starter battery flat after couple of hours

[vasant]

I'm astounded Vasant. Dont they do simple volts , amps, watts and DC in electrical engineering these days? Sorry that sounds unhelpful and maybe even rude and it isnt meant to be. But with an MSC in electrical engineering I would expect you to be providing the answer not the questions.
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**off topic discussion*****
Hey, no hard feelings its just what i hear from my mom.
Apart that my degree lies 20 years back what we call electrical engineering studies covers a broad range of subjects. In my case i have quite son chosen to get involved in the telecom business which is pretty far from DC engineering. But even if this wouldnt be the case, experience is something that is not able to be substituted by academic knowledge. So i trust my engineering studies when it comes to evaluating opinions and adapting them to the problem at hand.

Thanks for your notes i will take them into account actually a friend of mine will lend me a battery health check tool.

 

[PaulRainbow]

TAKE CARE when using jump leads. It is possible for small spark produced when connecting or disconnecting them to ignite hydrogen gas given off by the batteries.

The chance of it happening is small but it can, and from time to time does, happen. A battery exploding in your face will spoil your weekend and probably the rest of your life.

The instructions when using jump leads on cars are always to make the final connection and break the first connection ( a negative) away from the battery itself. That ensures that there is no spark at a battery terminal. A similar precaution may not be so easy to achieve in a boat.

I wonder where this hydrogen gas is coming from ? Do flat batteries give off hydrogen ? I suspect the advise is H&S gone mad stuff.

The advise to turn a battery charger off before disconnecting is good, as it may well have been gassing (giving off hydrogen) and they can very easily explode then.

 

[PaulRainbow]

I'm astounded Vasant. Dont they do simple volts , amps, watts and DC in electrical engineering these days? Sorry that sounds unhelpful and maybe even rude and it isnt meant to be. But with an MSC in electrical engineering I would expect you to be providing the answer not the questions.

Anyway, to try and be more helpful:

1/ the charge current that a battery will accept depends on its state of charge. So foe example I found that my battery bank might take 45 amps when half flat but 6 hours later this was down to maybe 5 amps and the batteries were just beginning to become fully charged as measured by hydrometer. No way would a flat lead acid battery charge up in an hour.
2/ It could well be that you have mistakenly been allowing the battery to remain badly undercharged and this definitely damages its ability to hold charge. It may now be knackered .
3/ Batteries can fail in a number of ways and an internal short is one of them. In that case the battery will lose charge without anything drawing current from it - the losses could be entirely internal. Lead acid batteries do that to some degree anyay. They have a self discharge rate but usually its pretty low.
4/ the other alternative is that you have a discharge via the wiring.

If I were tackling the job my first step would be to remove the battery completely, take it home , put it on the battery charger for a day or more and then monitor it measuring its voltage every few hours. Is it self discharging or not? If it isnt then I would take it to my local garage and ask them to do a discharge test on it to test its capacity. Alternatively use a known resistance ( a headlight bulb for example) and discharge the battery down to 12.2 volts through that resistance measureing the time it takes. That will give you a rough number for its capavcity to decide if it is bu66ered or not.

If the battery is OK and with it fully charged its back to the boat. I would try to find hwre and how it was discharging. You can ofetn get a hint from what gets warm with the the battery conected but nothing switched on. Or you can bung an ameter in circuit and measure whats happening. That would also allow you to check the alternator output both amps and volts.

At this point its a detective hunt, taking fuses out of circuit and measuring the drain until you find the culprit.

Did you read the OP ?

Now after 1 year with NEW battery boat has cranked we go for training when trying to start engine again battery is flat.

Your first points cannot be related to that. Point 4, if that happened in a short time something would be red hot, or on fire. The battery is only connected to the engine, not much to cause a drain, nothing that could drain a battery in short time without something getting ridiculously hot or burning and nothing that would do that intermittently.

You cannot discharge a battery in a short time without a major problem and you certainly cannot charge a totally flat battery back up in a short time.

 

[RichardS]

I wonder where this hydrogen gas is coming from ? Do flat batteries give off hydrogen ? I suspect the advise is H&S gone bad stuff.

The advise to turn a battery charger off before disconnecting is good, as it may well have been gassing (giving off hydrogen) and they can very easily explode then.

My batteries are all sealed anyway so any hydrogen risk is going to be vanishingly small even if the batteries were recently on charge.

Richard

 

[Daydream believer]

TAKE CARE when using jump leads. It is possible for small spark produced when connecting or disconnecting them to ignite hydrogen gas given off by the batteries.

The chance of it happening is small but it can, and from time to time does, happen. A battery exploding in your face will spoil your weekend and probably the rest of your life.

.

Happened to me in my early teens as I was disconnecting a battery charger. As i ran screaming from the shed my mother grabbed me & shoved me face down in the washing up bowl then turned me over & ran the cold tap into my eyes (& giving me a black eye with the tap in the process) . She effectively saved my sight.
I spent 4 days with my eyes bandaged so I have some small idea of what it feels like to a blind person.

On the 4th day she took me to an eye specialist & took my arm & marched me into the Nuffield hospital. She said " steps ahead" & up we went. She then took me through glass double doors. She went through the open one & forgot to tell me that the other was shut.
I walked straight into it & had a massive nose bleed & a telling off for "being a big girl"!!!
My face & eye lids were burned for some time I recall

 

[jac]

Did you read the OP ?



Your first points cannot be related to that. Point 4, if that happened in a short time something would be red hot, or on fire. The battery is only connected to the engine, not much to cause a drain, nothing that could drain a battery in short time without something getting ridiculously hot or burning and nothing that would do that intermittently.

You cannot discharge a battery in a short time without a major problem and you certainly cannot charge a totally flat battery back up in a short time.

Doesn't that assume that the battery was fully charged in the first place and was a decent size when bought . If OP only had a very small engine start battery that was perhaps only 60% charged when he set off then it doesn't take a massive load to discharge it back down to a point where it won't turn the starter over.

And I don't think we do know that it's only connected to the starter motor - it should be but as OP says it's an old boat who knows what bodges may exist.

 

[PaulRainbow]

Doesn't that assume that the battery was fully charged in the first place and was a decent size when bought . If OP only had a very small engine start battery that was perhaps only 60% charged when he set off then it doesn't take a massive load to discharge it back down to a point where it won't turn the starter over.

And I don't think we do know that it's only connected to the starter motor - it should be but as OP says it's an old boat who knows what bodges may exist.

we go sailing engine cranks normally after some hours of sailing battery is flat. Not even the lights of the panel light. After hand cranking the engine and going for half an hour battery is charged all is good.

The battery starts the engine. After "some hours" it won't even power the panel lights, not just to a point where the engine won't turn over, not even a panel light. Then after 30 minutes it's charged back up again ?

It's done it with two different batteries, but only 2 or 3 times in a 2 year period.

The OP has said, more than once, that it's only for the engine, but it's easy to verify that, turn the domestic isolator off and see if anything comes on. That said, even if everything was connected to the same battery i still cannot see how you can flatten it to the point of no lights on the panel, then charge it back up again in 30 minutes.

 

[halcyon]

It's done it with two different batteries, but only 2 or 3 times in a 2 year period.

The OP has said, more than once, that it's only for the engine, but it's easy to verify that, turn the domestic isolator off and see if anything comes on. That said, even if everything was connected to the same battery i still cannot see how you can flatten it to the point of no lights on the panel, then charge it back up again in 30 minutes.

The OP has classic signs of under charging, over discharging, resulting in sulphation and surface charge.

May be machine sensed low alternator volts, i.e. 13.6 volt reg, old blocking diodes with volt drop, thus will charge the battery with only a low current for short time. From memory OP has solar on service so no problem ?

Brian

 

[PaulRainbow]

The OP has classic signs of under charging, over discharging, resulting in sulphation and surface charge.

May be machine sensed low alternator volts, i.e. 13.6 volt reg, old blocking diodes with volt drop, thus will charge the battery with only a low current for short time. From memory OP has solar on service so no problem ?

Brian

That may be the case, but it doesn't explain why the engine started when he first arrived at the boat, but was flat as a pancake after "some hours" sailing, IMO.

 

[halcyon]

That may be the case, but it doesn't explain why the engine started when he first arrived at the boat, but was flat as a pancake after "some hours" sailing, IMO.

Because he motored into his birth, shut down the boat and went home, leaving a small charge in the battery.

Brian

 

[PaulRainbow]

Because he motored into his birth, shut down the boat and went home, leaving a small charge in the battery.

Brian

But it's only done it once in the last year ?

I'm not convinced, but this cyber diagnosing isn't an exact science

 

[jac]

But it's only done it once in the last year ?

I'm not convinced, but this cyber diagnosing isn't an exact science

Could be a combination of several factors rather than 1 thing.

I agree that 30 minutes charging isn't enough to charge the battery so suspect something like a surface charge only caused by poor charging regime - after 30mins charging the volts looked good hence OP thinking was charged. Same poor charging regime knackered the last battery, wasn't addressed and has damaged the new battery over the last year to the point that it's only now showing.

But there must be some discharge going on - I didn't think batteries could self discharge that quickly without external symptoms.

Given the age of the boat I would suspect some load wired to it put in by previous owner

 

[halcyon]

But it's only done it once in the last year ?

I'm not convinced, but this cyber diagnosing isn't an exact science

I spent 35 years supplying switchgear and charging systems to UK boat builders, you learnt cyber diagnosing during that period.

Brian

 

[Pye_End]

But there must be some discharge going on - I didn't think batteries could self discharge that quickly without external symptoms.

Given the age of the boat I would suspect some load wired to it put in by previous owner

Agreed. Doesn't take long for an engine to replace what it took out in starting, and to go from a lack of welly to re-start to absolutely flat as a pancake doesn't feel like poor charging. Must be another load on it or a dodgy connection or a duff battery (not so likely if 2 different ones giving same result).

Clamp meter is your friend. Much easier to find out what it going on.

 

[barryhall]

I once had a car that periodically did this. After much investigation I found that a diode in the alternator was breaking down and discharging the battery. I happened to notice the alternator was hot (really hot) at the same time as the battery was flat. Luckily it was one of the last cars with a starting handle - Citroen GS.

 

[CLB]

I once had a car that periodically did this. After much investigation I found that a diode in the alternator was breaking down and discharging the battery. I happened to notice the alternator was hot (really hot) at the same time as the battery was flat. Luckily it was one of the last cars with a starting handle - Citroen GS.

Beat me to it!

I had a van that, 99 times out of 100 would start at the flick of the key. Then, once in a blue moon and always after being run just a couple of hours before, it would not start due to a flat battery. The lights would come on, but only a click from the starter motor. Both times a jump start got me going again and after a full charge when I got home, the battery was OK. It was finally diagnosed as a faulty alternator. Don't know the exact details, but it was getting hot, although the fault was obviously intermittent and draining the battery in a couple of hours.