• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.
[4]

Experimental Capacitance Battery Charger !!WARNING HIGH VOLTAGE!!

January Project of the Month [3]
[10] Like what you see?
Click here to donate to this forum and upgrade your account!

petcnc

Active User
Active Member
Joined
Dec 29, 2012
Messages
277
Likes
396
#1
Having a pile of old "dead" Lead Acid batteries I was looking for ways to revitalize them.

Batteries.jpg

Long time ago I have build a “battery desulfator” that supposed to desulfate battery cells and give them a new life.

As the desulfator I have builded, gets its power from the battery itself, there was a problem in revitalizing batteries that have a nominal voltage under 10 volts. If a battery has a voltage around 12 volts is probably in working order and you can charge it. On the other hand, all dead batteries have low voltage for the device to work efficiently. So I was looking for a charger that revitalizes batteries and at the same time charges them.

My research brought me to a devise called “Capacitance Charger”.

It is a very simple circuit, it claims to be very efficient but needs VERY CAREFUL HANDLING as:

it gives HIGH VOLTAGE THAT CAN KILL and

if left unattended it overcharges the battery!!

Living dangerously, I decided to build and test it!


CIRCUIT DESCRIPTION

The basic circuit is very simple as it uses MAINS VOLTAGE, a motor-run capacitor and a bridge regulator.

Schem1.jpg


In reality it looks like this

CircuitReal.jpg

NOTE that all components are insulated and go in a plastic container to protect the operator of the charger!

CircuitReal1.jpg

Note that I do not use the classic alligator clips of a normal battery charger but small fully isolated clips!

Container sealed and charger ready to use.
CircuitReal2.jpg

HOW IT WORKS

The role of the capacitor, in line to mains voltage, is to limit the current going into the rectifier and to the battery. Amazingly, it does this without any power loss (like in a resistor).

A crude rule-of-thumb is to use 20uF of capacitance for each Amp of charging current you want to deliver to the battery or battery pack.

If a lead acid battery is left for too long in a discharged state it becomes unusable through a process called Sulfation. This Wikipedia article describes it in greater detail.

As the DC out from the charger is not smoothed, it gives pulses of positive charge at a frequency twice that of the AC current (120 Hz in USA, 100Hz in Europe). These pulses, in theory, dissolve the crystals formed on the surface of the plates in the battery and gradually a dead battery comes back to life.

It is essential though to Monitor the battery voltage as it is charging and know ahead of time what voltage is required for a full charge.


BASIC INFORMATION FOR FLOODED LEAD-ACID BATTERIES:

CHARGING

80% charged is 2.38 volts per cell (14,28 Volts for a 12 Volt battery)
Bubbling and gassing starts to occur at 80%.

100% charged is 2.58 volts per cell (15,48 Volts for a 12 Volt battery).
Vigorous bubbling and lots of gassing occurs at 100%.

DISCHARGING

When a Lead Acid battery is 80% discharged you measure 1.75 volts per cell (10,5 Volts for a 12 Volt battery pack).

At the beginning of the charge cycle, using the capacitive charger, the power going into the battery pack is the highest. As the battery pack charges, the power going into it drops until it settles out at some nominal value and the battery reaches a full charge.

CAUTION!

NEVER TOUCH the poles or leads of charger while it charges!

LETHAL VOLTAGES


You must monitor the process as you might boil away batteries if you do not switch off the charger after battery is fully charged.



TESTING THE CHARGER

In order to monitor Voltage and current, to avoid overcharging the battery, I connected a DC Amp meter and my multimeter to monitor charging as you see in the previous picture.

Before starting any charge procedure make sure that the battery is filled to maximum with distilled (de-ionized) water!

Take all usual precaution measures here as you deal with acid: Plastic gloves, eye protection, etc.

Refilling SLA's (Sealed Lead Acid Batteries), is like refilling a car battery, only on a smaller scale!
Use a small flat head screwdriver to pry off the cover, There is usually a slot that the screwdriver will fit in.

Take the Cell Vents Off (those small loosely fit rubber caps) and using a small syringe (or any device which can suck up and dispense water into narrow places) fill slowly the cells with de-ionized water. (A more detailed procedure for SLAs here.

After preparing my batteries I started charging.

Measured voltage of a dead SLA battery 2 Volts!

CircuitReal2.jpg

As expected, when I powered on the charger initial voltage starts high and drops quickly. My SLA batteries started at 135 volts!

InitHighVoltage.jpg

My charger, using a 6uF capacitor provides 0.2 Amps.

Start charge2.jpg

Initial energy consumed by the charger was high (41 Watts).

Start charge3.jpg

Gradually voltage drops to “normal” levels (around 12 volts) and battery starts charging.

Normal chargingInit.jpg

Depending on the battery capacity and status, charging takes different time. Small capacity SLAs charge fast and you need to monitor them so they not exceed 15,4 volts (100%).

Start charge4.jpg

Charging classic “Flooded” Lead Acid Batteries (FLAs) took more time as charging voltage rose very slowly. For instance charging a dead motorcycle battery at 0,2Amps went from 80v initially down to 12,7 volts in half an hour…

Normal charging.jpg

…and then took another hour to reach 13,4 Volts.

FLACharge2.jpg

The energy consumption during charging was negligible, just 6 watts.

Normal charging1.jpg

CHARGING RESULTS

24 hours after charging I measured the voltages of each battery. As 3 of my SLA batteries were badly damaged (cracked and swollen) by overcharging due to an overenthusiastic Uninterrupted Power Supply (UPS) that overcharged them…

Damaged.jpg

Their charging results with my Capacitive Charger were disappointing. Some cells were getting hot (too hot) and the electrolyte inside sounded boiling. For that reason I never finished the charging procedure with my 3 UPS SLAs.
After 24 hour they had no charge as you can see below.

24HUPSSLAs.jpg


A smaller SLA removed a year ago from my burglar alarm behaved better. After 24hours
it had some 11,17 volts.

24HsmallSLA.jpg

Best performer proved to be the flooded type “dead” motorcycle battery! After 24 hours it still had 12,2 volts.

24FLA.jpg

CONCLUSION

I never expected miracles out of the capacitive charger! I am very happy though as 2 of the batteries follow a revitalization path. I still need to experiment with larger capacity “dead” batteries to come to a final conclusion but for such a procedure I need to make a more elegant charger capable of delivering a wide range of power not just 0,2 Amperes!

I already have some ideas in my head and I will start building it instantly.

Thanks for reading and...

Stay tuned!


Petros
 
Last edited:

kvt

Active User
Active Member
Joined
Oct 21, 2014
Messages
1,869
Likes
903
#2
Interesting I have a couple of dead motor cycle batteries and a couple of old car batteries also. This would be nice.
 

petcnc

Active User
Active Member
Joined
Dec 29, 2012
Messages
277
Likes
396
#3
As I said BE VERY CAREFUL WITH IT! We are used to touch 12volt charger wires as they charge! In this charger there is LETHAL VOLTAGE for humans if you touch the poles during charge. You would better have the poles covered with some insulating material!

As we speak I'm bulding a better one capable of providing 0.2 to 2A for larger wet cell batteries. Give me a couple of days and I will post it here!

But do not expect resurection of the dead!!! If they have some life well hidden under sulfated crystals they will be revitalised. If they are completely dead their place is in the recycling field.
 

tq60

Active Member
Active Member
Joined
Jan 11, 2014
Messages
557
Likes
313
#4
Being blunt....BAD IDEA!!!!

The capacitor in this application is just acting as a resistor.

Yes a sulfated battery will respond to this as we have done similar via strapping a couple chargers in series to bump up the voltage to overcome internal resistance.

The maximum charge rate of most VRLA batteries is usually 20% C where C is 8 hour amp hour rating while they can take a rate of C for short periods.

If they get fully charged then they are in float mode and the rate of charge is 0.1% C.

Then it gets silly.

The typical VRLA battery that has gassed out due to overcharging , most UPS are cycle service and charge on high side so likely gassed.

Others may be sulfated due to under charging or age degradation.

Either way the capacity is smaller and the formulas stay the same.

So using a 100 amp hour for easy and lazy math.

A fully discharged good one can take a rate of 100 amps for a short period and if using constant voltage charging the current will drop off in a reasonable time as it goes from bulk to absorbing charge.

After some time the charge will drop and should be limited to maybe 20 amp maximum.

These are specified in the data sheet.

When fully charged the rate is 0.1 amps maximum.

Exceeding the above can cause excess gassing and if enough to pop the V in the VRLA the gas is released and can't be restored.

If the battery capacity is only 20% of above then above numbers reduced same.

The high voltage can cause things to explode as well as voltage potential.

Back in the day old school automotive guys would use a light bulb , diode and a power cord and connect a stack in series and plug into the 120 volt line and the light limited the current.

Currently batteries are stupid cheap on ebay and when the die usually they ate done and not usually recoverable with any suitable capacity.

If this is attempted do it outside on a gfi circuit and control it via opposite end of long cord...

Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 

Silverbullet

Active Member
Active Member
Joined
May 4, 2015
Messages
2,639
Likes
1,239
#5
I have several sets of deep cycle spiral wound optima batteries , and some sealed wheelchair batteries. I converted my wrangler scooter to the optima blue top ones cause I get six years out of a set and only 1 1/2 years on there batteries. Same cost even less. Be nice to revitalize them.
 

petcnc

Active User
Active Member
Joined
Dec 29, 2012
Messages
277
Likes
396
#6
Being blunt....BAD IDEA!!!!

The capacitor in this application is just acting as a resistor.

Yes a sulfated battery will respond to this as we have done similar via strapping a couple chargers in series to bump up the voltage to overcome internal resistance.

The maximum charge rate of most VRLA batteries is usually 20% C where C is 8 hour amp hour rating while they can take a rate of C for short periods.

If they get fully charged then they are in float mode and the rate of charge is 0.1% C.

Then it gets silly.

The typical VRLA battery that has gassed out due to overcharging , most UPS are cycle service and charge on high side so likely gassed.

Others may be sulfated due to under charging or age degradation.

Either way the capacity is smaller and the formulas stay the same.

So using a 100 amp hour for easy and lazy math.

A fully discharged good one can take a rate of 100 amps for a short period and if using constant voltage charging the current will drop off in a reasonable time as it goes from bulk to absorbing charge.

After some time the charge will drop and should be limited to maybe 20 amp maximum.

These are specified in the data sheet.
As stated to the title the device is EXPERIMENTAL!
I do not promise resurection! The charger is used to batteries that are declared "dead" already and is used under constant supervision.
You might be right to all you statetments above, I'm no expert on lead acid battery technology and I welcome all info on that.
Thank you for sharing your knowledge on the subject.

Petros
 

tq60

Active Member
Active Member
Joined
Jan 11, 2014
Messages
557
Likes
313
#7
Yes you did state experimental and other warnings so good job.

We have went down similar roads over the years as we are very cheap...

We placed the long winded warning as many may just copy and go so we added some information for folks to consider.

Your thought are good and adding a "discharger" to place a load on the battery to cause the internal chemicals to dance" may improve the results.

Simple light bulb and old school turn signal flasher is an example.

Pleas note if you see stains on top of a sealed unit they have gassed off and material needed is gone and cannot be replaced.

And we have recovered many batteries but in recovery the observation is they change from what appears to be open condition (full sulfation) to something we can charge and they take current but then they just do not hold it well indicating inter plate leakage or still sulfated causing limited capacity so if the battery will not take a charge it is usually done.

Tried lots of things with a forklift battery as it is expensive battery but only could get a tiny output so made new one.

To folks with wheel chair or ups systems there is much to be done.

A VRLA battery is designed for 10 year life in float service and maybe 3 years in cycle service.

The area of plates determines capacity but every time they are cycled they wear a bit.

Capacity is important so plates are thinner allowing larger.

Most chargers in ups systems charge at higher rate for faster recovery and as such often charge at a slightly higher voltage to get the higher current.

Early wheel chair chargers were not regulated well and often were too high aa well.

Plus folks want full charge fast.

Lowering the RATE of charge while regulating the float voltage to what each specific battery likes can greatly extend the life by reducing the "wear and tear".

Float voltage of 2.25 volts per cell is a generic float voltage but temperature and model can vary this a bit.

Focus on your power systems and in service batteries will like it.

The bad batteries may be recoverable but performance likely poor but place them on a good charger and they may heal a tiny bit.



Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 

rwm

Active User
H-M Supporter-Premium Member
Joined
Mar 25, 2013
Messages
1,144
Likes
1,293
#8
Would it be useful to change out the acid for fresh after this process?
Robert
 

markba633csi

Active Member
Active Member
Joined
Apr 30, 2015
Messages
1,805
Likes
886
#9
Not really Robert. The acid is still there, it's just turned into lead sulfate and it often means the plates are ruined. There have been many battery rejuvenator
schemes tried but they generally only give marginal results. Once the battery's life is over it's pretty much done for. Too much shed plate material at the bottom of the cell.
Mark S.
 

tq60

Active Member
Active Member
Joined
Jan 11, 2014
Messages
557
Likes
313
#10
Wear and tear on something with zero moving parts is something that is difficult to explain or understand.

But a lead acid battery is full of moving parts...at the molecular level.

Others usually fire off actual chemical names but there are not important to understand the process.

Basic battery is a 2 function device.

It is either a resistor or power source and if we treat it as a resistor at all times simple...A bank of identical batteries should be identical resistance so Ohms law determines how measurements should be evaluated.

Back on topic....
When battery is being charged chemical reaction is under way to charge the battery.

When charge is removed and a load is applied a completely different chemical reaction is happening.

Just think walking up and down a flight of stairs as charge and discharge.

Your legs get tired over time.

You can rest but your bones wear out and cannot be repaired.

Battery is same.

The lead detaches from a plate or the suffer binds to them.

VRLA has acid in a glass sponge material and the chamber is sealed to contain the gasses but they do burp and gasses are lost removing some of the needed chemical compounds as well as sulfation where the plates get covered and not effective and lastly where lead simply falls off the plates.

These are the 3 common issues and the last 2 are associated with age degradation and the op device could recover some sulfated cells but usually batteries too far gone to be suitable.

We currently are working on a electric wheel chair for yard work using a bunch of old smaller ups batteries as power source....not worth a hoot but able to use for prototype and build then buy batteries....

Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 
[6]
[5] [7]