Charging on damaged batteries.

[kasperb]

Hello folks

I have a few newbie questions on "broken" batteries from an electric car.

The scenario:

24 2V maintaince free batteries, 150ah (5 hour) are connected in a series providing 48V to drive the car.

The car has not been used for 1½ year, which means that the batteries are close to, if not already, dead.

When I initially got the car each battery gave approximatly 0.3v-0.7v and I thought that the battle were over even before it started. - even though I tried to connect a 10A battery charger to 6 of the batteries with 13.5V charge, and after some time, the amneter started to rise, when the amneter hit 2A-4A I went on to 6 others and so forth until there were reaction on all 24 batteries, this took a few days.

At this point I thought that the cars charger might be able to take on charging (instead of the external battery charger I had been using) - but that didnt work - it would charge for some hours and the stop again.

At this time (after the batteries had rested for 5 hours with) the charge were at 0.7V-1.04V.

Now I'm back on 2 external chargers, each charging 12 batteries at 26V/10A, they have been charging for almost 2 days now - the amneter on both says close to 7A, and it seems that it has stopped climbing.

When I messure the voltage on the individual batteries, when charging, there are some "abnormalities", most of the batteries is in between 1.5-1.8V but a few batteries (as in two batteries) is  up on 2.5V, and a single one up on 3.3V.

Which brings me to my question (one that I should have asked before "try/error")

How can I regenerate (if possible) these kind of damaged batteries - and are the approach that I've taken completely off track?

(As stated I'm newbie, so here's one from the newbiebook)

when the amneter on my charger says 7A and have stoppet climbing - what information can I get from that:

1. : Why did it stop climbing and why 7A?
   
2. : Should I expect it to fall again when the batteries stop accepting charge?
   
3. : The two batteries where the voltage is approx 2.4-2.6V when charging and in particular the one with the 3.3V - are they "even more" dead and am I killing them more by doing what I'm doing?
   
   

I hope I've made myself undestandable, and thanks in advance for any help and guidance.

*/Kasper

[AbyssUnderground]

It sounds like these have sulphated so much they wont accept the charge, its just going in one end and out the other. Try a charger with a slightly higher voltage of say 14 or 15 and leave it on for a few days and see what you get.

[altosack]

Caveat: I have rejuvenated a few cells, but my experience is limited, most of the below is talking to others in the home power field and reading.

The cells that are 2.4-2.6 V are good; the > 3 V cells are probably gassed dry (yes, maintenance-free can gas too, you just can't put it back in like flooded batts) or are really sulfated; i.e., they can accept a charge, they just can't keep it (sort of like accepting a reservation but not keeping it). Since they can't hold a charge and are overvoltage, they are "taking away" some voltage from some of the near dead cells that aren't charged yet and need a higher voltage (per cell) to charge.

I feel that most batteries can be rejuvenated, but it takes a lot of patience and know-how, and you have to be able to treat each cell a little differently.

For your questions:

1. The charger is probably regulating the voltage, and some of the bad cells (+3V) are allowing the whole string voltage to be up around the regulation voltage (it should be 27.6-28V, not 26V, though).
   
2. I think that some of the lower V cells are still accepting a charge and it would eventually go down, but I would not continue the way you are (see below).
   
3. The 3+V cells are not good, but the 2.4-2.5V cells are probably good; they are just gassing to stay at that voltage, and NO, do not continue what you are doing.
   
   

I would take the good cells (2.4-2.6V) out of the string, and charge what's left. You need to keep an eye on it, though, because your charger expects a certain nominal voltage and you don't have it. The cells that are still good are accepting an over-voltage charge and are slowly being damaged by what you are doing.

As soon as any more cells make it to 2.3-2.4V, take them out, they might be good. You might be able to rejuvenate the rest a little (probably not more than half capacity, at best), but you will need a charger that can charge individual cells and a battery desulfator (not a commercial one, you'll have to build your own; google it to get the circuit you need).

If you're not up to this (and it will be a lot of work and close attention to get maybe half the capacity in half of the bad cells), take them to a recycling center.

Dave

[Flux]

I think he means battery voltage not cell voltage.

Sorry I can't be optimistic like the others, try anything you can but from past experience you are wasting your effort.

Flux

[Roamer195]

kasperb,

 Here's what I would do. This has never failed to work for me, except in cases where the batteries have been physically damaged inside. Car and trolling batteries can sometimes be restored this way if the grids haven't been eaten away already. Regular deep-cycle battery plates seem to really love this "therapy".

 Make two 12v banks and wire them in parallel.

 Take a regular 12amp automotive type charger and connect it to a 1 Farad stereo capacitor.

 Build low impedance pulsing circuit to discharge the capacitor into the battery bank. You can do this with bipolar transistors, mosfets, heavy-duty solid-state relays, etc...

 Just make sure you use less than 12" lengths of #10 (or heavier) wire to connect the capacitor, pulse switch, and battery bank connections.

 Set the pulse width so that the cap is discharged down to about 80% with each pulse Then all you need to do is adjust the pulse frequency up or down to change the total amperage drawn from the battery charger on the front end. Adjust it for about 6 or 7 amps drawn from the charger.

 If you put a scope across the capacitor, you'll see a very low voltage sawtooth waveform. The battery only sees the small bursts of current from the capacitor discharge.

 Run the pulser for a few hours. Then run a C/20 discharge rate load using a power inverter, until it shuts itself off.

Run the pulse charger again until all the cells are fully bubbling. Then run the C/20 load again and see how long the bank holds up.

If you cycle back and forth like this several times, you should see the total stored charge growing each time. Check the SG in the individual cells to see where the real individual charge levels really are.

As long as you don't have any major build up of crud in the bottom of the battery that might short out the plates, and as long as the plates are in good mechanical condition, this should bring your deep-cycle batteries back to a usable condition.

Once you've "opened up" the battery capacity again. Leave the pulser on for a day or so to get a good equalizing charge on the cells. There will be much slow bubbling.

R

For more on this subject you might want to start here:

http://www.fieldlines.com/story/2004/2/8/2111/95728

[asheets]

Go a search here for watgas.gif, and give those batteries a good "buzzing".  Does wonders for me.

[kasperb]

Hello Flux

I have 24 batteries that each should give approximatly 2V, they each were at 0.7-1.04V

They are connected in series of 6, which should have given approx 12V, when I measured on each serie they was between 5V and 5.8V.

*/KasperB

[kasperb]

I'm not sure I undestand this, there is no results

[kasperb]

Hello

Thank you for your responses (even thouth they confused me a bit) - I'll try to summarize a bit, instead of working of different threads.

Suggestions:

1. : "Try a charger with a slightly higher voltage of say 14 or 15 and leave it on for a few days and see what you get."
   
2. : Take out the cells with a voltage of 2.4-2.6V and charge on the rest. (freely quoted)
   
3. : Roamer195
   
   

"Make two 12v banks and wire them in parallel" ... "Farad stereo capacitor."

 "Set the pulse width so that the cap is discharged down to about 80% with each pulse Then all you need to do is adjust the pulse frequency up or down to change the total amperage drawn from the battery charger on the front end. Adjust it for about 6 or 7 amps drawn from the charger."

1. +2: I can raise the voltage from the chargers up to approx 30V/10A - in 0.1V intervals, the reason for charging at 26V was that I was afraid of overheating the batteries (and I'm charging 12x2V at at time), so I can set the voltage to whats appropriate if I removed some batteries.
   
3. : I'm not sure I have the capability to do what you are suggesting, is it possible that I might be able to lease/loan some equipment by an autogarageman that does what you are suggesting (pulsecharging).
   
   

It seems that there are no uniform way of regenerating batteries, but just to be sure, does all three methods apply to closed "maintainence free" gel batteries ?

*/Kasperb

[Flux]

If that is cell volts then you may have a chance.

One method that may be worth a try is to drain the acid off and fill with water with a spoon full of EDTA per litre. Leave to stand for a while and charge at a fairly low current and see if the s.g rises or if the volts come up.

If you get some response then cycle a couple of times. If you look to be having reasonable luck then replace with acid of the correct sg for about half charge. continue to charge and partly discharge until sg doesn't rise any more and adjust to correct sg.

I have had no luck with small inductive pulse desulphators, perhaps the more drastic capacitor method will be effective at blowing away shorts (dendrites) that seem to form when you think you are going somewhere.

Good luck

[pepa]

hi flux, do you have a supplier for the edta, i printed a pape( new life for sulphated lead-acid cells) by richard perez a while back, but have not been able to locate the chemical locally. thanks, pepa.

[Roamer195]

Kasperb,

 I don't mess with sealed batteries. They can get dried out too easy for my tastes. Unless you have a good way to rehydrate them, any sort of standard restoration techniques would be of questionable effectiveness.

 Maybe someone else here will know more about restoring gel cells.

R

 

[Flux]

The stuff is supposed to be a common food agent but for all that it seems difficult to get.

I think you need the tetra sodium version for batteries. Try laboratory suppliers perhaps.

This is a U.K. reference but you must be able to find a source nearer home.

http://www.courtiestown.co.uk/SHOP.htm

Flux

[jimjjnn]

Auto supply stores used to carry EDTA.

It had many different labels, such as battery restorer, battery boost and other names that I don't remember

[ghurd]

I think Richard Perez got it from a winery. ?

They, winery guys, were helpful to me, but the cost was crazy. More than new batteries.

It is widely available in the US.  Ask for "Not Food Grade".

G-

[zap]

I'm pretty sure the actual watgas.gif (a gif [i.e. picture] of the watgas circuit) has disappeared from this site and the internet.  I think I have this gif in my files somewhere and if you still want to see it I'll dig it up and post it.

[asheets]

Here it is:  http://www.otherpower.com/images/scimages/231/pulsecrg.GIF