Ammeter Reading

[Mr Tiger]

Up until today the ammeter on my 2500 has shown a reading of around 0 when driving with all electrics off and a slight positive reading with the radiator fan or lights on.

Today, with all electrics off it's reading around +15 at tickover and up to around +40 when driving.

I don't understand ammeter readings. Either something has gone wrong (most likely) or it's suddenly started working correctly (least likely).

Any ideas?

Thanks,

Chris

[Mr Tiger]

Thanks for your reply.

I've just checked the battery and it's showing a healthy 13.5 volts stone cold (closer to freezing). It also had plenty of life yesterday when starting up after standing for 8 days.

I risked switching the ignition on and everything seems OK with a slight -ve reading on the ammeter. With lights on it had a slightly more negative reading.

I had quick look under the bonnet and noticed the fan belt is loose. If I'm really lucky perhaps this is the cause.

I still don't understand ammeters.

I think you made a good point about a volt meter being better with an alternator. I read something similar in Practical Classics many years ago.

Chris

[Mr Tiger]

Thanks for the replies, info and advice.

Just to clarify, the car has an alternator. I've checked the handbook and an alternator is correct for the model. It states it's a Lucas 17 ACR. A quick Google reveals this is a 36 amp unit. The chances of it being original are probably zilch so it may well have a more powerful replacement.

I think an ammeter is correct for the Vixen chassied 2500 and maybe a volt meter for the later S4? The handbook just lists the gauge as a battery condition indicator. I've just found a few pages further on a small paragraph about the ammeter.

It's looking like TVR built a fire hazard into these cars, along with just two fuses as standard. Luckily mine has a modern fuse box and a battery isolator switch. It should be safe for now, at least until I try running the engine again!

Chris

[Mr Tiger]

I tried tightening the fan belt but that made no difference. I ran it briefly with the alternator unplugged. It ran rough but not surprisingly stopped the dangerously high reading on the ammeter. I put a volt meter across the fuses one by one and could find no electrical flow. I then got a new alternator from my local motor factor. It cost all of £36 and even came with a fan & pulley. The spec sheet said its 36 to 43 amps so I hope it'll be safe. I fitted it on the weekend and touch wood it seems to have sorted the problem.

I still think a volt meter would be better. Does anyone know if AC made them?

On the other hand would it be possible to fit a hidden switch and probably some extra wiring so the car could run with the ammeter disconnected most of the time and just switch it in occasionally to check things are OK?

Chris

[Mr Tiger]

I think the new alternator has solved the problem - although I haven't driven the car since fitting it. The ammeter had suddenly started reading +40 when driving with no electrics on. I thought this was probably dangerous. It now reads around zero with the engine running at about 2000 rpm. It shows a negative reading when cranking and about +15 with the radiator fan on with the engine running. I hope this all sound about right.

Thanks for the input and ideas. I hadn't heard of a plug in volt meter before.

Chris