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Old 1st November 2012, 17:41   #1
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Default DIY - Double Crank Prevention

Friends,

I'm planning to make Double crank prevention circuit for my friend's 2001 model Hyundai Santro LE.

Here is the circuit diagram in my mind.

DIY - Double Crank Prevention-circuit.jpg

Please suggest me how should I take the signal for NC relay. My intention is once the engine is running (i.e., alternator is running) a signal from alternator should open the NC relay, preventing current flow to starter solenoid.

I worry if I take the signal directly from alternator, even during cranking this circuit may get opened (during cranking alternator starts supplying current) Please correct me if I am wrong

Help me out guys.
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Old 3rd November 2012, 14:31   #2
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Default Re: DIY - Double Crank Prevention

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Originally Posted by Mr.Boss View Post
I'm planning to make Double crank prevention circuit for my friend's 2001 model Hyundai Santro LE.

I worry if I take the signal directly from alternator, even during cranking this circuit may get opened (during cranking alternator starts supplying current) Please correct me if I am wrong
Hello Boss,
You have almost attacked at the logic correctly. Instead of tapping the 12V point of the alternator you may use the warning lamp pin (usualy called as the WL pin). +12V is available there once the engine is powered up. Also you might need a comparator or atleast a transistor for this circuit.
-Ilango
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Old 3rd November 2012, 15:07   #3
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Default Re: DIY - Double Crank Prevention

Excellent idea, but it has got me wondering if it is so simple then why don't the manufacturers implement it themselves? Logically they should have this system built in to every car.

@ilangop - I'm no guru in electricals but doesn't the WL pin get it's power from the battery directly? Isn't this the reason it comes on when we switch ignition on and then goes off after the ECU has completed its diagnostics? During this stage the alternator is not producing any electricity. If this doubt of mine is valid then I think what Mr. Boss has done is correct. Alternator producing current would mean that the engine is running.

Disclaimer: Like I said earlier, I'm not an electrical guy but a mechanical one and have based my above statement on my understanding of the WL pin and current being available to it even when the engine is not running.
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Old 3rd November 2012, 17:42   #4
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Default Re: DIY - Double Crank Prevention

Your doubt about the relay cutting itself before the engine cranks fully is theoretically correct. But that depends upon when +12v or even +14v is available to the relay. That depends upon alternator output. Hold a multimeter across the alternator DURING crank and monitor the voltage. If the alternator output becomes optimal after the engine cranks successfully, then your logic would work Perfectly. Also, this will ensure that one does not hold the key for a longer period of time.

If not, then as soon as you crank the engine, the relay might trigger prematurely and cut supply to the starter relay. This will become a cycle of starting attempts thus damaging the starter relay as well as the starter motor. If this is happening, you might have to consider a delay inducing circuit along with the relay. This will ensure that the relay will cut supply right after the engine cranks up successfully.

Last edited by audioholic : 3rd November 2012 at 17:44.
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Old 3rd November 2012, 22:29   #5
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Default Re: DIY - Double Crank Prevention

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Originally Posted by vikram_d View Post
Isn't this the reason it comes on when we switch ignition on and then goes off after the ECU has completed its diagnostics? During this stage the alternator is not producing any electricity. If this doubt of mine is valid then I think what Mr. Boss has done is correct. Alternator producing current would mean that the engine is running.
Vikram,
One end of the warning lamp is always powered On from the ign switch. The other end is connected to the WL terminal of the alternator. Until the voltage no voltage is generated or generated voltage is less than the battery voltage, the warning lamp is held ON. As soon as the battery is being charged by the alternator the voltage at WL and battery + terminal are same and the warning lamp turns off. Hope this clarifies your doubt. It is not always necessary that the ECU is informed about the alternator satus. It can vary from vehicle to vehicle.
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Old 3rd November 2012, 23:27   #6
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Default Re: DIY - Double Crank Prevention

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Originally Posted by ilangop View Post
...you may use the warning lamp pin (usualy called as the WL pin). +12V is available there once the engine is powered up. Also you might need a comparator or atleast a transistor for this circuit.
Thanks Ilango. Let me try this out and let you know the result.
BTW can you please explain the need and function of comparator / transistor? Sorry, I don't have much idea about Electricals.
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Old 3rd November 2012, 23:43   #7
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Default Re: DIY - Double Crank Prevention

The ford figo already has it I guess. Why not take a look at the workshop manual to get an Idea about its technicalities.
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Old 4th November 2012, 00:05   #8
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Default Re: DIY - Double Crank Prevention

Can someone please explain what a Double Crank is? And why would one want to prevent it?
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Old 4th November 2012, 00:31   #9
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Default Re: DIY - Double Crank Prevention

I always prefer to go for embedded logic- a consistent 12V signal from the alternator over 2 seconds would be about right. Does not really need a microcontroller, but then you can read analog values multiple times a second to be sure. Wouldn't be that expensive either. And I am sure it varies from car to car whether the alternator produces power during crank- in theory, it can, since the belt is still rotating. But I believe (I may be wrong here) some alternators have a clutch type system (like the A/C compressor) that may keep it out of the circuit during a crank.

It is impossible to double crank on my Ikon... mainly because you cannot physically turn the key after a crank attempt, even if it does not start the engine.
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Old 4th November 2012, 02:07   #10
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Default Re: DIY - Double Crank Prevention

Quote:
Originally Posted by Mr.Boss View Post
Friends,

I'm planning to make Double crank prevention circuit for my friend's 2001 model Hyundai Santro LE.

Here is the circuit diagram in my mind.

Attachment 1008822

Please suggest me how should I take the signal for NC relay. My intention is once the engine is running (i.e., alternator is running) a signal from alternator should open the NC relay, preventing current flow to starter solenoid.

I worry if I take the signal directly from alternator, even during cranking this circuit may get opened (during cranking alternator starts supplying current) Please correct me if I am wrong

Help me out guys.
Use a general purpose diode clamped with a zener diode from the Alternator and power the relay. Once the alternator is generating voltage, that will keep the relay activated to prevent second crank attempt.

The idea should be like this:

+ ------GP DIODE-R- ---
ALT ZENER DIODE (12v) RELAY
- ------------------ ---

The GP DIODE is in series and Zener diode is clamped between +/-. If you noticed I have placed a resistor in series to limit current. Zener Diodes are not capable of handing the large bias current the alternator or battery supplements, hence the resistor. This also means you will need a low power relay tandem to a larger relay circuit to actually actuate your switching circuit to key switch.

The other idea is to use a GP NPN transistors in astable multivibrator circuit to get triggered from alternator voltage to drive the relay. Basically the base of the of the transistor is triggered at a certain voltage (which is stabilized only after the engine is revolving at a certain minimum RPM) to trigger the relay. You can search for a voltage controlled relay to build this project.

Alternatively, training your muscle reflexes to not double-crank would be much easier
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Old 4th November 2012, 03:47   #11
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Default Re: DIY - Double Crank Prevention

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Originally Posted by Mr.Boss View Post
Thanks Ilango. Let me try this out and let you know the result.
BTW can you please explain the need and function of comparator / transistor? Sorry, I don't have much idea about Electricals.
Boss, refer to the attached picture. Though not sure about the first curcuit, the circuit shown in the lower half should work.
K1 is a relay and R1 has to be calculated from relay resistance. This is a very simple which you may try out with 50 bucks and half an hour of time.
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Old 4th November 2012, 07:52   #12
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Default Re: DIY - Double Crank Prevention

Quote:
Originally Posted by Warwithwheels View Post
Why not take a look at the workshop manual to get an Idea about its technicalities.
Workshop manuals are not available in India for general publicc.

Quote:
Originally Posted by kmadhok View Post
Can someone please explain what a Double Crank is? And why would one want to prevent it?
Double crank: Cranking the engine when the engine is already running.

Try this in your car (if you want a practical demo, and if your car allows double cranking): Start the car. With the engine running, turn the ignition key again (like you would do to start the car). There is a "krrrrr" sound. This is double-cranking. And it damages the starting mechanism, esp the starter motor.

To prevent this damage, we try to have double-crank protection. Very useful feature


Flip side: if you stall in traffic, you cant immediately turn the ignition key to start the car. You will have to turn it to off and then turn the ignition key to start the engine. (This is how it is in my Ford).
Quote:
Originally Posted by RM2488 View Post
It is impossible to double crank on my Ikon... mainly because you cannot physically turn the key after a crank attempt, even if it does not start the engine.
Another way that Double-crank prevention mechanism is implemented.

Last edited by condor : 4th November 2012 at 07:54.
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Old 4th November 2012, 08:03   #13
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Default Re: DIY - Double Crank Prevention

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Originally Posted by kmadhok View Post
Can someone please explain what a Double Crank is? And why would one want to prevent it?
Double crank is when one turns the ignition key (mistakenly) after the engine has already started. The starter motor gear engages the flywheel teeth when the flywheel is already rotating at high speed & can cause damage to the starter motor.

This is a system to prevent that from happening.
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Old 4th November 2012, 21:36   #14
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Default Re: DIY - Double Crank Prevention

Essentially one needs to distinguish between a running and stopped engine.

Vehicles with electric fuel feed pumps will have some system of cutting off power to the pump in case of an accident. Possibly this can be used (after inversion of logic).

Regards
Sutripta
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Old 5th November 2012, 07:41   #15
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Default Re: DIY - Double Crank Prevention

^^ Sir how can that be used to prevent a double crank? Could you please explain?
Taking the logic of fuel pump being cutoff on impact, the default state will be logic 1. That if we invert, we will have logic 0 signal until there is an impact and only then will it turn to logic 1. That will help prevent cranking when there is an impact from what I can think of.

Last edited by audioholic : 5th November 2012 at 07:44.
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