EAA Sport Aviation 113

nu t s & bo l t s

craft & technique

A Pulse Desulfator Restoring weak or sulfated lead acid batteries

DAVE BARKER, EAA 587700

The chemical reaction responsible for the function of lead acid batteries has several competing chemi-cal processes ongoing in the cell. The most familiar

and desirable process is the production of electric current due to ion exchange in the acid electrolyte.

Most batteries have a maximum life of about four to maybe fi ve years, whether you use them or not. The pri-

mary battery failure mechanism is current overage, which buckles the lead plates, leading to a short circuit of the cell. Those failures are not repairable.

However, the more common failure is sulfating. This is an alternative chemical process within the cell that rains down a snowy white sulfate-fl ake precipitation that accu-mulates at the bottom of the cell and gradually reduces

The desulfator dumps very short high

frequency bursts of current into the

battery. These high frequency currents

are at a low enough duty cycle to prevent

any buckling of the lead plates.

114 DECEMBER 2006

craft & technique

its output and current discharge capacity to zilch. The good news is that this can be fi xed, and by doing so you can about double the life of your battery.

Pulse Desulfator This project is a lead acid battery pulse desulfator for restoring and maintaining low-use battery applica-tions such as in boats and airplanes. The device will restore a completely sulfated (not shorted) battery in about two weeks. It will also just about double the life of a conven-tional battery with regular use.

Here’s how it works: The desulfa-tor dumps short, high-frequency bursts of current into the battery. These high-frequency currents are at a low enough duty cycle to prevent any buckling of the lead plates. It is delivered at a 3.6 MHz frequency that roughly matches the molecular resonance of the sulfate molecule. This burst has suffi cient energy to cause some secondary or deep ion-ization in the sulfur atom that will allow the sulfate molecules to move it back into the acid electrolyte solu-tion.

Circuit Operation The pulser rides the 12-volt line on a trickle-type battery charger and bat-tery. The L2/C2 input fi lter isolates the pulsar circuitry from the battery and charger. Stored energy from C2, the 100uF capacitor, is switched into

You may place the circuitry in the battery

charger case or in an external chassis

box.

EAA Sport Aviation 115

inductor L1. When the transistor switches off, the inductor fi eld col-lapses and generates a burst of volt-age on the order of 50 volts to 60 volts and approximately 40 amps or more for about 20 microseconds. This burst is repeated 1,000 times per second. This high current is then dumped via the fast recovery diode back into the battery. High-current pulses produce the second-ary resonant ionization of the sul-fate precipitate electrochemistry and move it off the bottom of the cell and back to work in the electro-lyte solution.

ApplicationUse a 2-amp fuse with the pulser. Be careful not to hook it up backward. Attach the pulser unit to the out-put leads of a trickle battery char-ger and to your battery. A highly sulfated (non-shorted) battery may take as long as two weeks to recover to nearly new performance. Regu-lar use on your aircraft battery will restore the battery’s rated amp-hour performance life and discharge capability.

If you use the pulse desulfator on a battery installed in your aircraft, do not turn on the aircraft master switch while it is connected. It is unlikely but not impossible that the high-voltage pulse may get through your avionics power input protec-tion circuitry. Be smart, be prudent, and take care of your radios.

ConstructionUse 560K (Green, Blue, Yellow) col-or code resistor for R2. For R1 use 15K (Brown, Green, Orange). R3 is

Carburetors You Can Bank On!

Answer: Yes you do!*

Ellison Fluid Systems Inc. • 350 Airport Way • Renton, WA 98055 • 425-271-3220

* Question: Do I need one of these? Find out why at:

www.ellison-tbi.com

Regular use on your aircraft battery will restore the battery’s rated amp-

hour performance life and discharge capability.

116 DECEMBER 2006

craft & technique

300 ohms (Orange, Black, Brown). Note the polarity marks on the elec-trolytic capacitors and orient prop-erly. The C3 100uF negative lead is near the white stripe. C2, the yellow 10uF Tantalum caps’ positive lead, is nearest the black stripe. Remove the label tape on the inductors L1 and L2. Pull loose the lead that crosses the diameter, strip off the insulating lacquer, and position each wire in the L1 and L2 terminal holes and set the inductors in place as shown with hot glue.

Install the components in the cir-cuit card as shown and solder using short pieces of 16 gauge wire to con-nect the circuit board to the plus and

minus leads of the battery charger. The box enclosure of the circuit card is left up to the imagination of the user. You may mount it in the bat-tery charger case or in an external chassis box available at your local electronics supply shop. If you have a 24-volt battery system, increase the value of R3 to 620 ohms and add a 12-volt zener diode in parallel with C3 to limit the voltage on the time and inverter components.

A do-it-yourself pulse desulfator kit is available from www.Geocities.com/powertugs. This includes all elec-tronic components, printed circuit board, instructions, kitting, shipping, and handling.

Dave Barker, EAA 587700 helps produce the EAA Chapter 79 craft and techniques page.

Oscilloscope photos at left show

the typical ringing waveform.