has an alternator and Kenlowe fitted with no other electrical equipment added. Original distributor/points rather than electronic.

 

When I switched it on this morning (but didn't start the engine) I noticed that the Kenlowe was coming on and the ammeter dipping exactly as I had noticed when driving home late last night. Must investigate more.

 

Edmond

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Hi Edmond,

I am sure I have read somewhere that the electric fan can act as a dynamo and put ripples into the system - this could have been the pills or a dream!!!

 

 

Is it operated by relay etc (should stop this effect)

 

Roger

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If it's swinging fully negative then even given the inherent inaccuracy of the ammeter it implies that the Kenlowe is drawing around 30A and the alternator isn't compensating so that's not right. Disconnect the Kenlowe for a short while and see if the problem stops.

Edited by peejay4A
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Edmond

Could it be that that the Kenowe has an intermittent short to earth causing the flicker discharge and now the contacts have welded themselves together causing the fan to be on when it should be off.

(Roger

My electric fan was originally wired directly to the ignition circuit and this had the effect of the engine continuing to run after the key was turned off until the fan ran down)

 

Best of Luck finding your problem

 

Rog

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Roger funny you should mention the fan as dynamo effect. I have a revotec fan operated via a relay. However, I have wired up a warning light to come on when the fan is running as well as an override switch so I can turn it on before the temp sensor does so. At high speeds, when the engine is not warm, the warning light glows (not as brightly as when the fan is actually on). The only explanation I can think of is that the fan turns at high speed an generates a current!! I thought I was going mad...perhaps not!

 

Bob

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OK, that looks like a fault in the fan drive module - or perhaps a faulty temperature sensor. Obviously it should not keep cycling like that.

 

Rob

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