Charging Lead Acid Batteries in Series: Capacitor Effect

Thank you for your quick response. I was unaware of any "capacitor effect" regarding the charging of lead acid batteries. However one member of our group insisted that the first battery is a series of batteries would fail sooner than the other because it would receive a voltage surge due it's capacitor effect. I would assume any electrical device that has two lead plates separated by some form of dielectric would have a minimal capacitively, but not to the level this individual was suggesting.

In theory I would assume that more or less if all batteries are of equal condition that they would see equal current flow and equal voltage drops in a series charging circuit arrangement.

Thanks again,

Davew01

I think that could not be true since a standard lead-acid battery is several smaller cells in series. Back when I was poor (not genteel poor like now), we would salvage old batteries with a single bad cell, drive spikes into the plates on either side and have a somewhat lower voltage battery that worked OK.

In principle a battery is not such a far cry from a capacitor ie. in a battery the dielectric, as in the case of a capacitor, is replaced is replaced by the electrolyte. In the event when one fills a battery initally with distilled water (which is not such a great conductor) the distilled water can act as a poor dielectric to render a capacative effect. The thing to do in such cases is to begin charging at the lowest applicable charging voltage wit very low current. Charging time would be considerably longer but so would be the battery life. In such a circuit, except for the instant that it is switched on, there is no first or last or in between. However if the resistances of the batteries are very great problems might arise. Lets look at two batteries in series, bearing in mind that in a series ckt while the current is the same through the loads, the voltage is divided, according to the resistances, among the loads. The battery with the greater internal resistance would receive the bulk of the voltage while the battery with the lower internal resistance would just serve as a regular conductor. Such a condition can cause over charging (thus, damage) in the battery with the higher resistance if one waits for both batteries to be fully charged before removing the charging source.

Hello Davew01

Because the cells are in series, equal current flows in them all, whether charging or discharging.

However, the cells are never absolutely identical, in spite of being assembled in the same factory.

So, in a battery situation, one cell will always have a slightly higher internal resistance than the others, which will cause a greater voltage across that cell while it is being charged.

This will cause the cell temperature (W = I²R) or (E²/R) = Heat in watts, to rise apart from any other reason.

So as the cell has a higher voltage across it, plus that higher temperature than the rest of the cells connected in series in the battery, the rate of bubbling at the plates is higher than the other cells too, which leads to the paste falling faster off the positive plates, and further increasing the internal resistance of that cell, which is going to be the first to fail in the battery.

Note that pwr2thepeople gives environment reasons for early cell failure here:

http://cr4.globalspec.com/comment/179004/Re-Charging-Lead-Acid-Batteries-in-Series-Capacitor-Effect

In earlier years, when Automatic Telephone Exchanges were electromechanical stepping switches, plus electromechanical relays, the Exchange batteries were composed of very large individual open top cells, each cell weighing sometimes more than 2 tons, in a ventilated room, and the temperature of individual cells were the same.

All cells had the electrolyte readings, temperature of electrolyte taken daily, along with the individual cell voltage.

If a cell had a voltage slightly above the rest of the battery cells, it could thus be carefully monitored, bypassed with heavy cables as required, and a replacement cell inserted into the battery.

If purchasing lead-acid batteries for a vehicle or boat, best to spend a bit more and get the xxxxZ battery - the last letter Z = Anti-vibration for use in Marine or Diesel situations.

These anti-vibration batteries also have more space under the plates, so that fouling and subsequent short circuiting of the + and - plates occur far less frequently.

There are lead-acid batteries which have an indefinite life, by being lower electrolyte specific gravity, and the plates + separator rolled up in cylindrical form, unlike the standard rectangular or square plates in most vehicle batteries.

History:

Storage and re-chargeable batteries have been around for much longer than previously thought: China used rechargeable batteries and did exquisite electroplating over 4,000 years ago, while Babylon used these same methods over 1000 years earlier.

There are many references to the use of batteries, several thousands of years before Alessandro Volta "invented" his "voltaic pile" in 1800.

Kind Regards....

If the plates were dry and the separaors were dry you might be able to make a capactitor with a battery.

However the eletrode in a battery is conductive and thus would null and capatitor effect.

In the old days, when you could run a car with the battery disconnected (cheap people could share a battery), the am radio would pick up all kinds of noise from the power supply. The battery would act like a filter cap and eliminate all that.

The battery would be charged by a varying voltage and then put out a constant voltage. The noise was generated by the brushes arcing on the generator.

The battery was a smoothing resistive load on the generator. Also the voltage regulator would be all screwy not having a constant reference voltage from the battery.

You would get a hum from the commentator even with the battery in place. The vibrator would chop the dc voltage to drive the transformer to get plate voltage. This also needed a stable voltage.

But the battery was never a capacitor!

"The battery would be charged by a varying voltage and then put out a constant voltage. The noise was generated by the brushes arcing on the generator." And, that is what a filter cap does.

Sorry, but I disagree with you. A lead acid battery isn't a great capacitor, but it is one. In working with railway power and signaling circuits, I've seen a whole lot of capacitors that most people would barely recognize (wet gravel at Ogden Utah, e.g.). My criteria is that, if I can measure the capacitance, it's good.

Good post.

You wrote:-

But the battery was never a capacitor!

Which is really wrong! Sorry.

Think about it, what does a capacitor do and what does a battery do?

Both let them self be charged up and discharged from a voltage source, both in fact "store" electricity. Which is why as someone else posted, running a car with the battery removed makes lots of strange noises on the radio, that the battery/capacitor would have filtered out!!!

In fact, the modern "Gold Cap" can be and is used as a battery in many applications, keeping clock chips supplied with voltage for weeks and weeks, till the machine is again plugged into the mains!

Gold Caps have also a very quick charge rate, only slowed down by the limiting resistor that has to be in series with the supply!! But a recharge can be made in a few minutes usually!!! Batteries generally need far longer.....GoldCaps do not care if they are completely discharged, most batteries get damaged if so treated, but the principle remains the same....

If you are over 30 years old, you will have trouble understanding what I have written as it goes against what you learnt years ago, but today, caps can do many jobs that only a battery could do only 10 years ago!

You also wrote:-

The battery would be charged by a varying voltage and then put out a constant voltage.

The battery (lead Acid) will ONLY be charged by a voltage that is GREATER than the terminal voltage of that battery at the time. Hopefully the "Varying Voltage" is always above the Battery's voltage, otherwise charging will stop!!!

The Battery might have a voltage well under 12 volts at the beginning of the charging, but could well go to around 14 volts when fully charged, which is why modern car alternators are set to supply around 14.4 volts, which means that there will always be a small difference, therefore charging current can and will flow.....but that also means that the battery will eventually gas (like humans after a heavy dinner! )and eventually need to have the gas replaced with distilled water!!!

Conclusion

Sorry to be negative, but I have the impression that electrics and electronics are not your strong suit, therefore may I gently recommend that you either do some serious study or not jump to conclusions that are just wrong enough to provoke relies such as mine.....We in CR4 have to make sure such errors are corrected, otherwise other "Newbies" will go away with the wrong information or the wrong slant on a topic!!!! I hope you fully appreciate the spirit in which this has been written.I can answer any further questions that you may still have in this area if you wish.....

Batteries have a chemical change to store or produce a charge. A capacitor stores an eletrical charge on a plate.

CHARGE: BATTERY OR CELL

The act of adding electrical energy (e.g., supplying current, etc.) into a battery or cell from a diverse source of electrical energy to increase the amount of useful and available chemical energy stored in the battery or cell; or, the amount of chemical energy stored in a battery or cell that is available for useful conversion to electrical energy for supplying an electric load.

CHARGE: CAPACITOR

The act of applying an electric potential across the electrodes or plates of a capacitor from a diverse source of electrical energy to increase the amount of useful and available electrical energy stored in the capacitor, or the amount of energy stored in a capacitor that is available for release to usefully supply electrical energy to an electric load.

...and the point is? that you are trying to make?

can someone help me out with this, i constructed a 48v charger and i had two problemswith it. (1) whenever i connect a capactor the float wil be around 73v !!! and when i remove it it gives around 49.1v but when i connected the charger, the voltage accross the first battery was around 17v and others are almost normal pls what can i do help me out

Oy Vey! When you say you constructed a 48 V charger, what was the rms voltage that the transformer put out? What is the maximum charging Voltage you need for your batteries? I'll try to show a little bit, using the example of a 12 VDC lead-acid battery.

A fully charged 12 V battery has a terminal Voltage of 13.6 VDC. So, you need a charging Voltage of about 14.1 VDC more or less, depending on how fast you want to charge it. If you're using a full wave diode bridge, you'll have two 0.6 VDC drops from the bridge, so you need to start with 14.1 VDC + 1.2 VDC = 15.3 VDC.

If you have no filter on the charger, you'll need a secondary rms Voltage of 15.3/0.9 = 17.0 VAC.

If you were to put a capacitor filter on this output, the output would now depend on the size of the capacitor. In the worst case, the Voltage would rise to the peak Voltage minus the diode drops, or (17 VDC)(1.41) - 1.2 VDC = 22.8 VDC.

So this whole thing can be all over the place if you're just sort of guessing.

I'd go back and use a Voltage regulator and charge it at constant Voltage if I were available to monitor it. Otherwise, you need to design in some control to vary the output Voltage.

There are some charger schematics online. I don't have any links (I haven't built a charger for probably 20 years!), but do a little Googling or maybe somebody a little more up-to-date can jump in.

Hello TVP45 and others,

Bosch pattern (Ingrams in Australia and New Zealand) alternators for 12 Volt car/Truck batteries, have 2 alternative easily exchangeable electronic regulators.

14.3 Volts - for cars.

14.7 Volts - for trucks, Tractors, Boats, RV's and installations where the battery capacity is large.

The Bosch 12 Volt alternators come with the standard 14.3 Volt regulator, which is a small unit including the pair of brushes. Undo a couple of screws, to replace regulator/brushes etc, nice and easy.

The higher Voltage regulator is to compensate for the longer battery connecting cables, in a truck etc, and if you get a 98 Amp version, your 12 Volt battery will last many years, providing you ensure the electrolyte level does not drop to the plates level.

Over the years, I installed dozens of these 14.7 Volt 98 Amp Alternators.

Kind Regards....

That's what I like about this forum - all these guys that know things that actually work rather than just "pie in the sky" ideas. Thanks, Sparky.

thanks TVP i really like that. the i wound the transformer to 52volts rms @ 230v input and i used 2 pieces of KBPC3510 bridge rectifier connected in parrallel and it gives around 48volts after rectification. but when the charger is connected to the batteries, it gives around 55volts float {without capacitor}. Meanwhile, the first battery receive around 18volt, the second 13.7volt and the third. but the last one was around 12.5volts. but when i connected a 470uf/200v capacitor, the output voltage rised to 73volts which is definitely too much for the battery. i only used a timer delay circuit. no circuit for output voltage/current regulation. if anybody can be of help, maybe a control circuit and how the float can be the same for the batteries and any idea on how to design a 20A or more charger i will be very gartefull.

Hello waleshadow

Your 4 12 Volt Batteries will need to be bought at the same time, from the same make and size/batch.

If you have batteries of different electric internal resistance, the cell with the higher resistance is going to have a higher voltage across it, than the rest in the series string.

This higher resistance cell is going to have more watts dissipated internally, and thus heat up more than the others.

This increased heat in that cell is going to increase the internal resistance further, and in the end the cell is destroyed, because it never reaches full charge, yet discharges faster than the other cells.

As far as "designing a Battery Charger" for 48 Volts, it's not really worthwhile, my friend.

Most good battery chargers are computer-controlled, via a micro-chip arrangement inbuilt to the charger unit.

Because these chargers are made by the hundreds of thousands, the price per unit has dropped below the cost of purchasing the individual parts, even at normal wholesale rates from your nearest wholesaler.

The computer-controlled chargers are made in different Voltage Outputs and currents, and are able to charge "normal" lead-acid batteries, also having a setting for "sealed lead-acid batteries".

These computer-controlled battery chargers are controlled by the voltage/current profile (Mathematical Algorithm) built into an EPROM chip in the controller of the unit, resulting in a charger which may remain connected indefinitely to the battery, without damage to charger or battery.

For a typical explanation, go to: http://www.techonline.com/learning/techpaper/200001044

Also read about it here:

http://books.google.com/books?id=r3ukOOl16Y4C&pg=PA192&lpg=PA192&dq=Lead+Acid+Battery+%22smart+charger%22&source=web&ots=_NQIBiXdIs&sig=pv61DShUc1Bf-f9nlZgGVOwv7I8&hl=en

To take four 12 Volt batteries, without carefully ensuring the individual cells are matched, is going to give you trouble.

When using a large electrolytic capacitor across the output of any rectified (pulsating) DC supply will result in a much higher Voltage than expected, because the capacitor up-stores the fluctuating voltage, which then builds up towards the peak Voltage, unless loaded.

When the Power Supply/Charger is loaded, the voltage drops to a level in accordance with both the Power Supply/Charger internal resistance, resistance in the cabling/wiring, and internal resistance of the load/battery you connect.

The fact you show different Voltages across your 12 Volt batteries is a warning not to continue, unless you replace the batteries with matched set as explained above.

Refer for typical chargers: http://www.batterystuff.com/battery-chargers/48-volt/

Trust that assists you.

Kind Regards....

Like give us some concrete infos.....

How about starting with a circuit diagram.....?

For help we need info. Does that ring a bell with you?

And make sure you identify the four batteries that are in series and tell us about their condition (age, A-hr, etc). That's gonna be important.