Alternator problem JD Engine Bateman Hi LO

Neddy flanders · Jan 20, 2017

Hi,
before I turn key, alternator light is already on.
turn key and light goes off.
alternator is not charging.

is it
a) alternator is knackered?
b) alternator is fine, but something called the 'exciter' has broken

have recently changed ignition switch. think I got it right. also fresh battery wont hold charge.
thanks if anyone can help

Mur Huwcun · Jan 20, 2017

Ignition switch issue. Whichever wire feeds the alternator light is being powered from thw wrong pin on ignition switch. Alternator only provides an earth (ground) to the light. Was the ignition switch one with a plug fittment or individual wires?

Neddy flanders · Jan 20, 2017

Mur Huwcun said:
Ignition switch issue. Whichever wire feeds the alternator light is being powered from thw wrong pin on ignition switch. Alternator only provides an earth (ground) to the light. Was the ignition switch one with a plug fittment or individual wires?

individual wires with spade fittings. sure ive got them in right order, but now I'm not sure.
ive even taken them all off and alternator light is still on.

Mursal · Jan 20, 2017

As above .........
Just to test, disconnect the small warning light wire from the alternator and connect it to the alternator body (clean steel/an earth)
Now you know the warning light should only be ON in the ON key position?
If not its definitely the key connected incorrectly, easy done ..............
Without the light working correctly, you will have to have very high revs, to get the alternator "excited", so hopefully it will charge when you get key switch sorted?

Battery:
Charge up (jump leads or alternator after fixing) and then disconnect overnight?
If its flat the next morning its the battery, if not, something is draining it overnight?

Neddy flanders · Jan 20, 2017

thankyou

Mursal · Jan 20, 2017

Warning light ON with all ignition wires disconnected?
If so, see does it go out when you disconnect the alternator?

The "exciter" circuit is in the back of the alternator ..........

The large output alternator wire goes straight to the positive on the battery, so dont earth that by mistake.

Mur Huwcun · Jan 20, 2017

Hmmmm!!! As you know I'm sure a bulb needs a complete circuit to glow. Power (positive) from ignition and ground (negative) from the alternator. Do the oil light etc work? They usually take a feed from same supply. You could have a dash wiring issue as the charge light usually will not be wired seperately from ignition switch.

One thing you could do is either use a bulb test lamp or any other lamp, rig them up with power from battery and use the small wire from alternator as ground, start her up and light should go off. That then would indicate a wiring issue.

Mursal · Jan 20, 2017

Charging circuit at its very simplest ..........................
Your circuit may well be slightly more complicated, but its a good starting point.
Diode at the bottom, not important .........

Neddy flanders · Jan 22, 2017

Mursal said:
Warning light ON with all ignition wires disconnected?
If so, see does it go out when you disconnect the alternator?

The "exciter" circuit is in the back of the alternator ..........

The large output alternator wire goes straight to the positive on the battery, so dont earth that by mistake.

yes, warning light is on when all four wires are disconnected from ignition switch.
it does go out when the wires from light to alternator are disconnected.

Neddy flanders · Jan 22, 2017

Mursal said:
As above .........
Just to test, disconnect the small warning light wire from the alternator and connect it to the alternator body (clean steel/an earth)
Now you know the warning light should only be ON in the ON key position?
If not its definitely the key connected incorrectly, easy done ..............
Without the light working correctly, you will have to have very high revs, to get the alternator "excited", so hopefully it will charge when you get key switch sorted?

Did this and yes warning light only on when key turned on, so guessing ignitin switch is wired ok.

Neddy flanders · Jan 22, 2017

With battery connected and ignition off, the little cylindrical thing (capacitor or diode) in the photo gets hot. This is obviously what's draining battery overnight. @Mursal @Mur Huwcun

Mursal · Jan 22, 2017

That alternator is slightly different to the one I thought you had fitted.

Just having a bit of a head scratch, give me a minute ..................
How do you know the warning light wire?

Mursal · Jan 22, 2017

What wire did you earth to turn the warning light on?

Mursal · Jan 22, 2017

The reason I ask, an alternator with built in regulator (99% of alternators) will only have 2 wires as in the above diagram. One large output wire going to the battery and a warning light wire.
As you can see you have 4 wires, which usually (but not always) indicates that the voltage regulator isn't in the back of the alternator. It will be at the end on the small 3 wires, somewhere on the sprayer?
Leaving it extremely difficult to fault find, if not charging.

Neddy flanders · Jan 22, 2017

The brown and yellow wire in the bottom left is the one which runs to the light. Earthing that on the alternator housing makes light go on when key on.
Is the cylindrical thing not the exciter?

Mursal · Jan 22, 2017

No as far as I'm aware, the exciter will be in the back of the alternator, and consists of 3 diodes to excite the rotor magnet at low revs, so the alternator starts to charge more easily.

Would I be right in thinking the black wire is connected to chassis/steelwork?
The Red wire goes from the large output terminal into the white plug (just cant see it properly in the picture)?
The blue wire isn't connected to the alternator, just to the cylindrical component?
I would disconnect the cylindrical component, while testing ...............

Also check that the large brown wire is actually connected to the positive on the battery?
And if the alternator is mounted on rubber (most Bosch alternators are) the alternator will need an earth, from alternator body to engine block?

Neddy flanders · Jan 22, 2017

the orange and red wires come out of the white plug on the alternator into the black plug which also holds the cylindrical thing. the wires out of the black plug go to the ignition and oil lights

Mursal · Jan 22, 2017

I would try disconnecting the cylindrical component and check if the alternator is on rubber, that the earth strap isn't broke going from the alternator frame to engine block. A jump lead will do to test ...........

If not:
Black wire, where is it going?
Have you battery voltage on the blue wire with the key turned ON?

Mur Huwcun · Jan 22, 2017

Obviously the wiring around the alternator is not original. Has anything been done to it recently? I'm not 100% sure why there are two wires connected externaly to the 12v+ terminal.

What's the diode doing there I have no idea, is it looping the two cables?

the black plug looks like it should be connecting to something else, that's if it's original to the machine.

Alternator problem JD Engine Bateman Hi LO

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