Posted by Piccolo Pete on July 5, 2008, 8:18 pm
> ====snip====
>> So I'm not sure what you're saying here. Sounds like the really old
>> batteries could deal with their polarities being reversed but the new
>> ones
>> can't. By the way, I already blew up one charger by accidently reversing
>> polarity. I don't want to blow another one.
> The preformed plates type of battery can be reverse charged but you
> need to totally flatten them first and use some sort of current limiting
> at the start of the reverse charge cycle since you can't totally flatten
> a battery within the 24 hour grace time allowed before the lead sulphate
> starts to crystalise into a form that no amount of charging will be able
> to completely reverse.
> This sort of treatment should only be resorted to when all else fails.
> In practce, a lead acid battery can tolerate having one or more of its
> cells reverse charged provided the whole battery isn't left in the
> resultant 'flattened' state for very long (usual advice is to put it on
> charge within 24 hours of being fully discharged to avoid significant
> permanent damage).
> Batteries assembled with other forms of secondary cell such as NiCads
> and NiMH types cannot tolerate such abuse where any such reverse
> charging would permanently reduce their AH capacity.
> Equipment designed to be powered by such batteries have battery voltage
> monitoring circuitry to disconnect/switch off once the per cell voltage
> gets down to around 1 volt in order to avoid this harmful condition
> (lowest capacity cell being reverse charged by the discharge current
> from the rest of the battery pack).
> The problem of reverse charge protection increases as more and more
> cells are used to create higher battery voltages. Equipment powered from
> a 2 cell battery pack (eg. a digital camera) often use the battery
> voltage monitoring primarily to trigger a controlled shutdown to protect
> the equipment rather than for the sake of the battery pack's health. It
> just so happens (rather neatly) that such equipment protection happens
> to save the battery pack as well.
> The ideal "battery" would consist of just one cell since this avoids
> the problem altogether. The problem with this ideal is that very little
> equipment can be directly powered from 1.2v and the losses in even the
> most optimised of switching converters required to generate the higher
> voltages required become unacceptable when more than a watt or two is
> required.
> The problem is eased somewhat when a 2 cell pack can be used. At a 2
> volt end point, it's virtually impossible to reverse charge a cell and
> the two cell battery pack represents an optimum battery cell count size
> for a lot of portable equipment which can be designed to work off a 2.4
> volt supply.
> Considering the reverse charge issue with NiCad and NiMH batteries,
> there's a lot to be said for the good old fashioned lead acid battery,
> especially when 12 or more volts at high power levels are required. You
> just have to make sure you're using the right type of lead acid battery
> for the type of service they need to provide (and the appropriate care
> and attention).
Tilt... God, I've been doing electronics for over thirty years and you guys
make me feel like a total idiot when it comes to batteries. I'll try
rereading your post a few more times to see if I can get a grip on what you
are saying.
Thanks for the info though.
Bart
Posted by Eric Sears on July 9, 2008, 12:16 pm
>I knew a guy who used to sell " reconditioned batteries", he used to
>swear that reversing the polarity when
>charging them was his secret ;`) I bought one off him and it lasted over
>a year before it died.
I've been watching this thread to see what this comment came to - re
the reverse charging.
A comment and then two real life "i done 'ems".
Re the matter of "blowing up chargers" - of course if you stick one on
a low resistance battery - ie very flat (but not too sulphated), or
reversed - well the current will likely kill the charger - that's why
you would use current limiting like a bulb in series with the charger.
About 15 years ago, my son "rescued" some old flat 12v,6ah gell
batteries, found by a rail depot. One had "claim" written on it. They
all (about 6 of them I think) measured between about 2v and 6v as I
remember. Trying to charge them resulted in less than about 1mA (much
less I think) in the "charging" direction. They appeared very
sulphated, with 1000's of ohms impedance.
Then I discovered that with a reverse charge voltage, the current very
gradually increased. I watched it carefully until it reached a maximum
and began to decrease again, then reversed the charge again. After a
while (you had to watch it carefully!!) the charging current would
begin to kind of "pulse" up and down, and then begin to run away. Out
of about 6 batteries, I was able to restore 3 of them to some
semblance of working order. In fact I still USE two of them today.
they will still light a 12v,25watt bulb with dropping below 12v under
load, for some while. I use them with electronic circuits - as power
supplies, when experimenting. They are probably about 20 years old
now!
Second, much more recent example.
About 8 years ago I was given a brand new 80ah, 12v deep cycle
battery. I would call it an "ersatz" deep cycle - it looked like a car
battery.
This year I was about to throw it on the lead scrap heap, as it would
take no appreciable charge at all - even after charging for a good
number of days. Note - it had had very little use over the intervening
years, though it had got "left" without regular charging at times.
Then I tried the reverse charge trick. Again, it began with a small
current, which gradually rose, and I monitored the voltage across it
(falling) until it just reached zero volts. I then reversed it again.
After some playing with forward and reverse charging, it now seems to
hold about 40ah, and lights a 60 watt bulb for a good number of hours.
Ok guysand gals - have you tried it?
It doesn't seem to work with all states of batteries (definitely not
shorted cells!), and sometimes they have not recovered. The critical
thing seems to be the point at which the "reversing" takes place.
I don't fully understand the "right" way it might be done - but I DO
now have a useful battery in place of a piece of scrap.
Eric Sears.
Posted by Ron Rosenfeld on July 5, 2008, 11:24 am
>For some reason, most likely laziness, I find a lot of used deep cycle
>batteries in parking lots and such. My charger has a "desulfate" setting on
>it to recondition wet cells. If I find a wet cell that doesn't look like
>it's been through the wringer, do you think it is possible I might be able
>to recondition it and get some use out of it? When my system is running at
>peak, I have more power than my regular house batteries can handle and I was
>just wondering if this might be a cheap way to get more back up power.
>Bart
Depending on what shape they are in, you might be able to improve them by a
controlled overcharge, or possibly with a desulfator. Just be careful to
monitor the water level and the temperatures during this process. If there
is no mfg recommendation, my advice would be to make sure the cell
temperatures stay below about 110°F or so.
Some have found that several weeks of "equalization" might be required
though.
But, if you are going to just add these batteries to your existing system,
you should be aware that mixing batteries is not generally recommended.
You'll probably wind up with a bank that reflects the worst cell condition.
--ron
Posted by Piccolo Pete on July 5, 2008, 1:27 pm
> But, if you are going to just add these batteries to your existing system,
> you should be aware that mixing batteries is not generally recommended.
> You'll probably wind up with a bank that reflects the worst cell
> condition.
> --ron
Certainly not. I would switch the line when one bank is low.
Bart
Posted by Ulysses on July 5, 2008, 4:32 pm
> >For some reason, most likely laziness, I find a lot of used deep cycle
> >batteries in parking lots and such. My charger has a "desulfate" setting
on
> >it to recondition wet cells. If I find a wet cell that doesn't look like
> >it's been through the wringer, do you think it is possible I might be
able
> >to recondition it and get some use out of it? When my system is running
at
> >peak, I have more power than my regular house batteries can handle and I
was
> >just wondering if this might be a cheap way to get more back up power.
> >
> >Bart
> >
> Depending on what shape they are in, you might be able to improve them by
a
> controlled overcharge, or possibly with a desulfator. Just be careful to
> monitor the water level and the temperatures during this process. If
there
> is no mfg recommendation, my advice would be to make sure the cell
> temperatures stay below about 110°F or so.
> Some have found that several weeks of "equalization" might be required
> though.
> But, if you are going to just add these batteries to your existing system,
> you should be aware that mixing batteries is not generally recommended.
> You'll probably wind up with a bank that reflects the worst cell
condition.
> --ron
I have had *some* luck with the Desulfate setting on my charger, but it's
not a miracle worker or anything. I suggest running the Desulfate four or
five times before trying the Equalize setting. The Desuflate uses little
power so it won't overtax your system (probably). 17 volts was mentioned--I
think that is way too high. It should probaly be more like 15.5 volts for
equalization. If your battery continues to draw high current after being
charged for a long period of time and it feels too warm my experience says
it's wasted and you would just be wasting a lot of power trying to restore
it. Ron says 110F. Maybe stick a thermometer in the cells?
I think the Desuflate setting can be helpful if used occasionally on
batteries that otheriwise are in good condition. Equalization should be
done as routine maintenance on good batteries every four-six weeks or so.
Another trick I have used with a battery with a couple of weak cells is to
remove and save the electrolyte from the good cells, remove some electrolyte
from bad cells, put the good electrolyte in the bad cells and distilled
water in the good cells in an attempt to get the cells more even. It works
sometimes. You don't end up with a good battery but you might end up with
one that is still usable to some extent.
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>> So I'm not sure what you're saying here. Sounds like the really old
>> batteries could deal with their polarities being reversed but the new
>> ones
>> can't. By the way, I already blew up one charger by accidently reversing
>> polarity. I don't want to blow another one.
> The preformed plates type of battery can be reverse charged but you
> need to totally flatten them first and use some sort of current limiting
> at the start of the reverse charge cycle since you can't totally flatten
> a battery within the 24 hour grace time allowed before the lead sulphate
> starts to crystalise into a form that no amount of charging will be able
> to completely reverse.
> This sort of treatment should only be resorted to when all else fails.
> In practce, a lead acid battery can tolerate having one or more of its
> cells reverse charged provided the whole battery isn't left in the
> resultant 'flattened' state for very long (usual advice is to put it on
> charge within 24 hours of being fully discharged to avoid significant
> permanent damage).
> Batteries assembled with other forms of secondary cell such as NiCads
> and NiMH types cannot tolerate such abuse where any such reverse
> charging would permanently reduce their AH capacity.
> Equipment designed to be powered by such batteries have battery voltage
> monitoring circuitry to disconnect/switch off once the per cell voltage
> gets down to around 1 volt in order to avoid this harmful condition
> (lowest capacity cell being reverse charged by the discharge current
> from the rest of the battery pack).
> The problem of reverse charge protection increases as more and more
> cells are used to create higher battery voltages. Equipment powered from
> a 2 cell battery pack (eg. a digital camera) often use the battery
> voltage monitoring primarily to trigger a controlled shutdown to protect
> the equipment rather than for the sake of the battery pack's health. It
> just so happens (rather neatly) that such equipment protection happens
> to save the battery pack as well.
> The ideal "battery" would consist of just one cell since this avoids
> the problem altogether. The problem with this ideal is that very little
> equipment can be directly powered from 1.2v and the losses in even the
> most optimised of switching converters required to generate the higher
> voltages required become unacceptable when more than a watt or two is
> required.
> The problem is eased somewhat when a 2 cell pack can be used. At a 2
> volt end point, it's virtually impossible to reverse charge a cell and
> the two cell battery pack represents an optimum battery cell count size
> for a lot of portable equipment which can be designed to work off a 2.4
> volt supply.
> Considering the reverse charge issue with NiCad and NiMH batteries,
> there's a lot to be said for the good old fashioned lead acid battery,
> especially when 12 or more volts at high power levels are required. You
> just have to make sure you're using the right type of lead acid battery
> for the type of service they need to provide (and the appropriate care
> and attention).