Dometic DCM-45 Ignition Question

[Don Smith]

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During my troubleshooting of the Dometic DCM-45 I find that there is no spark to the plug. Checked the hot wire to the spark coil while cranking and found no voltage from the ignition module unless it is disconnected from the spark coil. Disconnected I could see spikes of voltage on the wire. I checked the Spark coil and found less than 1 ohm between the ground and hot lead. The HIV lead seemed open or at least very high resistance.
Does anyone have the same generator that could measure the resistance readings of the spark coil and forward them to me? I am using the online manual listed im my other post and find it very close even though the diagram shows two spark plugs. Thanks Don Smith

[Fred M.]

Don-

This may not be an accurate comparison. I have a magneto from a Generac (Nagano) GN-190 engine rated at 6.5 HP. It has the electronic "points" built-in, but is excited by the flywheel magnet rather than from a battery.

Using a Fluke multimeter, the primary winding is 1 Ohm, or maybe a little lower considering contact resistance. The High Voltage winding is 18,000 Ohms, which could be higher than some meters can read.

Your primary resistance reading sounds like it might be OK. Although 1 Ohm sounds low, current is limited by the reactance of the primary winding (unless there is a short-circuit!).

Fred

[Don Smith]

Hi Fred thanks for the email. Sounds like you have the same system. I use the flywheel pickup winding as well. It goes into a ignition module that looks like a bunch of parts diped into some sort of plastic on the end of a 6 pin plug. While I am not sure which is pin one I find that the first two on the end go to the Spark coil. It is a square potted module with the HI-V wire plugged into the center of the top. I measured the resistance of it and the primary seemed to be a bit lower than one ohm. Secondary agreed with your readings. When I disconnected the hot lead going to the ignition module I could see votage when I cranked the engine. Seemed to be over 100 volts. When reconnected I see no voltage when cranking. I tried applying a short burst of 12 volts to the primary while it was disconnected form the module and could see a small spark being generated off the HI-V when I brushed the 12 volts across the primary winding. Nothing however when the primary is reconnected to the ignition module and cranking of the engine. I also made sure that the other safety switches were not shorting it out. Would love to get a schematic for the ignition module. Any other troubleshooting ideas you might suggest. thanks Don

[Fred M.]

Don-

I don't think mine is quite like yours, since mine does not have a separate ignition module. It is all in one unit. The only external connections are to the on-off switch and the low-oil shutdown switch. If either line is grounded, there is no spark.

Have you checked the measurements listed in the electrical test specifications table on page 1.2 of the manual? I see there is also an engine troubleshooting procedure in section 3.

Fred

[Don Smith]

I have one of those transistorized ignition modules used by Briggs and others for point elimination. This uses a Power Tab type package and only two connections; coil primary and ground. I believe that when the primary gets to a high enough voltage the module shorts it to ground, much like the points do. This should produce a spark on the HI-V winding. It will be interesting to see if I can develop a spark to the plug. Might help in checking out the coil. Would still love to have someone give me the readings on a working ignition module from their machine. Don