Here is an illustration, this shows two windings (I didn't know that) in the solenoid, one goes to the brushes and gives the oomph to move the arm and engage the drive gear, the little winding continues to hold the solenoid in. So if the brushes are not connecting then the solenoid will not fly along and complete the circuits. Figure 4
Thanks for the info; it's quite a clever system.
Dual-wound solenoids are pretty common in industrial applications, but I've never come across them in automotive applications before.
WRT fixing my Focus, I don't think the solenoid part is available separately from what I can see, so replacing the whole thing was the only option. The local garage, that actually have a pretty poor reputation, did the job quickly for me and for not a lot more than I would have paid for the starter.
Chris
Normally to prevent excessive current consumption/heat, since you don't need the same energy just to hold it in. But I've no idea why you'd want this on a starter, which only get used for seconds.
to avoid needing a relay to power the solenoid (relay) in order to avoid burning out the starter switch if the starter operates for more than a few seconds, also it gives a little more oomph to the actual starter (it takes
20 plus amps for the pull in windings)
Although in the Focus (and I suspect most other reasonably modern cars), there is also a relay employed to reduce the switch loading.
Chris
on the page I referenced there is some mention of cheap 'import' cars (you can almost hear the spitting) burning out ignition switches due to the high load.
Yes, I was amused by that!
It was very common for the US Focus to have the ignition switch fail on early models, although I think the failure mode was more mechanical than electrical.
Chris
It's normally the making or breaking of a switch that causes 'wear' - not the steady state. And anyway, don't all cars with pre-engage starters have a relay?
But I suppose a few extra amps might be useful on a marginal start.
They probably do nowadays (or nearly all) My granada and cavalier certainly did not have a relay, I added one on both which was an improvement on both cars, mainly because of reducing the voltage drop over the back and forth to the ign switch which then gave extra oomph to the slam in of the solenoid.
The USA focus had a key made of pressed tin foil which was very different to the more substantial key on European models.
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