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Starter Alternator


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Hi All,

 

I've noticed for some time that i have to get the engine revs up to quite a bit before the rev counter works on my beta 43 and im wondering is this was an early symptom of a failing starter alternator?   i ran the engine today and i'm only getting .5v on the positive from the alternator and the rev counter reads nothing regardless of high/low revs.... is this a typical sign of a dead alternator?   im at the boat today/tomorrow so seeing if i need to do any further fault finding... any suggestions gratefully receive, many thanks!!!!  rob

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The voltage on the W alternator terminal is AC, so if you try to measure it with a meter set to DC you won’t get anything meaningful. 
 

Although it’s a 6 diode machine, chances are that if the warning light is extinguishing at fairly low revs, and the starter battery voltage rises ditto, that the alternator is ok and it might be the rev counter or the wiring/multiplug. Anyway, what is the AC voltage on the W terminal?

 

Edit: just re-read your post, you say 0.5v on the alternator positive. Are you sure? Alternator positive is connected to starter battery positive so it will be at the same voltage. Unless eg the battery isolator switch is off or faulty. When you say 0.5v, what is that relative to?

Edited by nicknorman
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I don't know this for certain, but if it is a six diode machine (and I am by no means sure all Beta 43 alternators are) then I would have thought that the alternator rev counter feed would be via a diode fed from one phase, to produce a half-wave rectified out put to provide pulses for the rev counter that are the same as those from a 9 diode machine.

 

I hesitate to say Nick might be wrong but alternator terminals are not pure AC output. They are half-wave rectified AC, so pulsing DC. He is correct that the DC voltage reading will be pretty meaningless value wise, but it usually rises a bit as the revs rise. I prefer to use the Hz scale if your meter has one, and that should rise and fall with revs.

 

If this is a nine diode machine, then you have the classic symptoms of one or more failed field diodes. Make and model of alternator or photo would help identify it.

 

I agree with nick that if you are seeing 0.5V on the positive on the rev counter with the ignition turned on (rather than at the W alternator terminal) then it should read engine battery voltage, so something wrong, probably between the ignition switch and counter. If the warning lamps and instruments are odd, then the ignition switch itself could be implicated.

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34 minutes ago, nicknorman said:

The voltage on the W alternator terminal is AC, so if you try to measure it with a meter set to DC you won’t get anything meaningful. 
 

Although it’s a 6 diode machine, chances are that if the warning light is extinguishing at fairly low revs, and the starter battery voltage rises ditto, that the alternator is ok and it might be the rev counter or the wiring/multiplug. Anyway, what is the AC voltage on the W terminal?

 

Edit: just re-read your post, you say 0.5v on the alternator positive. Are you sure? Alternator positive is connected to starter battery positive so it will be at the same voltage. Unless eg the battery isolator switch is off or faulty. When you say 0.5v, what is that relative to?

thanks nick.. my alternator is wired directly to a battery combiner, which has two outputs, one to the starter and one to the bt battery., so it charges both.. not orthodox i know!  this would explain not seeing any 12v on the 12v post on the alternator....

56 minutes ago, Tony Brooks said:

I don't know this for certain, but if it is a six diode machine (and I am by no means sure all Beta 43 alternators are) then I would have thought that the alternator rev counter feed would be via a diode fed from one phase, to produce a half-wave rectified out put to provide pulses for the rev counter that are the same as those from a 9 diode machine.

 

I hesitate to say Nick might be wrong but alternator terminals are not pure AC output. They are half-wave rectified AC, so pulsing DC. He is correct that the DC voltage reading will be pretty meaningless value wise, but it usually rises a bit as the revs rise. I prefer to use the Hz scale if your meter has one, and that should rise and fall with revs.

 

If this is a nine diode machine, then you have the classic symptoms of one or more failed field diodes. Make and model of alternator or photo would help identify it.

 

I agree with nick that if you are seeing 0.5V on the positive on the rev counter with the ignition turned on (rather than at the W alternator terminal) then it should read engine battery voltage, so something wrong, probably between the ignition switch and counter. If the warning lamps and instruments are odd, then the ignition switch itself could be implicated.

thanks Tony. pics attached hope that gives you enough to id it?

not getting any ac/dc out of it anywhere near to 12v.....  looks original so maybe its died?

 

20230311_101042.jpg

20230311_101056.jpg

20230311_101216.jpg

20230311_101231.jpg

20230311_101305.jpg

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Looking at the black crud clogging the fins on the diode/regulator heat sinks, I fear that you may well be correct about a dead alternator.

 

The voltmeter between the large pos and neg terminals should read battery voltage with the master switch turned on. Then, when you rev the engine it should jump up as it energises.

 

The three thin wires suggests Nick is correct about it being a six diode machine, the three wires being live with the ignition switch on and dead with it off, pulses to the rev counter, and from the warning lamp.

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9 hours ago, Tony Brooks said:

I don't know this for certain, but if it is a six diode machine (and I am by no means sure all Beta 43 alternators are) …

 

I hesitate to say Nick might be wrong but alternator terminals are not pure AC output. They are half-wave rectified AC, so pulsing DC. He is correct that the DC voltage reading will be pretty meaningless value wise, but it usually rises a bit as the revs rise. I prefer to use the Hz scale if your meter has one, and that should rise and fall with revs.

 

 

Beta 43 has been around for a long time so nothing is certain, but the owners manuals I’ve seen show a 6 diode starter alternator and a 9 diode domestic.

 

As to the W terminal, as far as I’m aware it is just connected to one of the stator phases and as such is AC. Maybe there is an alternative way of doing it but the only way to get 1/2 wave rectified output would be for it to have a dedicated diode. Here is a random pic from the internet showing W is one phase of the stator and thus AC.

 

275DAD43-34E2-4B1B-B666-AA91FCE14A32.jpeg.b49f648ce29857b8d249298679423d94.jpeg


 

With a 6 diode machine it’s worth bearing in mind a few things: there is an “on /off” connection normally operated by the ignition switch. It needs 12v on that to tell it to wake up and start working. The warning light circuit is just that, it doesn’t play any part in getting the alternator going as it would in a 9 diode machine. And the field current comes from the B+ terminal which initially comes from the battery before the alternator is spinning fast enough to be “self-sustaining”.

9 hours ago, robtheplod said:

thanks nick.. my alternator is wired directly to a battery combiner, which has two outputs, one to the starter and one to the bt battery., so it charges both.. not orthodox i know!  this would explain not seeing any 12v on the 12v post on the alternator....

 

 


Has this ever worked properly? I would have thought there needs to be 12v on the B+ terminal to get things going. I would try connecting starter battery directly to B+ and see if that makes it work.

 

Also check you are getting the “12v wake up” signal on the IGN terminal of the alternator when the ignition is turned on.

Edited by nicknorman
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16 minutes ago, nicknorman said:

As to the W terminal, as far as I’m aware it is just connected to one of the stator phases and as such is AC. Maybe there is an alternative way of doing it but the only way to get 1/2 wave rectified output would be for it to have a dedicated diode. Here is a random pic from the internet showing W is one phase of the stator and thus AC.

 

I think it will be half-wave rectified by the relevant negative diode, as it is on 9 diode machines, so spouted a bit of duff info this morning.

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I had the same problem 4 years back with mine.

This looks like the standard kubota fitted 45amp alternator as used on all the commercial and tractor kubota engines also.

Plenty about but beware not all have the W tacho terminal wired

It is a Denso item but equivalents on ebay around £120.

Search kubota 45 amp or get the model number from your existing one.

 

 

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41 minutes ago, Tony Brooks said:

 

I think it will be half-wave rectified by the relevant negative diode, as it is on 9 diode machines, so spouted a bit of duff info this morning.

But that pic is of a 9 diode machine and the W is connected directly to one phase of the stator winding, so it must be AC.

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2 hours ago, nicknorman said:

Has this ever worked properly?

 

A question rarely asked in the techy threads in this forum and one I always find worth asking early on, when answering weird boiler failure enquiries! 

 

 

 

 

 

 

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1 hour ago, nicknorman said:

But that pic is of a 9 diode machine and the W is connected directly to one phase of the stator winding, so it must be AC.

No because the return is via a main negative diode, just like the charging current for that phase, so it is half-wave rectified for the W terminal and with the positive diode in circuit for the actual output of the phase is full wave rectified.

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17 minutes ago, Tony Brooks said:

No because the return is via a main negative diode, just like the charging current for that phase, so it is half-wave rectified for the W terminal and with the positive diode in circuit for the actual output of the phase is full wave rectified.

You’re right! I was looking at it relative to the centre of the star, but relative to the B- it is as you say.

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43 minutes ago, MtB said:

 

A question rarely asked in the techy threads in this forum and one I always find worth asking early on, when answering weird boiler failure enquiries! 

 

 

 

 

 

 

it has worked fine before. always needed a fair rev to get the tacho going but thought that was usual. i'll try to find a part number on it tomorrow when in the bay.  thanks so much to everyone who's replied... its always a school day for me!

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10 hours ago, robtheplod said:

it has worked fine before. always needed a fair rev to get the tacho going but thought that was usual. i'll try to find a part number on it tomorrow when in the bay.  thanks so much to everyone who's replied... its always a school day for me!

 

If it is a nine diode machine, a higher wattage warning lamp bulb or a parallel resistor may solve the high revs issue.

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I am pretty confident you have done this but I had exactly the same symptoms and mine turned out to be really dumb.

To be belt appeared to be well adjusted but rather than sitting in the V groove on the bottom pulley it was just running on the pulley extension for the domestic alternator.

Due to space on mine it was impossible to see until you were basically up side down in the engine bay.

Pete

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RML Units turned out to be really nice people.....

 

ordered the above, but spoke to them who changed the order to this one:

Alternator - RML Units

 

Hope this is ok. Arrived today and pretty much identical...... will find out if it works at the weekend. Also got a new plug on order as the old one looked tatty...

image.png.bd755a68e880000269dd456c1785ba2a.png

P Phase
IG Ignition (+)
L Lamp

 

 

Unit Type Replacement Unit
Pulley Pulley 62-69 mm Single
Application Kubota Various Equipment
Replacing 101211-1100

Standard lamp function
L Terminal Has No Output When charging

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Just thought I'd update you all....

 

Fitted the new alternator..... and exactly the same issues - no tacho, no charge, red light on.....  ahh!

 

scratched head a bit and then took the battery isolator out of circuit, so the positive on the alternator goes to the battery + direct.... worked fine.... 14.4v on output of alternator, tacho working again and charge light out!  so thinking alternator was fine... so put the old alternator back (with the changed wiring direct) - issue returned....... now very confused...

 

put new alternator back and everything working fine.... so have i been really unlucky and had a duff alternator connected to a battery isolator which may also be faulty/have some compatibility issue all of a sudden???  things have been working fine for 3 years until the other day......all very odd as nothing changed...

 

oh well, its all working fine now, thanks for all the help!

 

................................................just had a thought, its not true nothing has changed.. the boat did have a smartbank with relay (VSR) between engine/leisure batteries.... i'm now wondering if this may have been masking the problem? I have no idea when this was energised........ just a thought!

Edited by robtheplod
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The faulty battery isolator switch may have been intermittently

going open circuit with the alternator charging, I understand that this can blow the diodes.

Alternatively like mine when it failed it had worn out the brushes after a lot of heavy usage.

On an original kubota they only charge the starter battery so it is asking a lot for this small alternator to charge domestics as well

Did you manage to buy the plug?

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11 hours ago, adrianh said:

The faulty battery isolator switch may have been intermittently

going open circuit with the alternator charging, I understand that this can blow the diodes.

Alternatively like mine when it failed it had worn out the brushes after a lot of heavy usage.

On an original kubota they only charge the starter battery so it is asking a lot for this small alternator to charge domestics as well

Did you manage to buy the plug?

The alternator looked like the original (with green paint!) so that would make it 18 years old, so not bad going!  it just charges the starter battery and BT battery (which is why it had a battery isolator). The leisure side has its own alternator. yes got the plug a popped that on as well... cheers!

10 hours ago, Tony Brooks said:

This is why I usually suggest that you take the suspect on off and get it tested. I am sorry I got sidetracked by the Rev counter terminal delivering half-wave rectified pulses.

no need to apologise Tony, your help as ever is gratefully received!!!!!

 

 

 

So with the battery isolator out of play I'm left with a dilemma. The layout as it is now is as below, but i know this isn't good as if either battery is low it will attempt to draw over the long cables going stern to bow which isn't good and will overload the cables.

 

I'm thinking i either need to pop in a fuse at ether end or fit some sort of VSR?

 

any suggestions over best way to sort?  thanks!!

 

 

Untitled.png

Edited by robtheplod
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12 hours ago, Tony Brooks said:

This is why I usually suggest that you take the suspect on off and get it tested. I am sorry I got sidetracked by the Rev counter terminal delivering half-wave rectified pulses.

I’m not sorry because it made me think about it properly! But having done so, I wouldn’t really describe the waveform as half wave rectified. That implies a sine wave with the bottom half lopped off. Whereas in fact it is more of a square waveform with the bottom part a diode-drop (say 0.8v) below 0v ie around -1v and the top half a diode-drop above battery voltage ie around 15v). Looks like this, there’s some noise presumably from the other diodes switching.

EE6C1AFE-5C53-40EB-A684-E58E45B89F51.jpeg.2ba045906ac95c8a7c01478e72d42962.jpeg

 

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2 hours ago, robtheplod said:

The alternator looked like the original (with green paint!) so that would make it 18 years old, so not bad going!  it just charges the starter battery and BT battery (which is why it had a battery isolator). The leisure side has its own alternator. yes got the plug a popped that on as well... cheers!

no need to apologise Tony, your help as ever is gratefully received!!!!!

 

 

 

So with the battery isolator out of play I'm left with a dilemma. The layout as it is now is as below, but i know this isn't good as if either battery is low it will attempt to draw over the long cables going stern to bow which isn't good and will overload the cables.

 

I'm thinking i either need to pop in a fuse at ether end or fit some sort of VSR?

 

any suggestions over best way to sort?  thanks!!

 

 

Untitled.png

 

If it has worked satisfactorily for years then why worry. It is not too good to overthink theses things. At present you seem to have one large battery bank so any starting or bow thruster load will discharge both batteries, but until a clown leaves the ignition turned on when you leave the boat for a period or a battery fails I don't think it will be a problem. That is what I would use  VSR for, it would not help the volt drop along the cable.

 

I suspect (but do not know for sure) that with batteries in good condition and the correct use of the thruster burning the cable will not be a problem because as the current rises so will the volt drop and that will limit the current flow (happy to have this disagreed with/discussed).  The "bad" thing with this layout is that it will tend to lengthen the time needed to fully charge the bow thruster battery. As the thruster battery charges it will start to limit the charging current so the volt drop falls and the charging voltage at the thruster battery rises, but the voltage  will be lower for longer than at the engine battery, although they are both fed from the same source.

 

Best practice is for a fuse at either end of the cable so if a short to the hull developed along the run the fuse or fuses would blow and prevent further damage.

Edited by Tony Brooks
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