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Good post Tony!

This is 'must know' info for anyone boating, or new to boating.

The only thing I would add is the voltage required during the Absorption phase of the charging. This needs to be above 14.0V and more likely 14.2-14.8V dependent on battery type, temperature etc. The reason I am posting this as it is not obvious that the voltage during Absorption will be at this level. Yes, most of the time it will be but is it on your boat? We bought our NB in April last year and our absorption charge voltage was circa 13.9V. On our lumpy water boat, bought new in 2005 with a new Volvo Penta engine (and alternator), its absorption charge voltage was 13.9V. This is too low for adequate charging. Many engines around this build date used alternators that were designed for cars and not for charging lesiure batteries on boats - Gibbo refers to this in the smargauge manual - and are just not up to the job of keeping a live aboard batteries alive. On both our boats, the solution was to add some sort of charge control - and specifically I chose the Sterling AtoB which seems to work very well (6 years experience on our lumpy water boat).

I am adding this post to Tony's excellent summary in case there are others out there who just aren't getting to 14V on alternator charging and thus risking undercharging. There must be a load of boats from 2000-20005 that suffer the same problem.

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1 hour ago, Dr Bob said:

The only thing I would add is the voltage required during the Absorption phase of the charging. This needs to be above 14.0V and more likely 14.2-14.8V dependent on battery type, temperature etc.

That’s too specific for the intended audience. I spoke of the ‘preset level’ which will vary according to battery chemistry, battery type, temperature compensation etc. I was attempting to describe what the absorption stage ‘is’, not how to set it up. 

Nevertheless I’ll add a ‘typically’ clause. 

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10 minutes ago, WotEver said:

That’s too specific for the intended audience. I spoke of the ‘preset level’ which will vary according to battery chemistry, battery type, temperature compensation etc. I was attempting to describe what the absorption stage ‘is’, not how to set it up. 

Nevertheless I’ll add a ‘typically’ clause. 

The trouble is that the intended audience won't realise what their absorption voltage is and hence some will be surprised when their batteries fail due to low voltage when following your advice. Those people need to understand if their alternators need a boost.

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  • 2 weeks later...
On 06/02/2018 at 19:32, WotEver said:

 

Equalisation

Yes, I know it's not a 'charge mode' but I thought I'd add a little about it here anyway. Some chargers will enable you to give an equalisation charge at a much higher voltage than usual, probably above 15V for a 12 volt system. This has the effect of ensuring that all the cells in the bank have been fully charged and that as much sulphation as possible has been removed from the plates. 

Some warnings about equalisation:

1. Sealed, AGM and gel batteries should not normally be subject to equalisation. If you are considering doing so, take expert advice first.

2. Some items of equipment in the boat may not be able to handle the high voltage and should be disconnected. The safest way is to isolate the bank before proceeding.

3. Hydrogen gas will be given off during the process. The bank should be well ventilated and must never be left unattended. During equalisation, check the temperature of the batteries from time to time, say every 15 minutes. They may well become warm to the touch but serious heating is a bad sign and the process should be stopped at once. It is not unknown for batteries to boil or even explode if a cell has failed.

4. The cells will need topping up with distilled water after being equalised.

A couple of general bits of safety advice should be added here:

1) A permanently installed charger must never use crocodile clips to connect to the battery.

On 06/02/2018 at 19:32, WotEver said:

.... 
2) Temporary chargers should only be connected with the input (230V mains) power turned off, and only disconnected 3 minutes after turning off the charger input power to minimise the risk of explosion from hydrogen gas generated during charging.

 

I am not sure exactly what this means, what is a temporary charger,   

If it is a thing with crocodile clips, 

 is it is not something connected to 240volts? 

Edited by LadyG
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4 hours ago, LadyG said:

I am not sure exactly what this means, what is a temporary charger,   

If it is a thing with crocodile clips, 

 is it is not something connected to 240volts? 

Yes, a thing with croc clips. The advice is suggesting that you connect it to the battery using said clips before you plug it into the mains. And that you disconnect the mains three minutes before you disconnect the clips. 

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I found it useful but I'd still like to know a straightforward way of charging over 15v when your charger doesn't show an obvious way of doing it.  This, more than anything else, is what puts me off forking out for 'decent' batteries.

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15 minutes ago, Dave_P said:

I found it useful but I'd still like to know a straightforward way of charging over 15v when your charger doesn't show an obvious way of doing it.  This, more than anything else, is what puts me off forking out for 'decent' batteries.

Buy a charger that does! We've just bought the victron IP22 blue smart. Less than £200. Very easy to get it to do an equalisation charge.

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11 minutes ago, Dave_P said:

I found it useful but I'd still like to know a straightforward way of charging over 15v when your charger doesn't show an obvious way of doing it.  This, more than anything else, is what puts me off forking out for 'decent' batteries.

I believe some of the more modern chargers now have an option to charge at 14.8V and equalise at 15V+ (like the Sterling Pro Charge Ultra). Another option for equalisation charging is a bench power supply. 

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2 minutes ago, WotEver said:

I believe some of the more modern chargers now have an option to charge at 14.8V and equalise at 15V+ (like the Sterling Pro Charge Ultra). Another option for equalisation charging is a bench power supply. 

What's a bench power supply?

 

This? https://www.maplin.co.uk/p/100w-slim-bench-power-supply-n93cx

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Yes, you just 'dial in what voltage you want, dial in what amps you want and the output is exactly as YOU dictated.

If you want 15.5 volts and 5 amps you can get it.

That particular one is a bit limited on current but would do the job - you don't need a huge current for equalisation.

 

Mine is a 1-30 volt and up to 3.5 amps, It rarely gets used as my cheapo 6 amp Halfords charger goes up to 16v (maybe higher, I just switch it off when I think its had long enough).

 

CAM00284.jpg

Edited by Alan de Enfield
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  • 1 month later...
16 minutes ago, Dartagnan said:

@WotEver

I am a numpty when it comes to the electrickery dept.  Thank you very much for a guide in plain English that even I can follow.

I realise there is much more to the subject but this has given me a base from which to start.

Great :)

That was the sole intention.  

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  • 7 months later...
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  • 4 months later...

Just re-reading this for the third or fourth time! It's very useful, although there are a couple of points on which the advice apparently differs from what elsewhere seems to be 'received wisdom'. I'm thinking especially of this:

 

"This table shows the relationship between resting voltage and charge state of a typical 12V bank:

12.65V - 100%

12.45V - 75%

12.24V - 50%

12.06V - 25%

11.89V - 0%"

 

I've seen multiple tables elsewhere that suggest 11.9 volts represents a 40% state of charge, while a 0% SoC would be 10.5 volts. That's a huge difference - I wonder what's behind it?

 

Also - I've read multiple times in threads on this forum that an alternator will typically only put out its maximum rated current for a short time, perhaps a matter of minutes, before tailing off dramatically; or that they always provide a current well below the rated value. But based on the information above and my understanding of the 'amp hour rule', if you have a 400Ah battery bank discharged to 50%, say, and a 70A alternator, the batteries would happily accept a 70A charge for the first hour and most of the second hour of charging, with that current only just beginning to tail off (to 60A) as they hit 340Ah capacity (c. 85%). And with a 110A alternator, the batteries would accept a 110A charge for more than 90 minutes. So does that caveat about alternators' rated output vs real-world performance only apply if you're talking about charging from 80%-ish to 100% (for typically sized battery banks and alternators)? Or is there some other reason why alternators don't really put out the rated current?

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4 minutes ago, magictime said:

Just re-reading this for the third or fourth time! It's very useful, although there are a couple of points on which the advice apparently differs from what elsewhere seems to be 'received wisdom'. I'm thinking especially of this:

 

"This table shows the relationship between resting voltage and charge state of a typical 12V bank:

12.65V - 100%

12.45V - 75%

12.24V - 50%

12.06V - 25%

11.89V - 0%"

 

I've seen multiple tables elsewhere that suggest 11.9 volts represents a 40% state of charge, while a 0% SoC would be 10.5 volts. That's a huge difference - I wonder what's behind it?

 

Also - I've read multiple times in threads on this forum that an alternator will typically only put out its maximum rated current for a short time, perhaps a matter of minutes, before tailing off dramatically; or that they always provide a current well below the rated value. But based on the information above and my understanding of the 'amp hour rule', if you have a 400Ah battery bank discharged to 50%, say, and a 70A alternator, the batteries would happily accept a 70A charge for the first hour and most of the second hour of charging, with that current only just beginning to tail off (to 60A) as they hit 340Ah capacity (c. 85%). And with a 110A alternator, the batteries would accept a 110A charge for more than 90 minutes. So does that caveat about alternators' rated output vs real-world performance only apply if you're talking about charging from 80%-ish to 100% (for typically sized battery banks and alternators)? Or is there some other reason why alternators don't really put out the rated current?

On the battery voltage table, there are variations around. It depends on battery chemistry to some extent (amount of calcium/antimony, gel, AGM, starting sg of acid etc. I would agree that a battery is considered fully flat when the voltage gets down to 10.5v. But anything below 50% / 12.2v should be out of bounds anyway!

 

Yes a small alternator charging a big bank will hold its full output for a good while. The reason why the current tails off is more down to the batteries rather than the alternator. As the battery voltage rises the alternator starts to reduce its output as the regulated value is approached. So if the battery bank is large and takes a long time to acquire charge, and has relatively low internal resistance, the system voltage will stay low and the alternator will be near maximum output. But a smaller battery will acquire charge quicker and has a higher internal resistance, so the system voltage will rise more quickly, resulting in reduced alternator current.

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1 hour ago, magictime said:

I've seen multiple tables elsewhere that suggest 11.9 volts represents a 40% state of charge, while a 0% SoC would be 10.5 volts. That's a huge difference - I wonder what's behind it?

It’s unimportant because, as Nick points out, you don’t want to be going much below 50% (around 12.2V) anyway. You could argue that the battery isn’t really flat until you get to 0V...

 

1 hour ago, magictime said:

I've read multiple times in threads on this forum that an alternator will typically only put out its maximum rated current for a short time, perhaps a matter of minutes, before tailing off dramatically...

This is the trouble with sweeping statements. Again, Nick describes it well. How long an alternator will stay at full output depends solely on the relationship between the alternator output and the bank size. The AmpHour ‘rule’ generally holds true. 

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15 hours ago, WotEver said:

It’s unimportant because, as Nick points out, you don’t want to be going much below 50% (around 12.2V) anyway. You could argue that the battery isn’t really flat until you get to 0V...

 

This is the trouble with sweeping statements. Again, Nick describes it well. How long an alternator will stay at full output depends solely on the relationship between the alternator output and the bank size. The AmpHour ‘rule’ generally holds true. 

Thanks - that clarifies the alternator issue considerably.

 

I appreciate that best practice is to keep batteries above 50%/12.2v, but my immediate issue is that mine are clearly on their last legs and I'm waking up some mornings to readings lower than that (11.8 this morning was a new low). Someone is due to come and fit new batteries and monitoring equipment in 2-3 weeks, but meanwhile I'm trying to stave off the fear that one day before then the leccy is just going to go off!

 

(FWIW I don't feel I've done TOO badly as a newbie - my Trojans were 4 years old when we bought the boat and have lasted a further two years - but obviously I'm wanting to stay properly on top of things with my first 'from new' batteries).

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14 minutes ago, magictime said:

Someone is due to come and fit new batteries and monitoring equipment in 2-3 weeks,

Firstly, I dont think you will have a problem over the next 2 or 3 weeks if they are Trojans and you charge them up to 100% of current capacity each day. How are you charging them? for how long? and how are you deciding when they are full enough to stop charging?

 

Secondly.... who is coming? what batteries are they going to fit for you and how many? Which monitoring equipment are you getting.

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35 minutes ago, magictime said:

 

 

(FWIW I don't feel I've done TOO badly as a newbie - my Trojans were 4 years old when we bought the boat and have lasted a further two years - but obviously I'm wanting to stay properly on top of things with my first 'from new' batteries).

And you don't know how well they were treated in that 4 years or when the boat was for sale. Even so a good sesion of charging may improve matters providing the electrolyte is at the correct level.

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46 minutes ago, Richard10002 said:

Firstly, I dont think you will have a problem over the next 2 or 3 weeks if they are Trojans and you charge them up to 100% of current capacity each day. How are you charging them? for how long? and how are you deciding when they are full enough to stop charging?

 

Secondly.... who is coming? what batteries are they going to fit for you and how many? Which monitoring equipment are you getting.

I've opened a can of worms here, haven't I?

 

I very much doubt the batteries are getting charged to 100% each day. That might well take 8 hours plus, mightn't it? I did run the engine for that long on Sunday, but most days I've been doing something like three hours morning, one hour evening. I'm only getting a trickle of 2 amps or so from solar most days.

 

The only 'monitoring equipment' I have is my solar charge controller, which gives a simple voltage reading. So I have a fair idea of state of charge morning and evening (before and after solar kicks in), but no real way of telling when the current has dropped right off as they get close to 100%. Hence I'm just guesstimating, really.

 

The logic behind the two separate charges is that (1) I'm pretty sure the batteries wouldn't last say 20 hours between 4-hour daily charges, and (2) by hour 4 of a continuous charge, surely they're likely to be accepting only a pretty low current, whereas when they're back down to 12.2 or 12.3 they're presumably more likely to accept a decent charge for an hour. Starting today I think I'm going to try flipping it though: longer charge between say 5 and 8pm, since they've then got to last 12 hours at least before any top-up (including evening use of lighting); shorter charge in the morning if they need it to tide them over till 5pm tomorrow.

 

Four Counties Marine Services (Ed Shiers) is doing the work. Leaning towards two 252Ah Leoch Pure Lead Carbons (although they look pretty unwieldy at 61kg). Will be getting a Smartgauge plus probably either a Victron or Mastervolt battery monitor.

27 minutes ago, ditchcrawler said:

And you don't know how well they were treated in that 4 years or when the boat was for sale. Even so a good sesion of charging may improve matters providing the electrolyte is at the correct level.

Yeah I gave them 8 or 9 hours on Sunday hoping it might improve things. Trouble is, I just don't have the facilities to do an equalisation charge - no shorepower, and no appropriate setting on my charger anyway - otherwise I'm sure I'd stand a better chance of breathing some life back into them. They were topped up recently so no issue there.

Edited by magictime
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