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Old 03-03-2012, 11:56   #1
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Where to Found 12V when the Engine is Running

Hello
I am adding a temp sensor on my engine
I need to found 12V when the engine is running to power the sensor unit
And of course 0V when it is not running

As i just remouved the isolator diode so, the alternator is conected directly to the batery

I have a relay to swith on the starter
Engine Yanmar GM (see pic for wiring diagram)


Any solution
thank you
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Old 03-03-2012, 12:01   #2
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Re: Where to found 12V when the engine is running

Do not remove isolator diode from alternator,,,you will end up bleeding all your battery voltage through the stator windings.

As to finding a switchable 12 volt source,,why cant you go to the key on power?


As i just remouved the isolator diode so, the alternator is conected directly to the batery

I have a relay to swith on the starter
Engine Yanmar GM (see pic for wiring diagram)


Any solution
thank you[/QUOTE]
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Old 03-03-2012, 12:05   #3
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Re: Where to found 12V when the engine is running

The pin marked AC on switch 17 is the "ignition on" switch that feeds 12v into the engine system, That can be tapped off to give you 12v and zero volts when the key is turned off

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Old 03-03-2012, 12:13   #4
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Re: Where to found 12V when the engine is running

After some consideration, I installed a gauge with a mechanical sensor on my boat. Still ran a hot wire for instrument lights with a switch.
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Old 03-03-2012, 12:21   #5
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Re: Where to found 12V when the engine is running

If the 12v positive output on the key switch is not convenient, then that same output feeds your 12v input on the DC bus bar.

Typically on the DC breaker panel. You could tap off there with a fuse holder to the new sensor. Or maybe you have an unused breaker still available on that panel.
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Old 03-03-2012, 12:26   #6
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Re: Where to found 12V when the engine is running

Do not remove isolator diode from alternator,,,you will end up bleeding all your battery voltage through the stator windings.

Not Sure about this : they is the retifer diode before the stator windings
so the courant must be stoped before

As to finding a switchable 12 volt source,,why cant you go to the key on power?

I to Check the The key On power (but as itis in serial with the push buton) not sure to found 12 V
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Old 03-03-2012, 12:30   #7
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Re: Where to found 12V when the engine is running

I will try with this pin, but i am afraid i will found it in the control panel
far away from where i want, but sound like the best solution


Quote:
Originally Posted by goboatingnow View Post
The pin marked AC on switch 17 is the "ignition on" switch that feeds 12v into the engine system, That can be tapped off to give you 12v and zero volts when the key is turned off

Dave
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Old 03-03-2012, 12:33   #8
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Re: Where to found 12V when the engine is running

The diode even one which goes between mains power and alternator,,is meant to protect the alternator and batteries.
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Old 03-03-2012, 12:34   #9
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Re: Where to found 12V when the engine is running

Actually the starter push button, warning lights, alarm buzzer and tach are all "paralleled" off the switched output of 17, the key switch.
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Old 03-03-2012, 13:10   #10
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Re: Where to found 12V when the engine is running

All you need to do is to find the same circuit that powers the rest of your engines instruments. Just trace where the oil pressure or the other temperature sender wires or where the tach is are powered from. That circuit is normally right at the key switch.

It is completely unnecessary to mess with the alternator to accomplish what you want to do. Messing with the alternator could also cause other problems.
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Old 03-03-2012, 15:37   #11
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Re: Where to found 12V when the engine is running

Ok
thank again to all off you
fynaly i used the wire connecter to the hours meter

must be the same wire as :

The pin marked AC on switch 17 is the "ignition on" switch that feeds 12v into the engine system, That can be tapped off to give you 12v and zero volts when the key is turned off

thank you
everything work as i want

Iwill open a new threat about the alternator diode
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