6 pin CDI problem under temp.

[HKZ Bob]

Originally Posted by ischmitz

Guys - the issue is most likely NOT the SCR. I agree that putting in an SCR with lower tq will help but you are band-aiding the real problem.

The main capacitor becomes part-ohmic with elevated temperatures. This increases the load on the DC-DC converter producing even more heat from the 2n3055. Heat degrades the SCR performance (tq). And it leads to the capactor to become even more ohmic. It's a typical run-away situation.

Eventually the SCR is unable switch off and the box locks up. Even devices with tq=15 usec will lock up eventually. Ask me how I know.

Change the capactor C8 and your problems will magically disappear, even at 8k RPM on a hot summer day.

Ingo

Isn't this normal that the reactive power at high frequency make C8 part ohmic.

how to measure this and rate.

Bob

[HKZ Bob]

My 6 pin CDI takes 1.9A at 14V without trigger.

I assume that is to high for a 6 pin.

What is your CDI value

Bob

[jmchrist]

Originally Posted by HKZ Bob

My 6 pin CDI takes 1.9A at 14V without trigger.

I assume that is to high for a 6 pin.

What is your CDI value

Bob

The 6 pin CDI I have presently on my bench takes 1.4 A at 14 V without triggering.
jmc

[HKZ Bob]

JMC

what T1 is the correct part 2N3055 or 2N3055HV.


Now I might come closer.

I am using a 2N3055 which has a PD of 117W

in the Bosch schematic they are reffering to an 2N3055HV which has an PD of 90W.

Could that be the root cause of 1.9 A and addtional heat?

bob

[jmchrist]

Originally Posted by HKZ Bob

JMC

what T1 is the correct part 2N3055 or 2N3055HV.

Now I might come closer.
I am using a 2N3055 which has a PD of 117W

in the Bosch schematic they are reffering to an 2N3055HV which has an PD of 90W.
Could that be the root cause of 1.9 A and addtional heat?

bob

I do not think that using a 2N3055 instead of a 2N3055HV could change anything in term of efficiency.
I think that the original reason to choose the 2N3055HV was a higher VCEo and may be a second breakdown specification. This provides for a higher margin against a possible overvoltage but has no influence on the overall efficiency of the converter.

By the way, the dispersion on the conduction voltage of ZD1 (82 V nominal) has a notable influence on the consumption of the unit (higher consumption for lower conduction voltage), but not to explain your 1.9 A.
What is your output voltage on C8 for Vin = 14 V ?
What is your consumption for Vin = 10V ? (in order to prevent ZD1 to conduct), my CDI drop to 0.75 A in these conditions.

jmc

[wwest]

And the answer is:

The input to the DC-DC converter is UNREGULATED.

An overcharged battery would probably result in an already HOT (heat hot) SCR beginning to self-fire. After a few days of running with the battery being overcharged the CDI will beginto exhibit intermittent failures due to the SCR being locked on.

Long term fix would involve a series pass power transistor to keep the DC-DC converter supply voltage from rising above 14 volts.

[rick-l]

Originally Posted by wwest

And the answer is:

The input to the DC-DC converter is UNREGULATED.

What was the question?

[ischmitz]

7 o'clock - the answer is 7 o'clock......

Seriously, the input to the DC/DC converter should never rise above 14.2 volts. If it does your battery and/or charging system have issues and you will damage the CDI unit. There is a Zener diode to filter transients on the input - prolonged overvoltage will fry that and other things in the box.

I have had many boxes that were damaged due to overvoltage. It makes for about 1/3 of all the failures I see coming through.

Ingo

[wwest]

There are two zener's one to protect the 3055, and the second to regulate the voltage, provide a smooth constant voltage regardless of battery charge level, for the trigger circuit.

Not sure if the 3055 protective zener really has to fail to cause any problems, depends on the step-up turns ratio of the transformer.

[ischmitz]

the 3-pin boxes have three Zener diodes. For the 6-pin they did away with the third......

[kellcats521]

Has a possible solution to this issue been identified? I also have a CDI that shuts down when hot - I have replaced C8 and the SCR. It also still whines when it will not produce a spark.

I would also like to know if this is a common failure. Most failures that I've seen involve the transformer, SCR, or C8, none of which seem to be at issue with this hot failure.

Thanks!!

[bartvon]

Hello All-

As a technical novice, is it safe to conclude from this thread that the so-called "telegraph test" of the 6-pin CDI unit (where pin #7 in momentarily grounded) is not sufficient to trigger a single spark from the unit?

Rather the hall effect "reluctor" in the distributor actually produces a +/- sine wave voltage, and the - voltage (not simply 0V or ground produced in the telegraph test) is required to trigger the output SCR?

Just trying to do some in-car diagnostics and don't have a scope nor triggering circuits.

Also, is there a simple test for the reluctor?

Thanks so much - Fantastic board!

[ischmitz]

A simple way to trigger a 6-pin unit is to hook up a AAA battery with the positive pole to GND and the negative pole to the trigger input. The 6-pin triggers slightly after the transition from positive to negative on the trigger input and the input is a sine wave of sorts.

Ingo

[bartvon]

Thanks so much!

Success! I tested C8 and found it shorted, so sourced a replacement locally (actually wound up putting a 1.0 mF and a 0.47 mF in parallel to get close to the 1.4 mF spec) and the car fired right up!

Next it's on to rebuilding the brake calipers (and will search thru all the posts for tips on that, too).

Thanks again.