Ignition modules

[Tony Smith]

A couple of weeks ago there was a discussion of the "new" heavy duty ignition modules for the .5ohm coils.

I checked the new coil I bought recently and sure enough - guaranteed to fry the brand new  old style Bosch Ignition amplifier I had fitted.

By chance I had accidentally bought a VW "heavy duty" module, I promised to fit it and report once I received the revised BMW mount for the larger HD Ignition amplifier.


OK, the photos.

firstly my cheap polish module, next to my just purchased EnduraLast module. I regret that I cannot find the purchase details for the cheapie, the following details may help:

The box bears the stylized log 4Max

The contents are described as : Modul Zaplonowy

Other  writing says VW-A Zastosowana

And Part number 0608-21-8004P


Ok, and n ow the mount. It is really quite simple, using the bolts supplied the new mount fits to the frame in place of the old heatsink and the module is the bolted to it.

[georgesgiralt]

Tony,
I've the OEM original ignition module on my 1982 R65. And, I've changed the Crack-O-Matic for the new expensive BOSCH .5 Ohm primary coil. (I did not know I could fry something at the time I bought the coil)
May I say to you that the ignition module is still going strong ?
Afraid to stay stuck somewhere, I've bought a new replacement OEM module (second hand) and carry it in my tool tray. 2,5 years I travel the ignition module in the tool tray and still no problem ;-)
My bracket is different from yours. But it bears the same P/N .... Go figure !

[montmil]

I'd bet on which of two birds would first fly off the wire. So I feel confident that either one of Tony's ICMs would mate happily with the Bosch-labeled unit in my VW Cabriolet. Right down to the heat sink. As Georges says, "Go figure".

[Tony Smith]

Tony,
I've the OEM original ignition module on my 1982 R65. And, I've changed the Crack-O-Matic for the new expensive BOSCH .5 Ohm primary coil. (I did not know I could fry something at the time I bought the coil)
May I say to you that the ignition module is still going strong ?
Afraid to stay stuck somewhere, I've bought a new replacement OEM module (second hand) and carry it in my tool tray. 2,5 years I travel the ignition module in the tool tray and still no problem ;-)
My bracket is different from yours. But it bears the same P/N .... Go figure !

I would think that it may be the case that you will never have a problem, but running a .5ohm  coil is apparently pushing the original spec module beyond its design limits - I have been unable to verify this as there is simply NO information available on the BMW module and the Bosch sources have sparse informaton, I presently have a Bosch module as my OEM 1984 module developed a failure mode where it would not allow the engine to rev much past 1500RPM and coughed and backfired a lot.

Like you I feel no particular pressure to change the module, but will do so and carry the Bosch as a spare- just in case.....

[Barry]

I would think that it may be the case that you will never have a problem, but running a .5ohmcoil is apparently pushing the original spec module beyond its design limits - I have been unable to verify this as there is simply NO information available on the BMW module and the Bosch sources have sparse informaton, I presently have a Bosch module as my OEM 1984 module developed a failure mode where it would not allow the engine to rev much past 1500RPM and coughed and backfired a lot.

The key issue with a coil of such low resistance is that no ignition system designed for such a coil does so without current limiting and active dwell control to stop the coil and ignition module overheating in an "ignition on engine not running" scenario and also to a lesser extent at low revs when the coil saturates in a fraction of the time available.  There is so little detail information on the BMW ignition modules that the best way to know if they are clever enough to driver the coil would be to monitor the primary current with an oscilloscope.     On the face of it a 0.5 ohm coil should pull 24 amps !!! when the ignition is turned on and something like half that current with the engine running so In the absence of a scope just measuring the primary current with an ammeter might yield an insight in whether the module was smart or dumb.

If it turns out to be dumb then even if it survives it's still  putting an unnecessary load on the electrical system when compared to a smart module.

[georgesgiralt]

Barry,
In my driver's manual there is something saying that the ignition is cut off if one does not start the engine in a short time interval after ignition on. I've confirmed this as the voltmeter shows the lessening in current after a couple of seconds.
My bike came with the kick starter option when i bought it and I've read somewhere that the ICU on these bikes where different. I do not know the difference, though.
Last but not least, the local BMW guru has cases filled with the awful Bosch original coil and none ICU exchanged in 35+ years of work. When I searched for a replacement ICU he told me that it was unnecessary because he had not seen any fried in service. So my buying of a "new" ICU was kind of belt and suspender approach.
What I can do is that a friend of mine having lost it's ICU during a move has bought a cheap automotive "compatible" ICU in an auto parts WEB store. This ICU worked a few minutes in the R65 and produced a lot of smoke of very bad smell... I leaned my spare to him until he got the money to buy a new one.  

It is not so difficult to limit the current on these modules. I bet this was implemented by BOSCH then. It may be what causes them to be expensive compared to "equivalent" Chinese one.

[Barry]

My bike came with the kick starter option when i bought it and I've read somewhere that the ICU on these bikes where different. I do not know the difference, though.

Sounds like the module is smart. A current measurement would confirm if there is a current limiter while the engine is running. I imagine there must be if the module has survived.  The coil wouldn't quite pull the full theoretical 24 amps anyway due the resistance in the wiring up to the ignition switch/kill switch and back being significant relative to 0.5 ohms.  

I think the difference on the kick start models was a few more seconds delay to give the rider time to use the kick start before the module switches the current off.

[Tony Smith]

Barry

I think that all of the modules have both current limitation and switch off after a period of time with no sensor pulse.

I didn't feel like rigging a ammeter so i simply turned the ignition on and waited - when the module didn't get blazing hot I was pretty sure it had switched off and confirmed by hitting the starter and in spite of the engine turning over - no start.

Then I flicked the kill switch off and then back on and hit the start button - instant start. I ran the engine for 5 minutes wit my hand on the heatsink and it only became moderately warm - certainly not hot.

The electronic component "rule of thumb" I have always used is that if it is too hot to keep your finger on it, it is running too dammed hot.


Obviously not a 100% maxim as the MOSFETS in my amplifier and in the computer power supplies prove every day. but a useful rule.


The sad thign is that I did all of the above with the Mercury Outboard (1.5ohm) coils fitted and I have not repeated since fitting the new BMW coils.

This weekend I am going to try the polish module to see if it works - if it does it goes into spares, then I will fit the EnDuraLast module and it will stay on the bike - the current BOSCH module goes into the "glovebox" as an on board spare.