back to the wiper park switch. I have spent ages trawling the interweb for ideas about slowing things down around the Mosfets.
Sadly I had no luck. However due to my lack of training in all things electronics very little puts me off and there is one heck of a lot of smoke to release.
The problem I had a few weeks ago was a schoolboy error. I have two transistors connect side by side between 12V + and ground.
One is turned off and the other turned one - sadly not at the same time. There was a very small overlap in time and this causes a short circuit albeit for a very short time.
One of the good characteristics of a MOSFET is that it has almost no resistance when turn on - 5 or so MilliOhms (0.005Ohms) - this equates to a dead short (almost)
Did you notice your house lights dimming the other week - that could have been me.
Any way after a great deal of head scratching (and other parts of my body) I had a brainwave. So between the two transistors I have inserted a resistor.
Not a big one, just 5 Ohms but this is enough to limit the National grid draining short (should it happen).
So the two transistors each have a job. The first one (we will call it #1) drives the motor to get the gear wheel around to the park position. This handles the motor current - apprx 2amps.
The second transistor (yes that's it - #2) applies the regenerative braking of the armature.. If you short the slow speed motor wire (Red/Green) to earth when the motor is spinning with no power it will stop dead - very very dead. The problem I have is that I have put a resistor (10 Ohms) between the motor and earth. It stopped quite quickly but not dead stop.
I reduced this to 5 Ohms and it stops much much better. Tomorrow I shall put a 1 Ohms resistor in the circuit - this should be pretty stoppy.
A 1 ohm resistor will allow 12 amps to flow during a short - but !!! it will be for just a few milliseconds and the TRansistor will easily handle 30+ amps.
So did it work. Yes. Even with the 5 ohm resistor in place it works very well. So tomorrow I will try the 1 Ohm resistor and then consider how it all mounts on the motor.
I know most of you will not have a clue what I am rambling on about but there are a few here that will have a good smirk at my disasters.
I tend to do minimal with my circuits and this can be a recipe for a disaster. But a good sense of achievement can be had when you confound the experts.
When I finished I post the circuit diagram - just for a laugh.