diesels and revcounters?

[aztec]

1) can someone explain where/how revcounters are run from altanators fitted to diesels.

2) what are the differences between the revcounter for a diesel, and that for a petrol.

3) where can i get revcounters for my diesels.

cheers,steve.

 

[Strathglass]

1. The drive for a diesel rev counter comes from the Y terminal on the alternator. There is a switch on the rev counters which is set to match , the type of alternator and the ratio of drive to driven pulleys.
2. Petrol engines have a spark which is used to drive the rev counter. Diesel engines have no spark so an alternative system is used.
3. www.asap-supplies.com have an extensive range of alternators.
I hope this helps. If you need more infi PM me.
Iain

 

[hlb]

But dont expect them to be very accurate. I have four rev counters and they all give different readings.

Haydn

 

[Guest]

I'm sure pb did an artical about building your own rev counter. it was in the last year or so but i can't remember exactly when. sorry to be so vague.

 

[mtb]

Hi Steve

What about a pulse sensor type fitted to an injector pipe ,I know you can get them for servicing.
Modern engines have a sensor fitted to the crank /fly wheel, this might be a cost effective way of making one up.
What about early dynamos which had the cable fitted ,then up to a rev counter
If you could work the ratios out then this could be quite cost effective as well.
Cheers
Mick

http://homepage.ntlworld.com/boats
I want a big steel ex trawler / tug v/cheep or swap for tug

 

[toad]

Older diesels sometimes have a mechanical drive,taken of the camshaft or injection pump.Take your altanator to a auto electrician who if you have not got a rev counter take off will fit a phase tap for you.Buy a rev counter from asap supplys or car accessory shop but make sure it has a coarse and fine adjustment as it must be calibrated for the type of engine.To get it spot on you will have to beg or borrow a infrared handheld rev counter.

 

[chrisc]

four seems a bit exessive ,Haydn,are they all connected?

 

[oldharry]

Usually the cheapest, and most accurate means of diesel rev counting is to use an optical pick up. This usually invovles a white (or light coloured) mark on the flywheel or some other accessible shaft, with a photosensor cell to provide the trigger. Usually there is a small light source - often an IR LED incorporated in the sensor to ensure accuracy. Another system is to provide a small magnet which operates a magnetic switch - either a reed switch or a hall effect transistor.

Maplin Electronics should be able to help.

Alternator sensed rev counters use the a/c output from the alternator and count the frequency of the a/c cycles, which of course varies with engine speed. Unfortunately drive belts usually suffer some degree of slip, giving innacurate readings!

Petrol engine rev counters simply count the on/off sequence of the contact breaker circuit. It would be possible to adapt an electronic rev counter for optical or magnetic switched input with a bit of messing about.

 

[vyv_cox]

I made an optical pick-up tachometer for an old Yanmar 12 many years ago. It was very cheap and simple to build. I was able to use an electronic head from a car and the unit was calibrated against a hand-held mechanical unit borrowed from the maintenance department at work. Calibration consisted of tuning a dust coil adjustment on the back of the unit.

 

[hugh_nightingale]

They sure did.

I can sort it out if you want but you could probably get a reprint

Hugh

 

[hlb]

No. Not exessive at all. One for each engine upstairs and one for each downstairs. Same trouble on last boat and the volvo ones are not calibratable.

Haydn

 

[Robin2]

What horsepower are the upstairs engines?

 

[billskip]

Brilliant Robin..I missed that one..

Bill
www.aegeansailing.co.uk

 

[ToMo]

Oh didn't he tell you his other one is a Catilina Flying Boat!!!

 

[aztec]

cheers ian, i couldnt see how the tacho knows what revs are going on. as i dont think the altanator has a pulse, like a dynamo or coil.

 

[aztec]

guys....what can i say? thanks one and all for the help, i think i can get over the problem now. i still need to source the thacho head but think i know where to get one.

cheers again, steve.