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Curious alternator problem...


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14 minutes ago, Mike the Boilerman said:

Right, having thought about it, I think a possible, likely even, cause of these symptoms is a wiring error, the light is powered up other than via the alternator. 

I refer you to post #2 ...

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12 minutes ago, TheBiscuits said:

I refer you to post #2 ...

 

To paraphrase that nice Mr Morcambe, all the right wires are there, they just don't necessarily go to all the right places....

 

i suspect :)

 

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5 hours ago, Mike the Boilerman said:

 

Oops sorry, its an A127 type, not an ACR. I get the two confused. Will post a photo in a sec. 

 

Anyway I just started the engine to observe exactly what it does. As follows:

 

1) Ignition ON. Light glows brightly.

2) Turn engine over to start. Light dims to perhaps 3/4 brightness while starter spins engine.

3) Clamp meter on alternator output rises to 20A or so during starter operation

4) Disengage starter operation and engine ticks over (at starter turn-over speed), light returns to full brightness. Charge current remaisn at about 20A

5) Increase engine revs and charge current rises to 67A and light stays at full brightness, with no change.

 

Do you still think this might be an alternator problem Tony? Will PM you if you think so. Thanks for your offer.

 

 

 

Yeh, A127 type but not an actual A127, wrong regulator. I think that needs a fair amount of disassembly to get at the diodes so I would rather not do it at home and without an alternator tester.

 

All your "symptoms" sound normal for a typical alternator apart from the light being at full brilliance and not going out. The dimming is just the starter motor load pulling the voltage down and is normal.

 

I think there are two possibilities:

 

1. For some reason it self energises and there is a short to negative on the alternator side of the D+ cable.

 

2. It is not a 9 diode machine and the internal warning lamp control has failed but I recall Sir N mentioned that it was possible to ruin six diode machines by wiring as if they are 9 diode machines.

 

I would disconnect the D+ cable and see if the warning lamp goes out. If it does then you know there is no short between warning lamp and alternator. If the lamp stays on insulate the terminal the start & rev the engine to see if it energises. If it does then I would suspect its an alternator fault.

 

Maybe take it to Burghfield Starters & Alternators if you are this way and get them to put it on their test bench.

 

Actually it might be a very late ACR design but I thought they had the flat plastic cover over all the end bracket.

 

The "white pot" is a radio suppressor and even if it was faulty it would either simply not suppress (open circuit) or would burn its connecting cable, if not the case (short circuit).

 

Can't say much more of any help.

 

 

PS I suspect its an Iskra design.

Edited by Tony Brooks
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Iskra. A bit left field but the only thing that fits the symptoms in my mind is the D+ and W connections reversed. The connections are made inside with flyleads soldered in place and if they have been assembled arse backwards.......  Try the warning light connected to W and see what happens.

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2 minutes ago, Sir Nibble said:

Iskra. A bit left field but the only thing that fits the symptoms in my mind is the D+ and W connections reversed. The connections are made inside with flyleads soldered in place and if they have been assembled arse backwards.......  Try the warning light connected to W and see what happens.

Now that is the value of very specific product knowledge. Another one filed for future reference. Cheers Sir N

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2 hours ago, Sir Nibble said:

Iskra. A bit left field but the only thing that fits the symptoms in my mind is the D+ and W connections reversed. The connections are made inside with flyleads soldered in place and if they have been assembled arse backwards.......  Try the warning light connected to W and see what happens.

I have never played with alternators, but if you take a standard 12 volt one and fittes a 24 volt regulator would it produce 24 volts as the field voltage would be different?

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1 minute ago, ditchcrawler said:

I have never played with alternators, but if you take a standard 12 volt one and fittes a 24 volt regulator would it produce 24 volts as the field voltage would be different?

Yes, but it would be a race between rotor and regulator as to which dies from over current first.

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18 minutes ago, Sir Nibble said:

Yes, but it would be a race between rotor and regulator as to which dies from over current first.

OK thanks, it was just an idle thought and as you had just posted I thought I would ask.

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8 hours ago, Sir Nibble said:

Iskra. A bit left field but the only thing that fits the symptoms in my mind is the D+ and W connections reversed. The connections are made inside with flyleads soldered in place and if they have been assembled arse backwards.......  Try the warning light connected to W and see what happens.

 

Thanks Snibs. 

 

I won't be back to the boat until the weekend but will post again with some results once I've done as you suggest. 

 

 

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4 hours ago, Mike the Boilerman said:

 

Thanks Snibs. 

 

I won't be back to the boat until the weekend but will post again with some results once I've done as you suggest. 

 

 

Righto Mike. It's a bugger trying to diagnose over the internet as you know from your own area of expertise. If this alternator has actually been assembled with an inbuilt fault then I think that would be damned unfair, ungentlemanly and should be ruled out of order. Thing is that the warning light is connected directly to the positive brush and if the light is finding a negative then it's not a positive on the positive brush, ergo, no charge. But it is charging so the lamp cannot be connected to the positive brush. So I reckon it's finding a DC earth through the stator and an AC supply from the same place. Nothing else makes sense. Bastards!

And if I'm wrong, I want you to send me that alternator.

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1 hour ago, Sir Nibble said:

Righto Mike. It's a bugger trying to diagnose over the internet as you know from your own area of expertise. If this alternator has actually been assembled with an inbuilt fault then I think that would be damned unfair, ungentlemanly and should be ruled out of order. Thing is that the warning light is connected directly to the positive brush and if the light is finding a negative then it's not a positive on the positive brush, ergo, no charge. But it is charging so the lamp cannot be connected to the positive brush. So I reckon it's finding a DC earth through the stator and an AC supply from the same place. Nothing else makes sense. Bastards!

And if I'm wrong, I want you to send me that alternator.

 

Ok, I thought this was an interesting fault!

 

I'm still inclined to suspect the warning light is not connected to the alternator at all, getting its power from somewhere else, and the alt is self-exciting. But will find on on Saturday...

 

And yes I'll send you the alt for a post mortem if swapping the warning light cable to the W terminal fixes it. 

 

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On 21/05/2019 at 07:51, Sir Nibble said:

Iskra. A bit left field but the only thing that fits the symptoms in my mind is the D+ and W connections reversed. The connections are made inside with flyleads soldered in place and if they have been assembled arse backwards.......  Try the warning light connected to W and see what happens.

 

Ok, back on the bote now. 

 

I think my own hypothesis turns out to be correct actually. Disconnecting that purple lead in my photo from the D+ terminal ought to make the warning light go out I reckon. Is that right?

 

Thing is, with the purple wire connected to nothing, the warning lamp stays ON, so I reckon this shows the warning lamp wired up wrong, somehow.

 

Does The Team agree?

 

 

 

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19 minutes ago, Mike the Boilerman said:

Does The Team agree?

Well I do. :)

19 minutes ago, Mike the Boilerman said:

Disconnecting that purple lead in my photo from the D+ terminal ought to make the warning light go out I reckon. Is that right?

Yes. 

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5 minutes ago, WotEver said:

Well I do. :)

Yes. 

 

Fanx. Fairly sure I know how basic alternator wiring goes but rarely needing to wire them up, thought i'd check. 

 

Now for some wire-tracing to see where the fekkn bulb is getting the juice from when it shouldn't....

 

 

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3 minutes ago, Mike the Boilerman said:

Now for some wire-tracing to see where the fekkn bulb is getting the juice from when it shouldn't....

Nope. You’re looking for where it’s getting an earth when it shouldn’t. Getting 12V is correct, having the other side permanently connected to -ve isn’t. 

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1 minute ago, WotEver said:

Nope. You’re looking for where it’s getting an earth when it shouldn’t. Getting 12V is correct, having the other side permanently connected to -ve isn’t. 

 

Ah, the D+ connection goes to earth. Of course.

 

Just the sort of skoolboy error I was thinking of!

 

Another thing which is probably a clue, is the D+ wire carries exactly 3A when the 'ignition' switch is on. Zero when off. Just as though the bulb was wired correctly..

 

 

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1 hour ago, Mike the Boilerman said:

Another thing which is probably a clue, is the D+ wire carries exactly 3A when the 'ignition' switch is on. Zero when off. Just as though the bulb was wired correctly..

Only if the bulb was 36W

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1 hour ago, Mike the Boilerman said:

Ah, the D+ connection goes to earth. Of course.

Not quite the D+ provides a path to -ve when the alternator is not energised 

When alternator is energised and working the D+ is at 12v hence the light goes out

Same voltage either side of the lamp. ;)

 

Edited by Loddon
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8 minutes ago, ditchcrawler said:

Twin alternators?

 

 

You haven't read the thread, have you!!

 

:giggles:

 

Ok this is the wiring of the warning light. (Pic to follow from my phone.)

 

Explains the behaviour of the light. Next, what to do about it....

 

 

 

 

 

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Ok I can see no reason for having the relay, other than if the warning lamp was an LED, which I don't think it can be at 13.1 Ohms.

 

 Can anyone else figure out a reason for the relay?

 

If not, I'll take it out of the circuit and wire the warning lamp in the conventional manner.

 

 

 

 

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