Bit of a pickle - bad battery

[sailorbenji]

I didn’t want to contribute because some were definitely experts and I felt out of my depth.....and when I was about to be brave, you said you wanted to preserve your 24 v set up...so I hadn’t anything left to contribute. But my idea would have been that getting home was priority number one and everything else is sacrificed to allow that...so I would have replaced your starter battery with both your house batteries...but put them in parallel to give them enough cranking amps (assuming they were deep cycle).
However I’m no expert so I deferred to the others

Certainly would have worked, but would have needed a lot of cabinetry removal to get them both out Certainly agree on the mentality of sacrificing anything (and everything) to get home, I think had this for whatever reason not worked, it would have been next option....it's just that as it was going dark, and as potentially we were drifting around all night (and with an expectation of fog), I was especially keen not to lose AIS transmission and nav lights at that point in time!

 

[Refueler]

"It's amazing how there's no consensus on how (safely) to disconnect an alternator, or stop one generating...I suppose it's because there maybe is no single answer, and is model dependent?"

Actually replies in this thread are consistent on the action to disable an alternator. As long as alternator power out is disconnected BEFORE engine starts / alternator starts to spin - it will be fine.
If you disconnect an alternator when its running - THAT is a NO-NO ... then you can damage the diodes / rectifier ...

 

[sailorbenji]

"It's amazing how there's no consensus on how (safely) to disconnect an alternator, or stop one generating...I suppose it's because there maybe is no single answer, and is model dependent?"

Actually replies in this thread are consistent on the action to disable an alternator. As long as alternator power out is disconnected BEFORE engine starts / alternator starts to spin - it will be fine.
If you disconnect an alternator when its running - THAT is a NO-NO ... then you can damage the diodes / rectifier ...

Sorry should have been clearer, I meant across the internet as a whole (I was frantically googling as you can imagine).

 

[ProDave]

So now after the engine battery has been disconnected, cooled down, and had no charge or discharge for a while, what is it's terminal voltage now?

 

[sailorbenji]

12.4V it seems to have stabilised at, at least when I checked it as I left the yard Sunday evening.

 

[ProDave]

12.4V it seems to have stabilised at, at least when I checked it as I left the yard Sunday evening.

That sounds about right. If it was a dead cell and the alternator was overcharging the remaining good cells, I would have expected more like 11V by now.

 

[B27]

....

This points to a very sick 12V engine start battery as being the cause of all our woes........

I don't think there's anything fundamentally wrong with our set-up.

TBH, I doubt the battery is the fundamental cause of your problem, had it been killed by going flat in the winter, it wouldn't be likely to fail by overheating after starting the engine.
Your system is over complicated and a single failure put you in a bad position.
It's not fit to go to sea with.

Some people seem to delight in complex electrics on sailing boats, without proper consideration for the fact that things like batteries do eventually wear out or fail. These are events which a competently spec'd system will survive without immobilising the boat or threatening to set fire to it.

 

[mikefleetwood]

From the monitor, I could see the engine start battery at around 14V, but with the alternator still outputting 18-22A into it, and with the battery temp (bear in mind this is measured at the terminal) north of 45 degrees, it was clear something was very amiss.

Sorry not really expert but this bit caught my eye.
Surely if the terminal voltage of the battery is 14V and the alternator is still pumping 20A into it - the problem is the regulation of the alternator? Shouldn't it be reducing output by the time it reaches that voltage? The fact that, after cooling, the battery is still more than 12V and able to start the engine suggests it might be still OK.

 

[Rappey]

Diesel common rail injection system. Pumps + ECU + injectors 20A
My experience is with vehicles.
Add HID headlamps and you're looking at a total current draw of 80A.

Im sure you have mis-typed as i read the above as hids adding another 60A

 

[Refueler]

Correct. 20 amps draw. My bad.
Diesel common rail injection system. Pumps + ECU + injectors 20A
My experience is with vehicles.
Add HID headlamps and you're looking at a total current draw of 80A.
No alternator and your battery goes flat in 15 minutes.
Ok?

80A ..... given that most cars do not have alternators to cover that ampage ... I think maybe an error in the figure ?? If 80A is correct - it would mean the battery is providing on top of what alternator does ... instead of being charged .......

 

[bedouin]

80A ..... given that most cars do not have alternators to cover that ampage ... I think maybe an error in the figure ?? If 80A is correct - it would mean the battery is providing on top of what alternator does ... instead of being charged .......

I think he might be confusing A and W (or be thinking of VERY big trucks)

 

[B27]

Correct. 20 amps draw. My bad.
Diesel common rail injection system. Pumps + ECU + injectors 20A
My experience is with vehicles.
Add HID headlamps and you're looking at a total current draw of 80A.
No alternator and your battery goes flat in 15 minutes.
Ok?

I don't think that's exactly right.
Diesel injectors draw a big pulse of current but only for a fraction of a millisecond every cycle.
The injection pump is usually mechanical?
HID headlamps use about 50 to 70W from the 12V, so 10A a pair
For sure there's some electronics, lift pump. etc.
A typical modern car will have electric power steering heated seat, the heater fan and all sorts of stuff, but the alternator will keep up at idle.
I wouldn't be surprised if it went into limp mode or shut down with no alternator though.

 

[sailorbenji]

TBH, I doubt the battery is the fundamental cause of your problem, had it been killed by going flat in the winter, it wouldn't be likely to fail by overheating after starting the engine.
Your system is over complicated and a single failure put you in a bad position.
It's not fit to go to sea with.

Some people seem to delight in complex electrics on sailing boats, without proper consideration for the fact that things like batteries do eventually wear out or fail. These are events which a competently spec'd system will survive without immobilising the boat or threatening to set fire to it.

Not sure why you doubt something that I since explained to be fact. The battery is 100% the fundamental cause of the problem. There's some internal short within it that couldn't be foreseen, and didn't evidence itself until the point it was a problem.

I'm not really sure what you're trying to say, or if you're just out to provoke. The system is absolutely fit to go to sea with, with the arguably "complicated" parts, i.e. the 48V storage and 24V house banks working perfectly well, and as it turns out, actually being the salvation in terms of jury rigging something up.

Allowing for the fact then, that our only issue was around the 12V engine system, are you trying to say that a single, dedicated engine battery, charged via an alternator, is somehow over complicated?

Many, even most, go to sea with nothing but a single 12V battery charged off an alternator, not only for starting their engine but also doing all their service loads ...is that also not fit for sea then?

We have multiple redundancies built in (the trickle charge from the house bank, for instance, is a back up for the alternator failing to charge the engine battery). In fact this circumstance is about the only one I can think of, where I had no easy option to rectify it. (or at least not within my knowledge base..I could, as it turns out, simply have disconnected the alternator leads).

The perverse irony, of course, is that our "over complicated" system, actually provided the ultimate solution to get us up and running again.

I'll go to sea again, quite happily, thanks, despite your concerns.

 

[sailorbenji]

Sorry not really expert but this bit caught my eye.
Surely if the terminal voltage of the battery is 14V and the alternator is still pumping 20A into it - the problem is the regulation of the alternator? Shouldn't it be reducing output by the time it reaches that voltage? The fact that, after cooling, the battery is still more than 12V and able to start the engine suggests it might be still OK.

I also can't really explain this, of course it was a concern of mine once I'd jury-rigged the engine to 1/2 of our 24V bank.

However, we have temperature, current and voltage sensing on every battery of all our banks.

Hence I could read the 14V (it might have been 13.8V or so, I can't remember in exact detail), the 20A going in, and not least the high temp on the 12V faulty battery.

Once we'd got up and running, I kept an extremely keen eye on the current flowing into the jury-rigged battery, and its temp. The initial voltage raised slightly once the alternator was active, but the current quickly dropped to something around 2-3A....once I saw that, I was sure the alternator itself wasn't the issue.

I can't explain why, despite high 13V readings, the alternator wasn't dropping output to the faulty battery. I guess it was just failing to get to whatever voltage the regulator needs to see to reduce output?

 

[sailorbenji]

I don't think that's exactly right.
Diesel injectors draw a big pulse of current but only for a fraction of a millisecond every cycle.
The injection pump is usually mechanical?
HID headlamps use about 50 to 70W from the 12V, so 10A a pair
For sure there's some electronics, lift pump. etc.
A typical modern car will have electric power steering heated seat, the heater fan and all sorts of stuff, but the alternator will keep up at idle.
I wouldn't be surprised if it went into limp mode or shut down with no alternator though.

Indeed, it seems way too high, if you read post above, once we'd run a while, the alternator seemed to be outputting between 2-3A which I guess would match, more or less, the consumption of the engine....so on that basis, even the faulty 63Ah battery would actually hav lasted a reasonable amount of time, had I been confident enough to simply remove the alternator leads.

 

[PaulRainbow]

Not sure why you doubt something that I since explained to be fact. The battery is 100% the fundamental cause of the problem. There's some internal short within it that couldn't be foreseen, and didn't evidence itself until the point it was a problem.

I'm not really sure what you're trying to say, or if you're just out to provoke. The system is absolutely fit to go to see with, with the arguably "complicated" parts, i.e. the 48V storage and 24V house banks working perfectly well, and as it turns out, actually being the salvation in terms of jury rigging something up.

Allowing for the fact then, that our only issue was around the 12V engine system, are you trying to say that a single, dedicated engine battery, charged via an alternator, is somehow over complicated?

Many, even most, go to sea with nothing but a single 12V battery charged off an alternator, not only for starting their engine but also doing all their service loads ...is that also not fit for sea then?

Maybe picky, but I don't think that's correct, most boats these days have more than one battery.

We have multiple redundancies built in (the trickle charge from the house bank, for instance, is a back up for the alternator failing to charge the engine battery). In fact this circumstance is about the only one I can think of, where I had no easy option to rectify it. (or at least not within my knowledge base..I could, as it turns out, simply have disconnected the alternator leads).

The perverse irony, of course, is that our "over complicated" system, actually provided the ultimate solution to get us up and running again.

I'll go to sea again, quite happily, thanks, despite your concerns.

I do think your system is complicated and has a few things that could cause you an issue, but i'm not getting into suggesting you change it, because i know you won't

What i would suggest, is that you look into a way of easily overcoming a failed engine battery. You need a way to jump start the engine and a way of continuing with a totally knackered engine battery. One solution could be to make sure the alternator is connected to the load side of the engine isolator switch, so if you turn the isolator switch off the battery is isolated from the engine and the alternator (it's likely wired like this anyway, but double check). Under no circumstances may you turn the isolator off with the engine running, or you'll damage the alternator. Fit another isolator, connected to the load terminal of the engine isolator and to one of the AGM batteries.

Engine battery a bit flat, turn the emergency switch on and "jump start" the engine, then turn the emergency switch off.

Engine battery knackered, turn the engine isolator off and then the emergency switch on. You can now start the engine from the AGM battery and leave it there until you get to your destination.

Under normal circumstances you wouldn't take a load from a single battery in a 24v bank, but in an emergency it's fine.

 

[PaulRainbow]

I also can't really explain this, of course it was a concern of mine once I'd jury-rigged the engine to 1/2 of our 24V bank.

However, we have temperature, current and voltage sensing on every battery of all our banks.

Hence I could read the 14V (it might have been 13.8V or so, I can't remember in exact detail), the 20A going in, and not least the high temp on the 12V faulty battery.

Once we'd got up and running, I kept an extremely keen eye on the current flowing into the jury-rigged battery, and its temp. The initial voltage raised slightly once the alternator was active, but the current quickly dropped to something around 2-3A....once I saw that, I was sure the alternator itself wasn't the issue.

I can't explain why, despite high 13V readings, the alternator wasn't dropping output to the faulty battery. I guess it was just failing to get to whatever voltage the regulator needs to see to reduce output?

A 12v battery with an internal short between two cells becomes a circa 10v battery. The alternator will try to charge that at full output, it will not be able to get the battery to 14v, but will keep trying. The battery will get very hot and gas a lot.

Perhaps you had an intermittent short ?

 

[sailorbenji]

Maybe picky, but I don't think that's correct, most boats these days have more than one battery.

Possibly right, but then so do we, so the OPs argument there is all boat systems are over-complicated...hard to argue with that!

Thanks for your other comments which are very constructive!

I don't deny it's a complicated system, compared to most. However, I do have full confidence in that side of things, the lithium 48V bank is very well protected, also from draining of course, and for me the biggest risks there are breakdowns of the 48DC-24DC converters. We could easily lose half of them, and still have sufficient capacity, and in addition to that we carry a couple of spares as backup. Other than that, the 24V bank is basically unaltered from when the boat was new 20 years ago...we do have mitigation to stop the 24V-12V battery maintainer draining the 24V bank below a set threshold and other than that the only long term loads potentially left on are the bilge pumps on float switches.

I can confirm the alternator is definitely connected to the load side of the engine isolator switch.
The option of the second "emergency switch" is good, essentially a permanently rigged version of what I ended up doing....had considered it already as a sensible addition. I presume I would have to run positive and negative cables across there, though?

 

[sailorbenji]

A 12v battery with an internal short between two cells becomes a circa 10v battery. The alternator will try to charge that at full output, it will not be able to get the battery to 14v, but will keep trying. The battery will get very hot and gas a lot.

Perhaps you had an intermittent short ?

Sounds like a very reasonable explanation of what happened to me, yes. The last measurement I took off it was 12.3V I think, but it was certainly dropping still, and had dropped obviously since the point of disconnection very quickly indeed.

 

[B27]

Not sure why you doubt something that I since explained to be fact. The battery is 100% the fundamental cause of the problem. There's some internal short within it that couldn't be foreseen, and didn't evidence itself until the point it was a problem.

...

Batteries should not just fail like that, unless they are really quite old.

How old was the battery?
Why did yours fail in a dangerous way when 30 million cars in the UK have batteries not failing in a problematic way?

I think you're not alone in having a system where the engine battery will show no symptoms of old age until suddenly it fails totally, but that should only be happening when the battery is a dozen years old or has done several thousand engine hours, in which case we should maybe be changing them as a service item before they fail.
Most people either have a 12V house bank which will start the engine, or a second start battery from the generator or something which they can swap over in a few minutes with one spanner.