Battery Desulfator
- Battery Desulfator Website -
Original website describing a 'pulsing' de-sulphating charger:
www.rst-engr.com/kitplanes/KP0204/KP0204.htm
(This is Jim Weir's original website describing this desulfator which also has PCB artwork and schematic in Circuitmaker and Traxmaker format.)
- Schematic -
A schematic of circuit in pdf format:
www.rst-engr.com/kitplanes/KP0204/KPsch.pdf
- Text -
The full text of the original author's description of this particular battery desulfator in pdf format is available here:
www.rst-engr.com/kitplanes/KP0204/KPtext.pdf
- Parts List -
A download Parts List in pdf format is available here: www.rst-engr.com/kitplanes/KP0204/KPparts.pdf
Scope-o-gram Annotations
The following images from the above web site were 1) reduced in size and 2) annotated to facilitate comprehension (IOW, I did this to facilitate and insure my own grasp of the theory and design of this desulfator; there is no better way to learn something than to learn it with the intention of teaching others).
Picture #1 (Bad battery)
The waveform at the (test point) X105 terminal when at the beginning of the desulfation process.
The horizontal scale is 2 msec/cm and the vertical scale is 5 volts/cm. Note that the battery voltage between pulses is about 12 volts and the pulses are about 35 volts by the time they get to the battery.
Calculated current is about 30 peak amps in each pulse.
Picture #2 (Bad battery)
This is the "ringing" part of the waveform expanded out so that you can see the exponential decay of a fairly constant frequency. (The upper trace is an unavoidable ghost trace that is necessary to see the ringing clearly. It means nothing; disregard it.)
Picture #3 (Bad battery)
The desulfation pulse expanded out to 1 microsecond/cm.
Note how the voltage peaks to 35 volts and then slowly lowers to about 25 volts. This sloping pulse is indicative of relatively high internal battery impedance.
Note the "ringing" at the end of the pulse. This is the "battery resonance" noted in most of the desulfation articles in the reference.
Picture #4 (Good battery)
The waveform at X105 for a "good" battery that has gone through a complete desulfation process. Note how the pulses are limited by a good low impedance battery to 20 volts versus the 35 volts of a fairly well sulfated battery in photo 965 [and 970].
Picture #5 (Good battery)
The desulfation pulse expanded out to 1 microsecond/cm.
This is a "good" battery. Note how flat the top of the current pulse is. This is indicative of a good battery with low internal resistance. Battery ringing is still quite evident for this battery.
Picture #6 (Trashed battery)
A completely trashed battery. The vertical scale is now 10 volts/cm. Note how the desulfation pulse goes all the way up to 50 volts and then rapidly decays to near zero. The odds of recovering this battery hover somewhere around the odds of winning a shouting match with an FAA inspector.
Picture #7 (Trashed battery)
This is picture #6 expanded out to view the voltage 'decay'.
The same pulse expanded out to show that there is practically no current being driven into this trash battery. No ringing, no real chance at saving the battery unless after a few weeks of treatment something inside starts breaking down and begins allowing the desulfation pulses to drive current into the cells.
References:
- DOE Battery Handbook - PRIMER ON LEAD-ACID STORAGE BATTERIES
www.eh.doe.gov/techstds/standard/hdbk1084/hdbk1084.pdf
- Capacity Loss in PV (Photo-Voltaic) Batteries and Recovery Procedures
www.sandia.gov/pv/docs/PDF/caploss.pdf
Abstract excerpt:
To date, laboratory and system testing consistently identified the incomplete recharge of PV batteries as the predominant cause of premature capacity loss resulting in a lower than rated cycle-life.
Incomplete battery recharge introduces battery degradation mechanisms such as electrolyte stratification, gas bubble entrapment, excessive sulfation, and degradation of the positive active mass.
Recovery of the PV battery after extended periods in a deficit charge condition may or may not be possible depending on the extent of battery degradation and the resources available for recovery.
- Battery Desulfator Report 2003/5/14
www.kwantlen.bc.ca/electech/FinalProjects/p2003/Battery_Desulfator_Lin_Jao.pdf
- Lead Acid Battery Desulfation Pulse Generator
www.shaka.com/~kalepa/desulf.htm
This web page desribes 'the original', low power desulfator version which is suitable for most solar systems, vehicle starter maintenance, and gradual battery reclaimation. There are several flavors of this circuit described and documented.
This is a two terminal device - it draws power from the battery as it performs desulfation. This may confuse some people, as it would seem counter intuitive to the purpose at hand. It is recommended that a charger be connected in parallel with this device for extended desulfating of a battery. Extensive history for this design exists in the form of a .pdf file in the next reference.
- Lead-Acid Battery Desulfator by Alastair Couper
www.homepower.com/files/desulfator.pdf
This seems to be the 'Rosetta Stone' for a large amount of amateur research and testing on the subject of desulfators that has followed on the heels of this paper.
Opening excerpt:
Lead-Acid Battery Desulfator
Alastair Couper ©2000 Alastair Couper
It was twenty years ago that I left my on-grid home, and my job as an electronics engineer, to begin life on an alternative energy oriented organic farm. In the intervening years, I have installed, maintained, and experimented with numerous RE systems in my area.
What I have come to understand from this experience is that off-grid life tends to become very much focused on the battery bank and its fate.
All power sources and loads breathe through this crucial pathway. Batteries are heavy, toxic, inefficient, and—to the amazement of many—electrically very fragile. Weak or failing batteries are a very likely cause of breakdown, especially in smaller solar-electric systems.
Most newcomers to renewable energy are quite familiar with using water tanks or gas tanks, and naturally use this familiarity in trying to understand their battery banks. Everyone knows that a bigger water tank is better than a small one. Unfortunately, batteries are not like tanks, and the result is trouble.
It is definitely not true that a big battery bank is necessarily better than a small one. An oversized battery bank can be almost impossible to charge properly. Without a minimum daily exercise regimen, it can become the equivalent of a couch potato. The main culprit is sulfation, which is a gradual crystallization of the battery’s plate material, rendering it electrically inactive.
Some Theory
Past issues of Home Power (see Access) have gone into the details of keeping lead-acid batteries healthy, so I will only touch on the main points here. The usual practice in maintaining a battery in good condition is to apply a periodic equalization charge over and above what would be a normal full charge. Unfortunately, this is an energy-wasting tactic. It ultimately results in clean battery plates, but at a steep price, especially if the energy must come from a generator.
I initially went to the Internet to find any available information on the problem of sulfation. The search engines turned up several commercial sites that give useful details on the fine points of battery charging and equalization. A second resource is the IBM patent server (www.patents.ibm.com). I found relevant patents there, using keywords like "desulfate" and "rejuvenate."
What this wealth of data shows is that there are numerous strategies for charging and electrically desulfating batteries. Most of them were designed or developed in the last twenty years or so. Considering that lead-acid batteries have been around for more than a century, this is a relatively new innovation. Virtually all of the devices and patents I found have in common the use of some form of pulsing charge current. This is in contrast to the constant or slowly varying currents generated by sources like solar-electric panels.
I distilled and simplified these various techniques, and came up with a basic circuit that will keep small to medium sized batteries in desulfated condition. It can even be used to bring old, sulfated units back into service. Use of the circuit has dramatically reduced the need for equalization charges in my own home system.
...
Healthy Batteries
I have used this circuit in my main system for over a year, and have not seen the need to equalize in that time (I do not own a generator). All of the cells’ electrolyte levels remain in step with each other, and there has been no problem with starting big loads—a sure sign of battery health.
Patience is required in reclaiming weak and tired batteries, and no amount of desulfating will help a battery with a shorted cell, or one that has lost plate material through excessive use.
The device is especially useful for automotive batteries that sit for long periods. If you use a generator for equalization, this technique is a must. When you live off-grid, silence is golden.
MORE - see link above. -
www.rst-engr.com/kitplanes/KP0204/KPtext.pdf
Excerpt:
... battery sulfation has been with us for a very long time. The problem is that in a typical wet (sulfuric acid) battery, the lead plates want to be exercised. That is, they want to be charged and discharged on a regular basis. If they just sit there, the acid slowly, slowly builds up a film of sulfide that eventually causes the battery to "go weak".
This "weak" has everything to do with the fact that lead sulfide is a fairly good insulator, and as the sulfide layer builds and builds over weeks and months of disuse, the internal resistance of the battery goes up and up.
Finally it gets to the point where most of the voltage of the battery is dropped in the internal resistance of the battery and darned little gets to the point of intended use…like the starter motor.
...
4. There are going to be some batteries that are so far gone that leaving the desulfator on charge for a month will only get you four weeks and change. In my experience with these circuits, if you get the battery right when you notice that it is laboring to turn the starter, you have half a chance to make the desulfation process work. If it is so far gone that it won't even pull in the master switch relay, the odds of being able to save it are slim to none at all. See photo #6 for an example of a battery that will probably never be able to be brought back to life.
5. The sulfation process took weeks or months to develop. The desulfation process will take the same order of magnitude of time. Don't expect to put the battery on desulfate today and back in the airplane tomorrow. I've left batteries on this system for a month before I was happy with the end result.