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1986 VOLVO 240

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22 Jul 2019 13:23 #32069 by tim.smith1
1986 VOLVO 240 was created by tim.smith1
Any old school volvo mechanics here? This volvo will not charge customer put a new alternator on it the big power wire is good has system voltage the exciter wire is showing 12 volts when unplugged that wire goes to the charge light in the dash as i understand it the power going through the bulb excites the alternator the problem is with that wire plugged in to alternator i only get 1.2 volts does this mean i need an alternator? Last part that maybe i should not have done and may be why i am confused if i excite the wire with my power probe then the alternator will charge.

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22 Jul 2019 15:58 #32072 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic 1986 VOLVO 240
It will be an old style 3 wire ACR alternator probably Bosch or Lucas. The 1.2v is pretty normal on the small "WL" terminal when the ignition light is illuminated it shows the alternator rotor coils are getting energised and the alternator is trying to charge.
It looks like the alternator has an internal failure. It could be a failure of the diode pack or the a break in the windings or the regulator pack.

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22 Jul 2019 20:05 #32076 by tim.smith1
Replied by tim.smith1 on topic 1986 VOLVO 240
even if i can excite it with my power probe i am talking push power to exciter wire for like a second then take power probe away and unless i cycle the key the alternator will charge?

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23 Jul 2019 01:40 - 23 Jul 2019 01:59 #32083 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic 1986 VOLVO 240
With a Power Probe you are injecting full fat battery power into the rotor field coils without the current limmiting effect of the dash warning light bulb this means it is pushing about 6 amps through the rotor field coils. it shouldn't take that ammount of additional amps to kick the alternator to sef-excite mode.

The Volvo will be old school the bulb in the dash is an old style tungsten filament bulb that should provide enough current to kickstart the magnetic field without additional current. Most much more recent cars use LED warning lights in the dash and use a resistor in parrallel with the LED charge warning to privide additional current to the field coils at engine start..

Based on memories of Lucas ACR alternators which were fairly typical the field coils have a ressistance of around 6 to 8 ohms -- so when the alternator is running at max output and full fielded the the field coils are getting about 2 amps. At cold start to kickstart the field coils to self excite takes about 0.1 to 0.2 amps. A quick bit of Ohms Law based on your mearured 1.2 volts on the "W" termminal 1.2/6 = 0.2 amps which is normal.
Based on this and the test you have done I would say the cars wiring and dash warning lights are okay and you have a fault internal to the .alternator.

As a double check you could do the test you did with power probe but using a test light, even with the wire to the W terminnal disconnected the test light should be enough to excite the alternator or you coukd measure the current going through the wire from the dash to alternator "W" terminnal at Key On Engine Off which should be around 0.1 to 0,2 amps.

But my call without additional testing would be the alternator needs replaced or rebuilt, fitting a new regulator pack and brushes on this style of alternator isn't difficult and most likely to get several more years out the alternator however I would check the rectifier diodes as replacing the diode pack is likely to be more difficult

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Last edit: 23 Jul 2019 01:59 by Andy.MacFadyen.
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23 Jul 2019 01:54 #32084 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic 1986 VOLVO 240

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23 Jul 2019 17:52 #32099 by tim.smith1
Replied by tim.smith1 on topic 1986 VOLVO 240
okay thank Andy i guess i found it hard to believe the new and old alternator was bad lol i don't know why everyone knows parts a chitty now. I had already done the test light to excite it and it did not work.

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26 Jul 2019 14:54 #32141 by tim.smith1
Replied by tim.smith1 on topic 1986 VOLVO 240
as always seems like i get the weird one new alternator still same problem lol any other ideas?

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26 Jul 2019 16:52 #32142 by simclardy
Replied by simclardy on topic 1986 VOLVO 240
I never worked on these but... when the system is working i would expect a larger voltage drop on the motor field winding. If you only have 1.2 volts that means you have 10.8 on the bulb. The bulb must be lit? When you test the wire unplugged, did you use an incandescent test light?
Of course the field needs to build to create the resistance (inductive reactance).
I assume the bulb wire is in series with the field.

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26 Jul 2019 18:50 #32143 by tim.smith1
Replied by tim.smith1 on topic 1986 VOLVO 240
correct the bulb wire is the field/exciter to give perspective one side of the bulb has 12 volts fyi i checked it with a volt meter not a test light (hmmmm maybe i will do that although the dash light will light) the other side of the bulb goes to the exciter on the alternator.

as a side note i called the number in the alternator box that says STOP before you warranty this call this number and they told me if i can excite the alternator with a power probe it cant be the alternator of course they could not help me with what could be the problem ( i fully understand they have a vested interest in not condemning the alternator lol ).

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26 Jul 2019 18:53 #32144 by tim.smith1
Replied by tim.smith1 on topic 1986 VOLVO 240
one more thing i ran a jumper wire from the dash to the alternator and it still would not excite (i did remove the old wire before jumping it just incase it was shorted someway)

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27 Jul 2019 06:53 #32151 by simclardy
Replied by simclardy on topic 1986 VOLVO 240
So the dash bulb lights when the alternator is plugged in? This would confirm the integrity of the wire. Dumb question. Is the alternative spinning at the right speed? I just serviced an old liquid cooled generator and it took me a while to realize the belt was slipping. The pulley was spinning and there was no belt squeal. I know these volvos have a tension screw that likes to break.
This is puzzling.
Has the dash bulb been replaced with the wrong bulb?
Oh one more thought. Can you get the specs from the alternator people? Like resistance and proper current for the field?
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03 Aug 2019 18:48 #32438 by tim.smith1
Replied by tim.smith1 on topic 1986 VOLVO 240
Sorry for this being late before the spam attack i posted a close to this but it got lost so here goes the customer want his car back and from the beginning i knew i could run a keyed hot and put a bandage on the problem but i just dont like doing that but because of time i had no choice with that said i think something is wrong with the cluster in this car the good thing is i know the fuel gauge in the cluster is bad he was already planning to get it rebuilt so if the car returns for this i will update this post further to confirm a fix or not.

What i did unplugged original exciter wire ran a new one to a key hot and installed a diode in line explained to the customer that his alternator light would not function but he should be able to drive it.

I would call this one patched not fixed lol

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