Rev Counter

[Liam]

Wouldn't mind having a rev counter on the boat... but when it comes to electrics I am a complete noob. Are these relatively easy to fit or not?

 

Where abouts would I be able to get the appropriate rev counter from?

 

Thanks in advance...

[alan_fincher]

When I had a Perkins P3 many moons ago, the tacho was mechanical, and driven through a long cable with a rotating inner.

 

These days you would far more likely to to an electrically activated one.

 

As I understand it they require that your alternator has a "W" terminal, so actually measure the RPM of the alternator, but then have to be calibrated to reflect the engine speed.

 

Not all alternators have this terminal - ours doesn't for example, but I think you can open up the alternator and add a wire to do the same thing.

 

As well as on e-Bay, they are available from quite a few marine outlets.

 

Here's an example from e-Bay

 

http://cgi.ebay.co.uk/DURITE-12-24v-TACHOM...Q2em118Q2el1247

 

but as that one goes up to 4000rpm, you'd not be using a lot of the dial at canal speeds. I'm sure you could find ones marked up to, say, 2000rpm, and almost certainly cheaper ones too.

 

Alan

Edited May 15, 2008 by alan_fincher

[Liam]

Thanks Allen

 

Might be a daft question, but I suppose questions aren't daft when you don't know the answer...

 

If you have a twin alternator set-up, which alternator would it be hooked up to, and would this "W" terminal be labelled as such?

 

What other electrickery is involved??

[alan_fincher]

If you have a twin alternator set-up, which alternator would it be hooked up to, and would this "W" terminal be labelled as such?

If both have the required terminal, i can see no reason why you could not hook up to either.

 

I believe a 'W' terminal would normally be marked, unless you have an alyernator like mine where any original markings have been obliterated when the marinisers sprayed it all over in engine colour.

 

I've never wired one, but kind of assume it will need a 12 volts positive supply, a negative (earth) return, and that wire to the alternator. I can't immediately think of anything else. (It may also have a bulb to illuminate it, I guess).

 

What I don't know is how you calibrate them - you need to know your engine is turning at (say) 1000rpm, then adjust a preset on the meter to give the correct reading. Other than using some kind of stroboscope on a mark on the crankshaft pulley, I'm not sure how you know what is 1000 RPM.

 

I'm sure one of the gurus can tell us.

 

Keep us updated of progress, as I may well do the same at some stage, (although probably an oil pressure gauge, and a better ammeter should be higher priorities for us).

 

Alan