Fully charging a 24 volt 220AH lead acid battery bank with a 60 amp alternator

[cygnusv]

From. say 70%. How long would it take?

Fanx

 

[nigelmercier]

At least four times longer than a simple calculation would suggest.

 

[William_H]

Much depends on the voltage the regulator is set at. Assuming something like 28 volts and if your 220AH batteries need 66AH put in. You might if you are lucky get 20 amps in, in the first hour. That is an average much more at first but less near the end of the hour. You would probably find that the next 20 amp hours takes 2 hours to put in and the last 20 amp hours takes another 4 hours. You may not end up getting the last 6AH in.
Now these numbers are a wild guess. You will find that the 60amp ratng of the alternator does not relate very much to the current the batteries will take. The current they take depends on the difference between the inherent voltage of the battery and the regulated voltage of the alternator. The battery voltage rises quite rapidly so reducing the current going in. Except under very large loads the alternator current capabilty is not normally reached.
I would suggest you fit an amp meter so that if nothing else you can see that he engine run to charge batteries gets to the point where no much is going in so you might as well give up on engine run charging. of course if it is a MOBO and you are on avoyage it doesn't matter. If you want quicker charging then you need a smart charge regulator and then you may want a bigger alternator. (and better drive belts etc.) You might then halve the above times. good luck olewill

 

[Paddingtonbear]

Chris Gibson of Merlyn is who you need to consult if he is still around. A bit grumpy sometimes but seriously knowledgeable and doesnot mind sharing it.

 

[Stu Jackson]

Alternators, regardless of how BIG they are and whast their charging voltages may be cannot and will not fully charge a bank unless the engine is run literally forever (like 12 or more hours). It is a fact that battery acceptance rules how much charge a battery can, well, accept.

We've had some discussions about battery acceptance (search on "acceptance") in the past. I thought it might be helpful to describe just what happens, step-by-step when charging after, say, a simple day sail.

The battery acceptance drops off the ability to recharge, to an incredibly low rate of charge as the bank gets fuller and nearest to full. Many times, now based on my Link 2000 experiences, it takes almost overnight to fully recharge a bank.

What goes OUT of your house bank becomes easy to learn from the Energy Budget previously discussed and posted. It's what goes back IN that most people are missing, and relates to the state of charge of your house bank in a very direct manner.

What I've seen, for example is this, from our Link 2000:

--- Return from a day sail, bank is down 15 amp hours, plug into shore power with our 75 amp charger, batteries will only ACCEPT 15 amps (360 AH house bank, they're pretty fully charged if only 15 ah down)

--- Most people will then assume that it will take an hour to replace the 15 amp hours at 15 amps of charge

--- NOT!

--- As the batteries absorb that 15 amp charge, they get fuller

--- The charge RATE goes down to 10 amps after 15 or 20 minutes and the bank is now down to 10 amp hours down

--- Now, it should only take another hour to charge those minus 10 amp hours at 10 amps -- wrong assumption again; we're now up to an hour and twenty minutes to fully charge, right?

--- NOT again, because this keeps recurring

That's why a full charge takes a LOT longer that most people expect.

What goes OUT is easy, what goes BACK takes MUCH, MUCH longer. That last 15% to 20% takes a long time because of the REALITY of battery acceptance.

Please believe me, folks, because I see this all the time now that I have the Link 200 installed and working.

Please note that this true with alternators as well as shorepower chargers. Battery acceptance usually "rules" the charging regimen, so even with 100A alternators or shorepower chargers in excess of 40 A, the battery acceptance will determine the amount of charge that can go back into a house bank, usually around a max of 50A for a 400 ah bank. And it "tapers off" as the bank gets fuller as noted above.

This is why people say the BEST investment for un-knowledgeable and knowledgeable skippers alike is to buy a battery monitor FIRST. Wish I did, because I'd been chronically UNDERCHARGING my house bank, even after all the spouting I do here and on other forums! Crying Shocked Cool Rolling Eyes Nailbiter

Please, believe it!

 

[sailinglegend420]

.....That's why a full charge takes a LOT longer that most people expect....

Good info, but there is one other factor that many people don't realise and that is the battery efficiency which works against you when charging as we'll as the charge acceptance rate. Battery efficiency at 50% SoC may be very high at 95%, at 90% SoC it could be less than 50%. So at this rate every 10Ah put into the battery only 5Ah gets stored. The closer you get to 100% the worst this efficiency factor gets. What this really means is you can NEVER fully recharge a battery which is why they eventually sulfate and die.

it's also worth realising that at 90% SoC you are still 20% down on your useable Ah capacity.

 

[cygnusv]

Thanks for these illuminating answers. Presumably if my shore based charger was able to hold its charging voltage at say 28.5 to 28.8 volts I could leave it on for days without damaging the batteries and possibly get a more complete charge? Unfortunately my charger is of the dumb variety and if left unchecked can register 31 volts which presumably would cause battery damage?

 

[nigelmercier]

Get a proper multi-stage charger. This one will suffice, with a little in reserve if you ever increase your bank size: http://amzn.to/1fC37cI

 

[William_H]

Thanks for these illuminating answers. Presumably if my shore based charger was able to hold its charging voltage at say 28.5 to 28.8 volts I could leave it on for days without damaging the batteries and possibly get a more complete charge? Unfortunately my charger is of the dumb variety and if left unchecked can register 31 volts which presumably would cause battery damage?

Your dumb charger presumably continues to push current into the batteries even at a terminal voltagfe of 31.5. Presumably still at a reasonable current so yes that will boil batteries and overheat them causing damage. However with that charger you cna be assured of getting closer to full charge. (and more quickly) What you must remember is that the charger must be disconnected when the batteries are charged. You can't forget it which is what most chargers are designed for. (dummies)
The dumb charger might be described as a constant current charger. The voltage is relatively high but is dragged down by the internal ressitance of the charger to that of its rating so max current is the limiting factor. A solar panel (without controller) can do the same thing being limited by its current supply capability but will push that (small) current in at all charge states because of the 20v (40v to you) max voltage. good luck olewill

 

[Stu Jackson]

Good info, but there is one other factor that many people don't realise and that is the battery efficiency which works against you when charging as we'll as the charge acceptance rate. Battery efficiency at 50% SoC may be very high at 95%, at 90% SoC it could be less than 50%. So at this rate every 10Ah put into the battery only 5Ah gets stored. The closer you get to 100% the worst this efficiency factor gets. What this really means is you can NEVER fully recharge a battery which is why they eventually sulfate and die.

it's also worth realising that at 90% SoC you are still 20% down on your useable Ah capacity.

That is the very definition of battery acceptance. You're right.

 

[sailinglegend420]

Get a proper multi-stage charger. This one will suffice, with a little in reserve if you ever increase your bank size: http://amzn.to/1fC37cI

This is a car charger and they should NEVER BE USED ON A BOAT!

Deep cycle batteries need different chargers to starter battery chargers.

It takes a book to explain why, but put very simply:

You need proper AC-DC isolation for safety.
A 220Ah battery on a boat needs a 55 amp charger, not a 14 amp as you suggest.
You need to be able to set the charging voltages correctly for your type of battery.
A charger should have a proper equalising setting, not just a simple conditioning setting.
They should work with a genset that may not output a pure sine wave.
They should have battery temperature sensors to adjust the voltage as the battery temperature rises.
..............etc,.......

 

[nigelmercier]

This is a car charger and they should NEVER BE USED ON A BOAT! ...

What nonsense. It is an 8-stage charger, it does all the checks.

 

[sailinglegend420]

What nonsense. It is an 8-stage charger, it does all the checks.

Please don't post duff information. I have checked your last 100 posts and there is nothing to suggest you know anything about batteries or chargers.

For those interested in why car chargers should not be used on boats go to this site from an electrical engineer in the US who is trying to educate people and not just take their money.

http://www.pbase.com/mainecruising/installing_a_marine_battery_charger

 

[lw395]

Please don't post duff information. I have checked your last 100 posts and there is nothing to suggest you know anything about batteries or chargers.

For those interested in why car chargers should not be used on boats go to this site from an electrical engineer in the US who is trying to educate people and not just take their money.

http://www.pbase.com/mainecruising/installing_a_marine_battery_charger

I think that link is largely irrelevant.
I see the site belongs to 'compass marine inc', so I guess there's a commercial element.

But the point that 'mains' in boats is a serious business is fair comment

An 'auto transformer' based charger would be a menace, but that really isn't the same as 'auto' as in automotive.
If there was no isolation between the mains and secondary, you'd trip rccd's all the time.
I've not seen anything mains powered in the UK with a non isolated power supply and any external connections for a very long time.
Apart from variacs, where the output needs to be treated as mains anyway.
But TBH the charger Nigel linked to seems to have a marine price anyway, and it's a bit of fred drift from charging with an alternator.
A variable isolated 12-15 20amp supply works well for us, just knock it back to 13V to float charge when the bulk is done, spend the saving on more batteries or some solar?
As ever it depends on how you want to use your boat.

 

[cygnusv]

Perhaps I should have asked the question elsewhere.....

 

[nigelmercier]

Please don't post duff information. I have checked your last 100 posts and there is nothing to suggest you know anything about batteries or chargers...

Perhaps I haven't been replying to posts about batteries then. I have checked your last 1 post and there is nothing to suggest you know anything at all.

But TBH the charger Nigel linked to seems to have a marine price anyway, and it's a bit of fred drift from charging with an alternator...

The OP came back in Post #7 asking about mains chargers, hence my reply. CTEK make excellent chargers, and have advised me that their automotive and marine models are functionally similar, just different markets.

 

[sailinglegend420]

.... CTEK make excellent chargers, and have advised me that their automotive and marine models are functionally similar, just different markets.

They may be functionally different but the marine markets needs different engineering, which is exactly the point I was making. Their marine M300 at least goes up to 25 amps and does have an external battery temperature sensor, but it is only really large enough for a 100 Ah battery, not the OPs 220 Ah.

 

[sailinglegend420]

Perhaps I should have asked the question elsewhere.....

I think you are right!!! This forum has too many opinionated ignorant posters.

This thread had a good post from Stu Jackson who was shot down. He posts a lot on cruisers forum.com - they have about 30 different sub-forums, especially for batteries/generators and solar. Compass Marine man Maine Sail is one of their highly regarded posters, but here his article is regarded as "irrelevant".

If you have any serious questions that is the place to go. Search their archive first.

 

[nigelmercier]

[CTEK] marine M300 at least goes up to 25 amps and does have an external battery temperature sensor, but it is only really large enough for a 100 Ah battery, not the OPs 220 Ah.

The M300 is 12V, so not a lot of use to the OP.

Yes, ideally a charger would be capable of a current output of around 25% of the battery capacity in Ah, but this is not mandatory. The battery I linked to "Charges batteries up to 300Ah. Maintains larger batteries up to 500Ah"

The OP also said "Presumably if my shore based charger was able to hold its charging voltage at say 28.5 to 28.8 volts I could leave it on for days without damaging the batteries and possibly get a more complete charge?.." so the requirement is a long charge to full capacity, not overnight.

 

[GHA]

I think you are right!!! This forum has too many opinionated ignorant posters..

To allow others to get a handle on info posted on here, perhaps you could reveal your own level of experience in the business.

Have you decades in design and building in the industry like halcyon or self taught?