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Alternator energising for only a few seconds


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Hello,

My alternator seems to not be happy this evening. My engine/starter battery alternator is pretty new and works fine, giving around 14.5V. But my leisure battery alternator is only giving me 13.5ish (when it's energised) and this drops to a measly 12.7 after a few seconds of being energised.

I get both charge warning lamps on the first step of turning the ignition key, and they both go out after the engine starts up. I replaced these bulbs this summer, and paralleled them with a resistors, so I am confident they are drawing enough current to energise the alternators.

When the engine is running I can remove the energising cable, and when I plug it in I hear the engine revs drop slightly, so I think it gets energised. However it's only 13.5V at this stage, and this only lasts about 5-10 seconds before the engine revs pick up again, presumably the alternator is no longer energised. Then it reads 12.5-12.7V. I can't re-energise it by revving, at least not below 2000rpm.

 

Up until tonight, it was working ok. I may have done something when I was replacing my buzzer behind the control panel...I managed to short a terminal on the back of the engine stop button against the steel hull and there were a couple of small sparks. Nothing immediately was wrong, but I'm wondering if this could be related to the alternator problem?

 

I have a spare alternator of identical type which I've just fitted, but it shows the exact same problem, so I'm hoping it isn't the alternator that is faulty, instead something else.

I should add it's a lucas a127 type alternator.

 

Any help is much appreciated!!

Many thanks

Edited by GrahamSop
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Quite flat...

They are on their last legs really, and due for replacing soon.

I don't have a particularly accurate reading, it's just what my solar controller says - they can go right down to 12.2-12.5V if it's been a rainy day

But they've been like that for a few months now, and always charged at 14.x volts until tonight

Edited by GrahamSop
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31 minutes ago, GrahamSop said:

Quite flat...

They are on their last legs really, and due for replacing soon.

I don't have a particularly accurate reading, it's just what my solar controller says - they can go right down to 12.2-12.5V if it's been a rainy day

But they've been like that for a few months now, and always charged at 14.x volts until tonight

If that is the RESTED voltage then 12.2v is 50% charged, 12.5v is 80% charged so they are nowhere near 'quite flat', however they may be 'dead' due to sulphation (reduced capacity - NOT voltage)

 

 

 

How are you measuring the battery voltage ?

Are you measuring it at least 2 hours after all charging has been turned off ? (if not you are measuring the plate surface charge from the alternator / charging).

 

Voltage is not really a guide to capacity - have you done any test to measure the remaining battery capacity ?

A battery that has not been fully recharged (every day) gradually loses 'capacity' (amphours) so what may have been 110Ah battery could easily be 30Ah and it just takes a few hours of lights, TV etc and they are 'flat'.

 

 

battery-state-of-charge.jpg

Edited by Alan de Enfield
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Alan, thanks for the info.

I have this table in a book too, yes maybe they aren't 'quite flat' as you say. Tonight they were rested, I hadn't run the engine and it had been dark for 3 hours, the voltage was 12.2V, so 50-60% charged. In the past 2 weeks they've been down to 11.8V, so they desperately need a good charge.

I'm doing a long cruise tomorrow, partially to charge them well, but now the alternator is being funny I'm not sure how much charge they'll get.

They may well have suffered sulphation and be under capacity from not being kept fully charged. How does this relate to my alternator problem?

 

I've swapped back the original alternator as my spare was behaving the same, and also checked the wiring on the charge warning lamps and one of them was loose and came out easily. I thought ah-ha! But I've now made the connections good, started the engine, and still the alternator struggles. It seems slightly better, but the charge lamp flickers a tiny bit every few seconds, coninciding with slight variations in the engine rpm. It still seems it's not staying energised.

Edited by GrahamSop
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22 minutes ago, GrahamSop said:

Alan, thanks for the info.

I have this table in a book too, yes maybe they aren't 'quite flat' as you say. Tonight they were rested, I hadn't run the engine and it had been dark for 3 hours, the voltage was 12.2V, so 50-60% charged. In the past 2 weeks they've been down to 11.8V, so they desperately need a good charge.

I'm doing a long cruise tomorrow, partially to charge them well, but now the alternator is being funny I'm not sure how much charge they'll get.

They may well have suffered sulphation and be under capacity from not being kept fully charged. How does this relate to my alternator problem?

 

I've swapped back the original alternator as my spare was behaving the same, and also checked the wiring on the charge warning lamps and one of them was loose and came out easily. I thought ah-ha! But I've now made the connections good, started the engine, and still the alternator struggles. It seems slightly better, but the charge lamp flickers a tiny bit every few seconds, coninciding with slight variations in the engine rpm. It still seems it's not staying energised.

If the engine revs alter when the light flickers I reckon its momentarily puts out a good charge. Sounds like a bad connection being as both alternators act the same. Are battery terminals all clean and tight. Check for high resistance on any crimped terminals on the main alternator cable, both ends of it. Have you a volt or multimeter to check voltage directly at the alternator.

Edited by bizzard
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8 hours ago, bizzard said:

If the engine revs alter when the light flickers I reckon its momentarily puts out a good charge. Sounds like a bad connection being as both alternators act the same. Are battery terminals all clean and tight. Check for high resistance on any crimped terminals on the main alternator cable, both ends of it. Have you a volt or multimeter to check voltage directly at the alternator.

I do have a multimeter and I checked the voltage directly at the alternator which was around 14V for a moment (just after I managed to re-energise it by removing the lamp wire then reinserting it), but it then drops after a few seconds, when also the engine rpm increases slightly. The voltage at this point varies, I've measured from 13.6V down to 12.6V. 

I'll check/clean/tighten all the connections this morning and see if that makes a difference.

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If the alternator output goes through the multi-plug that most boats have in their main engine harness check that as well.

 

Edited to add, not that then if you checked at the back of the alternator on the B+ terminal.

Edited by Tony Brooks
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I think you really need a clamp ammeter to see how much current the alternator is putting out it could be it’s working flat out trying to get something into your knackered batts... 

 

I have found it useful to measure the voltage across cables /connections to identify poor connections. Eg measure between the alternator body or B- terminal and the battery -ve you are looking for a very small voltage say 0.2V.  If you see say a volt

or more you have a problem. 

 

Of course if the alternator is not

putting out anything then this won’t help! 

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As a workaround you could, once the engine is running, connect a jump lead between starter and domestic battery positives, so that you can charge both from the starter alternator. And at the end of the day's running, probably best to remove the jump lead and leave the engine running for half an hour to top up the starter battery before shutting down.

Edited by David Mack
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5 hours ago, Tony Brooks said:

If the alternator output goes through the multi-plug that most boats have in their main engine harness check that as well.

 

Edited to add, not that then if you checked at the back of the alternator on the B+ terminal.

Alternator output probably doesn't go through multi-plug due to the high current but the exciter lead from the lamp will, and yes they are a frequent source of weird faults.

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14 minutes ago, Detling said:

Alternator output probably doesn't go through multi-plug due to the high current but the exciter lead from the lamp will, and yes they are a frequent source of weird faults.

But once energised the rotor current comes from the field diodes,. I do wonder if there is a fcield diode problem or a bad joint between field diode pack and regulator/brushes. Actually it could be worn out brushes so worth a check.

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When I get trouble with those plugs I do away with them, twist and solder each wire back together, one at a time and bind them with self amalgamating tape, no more trouble. They're only there to make the engine installation easy for the fitters. Like most modern stuff,  plug and play.

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  • 1 month later...

After several weeks I realised I should follow up this thread!

Just to recap: I have 3 alternators: two identical ones that came with the engine originally, one of which (for the starter) has very tired bearings and is pretty noisy, and the other (for the leisure batteries) is ok, and a new one to replace the noisy original. This new one is a cheap jobbie from ebay but it has the same spec...well, what spec they provided, but it isnt an identical OEM model. My intention was to fit the new one for now and repair the bearings on the original and keep it as a spare.

After fitting the new alternator (for the start battery), the aux alternator would only become energised for a few seconds. I tried with both of the original alternators, and both behaved the same - stop charging after a few seconds and I can hear engine rpm jump up slightly. I cleaned every battery connection, checked the multi plug connector, reconnected everything at the charge warning lamps and resistors, and it didn't help. So I have now gone back to the two original alternators and all is back to normal, and the new alternator is set aside.

 

In the end, it seems the problem was being caused by having the new alternator installed as well as one of the old ones (either one). Could this cause some sort of unbalancing, which would cause the aux alternator to stop charging? The +ves are not connected though - my starter battery +ve is isolated from the leisure bank. Unfortunately the new alternator can't be installed as the aux alternator so I can't test it this way round. Would be interested to know your thoughts.

 

Graham

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59 minutes ago, GrahamSop said:

After several weeks I realised I should follow up this thread!

Just to recap: I have 3 alternators: two identical ones that came with the engine originally, one of which (for the starter) has very tired bearings and is pretty noisy, and the other (for the leisure batteries) is ok, and a new one to replace the noisy original. This new one is a cheap jobbie from ebay but it has the same spec...well, what spec they provided, but it isnt an identical OEM model. My intention was to fit the new one for now and repair the bearings on the original and keep it as a spare.

After fitting the new alternator (for the start battery), the aux alternator would only become energised for a few seconds. I tried with both of the original alternators, and both behaved the same - stop charging after a few seconds and I can hear engine rpm jump up slightly. I cleaned every battery connection, checked the multi plug connector, reconnected everything at the charge warning lamps and resistors, and it didn't help. So I have now gone back to the two original alternators and all is back to normal, and the new alternator is set aside.

 

In the end, it seems the problem was being caused by having the new alternator installed as well as one of the old ones (either one). Could this cause some sort of unbalancing, which would cause the aux alternator to stop charging? The +ves are not connected though - my starter battery +ve is isolated from the leisure bank. Unfortunately the new alternator can't be installed as the aux alternator so I can't test it this way round. Would be interested to know your thoughts.

 

Graham

Do the alternators feed direct to their individual batter banks with nothing else, relays, smart chargers, regulators etc. Also what happens to the voltage on the B+ terminal of each alternator?

Edit to add, or are you still using the solar controller to read voltages?

Edited by ditchcrawler
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52 minutes ago, ditchcrawler said:

Do the alternators feed direct to their individual batter banks with nothing else, relays, smart chargers, regulators etc. Also what happens to the voltage on the B+ terminal of each alternator?

Edit to add, or are you still using the solar controller to read voltages?

Yes both are direct to the individual battery banks with no other components. I checked with my multimeter, and when both original alternators are installed, both give about 14.3V. With the new alternator installed as the battery alternator, that one gives out 14.6V while the other one starts giving between 13.5V-14V and then it becomes 'unenergised' and drops to 13V or so.

7 minutes ago, Keeping Up said:

Do the batteries share a common isolator switch in the negative feed (quite common on older boats)? If so, and it is faulty, it might give these symptoms.

No, I have separate isolation switches for starter and domestic banks. Everything goes via these with 2 exceptions: the ouput from my solar bypasses the domestic isolator and goes straight onto the domestic bank, and my bilge pump bypasses the starter isolator and is connected straight onto the starter battery, with a fuse.

Edited by GrahamSop
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The one that de-energises. Is it the one on the batteries with the solar input? If so and the batteries are well charged the solar voltage just might be causing it to shut down but it should fire up again as soon as you turn an electrical load on it. However I suspect a bad solder joint or a sticking brush inside the alternator.

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Try this.

 

Fit the suspect alternator without any wiring connected. 

If its an insulated return alternator only, connect a negative cable, from the B- terminal onto the engine block.

 

Connect a wire from B+ on the alternator to a battery positive, preferably with a fuse at the battery end. You can use either the leisure or engine battery, both should give the same result.

Connect a 12v  light bulb, minimum 5w, between B+ and D+ on the alternator.

 

This will bypass all the boat wiring, warning lamps, ignition switch etc. The bulb should light as soon as you connect the wire to the battery.

Start the engine.  The bulb should go out. The alternator must charge if it is OK.

If it does charge, the fault must be in the wiring etc between the alternator and the control panel.

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16 hours ago, Tony Brooks said:

The one that de-energises. Is it the one on the batteries with the solar input? If so and the batteries are well charged the solar voltage just might be causing it to shut down but it should fire up again as soon as you turn an electrical load on it. However I suspect a bad solder joint or a sticking brush inside the alternator.

Yes, the one that de-energises is the one feeding the leisure batteries which also have the solar input. From what I have tested so far, I have had the new alt feeding the start battery and the one that de-energises is the aux alt, feeding the leisure batteries. But the de-energising happens with either of my original alternators installed as the aux alt - I've tried both of them. So I'd be surprised if it's a problem with the alternators as they both show the same behaviour. The new alt doesn't fit on the aux position so unfortunately I can't test it this way round.

I hadn't thought about the solar being the cause but it could be I suppose? But why would installing a new alt for the starter battery suddenly make a difference to the leisure/solar side? All was (and is) working correctly with both original alternators installed, with no de-energising, running day or night, with charged or discharged batteries.

6 hours ago, Boater Sam said:

Try this.

 

Fit the suspect alternator without any wiring connected. 

If its an insulated return alternator only, connect a negative cable, from the B- terminal onto the engine block.

 

Connect a wire from B+ on the alternator to a battery positive, preferably with a fuse at the battery end. You can use either the leisure or engine battery, both should give the same result.

Connect a 12v  light bulb, minimum 5w, between B+ and D+ on the alternator.

 

This will bypass all the boat wiring, warning lamps, ignition switch etc. The bulb should light as soon as you connect the wire to the battery.

Start the engine.  The bulb should go out. The alternator must charge if it is OK.

If it does charge, the fault must be in the wiring etc between the alternator and the control panel.

Thanks for the suggestions. As above, I don't believe there is a suspect alternator, unless both my original ones have suddenly become defective at the same time with the same problem, or the new one is defective...

Edited by GrahamSop
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23 minutes ago, GrahamSop said:

Yes, the one that de-energises is the one feeding the leisure batteries which also have the solar input. From what I have tested so far, I have had the new alt feeding the start battery and the one that de-energises is the aux alt, feeding the leisure batteries. But the de-energising happens with either of my original alternators installed as the aux alt - I've tried both of them. So I'd be surprised if it's a problem with the alternators as they both show the same behaviour. The new alt doesn't fit on the aux position so unfortunately I can't test it this way round.

I hadn't thought about the solar being the cause but it could be I suppose? But why would installing a new alt for the starter battery suddenly make a difference to the leisure/solar side? All was (and is) working correctly with both original alternators installed, with no de-energising, running day or night, with charged or discharged batteries.

Thanks for the suggestions. As above, I don't believe there is a suspect alternator, unless both my original ones have suddenly become defective at the same time with the same problem, or the new one is defective...

I accept that the alternator is unlikely to be faulty, but this quick test will prove it absolutely, leaving you to find the wiring fault with certainty..... 

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2 hours ago, Boater Sam said:

I accept that the alternator is unlikely to be faulty, but this quick test will prove it absolutely, leaving you to find the wiring fault with certainty..... 

True, I might be able to have a look at the weekend, although as I'm fine for now with the old alternators it may be a job for when its lighter in the evenings

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By which time your working alternator will break down and you will have no spare working, batteries flat and ruined, cold, dark, wet, snowing, miserable working conditions to be under a deck trying to get some power.

Better to sort it now in the mild weather?

 

I tried.

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