Charging efficiency

[Top cat]

What would people expect the charging efficiency ratio of some elderly wet cell lead acid batteries to be ?

 

My battery bank is 440 ah made up of 4x 110Ah batteries and is charged either from an alternator via and Adverc controller which takes them up to 14,4V on and back to 14.2 ish or a Ctek 4 step mains charger which does similar things.

 

I know getting the last few amp hours back in takes forever but am I right in thinking once the current drops of to less than 10 A they are pretty much charged ?

 

Thanks

 

TC

[nb Innisfree]

What would people expect the charging efficiency ratio of some elderly wet cell lead acid batteries to be ?

 

My battery bank is 440 ah made up of 4x 110Ah batteries and is charged either from an alternator via and Adverc controller which takes them up to 14,4V on and back to 14.2 ish or a Ctek 4 step mains charger which does similar things.

 

I know getting the last few amp hours back in takes forever but am I right in thinking once the current drops of to less than 10 A they are pretty much charged ?

 

Thanks

 

TC

 

Although it can take 24 hours or more for charge rate to bottom out, when charge rate has reduced to 2% of batt capacity it is considered fully charged but I believe Smartgauge works on 0.5%. So I would say 2% is a practical figure for day to day use but 0.5% or less indicates a true full charge. Of course as battery capacity is constantly reducing trying to guess it is a bit of a shot in the dark anyway.

 

We have roughly 40-50% of original capacity of 960ah left and we do an occasional 8hr absorption which reduces to about 5amp which is about 1% though if we leave it on shorepower with the Victron for a few days it can go as low as 0.2 amp.

 

ETA: Best leave it to Smartgauge.

Edited August 26, 2011 by nb Innisfree

[Gibbo]

OP's question is not really anytyhing to do with charge efficiency. That's a different subject altogether. As to when is a battery fully charged the most I ever wrote down was the following which is sketchy to say the least...

 

http://smartgauge.co.uk/sga_faq.html#full

[smileypete]

My battery bank is 440 ah made up of 4x 110Ah batteries and is charged either from an alternator via and Adverc controller which takes them up to 14,4V on and back to 14.2 ish or a Ctek 4 step mains charger which does similar things.

 

I know getting the last few amp hours back in takes forever but am I right in thinking once the current drops of to less than 10 A they are pretty much charged ?

 

To quote The Battery FAQ:

 

'The pattern of charging current delivered by a conventional voltage-regulated charger after a discharge is the most accurate method for determining state of charge. As the cells approach full charge, the battery voltage rises to approach the charger output voltage, and the charging current decreases. When the charging current has stabilized at the charging voltage, the battery is charged, even though specific gravities have not stabilized." It should be less than two percent of the capacity (C/50) at the manufacturer's recommended temperature compensated absorption charging voltage level of the battery'

 

2% of 440Ah is 8.8 amps, so you're about there.

 

cheers,

Pete.

[Top cat]

OP's question is not really anytyhing to do with charge efficiency. That's a different subject altogether. As to when is a battery fully charged the most I ever wrote down was the following which is sketchy to say the least...

 

http://smartgauge.co.uk/sga_faq.html#full

Well actually it was, sorry my second question seem to have diverted people attention

 

I'm using an amp hour counter (heresy I know) and as part of the set up I need to put in the charging efficiency ratio. Initially I put in the manufacturers recommendation of 95% but this seems too much in that it was indicating a full charge when the batteries were still taking something in teh order of 13A. So I'm going to enter a lower figure and wondered if anyone had a recommendation of a good place to start.

 

Regards

 

TC

[nb Innisfree]

We have a BMV monitor and I spent ages mucking about with various settings in an attempt to get an accurate percentage reading and in the end gave it up as a bad job relying instead on amps and volts to give me some idea of state of charge.

 

Sorry but shunt based monitors are ok as voltmeters and ammeters but apart from that are a pain in the arse.

[Top cat]

Thanks

 

I'll do likewise and deem the batteries charged when the current is under 9 A

 

TC

[nb Innisfree]

Thanks

 

I'll do likewise and deem the batteries charged when the current is under 9 A

 

TC

 

Reading your other post I believe you have 4x 110 a/h of batts? so on that assumption don't forget 9 amps is based on your batts still having their full capacity left, they will gradually but inevitably reduce and fully charged current will reduce accordingly.

[smileypete]

Well actually it was, sorry my second question seem to have diverted people attention

 

I'm using an amp hour counter (heresy I know) and as part of the set up I need to put in the charging efficiency ratio. Initially I put in the manufacturers recommendation of 95% but this seems too much in that it was indicating a full charge when the batteries were still taking something in teh order of 13A. So I'm going to enter a lower figure and wondered if anyone had a recommendation of a good place to start.

Generally if charging from 50% then 85-95% efficiency, so maybe try 85% to be on the safe side?.

 

However the most accurate way is from the charge current, as outlined above.

 

Once the batts are fully charged the amp hour counter is of some use to monitor discharge, but keep an eye on the off-load volts to check it recovers to about 12.2V

 

cheers,

Pete.

Edited August 28, 2011 by smileypete

[Top cat]

Thanks guys I'm guessing that my batteries are considerably down on their original capacity but I have no idea by how much. How quickly should they recover to 12.2V , immediately 2- 3 minutes ? I've yet to see them below 12.4 off load and 11.8 on load (62 amps) Typically we are taking less than 60 Ah out but I'm slowly pushing that up to try and find what the real capacity is.

 

Thanks

 

TC

[smileypete]

Thanks guys I'm guessing that my batteries are considerably down on their original capacity but I have no idea by how much. How quickly should they recover to 12.2V , immediately 2- 3 minutes ? I've yet to see them below 12.4 off load and 11.8 on load (62 amps) Typically we are taking less than 60 Ah out but I'm slowly pushing that up to try and find what the real capacity is.

Maybe see what they're up to next morning. Sounds like the batts are getting on a bit to say the least.

 

Bear in mind you're drawing a heavy load you'll get less Ah out of them due to the 'Peukert effect', bit like putting your foot down in a car lowers how far you can go on a tank.

 

cheers,

Pete.

Edited August 28, 2011 by smileypete

[Top cat]

Maybe see what they're up to next morning. Sounds like the batts are getting on a bit to say the least.

 

Bear in mind you're drawing a heavy load you'll get less Ah out of them due to the 'Peukert effect', bit like putting your foot down in a car lowers how far you can go on a tank.

 

cheers,

Pete.

 

Yes they are up to 6 years old and are not matched ( 3 different manufacturers) If we take 40 Ah out in 20 hours then they are at about 12.6V in the morning, I only pushed them with a 62 amp load to see how they handled it. Am I right in thinking that the Puerkert effect only applies if one is pulling more than the 20C rate ? because if I put the mean 2A discharge into a puekert calculator I get a capacity of over 800ah which seems a lot

 

Regards

 

TC

[smileypete]

Yes they are up to 6 years old and are not matched ( 3 different manufacturers) If we take 40 Ah out in 20 hours then they are at about 12.6V in the morning, I only pushed them with a 62 amp load to see how they handled it. Am I right in thinking that the Puerkert effect only applies if one is pulling more than the 20C rate ? because if I put the mean 2A discharge into a puekert calculator I get a capacity of over 800ah which seems a lot

12.6V after 40Ah discharge is pretty good, some way above 12.2V which means they need a charge. Could be handy to know how much they typically recover overnight.

 

I wouldn't worry toooo much about Peukert, the 'Peukert exponent' is more like 1.1 for a healthy leisure batt.

 

cheers,

Pete.

Edited August 28, 2011 by smileypete

[Top cat]

Thanks Pete

 

TC

[Gibbo]

the 'Peukert exponent' is more like 1.1 for a healthy leisure batt.

 

Hmmm, it isn't. Not even close.

[smileypete]

Hmmm, it isn't. Not even close.

OK, putting that aside for a minute, please explain:

 

Am I right in thinking that the Puerkert effect only applies if one is pulling more than the 20C rate ? because if I put the mean 2A discharge into a puekert calculator I get a capacity of over 800ah which seems a lot

 

ETA: What would you expect the Peukert exponent for a typical leisure battery to be?

 

cheers,

Pete.

Edited August 30, 2011 by smileypete

[Top cat]

Hmmm, it isn't. Not even close.

So what is it ? and how does it change as batteries age ?

 

TC

[Gibbo]

Right...

 

Typical leisure battery Peukert's exponent would be between 1.15 and 1.2 - as the battery ages it usually increases. Perhaps as high as 1.35 or so at the time the battery becomes unuseable due to massively decreased capacity. But it doesn't always happen () because it depends what caused the battery to lose capacity. If it lost it due to plate shedding then Peukert's exponent is hardly affected. If it's due to sulphation then that makes quite a big difference.

 

Proper deep cycle wet cells have a much higher exponent. AGMS and gels lower.

 

It gets a bit awkward at low discharge rates. If you just calculate the capacity according to the usual equation you find that the calculated capacity of the battery becomes ridiculously high as the discharge rate decreases. Obviously this doesn't happen in the real world. Well, actually it does, just not to the extent that Peukert's equation would show. Discharging a 100ahr battery at the 20 hour rate will, of course, get you 100ahrs. But discharging it at a 40 hour rate will get you well over 100ahrs. Not as much as a simple Peukert calculation would imply, but still more than a direct capacity/discharge would show. Also remember that self discharge makes a mess of it at very low discharge rates.

 

You have to remember that the equation is an empirically derived guestimate. Nothing better. The closest I have come to calculating figures that actually match reality at low discharge rates is to assume that the effect dissappears completely at the 100hour rate then interpolate between that and the 20 hour rate in a straight line. Discharging faster than the 20 hour rate reverts to the normal (proper - not the usual one you see in books and websites) Peukert's equation and doing it that way gets remarkably close to reality. That's the way I've always done it in amp hour counting devices. Cruising Equipment (Link 10 etc) use a similar, though slightly different, trick to get it right at low discharge rates.

 

Top Cat. You can't average the current draw over a period then apply Peukert to that. It simply will not work, at all. You have to do it constantly. But even that will fail because there is a substantial recovery between the discharges which extends the total discharge time even further. There are algorithms for that but believe me you wouldn't want to do it manually!

 

If doing it manually I would say assume Peukert's effect dissappears at discharges slower than the 20 hour rate. The difference won't be huge on a single discharge run.

 

Does that make sense? It does to me, but I'm not reading it trying to understand it!

[nb Innisfree]

So get a Smartgauge and take advantage of all the buggering and farting about that a certain person once did

[Gibbo]

So get a Smartgauge and take advantage of all the buggering and farting about that a certain person once did

 

Or, if you're rich, wait for the new one which has even more buggering and farting around in it

[nb Innisfree]

Or, if you're rich, wait for the new one which has even more buggering and farting around in it

 

You're a little bugger aren't you?

[smileypete]

Or, if you're rich, wait for the new one which has even more buggering and farting around in it

Well, I think 'Top cat' has shown it's possible to get good batt performance and life without a Smartgauge...

 

cheers,

Pete.

Edited August 30, 2011 by smileypete

[nb Innisfree]

Well, I think 'Top cat' has shown it's possible to get good batt performance and life without a Smartgauge...

 

cheers,

Pete.

 

Life can be very unfair...

[Top cat]

Thanks Gibbo you have explained it clearly

 

I take your point about not averaging the discharge rate but as most of the time we stay below the 20C rate I will just ignore Peukert.

 

Yes maybe I should have just bought a Smartgauge but I wanted to know what currents were flowing so I've had the extra installation hassle (more than I expected)and all the buggering about setting the BMV up .

 

But it was significantly cheaper and I could actually buy one over the counter rather than mail order with rip off postage charges. So If Smartguauge were cheaper had an ammeter and was readily available I would have bought one and probably have a better idea what my batteries are doing.

 

But the one I have is telling me enough to manage my batteries better and after rewiring the battery as per your recommendations they are performing much better

 

Yer pays yer money and takes yer choice and live with the consequences

 

Regards

 

TC

[Gibbo]

But it was significantly cheaper...

 

 

My mate just a bought a Squier guitar. At £52 it was significantly cheaper than my 1959 Les Paul. It's also crap.