After following recent threads on non-cranking no starts I did a couple of bench tests with an amp clamp. The size of the inrush current taken by the solenoid coil alone is surprising. Both starters were new, I also tested a non-geared Denso and the trace was more or less identical to the geared Denso.
The Denso starters ground directly to earth, the Lucas partly grounds through the main starter windings/
photos.google.com/share/AF1QipNCsVYLTZ9e...09RWURqemltdGtBZHpRS
Slide Show Video Version
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
Last edit: 7 years 8 months ago by Andy.MacFadyen. Reason: added youtube version
Nice captures, Andy! I think you're right about that kind of in-rush current exposing any kind of connection problem in the circuit.
Makes me think of the BMW systems that have the solenoid controlled directly by a module Having that kind of output current run through computers makes me nervous!
Thanks for taking the time to share with us Andy.
I'm most intrigued by the corresponding voltage measurement. It's more of a gradual decreasing slope when compared to the immediate rise in amperage. Very cool.
I love using an amp clamp for testing starters. It's amazing how much they can reveal about a starter.
I had a friend call me and he was concerned his battery or alternator was going bad so we started checking it out. We did the basics, voltage dropped power and grounds at the starter and measured alternator output. All ok. Checked the starter draw and found only half the bars on the commutator were working properly. The amperage was all over the board. Peaked at 140 amps and hit as low as 25 on the bad segments.
A word of caution though. Make sure you do a clear flood crank and listen for any possible compression issues first.
Topic Author
Having that kind of output current run through computers makes me nervous! 
