Alkaline battery charging ...

Various articles copied from the WEB 

The following articles are copied from the web. Text is left almost as was found apart from translation where needed. The author cannot attest to the functionality of the circuits presented here. Designs and thoughts, presented here, have been used for the developement of a "new" charger design by the author.

Alkaline battery regeneration (Simple circuit 1)

Introduction

Children's toys devour nowadays tons of battery power. It's heavy for the purse - especially with alkaline batteries. Although these last much longer than the conventional zinc-carbon batteries, they come at a price.

Batteries vs batteries

The alternatively is rechargeable batteries available on the market. They are due to a specified number of charging cycles - gem. up to 500 times for more manufacturers - represent a much cheaper and more ergonomic solution to the conventional battery. Today mainly nickel-cadmium (NiCd) and nickel-Matallhybrid (NiMH) battery round cells are used because they can be used easily instead of normal batteries. But rechargeable batteries are more expensive than alkaline batteries and often live only a fraction of the specified lifetime (charging cycles), especially when they are not handled with care (memory effect). Whoever wants to know more, can choose on of the closing links.

Another problem may represent the battery voltage. This is a nominal 1.2V compared to the battery with 1.5V. Some devices and even toys therefore do not work or only for a short time when you try to replace the batteries with rechargable batteries.

But the real problem is however, that exactly at the moment where the device or toy would urgently be needed this is not operational because of drained batteries. For me this is the case always with the Digital Camera. Although these uses lithium-ion batteries (Li-Ion). But both Li-Ion and Ni-Cd and Ni-MH batteries show this effect; they all discharged by itself - even if they are not needed. These so-called. Self-discharge does not occur in batteries, or to a very small mass. Therefore, batteries can be stored for long without losing much in charge.

The high price and the above-mentioned disadvantages of rechargeable batteries move again many to use the plain batteries, as they are just yet practical, cheaper and easier to handle.

Discard reusing instead

Many batteries end up too early in the garbage because they are eampty after a short period of use particularly in complex electronic devices such as Digital Camera, CD players, Walkman, Gameboy, boombox, walkie-talkie, etc. which are no longer fully functional. This need not be, because the batteries can still be used in other devices for an extended period. For example, in pocket radios, flashlights, TV / video remote controls, digital alarm clock / clocks, mechanical toys (cars, locomotives, dolls), etc. These devices work partly with battery voltages less than 1V still properly. Especially so-called. Kitchen clocks, which with a AAA Round cell operated AA or function due to their low power consumption even for months and even years! But also for the power-hungry battery consumers there was an alternative; the alkaline battery regeneration. More on this in the next section.

If the battery is definitively no longer usable, then please dispose of it properly.

According to the current legislation need batteries be returned to vendor or other collection points.

What the industry conceals!

The consumer is tricked by battery manufacturers due to statements and inscriptions, eg on alkaline batteries with the note

WARNING: Not rechargeable!

or even better with the addition

Risk of explosion!

which are just plain wrong!

Correct is:

• Alkaline batteries can be quite a few times recharged or regenerated.
• Alkaline batteries can not explode, but probably other battery and battery types may, particularly if mishandled.

A scientific paper by Dr Rolf Zinniker (ETH Zurich) takes the interested reader under Zinnikers battery and battery Sites

Regeneration of alkaline batteries

! ATTENTION !

The instructions described here apply specifically for alkaline batteries.

Conditions

To regenerate alkaline batteries successfully, please note the following:

• The alkaline battery should be only partially discharged - Battery voltage> = 1.2V
• Fully discharged alkaline batteries <1.0V can no longer be regenerated
• The internal resistance of the alkaline battery should be <5 Ohm
• For regeneration of the alkaline battery a special charger is needed
• An alkaline battery can be regenerated up to 3 - 10 times - depending on the brand
• The loading capacity decreases with each regeneration

Determining the internal resistance

According to the above equivalent circuit, the internal resistance of the alkaline battery be determined as follows:

1. With a digital voltmeter or -Batterietester the open circuit voltage (no load resistance RL) of the alkaline battery as possible accurately measure (Example: Uo = 1.34V)
2. Load resistor to the positive (+) and minus (-) poles of the alkaline battery (Beipsiel: RL = 47 ohms)
3. With load resistor connected (RL) again the alkaline battery voltage measure (Example: UL = 1.25V)
4. Internal resistance gem. the above formula calculated (example: Ri = 47 ohms * (1.34V - 1.25V) / 1.25V) -> R = 3.384 ohms)

Features brand new alkaline batteries

Type:	Uo:	Ri	Charge (mAh)	Wh	in J (joules)
AAA, LR03, AM4	1.6 - 1.65V	<0.5 Ohm	1150	1:41	5071
AA, LR06, AM3	1.6 - 1.65V	<00:25 Ohm	2122	2.6	9360
C, LR14, AM2	1.6 - 1.65V	<00:15 Ohm	7800	9:56	34398
D, LR20, AM1	1.6 - 1.65V	<00:07 Ohm	17000	20.83	74970

Charger for alkaline battery regeneration

In the charge / regeneration alkaline batteries following points should be noted:

• The charging voltage must not exceed 1.7V because the alkaline battery otherwise undergoes irreparable damage through the so connected chemical process and oxidation there.
• The charging current should be moderate (approximately 20mA - 80mA, 100mA max). With too high a charging current inside the alkaline battery leads to a high pressure due to the accelerated chemical conversion process that consequently leads to the rupture of the pressure membrane on the negative alkaline battery pole and thus battery electrolyte leakage arises. The result is not an explosion, but the well-known mess caused by the leaking battery acid.
• The charging process should be stopped when it reaches the final voltage 1.65V (max 1.7V). More charging does not increase the capacity but only shortens the lifetime of the alkaline battery due to overcharging.
• Do not attempt recharge alkaline batteries with charging devices especially rapid charger for NiCd or NiMH batteries. The charging currents are too high and result in "frying" the alkaline batteries a short time. The consequence of this is? Right: no explosion, but a mess.

So, the charge / regeneration of alkaline batteries a special, suitable charger is required. Unfortunately, there are on the market only a few chargers for regenerating alkaline batteries and of these only few models are good. In addition, these are much more expensive than the known NiCd or NiMH battery chargers.

Actually, it should not be too difficult to design a charger that is not just beyond the household budget of a small family.

Prototype and schematic

The requirements for the prototype were:

• Simple circuit with standard components
• End charging voltage must be limited to a maximum of 1.7V, the threshold should not be exceeded
• Charge current should be between 50mA ... 100mA and upon reaching the end charging voltage should go to zero (charging stop)
• If possible a pulsed charging current should be applied to the alkaline battery instead of a constant charging current. Pulses have a positive effect on the chemical process by which a higher power and ultimate capacity is reached.
• If possible, the open circuit voltage of the alkaline battery should be used or measured Uo for threshold determination and not the charging voltage. This because as a result of the charging current and of Ri> 0 the charging voltage of the alkaline battery is higher than Uo. Thus charging would not reach the optimum or maximum allowable end charging voltage.
• The circuit should contain a power indicator (on / off, loading, loading-end)
• The circuit should work with the lowest possible voltage (about 2.5-3V) to keep the power dissipation small, and thus possibly a solar cell for charging of alkaline batteries can be used instead of an AC adapter.

Thinking done. After a few tries and tests the prototype was already developed in one evening:

 

Circuit Operation

The electronics technicians of us will immediately recognize the operating principle of this simple circuit. This is the classic "astable and bistable". T1 and T2 turn alternately back and forth. Whenever T1 is on, lights (flashing) the D1 (red LED) and if T2 is on, the charging current flows for a short term through the alkaline battery. In the cyclical phase in the T1 T2 conducts and blocks, the open circuit voltage Uo of the alkaline battery is measured by T3. Once this value of 1.65 - 1.7V reached (adjustable with potentiometer P1), T3 begins to conduct and prevents tilting on T2. That leaves T1 conductive and T2 flows no more charging current. Thus, the circuit stops charging automatically when the open circuit voltage of alkaline battery has reached the End voltage voltage.

Setting

The adjustemt (setting to optimal end charging voltage) is very simple:

1. A good new alkaline battery is inserted. This should be an open circuit voltage of at least 1.6V to1.65V.
2. The potentiometer P1 first turns to zero. The red LED should be blinking. Then the potentiometer P1 should rotate slowly until the LED just stops flashing.
3. Adjustment is finished.

Operation

Operation of the alkaline battery charging and regeneration circuit is as follows

1. A voltage source with about 3V / 100mA (eg mains adapter or similar from a Walkman or a solar panel with eg 8 x 0.4V / 100mA solar cells) is connected to the input of the circuit.
2. The red LED lights when still no alkaline battery has been inserted.
3. Insert or connect the output of the circuit to the alkaline battery. The red LED flashes and thus signalise the pulsed charging.
4. Once the alkaline battery reaches its end voltage, the LED flashes more slowly until it remains lit, finally. The charging is complete.
5. Take out alkaline battery and disconnect power adapter or solar panel.

Notes

Here are a few tips from experience:

• Alkaline batteries to be regenerated should only be partially discharged. The open circuit voltage of alkaline battery should be a minimum of. 1.2V or more. Trying to load a deeper discharged alkaline battery will fail in most cases.
• Fully discharged alkaline batteries - especially if the open circuit voltage is below 1V - are no longer regenerated and should be discarded.
• It can always happen that regeneration of an alkaline battery fails, for example, if this was discharged too deeply, too old, or already have been once or more times previously regenerated (to high internal resistance). The end voltage is never reached and the charging and regeneration circuit can not even after several hours get to a standstill (LED flashes on and on, though somewhat more slowly). In this case, any more charging should not be attempted, unless you run the risk of alkaline battery leakage. It is better to remove the alkaline battery and dispose of it.
• Regenerated alkaline batteries are more likely to leak, and should no longer be used in expensive or valuable devices, especially those that also still need a lot of power. Regenerated alkaline batteries do their work pretty well in less complex devices. for a long time

Experiences and Conclusion

The circuit is now regularly in use for quite some time and have proven itself. The gentle charging process (pulsed and moderate charging current) is hardly to make the alkaline batteries leak (although this is highly possible and there may be times that will actually happen). It has been found that some brands can be regenerated better and more times whilst other brands tend to leak (interestingly, rather the alleged hot shots on the market). However too much should not be expected of this regeneration. In each charging cycle, the alkaline battery loses inevitably of chemical substance and thereby its capacity to charge. Nevertheless, the life of an alkaline battery can be significantly prolonged. The environment thanks ;-)

Links to further information

• Zinnikers battery and battery Sites
• Zinnikers alkaline battery page
• Zinnikers sources (chargers etc.)
• Swiss Recycling on batteries
• Conrad Electronics - Components (eg, solar cells)

 

 

Alkaline battery charging circuit (2)

Here is a low current charger I designed in an attempt to extend the life / recharge regular non rechargeable alkaline batteries. The trick to doing this is three things.

• Use a low current over a longer period
• Charge before they become too drained
• Charge to no more than 110% of the cells capacity (eg 1.5v charge to 1.65v and stop)

The nice thing about using alkaline batteries is that they have no internal discharge unlike Ni-Cd and Ni-Mh rechargeable’s, and are therefore suited to low current drain applications such as remote controls, clocks or things you don’t use often such as torches. In my tests I have found the lower charge rate, the better the charge and the less chance of a cell leaking electrolyte. Also, if a cell becomes too flat or completely flat, it will not take a good charge and will also probably leak electrolyte and possibly even pop open. The idea here is to keep them topped up. Lets say you have fresh batteries in a torch and you used it for a while. The cells have drained to around 1.3v for example. Put them on gentle charge with this circuit, monitor the voltage and stop when it reaches 110%. That would be 1.65v for one cell or 3.3v for two cells in series. Do not charge beyond 110% or there is a risk of cell leaking or even popping open / exploding. Its also advisable not to try to charge an alkaline battery that is completely flat. They don’t absorb a charge and just leak in my experience. Some of my tests I done outside in the winter (around 2°c) and I found the cells hit 1.65v quite fast but didn’t absorb much of it due to high internal resistance at cold temperatures. Charging should be carried out at room temperature, around 20°c.

Here is a constant current supply circuit schematic diagram using the LM317 variable voltage regulator. It is a very simple circuit for charging alkaline batteries. It will provide a stable constant current which is adjustable by switching different values of resistors. The input voltage must be at least 6v higher than the battery(s) you wish to charge. The LED, BC548 and 470Ω resistor provide an indication of current flow to show that your battery connections are good. They can be omitted if you wish to make the circuit simpler. I used a 12 way rotary switch set to 5 way to select different resistors to give output currents of around 5, 10, 20, 30 and 40mA. The idea being for 9v PP3 types I would use 5mA. For AAA’s 10mA. AA’s 20mA, C’s 30mA and D’s 40mA. This is just my guideline, you can try what you like! Just remember more current is not good for charging alkaline non-rechargeable batteries.

You can use no switch and fix the current, or use a simple toggle switch to toggle between 2 or 3 different currents or whatever you prefer!

The constant current may be set by choosing the appropriate resistor. R = 1.25 ÷ I Where R is the resistor value in ohms, 1.25 the regulator’s reference drop voltage in Volts and I is the constant current in Amps. For example, if you want a 100mA constant current, the R value will be: 1.25 ÷ 0.1 = 12.5ohm. The dissipated power on the resistor R in this example is: P = V x I = 1.25 x 0.05 = 0.125W or 125mW. The dissipated power on the LM317 IC is:(Vin – Vout) x Charging Current. A heatsink is not required for the LM317 (TO220) in this low power circuit. If you design one with more than 40mA output current, you should heatsink it. Notice that the IC’s metal package or tab also carries the Vout, so it’s necessary to use isolating washers if you attach the heatsink to a metal case. High power resistors will be required over about 200mA but not needed here as we are using low currents to charge alkaline batteries! (200mA=¹⁄₄w @ 1.25v)

How this works: The LM317 keeps a constant 1.25v over the resistor regardless of input voltage or output load. This means when the load current increases or decreases, the regulator adjusts its output to keep a constant voltage over the resistor of 1.25V at all times and therefore a current of 1.25÷R.

One of the reasons this circuit is so simple is that most of the circuitry is inside the LM317 itself. It’s complicated circuit can be seen in its internal schematic diagram below:

LM317 internal schematic

Yes that whole circuit is packaged inside the LM317. The three pins in, out & adjust can be seen on the left of the schematic. Inside are 26 transistors, 26 resistors, 3 capacitors and 4 zener diodes.

Disclaimer: Battery manufacturers clearly state that alkaline batteries should not be recharged. There is a possibility of leaking of chemicals / gasses and/or an explosion. Some alkaline batteries contain small amounts of mercury and/or cadmium. Always wear safety equipment such as gloves and goggles when experimenting with batteries, and clean up any spills of battery fluid immediately. Do not leave charging unattended indoors. Use this circuit at your own risk!

Another circuit(3)

We regenerate these type of alkaline batteries here: http://en.wikipedia.org/wiki/Alkaline_battery (not normal rechargable ones…)

The Schematic

The schematic is rather trivial. A voltage regulator brings down a supply voltage (which might be from a car battery) to 5V. An additional built-up voltage regulator generates an adjustable voltage of 1,95V. The reason why to use two voltage levels is to distribute the heat losses better, and to have the final voltage more stable. But if your power supply outputs a stable 4 to 6 V, you can omit the 7805.

An oscillator generates roughly 10 Hz with symmetric impulse/pause ratio. This signal is fed to the transistors below the batteries and switches them to the regeneration voltage. So this is “charging” with pulsed current. In some publications also reflex charging is recommended, but it works equally well with just having a “relax” time instead of a reflex time (inverted charge, short-time load). The impulse/pause ratio is 1:1, or the impulse/period time is 50%. This is conservative, as some publications use longer charge, less relax time.

The chemical process of regenerating is different from charging a rechargable battery. It is more an activating of hidden reserves than an exact reversal of the chemistry during discharge.

Regeneration or disposal?

Don’t regenerate the battery if:

• the battery is deep discharged below ca 0.8V especially over a long time
• the battery is more than 3 years old (estimate by printed-on date, visual impression or application )
• any traces of leakage are visible or the contacts are strongly corroded, which indicates a former electrolyte
• the lid on the minus side is curved, indicating internal pressure
• the battery is longer than before (presumes that you have measured it)
• the outer casing shows bubbles (this especially in case of the old cheap zink-carbon batteries)

Regenerate the battery if:

• the voltage level is 1.0 to 1.4V
• the battery is less than 1-2 years old
• it is a high-quality battery, usually high price and famous name on it
• the minus side shows not the slightest trace of electrolyte

Between these extremes it is your own compromise between saving money for new batteries or losing money due to spoiled appliances by leakage. Sometimes I take some risk and use rather old batteries, but then I use it only in a low-level application. I put some tissue around the minus range and some silicone grease on all contacts to keep the damage in limits if the battery should leak.

         

Voltages, overview

• 1,5V -Rated voltage for Zink and Alkaline cells
• 1,56 – Typical voltage of brandnew batteries
• 1,6V – Buffering starts, no regeneration yet
• 1,65V – Typical buffer range, very slight regeneration possible
• 1,70V – Regenerating with small risk but the battery will not become full
• 1,75V – Correct voltage level for regenerating of good rather new cells.
• 1,80V – Very risky for one-way batteries, high risk of leakage. Maximum acceptable voltage for RAM cells.
• 1,85V – and more Both RAM and normal batteries are damaged

How much regeneration?

It depends on the battery condition, age and your risk level. This is why we cannot so easily add charge stop criteria like as it is with NiMH.A rule of thumb: Regenerate that the battery voltage has been 6 hours on 1.7V or 3 hours on 1.75V. The charge time is between 5 hours for a slight, and about 18 hours for a full regeneration. After some experimenting you can use a time switch, converted to self-holding. Adjust a short time first, test, add some regeneration, write down the times and make your own lookup table by experience.

Testing

• Leakage? => Dispose it
• No leakage but curved lid on the bottom, increased length? => either into long quarantine or disposal
• Nothing special? => voltage peak removal and quarantine.

Length testing

This seems to be a new idea. Measure the length before and after regenerating. If you use a metal caliper, put a piece of thin paper between, else you make a short-circuit. Increased length indicates that the minus-lid is being pressed out and the risk of leakage is rather high. Also, if the minus-lid becomes spherical, this indicates some danger. In another discussion in this forum, someone proposed to let the batteries jump back from a hard surface. I guess that this correlates with a belly shaped lid in combination with internal gas pressure, making something like a football structure. Springy cells = bad and non-springy=good.

Removing the voltage peak

The fresh regenerated battery has still 1.70 to 1.75V. As I guess that the voltage correlates somehow with the internal pressure, I take away this voltage peak by connecting a small bulb for a few minutes. When the battery is down to 1.65V it goes for quarantine.

Battery Quarantine

I put the batteries on a piece of tissue for a week. If there is no leakage, they come into the refrigerator for storage, but for safety they are stored in tissue in a plastic bin.

How often can I regenerate the batteries?

About 5 times. The older the battery is, and the more it has been regenerated, the least it can take a regeneration. In case of an old battery, it is advisable to regenerate only with 1.70V and accept, that the use voltage is just 1.4V after regeneration.

Where to use regenerated batteries?

• Bicycle light
• Flashlight/torch for cellar and attic (in Finland there is no electricity there)
• Head lamp for fine work and electronics
• Wall clock
• DCF-77 desktop clock
• Electronics experiments, for example heating a DY86 tube which is on 10 kV voltage level.
• Appliances with watertight battery case

Where not to use regenerated batteries

• Cameras
• MP4 player
• Wireless mouse or keyboard
• Radio (besides if it is a rather worthless one)

The consequent damage of electrolyte leakage is so large that the saved money for new batteries is not justified.

Can it explode?

Unfortunately, not. You need to mix up your own gunpowder The worst what happens in case of overcharging, is, that the minus-lid comes slowly out and the electrolyte drips out.

Is a leakage dangerous, is it poisonous?

The electrolyte is potassium hydrochloride. http://en.wikipedia.org/wiki/Potassium_hydroxide This fluid is a base (the opposite of an acid). It causes corrosion in electronics, can make stains in clothes and slightly attacks the skin. When you get it on your fingers, it is recommended to wash them soon. I tried it, the stuff is far less aggressive than lead-battery acid. Of course, don’t eat it.

Preventive actions against a possible leakage

Toilet paper or kitchen tissue around the minus range, small hole in the middle for the contact. silicone grease on all contacts. Possibly additional tissue in the battery pack. This limits the damage if a battery should develop leakage. The water of the electrolyte evaporates, leaving crystals in the tissue.

Flight pressure (!)

An airplane with pressure cabin has a pressure inside, corresponding to ca 2000m height. This reduced atmospheric pressure is already enough to make freshly generated batteries leak.

What about rechargeable alkaline batteries, RAM?

http://en.wikipedia.org/wiki/Rechargeable_alkaline_battery
In Europe we have Accucell and I-go-green, in the USA among others Rayovac and Grandcell. The difference to a one-way cell is mostly the pressure-resistant casing, the internal chemistry is nearly the same. I made my experiments with http://www.accucell.de/technik.php They can withstand more regeneration cycles than a one-way battery but also start leaking after some years of usage or ca 5 charges.

A special effect

It can happen, that during regeneration, or some time afterwards, the voltage suddenly drops down to 0.4V and below within a few hours. In this case, crystal growth inside the cell has caused a short-circuit. It happened to me in 3 or 4 cases out of ca 100. The battery is then dead and has to be disposed.

Literature:

Wikipedia: http://en.wikipedia.org/wiki/Recharging_alkaline_batteries

Homepage of Rolf Zinniker, Switzerland: http://www2.ife.ee.ethz.ch/

Günther Hager, Modellflug und Elektronik http://www.aero-hg.de/

describes a very simple schematic. It needs active supervision, as there is no voltage limit (in german)

Elektor, 2002 Schaltungen, Page 4216 there is a simple reflex regenerator.

Elektor, 2002 Schaltungen, Page 4491: Alkali-Akku Lader, more sophisticated schematic.

Note: Elektor (Elektuur) is available in dutch, german, english in parallel. Comes originally from the Netherlands.

ELV 5-2000 Ladeschaltung für RAM-Zellen im seriellen Betrieb. A balancer is described which allows the use of solar cells to buffer RAM cells to make the lifetime longer.