Engaging starter while engine is running

[noctorum]

Well, not quite. I'm working on a DIY RFID engine starter. You'd present a scanner in your car with the proper rfid chip embedded in whatever object you'd like (ring, wallet, etc.) and it would start the engine.

Ignoring the electrical specifications of the circuitry, it is considerably more complex for me to add components to detect when the engine has been successfully started and end the circuit. However, I can simply program the chip to turn the starter for x amount of seconds. However, this may cause the starter to continue to operate for 2-3 seconds after the engine has started. I was under the impression that the starter has a clutch that disengages it to prevent damage from the engine, however some people I've spoken to have stated otherwise.

So, is running the starter for 2-3 seconds after the engine started on a frequent basis going to cause damage?

[shorod]

Why not just do like the common remote starter system and monitor the tach signal? If you're doing a PIC or similar microcontroller, it should be pretty simple to program an input to monitor the tachometer signal and determine when the engine is running.

-Rod

[noctorum]

Originally Posted by shorod

Why not just do like the common remote starter system and monitor the tach signal? If you're doing a PIC or similar microcontroller, it should be pretty simple to program an input to monitor the tachometer signal and determine when the engine is running.

-Rod

That was my original idea, but I can't for the life of me find a wiring diagram with the tach wire listed so I can tap into it (2000 BMW 323i).

[shorod]

I did a quick look and can find the service procedures for it but not the wiring diagrams.

-Rod

[2.2 Straight six]

I'll have a look at work on monday, i may have the wiring diagrams there.

[noctorum]

Found the wire. I do not have a multimeter though, and I'd rather not have to go buy one. Does anyone know how the tach wire on this model works? Is there going to be a signal during cranking but prior to start?

[noctorum]

P.S.:

Wasn't answered in the thread, how much wear would it be on the starter if I was to set it to crank for 3 seconds? Like I said, I was under the impression that there was a clutch involved to prevent damage to the starter on start-up. And it really makes this project worlds easier, as the chip I'm using now can't monitor it, easily doubles the amount of circuity I need.

[shorod]

There will be some added wear on the starter and flywheel to just keep the starter engaged after the engine is started. There typically isn't a clutch or one-way bearing on an automotive starter, so the starter motor will be dragging and loading the engine once the engine starts up.

-Rod