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 Post subject: backfeeding alternator
 Post Posted: Sun Jun 27, 2010 6:57 am 
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i found today that if i switch the motor off it continues to run until it runs out of fuel,, is it possible that the alternator is backfeeding the ignition system.. if i disconnect the alt light wire at the alternator motor stops as soon as i turn it off, also if i remove the bulb it stops when turned off.. when i turn it off the warning light comes on and stays on until motor runs out off fuel..alternator is a powermaster 7294


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 Post Posted: Sun Jun 27, 2010 8:08 am 
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You need to add a diode to your dash light/exciter circuit to prevent current feedback to the MSD. The user manual from MSD has a section in it to deal with this issue.

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 Post Posted: Sun Jun 27, 2010 8:59 am 
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zephyrc wrote:
i found today that if i switch the motor off it continues to run until it runs out of fuel,, is it possible that the alternator is backfeeding the ignition system.. if i disconnect the alt light wire at the alternator motor stops as soon as i turn it off, also if i remove the bulb it stops when turned off.. when i turn it off the warning light comes on and stays on until motor runs out off fuel..alternator is a powermaster 7294


When you turn off what switch? Main battery disconnect or the ignition switch?

Did you change something or when/how did this happen.

Rick


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 Post Posted: Sun Jun 27, 2010 11:23 am 
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rick,, it is happening when i turn of the ignition switch,,, my ign live is fed from a fuse board to all ign live parts including the alt light and oil pressure light.. its been that way for 3 years or more, but only now has it started back feeding.. have i wired the car incorrectly or is the alternator faulty


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 Post Posted: Sun Jun 27, 2010 11:52 am 
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alternator has 3 wire connectios,,. main power feed to battery,,, alternator warning light and another terminal which i am told is to sense battery voltage


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 Post Posted: Sun Jun 27, 2010 1:34 pm 
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It's strange that it did work and doesn't now, but I'd look into the MSD info like Ken suggested. You are definitely getting power back to your ignition from your alternator. A diode should prevent that. On 3-wire alts I always wired them as 2-wire using only the main large wire and a single wire from ignition with a diode between the terminals. I remember when the diode was backward the car wouldn't turn off.

Rick


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 Post Posted: Sun Jun 27, 2010 5:08 pm 
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have ordered the diodes, will be a couple of days i guess, will fit one and let you know.. is this a fault in the alternator that has arisen..


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 Post Posted: Sun Jun 27, 2010 5:13 pm 
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zephyrc wrote:
have ordered the diodes, will be a couple of days i guess, will fit one and let you know.. is this a fault in the alternator that has arisen..


Can't answer that but I run a 3 wire on both my cars. One has a 7AL and the other has a Digital 7 and both require that diode before they will shut off by the switch.

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 Post Posted: Fri Jul 08, 2011 12:00 am 
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Location: COLORADO We got no air!!!!
Just curious if the diode took care of it or was it something else?

PHILLYGOAT

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 Post Posted: Fri Jul 08, 2011 5:22 pm 
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I use a separate 150 amp circuit breaker in the feed line to the alternator. One click shuts the entire car down... no worries about something left on and draining battery dead.

Paid $15.00 for it, solid piece of equipment, gave me a 10% online order discount, the ride to NJ from Cali was $6.80.

Quality Power Auto, Inc., in Yucaipa, Ca. 92399.... 909-794-1600. Qualitypower@aol.com

CB-150 Circuit breaker-150 amp... was called a Scorpion IIRC.


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