Alternator Problem? Assistance needed

[nicknorman]

So just to summarise then, you need to check the voltage on the domestic battery with the engine running. If this is 14.2v or thereabouts, the domestic battery is getting charged. If the current has fallen to near zero (and if you are sure the measuring device is working properly and connected in the right place) then the battery is fully charged. Of course it may be knackered and have very low capacity.

 

14.2v is on the low side for a charging voltage and there may be some modest benefit to increasing it by means of a new regulator (internal or external) but it won't address a fundamental major problem. 14.2v will charge the batteries, just slightly slower than say 14.6v.

[alan_fincher]

So just to summarise then, you need to check the voltage on the domestic battery with the engine running. If this is 14.2v or thereabouts, the domestic battery is getting charged. If the current has fallen to near zero (and if you are sure the measuring device is working properly and connected in the right place) then the battery is fully charged. Of course it may be knackered and have very low capacity.

 

14.2v is on the low side for a charging voltage and there may be some modest benefit to increasing it by means of a new regulator (internal or external) but it won't address a fundamental major problem. 14.2v will charge the batteries, just slightly slower than say 14.6v.

 

From my understanding, exactly this ^^^^^^^

 

If you are genuinely able to measure 14.2 volts at the battery, but charging current has quickly fallen to near zero, I can't see how adding an alternator controller, but leaving everything else untouched can improve things much at all.

The alternator is giving adequate voltage at the battery already, I would say, and your problem is something different.

[WotEver]

Yup, just to add another voice, as said a few times now, either the ammeter is misreading or the batteries are full (assuming you're reading that 14.2V at the batteries).

[acdbox]

Hi, thanks for all the replies.

I can confirm that the leisure bat measures 14.2 when engines running. Measured at batteries.

The leisure is wet lead acid, but my starter is sealed so really has to be run to accommodate the starter from not over charging.

The leisure battery is also about 9months old, which is why I think there may be some life In it still and not where the issue lies.

[WotEver]

You can kill a battery in a month with misuse. 9 months means nothing in and of itself.

 

The 14.2V makes sense if you're charging a SLA but (assuming it's correctly wired and not faulty) the ammeter reading of 0 indicates that the batteries are full which in turn suggests that the leisure battery needs replacing (and that your charging regime requires improving).

 

Tony

[Tony Brooks]

And as for any given charging voltage it is the battery that controls the charging current (up to the alternator's maximum output) things point more towards a battery issue (be it sulphated or very well charged) than an alternator one.

 

You said that you have a split charge relay, how is the main charging cable wired, is it to the engine or doemstic battery? From there do both banks show the same charging voltage? If so and if your figures are correct it points back to the batteries, I would suggest sulphated doemstic ones.

 

If you have 14 volts plus at the batteries do not get over concerned about the 14.5V quoted in another post, although arguably ideal anything above 14 volts should do the job although of course a few more tenths of a volt is always useful..

[Loafer]

 

10, shirley

 

Sorry, fingers like pigs tits. Should have been base 3!

[Loafer]

My recommendation would be to try to get your charging voltage increased. You could then still use your split charge relay, but with a suitable diode in the line to the starter battery to keep the SLA battery happy.

 

That means you could get a 'proper' 14.8 at your domestic battery but only 14.8-0.7 =14.1V at your starter battery, which is plenty.

 

The higher voltage on your domestic battery would help keep sulphation down, especially if your tail current measurement is accurate and gets down to 1A or so.

 

I think your domestic battery is bug*ered, personally.

 

If you can afford a Lifeline AGM domestic battery, you can forget increasing your alternator voltage and continue as you are. That battery will last you 10 years if well charged. If funds don't run to one of those, then get the best you can afford.

[Chewbacka]

If you are not sure about your ampmeter you can check it by measuring the volt drop across the shunt using a voltmeter. You do not need to disconnect the existing ampmeter.

The shunt rating is usually marked on the side - it will say something like 100A 75mV.

This means that at a current of 100A there will be 75mV drop. So in this example you will get 0.75mV per amp flowing.

Most but not all shunts are 75mV at rated current.

 

As to leisure battery capacity, if you think the battery is shot, you can get a rough idea by fully charging it, then putting a load on it and measure the current and run battery down to 12V and seeing how long it takes. So if your load is say 10A and it is a 100Ahr battery and you discharge to about 50% SOC then the amps times the hours will give you the 50%, so double that and you will get the battery capacity at fully discharged if you get my meaning. Then recharge the battery.

[bottle]

Oh... Sounds like the hope of the external regulator helping resolve the matter maybe a miss.

Yeah I'm a cc'er and reckon if my70amp put out 70aamps to the batteries things would be smooth sailing or should I say cruising? Just haven't had that joy since I've had the boat.

 

And Paul, just a basic shunt based battery monitor currently have one mostly connected to the leisure and swap it over to check the starter... Have another waiting to be installed so can monitor both simultaneously. That monitor you have sounds impressive, may have to aim for one, one day. The voltage of the starter/leisure tend to be the same due to the voltage sense relay having been at play with solar in the day for when I get home. Until the leisure gets put under a little load and starts to drop to reveal where it's really at.

Always shows 12.7ish maybe more until a loads put on, quickly levels out.

 

Not going to add anything that has not already been said, just to pick up on this.

 

To see 70 amps out of a 70 amp alternator is almost impossible, to see that your battery would need to able to hold its stated capacity, be 'flat' and your alternator to be spinning at over 5,000 rpm, probably nearer 8,000 rpm. You may not see it then.

 

All the above depends on many variations but as a rough guide, the maximum you will see is about half the rated output, with the alternator spinning at over 3,000 rpm.

 

Assuming that you have a three to one ratio on your engine, alternator pulleys then the engine needs to be spinning at a minimum of 1,000rpm

 

ps. Batteries do the 'controlling' not the alternator, you cannot put in more amps than the battery will take.

Edited February 8, 2016 by bottle

[Keeping Up]

Not going to add anything that has not already been said, just to pick up on this.

 

To see 70 amps out of a 70 amp alternator is almost impossible, to see that your battery would need to able to hold its stated capacity, be 'flat' and your alternator to be spinning at over 5,000 rpm, probably nearer 8,000 rpm. You may not see it then.

 

All the above depends on many variations but as a rough guide, the maximum you will see is about half the rated output, with the alternator spinning at over 3,000 rpm.

 

Assuming that you have a three to one ratio on your engine, alternator pulleys then the engine needs to be spinning at a minimum of 1,000rpm

 

ps. Batteries do the 'controlling' not the alternator, you cannot put in more amps than the battery will take.

That does depend on the alternator. Our new Beta engine is fitted with a 170 amp alternator and most mornings (when the batteries are typically about 25% discharged, ie 75% remaining) the ammeter starts by showing at least 150 amps for a short time - with the engine at about 1200 rpm. Indeed on the first day we had it, when the batteries were also new but were down to 50%, the ammeter registered 172 amps.

[WotEver]

Yes indeed, modern alternators have a pretty flat curve across the rev range.

 

The point that is valid however, that I don't believe OP was aware of originally and is worth repeating, is that you cannot 'force' amps into a battery. You could have a 300A alternator but if the battery is approaching full you'll still only charge at an amp or so. The charging current is set by the battery, up to the available output of the charge source.

 

Tony

[Sir Nibble]

I think you are chipping at symptoms instead of considering a whole system. In my opinion your original battery problems stem from a 3A standing discharge from some dickhead having wired a permanent supply to the alternator D+. I think it quite possible you still have a split charge relay permanently supplied because having got the alternator working the last thread was abandoned before the issue could be raised. Check the operation of all the hardware.

[WotEver]

I think you are chipping at symptoms instead of considering a whole system. In my opinion your original battery problems stem from a 3A standing discharge from some dickhead having wired a permanent supply to the alternator D+. I think it quite possible you still have a split charge relay permanently supplied because having got the alternator working the last thread was abandoned before the issue could be raised. Check the operation of all the hardware.

 

Hey Snib, well spotted that this is the same OP as the other alt thread. I hadn't seen that.

So that's what's probably killed his Doms.

[dmr]

Even with a battery fully charge there should be a small but measurable current going into the batteries, how small a current can your current monitor measure? If you have a half decent multimeter that can read small DC voltages you can double check the current monitor by measuring the small voltage accross the shunt.

 

And at the risk of argument, I don't agree with the others here, 14.2volts is Much Too Low for an off grid liveaboard, For "open" batteries its 14.6 minimum, ideally 14.8, and an external controller will really help, but they are not cheap.

 

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

[Tony Brooks]

The immediate problem as the OP sees it is that the charging current is dropping too fast. Increasing the charging voltage above 14.2 will not have a significant affect on that and may make it drop even faster. What raising the charging current will do is to decrease to a degree the overall charging time when he has batteries of sufficient capacity. Spending money on anything to boost the charging voltage is very unlikely to solve the immediate problem and once a suitable charging regime is introduced may even then make only a marginal difference because its getting the last few % into the battery that takes time.

 

SirN has reminded me exactly which topic the OP had asked about before and that it just seemed to die before the problem has been solved or reported back on.

 

I am sure messing about getting a few tenths of a volt extra charging current will not solve the immediate problem, but new batteries might. Then if the original problem is still there the new batteries may be ruined again. If the original fault has been cleared and the OP can establish a sensible charging regime only then would spending money to boost the charging voltage make any sense. However I would have thought that increasing the charging time would do just as well.

[dmr]

There are two very separate issues here and they have got a bit intertwined.

1 Will increasing the charging voltage be a good thing...answer Yes

2 The charge current falls very quickly.......answer something appears to be wrong.

 

Even if the batteries are heavily sulphated the current will not fall to zero in two minutes, and we know the starter is ok.

First thing to establish....Is the current monitor telling the truth?

Can the op record current every ten seconds or so, I would like to see the characteristic as the current reduces to zero.

 

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

Edited February 8, 2016 by dmr

[Paul C]

I missed the other thread about some kind of alternator problem. Does anyone have a convenient link to it?

[Sir Nibble]

To recap. Originally there was an evident loss of battery charge which has since been explained by the constant draw of rotor current from an ill advised work around "repair". When that thread ended I suggested the split charge relay may still be permanently energised, that may still be the case, can we check that please? Now the rapid fall off of charge current. The fact that there is no evident volt drop between alternator and battery suggests a minimal current flow ( I think there is bound to be a little resistance in there somewhere). So, I would suggest first, check the split charge system is operating correctly, Fit a "battery boiler" regulator. check for volt drops and rectify, check batteries and almost certainly replace them. The stop and start nature of this saga doesn't make for continuity of thought, evidence the number of posters who have not spotted the history of the problem.

I missed the other thread about some kind of alternator problem. Does anyone have a convenient link to it?

http://www.canalworld.net/forums/index.php?showtopic=81983&hl=

Edited February 8, 2016 by Sir Nibble

[markgregoryuk2000]

The current falling to zero could mean that there is an alternative ground return to the batteries (shunt connected to the negative return to the batteries). While the alternator is putting out the max current, current can be seen through the shunt but as the current drops the alternate route carries all the current as the shunt acts as a blocker and so reads zero.

[Sir Nibble]

The current falling to zero could mean that there is an alternative ground return to the batteries (shunt connected to the negative return to the batteries). While the alternator is putting out the max current, current can be seen through the shunt but as the current drops the alternate route carries all the current as the shunt acts as a blocker and so reads zero.

A possibility but the lack of volt drop does support the current readings

[markgregoryuk2000]

True, this is only a thought as to why the current falls to zero (have had problems with alternate ground routes before). The current through the shunt created a voltage drop that the meter can see, no current no volt drop. But this has nothing to do with the low 14.2V at the battery terminals.

[nicknorman]

True, this is only a thought as to why the current falls to zero (have had problems with alternate ground routes before). The current through the shunt created a voltage drop that the meter can see, no current no volt drop. But this has nothing to do with the low 14.2V at the battery terminals.

Incorrectly wired shunts are always a possibility, but the consequence of an alternate ground path would be that the gauge read low by some factor, it would not go to zero if there were significant current flowing via another path. It shows 30A so it could only be under-reading by about a factor of 2 (70A alternator) at worst.

[Paul C]

Given the alternator seems/is wrongly wired, I'd place a large amount of suspicion on the shunt also being wrongly wired too.

 

Looking at this thread at face value, it does suggest the batteries are now a much lower capacity than they were new, possibly due to 1) the split charge relay being miswired or faulty and jammed closed and 2) a constant current drain due to the miswired alternator.

 

Without close inspection of the wiring, its not really possible to eliminate a wiring issue, so any troubleshooting online is reduced to guessing as I see it. Its possible that someone else has a better or more educated guess than me, though!

[Tony Brooks]

Given the alternator seems/is wrongly wired, I'd place a large amount of suspicion on the shunt also being wrongly wired too.

 

Snip paragraph

 

Without close inspection of the wiring, its not really possible to eliminate a wiring issue, so any troubleshooting online is reduced to guessing as I see it. Its possible that someone else has a better or more educated guess than me, though!

 

I agree, that is why I said that I would not advise spending money to up the charging voltage. perhaps I should have said "at this time".