Diagnosing AC CDI (3-pin)?

Thread Starter

CDI-Mike

Joined Mar 10, 2019
3
Hi all!

I am stumbling with diagnosing an old Honda AC-CDI (G300 engine late 70 early 80, which has 3 connectors two go to a coil beneath the flywheel and one to the kill switch. The ignition coil seems to be build in the CDI, as the output is the sparkplug wire.

If you scroll a bit down you see the CDI-Unit:

https://www.jackssmallengines.com/jacks-parts-lookup/manufacturer/honda-engines/engine/g/g300-hzc1-engine-jpn-vin-g300-1000001-to-g300-1457696/c-d-i-unit-exciter-coil

Has anyone some hint how to go about diagnosing. After cleaning the coil (under flywheel), I get a small reading on a cheapo voltmeter, set to AC.

Thx for reading
 

danadak

Joined Mar 10, 2018
3,912
If you are trying to measure output to plug with a "cheapo voltmeter" you have probably
fried the voltmeter, they are not meant to handle 10's of KV from ignition systems.

Regards, Dana.
 

Thread Starter

CDI-Mike

Joined Mar 10, 2019
3
If you are trying to measure output to plug with a "cheapo voltmeter" you have probably
fried the voltmeter, they are not meant to handle 10's of KV from ignition systems.

Regards, Dana.
Hi Dana!

No I have not tried to measure the ignition coil (which is inside the CDI) output. I have measured the coil generating the AC for the AC-CDI, which might be in the terms of 12-60 V or so (sadly no specs online?), though there is no battery and alike, just a pull starter.
 

debe

Joined Sep 21, 2010
1,156
The exciter coil will be low voltage at cranking speed. I doubt its a CDI unit, as CDI units have a HV exciter & a separate trigger coil. The coil most likely is driven by a transistor ignition module. To measure the Exciter coil voltage at crank use the circuit below, it wont be very high.PEAK VOLT ADAPT.JPG
 

Thread Starter

CDI-Mike

Joined Mar 10, 2019
3
Hi Daryl!

Many thanks for the "Peak Voltage Adaptor" circuit. Have to get my hands on the parts and will reply asap.

It seems a pretty old AC-CDI, it says on the flywheel cover "HONDA CDI", strange enough it has no pick-up connector. Perhaps it calculates the ignition moment out of the received AC pulse(s)?

Mike
 

danadak

Joined Mar 10, 2018
3,912
You can get a KV diode out of a microwave oven at the dump, but its a "crappy" diode.
Large Vforward. If my memory serves me I think you can get HV caps out of PC SMPS
at the dump as well.

I get laptops at dump that people throw because they are so compromised by malware
and no longer function real time. I once restored 13 systems from dump and gave
them to a church for distribution to families that could not afford one. Then dump
shut off all reclamation. Idiots. Lots of good stuff at the dump.


Regards, Dana.
 
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