Board logo

Alternator driven rev counter??
Chippy - 7/1/10 at 10:29 PM

Hi, anybody know what is required to use the above system. Special alternator? Special rev counter? Is it possable to alter rev counter for differing alternator drive ratio's? Thanks Ray

russbost - 7/1/10 at 10:43 PM

I've not seen an alternator driven rev counter, but I've got an alternaor driven set of shift lights.
They are very accurate & are driven simply by the increase in the frequency of the waveform generated by the alternator (so far as I understand it!).
The downside is that they need to be calibrated to the vehicle so you need an accurate rev counter (frequently available on timing lights) to be able to accurately set them up in the first case.

I can see no reason (other than the calibration issue) why a suitable rev counter wouldn't work in this way, but haven't had any personal experience outside of the above. HTH

Dingz - 8/1/10 at 08:36 AM

They old ones were a mechanical rev counter, cable driven off the back of the alternator/dynamo

Breaker - 8/1/10 at 09:37 AM

I have an alternator driven rev counter on my '96 Volvo 940. It has a seperate connection on the alternator and works on the frequency of the generated waveform I think. (taken into account the crankshaft and alternator pulley diameter ratio)

sebastiaan - 8/1/10 at 09:57 AM

Back in the 'ol days, diesels used to be like this. The alternator indeed had a special connection on the back and the rev counter needed to be calibrated to the engine's pully arrangement.

02GF74 - 8/1/10 at 11:13 AM

quote:
Originally posted by Chippy
Hi, anybody know what is required to use the above system. Special alternator? Special rev counter? Is it possable to alter rev counter for differing alternator drive ratio's?


As already said, some alternators have a separate terminal to provide electrical signal for a rev counter - as used in diesel engined cars.

Asuming you want t o do this, then simplest would be to take the above and ensure that your cank pulley is in correct ratio i.e. as per the original engine.

M understanding is that the terminal taps into one of the stator coils - 3 of them to privide AC signal.

I is easy enough to do this yourself if you know where to connect.

The signal may need some conditioning i.e. limit to 12 V to be like that from the coiul although that has high voltage peaks due to switching the coil.

Te trickiest part would be to get the rev counter to dislplay rpm correctly. You would need to sort out the gearing = crank and alternatopulley diameters. Then depending on the rpm counter, if after market are settable for 4,6 or 8 cylinders you woujld need to ensure your alternator signal is one of those frequencies.

It may be possible to use a frequency converter - speedo healer.

Or if you know your way round the internals of rpm counter, a simple resistor change would allow correct display.

In short, yes, it can be done but in reality is non trivial.

[Edited on 8/1/10 by 02GF74]

Chippy - 8/1/10 at 02:16 PM

Hi, thanks for that guy's, this is for a couple of diesels due to be fitted in a boat, so the alternator powered rev counter seems the easiest route to go down. So should be fairly easy to find the correct alternators and a couple of electronic rev counters. Thanks for the help. Cheers Ray