| Hi Gordon,
The starter solenoid is indeed different than the continuous duty master solenoid. While they look the same and have a similar contact structure, the starter solenoid has a much heavier spring to break the contacts which in turn requires much more coil current (therefore power) to offset the strong spring. That is why the starter solenoid cannot sustain continuous operation and overheats. The master solenoid has a much weaker spring which allows less power to activate it and in turn allows continuous operation. The weaker spring in the master cannot overcome the normal welding (called wetting in the relay world) that results from the high starter current during both contact closure and break. The master can conduct the starter current fine once closed due to the large contact structure similar to the starter solenoid.
You are not the first, nor will you be the last, to suffer this fate when the two similar looking relays get mixed up. If you open up your failed solenoid carefully you will find the movable solenoid armature is welded to one or both of the side fixed contacts. The tiny weld will be relatively easy to break and the solenoid will be otherwise fine.
The above experience is just one of the many ways to get burned by improper relay application. Aint this electrical stuff fun.
Jack Morgan
On Nov 28, 2013, at 6:00 AM, Lancair Mailing List wrote: Subject: stuck starter solenoid
Date: November 27, 2013 10:50:42 AM EST
Just thought I would throw in a data point here amidst all the relay talk. Two weeks ago I had what turned out to be a stuck starter solenoid. I had been troubleshooting my noise issue and had done a series of startups and shutdowns. Four over 20 minutes or so. On the last shutdown, I momentarily grounded the mags as normal and pulled the throttle and mixture. Prop kept going….thought it was what we used to call dieseling. Turned off mags…still running. Fuel off.. still running. Master off killed it. Master back on turned prop again, and quickly blew the fuse on my Vertical Power system at the main battery. I thought I had a problem with the dreaded starter adapter, but that looked OK. I'll save the whole troubleshooting story, but it was indeed the starter solenoid. 2007 kit, about 90 hours total time. It was a Hersee solenoid that I got directly from Lancair in the FWF kit for the starter circuit. The part number was 24144 if my memory is correct (I do have a pic). I looked it up on their website. It was a continuous duty solenoid like you would use for a master, and not an intermittent as needed for the starter circuit. It seems to really make a difference. Someday I will cut it open to see what it looks like. Gordon
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