High Pulse Impact Battery Restoration Technique

For Engine Starting and Deep Cycle Lead Acid Batteries

Brief History

Since the beginning of the 200 year history of the commercial use of batteries, there was a quest for methods of restoring depleted batteries and cells. Until the 1880’s there were no chargers as such, and the lead plate electrodes of the cells had to be replaced with new active plates and sulfuric acid electrolyte. The advent of DC commercial power brought generator charging, and commercial AC introduced many types of Transformer/rectifier charging units.  

As examples of the word’s growing dependency on batteries during the 1920’s and 30’s automobile and tractor batteries were often brought indoors for protection from extremes of weather, and early radios required three separate battery packs. In general, battery restoration entailed battery take- apart, and cleaning or replacing plates, separators, and lengthy charging. Additives and restoratives for the electrolyte proliferated with the same effect as patent medicines did for people in those days, and batteries and chargers were costly, and treated with respect. However, after World War II , batteries were ubiquitous and relatively inexpensive, were often mistreated or ignored, and often used without thought of proper recharge until they failed and had to be replaced.  

Things changed about a year after the beginning of the Iraq war, as there were serious problems with Ground Support Equipment (GSE) below decks on Aircraft Carriers and some military bases. The GSE or vehicle often did not start after two or three weeks of non-use after insufficient charging, and might have expired (dead from sulfation, explained below).

This situation has been changing over the last three or four years. A huge Carrier in the Persian Gulf cannot simply put in to port to pick up a few dozen batteries, and Humvees or Strykers have to start in a hurry. Batteries are heavy for airlifting, and often storage facilities means batteries being left baking in a sealed container on a loading dock. In the last few months another situation changed—batteries have become very expensive. China and India are buying old batteries in bulk for scrap lead, and lead prices are now about four times as high as in 2005, at $4000 a metric ton (2200 lbs.) as of October 2007.  Civilian, industrial, and back-up power requirements in the Far East have skyrocketed.

Please note that the only references herein are to lead- based batteries, although all types are affected. At this time there is no practical alternative, for large batteries, to Lead Acid. Even in US military aircraft, there is only about 12%  Nicad, almost all the rest being Sealed Lead Acid Batteries,(SLAB). Ground vehicles are 100% lead acid in various forms except for some special, hybrid, and experimental units. Various types of Lithium and other chemistry based batteries are being developed, as are fuel cells, etc.  But for now, lead acid is king.

Ecology

Ecology is a crucial factor for all types of batteries today.  Aside from the issue of mining for lead resources, battery recycling with its costs of pick-up, separation of plastics and lead, contaminants, and carbon emissions of smelting are environmental nightmares.  This renders it essential to recover existing batteries. Data from U.S. military sources which practice recovery demonstrate that 80-85% of batteries have been put back into full service lasting as longer or longer as the service time they had before restoration, and at the least add one or two years of additional service life.

Sulfation, a primary cause of battery failure

There are many causes of battery failure, many of them obvious such as misuse by polarity reversals, extreme short circuits, physical damage, and simple cycle and life span of the battery. Aside from the obvious, the most prevalent failure is due to sulfation. Essentially, sulfation starts with lead sulfate, which is a product of the normal discharge of a battery, collecting on the battery plates. If the battery is charged within a short period of time after the discharging, the sulfate is dissolved back into the acid/water electrolyte, and the battery is restored to its full capacity.  However, if the battery remains discharged for, depending on factors such as ambient temperature, as little as 24 to 36 hours, the lead sulfate becomes crystallized and electrically non-conductive, and very often cannot be dissolved by standard charging methods.

However, standard charging methods applied to a sulfated battery will sometimes eventually generate enough internal heat to dissolve the sulfate. This is especially true of constant current charging where the charge voltage continuously rises to force current through the battery. Even without charging, a steady application of a high temperature such as 50o C/122oF ( not recommended ) may allow desulfation and recovery  enough to accept charge. However these methods work only with lesser depths of sulfate crystals, and often require many days of operation on a single battery. Constant current charge, unless carefully monitored, may also cause out-gassing.

Desulfation

The sulfated battery may have an Open Circuit voltage as low as 1 or 2 volts.  In order to eliminate the crystal structure of the lead sulfate, very high energy, high peak amplitude pulses with sharp rise time at frequencies which range from 70 to 400 HZ are imposed across the battery, The unit generating and controlling these pulses will be named an “IMPACT CHARGER”  The charge algorithm is such that voltage levels applied across the battery assures that the battery will accept current, and yet will not cause out-gassing. The pulses are of sufficient impact so that even with an average ammeter reading of  2 or 3 amperes the pulse amplitude can be 80 to 100 amperes. (The pulses can be viewed only with an oscilloscope). As the battery voltage rises and current is being accepted by the battery, pulse amplitude lowers, duty cycle increases, and charge voltage lowers below the excess gassing value. Charge currents are controlled by the algorithm and bulk charge is in the 28- 30 ampere range.

If the supposition is made that there is only one pinhole in the crystallized sulfate, a peak pulse of 100 amperes, by simple Ohm’s law ( Watts (heat) = Current( amps) squared  x  Resistance ( the resistance of  metallic lead through the pinhole is  relatively low)   theoretically causes a very high temperature at the microscopic opening and essentially blows away a bit of it to be re-dissolved in the electrolyte. Thus it can be visualized that a train of pulses through an enlarging hole or holes can quickly expose the lead surface to normal charge.  ( One user of this recovery method has theorized as to the deeper physics occurring when a 100 ampere pulse of current, squared,( which is 10,000 amps)  passes through a hole which may be only microns wide in the crystalline material and onto a microscopic bit of conductive lead. He theoretically attributes the rapid dissolution of the sulftate to intense heat which may be a form of high frequency radiation, such as X-rays. we have not pursued this type of study. However, empirically, this may indeed be the case)

Practical applications

The Impact Charger, is being used successfully by the US military in bases and ships throughout the world for their ‘Optima’ brand Sealed Lead Acid 12 volt Ground Support Batteries which average 800 Cold Cranking Amps (CCA), and by the Marine Corps with Honeywell as the contractor for the sealed Hawker ‘Armasafe’ brand of vehicle batteries used in Humvees, Bradley fighting vehicles, Strykers, etc. The Armasafe is a 12 volt 1250 CCA battery. Both of these types are often in series and series- parallel combinations for 24 volt, very high CCA service. (A typical Auto battery is 550 CCA)

The prime attribute of this method as compared to days of build-up to charge acceptance by conventional chargers, lies in the very quick amount of time, usually within 1 to 8 hours, that it takes to allow the battery to accept normal charging as compared to days of build-up to charge acceptance by conventional chargers. This is for a discharged and sulfated but otherwise healthy battery. Also the fact that when the battery is restored it will continue to function for at least one and often two rounds of restoration if the battery again becomes sulfated due to lack of timely charge. The first round allows long service life, in some cases two or Five years of additional operation.

Another result of using the Impact Charger is that if the battery is only marginally healthy the unit may hurt the prospects of recovering the battery by sometimes causing cells to short circuit, puncture their separators, and overheat the battery. This is an attribute in that it weeds-out marginal batteries, but if it damages the battery, precludes recovery by slower methods.  Also it is a fast enough method that it can be known in perhaps 10 or 20 minutes whether the battery can be recovered, and after being conditioned to accept charge can be removed from the unit and placed on a conventional charger while another battery is placed on the recovery unit, or left on the recovery unit to completion of charge. The recovery rate noted by the military for the batteries described above has been typically 85-90%. Previous recovery rates using only conventional chargers were about 10%.

Battery Temperature Rise

If the battery presents internal problems and reaction to the very high current pulses of the Impact Charger,  the temperature of the battery rises. This is true in standard charging as heat is generated by the chemical reactions of charging. However, with the Impact Charger, these reactions are amplified. Unique conditions of the battery occur with the high power pulses of this unit. The conditions exhibited in both the Optima and Armasafe sealed batteries if and when the battery is going to fail the recovery procedure involves terminal temperature differential.  Background of the observations and the condition involving terminal temperature differential is as follows:

Terminal Temperature Differential & Prediction of Failure

When being used with the Optima battery, a temperature plate is provided  which conforms to the top of the battery and must be placed on the battery in order to connect the charging leads. If, during the conditioning process the battery temperature rises to 50o C/122oF the conditioning process stops and an  Over-Temperature Led lights. After cool-down to about 35oC/95oF conditioning resumes. For the Armasafe batteries, the negative and positive clamps each have a sensor with the same temperature limits as for the Optima, and also cuts-out charging upon over-temperature.

The reason for this difference is because the top of the Optima and the internal plates are physically close, whereas the Armasafe has a 3 inch gap between the top and the plates and temperature sensing at the terminals of the Armasafe was the most convenient location, although, it was thought, not the most accurate. However, after months of testing the condition with Armasafe batteries that were supplied  we made two observations:

1. Temperature sensing at the terminals is a reasonably accurate reflection of total battery temperature, at least in the two configurations where the terminals were close to the battery and where they were located with a 3 inch gap between the top of the battery and the terminals.
2.  If there were a significant different temperature of 4 degrees C or more between the positive and negative terminals, the battery would probably not recover and eventually overheat.

 In about 75% of batteries where the differential occurred (as estimated by the Honeywell operators) the negative terminal became hotter.(where hydrogen is produced during charging), In some cases, the positive became hotter and the positive terminal appeared to have more corrosion. The differential can occur before the battery reaches its charge cutoff temperature of 45oC.  

We also observed that if the battery reached a 4 or 5 degree differential at the terminals and the high impact pulse conditioning, (as a test), were allowed to continue, the battery would get progressively and rapidly hotter and the differential would widen to between 10 and as high as 15 degrees C. One of four test batteries vented with a sulfur odor when one terminal reached 55oC.   Therefore charge cut-off should be at the time the differential is above 4oC .  After cool-down, a second attempt at recovery is made, and if the differential recurs, the battery should be rejected.

We supplied this information to a Honeywell battery facility that was this system for ongoing recovery of quantities of Armasafe batteries being removed from Marine Corps fighting vehicles. The operating chief of the facility used the information to great advantage as a diagnostic tool as to whether to proceed with the recovery process or reject the battery. A thermistor temperature sensor is used for our tests which will eventually be added to the  unit’s terminal clamps, but in the interim the operators are using their fingers to feel the battery terminals. The total temperature cutoff sensing at 45oC is always in effect, and both sensing features, high temperature and differential temperature, have been effective in considerably increasing the production of recovered batteries.

We never found this differential condition in battery literature or in discussions with the battery industry and members of the American Electrochemical Society. We have also tried differential temperature tests with the Optima battery as well as the Armasafe batteries, with similar results, and have tried this with flooded batteries with less definitive readings. It may be that the flooded batteries can dissipate heat more readily than sealed batteries.  

At the present time we are  proceeding with its investigation of battery terminal temperature differential and expects to have further information by the end of February 08.  However, as previously mentioned, battery differential is presently being used with this high pulse method to achieve high production rates for recovery by accepting only those batteries which have a low terminal temperature differential.  

We also an even higher power unit for 12, 24, and 36  volt batteries  which are being used by experienced battery restoration companies, for recovery of large flooded batteries such as used for diesel engine starting, fork lifts, scissor lifts, golf carts and other traction uses.

Conclusion

Battery recovery is environmentally and economically important.   

A method which generates a particular range of  frequencies of extremely sharp rise, high peak amplitude, high energy pulses rapidly allows the battery to accept charge. The charge algorithm controls out-gassing and has proven to quickly recover sulfated lead acid batteries for continued long-term service.

The method also senses battery temperatures for safety charge cut-off when required, and    terminal temperature  for any significant temperature differential between the battery terminals. The method has proven to amplify internal battery problems and uses the differential as a diagnostic tool to quickly determine if  the battery will recover.