Alternator cutting tacho output

[cmedsailor]

Suggest OP apply a large load to the alternator (fridge lights or what have you) and see if that brings tacho back to life. If not i suggest perhaps the tacho itself is failing when hot. good luck olewill

I was not planning to post anything in this thread as I have absolutely no knowledge in these things. However, I had a very similar problem some years ago that an electrician managed to fix. He explained me what he did but as expected I understood nothing!! The only thing I have managed to understand is that a resistance was necessary and so he connected this light somewhere under the tacho and that fixed everything. Just don't ask me why he did that.

 

[Birdseye]

The rev counter on my Volvo 2030 drops to and stays at about 800 RPM, regardless of actual RPM, after a period of running. I'm exploring various avenues why that could be. But I've read on CruisersForum that when the battery is fully charged the regulator will cut the alternator output (as it should) which will also cut the voltage to the tacho out put (W+ on the Volvo). That doesn't seem right to me??

The tacho works off the alternating voltage generated by one coil of your alternator. The fact that it still records 800 rpm suggests to me that its not the alternator coil which is failing. If it were, then the revs recorded should fall to zero. If the issue was a bad or intermittent wiring connection then I would expect rev figures all over the place not a steady 800. Much more likely is a fault in the tacho itself. The 2030 tacho isnt a good one and does suffer from dampness getting in and affecting the hours meter etc.

Can you beg / borrow / steal another tacho and check the signal that way? Failing that try taking the tacho out, bring it home and bung it in the airing cupboard. If you are handy, take it to bits and check inside it for corrosion / damp - its easy enough to get apart

 

[charles_reed]

It's not right. The rev counter is driven by a feed from the W terminal on the alternator. This terminal outputs an alternating current, the frequency of which is proportional to the alternator speed (and hence to the engine speed). If it works OK for a time, it's possible that your rev counter may be faulty.

Either rev counter or, in my experience, the alternator is about to pack in.