Rev counter RVI to RVC conversion

[benedict_h]

Hi all,
My 'tacho woes' as someone here described them, have finally been resolved. As I never got my British Jaeger RVI rev counter to cooperate with electronic ignition (Powerspark, later 123ignition), I installed an RVI to RVC conversion board as offered by Spiyda on Ebay.

The board comes with clear instructions and Spiyda have put four additional instruction videos on Youtube. The conversion involves some soldering. Calibrating the RVC set up is done by playing sound (wav) files, preferably from a pc or mac, Calibration is a bit of a hassle, but on the whole, the process is straightforward. At some point I needed support, which Spiyda gave promptly.

A few pictures of the conversion.

The rev counter being removed. Black wire (earth) is not visible, but should be attached to the rev counter. Brown is 12v from ignition, the two white/other coloured wires were used to create the inductive loop inside the instrument. In the new setup, one of them goes to the '-' of the coil for picking up the signal. Red is for the bulb, obviously.

The inside of the RVI tacho:

Switching the components. New board is at the top:

The new board in place:


The rev counter seems to be calibrated well. The needle makes no swinging movements as did the RVI setup, and indicates the number of revs one would expect. 
Regards,
Benedict

[enigmas]

Good photos but can't determine what you actually did! Can you elaborate on the problem and the fix?

[djm16]

The RVI tachometer relies on current pulses in the distributor power feed to trigger a voltage signal in the tachometer. It does this by having a single turn of the power feed cable take a loop around the primary side of a little transformer on the back of the tacho.

I also had some difficulty getting my tacho to work with a Pertronix system, although part of the problem was using a 0.3uF capacitor on the power feed line close to the distributor which reduces the size of the current transient through the power feed line.

The problem was overcome simply by adding an extra turn of the power feed line around the external inductor on the tachometer.

[benedict_h]

Hi Vince,
I could indeed have been more clear. Pictures are not always that self-explanatory, even to obvious tech chaps like yourself . The post was meant to be of some guidance for those members contemplating a similar conversion like the one I did with my rev counter, but as it seems, I told/showed half the story.

To elaborate, then, facts first:

• My rev counter had never worked since I changed from points to electronic ignition.
• Looking for a solution, the relevant frequently asked question in the support section of 123ignition.nl (supplier of my current dizzy) specifically stated Smiths RVI rev counters and their systems do not work in combination.
• An extensive forum search ('tacho', 'tachometer', 'rev counter' 'rvi' 'rvc', '60.000 days', 'show as threads' )gave lots of info, but also offered a somewhat puzzling view: some members had managed to get their electronic ignition to work with RVI, others hadn't. Some had their rev counter converted to RVC for that reason. For instance by a UK based company like JDO-instruments.
• I came across Spiyda on Ebay, an also UK based company offering a do-it-yourself RVC circuit-board for what I considered to be a reasonable price: about € 50, as I recall.
• From what I gathered, the job would be 'doable', my poor knowledge of car electronics taken into account, and possibly very rewarding (which it proved to be).

So I ordered the kit.

For the conversion, there are 4 steps to take. I have linked them to the corresponding videos by Spiyda on Youtube, because these show exactly what needs to be done, and how, in just a few minutes. Far better than any attempts I would make to describe the process.

1. Dismantling the rev counter 
2. Fitting the circuit board
3. Powering up the board
4. Calibrating the board

Note: the rev counter in the videos is not the same type as the British Jaeger installed in the P5Bs, but the connections are completely similar. 
Note2: for proof of concept as to the wiring, I used the wiring page at spiyda.com as guidance.
Note3: the circuit board has worked fine so far. Haven't done many kilometers yet though. I will post my experiences over a longer period of time under this thread. 

Hope this clarifies things, Vince.

Regards,
Benedict

PS As a side note: inspired by my own recent efforts, I took up further reading on classic car electronics. Interesting stuff, classic car electronics . I think it was johnwp5bcoupe who brilliantly directed someone on this forum to the downloadable version of this book: Classic British Car Electrical Systems, by Rick Astley. Just what I needed. Thanks John!

[enigmas]

A well organised, informative reply Benedict. I'm certain it will be of use to many on the forum.

As an aside, I asked for clarification as a number of years ago I modified a Jaguar 6 cyl tacho to work with the SD1 Rover V8 in my MG Magnette coupe project. I used a Jaguar conversion resource on the web and found that after adding a component to the electronics that the tacho is accurate to about 2500 rpm...and then the needle freezes! So any related info is alway of interest. Oddly enough when I hook it up to my RoverP5 coupe...it works fine! So there's obviously some issue with triggering signal.

[benedict_h]

A small update on the new RVC circuit board in my tacho. Since installing it, I have done some 800 kms with the car, and the tacho behaved very good. Steady needle, no hickups or hesitations of any kind. Think it's well calibrated too, although I'm not quite sure as I don't know the official indications at certain speeds. I do have the 123ignition app for comparison though. In the picture, you can see rev counter of the app (centre dial) showing just above 3000 RPM at 100 km/h, with the needle of the Jaeger rev counter indicating virtually the same number of revs.



Think it can be safe to say Spiyda offers a good product. Haven't put the system to the test at higher speeds / revs. Normally don't drive much faster than 100-110 km/h.


Regards,
Benedict

PS
Yes, the situation in the picture is not quite legal. Quite illegal, really. That's what my son said when he took it. Not setting a good example, I know. Well, done with testing anyway. It's King's Day here in Holland, with a free market. And low temperatures and some showers too, alas. Ah, well, off to the shed, then :-)

[Phil Nottingham]

The revs seem correct at that speed - the calibration is not linear in any event but small enough error not to matter

[barryr]

I feel the need to comment on the cool driving gloves!

Very Austin Powers!! " yeah baby - groovy!"

[Warwick]

Interesting. That's the same gearing as my 3.5L EFI 5-speed manual Range Rover in top.
3,000rpm at 100km/h.

[benedict_h]

May 2, 2017 8:33:55 GMT Warwick said:

Interesting. That's the same gearing as my 3.5L EFI 5-speed manual Range Rover in top.
3,000rpm at 100km/h.

Hi Warwick,
One would expect a lower Rev reading with a 5-gear box at that speed. I've always heard the V8 makes many revs in combination with the BW35.
Regards,
Benedict

[Warwick]

And 5th is an overdrive gear. 4th is 1:1
It does 4,000 in 4th at 100km/h.