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dklawson wrote:Spider. Yes, that is an impulse tach. If it is not Smiths, it is similar. Current flowing through the coil also flows through that loop of white wire on the back of the tach and induces a pulse inside the tach which is then measured/processed. Later impulse tachs put the loop of wire completely inside the gauge case. Later impulse tachs can be identified by the presence of a pair of male and female bullet connectors on the back instead of the loop of white wire.

Thanks dklawson. I just went back and re-read my badly worded question! Yes, I know how the RVI style Tachos work, I was just wondering if almondgreen's Speedwell Weston Tacho is connected the same way? Sorry for that!

If so, then instead of trying to pick up the current from 12+ve to to the Coil, try the wire between the Coil and the Dissy.

Remember, being an electronic dissy, there is a constant current flow powering the electronics and no doubt it will have an internal filter so the back emf pulses don't mess with the electronics in the dissy. Result - instead of pulsed current (which can be sensed), it would be far smoother and less likely to be sensed.

Andreas,

123 ignition wave some solutions on their website http://www.123ignition.nl/faq.php#12 ;

Will my tachometer (RPM meter) work with a 123ignition distributor?
Yes, by far most of the tachometers work in combination with a 123ignition.
RVI type tachometers manufacturedby the Smiths Company, will not work properly though.

We have found two companies that offer solutions to this problem. They use the existingrev.counter to replace the electronics with another printed circuit board.
In the UK this is done by JDO-instruments ( www.jdo1.com ), and from the Netherlands
this is done by CASU-Utrecht ( www.casu.nl )

Maybe help to you?

Thanks for the link, but they do Jaeger und Smiths only.


I have to tell something more about my instrument.
It is not a real old Speedwell Weston instrument.
It is a Weston instrument that has been converted to a Speedwell Rev counter.
I bought it last year.
I opened it yesterday and saw that there is a circuit bird in it that looks very modern.
So it will be no problem to put another board into the case that will work with my dizzy.

I will keep You informed

Andreas, I was wondering why you were asking about a Weston when you had bought that repro one

It all becomes clear!

I am SURE that an ORIGINAL Speedwell Weston would have worked OK. Clearly the Repro guts are more akin to the Smiths type movement. I am sure that JDO1 will be able to sort this for you.

News from my Weston.
I put a diode into the signal wire, and it works....

Great! Congratulations on the economical and easy fix!

Excellent news!

A nice easy fix.

I can help with the various examples posed in this post.
Not all of the speedwell weston tacho's are potted ( including one i bought from you mark ) and ultimately the meter movement is always unpotted so the bypass method described previously is possible in each case wilst being reversible. the standard weston does not work on electronic ignition accurately. The rvi smiths also does not work correctly. As a rule any tacho made before ic's were used (70's) has an issue including the thick film smiths of the 70's.the issue is that early tacho's operate by sensing and clipping large voltage spikes present in a points system. Pm me if you have a question and i will try to help.

This comment posted by Jack of all Trades is NOT, repeat NOT, true "RVI type tachometers manufactured by the Smiths Company, will not work properly though".

Larry, I have acknowledged several times over the years that there are some RVI tachs that for whatever reason will work with electronic ignitions. I know you have had success. However, the lion's share of RVI tachs will not work with electronic ignitions. There are simply many more that won't work than those that will. You will find this information not just on Mini forums but on various other car forums and gauge repair web sites. For example, see the very bottom of the page Speedy Cables web page linked below.
http://www.speedycables.com/wiring_tacho_faq.html

LarryLebel wrote:This comment posted by Jack of all Trades is NOT, repeat NOT, true "RVI type tachometers manufactured by the Smiths Company, will not work properly though".

Hello LarryLebel, the quote you're reffering to is not mine but straight from the FAQ of the 123 ignitions website(as it says in the text).

123 Ignitions claim it doesn't work, as i havn't got a ignition like that i can't comment on the subject.

I do have several Aldon igniters in my distributers and in all those cases my Smiths RVI's didn't work or were erratic, so i modified them and had good result with that, that's all.

OK the 123 quote is wrong then. I have an RVI working no problem with a 123 distributer on my Traveller. It doesn't make any sense that some work and some don't. The guy who developed the advance curves for the 123, Marcel Chichak in Edmonton Alberta Canada, told me no problem as well.

Larry, as I have said multiple times in different forums, you and your tach are an exception, not the rule. You will find many more articles explaining how to convert RVI tachs to work with electronic ignition than you will articles and posts saying there is no problem. Perhaps Marcel also has an exceptional tach but if the 123 and Speedy Cables web sites acknowledges incompatibility then you have to believe they have both seen the problem. EDIT: RVI incompatibility is also mentioned on the Nisonger Instruments web site and instructions for Lumenition products.

Hi,

I just came across this thread and have been reading with interest..

I first designed the Spiyda Design RVI to RVC internal and external conversion kits some time ago
They have both just been updated (August 2014) to make them easier to fit and calibrate, as well as using more SMT components for reliability.

But it seems that rather than modify the tacho, some folks want a module to make an unmodified current sensing tachometer work on electronic ignition systems.

If that is the case I can certainly design a module...

Is there any interest ?

Chris (Spiyda Design)

Chris, after you first introduced your web site here I have posted links to it in multiple threads on several message boards (both for the tach converter and low fuel level indicators). There are many people who convert to electronic ignitions and find their RVI tachs no longer work. It would be fair to say that many are intimidated by the idea of converting a tach themselves and would be very happy to find an external product that they could simply hook up to make their tach work. So in a word... yes... there would be a market for an external interface that would allow an unmodified RVI tach to work with electronic ignition.

That being said, RVI tachs are typically 40+ years old. There are internal components that fail and if a person were to buy an external conversion device and their tach did not work... or stopped two months later... they are likely to think the fault is with your device, not their antique tachometer. Therefore, developing the interface would have some potential issues.

MSD Ignitions makes a tach adapter (their 8920) that probably does this task already though I have not tried it yet with RVI tachometers. The device takes 12V square wave pulses from the tach output of an electronic ignition module and converts them to a current pulse (I think equivalent to a 34% duty cycle).
http://www.msdignition.com/Products/Acc ... igger.aspx
In theory this converter should also be able to accept a 12V pulse from coil (-) on less sophisticated aftermarket ignitions and drive a current pulse sensing tach.

I would love to see you develop a product that allows an unaltered RVI tach to be connected to an electronic ignition. It would have applications on many non-Mini British cars built into the mid-1970s... not just Minis.

Thanks,

I get quite a few folks land on my website from the forum..

re this module.. I can't see a problem, but rather than drive the tacho from the output from an electronic ignition, I will build one to drive from the coil -ve terminal. That way it should be pretty universal, like my existing conversion board.
It will probably go in the same style case as the external version of the conversion board.


It isn't the next project on the list as I already have three new products on the go
but it should be done for The Classic Motor Show at the NEC here in the UK 14 - 16 November.
I have stand TV122 which is not far from the mini club stands... so if you happen to be visiting the UK
perhaps pop along and say hello!

Chris

I was not suggesting that the MSD device would only work using the tach output from their ignition system. I believe it should work with a coil (-) connection as long as their device would not be damaged from voltage spikes above 12V. However, that could be a problem as the MSD tach adapter was designed to work with the very clean square wave provided by their ignition's tach signal connection.

Regardless, I think there is a market for what you are suggesting to design. There are lots of late '60s early '70s British cars with RVI tachs that could use the adapter. As I mentioned, most people do not want to open up their gauge to make a conversion so your interface would be just the thing for them.

Thank you for the invite to see you at the show. I do hope to visit the U.K. within the next year but we have not made our travel plans yet.

Well,

the new adapter board seems to be working well.
It is on test at the moment and provided it keeps working continuously for the next 48 hours, I will order in some parts to make a batch.
It has three inputs, for Coil -ve, 12V and TTL. so it should work with most ignition systems.
The biggest issue is that it does need to be mounted where the air can circulate as it does get hot.

In principle, what is does is accept a voltage pulse input, clean up and shorten the pulse in a conditioning circuit, then use that to generate a fixed length pulse in an astable. That pulse is then used to trigger an FET which sends current round the loop on the tachometer.

It would be possible to alter the circuit to not generate as much heat, but that would mean sacrificing reliability.

The majority of components are surface mount and it is all housed in a nice ABS box.

The reasons for choosing this over the other kits I do would be
a) if the tachometer is very valuable as it requires no changes to the tacho whatsoever.
b) someone is not confident enough to take their tacho (which worked on points) apart but can connect a couple of wires.

Once I am happy I will add a link..

Chris (-=spiyda=-)

That sounds great Chris. Any chance of modifying the packaging to allow a heat sink or perhaps integrate a heat sink into the mounting foot for the package? Since earlier you asked about the market for such a board, have you considered the possible demand for positive earth versions of this board? A lot of the RVI tachs were made and installed on cars prior to the transition to negative earth.

I look forward to hearing your results and seeing it added to your web site. Is it too early to ask if you have a target price in mind?

dklawson wrote:That sounds great Chris. Any chance of modifying the packaging to allow a heat sink or perhaps integrate a heat sink into the mounting foot for the package? Since earlier you asked about the market for such a board, have you considered the possible demand for positive earth versions of this board? A lot of the RVI tachs were made and installed on cars prior to the transition to negative earth.

I look forward to hearing your results and seeing it added to your web site. Is it too early to ask if you have a target price in mind?

I took a second look and with a bit of lateral thinking managed to remove most of the heat !
Positive earth may work, but it will need to be tested to confirm. (I don't have a positive earth test rig, so I will have to concoct something)
The Modified version has been on test at 6000 rpm for about 24 hours and seems fine

price will be in the £39 + Postage ballpark

Once I have a batch made, I will list on the website and eBay.

case is like the one below, about 80mm over the longest part