Electronics Question: Starter Motor(Car) - Engine Started or not?
Harrison H Jones
Posts: 22
Hello Parallax Forum Members,
This question/problem came up during a conversation I had earlier with a friend:
How do the cars with 1 button automatic start tell when to turn off the starter motor as to not burn it up?
My solution was to put some kind of simple oscilloscope that gave voltage direction(normal vs reversed) outputs based one two wires going to either side of the starter motor. When the motor was starting the engine it would show a "normal" flow of voltage. When the engine finally kicked over and started running on it's own it would treat the motor as a generator and the oscilloscope should see a reverse voltage direction. When that happened the motor would be turned off.
Would this work? If so, is this how they do it or do they do it another way?
This question/problem came up during a conversation I had earlier with a friend:
How do the cars with 1 button automatic start tell when to turn off the starter motor as to not burn it up?
My solution was to put some kind of simple oscilloscope that gave voltage direction(normal vs reversed) outputs based one two wires going to either side of the starter motor. When the motor was starting the engine it would show a "normal" flow of voltage. When the engine finally kicked over and started running on it's own it would treat the motor as a generator and the oscilloscope should see a reverse voltage direction. When that happened the motor would be turned off.
Would this work? If so, is this how they do it or do they do it another way?
Comments
No. A good number of starter motors have spring loaded pinions, so as soon as the flywheel is moving faster than the pinion it kicks back. If you hold the starter on at this point, the pinion just bounces off the flywheel teeth.
Measure the engine RPM. You are going to have quite a slow rotation while under starter. You will be able to see it start to fire by watching the flywheel start to speed up.
Most starters I've seen simply set a threshold. RPM < Thresh - Cranking | RPM > Thresh - Running.
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If you always do what you always did, you always get what you always got.
You could actually do this with a simple voltage divider and adc.
James L
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James L
Partner/Designer
Lil Brother SMT Assembly Services
Are you addicted to technology or Micro-controllers..... then checkout the forums at Savage Circuits. Learn to build your own Gizmos!
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Alan Bradford ·N1YMQ
Plasma Technologies
Canaan NH 03741
www.plasmatechnologies.com
-Phil
Except the knock sensors are piezo devices that generally have a big fat analog processor applied to it before it gets to the processor, so it's listening for the specific knock signature for that block. It's not a microphone and should generate zero output until it hears the ring of a knock.
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If you always do what you always did, you always get what you always got.