Rev counter

[Gordonmc]

Can anyone explain the failure of a replacement rev. counter.

I bought a VDO unt at a boat jumble to replace the duff one a got with the boat. Make, not known, but its German. The alternator has no "W" terminal and the feed is a field winding connection. I wired up with the alternator going to the S terminal, live and earth. On switching the engine on the rev counter goes off the scale. Using the calibration screw on the back will only turn the counter down to 3,000 revs on tick-over.
I can only think the a/c sine feed is over-high for the counter.
Any thoughts? If UI have to go for another counter, what type/make?

The engine is a T90 1.5 BMC

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[BrianMoffat]

Gordon

Do you know (at least) what make the alternator is?

If by the " S " terminal you mean the AC TAP then I suspect that the AC signal is indeed too high, but knowing the alternator would help...

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[paulrossall]

I bought VDO unit for my Yanmar 2GM20 which has an Hitachi alternator with no "W" terminal. Took alt. to local Lucas service chap (went in my scruffy boat working clothes) and he put a "W" terminal on for the cost of a drink (£5). Then I put + to the ignition switch so alt. goes live when key switched on. Wired the lights with a seperate switch into the cabin lights circuit. Hope this helps.
Paul

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[Jools_of_Top_Cat]

Also, you need to set the pully ratio on the unit, on a yanmar you also need a capacitor across the signal to gnd on the rear. This may have been the fault with the first unit?

If you feel able you can solder on your own signal wire, remove back of alternator you will see a plate with diodes on, and 2 3 or 4 heavy copper wires soldered up to it, take your signal from any of these copper wires. Only do this if you are sure.

A helpful webpage http://www.fwmurphy.com/Bulletins/SECTION 20/TAH-97026B.pdf

It may answer some of your questions

<hr width=100% size=1>Julian

<A target="_blank" HREF=http://www.topcatsail.co.uk/Honda_00.html>Honda Formula 4-Stroke racing</A>

 

[terryw]

I had a problem with a rev counter on my boat. One was reading higher than the other, and the difference got progressively larger as the revs were increased. The problem was with the selector switch on the back, which tell the counter how many cylinders the engine has. Does yours have this selector, and is it set correctly?

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[paulrossall]

I agree you have to adjust the calibration switches on the back of the VDO unit so the scale reads correctly. I do not understand your comment about a capacitor. I did not fit a capacitor and the VDO instructions did not say anything about fitting one. I did go through the fitting of the unit with the electrical/electronic engineer who wirede my "W" terminal and he did not mention a capacitor at all. He just confirmed I fit it as I have described. It works well.
Why do you think that a capacitor should be fitted and what purpose does it serve?
Paul

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[paulrossall]

I agree you have to adjust the calibration switches on the back of the VDO unit so the scale reads correctly. I equate this to your "set the pulley ratio". I do not understand your comment about a capacitor. I did not fit a capacitor and the VDO instructions did not say anything about fitting one. I did go through the fitting of the unit with the electrical/electronic engineer who wired my "W" terminal and he did not mention a capacitor at all. He just confirmed I fit it as I have described. It works well.
Why do you think that a capacitor should be fitted and what purpose does it serve?
Paul

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[Jools_of_Top_Cat]

On the hitachi alternators you need a capacitor to drive a alt sensed tacho, or at least the one I have, part number FAR32842 at ASAP see below>

100mF across the signal. I presume to dump AC leaving a DC to drive the tacho, I was sent these with my order from ASAP. without it the counters will not read at all. I think it is only for hitachi alts.

here >> http://www.asap-supplies.com/

search for product code 708194

or speak to the guys at ASAP, they are very helpful.

Which alternator do you have, If it is on a yanmar and you counter is the same as mine you will definately need them.

<hr width=100% size=1>Julian

<A target="_blank" HREF=http://www.topcatsail.co.uk/Honda_00.html>Honda Formula 4-Stroke racing</A>

 

[paulrossall]

I was aware I did need a capacitor for the FAR tacho. Maybe it works on DC? You do not need one with a VDO tacho.
I paid £35 for my VDO tacho (new) from boat jumble. I did go to the ASAP stand at the London boat show and was quoted about £100 for the Far unit and decided at that price I was not buying. ASAP told me I needed a capacitor with the Far unit.
My VDO tacho works well and I found the fitting easy. How much did you pay?
Paul


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[Jools_of_Top_Cat]

ok, sorry, different units then, I did think they worked on the same principal, if I have led you down the wrong alley I appologise.

I bought a pair of FAR tachos at £35.00 each ASAP had them on special offer, and I could not resist at that price.

The unit is now back to £53.85 so I am not sure why you were quoted £100, I presume it is the same unit you wanted?

sorry for misleading advice.

<hr width=100% size=1>Julian

<A target="_blank" HREF=http://www.topcatsail.co.uk/Honda_00.html>Honda Formula 4-Stroke racing</A>