A list of battery charging figures

[Graham.m]

 

I looked back, this was the one that struck me as being wrong, I gave you credit by describing the terminology as "uncommon". The way you've used "capacity" in two different ways, to mean two different things (in red, amount of stored energy; in green, actual battery capacity) is the illogical bit.

 

But whilst you may find it illogical. What the person I am writing to needs to know is that at the end of day x he has capacity Y that is usable from the battery, not the initial battery capacity of 200Ah. The last sentence is very specific it states battery capacity left. I think that possibly engineers can go to engineery and the layman has problems. I try to avoid that, although one of my engineers has just read it and told me what I was saying.

[nicknorman]

It's an obvious case of muddling capacity and state of charge. And stating recharging to 90%, without saying 90% of what, is meaningless.

Edited February 17, 2016 by DHutch
Later comment removed.

[Paul C]

Ok no worries (see post 42) etc

[bottle]

It's an obvious case of muddling capacity and state of charge. And stating recharging to 90%, without saying 90% of what, is meaningless. You are definitely not an engineer.

 

I knew that hence the bucket of water analogy and I do not have any bits of paper to prove any qualifications because I do not have those either.

 

Edit: fat fingers and English grammer, failed GCE.

Edited November 22, 2015 by bottle

[swift1894]

Equalisation is best done once the batteries are fully charged. Not really sure why, but I suppose you will get a lot of gassing for longer, possibly more plate corrosion in the long term. I would leave it on "traction" until the current drops to around 1% (ie around 7A, although we could be generous and say 10A!). That is the current going into the batteries, not the current coming out it of the charger which will include anything the boat's services are using. When you say

OK yesterday I ran the genny for 5 hours, having changed the dip stitches to traction + diode which gives a potential charging voltage of 15.2v, The voltage from the charger started off at 14.05v 85A. After 1 hour this had changed to 15.04v 37A. After 2 hours 15.14v 24A. After 3 hours 15.11v 23A. Readings virtually stayed at 15.11v 24A for the next 2 hours, actually rising to 15.12v 27A before I turned the genny off. Ran it for 3.5 hours today started at 14v 85A , 3 hours later 15.15v 23A no change again for next 30 minutes. Batteries were bubbling away merrily, but didn't get warm at all.

I will get plugged into a landline when I can to give A good 48 hours but I couldn't get down to 10A, let alone 7A, after 5 hours. What do you think?

Edited November 26, 2015 by swift1894

[Loafer]

OK yesterday I ran the genny for 5 hours, having changed the dip stitches to traction + diode which gives a potential charging voltage of 15.2v, The voltage from the charger started off at 14.05v 85A. After 1 hour this had changed to 15.04v 37A. After 2 hours 15.14v 24A. After 3 hours 15.11v 23A. Readings virtually stayed at 15.11v 24A for the next 2 hours, actually rising to 15.12v 27A before I turned the genny off. Ran it for 3.5 hours today started at 14v 85A , 3 hours later 15.15v 23A no change again for next 30 minutes. Batteries were bubbling away merrily, but didn't get warm at all.

I will get plugged into a landline when I can to give A good 48 hours but I couldn't get down to 10A, let alone 7A, after 5 hours. What do you think?

 

How big is your battery bank? Those figures suggest it's enormous and not yet fully charged. More than 14.8V for that length of time is unwise - I'd drop it to 14.8V max, until your charge current is down to 1-2% of your estimate of battery bank capacity as it is now.

 

THEN increase to 15.5 max for about an hour or two. That is then an equalisation charge 'proper'.

 

This is all assuming they're wet lead-acid and that all the current is going to the batteries, not your washing machine. You need to check the electrolyte levels after all that over-voltage.

Edited November 26, 2015 by Loafer

[nicknorman]

OK yesterday I ran the genny for 5 hours, having changed the dip stitches to traction + diode which gives a potential charging voltage of 15.2v, The voltage from the charger started off at 14.05v 85A. After 1 hour this had changed to 15.04v 37A. After 2 hours 15.14v 24A. After 3 hours 15.11v 23A. Readings virtually stayed at 15.11v 24A for the next 2 hours, actually rising to 15.12v 27A before I turned the genny off. Ran it for 3.5 hours today started at 14v 85A , 3 hours later 15.15v 23A no change again for next 30 minutes. Batteries were bubbling away merrily, but didn't get warm at all.

I will get plugged into a landline when I can to give A good 48 hours but I couldn't get down to 10A, let alone 7A, after 5 hours. What do you think?

I wouldn't recommend charging from a low state of charge with the traction + diode setting. Fully charge the batteries just on the traction setting first. With that setting, you should be able to get down to 1% if the batteries are in decent condition. Only then select the diode mode. The reason is that it takes a fixed amount of time to get the chemical reaction (aka charging) deep into the plates. If you try to force the charge in too quickly you don't speed up the rate at which the chemicals react deep within the plate, but the chemicals near the surface are already reacted fully (aka fully charged) and so the high voltage and current causes a lot of gassing and probably accelerated plate corrosion (long term).

 

So in summary, charge on the traction setting until 1% or the current stabilises, then switch the diode mode on to equalise. You won't get the current down to 1% on that setting though.

 

What you really need to do is to check the specific gravity in order to determine when to stop equalising. During equalise the specific gravity will hopefully rise as the sulphate crystals are broken down, and at some point the gravity will stop rising. I don't think there is a significant change of current at that point. It can take many hours to de-sulphate badly sulphated batteries.

 

Once you have given it a good de sulphating it should only require short equalisation charges say every month, or anyway when you find the specific gravity is not as high as it should be after fully charging on the traction setting.

[dmr]

I am not sure but I think Nicks 1% might be a bit optimistic and you might have to accept 2 or even 3% as the point to start equalising.

Based of fairly superficial (and certainly not scientific) observations I suspect my tail current sits at quite a high value in the winter when the batteries spend a lot of time at less than 100% charge. Its only in the summer when we cruise everyday, and hence get the batteries really well charged, that I see tail currents of just under 1%.

I suppose Nicks "batteries in good condition" clause does sort of say this. Trouble is that if you are contemplating an equalisation then the batteries are probably not in their best condition at that time.

 

...............Dave

[Paul C]

I'm not sure if "achievable tail current" (which we're aiming for 1% here) varies according to previous recent discharge, or ambient temperature (eg related to time of year). Firstly, let's properly define (what I mean by) tail current:

 

1) you need to be measuring the right thing - its the amps going into a battery - so the shunt must be the ONLY thing connected to the negative terminal, if there's anything else then its not going to measure the amps going into the battery solely/properly

2) its the current which is flowing into the battery once (change in current/unit time) is 0, ie its steady

 

I suspect (again not 100% sure) that a "tail current" higher than about 2% of the nominal battery capacity, once you've met 1) and 2) above, indicates some kind of fault with the battery (beyond simply being sulphated and low in actual capacity).

[nicknorman]

I am not sure but I think Nicks 1% might be a bit optimistic and you might have to accept 2 or even 3% as the point to start equalising.

Based of fairly superficial (and certainly not scientific) observations I suspect my tail current sits at quite a high value in the winter when the batteries spend a lot of time at less than 100% charge. Its only in the summer when we cruise everyday, and hence get the batteries really well charged, that I see tail currents of just under 1%.

I suppose Nicks "batteries in good condition" clause does sort of say this. Trouble is that if you are contemplating an equalisation then the batteries are probably not in their best condition at that time.

 

...............Dave

Hi Dave, yes perhaps 1% is a bit purist but I thought I would leave it to the OP to take his own shortcuts rather than add mine first and then have him add his on top!

 

I'm pretty sure we get down to 1/2% (half a %) or so in our T105s but typically there are pretty much fully charged by lunchtime and then get perhaps another 4 or 5 hours of cruising at 14.5v. And of course they are on shore power float when we are away from the boat. So quite a different usage pattern from you.

 

For the OP - the answer is perhaps not to look for a specific % figure of AH, but rather to look for no significant reduction in current for an hour, as the signal to switch to equalisation.

[Paul C]

For info I've regularly seen a tail current of 0.7% on my batteries.

[nicknorman]

... (change in current/unit time) is 0, ie its steady.

Can we say dI/dt or do most people not understand that? Anyway, I'm going to use my favourite term again and say that dI/dt only asymptotically approaches zero. So in the same way that one could specify a tail current as a % of capacity as "fully charged", one also has to define a dI/dt that can be considered fully charged. Ok I suppose measurement accuracy and other influencing factors (change of temperature etc) might become predominant fairly quickly.

 

However, I agree that a specified dI/dt is a better measure since it is probably less dependant on battery condition.

[Paul C]

Can we say dI/dt or do most people not understand that? Anyway, I'm going to use my favourite term again and say that dI/dt only asymptotically approaches zero. So in the same way that one could specify a tail current as a % of capacity as "fully charged", one also has to define a dI/dt that can be considered fully charged. Ok I suppose measurement accuracy and other influencing factors (change of temperature etc) might become predominant fairly quickly.

 

However, I agree that a specified dI/dt is a better measure since it is probably less dependant on battery condition.

 

Agreed, in theory it asympotically approaches zero but pragmatically it will go below measurable limit at some point. Also pragmatically, and I shudder to introduce made up terminology, or muddle things, but we're not actually seeking "fully charged", we're seeking "near as dammit fully charged" which will have "near as dammit dI/dt=0". Some compromise for real-world situation (ie not running a generator for days at a time) needs to be made, for it to be useful in the real world.

 

Whether this should be 1 A/h, 0.1 A/h or 0.01 A/h is what's key here. I'd say looking at the original figures (post #1) 16 A/h is not near enough (but also respecting that the OP has done further charging since then, without posting the detailed figures of dI/dt). I'd boldly suggest 0.1A/h but based on nothing more substantial than my own experience.

[Loafer]

 

Agreed, in theory it asympotically approaches zero but pragmatically it will go below measurable limit at some point. Also pragmatically, and I shudder to introduce made up terminology, or muddle things, but we're not actually seeking "fully charged", we're seeking "near as dammit fully charged" which will have "near as dammit dI/dt=0". Some compromise for real-world situation (ie not running a generator for days at a time) needs to be made, for it to be useful in the real world.

 

Whether this should be 1 A/h, 0.1 A/h or 0.01 A/h is what's key here. I'd say looking at the original figures (post #1) 16 A/h is not near enough (but also respecting that the OP has done further charging since then, without posting the detailed figures of dI/dt). I'd boldly suggest 0.1A/h but based on nothing more substantial than my own experience.

 

Wow. Correct use of the term 'Amps per hour' for a change!

[nicknorman]

Agreed, in theory it asympotically approaches zero but pragmatically it will go below measurable limit at some point. Also pragmatically, and I shudder to introduce made up terminology, or muddle things, but we're not actually seeking "fully charged", we're seeking "near as dammit fully charged" which will have "near as dammit dI/dt=0". Some compromise for real-world situation (ie not running a generator for days at a time) needs to be made, for it to be useful in the real world.

 

Whether this should be 1 A/h, 0.1 A/h or 0.01 A/h is what's key here. I'd say looking at the original figures (post #1) 16 A/h is not near enough (but also respecting that the OP has done further charging since then, without posting the detailed figures of dI/dt). I'd boldly suggest 0.1A/h but based on nothing more substantial than my own experience.

Yup. Although of course we are both slightly wrong since absolute dI/dt isn't the general criteria, it has to take account of bank size. So dI/dt = x % of bank capacity (apologies for dimensional inconsistency!).

[Paul C]

Yup. Although of course we are both slightly wrong since absolute dI/dt isn't the general criteria, it has to take account of bank size. So dI/dt = x % of bank capacity (apologies for dimensional inconsistency!).

 

Yes its units should be h^-2 or probably s^-2 but either of these give very small numbers....so maybe best expressed in days^-2

 

My change in tail current for my battery bank would be 0.17 days^-2 (change of 0.1A over 1 hour, on a 330Ah battery bank)

[Top cat]

On the solar charger our batteries have been sitting at 14.4V and 0.1%C lately, now thats what I call fully charged. The charger then drops back to 13.8V and the sit thereat zero amps till itgets dark then next day the get the 0.1% again for a few hours. Btw they are sealed liesure cells a few years old.

 

Top Cat

[dmr]

Does charge current asymptotically approach zero, or does it approach some small fixed value? I reckon the latter.

Thinking about my previous post saying my tail current was more than 1%, I have thought a bit more and suspect voltage is a complicating factor.

We have an Adverc so the charge voltage does keep cycling, and also I charge at 14.9 or 15 in the winter, but dropped down to about 14.6 in the summer to give the batteries an easier life.

If you charge at a lower voltage then I suspect the tail current will drop to that 1% (or whatever) sooner, but that does not mean a higher state of charge?

I got down to 4 amps into a 650Ah bank in summer but that was at 14.6 volts.

 

...............Dave

[Loafer]

Does charge current asymptotically approach zero, or does it approach some small fixed value? I reckon the latter.

 

We USED to get down to zero amps in marina winters at sea, after about a week at float (on mains hook-up). Lifeline AGMs in those days. Wish I could afford them now!

 

ETA Well our hopelessly inaccurate Sterling BM used to say so!

Edited November 26, 2015 by Loafer

[nicknorman]

Does charge current asymptotically approach zero, or does it approach some small fixed value? I reckon the latter.

Thinking about my previous post saying my tail current was more than 1%, I have thought a bit more and suspect voltage is a complicating factor.

We have an Adverc so the charge voltage does keep cycling, and also I charge at 14.9 or 15 in the winter, but dropped down to about 14.6 in the summer to give the batteries an easier life.

If you charge at a lower voltage then I suspect the tail current will drop to that 1% (or whatever) sooner, but that does not mean a higher state of charge?

I got down to 4 amps into a 650Ah bank in summer but that was at 14.6 volts.

 

...............Dave

Yes I doesn't asymptotically approach zero, but dI/dt does as does SoC (well, approaches 100% I mean). Certainly the 100% SoC I (Ift for final tail current) will vary with charge voltage as well as temperature, although I suspect in a fairly non-linear way as isn't there some sort of "gassing threshold" which if you exceed, I will increase rapidly? However under stable conditions I would doubt there is much difference in Ift between say 14.2v and 14.5v for modern leisure batteries with plenty of calcium.

We USED to get down to zero amps in marina winters at sea, after about a week at float (on mains hook-up). Lifeline AGMs in those days. Wish I could afford them now!

 

ETA Well our hopelessly inaccurate Sterling BM used to say so!

Yes at float voltage (say 13.25) you would expect the current to eventually get to zero, or very close (very close because lead acid batteries have some self-discharge which the float charger would have to replace).

[Loafer]

...for modern leisure batteries with plenty of calcium.

 

Yes at float voltage (say 13.25) you would expect the current to eventually get to zero, or very close (very close because lead acid batteries have some self-discharge which the float charger would have to replace).

 

I consume plenty of calcium Nick, but it hasn't done anything to reduce MY self-discharge!

[swift1894]

I wouldn't recommend charging from a low state of charge with the traction + diode setting. Fully charge the batteries just on the traction setting first. With that setting, you should be able to get down to 1% if the batteries are in decent condition. Only then select the diode mode.

So in summary, charge on the traction setting until 1% or the current stabilises, then switch the diode mode on to equalise. You won't get the current down to 1% on that setting though.

What you really need to do is to check the specific gravity in order to determine when to stop equalising. During equalise the specific gravity will hopefully rise as the sulphate crystals are broken down, and at some point the gravity will stop rising. I don't think there is a significant change of current at that point. It can take many hours to de-sulphate badly sulphated batteries.

Once you have given it a good de sulphating it should only require short equalisation charges say every month, or anyway when you find the specific gravity is not as high as it should be after fully charging on the traction setting.

OK will do. I need to get to a mains power point and get a hydrometer then I can sort things out.

Thanks to everyone for all their advice.

[swift1894]

How big is your battery bank? Those figures suggest it's enormous and not yet fully charged. More than 14.8V for that length of time is unwise - I'd drop it to 14.8V max, until your charge current is down to 1-2% of your estimate of battery bank capacity as it is now.

 

THEN increase to 15.5 max for about an hour or two. That is then an equalisation charge 'proper'.

 

This is all assuming they're wet lead-acid and that all the current is going to the batteries, not your washing machine. You need to check the electrolyte levels after all that over-voltage.

720Ah wet lead-acid. Yes I'll drop back down to 14.6, get on mains until I get down to 1% then do the equalization. Fingers crossed I can get back to a higher capacity. Edited November 26, 2015 by swift1894

[Loafer]

720Ah wet lead-acid. Yes I'll drop back down to 14.6, get on mains until I get down to 1% then do the equalization. Fingers crossed I can get back to a higher capacity.

Don't forget to check the electrolyte levels, preferably after a charge, to be on the safe side.

[Graham.m]

720Ah wet lead-acid. Yes I'll drop back down to 14.6, get on mains until I get down to 1% then do the equalization. Fingers crossed I can get back to a higher capacity.

 

 

What are them temperatures llke there?