Goofed or malfunction ?

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Externet
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Goofed or malfunction ?

Post by Externet »

My car is not nearby to do the troubleshooting now, I would like your suggestions. After engine transplant :

The relay coil uuuu has 5.1 V when keyswitch opens turning off, enough to not release. Engine stays running.

The relevant part of the wiring is:

Code: Select all

+12Va-------------------ALT----------------------GND
+12Vb-------------------/ \
+12Vc-----./.-----lamp-----\
                \-----------------uuuu-----------GND
+12Vd-----._.---------------------Dist-----------GND
The suspected trouble current route is +12Vb-> up to ALT-> down to lamp -> down to uuuu -> Gnd

./. = keyswitch
All / and \ = connect to above line
lamp = 2 watt "ALT" bulb on dash.
uuuu = relay coil
._. = relay contacts
Dist = distributor

Is it a malfunction of the car alternator/internal regulator (plain GM 12SI) or miswiring ?
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Miguel
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MrAl
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Re: Goofed or malfunction ?

Post by MrAl »

Hi,

Hard to analyze from here, but who did the transplant? Maybe ask them what they did?
LEDs vs Bulbs, LEDs are winning.
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Externet
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Re: Goofed or malfunction ?

Post by Externet »

Hi Al.
I did it all; wiring too, and same circuit has worked in other cases just fine.

Found a clue, perhaps the relay am using is too sensitive and needs a diode to prevent the 'holding' status :
http://holdenpaedia.oldholden.com/HEI_C ... structions

Miguel
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MrAl
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Re: Goofed or malfunction ?

Post by MrAl »

Hi again,


That does sound reasonable, as many relays will pull in at a much lower voltage than they are
rated at and that means that they will 'hold' at a much lower voltage too.
You are right too in possibly using a diode or two or even three to drop a little
more voltage...cheap and effective.
LEDs vs Bulbs, LEDs are winning.
richfloe
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Re: Goofed or malfunction ?

Post by richfloe »

The problem is most likely 12v coming out of the alternator on the lamp wire, thru the lamp, thru the relay coil to ground.

When the alternator is not generating power (such as when you first start the engine), a small amount of current flows from the key, thru the lamp and into the alternator in an attempt to excite it. This causes the lamp to glow and tells you the alternator is no producing power.
When the alternator IS producing power, it uses some of it to excite itself and therefore does not need the power that was coming in thru the lamp and the lamp goes dark (indicating all is well).

When you turn off the ign key, the alternator is still producing power and now will feed that power out thru the lamp to any path it can find to ground. Normally since you turned the key off, the engine dies so all you get is about a second of the lamp coming on when you switch off the key, who cares.

In your case, my guess is that the power is finding the path to ground thru the relay which is keeping the engine running.

This is not a matter of needing to drop any voltage, all you need to do is block the current from getting out of the alternator and to the relay. Cut the wire on either side of the lamp (doesnt matter which) and insert a diode with the arrow pointing or K (cathode side) towards the alternator. Problem fixed. The diode needs to stand the max voltage that the alternator could produce (clamped to battery voltage so a 50v diode is adequate) and rated to handle the current that the lamp will draw (typical indicator lamp will be under 1/2 amp). Be sure that the relay coil is hooked to the keyswitch with the diode only affecting the lamp circuit.

If this is the typical GM alternator with internal regulator, I would probably just cut the lamp wire 3" from the alternator and splice the diode in there (it will be the smaller of the two wires going to the plug on the side of the alternator). This is probably going to be a lot easier than trying to find the right wire under the dash.

Rich
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Re: Goofed or malfunction ?

Post by Bigglez »

richfloe wrote:The problem is most likely 12v coming out of the alternator on the lamp wire, thru the lamp, thru the relay coil to ground.
Excellent post! You have reminded us of this electrical problem,
which was common on USA cars in the past.

Hope to see more posts here from you!
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