can I charge Numax sealed batts 14.9V?

[Keeping Up]

Well described Nick, and that is what I would expect to see. The point at which the current starts to increase would be, I agree, the point at which significant gassing has started; above this point, as has been agreed on previous occasions here, you can continue to supply as much energy as you wish but its only function is in converting water into gas. The level of charge of the battery is not increased, it is "full". I would contend however that over that range from 14.4 to the gassing voltage, if the battery will take no current (other than a momentary pulse at the instant after the increase in voltage) then the battery was fully charged at 14.4 - after all, how can you increase the level of charge of a battery if you are supplying zero energy to it?

[Nickhlx]

Well described Nick, and that is what I would expect to see. The point at which the current starts to increase would be, I agree, the point at which significant gassing has started; above this point, as has been agreed on previous occasions here, you can continue to supply as much energy as you wish but its only function is in converting water into gas. The level of charge of the battery is not increased, it is "full". I would contend however that over that range from 14.4 to the gassing voltage, if the battery will take no current (other than a momentary pulse at the instant after the increase in voltage) then the battery was fully charged at 14.4 - after all, how can you increase the level of charge of a battery if you are supplying zero energy to it?

 

Thanks..

 

As you say, more energy just increases the rate of gassing.. I drop the "float" voltage back to around 13.2 after it has reached this point, to help minimise positive plate corrosion..

 

Nick

[smileypete]

Apart from the fact that I don't have the ability to change the voltage as easily as all that (the Adverc does it all the time) I'm not sure that I agree with your conclusion. By my reckoning, if the battery takes no current at 14.1, and then if after the brief jump at 14.4 it also returns immediately to zero, I would reckon that it MUST be full. Certainly if after the initial jump the current did NOT return immediately to zero, that would be a sign that it was not yet full and is exactly the pattern always I observe while it is charging in absorption.

 

If indeed an increase to 14.8 were to cause a jump to 25A for a second followed by a return to zero over the next few seconds, as you postulate, then since no further charge was being put into the batteries I would take this as a sign that they were already full.

Fair enough, but if they're losing capacity at the same rate, it's almost certainly due to sulphation or battery stratification, which amounts to the same thing.

 

Came across this post by Dor last year:

 

"My set of Numax sealed batteries showed clear signs of sulphation after about 18 months. Disappointed, I bought some open cell batteries which showed the same results after about 12 months. I know that my boat usage was going to challenge the batteries as we tended to go out for two or three days and not travel enough going home to recharge the batteries.

 

So I dug out the old Numax batteries and put each one on a battery charger for a couple of days floating at about 13.6V, followed by 12 hours at about 15V off a bench power supply. They took only an amp or so being fully charged, but that did seem to rejuvenate them. They went back on the boat and are now over four years old and still in service - quite good by all accounts for this type of battery! Having said that, fitting a 100W solar panel last summer has done much to prolong them by charging them up for a few days when we are not on the boat."

 

cheers,

Pete.

[Nickhlx]

Fair enough, but if they're losing capacity at the same rate, it's almost certainly due to sulphation or battery stratification, which amounts to the same thing.

 

Came across this post by Dor last year:

 

"My set of Numax sealed batteries showed clear signs of sulphation after about 18 months. Disappointed, I bought some open cell batteries which showed the same results after about 12 months. I know that my boat usage was going to challenge the batteries as we tended to go out for two or three days and not travel enough going home to recharge the batteries.

 

So I dug out the old Numax batteries and put each one on a battery charger for a couple of days floating at about 13.6V, followed by 12 hours at about 15V off a bench power supply. They took only an amp or so being fully charged, but that did seem to rejuvenate them. They went back on the boat and are now over four years old and still in service - quite good by all accounts for this type of battery! Having said that, fitting a 100W solar panel last summer has done much to prolong them by charging them up for a few days when we are not on the boat."

 

cheers,

Pete.

 

 

I reckon solar is still overlooked by many, and they are superb for (especially) the "weekend cruiser" if you are not on a shoreline, as they provide exactly what a battery needs, i.e. prolonged charging periods at a relatively low rate.

 

Nick

Edited March 17, 2012 by Nickhlx

[by'eck]

Well described Nick, and that is what I would expect to see. The point at which the current starts to increase would be, I agree, the point at which significant gassing has started; above this point, as has been agreed on previous occasions here, you can continue to supply as much energy as you wish but its only function is in converting water into gas. The level of charge of the battery is not increased, it is "full". I would contend however that over that range from 14.4 to the gassing voltage, if the battery will take no current (other than a momentary pulse at the instant after the increase in voltage) then the battery was fully charged at 14.4 - after all, how can you increase the level of charge of a battery if you are supplying zero energy to it?

 

Have a look at this and see if it helps explain your lost capacity.

 

I know Charles gets bad press from time to time and can be his own worst enemy, but these tests seem quite clear.

 

I wonder if regular charging to a lower than optimum voltage allows some form of minor conditioning (slight sulphation?) which could be broken with a discharge/re-charge at higher voltage regime.

 

In the 70's I worked on Outside Broadcast vehicles fitted with shed loads of traction batteries. Twice a year we cycled them with a gently but deep discharge followed by a long charge with the not so sophisticated chargers of the period.

Edited March 17, 2012 by richardhula

[Keeping Up]

I agree with your comments about Charles Sterling, but I don't think this article explains anything new here. It proves without a doubt that a higher charge voltage will drive more current into the battery, a fact of which there is little doubt. It also explains how you can use a particularly high charging voltage such as 14.8 to charge them very quickly and effectively, provided you sense when the battery is actually full and you then back the voltage off to prevent excessive gassing. Again, no problem with the theory behind this . It quite correctly observes that a battery that takes little or no current (1 Amp he suggests) at 13.2 volts is demonstrably not yet fully charged; I wouldn't argue with that either. However what it most certainly does NOT do is to advocate the continuation of a high voltage, once you have passed the point where the battery at 14.4v would take only 1 amp, because gassing would be inevitable, and definitely unwanted in the case of a sealed battery

 

So unfortunately I don't believe it shows any reason for the loss of capacity. Most days after ceasing to take more than a couple of Amps at 14.4v my sealed Numax batteries then spend several hours at that voltage of 14.4, with the occasional rest period that the Adverc provides to eliminate any gas bubbles, so I still can't work out why they lose capacity.

 

The first two sets of batteries that I returned under guarantee were all open-cell Varta types, and in each case the manufacturer did manage to restore some capacity by repeated cycling to a very high voltage indeed; but it took nearly two months of daily cycling before they recovered to 50% of their nominal capacity, which was why the suppliers admitted defeat and provided me with these Numax instead. They've now been on float at 13.2 all winter, I wonder if they've improved?

[pistnbroke]

Certinly standing orders on a submarine to cycle the batteries

[by'eck]

I agree with your comments about Charles Sterling, but I don't think this article explains anything new here. It proves without a doubt that a higher charge voltage will drive more current into the battery, a fact of which there is little doubt. It also explains how you can use a particularly high charging voltage such as 14.8 to charge them very quickly and effectively, provided you sense when the battery is actually full and you then back the voltage off to prevent excessive gassing. Again, no problem with the theory behind this . It quite correctly observes that a battery that takes little or no current (1 Amp he suggests) at 13.2 volts is demonstrably not yet fully charged; I wouldn't argue with that either. However what it most certainly does NOT do is to advocate the continuation of a high voltage, once you have passed the point where the battery at 14.4v would take only 1 amp, because gassing would be inevitable, and definitely unwanted in the case of a sealed battery

 

So unfortunately I don't believe it shows any reason for the loss of capacity. Most days after ceasing to take more than a couple of Amps at 14.4v my sealed Numax batteries then spend several hours at that voltage of 14.4, with the occasional rest period that the Adverc provides to eliminate any gas bubbles, so I still can't work out why they lose capacity.

 

The first two sets of batteries that I returned under guarantee were all open-cell Varta types, and in each case the manufacturer did manage to restore some capacity by repeated cycling to a very high voltage indeed; but it took nearly two months of daily cycling before they recovered to 50% of their nominal capacity, which was why the suppliers admitted defeat and provided me with these Numax instead. They've now been on float at 13.2 all winter, I wonder if they've improved?

 

Pardon me for saying it Allan but you seem to be sticking to your beliefs here which may be the correct ones, but without entertaining any other idea's. I know the Sterling tests are nothing new, I first read of them about 10 years ago.

 

I'm not sure where you got the idea of continuing to charge at a high voltage after gassing has started. It certainly wasn't from me or the Sterling article as far as I can see. What I advocated was a fresh start from a partially discharged battery to a higher absorb voltage for a fixed time only & whilst the battery was taking current, i.e. not yet gassing. This as a means to possibly regaining some of the lost capacity.

 

What I proved to myself was that long trouble free life was had by using 14.9 v as an absorb (only) voltage for a fixed time (2 hours I believe) as set on my Victron Combi with lead calcium batteries.

[Keeping Up]

Actually Richard I am not so much sticking to my beliefs as repeating the positions held by the technical departments of both Adverc and ManBat, in the hope that this will flush out some counter-proposals that I can put to them. Not so much Devil's Advocate as his intermediary perhaps - and in that role I am delighted to be seeing some new thinking around the issues.

 

I have to say that I have been 100% satisfied with the helpfulness, service, and technical responses from both these companies with just one glaring exception; their total inability to suggest any valid reasons for the loss in battery capacity. They have both inspected my installation, agreed with my voltage and current readings, agreed that my charging regime is adequate, agreed that the Adverc controller is providing the charge which the batteries require, and agreed that the batteries are becoming sulphated - yet they can offer no cure (although perpetual replacement under guarantee would suit me as n excellent cure).

 

Much as I like the idea of charging at a higher voltage under controlled conditions, there are some considerations that make it difficult to achieve, especially as a regular component of battery maintenance. While I am cruising for the summer, it is not that easy to derive and control the necessary voltages from the alternator, and I am concerned lest I should at any time produce a voltage high enough to damage any of the electronic equipment on board; yes I can disconnect everything including the various devices that need a permanent feed to maintain their memories and other settings, but it's a pain in the axxe to do so (and I get complaints from Pingu when all the electrics are disabled too). Anyway, surely the idea of a charging system with a controller is that it should be capable of charging batteries adequately.

 

So please, keep the ideas coming.

 

Returning to Mr Sterling's piece, I found it instructive to turn his first graph inside-out, and to plot it showing how the supplied current varied with the battery's state of charge, for a range of applied voltages. This comes out as looking very different from the usual current-versus-time graphs that are printed, such as those lower down the same article. Although the plotting is very inaccurate because I couldn't read the original very accurately, and of course the absolute values of current are relevant only to his particular battery, the results are remarkably like a series of straight lines and could perhaps be used (and extrapolated) to estimate SoC for a known battery bank if the values of voltage and current are known from a glance at the dashboard.

 

 

Charge Current by Keeping Up, on Flickr

 

Any thoughts on that ?

Edited March 18, 2012 by Keeping Up

[smileypete]

There's a bit in The Battery FAQ about calcium batts:

 

"7.1.3. Wet "Maintenance Free" (Ca/Ca)

 

Wet "Maintenance Free" batteries have a Lead with Calcium (Ca) alloy in the positive and Lead with Calcium (Ca) alloy in the negative plate chemistry or formulation, for example, Johnson Controls [formally Delphi], General Motor's ACDelco, or East Penn. They are available in non-sealed sealed (with removable filler caps) and sealed (with non-removable filler caps) versions. The non-sealed versions are recommended for use in hot climates, so lost water can be replaced. The advantages and disadvantages of wet "Maintenance Free" (Ca/Ca) car and deep cycle batteries over wet Low Maintenance (Sb/Ca) are:

 

Less preventive maintenance due to less water loss

 

More forgiving when accidentally overcharged

 

Require a slightly higher (.45 VDC) absorption charging voltage

 

Reduced terminal corrosion and ventilation

 

Smaller self-discharge rate

 

Less risk to consumers because there is less to service"

 

So maybe the question to ask Adverc/Manbat is whether the batts can be charged at 14.8V fine.

 

Experience does seem to show that where the batts can only be charged to 14.4V, bog standard non-sealed leisure/truck batts are the least risky option.

 

If concerned about higher voltages and equipment, a big diode in the supply lead (some bridge rectifiers have handy connections) will drop the voltage back down.

 

cheers,

Pete.

[Keeping Up]

I asked Adverc whether, in light of this article (I sent them the link), they still recommended that their Varta lead/calcium batteries should be charged to 14.4 volts. I have just received their emphatic confirmation that 14.4 is the correct charging voltage for those batteries.

 

I have also asked the same question of ManBat, in respect of both Varta and Numaax batteries. I have not had a reply from them yet.

[smileypete]

I have also asked the same question of ManBat, in respect of both Varta and Numaax batteries. I have not had a reply from them yet.

Why not ask Varta if their sealed calcium batts can be charged to 14.8V, get it from the horse's mouth, so to speak.

 

cheers,

Pete.

Edited March 29, 2012 by smileypete

[jakub]

I decided to remove diode thing in the end and now I am charging these batteries at 14.4V. At the moment they are on constant charge from solar at 13.70v anyway, so I expect them to serve me for years.

Not fussed by quick charging too much, prefere reliability.

[Keeping Up]

Why not ask Varta if their sealed calcium batts can be charged to 14.8V, get it from the horse's mouth, so to speak.

 

cheers,

Pete.

 

The Varta batteries were not sealed. Their website doesn't seem to show any 110 Ah batteries any more, nor make any reference to the "hobby" range at all.

 

I'll see if Numax care to comment if I ever manage to find any contact details for them.

Edited March 31, 2012 by Keeping Up

[Arthur Brown]

13.7 is a good float voltage, so stick with that. OVERfast recharging will kill batteries so with a fair generator you should get good life. Solar is getting a good reputation for charging batteries well and steadily and avoiding the killers of over charging, overfast charging and standing while discharged. IMO solar may add 30 - 50% to the life of your batteries just by keeping them in good condition unattended. -Good solar controller essential

[Theo]

I might be mistaken, but as far as I am aware most sealed batteries should not be charged at more than about 14.4v.

 

I don't know about the diode modification to your alternator, but couldn't you just remove it?

 

I'm sure someone will be along shortly to give some better advice.

 

The data sheets on my C90s say 14.2V

 

N

 

Before you do that I would try measuring battery voltage at the battery terminals. If the 14.9v you are seeing is at the alternator output terminal it will be a little less at the battery, but by how much I can't say.

 

Certainly the higher the voltage the better within the limits of the battery type. The Numax Leisure range are sealed but vented flooded cell batteries so I doubt any harm will be done with your present alternator arrangement.

 

As the charge rate falls with the increase in battery voltage the voltage at the battery will approach that at the alternator.

 

Nick

 

 

[Keeping Up]

Just a follow-up to this thread.

 

When my Numax batteries were supplied new last year they behaved rather oddly. After a few weeks they still behaved oddly, and also showed a loss of capacity.

 

When they were returned to me after testing by the supplier, as "some loss of capacity but no fault found", I assumed that they were the same batteries that I had sent back to them for testing. But now I'm not so sure.

 

EITHER a winter spent with them on float (at 13.2 volts I believe) has performed an utter miracle, OR ELSE they were exchanged for a new set of batteries but the supplier didn't want to admit that the originals had been faulty. I say this because they are now performing in a way that they never performed when new or at any time during the last few weeks of last summer; they are now performing exactly like normal batteries, and just like all the sets of batteries that I have had in previous years. I'm not sure what their capacity is now, as with out delayed departure this year I have so far only spent a fortnight using them, but all I can say is that the voltmeter is finally reacting exactly as I would expect it to.