Electrical help PLEASE.

classic kev said:

Morning folks!

Now I'm completely confuzzled. Have checked for ignition switched live to alternator - all good. So the problem is not there. The rectifier is brand new and as this didn't change the over charging I suspect the original rectifier was not the problem so this leaves the rectifier/diode pack or a short in either the armature or field coils (is that the right terminology?)

If I have understood what you guys have said, it is possible there is a problem in the rectifier so I guess I am pretty much up the proverbial creek without a paddle. Any other thoughts welcome.

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first things first - i think you mean the regulator - not the rectifier(which is the diode pack)?

Are you saying that if you ground the exciter wire (the one that comes from ignition, via the warning bulb) it will light the warning bulb but, when connected to the alternator, the warning light does not light with just the ignition on?

The Mad Hat Man said:

first things first - i think you mean the regulator - not the rectifier(which is the diode pack)?

Are you saying that if you ground the exciter wire (the one that comes from ignition, via the warning bulb) it will light the warning bulb but, when connected to the alternator, the warning light does not light with just the ignition on?

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You are of course correct. Have edited my last post.

To clarify - switch ignition on (not start) battery light comes on. Start engine, light goes out. I checked for ignition live by removing the wire and switching on ignition and checked with DVM. Wire shows battery volts.

At idle, DVM shows 18+v. If I switch on lights, heated screen and AC voltage drops to between 13.8v and 14.7v. If I raise engine speed with load on, voltage rises to 16 - 17v. As I understand it, this is a normal symptom of a duff regulator but this doesn't fit where I have fitted a new one.

You are correct - that is symptomatic of a duff regulator it is possible that the new one is defective, but the rectifier (diode) pack can also affect output. For the costs involved, I would replace the rectifier pack and check again.
The exciter circuit is working fine, so that can be now forgotten. It might also be worth checking the engine earths, just to be on the safe side, although I dont believe that is the problem.

edit.........

just re-read your last post

no load conditions = 18Volts.
loaded condition = 14Volts.

i reckon what is happening is that the alternator is putting out high volts, low current - this can be caused by half wave rectification - OPv=1.5IPv.

change the rectifier (diode) pack.

The Mad Hat Man said:

You are correct - that is symptomatic of a duff regulator it is possible that the new one is defective, but the rectifier (diode) pack can also affect output. For the costs involved, I would replace the rectifier pack and check again.
The exciter circuit is working fine, so that can be now forgotten. It might also be worth checking the engine earths, just to be on the safe side, although I dont believe that is the problem.

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I think the rectifier is now looking favourite. I did a rough check for earth using DVM, good clean tone off alternator case to battery neg, AC compressor mount, top of engine etc. I do regularly clean the main earth points so I was not surprised there was no problem here.

As for getting a rectifier sorted today I'm not sure. If I was back home, no problem but being 200miles away makes it more "interesting". Will go see what I can arrange. Thanks again for your help.

get yoself a borrwed alt -0 just to get yu home - someone around where yu are must be able to loan yu one??


ALL POINTS ALERT!!!!

these peeps have a good range of parts - not sure how convenient tho

The Mad Hat Man said:

get yoself a borrwed alt -0 just to get yu home - someone around where yu are must be able to loan yu one??


ALL POINTS ALERT!!!!

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Looks like that may be the only way out!!

Did try to borrow an alternator from someone my other half knows but it was the wrong one (A127/65) that has the Lucar 3 pin plug on it.

If anybody near Chester has a Lucas A133/80 kicking about I would be very grateful.

Will post a plea in Anything Goes.

Cheers.

O.K. frustrated doesn't even begin to describe today!!

j the range TOP MAN thanks for your help even though we couldn't get a result.

I went for plan "B". Borrowed my other half spare car. Drove home and back (3 hrs each way) and swapped alternators. No change.....aaaaarrrrrrrgggggghhhhhh.

The substitute alternator has new rectifier and new regulator but still chucking 18.8v at the battery, same as the one that was on there.

Have I missed something stupid?? can anybody give me options?

Sorry to be a pest but I really need to get the Rangie back home. Cheers.

Trailer?

rite - so you have changed the alternator and the problem still exists?

that means that....
the second alternator is also faulty or
the first alternator isnt faulty.

have you checked the voltage directly at the back of the alternator - output to alternator shell? What are these?
then check at batt + to alternator shell
then check batt + to batt -

then we think again.

The Mad Hat Man said:

Trailer?

rite - so you have changed the alternator and the problem still exists?

that means that....
the second alternator is also faulty or
the first alternator isnt faulty.

have you checked the voltage directly at the back of the alternator - output to alternator shell? What are these?
then check at batt + to alternator shell
then check batt + to batt -

then we think again.

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Was thinking match and petrol!! especially as it is such a cold night.

I did check volts between alternator and battery neg and got the same high output but haven't checked between output and shell. Will do so in the morning.

Is it possible there is a high resistance somewhere in the circuit wires?

What should I be looking for in terms of voltages between alternator output and shell?

Once again thanks for your input.

mite be a high resistance - not sure where, except earths tho.

max volts shud be about 14.7

The Mad Hat Man said:

mite be a high resistance - not sure where, except earths tho.

max volts shud be about 14.7

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My thoughts exactly. As you said it may well be that both alternators have faults - just my luck!! Mind you I suppose I could take the "spare" to the local auto electrician and see if they can bench test it in the morning or come up with any other suggestions.

Will let you know how I get on with further tests. Cheers.

It is certainly worth getting it checked, if you can.

would be inclined to start checking the alt loom, especially the plug for intermittent connections/shorts

Sean said:

would be inclined to start checking the alt loom, especially the plug for intermittent connections/shorts

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start with the obvious. Check the Alt first - then move away from it in recognised steps. Checking the loom, without being certain the alt is OK, wont tell yu ought.

Sean said:

would be inclined to start checking the alt loom, especially the plug for intermittent connections/shorts

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Seems to be another logical step who knows what I'll find in there.

The A133 doesn't have a plug on it. There are two terminal posts - main output and ignition feed, then there is a spade terminal to pick up the RPM signal and a further spade teminal connected to a supressor.

All of that said I take your point and will open the loom tomorrow and see if there is a break anywhere. Thanks.

just remove the main terminal from the back of the Alt.
there is unlikely to be a break in the loom, it is more likely to be a high resistive joint, but that would get very hot!.

The Mad Hat Man said:

just remove the main terminal from the back of the Alt.
there is unlikely to be a break in the loom, it is more likely to be a high resistive joint, but that would get very hot!.

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Terminals are fine but alternator does get very hot quite quickly. I mean you can't touch it hot. Would that suggest an internal short, probably on the field coil??

The Mad Hat Man said:

Checking the loom, without being certain the alt is OK, wont tell yu ought.

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yer but but

the wiring could be checked with the kit he's got now - something might turn up

whereas he's got to wait to get the alt tested ...

if ya get me drift

classic kev said:

Terminals are fine but alternator does get very hot quite quickly. I mean you can't touch it hot. Would that suggest an internal short, probably on the field coil??

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do they both do that ? - what charge state is your battery ?