Unusual alternator fault

[Tom and Bex]

I purchased a new alternator in August from a reputable supplier on ebay (item no. 181430420788) which has developed an unusual intermittent fault. I have contacted the supplier who doesn't have any idea what might be causing it but happy to do a straight replacement foc so no issues with them. I am just interested in what the fault might be.

 

The alternator will sometimes make a very slight buzzing noise even with the ignition off, and there is 12v on the D+ terminal even with the wiring to this disconnected. This causes the warning light to not illuminate but the alternator is still charging.

 

It does not do this all the time and will occasionally do this after some time sat idle. It was first noticed when the control panel warning buzzer sounded in the middle of the night due to the 12v on D+ terminal earthing through the warning lights and oil pressure sensor.

 

The alternator is installed in a dry internal engine room and the wiring checked for faults. I do have a split charge relay connected to D+ but there is nothing connected to the W terminal. The alternator is wired to the engine battery with the relay connecting the 2 banks together. I know this is not ideal and intend to change it at some point, but just interested in the current fault for now.

 

Thanks for any insight to this fault and apologies for the long post!

 

Tom

[Tony Brooks]

I am going to assume that you mean the actual D+ terminal blade or stud rather than whatever is in the end of the D+ cable.

 

I suspect one of the main diodes has failed short circuit. I am ignoring the buzzing because apart from the warning buzzer I do not see what inside the alternator will actually buzz when stationary.

 

If a main positive diode is fully or partially open circuit and the master switch is on (or the wiring is not in accordance with the BSS) then 12 volts can feed back through the diode and onto the field/aux diode which will then be forward biased so passing current to the D+ terminal and the regulator. I would expect the alternator to be slightly warm after standing over night.

 

One test would be to disconnect the B+ cable (take care not to short it out) and see if the buzzing stopped.

 

If there has been a bit of poor quality re-building going on you might have a poor solder joint one phase that overheat and caused this or it could even be a phase wire so close to the heat sink (diode case) it shorts out intermittently.

 

I just love it when people say reputable supplier and quote Ebay without giving more details.

 

PS not bothered to go through a wiring diagram so may not be correct, but I think it is a possibility.

Edited December 10, 2015 by Tony Brooks

[MoominPapa]

Sounds like maybe the regulator is providing excitation current to the rotor windings even when the alternator is not running. The regulator is an oscillator that switches the current on and off rapidly, varying the on time/off time ratio to control average current. That gives an oscillating magnetic field in the rotor which is vibrating something and making the buzzing.That also fits with the 12v on the D+ terminal.

 

The question is where the the 12v on the D+ terminal is coming from. You say it persists when the wiring is disconnected, which eliminates an external fault. In that case, the obvious cause is that one of the main positive diodes in the alternator has gone partially short-circuit and is allowing "backwards" current flow. That would allow current from B+ to flow backwards to a stator terminal and then forwards through a field diode to D+.

 

MP.

 

ETA. Rats! beaten to it by Tony. We agree on the fault though.

EATA. and I provided an explanation for the buzzing.

Edited December 10, 2015 by MoominPapa

[Sir Nibble]

This is the A127i alternator and it works somewhat differently to the 9 diode machines we are used to. In this machine the regulator detects the rotation of the alternator from an ac tap from one phase. It then switches a supply to D+ powering the field and extinguishing the light. I would suggest your regulator might be picking up an induced ac somewhere from the boats 230V or more likely it's just defective.

[DHutch]

I just love it when people say reputable supplier and quote Ebay without giving more details.

To be fair, he does give the item number.

 

ECUsDirect 99.7% Positive feedback on 2908 sales.

 

 

 

Daniel

[Tom and Bex]

Thanks for the ideas on possible faults, it just got me wondering what it might be. I'll ask the supplier to let me know what if anything they find and report back.

 

As to reputable supplier, I judged them on their very quick response to questions, advice, and technical details supplied before ordering. Ecusdirect is the ebay trading name for ATP electronics based at Cannock who are a big name in ecu testing for cars which I've used before. Very happy with their response and suggestion for a straight swap of the alternator without testing it first.

 

Thanks again

 

Tom

[OldGoat]

Don't dismiss eBay items as ALL being junk. There are an increasing number of good trade suppliers using eBay to expand their markets (which can tend to be only local anyway) or to sell out of date / end of line / excess stocks / wotever.

 

A always in life it's a matter of Caveat Emptor (as Mr. Moore of this parish might say)

[Tony Brooks]

Don't dismiss eBay items as ALL being junk. There are an increasing number of good trade suppliers using eBay to expand their markets (which can tend to be only local anyway) or to sell out of date / end of line / excess stocks / wotever.

 

A always in life it's a matter of Caveat Emptor (as Mr. Moore of this parish might say)

 

That is as maybe but why trust a marketing outfit that deliberately uses a payment system that voids your legal right of redress and in its place has a system that may or may not pay you when you are sold dangerous or counterfeit goods AND puts a time limit on claims.

 

Credit cad companies will not honour their joint enterprise in selling items if you pay via third party like Paypal.

 

Any marketing outfit that gets regularly caught assisting fraud and misrepresentation must be considered dubious and untrustworthy. It is up to individual businesses to decide of they want to deal through such outfits.

[Tom and Bex]

I'm resurrecting this thread as the same problem has reoccurred nearly 12 months later and warrantee is now out on alternator.

 

When you turn the engine off the alternator warning light does not come on, and split charge relay does not open. There is a very slight high pitch humming from the alternator and it remains slightly warm to touch.

 

With the warning light disconnected at the alternator (but battery +ve connected) there is 12.41v on B+ and 12.39v on D+ terminals of the alternator, and a current draw of about 1.4A from the domestic batteries (alternator connected direct to domestic batteries).

 

When starting the engine this morning the alternator appeared to be charging fine - about 80-90A into domestic batteries at just above tickover. Alternator fitted to Lister HA3 engine with original engine pulley of about 7.5".

 

From above responses it would appear to be either regulator or diodes at fault - how do I test which it is?

 

Is there anything I can do to prevent a reoccurrence?

 

Not sure if the following might have had any influence on causing the fault: I have a split charge relay connected to the D+ terminal, and a solar controller connected to the batteries set at 14.8v so in bright sunshine will sometimes cause the alternator light to come on as it raises the voltage higher than the alternator voltage. It will also sometimes do an equalisation at up to 15.4v (and I have done a manual equalisation at 16v with alternator connected but engine not running). Also wondering if the alternator is running too slowly for the current produced and overheating?

 

Hope I've included all relevant information and thanks in advance for any help you can give.

 

Tom

[Tony Brooks]

How is the split charge relay coil wired? If this is still an A127i that SirN talked about I doubt it should be wired to the warning lamp circuit and might overload the warning lamp turn off electronics.

 

I have had nothing to do with such alternators so am guessing.

[Tom and Bex]

 

How is the split charge relay coil wired? If this is still an A127i that SirN talked about I doubt it should be wired to the warning lamp circuit and might overload the warning lamp turn off electronics.

 

I have had nothing to do with such alternators so am guessing.

Yes it's still the A127i talked about further up. Split charge relay coil is wired into warning lamp circuit. It's a 180A relay so suspect the coil draws more than a normal sized relay. Looks like I might have to go with a voltage sensitive relay instead. Was wondering if this might be causing damage.

 

Any ideas on how to test regulator or diode pack for faults?

 

Many thanks

 

Tom

[Tony Brooks]

I am afraid I can not make further comment. From what SirN said I do not see how the relay can work but it obviously is. I fear you need him to comment.

[Tony Brooks]

I PMd Sir Nibble yesterday asking him to take a look to see if he could advise.

 

I think there may be crossed wires about this alternator somewhere so unless he can help I suspect you may need a good marine or electrician. Maybe WotEver can add to this, otherwise if NMEA can't help I think we are stuck here.

[Sir Nibble]

Well clearly the alternator thinks it's charging when stationary and is powering up it's field, but why? Either there is something in the system fooling it or something damaging alternators. I shall do a little reading and get back to you.

[Tony Brooks]

and I just realised I was talking carp about the relay not working but it is likely to be energised all the time the ignition is on.

 

I then had another thought. The circuit that turns the warning lamp off I suspect does not expect an inductive load so may not be very well protected from voltage spikes as the relay coil is turned off. The surges might have damaged the alternator warning lamp switching system. I think that if this were mine I would put a diode across the relay coil once the problem is sorted. This should damp any potential voltage surges. This is all theory so could be miles off the mark. Await Sir N's response.

 

 

[Sir Nibble]

Can I have a voltage reading on both ac and dc ranges taken from the W terminal please. When the fault is apparent of course.

[Tom and Bex]

Can I have a voltage reading on both ac and dc ranges taken from the W terminal please. When the fault is apparent of course.

Well fault is now permanent so that should make it easier to find.

 

Voltage on W terminal with engine off is 0v, engine running at fast tickover and alternator charging at about 30A gives 7.3v dc and 7.9v ac. At same time B+ and D+ both give 14.5v.

 

The puzzling thing for me is alternator still seems to be producing full charging output. It is getting annoying having to disconnect the main battery lead each day though!

 

Tom

[Sir Nibble]

Sorry to take so long, busy. Reason i wanted to know about voltage at W was that it's common with the phase connection that triggers the regulator to begin powering the field. We have established that there is nothing fibbing to the reg that the alternator is turning. Units or this type, the A127i, and it's little brother the A115i are part of a family of machines with a dozen or more different regulators. and made successively by Lucas, magnetti Marelli and nippon Denso with umpteen design variations. I had one on my pile of broken down bits of machinery awaiting my attention but unfortunately the regulator on that one is U/S and I can't source a replacement. I had hoped to try and provoke the same behaviour but as the French say, that's life. Firmly, you do not have a diode problem from the symptoms. there are two possibilities. Does the fault go away if you disconnect the D+ lead? Some of these machines on my test bench refuse to de energise until I have simulated ignition off by disconnecting warning light and/or sense lead, (yes I know you don't have a sense lead on yours). If the problem persists with only B+ connected then how about with any other sources of charge off and a little load?

The regulator is doing this for sure, it's just a question of whether some external influence is fooling it or, as seems increasingly likely there is a common fault with the regulators in the e bay units. If the above doesn't shed any light I will arrange to send you a regulator.

[Tony Brooks]

Do I conclude form this that you think there is a possibility that a charging voltage "back feeding" down the B+ may persuade the regulator/warning lamp control that it actually has output so is regulating the rotor current?

[Sir Nibble]

I have seen a tendency for the field to remain powered once it has cut in until the alternator sees what it expects from an ignition off condition on a vehicle. This is very hazy and not to be taken as reliable gen. I think the reg is at fault.

[Tony Brooks]

Thanks - so do I re the reg.

[Tom and Bex]

Does the fault go away if you disconnect the D+ lead?

 

If the problem persists with only B+ connected then how about with any other sources of charge off and a little load?

 

... it's just a question of whether some external influence is fooling it...

 

...If the above doesn't shed any light I will arrange to send you a regulator.

Been away for a few days so just catching up with this again.

 

Problem still persists with D+ disconnected and only B+ connected to alternator.

 

Problem also persists with no other charge sources connected (live off grid so no permanent hook up and not much solar this time of year).

 

As for external influence, the fault occurred after several hours cruising but with solar still connected and providing some charge. Prior to the fault, solar would at times be charging at higher voltage than alternator causing warning light to come on.

 

Also is there any merit to Tony's theory that the split charge relay could have caused a voltage spike causing damaged to the regulator?

 

Have pm'd you about regulator.

 

Many thanks again for your help and patience.

 

Tom