Domestic alternator doing my head in.........

[Bimbly1]

Having previously found my Barrus 110 amp domestic alternator consistently charging at 15 volts, as measured from rear of alternator, I removed it and had it bench tested. Nothing untoward was found.

 

I reinstalled it, separated and cleaned all connections, near and remote and checked the condition of all crimps. Having fully charged the battery bank, (4x 110Ah batts, new in June this year), I fired the engine up.

 

Initial output was 14.7volts, dropping within a few minutes to 14.6volts and remained so for an hour at 1200 revs.

 

When I drop the engine speed to tickover, 900 revs, the charge rate rose to 15volts, dropping to 14.6volts when I increased the speed to 1200 revs and higher.

 

I expected either no change in charging rate or a slight drop at tickover. Is this normal or is there something not right?

 

Anyone got any constructive thoughts please?

Bob.

[Tony Brooks]

I am not sure how this all fits together but see the thread nominally on alternator speeds. As output and//or speed goes up the charging voltage tends to fall so by educing your engine speed the current droops so the voltage may well rise. However to em 0.4 volt seems rather a lot.

 

I would be interested in SirN's take on this.

 

If I am correct about the cause then it illustrates why it is important to understand and accept what I outlined in the other thread. I suspect no fault here but I can not be sure without current readings as well.

[nicknorman]

I am not sure how this all fits together but see the thread nominally on alternator speeds. As output and//or speed goes up the charging voltage tends to fall so by educing your engine speed the current droops so the voltage may well rise. However to em 0.4 volt seems rather a lot.

 

No sorry Tony, it is wrong to imply that the voltage increases when the current decreases due to reducing rpm. The voltage only increases when the demand for current reduces - as the batteries become better charged. For a battery in a given state of charge, reducing the charge current will always reduce the battery voltage. Increasing the charge current will always increase the voltage. If an alternator is not producing much current due to low engine rpm, increasing the rpm should increase the voltage.

 

In the OP's case it would seem something is wrong somewhere. Is the measuring equipment faulty? eg a mechanical meter that is responding to changing engine vibration. Is the connection between alternator and batteries sound? When the alternator is putting out 15v at idle, what is the battery voltage? Obviously it should be essentially the same, but this seems highly unlikely.

[by'eck]

Would be interesting to see the voltage at batteries. If its the same or very close then as voltage rises so will charge current. Sounds like abnormal regulator behaviour given the significant range, but interested in other views.

 

Can I assume an external regulator/booster isn't fitted?

Edited October 22, 2014 by by'eck

[Bimbly1]

Thanks for your responses.

 

In the OP's case it would seem something is wrong somewhere. Is the measuring equipment faulty? eg a mechanical meter that is responding to changing engine vibration. Is the connection between alternator and batteries sound? When the alternator is putting out 15v at idle, what is the battery voltage? Obviously it should be essentially the same, but this seems highly unlikely.

Analogue meter reading from the bank, digital clamp from the alternator studs. Both give the same readings. Bank connections checked and sound.

 

 

Would be interesting to see the voltage at batteries. If its the same or very close then as voltage rises so will charge current. Sounds like abnormal regulator behaviour given the significant range, but interested in other views.

 

Can I assume an external regulator/booster isn't fitted?

Seems to be the same at alternator and bank. No external regulator/booster.

 

I'll run some further checks in the morning, (it is hissing down at the moment), and post the results.

 

Bob.

Edited October 22, 2014 by Bimbly1

[nicknorman]

Thanks for your responses.

 

Analogue meter reading from the bank, digital clamp from the alternator studs. Both give the same readings. Bank connections checked and sound.

 

 

Seems to be the same at alternator and bank. No external regulator/booster.

 

I'll run some further checks in the morning, (it is hissing down at the moment), and post the results.

 

Bob.

I would check the battery voltage at idle with the clamp meter. If it is still at 15v then I think there is something wrong with the alternator, regardless of what whoever bench tested it said. Seems an odd fault for an alternator though. It might also be interesting to try same with some modest load on - a few lights. Presumably (from you OP) you have a different alternator for the engine battery with no split charge devices?

[Bimbly1]

It might also be interesting to try same with some modest load on - a few lights. Presumably (from you OP) you have a different alternator for the engine battery with no split charge devices?

Yes, a separate 50A alternator for the engine batt. I'll run a few more checks in the morning.

[Nightwatch]

We have got a Barrus Shire. Had similar symptoms amongst many others until recent overhaul of injin room electrics. To put it mildly, the wiring was potentially dangerous. Dave Reynolds replaced 99.9% of the wiring and added a couple of gadgets. Same alternators, first class now. Not saying your wiring is suspect, just sounds familiar to our problem.

 

Martyn

[Tony Brooks]

No sorry Tony, it is wrong to imply that the voltage increases when the current decreases due to reducing rpm. The voltage only increases when the demand for current reduces - as the batteries become better charged. For a battery in a given state of charge, reducing the charge current will always reduce the battery voltage. Increasing the charge current will always increase the voltage. If an alternator is not producing much current due to low engine rpm, increasing the rpm should increase the voltage.

 

In the OP's case it would seem something is wrong somewhere. Is the measuring equipment faulty? eg a mechanical meter that is responding to changing engine vibration. Is the connection between alternator and batteries sound? When the alternator is putting out 15v at idle, what is the battery voltage? Obviously it should be essentially the same, but this seems highly unlikely.

 

 

If you accept that the pulsing magnetic fields in the stator (and you may not) cause the alternator to self limit the current the as the frequency of the pulses falls so will the voltage reducing effect. Like wise as the rotor speed decreases then the current the alternator is capable of producing at that speed will fall, hence the voltage reducing effect will also be reduced. Now, I said I am not sure how it all fits together but I have noticed a very similar effect on my Paris-Rhone alternator right from when it was new and it all works perfectly well. However mine doss it around 14.3 to 14.6 volts

 

I am sure 15 volts is wrong but remember Beta fitted (or still do) 14.8 volt alternators and that is close to 15 volts. Maybe Barrus do the same.

 

I am going to wait to see if anyone else has any comments to make but I am sure 15 volts is too high. I suppose we really need to establish if its a battery sensed alternator because if so the high voltage (not so sure about the voltage rises as it drops to idle) is much more likely to be a circuit resistance fault.

 

It would also be interesting if we could see the test sheet for that model of alternator.

[nicknorman]

If you accept that the pulsing magnetic fields in the stator (and you may not) cause the alternator to self limit the current the as the frequency of the pulses falls so will the voltage reducing effect. Like wise as the rotor speed decreases then the current the alternator is capable of producing at that speed will fall, hence the voltage reducing effect will also be reduced. Now, I said I am not sure how it all fits together but I have noticed a very similar effect on my Paris-Rhone alternator right from when it was new and it all works perfectly well. However mine doss it around 14.3 to 14.6 volts

Whilst I can believe there is a self limiting phenomenon relating to current induced back into the stator, the primary means of regulating the alternator is by means of the regulator! If the voltage rises above the regulated value, the regulator should reduce the current in the stator thus reducing the current and hence the voltage output.

 

Certainly in the old days of electromechanical regulators (on dynamos and some aviation alternators) you could hit a low rpm where the regulator contacts remained closed and the output was a little higher than if you increased the rpm and the regulator contacts started switching, but I wouldn't have thought that should happen with an electronic regulator. Maybe Snibbs will put us out of our misery!

[dmr]

I might have observed a related manifestation of this.

At the end of the cruising day I usually glance at the charging current (on the Adverc DCM) and with the engine at a fastish tickover it might be something like 4 amps (not bad for 3 year old Trojans!). I usually then slow the engine to minimum tickover (390rmp) before turning it off and the charge current sometimes jumps to about 8 amps. I have been thinking about investigating this but have got a "round tuit" yet..

The alternator output consists of obvious current pulses (the nature of rectified AC) at at very low speeds I suspect these upset either the alternators internal regulator, the Adverc controller or the Adverc DCM..

 

I have set a test for the grammar pedants in this post!

 

............Dave

[nicknorman]

I have set a test for the grammar pedants in this post!

 

............Dave

Where to start?... but I'll go for "alternators"!

 

Anyway, it is a theory but not something I've heard of before with electronic regulation. Maybe ours doesn't do it because it never spins that slowly. Perhaps the OP can tell us if the setup has always done this, or just started doing it?

[Tony Brooks]

I might have observed a related manifestation of this.

At the end of the cruising day I usually glance at the charging current (on the Adverc DCM) and with the engine at a fastish tickover it might be something like 4 amps (not bad for 3 year old Trojans!). I usually then slow the engine to minimum tickover (390rmp) before turning it off and the charge current sometimes jumps to about 8 amps. I have been thinking about investigating this but have got a "round tuit" yet..

The alternator output consists of obvious current pulses (the nature of rectified AC) at at very low speeds I suspect these upset either the alternators internal regulator, the Adverc controller or the Adverc DCM..

 

I have set a test for the grammar pedants in this post!

 

............Dave

 

 

I very much doubt a rise in current gas anything to do with what the OP observed. I suspect in your case it may be to do with worn/eccentric slip rigs and worn or sticky brushes mess with the rotor current.

Whilst I can believe there is a self limiting phenomenon relating to current induced back into the stator, the primary means of regulating the alternator is by means of the regulator! If the voltage rises above the regulated value, the regulator should reduce the current in the stator thus reducing the current and hence the voltage output.

 

Certainly in the old days of electromechanical regulators (on dynamos and some aviation alternators) you could hit a low rpm where the regulator contacts remained closed and the output was a little higher than if you increased the rpm and the regulator contacts started switching, but I wouldn't have thought that should happen with an electronic regulator. Maybe Snibbs will put us out of our misery!

 

 

The OP gave no indication of the stage of charging or how much current is flowing the alternator could well still be in "bulk" phase in which the phenomenon I described in the other post is active. It is only in this phase that one needs to even think about the effects of this phenomenon, at all other times the current is controlled by the difference between battery voltage and the regulated volatge.

 

I also would value SirN's opinion.

Edited October 22, 2014 by Tony Brooks

[Bimbly1]

Where to start?... but I'll go for "alternators"!

 

Anyway, it is a theory but not something I've heard of before with electronic regulation. Maybe ours doesn't do it because it never spins that slowly. Perhaps the OP can tell us if the setup has always done this, or just started doing it?

It started recently. Earlier this year it was charging at 13.8, rising over a couple of hours to 14.2volts, although the bank performed perfectly on this regimen.

 

The boat and engine installation is 8 years old and charging has previously been at 14.6-8 volts.

 

The bank is fully charged via land-line. I turn the selectors to off, disconnect the line and start the engine. I would expect the higher voltage of 14.6-8 but it doesn't drop to 13.6volts as the land-line charger does.

Edited October 22, 2014 by Bimbly1

[smileypete]

What sort of current do you see at 15V? Are the batts sealed ones?

 

cheers, Pete.

~smpt~

[RichLech]

Bob

 

I identified exactly the same issue with my Barrus Shire 45 earlier this year. I also took the 110A alternator off and had it checked out by a specialist who said it is OK.

 

I have now fitted a Smartguage so that I can accurately see what is happening at the batteries. All the time I am running at normal revs (1200 - 1400) I see 14.4/14.5 ish but once the engine is hot if it idles for a while I get towards 15V and sometimes just over. This triggers an error on the Smartguage.

 

The specialist who checked over my alternator said occasional charging of 15V or just over is not that unusual for an alternator and that short periods of 15V will not hurt the batteries. During the 250 hours I've motored this year the batteries did not get at all warm and did not use any electrolyte so I am inclined to believe him.

 

So, I've stopped worrying about it now. I've had the boat two years and assume it has always been like it. I have 3 110A leisure batteries and they certainly don't seem to be suffering in any way.

 

I think sometimes too much information is a bad thing. If I didn't know how to use a multi-meter and enjoy getting down into the engine bay I would never have known and got concerned about it!

 

Having said that I now ignore it, if you do by any chance identify anything, please let me know.

 

Richard

[Alan Saunders]

Maybe the alternator drive belt is slipping at higher rpm but gripping at tickover?

 

Alan

[smileypete]

IF the current is very low, might be residual magnetism in the rotor, diesel engines don't load the alt much.

 

cheers, Pete.

~smpt~

[Bimbly1]

What sort of current do you see at 15V? Are the batts sealed ones?

 

cheers, Pete.

~smpt~

Yes Pete, sealed. They have remained cool to the touch after running for 2 - 3 hours.

[bottle]

It started recently. Earlier this year it was charging at 13.8, rising over a couple of hours to 14.2volts, although the bank performed perfectly on this regimen.

 

The boat and engine installation is 8 years old and charging has previously been at 14.6-8 volts.

 

The bank is fully charged via land-line. I turn the selectors to off, disconnect the line and start the engine. I would expect the higher voltage of 14.6-8 but it doesn't drop to 13.6volts as the land-line charger does.

 

An alternator charging batteries is not 'intelligent' as your charger is.

 

The alternator only has one stage whereas the charger will have three. (bulk, absorption and float)

[Bimbly1]

I think sometimes too much information is a bad thing. If I didn't know how to use a multi-meter and enjoy getting down into the engine bay I would never have known and got concerned about it!

 

Having said that I now ignore it, if you do by any chance identify anything, please let me know.

 

Richard

Thanks for that info Richard. I'll let you know if I find anything.

Bob.

 

An alternator charging batteries is not 'intelligent' as your charger is.

 

The alternator only has one stage whereas the charger will have three. (bulk, absorption and float)

I see, I thought that it was due to having other stuff like the fridge on, so the bank was never fully charged; i.e. some going in but a little going out, if you see what I mean!

[nicknorman]

It started recently. Earlier this year it was charging at 13.8, rising over a couple of hours to 14.2volts, although the bank performed perfectly on this regimen.

 

The boat and engine installation is 8 years old and charging has previously been at 14.6-8 volts.

 

The bank is fully charged via land-line. I turn the selectors to off, disconnect the line and start the engine. I would expect the higher voltage of 14.6-8 but it doesn't drop to 13.6volts as the land-line charger does.

Ok I'm a little confused by this. When you say "turn the selectors to off" do you mean the AC mains selectors or a 12v DC selector?

 

Anyway, regarding your comment about not dropping back to 13.6v, this is to be expected. Multi-stage mains chargers got into float phase when the batteries are fully charged whereas a standard alternator doesn't have a float phase so the voltage will (should!) remain at the regulated value (normally 14.4-14.6v) all the time the engine is running with full batteries.

[trackman]

This may be irrelevant, but to me the story sounds very similar to the first stages of the failure of the external regulator fitted by Beta to the alternator on our JD3 Tug engine.

I started noticing this going up to 15V or so instead of 14.8 (we have a Smartgauge, so it was obvious). This didn't alarm me or the batteries too much.

However, after some time I realised that the peak voltage I was seeing had crept up. When I began to see peak values of about 15.5V I decided it was time to do something.

Beta no longer produce the external regulators so we got one of their new alternators. This only goes to 14.6V but it seems to do well enough.

I did get a local auto electrics guy to put a new 14.6V internal regulator into the old alternator after cleaning and checking it, so now keep that as a stand by.

I'd keep a close eye on the Smartgauge for increasing voltages!

[by'eck]

 

 

If you accept that the pulsing magnetic fields in the stator (and you may not) cause the alternator to self limit the current the as the frequency of the pulses falls so will the voltage reducing effect. Like wise as the rotor speed decreases then the current the alternator is capable of producing at that speed will fall, hence the voltage reducing effect will also be reduced. Now, I said I am not sure how it all fits together but I have noticed a very similar effect on my Paris-Rhone alternator right from when it was new and it all works perfectly well. However mine doss it around 14.3 to 14.6 volts

 

I am sure 15 volts is wrong but remember Beta fitted (or still do) 14.8 volt alternators and that is close to 15 volts. Maybe Barrus do the same.

 

I am going to wait to see if anyone else has any comments to make but I am sure 15 volts is too high. I suppose we really need to establish if its a battery sensed alternator because if so the high voltage (not so sure about the voltage rises as it drops to idle) is much more likely to be a circuit resistance fault.

 

It would also be interesting if we could see the test sheet for that model of alternator.

 

I don't see how the phenomena you refer to can exist whereby lower current supplied to batteries gives rise to higher voltage despite the self induction in stator effect you refer to. Remember that despite this and its increase with rpm, the output current curve of an alternator never trends downwards, just flattens off within its rev range, and is quite steep initially. As Nick suggest therefore the regulator performs the greater control.

As I mentioned in another thread the transition from bulk to absorb phase is contiguous and transparent and merely a function of charge source voltage control cutting in. Since the batteries receive no further voltage increase their current demand slowly tails off following the very soft transition from drawing max or near max current.

The above assumes an alternator running at rpm's to give close to max output though. As they are reduced so is the current. I suppose there could be some hysteresis from the batteries in as much as the voltage doesn't drop off as quickly or at least pro-rata to the current drop but that wouldn't represent an increase in voltage.

BTW to OP, an internally regulated alternator will not have a float phase unlike a multi-stage mains charger or external alt regulator.

The OP's observed voltage only readings could of course be normal for that particular alternator and maybe a function of the regulator when rpm is dropped, cue Sir N.

Edited October 22, 2014 by by'eck

[David Mack]

...slow the engine to minimum tickover (390rmp)...

 

I have set a test for the grammar pedants in this post!

Don't know about grammar, but is measuring you engine speed in rmp equivalent to measuring current in amps per hour?