Do I have a battery problem?

[PaulRainbow]

Our engine battery was a Numax 24MF 80ah and gave good service for several years, in April I replaced it with a new battery of the same make and spec. from Tayna. The battery was on the boat charger until launch in May and since has only been charged by the alternator. I noticed that the new battery did not seem to have the oomph when starting that the old one used to have and when I measured the voltage after about a week at rest it was showing 11.7v. I took the new battery out, brought it home and put it on charge using the Optimate 'intelligent' 3 stage charger that my wife used for her sports car. After 2 days the charger was showing that the battery was fully charged, the voltage when disconnected from the charger was 12.87, after an hour it was 12.62, +4hrs it was 12.48, +24 12.40 and +48hrs down to 12.33.
This suggests to me that this is defective and simply not holding charge. Before I contact Tayna can anyone confirm that I am right to think this battery may be duff?

The Optimate is a great little charger for leaving on your wifes sports car over Winter, or things like motorbikes, jet skis etc that sit around for months on end, it will stop the batteries from dying. It is not suitable for fully charging your Numax battery, it has a max output of 1A.

You need to fully charge the battery with a decent charger, leave it to rest, then check it for its discharge rate. It may, or may not, be knackered, but you need to charge it and check it to find out.

 

[LadyInBed]

When I bought a transformer style charger about fifty years ago I put a scope across the output on load and saw it going up and down like a yoyo, so I put the biggest capacitor that would fit in the box across the output which smoothed it nicely. It's still going strong but it has to be monitored, unlike smart chargers which I also have that can be connected up and left to look after itself, but can sometimes be too smart for its own good.

 

[Refueler]

When I bought a transformer style charger about fifty years ago I put a scope across the output on load and saw it going up and down like a yoyo, so I put the biggest capacitor that would fit in the box across the output which smoothed it nicely. It's still going strong but it has to be monitored, unlike smart chargers which I also have that can be connected up and left to look after itself, but can sometimes be too smart for its own good.

That 'yoyo' rate can in fact be to advantage ... it was regarded as a way to de-sulphate .. whether it actually achieved it or not ??

But as I posted earlier - the 'yoyo' effect negates any slight reduction in AC supply .... and lets be honest it was basically only UK that followed the 240V path .. most others followed the 220V route.

 

[Quandary]

Checked again this morning after a night on the 'dumb' charger. when disconnected it read 13.22 but after 10 mins was down to 13.02. I presume that what I do now is monitor it and as long as it stays above 12.7 it is okay? There is a little window which is supposed to be green when charged but it has always remained black, even now when showing over 13v.
If it goes lower I will contact Tayna about it in the hope of an an exchange.
I accept that the Optimate is a maintenance charger but am still puzzled by the drop in voltage, also by the failure of the alternator (which shows an output around 13.5v) when the battery was still in the boat to charge this battery with the engine running several hours per day. The older 105 amp domestic batteries are fully charged and holding.

 

[Refueler]

"alternator (which shows an output around 13.5v) "

I may be wrong ... but that sounds a bit low .... I would have expected about 14.5V .....

Do you have a split diode system or similar on board ? If not compensated - the diodes can drop the voltage by anywhere from 0.7 to 0.9V

 

[PaulRainbow]

"alternator (which shows an output around 13.5v) "

I may be wrong ... but that sounds a bit low .... I would have expected about 14.5V .....

Do you have a split diode system or similar on board ? If not compensated - the diodes can drop the voltage by anywhere from 0.7 to 0.9V

Whilst you are often wrong, you're correct in this case

 

[PaulRainbow]

Checked again this morning after a night on the 'dumb' charger. when disconnected it read 13.22 but after 10 mins was down to 13.02. I presume that what I do now is monitor it and as long as it stays above 12.7 it is okay? There is a little window which is supposed to be green when charged but it has always remained black, even now when showing over 13v.
If it goes lower I will contact Tayna about it in the hope of an an exchange.
I accept that the Optimate is a maintenance charger but am still puzzled by the drop in voltage, also by the failure of the alternator (which shows an output around 13.5v) when the battery was still in the boat to charge this battery with the engine running several hours per day. The older 105 amp domestic batteries are fully charged and holding.

To charge a battery you have to apply a voltage greater than that of the battery, bit like transferring water from one tank to another, the supply tank has to be higher, water won't run up hill, neither will your battery charge.

So, if you charge a battery at 14.4V, when you disconnect it, you will briefly see 14.4V or thereabouts. But that will slowly drop to the batteries true voltage 0f 12.6/7/8 Your little maintenance charger just can't get enough into the battery to fully charge it.

If the voltage was 13.2V when you disconnected the battery it is not fully charged. What was it before you disconnected it ?

If your alternator is only putting 13.5V out, it will never fully charge the battery, for the reasons above.

 

[TernVI]

With all the reported voltages being suspiciously low, I'm starting not to trust the OP's voltmeter....

If the domestic batteries are getting up above 14V and the engine batttery is not, there is a circuit fault of some kind.

 

[Quandary]

Latest episode, today I put the new battery on to the old, dumb charger, with a brick on top of the dodgy hi/lo switch on the charger it was putting about 14.4v across the terminals after rising gradually about half an hour, after four hours it had dropped back to 14.2 and the charger was quite warm.
Disconnected the charger now and after an hour the multimeter is giving a battery reading of 14.1 volts. I presume it will drop to 12.7 overnight, if it continues to drop below that I will presume that the battery should go back to Tayna, if it holds there for a couple of days I will put it back in the boat?
From the responses given above I assume that this battery was never fully charged despite being on the boats Guest charger for several weeks prior to launch in May and motoring at around 2000rpm for about a dozen hours since.

 

[Refueler]

Just to repeat myself and others ... looks like you have a problem with low voltage charge on the boat.

What I find strange is you say Domestics are good but this one is low ... that says to me - you have a fault in setup of charge regime ...
The low voltage is so alike a voltage drop due to diode situation ....

 

[Quandary]

Just to repeat myself and others ... looks like you have a problem with low voltage charge on the boat.

What I find strange is you say Domestics are good but this one is low ... that says to me - you have a fault in setup of charge regime ...
The low voltage is so alike a voltage drop due to diode situation ....

I am more inclined to believe that the new engine battery is the problem, (as reported by Ammonite in post 2), it is the only thing that has just been changed and it would seem that it is probable that it was not fully charged when delivered and has not reached full charge since. I have temporarily forgotten the name of the boats charging regulator but it is the reputable system that Paul Rainbow recommends when berating advocates of 1-2 both switches. By the way, I had a look at the Optimate, it claims an output of 8 amps from 220-240 volts.
When I find the answer I will report back.

 

[Refueler]

Regardless of system fitted - I would be trying to find out why you say there's 13.5V going to this battery - BUT you say the other batterys are fully charged.

Question : You swapped out the battery for this one - what happened to previous battery ? Are you sure that was not just suffering from lack of charge as well ?

Berating the old 1-both - 2 - off switch is all well and good ... but it works and I'm not only one who has all batterys full charged on board. Not saying VSR system is not good - of course it is ... but the 1-B-2-O is not the issue anyway.

Still doesn't answer the strange situation you apparently have. Even 'Paul' agreed with me that your voltage was too low.

 

[gordmac]

Worth checking the voltage at the alternator?

 

[Refueler]

Worth checking the voltage at the alternator?

Post #24 .... he says he has checked and its low ... which doesn't add up if his other batterys are full.

WOAH ..... just had a thought - if he's using battery sense - wonder if he has it on the other batterys ? If they say full - then that will drop the alternator back and not charge the suspect battery fully ?? Just asking ..

 

[gordmac]

If the alternator output is low that needs sorted before anything else. Either problem with the alternator or a very high current draw pulling the voltage down?
What defines the other batteries being full? Are they sitting at a higher voltage?

 

[Refueler]

If the alternator output is low that needs sorted before anything else. Either problem with the alternator or a very high current draw pulling the voltage down?
What defines the other batteries being full? Are they sitting at a higher voltage?

Can only go by what OP posts ... he says full ....

I agree - Alternator if only pumping out 13.5 is not helping .. and IMHO is the reason the battery is not full charged.

 

[Quandary]

Right, for a start I do not know what the alternator is putting out, only that the last time I checked the voltage of the domestic batteries with the engine running they were showing 13.5 on the voltmeter on the boats switch panel, I do not regard this instrument as particularly precise or reliable compared to the digital multimeter I have been using since. But the alternator is hardly the issue here, the new engine battery is at home, eight miles from the alternator and the efforts to charge it have been made with three separate chargers, the voltage while on the bench has been measure with a multimeter that I have had for years and has proved reliable to date.. The last attempt, yesterday, with the dumb charger at high output achieved 14.4 volts, when the charger was disconnected after 4 hours at that the battery showed 14.2 across the terminals and today after 15 hours rest the battery showed 13.0, after 20 hours still 13.0, so I am beginning to think the brutal treatment may have encouraged it to start holding its charge, this mirrors the situation described by Ammonite in the first response. I will check the alternator output with the multimeter after the battery goes back in the boat but it was in a reputable local electrical workshop about a year ago and I am inclined to think it should be fine.
Incidentally when I reported my experience to Tayna they came back the same day with an offer of a replacement, so well done them, however if the one I have now demonstrates a willingness to hold its charge I should not need to take them up on the offer, I have told them I will hold off on that for a week while I monitor the voltage at rest.
Meanwhile I offer my thanks to all those who took an interest in my problem, I hope I have learned something about batteries?

 

[Refueler]

Right, for a start I do not know what the alternator is putting out, only that the last time I checked the voltage of the domestic batteries with the engine running they were showing 13.5 on the voltmeter on the boats switch panel,

I understand your frustration - so please relax a bit ... no-ones out for you - we all want to help.

We all read the post where you said >

also by the failure of the alternator (which shows an output around 13.5v)

Like many threads - they evolve .. more info comes out ... path veers a bit as that info alters replies etc.

But the alternator is hardly the issue here,

But your previous indicated 13.5 ,, which is not good. Now we are updated and hope that Alternator is ok.

the new engine battery is at home, eight miles from the alternator and the efforts to charge it have been made with three separate chargers, the voltage while on the bench has been measure with a multimeter that I have had for years and has proved reliable to date.. The last attempt, yesterday, with the dumb charger at high output achieved 14.4 volts, when the charger was disconnected after 4 hours at that the battery showed 14.2 across the terminals and today after 15 hours rest the battery showed 13.0, after 20 hours still 13.0, so I am beginning to think the brutal treatment may have encouraged it to start holding its charge, this mirrors the situation described by Ammonite in the first response. I will check the alternator output with the multimeter after the battery goes back in the boat but it was in a reputable local electrical workshop about a year ago and I am inclined to think it should be fine.
Incidentally when I reported my experience to Tayna they came back the same day with an offer of a replacement, so well done them, however if the one I have now demonstrates a willingness to hold its charge I should not need to take them up on the offer, I have told them I will hold off on that for a week while I monitor the voltage at rest.
Meanwhile I offer my thanks to all those who took an interest in my problem, I hope I have learned something about batteries?

Question : When you say : "The older 105 amp domestic batteries are fully charged and holding " .... is this after charged on board or at home ?

So lets look at this ..

What was reason to change this battery originally ? Had it actually failed or was it just as this one has - shown not full charge ?

What is reason that this battery fails to reach full ?

Do the 'domestics charge fully on board ? If so why not the other battery.

Do you have battery sensing to decide charging ? If so - which battery is supplying the sense .. the problem battery or domestic ?

I am concerned that you get a fully charged battery at home .. checks out OK .. then drops back on board .... would be nice to help you get a solution .. and info is what is needed to arrive at possibles.

 

[Quandary]

Thanks Refueler, I know you are trying to help me; to respond to the points you have raised. The new battery went in in April but the boat was not launched until May, since then we did one trip of about a week when I felt that the starter motor lacked its usual oomph, taking several seconds to start. I went back to the boat last week and took the voltage of all three batteries with a multimeter, I can not exactly recall the rested voltage of the domestic batteries but it did not worry me so I did not note their voltage and am relying on a not very reliable memory. However the voltage of the new engine start battery was down at 11.6, hard to understand, it having has less than one or perhaps 2 minutes use in total turning over a small 19hp three cylinder diesel. So I ran the engine for about an hour without much improvement. Then I decided to fetch it home and try charging it there, the Optimate charger was on for two days before the charging lights went out, the multimeter showed 12.87 but next day it was down to 12.4. I now accept that this charger may not have been powerful enough but at rest with nothing connected surely the battery should have held rather than dropping steadily? On the basis of advice above I then had a go with an old wall mounted type charger which got quite warm but pushed the displayed voltage up to 14.2, a day later it is reading 13v. and seems to be holding at that. if it is still holding tomorrow it is going back on the boat.
Moody S31s were originally sold with one 105ah battery with a second as an option, ours had two, one domestic and one starting, both 105ah, a couple of years ago I made another battery box and installed a third smaller 80ah Numax and put the first two in parallel as a domestic bank. there is a removable switch under the panel which allows the domestic batteries to connect to the engine start if that battery is dead but I never have to use it.
What raised my concern was that the new engine battery was down to 11.7v having started the engine not more than half a dozen times, I could not understand how this could have happened if it had ever been fully charged, this concern increased when I isolated it, charged it and it immediately dropped again, I presumed that I had a faulty battery that was either not accepting charge , not holding charge or a combination of both. Now I think (hope)that after a heavier charge it is holding. On the basis of the answers given my suspicion remains that this battery came not fully charged, the first charger and the alternator failed to put charge in to it and the limited use exhausted it. Other respondents have reported this phenomenon. The supplier, Tayna, will replace it but if the heavy charge I have now given it revives it I would not want to trouble them, it does come with a three year warranty. I am inclined now to give it another chance but I will be checking it regularly

 

[TernVI]

So you think your wall mounted charger can charge your battery, but your alternator somehow cannot?

I suspect there is a problem with your boat.
How does the alternator charge the engine battery and the house batteries? VSR? Does it work?