Alternator help

[Newlands]

I’ve got a Lucas 15acr two-wire alternator on my little tractor which is giving me a headache. It started when the charging light stayed on, so I bought a rebuild kit - new brushes, new rectifier and new regulator which I’ve fitted. Stuck it back on the tractor and I got 12.5 volts at the battery before starting, and when I started it I got 14.36v, so it’s clearly charging. But I have no charging light at all. Checked the bulb this morning and it’s ok. Checked the output at the alternator terminals and the big fat wire is giving 14.36 volts and the thinner wire is giving nothing, but it should be the same as the other one.

it’s a mystery to me - I thought that if the bulb doesn’t light then the alternator won’t start charging. I would also have thought that if there was 0 volts out of that warning light terminal then it wouldn’t be charging at 14.36v.

Any ideas from someone who is more of an expert than me (ie just about everyone) ??

 

[knighty]

it shouldn't be putting out any power with the charge bulb wire disconnected because that feed also sorts out the regulator

but... maybe that's old fashioned now and modern alternators don't need it?

if you're pulling up to 14+v with engine ticking over then alternator is charging.... turn a load of stuff, lights etc. and see if voltage holds?

maybe wire a small bulb in temporarily direct to the alternator to test it?

 

[johnik]

on them stone age alternators, you should get voltage down the small (ind) wire, if checked with a test light the light and dash light should both glow at 1/2 battery voltage (6V).
without the ind voltage to turn the field winding they can self excite and still charge
if you are getting nothing down the ind wire suspect a broken wire
also check the casing is earthed

 

[Robotstar5]

A useful pdf here that may be of help.

 

[Newlands]

on them stone age alternators, you should get voltage down the small (ind) wire, if checked with a test light the light and dash light should both glow at 1/2 battery voltage (6V).

I’m getting nothing when checked at the spade terminal on the back of the alternator

without the ind voltage to turn the field winding they can self excite and still charge

That’s useful to know - when I start the engine I can see the kick on the ammeter needle as I increase the revs slightly from tick over 900rpm to about 1100.

if you are getting nothing down the ind wire suspect a broken wire
also check the casing is earthed

Do you mean the casing of the alternator? Or the warning light? The warning light has a plastic case and two wires, one from the alternator (brown/black) and the other (white) disappearing into the loom. I think that with the engine off the white wire should have 12v on it, and when the engine runs the brown/black also has 12v on it which makes the lamp go out. Maybe both these wires need replacing??

 

[Blobber]

Have you got the correct sized warning lamp, think it should be something like 2.2w

 

[hermetic]

Johnic has it, the charge light should be live all the time and gets its "earth" from the alternator via the small wire at the alternator end cap (ind) the "earth" dissapears when the alternator starts charging, and the light goes out.

 

[Newlands]

A useful pdf here that may be of help.

Thanks. Useful to confirm I connected up the regulator and rectifier correctly, and to confirm the exact model - apparently it’s the machine-sensing version of the 15ACR with European connections.

 

[frank horton]

the way I see it...the warning lamp get power from the ignition switch....the small wire just get's it to earth making the curcuit....
when it charges it's supposed to put a voltage back up the wire cancelling thebulb out...
had it loads'a times....dont let it worry u.....
or explain to the supplier of the kit it's faulty....

 

[Newlands]

Ok, so I get that the charge light goes out when it gets 12v on both of its wires. But I don’t understand why I’m not getting 12v at the IND terminal when I test between it and earth while the engine is running. What am I missing? Does it mean that one of the new components is faulty?

 

[johnik]

power for ind goes battery > ignition switch > through the bulb (casing not earthed) and down the wire to alternator and earths through the alternator casing, with the alternator at rest or not charging the potential difference is 12 V ( 12 V live, through bulb to earth), when the alternator starts charging over 12 V, there is no potential difference therefore the bulb goes oot
check the wiring and bulb for continuity

 

[Robotstar5]

Pull the small wire off the IND terminal and meter between the wire and ground with the ignition on, you should get battery voltage, if OK ground the small wire and the charge lamp should light. This will prove the tractor wiring is OK.

 

[not done it yet]

Did you change the commutator? If that is worn out there won’t be any rotor excitation via the ignition switch. If the rotor has some residual magnetism, it may well self-excite. Once it starts charging the normal situation is no more current from the ignition switch circuit, so nothing unusual. The problem is when the residual magnetism is lost - then it won’t charge.

 

[Newlands]

Just cleaned all the terminals I can find, tested the lamp again using a bench top power supply and confirmed it works. Checked the voltage in the lamp terminal* with ignition on, engine off, and I’m getting 4.8 volts so not enough to light the bulb but maybe enough to excite the windings.
* this is the terminal with the white wire, which looks as though it comes from the starter motor. Was just about to test this for continuity/resistance when it poured with rain/hail so had to chuck everything in the back of the van. Will try again later.
unfortunately the only wiring diagram for this tractor (Leyland 154) shows a Dynamo and regulator so not a lot of use. Also with different wiring colours, which is making it a bit tricky to work out what happens once they disappear into the loom.

 

[Morrisman]

I had that problem when fitting the two wire alty to my hot rod. First few times I ran it the charge bulb came on, and went out, as it is supposed to do. But then it simply stayed off one day, so the alternator was basically getting no trigger feed.... but it was still charging as it should

 

[johnik]

if you earth the ind terminal you should get the bulb to light full brightness,check with a circuit tester (bulb in a tube with a probe and earth lead) it should be half brightness check the voltage out of the switch and both sides of the bulb, it,s easier to do with a probe as it adds some load, sounds like wire is a bit past it,s sell by date

 

[not done it yet]

I’ll stick with the commutator not being changed and it being worn out. Until the OP persuades me otherwise. It is the only likely (or most likely) high resistance in the circuit - unless the regulator is duff - which would be unusual.

 

[8ob]

Ok, so I get that the charge light goes out when it gets 12v on both of its wires. But I don’t understand why I’m not getting 12v at the IND terminal when I test between it and earth while the engine is running. What am I missing? Does it mean that one of the new components is faulty?

With slow running engines like a tractor it may well need to be up on a rev to get a reading. Worth trying it on a rev before you tear it all down,also worth flashing the ind terminal with a live feed while its running and taking a reading.

Bob

 

[m_c]

If the slip rings were worn, it wouldn't charge.

The IND wire terminal essentially earths through the rotor/regulator when the alternator isn't charging. It connects to one of the field diodes, so once the alternator starts charging, it rises to roughly battery voltage.

Given you've replaced the rectifier pack, I'd be checking all solder connections are good, and checking for continuity between the IND terminal and the field diodes.

 

[Newlands]

I’ll stick with the commutator not being changed and it being worn out. Until the OP persuades me otherwise. It is the only likely (or most likely) high resistance in the circuit - unless the regulator is duff - which would be unusual.

Nothing wrong with the slip rings or brushes. Checked them and cleaned them when I replaced the rectifier and regulator.