Replacement CDI Unit

[Jonny H]

Originally Posted by mysocal911

Would you consider that those two design issues as key in any automotive system and especially
critical when that system is in the engine compartment? Given that, have you observed any aftermarket
replacement CDIs that lack compliance to those design issues recently, i.e. given that I would assume
you evaluate competitive products? And do you think that Bosch adhered to those design constraints
with their 911 CDI units? If not, where in their design?

You haven't shown how the under side (image) of your product complies with the above.

Yes, of course, heat and vibration are the two biggest killers of automotive (in fact, most) electronics. For a 'spark box', transient voltage spikes are high up the kill list too.

Yes, we have evaluated the competition. As far as I am aware, we are the only CDI maker to have conducted the relevant tests for CE Marking (and passed). That's how I know we ARE compliant with modern electronic standards.

As observed here, our units have more components and look 'complex'. Much of the circuitry relates to providing filtering, isolation and protection from the harsh vehicle environment.

The Bosch unit, when new, clearly must have met the orignal temperature requirements as they have given a long service life. The heat sink capability of the case would have been calculated for the early cars which had less cluttered engine bays. In latter years, the Turbo cars were crammed with equipment and had less airflow around the unit. This did cause the units to fail prematurely but still after years of service. Not a bad effort at all!

The design of the Bosch unit would have met the requirements set out by the design team but they did not have as many regulatory bodies in place to outline tests. Good design practice would have been instilled by education and validated by peer review. We still do this today but we also have the advantage of powerful engineering tools to validate design rules. We also have to (or should be) complying with today's standards ( CE / FCC ).

Interesting question about compliance of the Bosch unit. If I were reviewing the design of the Bosch unit today, I would raise the following issues with the design team:

1). The power supply is unregulated and relies on the external regulator in the vehicle. If the voltage goes too high, the output will rise to a level that will damage the unit.

2) There is no reverse voltage protection or short circuit protection.

3) There is no transient suppression.

4) There is no fuse.

5) The high voltage paths on the circuit board violate the air gap rule in several places.

6) The 6 pin plug pins violate the air gap rule and should be insulated.

7) Using the case as a conductive path (3 pin only) is not good practice.

8) Tall components that are likely to vibrate should be correctly secured. Similarly wires run close to edges of the case can rub through the insulation.

9) The design spares no thought at all for ease of assembly.

10) The design is not Rohs / WEEE compliant ( no surprise here!)


I have already stated that I won't show our internals but be assured that they are correctly thermally managed and protected against vibration.

[Fred Winterburn]

Dave,
Surely if you have gone to the trouble of removing the insides for photographs, you also hooked the unit up to your test equipment and tested it for the usual things such as: voltage control, both for battery and high voltage side, effective spark duration, current consumption at zero rpm and with increasing rpm, heat dissipation, wetting current to keep the points clean etc. The first thing I do when I test a new CDI, either old stock or new, is test it after ensuring there are no leaking electrolytics. I study the circuit later because the testing gives more useful information.
In this case, looking at the size of the transformer with the huge air gap, and the low parts count, I'm going to assume that this retrofit attempts to charge the discharge capacitor (of which there are 3 in parallel for a total of roughly 1.5µF) in one half cycle similar to the old MSD 6A series and some Permatunes and Bosch units. A simple test would show that if it is indeed true. I like the low parts count, but that doesn't always mean reliable. Fred

Originally Posted by mysocal911

My friend recently purchased a replacement CDI on his '73, which had a PermaTune CDI.
He had to buy a Bosch core, as the company (P....K......) uses the Bosch castings for their
electronics. Has anyone used that CDI and compared it to a Bosch or MSD? Maybe one of the
other CDI suppliers or those that have designed CDIs could comment on the physical design,
layout, and part types used.

Here are images of it:

[911T70]

Originally Posted by Fred Winterburn

Dave,
Surely if you have gone to the trouble of removing the insides for photographs, you also hooked the unit up to your test equipment and tested it for the usual things such as: voltage control, both for battery and high voltage side, effective spark duration, current consumption at zero rpm and with increasing rpm, heat dissipation, wetting current to keep the points clean etc. The first thing I do when I test a new CDI, either old stock or new, is test it after ensuring there are no leaking electrolytics. I study the circuit later because the testing gives more useful information.
In this case, looking at the size of the transformer with the huge air gap, and the low parts count, I'm going to assume that this retrofit attempts to charge the discharge capacitor (of which there are 3 in parallel for a total of roughly 1.5µF) in one half cycle similar to the old MSD 6A series and some Permatunes and Bosch units. A simple test would show that if it is indeed true. I like the low parts count, but that doesn't always mean reliable. Fred

Now that Fred's involved in the discussion, I'm subscribed! These CDI threads always turn out interesting and informative.

[mysocal911]

Originally Posted by Helix8

I would like to know why mysocal911 always seems to hijack threads as soon as Jonny H posts information which may be useful to OP's question? I for one appreciate an uncluttered thread -'kindly stay on topic.

Are you aware of who started this thread? Please inform us of the topic, OK.

[rwest]

Dave,

I posted a question in #19 for you, would you be kind enough to answer?

Thanks

[Fred Winterburn]

I'm not going to answer for Dave, but I can give you my opinion. So called credentials often mean nothing. A bright and prolific engineer would be bright and prolific without the degree. A dullard with no imagination but good at math could also be an engineer, but useless and easily replaced by a calculator. For the record, I am not an engineer, and nor was my father that invented the ignition system I build a version of.
Dave, (or Loren) is obviously quite knowledgeable about ignition systems and electronics which is why I find his question sort of amusing. I don't care about his formal schooling whatever that may be. Fred

Originally Posted by rwest

Dave,

You seem to have a lot knowledge of the CDI design and frequently post on these type of threads, would you please be kind enough to list your education, degrees, certifications etc.?

Most importantly, do you have any business or financial connections to any companies or do you profit from the design, manufacturing, sales or repair of ignition devices?

Thanks

[Jonny H]

^. I hear you Fred and I'm not so concerned about the the 'certificates' either. Even though I am a degree qualified engineer I've learned more through practical experimentation than anything else.

Rwest's second question is relevant though. 'Dave' asked for folks who have CDI experience to comment on a company's design. Since PK, Permatune and the like are unlikely to post a response, this question is aimed squarely at two people, me and you!

Questions is, why would he do this? My feeling is to try and undermine confidence in aftermarket CDI products and promote the 'original is best' message in an attempt to increase traffic for his repair business.

There is plenty of room in the market for repaired units and also replacements. We work with repair guys in the UK and US and there is no hard feeling between us.

If I was a repair guy, I would be promoting the quality of my work, showing examples of the care and attention given to customers equipment, showing test results etc. Dissing other people's work is bad form and does not generate extra business so why bother?

SInce Dave appears to be a expert on CDI systems, why did he not comment on the PK design himself? He's always happy to rip into ours!

[rwest]

From an ethical standpoint, it is very important for anyone who stands to profit (or suffer a loss)from a discussion, conversation, article or internet posting to reveal that information so everyone else can factor that into how they process the data.

From a DIY enthusiast standpoint, I'm very happy that we have so many choices and at so many price points. I also appreciate getting information from manufacturers and rebuilders on this site.

It is amazing how well the 40 year old technology held up and still is a viable source of ignition control. A lot has changed and been invented/discovered in the past 40 years as well that gives us choices and features if we want.

[911T70]

I personally find selecting a modern CDI replacement extremely frustrating. I've worked in the electronics field for over 25 years, including designing and commissioning of high-voltage discharge systems, so I'm quite familiar with the principles of ignition. Trying to make a decision based only on people's opinions posted on these forums is not easy, despite the obvious expertise of some members. Not having all the information required (schematics/block diagrams, test results, etc...) to make an informed decision is like of leap of faith. Whenever I think I've made up my mind, someone will post something that makes me doubt my decision.

I just wish someone trustworthy would tell me 'this option is the best choice for the right price for your 911'!

[Neil Harvey]

Originally Posted by Jonny H

^. I hear you Fred and I'm not so concerned about the the 'certificates' either. Even though I am a degree qualified engineer I've learned more through practical experimentation than anything else.

Rwest's second question is relevant though. 'Dave' asked for folks who have CDI experience to comment on a company's design. Since PK, Permatune and the like are unlikely to post a response, this question is aimed squarely at two people, me and you!

Questions is, why would he do this? My feeling is to try and undermine confidence in aftermarket CDI products and promote the 'original is best' message in an attempt to increase traffic for his repair business.

There is plenty of room in the market for repaired units and also replacements. We work with repair guys in the UK and US and there is no hard feeling between us.

If I was a repair guy, I would be promoting the quality of my work, showing examples of the care and attention given to customers equipment, showing test results etc. Dissing other people's work is bad form and does not generate extra business so why bother?

SInce Dave appears to be a expert on CDI systems, why did he not comment on the PK design himself? He's always happy to rip into ours!

Well said.

This is a forum meant for the DIY owner I thought.

To discuss a component like CDI, its great when a manufacturer comes on with a new product. I'm interested too, as we are always in need of better products. Better products make our engine product better.

I think the typical DIY owner comes here to know if there is a better product available to them. I think they could care less how they are made internally, but that real life experiences and users of that product give good feed back on its cost, reliability and performance.

[Fred Winterburn]

I thought if we are going to play show and tell, I would show a completed 12V unit and the bare circuit board associated with it. Components not on the board are: two 25 amp bridge rectifiers with the mounting screws hidden under the metal label(overkill as the unit only draws 3amps with a typical 3 ohm canister coil at maximum rpm, but I had good reasons for doing so), the power supply transistors, a 10W trigger resistor heat sunk to the case, and of course the switch. Note the size of the conduction paths on the circuit board (2oz copper). Total component count including the switch is: 30. There are necessary connection lead wires inside. Frankly, I see nothing wrong with using quality wire routed intelligently. I've ripped apart plenty of old automotive electronics and never seen a frayed wire from vibration. I've seen burnt insulation from failures, and I've seen bad connnections and pinched wires. I do use an adhesive wherever a wire is soldered to provide some mechanical reenforcement. I use the same adhesive on components likely to vibrate. All components on the board are through-hole which allows for thermal expansion due to the extra lead length. I also use 60/40 lead-tin solder because it is proven, especially in cold climates. The power supply transformer is wound with automotive grade magnet wire with layers of Kapton tape between windings and at the bottom of the bobbin to provide stress relief due to temperature changes. For the same reason, the transformer is not impregnated with resin as this can restrict the free movement of the windings with temperature extremes and lead to failure over a number of years (especially with the extreme temperature swings in Canada). Fred

Originally Posted by Jonny H

I can offer a similar view of our CDI+ internals:

There is no shortcut to delivering robust and reliable electronics. It is a time consuming and expensive process.

People are sometimes quick to criticise the price of CDI+ but you are paying for:

1) 1000+ Hours of design time.
2) 1 year of road and race trials before launch.
3) Dyno and engine cell testing.
4) $10,000 on CE/FCC Test and Approvals.
5) First class and rapid technical support.
6) Continual improvements. E.g. features added via firmware updates.

Classic Retrofit CDI+

[gomezoneill]

How about some pricing? How much for the units?

[Fred Winterburn]

The price for mine is $395 Canadian.(about $316USD at today's exchange rate). You can see more about it here: http //www.capacitordischargeignition.com
I really do not promote these for 911 cars that came with CDI. For the STD position to work, a 3 ohm(or higher resistance) coil must be used and a condenser fitted. Fred

Originally Posted by gomezoneill

How about some pricing? How much for the units?

[mysocal911]

When comparing the CDI+ to the Bosch CDI, one finds that CDI+'s positive going pulse
is less beneficial as its voltage (180V) is significantly less than the Bosch's positive pulse (275V).
The CDI+'s second pulse overall burn time (<10us) is too short and basically insignificant.
So the CDI+ spark output has marginal benefit over the Bosch unit. The PK ignition pulse is
a short 10us pulse like the MSD pulse providing less overall spark burn time. The basic spark
energy development circuitry of the PK design is similar to the Bosch CDI. All three
non-Bosch CDIs have the inherent higher probability of failure given the much higher (+3X)
part count than the Bosch CDI.

The 911 3.2 inductive discharge spark has a much greater burn time than any CDI ignition,
whereby all the stored inductive energy is dissipated in the spark, since once the drive circuitry
is switched off, the coil primary is open. This is not the case for a CDI system since the primary
of the ignition coil is basically always connected, i.e. the stored energy cycles (rings) in the
primary of the ignition coil via the capacitor and the switching device, resulting in the remaining
stored energy being dissipated in resistive losses, dumped back into the CDI system or is lost
(diode across the coil primary).

PK Ignition Pulse



Bosch CDI - Negative Going Pulse




Bosch CDI - Positive Going Pulse



CDI+ Waveforms (per website)



911 3.2 Inductive Discharge Pulse

[Jonny H]

I'm pretty sure product reviews are usually done by people who have actually used the products?

Send me your address and I'll get one of our LA customers to take you for a spin in their car, Bosch CDI and on CDI+.

[rwest]

Dave,

Do you design, make, repair or sell ignition components or work for a company that does?

Just want to know if you have "skin in the game."

[Fred Winterburn]

With inductive ignition systems there is also a significant amount of energy lost once the spark extinguishes, except that there is no option of recovery, because the coil is disconnected from the circuit. It simply rings in the self capacitance and inductance of the coil and wasted as heat. Your inductive waveform is a poor one and does not show this clearly as in most typical inductive screenshots. Which brings up another point, and that point being that these are strictly voltage waveforms that do not properly represent the quality of a spark which also needs the current component. IE, power versus voltage. The ringing also doesn't show that the capacitor may be being recharged from the power supply as well as the ringing waveform as the high frequency of the oscillator is superimposed on the ringing frequency. At least this can apply to the type of CDI that uses an oscillator, not a one-shot type that charges the capacitor in one half cycle. Fred

Originally Posted by mysocal911

When comparing the CDI+ to the Bosch CDI, one finds that CDI+'s positive going pulse
is less beneficial as its voltage (180V) is significantly less than the Bosch's positive pulse (275V).
The CDI+'s second pulse overall burn time (<10us) is too short and basically insignificant.
So the CDI+ spark output has marginal benefit over the Bosch unit. The PK ignition pulse is
a short 10us pulse like the MSD pulse providing less overall spark burn time. The basic spark
energy development circuitry of the PK design is similar to the Bosch CDI. All three
non-Bosch CDIs have the inherent higher probability of failure given the much higher (+3X)
part count than the Bosch CDI.

The 911 3.2 inductive discharge spark has a much greater burn time than any CDI ignition,
whereby all the stored inductive energy is dissipated in the spark, since once the drive circuitry
is switched off, the coil primary is open. This is not the case for a CDI system since the primary
of the ignition coil is basically always connected, i.e. the stored energy cycles (rings) in the
primary of the ignition coil via the capacitor and the switching device, resulting in the remaining
stored energy being dissipated in resistive losses, dumped back into the CDI system or is lost
(diode across the coil primary).

PK Ignition Pulse



Bosch CDI - Negative Going Pulse




Bosch CDI - Positive Going Pulse



CDI+ Waveforms (per website)



911 3.2 Inductive Discharge Pulse

[mysocal911]

Originally Posted by Jonny H

I'm pretty sure product reviews are usually done by people who have actually used the products?

Send me your address and I'll get one of our LA customers to take you for a spin in their car, Bosch CDI and on CDI+.

I'll suggest my friend buy one. He always likes to try new parts for his 911.

[m42racer]

Originally Posted by mysocal911

I'll suggest my friend buy one. He always likes to try new parts for his 911.

Dave/Loren, whatever your name is,

You keep feeding this dead horse!! When are you going to realize it isn't going to get up????

[mysocal911]

Additional images of an inductive discharge ignition spark signal on a 911 3.2,
and later Porsches.

This one indicates the initial spark pulse (350V) at the primary side of the coil.
As can be seen, the spark breakdown occurs for about 50us after which the coil's
stored energy is being delivered (burn time) to the fuel charge.



This one indicates the basic spark burn time (full energy release) which lasted over 2ms.