Thinking about fully discharging (deep cycling) my power tool batteries to try and revive them

[Robert Hill]

Hi all,

I've been reading on the excellent website battery university: http://batteryuniversity.com/learn/article/how_to_restore_nickel_based_batteries

About totally discharging NiCd batteries in order to somewhat restore capacity after batteries have been used for a long time.

Has anyone used this technique and did it work?

I'm thinking of attaching a bulb or LED across the battery pack with a resistor to keep the current down and just leaving it until the light turns off, then recharging the battery.

What do you recon?

 

[Martaine2005]

Hi Robert,
My 29 year old nicads still work just fine. Although flight time does deminish.
I have always charged fully three or four times a week from the last charge state and completely drained them by leaving my receiver on all night once or twice a week.
I also fast charged on the field too.

However, it does depend on how long the nicads have been left before charging.
I have 20 year old nicads left discharged that are now dead.
They used to call it the "memory effect", which did seem to be true.
Changing the rate of charge, length of charge and of course the discharge seemed to help with no "memory" on the battery.
All that said, I wouldn't trust mine for more than testing on tethered ground only.
But the transmitter batteries still run for 22 hours. The receiver batteries for about 3 to 6 hours depending on the model and amount of servos obviously.

Martin

 

[Bluejets]

Older nicads would respond to some degree and some would last for ages.
I built a "cycler" that would discharge a fully charged pack at a constant low rate(say 300mA), measure the time and compare this to the manufacturer specs for C20 rating or better.
These days there are smart chargers that will do the job for many types of battery in the one unit.
Newer batteries these days are basically throw away, especially for r/c aircraft work where even back 20 years ago I would chuck them out after 2 years.
My conclusion was, they had come up to manufacturers specs, done the job. Aircraft, engines and associated r/c gear were worth hundreds of times more and not worth the risk.

 

[Martaine2005]

Possibly that was your failure then. A constant rate of discharge 'did' have the memory effect with these batteies.
That's why I said I always changed it.

Martin

 

[Rowdy]

My experience with NiCads is that they will last almost forever if manuf with good materials, AND properly maintained. If you use them (Just regular use and charging as needed, except once a month you drain it all the way down and then fully charge it, probably a couple of times). I think what actually happens here is that in the process of charging and discharging you keep the molecules of the Ni and Cd, and the electrolyte, active and warmed up gaining and losing electrons from their bonds. If they are left idle the charge slowly dissipates, leaving the molecules to a stable neutral state where they tend to form crystalline structures (I think they are called dendrites, a lot of this is off the cuff, been awhile, SO) that the valence electrons are locked stable and neutral in the crystals (doesn't battery well). I think that the only thing that really dies in a nicad is the electrolyte. No matter what happens eventually it will evaporate (I think mainly effected by the quality of the product, and the quality of the construction of the case to contain it). Improper use or abuse will accelerate it. I have learned how to rejuvenate them to some degree. When I have left them unmaintained for a long period the above happens and they will hold only a very small charge, or maybe none at all, the not at all units are real hard to recover. I think what happens here is that you have to walk a tight wire in recovering them between running enough current through them to warm them up enough to melt the crystals without getting them hot enough to boil off the electrolyte. As the electrolyte boils or evaporates off it increases the concentration in the electrolyte and the crystals grow more readily and it becomes less viable. So it is a downhill slide but proper care can help the situation greatly. The technique I use to revive them is to drive them with a bench top power supply with constant current/ constant voltage controls. 1.2V cell I set voltage to 1.2 volts and see how much current it will draw. If it draws 3 ma it has a bad problem, if it will draw half an amp, it's in pretty good shape. I start raising the voltage while watching the current until you get around 100 ma, and according to how bad it is the ma will slowly/quickly start to decrease as a charge is taken on. You wear a safety shield and some gloves in case of explosion. And yes I have. You feel the battery for temperature increase. I tend to pulse the power on and off to insure a slow temp increase to prevent any greater loss of electrolyte. As the charge increases the current decreases, Here becomes a reasoning challenge. Feeling the batt temp (if the batt gets uncomfortable to hold it is TOO HOT) and watching the current draw, start increasing the voltage to bring the current back up. After a while as the temp comes up you will reach a point where the crystals start to melt, you will know because the current will stabilize, and or start to increase with time rather than decrease as the battery starts to function more properly again. Keep the temp and current within reason until charged and then immediately discharge it and do it again. I have had to cycle a batt 3 - 4 times to revive a bad one. Some are just locked dead. Hopefully I conveyed my theories clearly enough to be of some help somewhere.

ljl

 

[Robert Hill]

Thanks for the feedback.

I've heard some items will stop working when batteries are still somewhat charged as the required voltage will no longer be present after only a small loss of charge.
Any suggestions for fully discharging the battery separate from the tool itself?

 

[Bluejets]

Possibly that was your failure then. A constant rate of discharge 'did' have the memory effect with these batteies.
That's why I said I always changed it.

Martin

No.... as the above test was done perhaps once every 2 months and for the purpose of gaining the cell capacity average , it gave no memory effect.
I made many of these units and all worked successfully.
It was even an indicator of the dreaded "black wire" which was another unseen problem.

 

[Martaine2005]

Nice info there Bluejets.
I have to admit that the 'black wire problem', I have never heard of..
Please share more info.

Martin

 

[Rowdy]

If your talking about a normal battery cycling,the discharge has been accomplished when the tool stops working. If you are talking about regenerating the bat then you have to understand that it is a risky process that at very best will cause some degeneration of the over all life and quality of the bat, but should/could greatly increase the usable performance level over the short term. I just use a current limiter resistor 1W. Has to be selected according to bat pack voltage, charge holding capability of the bat. Needs to keep the current down between 20 ma and say 400. This needs to start low at around 20 - 40 ma and increase so that the total time of discharge to about 25% of spec takes about 4 hours. And this will always vary so it needs to be adjusted intuitively and quickly, and frequently as the discharge proceeds. The more you have done this the easier it will be. Hope this helps.

 

[Bluejets]

In dc circuits, the copper wire on the negative (for some unknown reason....at least to many) will deteriorate and go black and eventually it will rot completely away. Do not know why.

The effect in r/c is that the charge and discharge is effected, and eventually the black wire rot will work it's way from the battery to the switch and I have also seen it penetrate well into the receiver making the complete system unrepairable.

At any early dectection,any affected bits would be chucked immediately and trace through until clean wire was found.

Sometimes detection could be when a flyer would complain of his system appearing to have a flat or near flat battery after having fully charged the night before or his battery appearing to get deteriorating capacity over time, much the same pointers as cell memory.
Cell memory is the result of shallow charge or/and discharge to a voltage level less than the normal range on NiCads of approx. 0.8V to 1.4V on a constant basis.

Used to see the black wire rot initially during my apprentiship with the old 300 ohm TV downlead ribbon from the antenna for whatever reason there also. Again only in one of the conductors.

Initial detection in r/c was during battery pack capacity tests, checking the battery plug for any signs of black near the terminal pins which are usually gold or silver.
If the latter then a tug on the plug would usually see it stretch the plastic and snap the wire with the black obviously visible.
Either that or cut into the lead and check as the lead is cheap compared to crashing a model.

 

[Rowdy]

If your talking about a normal battery cycling,the discharge has been accomplished when the tool stops working. If you are talking about regenerating the bat then you have to understand that it is a risky process that at very best will cause some degeneration of the over all life and quality of the bat, but should/could greatly increase the usable performance level over the short term. I just use a current limiter resistor 1W. Has to be selected according to bat voltage, charge holding capability of the bat. Needs to keep the current down between 20 ma and say 400. This needs to start low at around 20 - 40 ma and increase so that the total time of discharge to about 25% of spec takes about 4 hours. And this will always vary so it needs to be adjusted intuitively and quickly, and frequently as the discharge proceeds. The more you have done this the easier it will be. Hope this helps.

I forgot, I do not recommend regen on a battery pack, the only way to regen NiCd's is individually.

 

[Bluejets]

I doubt many packs would have that possibility open to them.

 

[Rowdy]

Open, that is the key word here. I haven't found a pack that I couldn't open one way or another. You just don't have control over current and temp of each individual bat if you don't have individual units, and control of the process is essential. If you try to regen a PACK you will GREATLY increase the odds that you will throw ALL of those batteries, and the shell in the trash. Whatever, creativeness is the name of the game when your haking. And that is exactly what this is. You are attempting to bypass the engineers attempts at forced obsolescence, and that is basicly haking. If you can't break it down to individual cells don't waste your time and energy, your chances of success decreases greatly with the number of cells in the pack. It just will not work. Success or failure is your choice. Just look for seams in the plastic shells. Most are friction welded shut somewhere, and can more easily be broken into there, if necessary with a dremmel tool. Regen or replace individual cells and then super glue is your friend. If you have to grind a seam, when you close it you may need to use the super glue, baking soda filler technique to reassemble it. Make it work, geterdone mentality. That's what got our astronauts back from the moon when they faced equipment failure and death. Surely a battery pack isn't that great of a challenge.

 

[Bluejets]

Yes well that may apply to "hacking" however my experience within over 50 years of r/c work that simply is not the case.
Op may be interested in "hacking" though so go for it.
Just be aware that nicads can deliver quite a large short circuit current that can cause burns and explosions.

 

[Rowdy]

Oh I see. That r/c work really is some frontier breaking, ground shaking experience. I guess I will just have to plod along learning what I can where I can, even haking. Those that are hakers will explain to you that it is not "hacking" it is "haking" Haking is simply reverse engineering an item and then making changes in it (hopefully in an effort to make it more reliable, more serviceable, more adaptable, a better product than the crony capitalist’s created to reap money from you). Oh and thank you for the warning that a battery stores a charge of elecemtricity, I would never have suspected that.