Looksa Lot Like the Old Kick Back Circuit

http://leadacidbatterydesulfation.yuku.com/topic/1193/Voltage-Doubler-Desulfator-Design

http://leadacidbatterydesulfation.yuku.com/topic/1193/Voltage-Doubler-Desulfator-Design?page=5

http://www.batteryfaq.org/

Time for a new design
This new design fills the gap between the low power kick back and the direct drive desulfators and has features that a lot of you will like.
Here is a list of its features:
- It is as simple as the kick back circuit but capable of >30 amp pulses.
- No custom inductors!! All parts are off the shelf.
- Powered from the battery.
- Pulse width and rate fully variable.
- Very efficient (75 to 85% depending on load)
- No audible sound
- Very fast rise and fall times

Looksa lot like the old kick back circuit.

D1 - 12 volt zener diode. In this circuit it is mainly for protection of the driver and 555. I use a1N4742A 1 Watt diode but a 1/2 watt will do also.
D2,3,4 - this is a 40 volt 3 amp (or greater) schottsky diode. Almost any switching type diode will work. Don't use the standard power supply rectifier like a 1N5404. They are too slow. the short list of parts numbers is:
HER302 thur HER308
MBR340 thur MBR360
SR304 thur SR306
1N5822, 1N5824
50WQ10
50SQ060, 080
D2 - (listed twice) - You can push this circuit to over 100 amps peak with really good caps. If you do, you need to use the 50SQ060 or 50SQ080 for D2.
L1,2 - 20uh and 2.5 amp saturationcurrent minimum. Here is where powdered Iron cores workvery well. Pulse Engineering, Renco, etc.make a line of "simple switcher" inductors that work well. Read the early posts in this thread for PE part numbers. The Micrometals -8, -26 and -56 toroid cores that are about 3/4 inch in diameter work well here. Ferrites actuallyshould not be used here.
C6,7 -The capacitance is not important, the ESR is. The lower the ESR the more output current you will get.If you can achieve .01 ohm ESR for these caps you can get over 100 amps peak out of the circuit.
R3 - indicated as 10 ohms in the schematic. Value not critical. You can use 100 ohms if you want. This resistor is just part of the protection of the 555 and mosfet driver.
Q1 - an IRF1404 works great. Lowest "ON" resistance wins. The part needs a Vds of at least 30 volts (40 and above is better) Beware of counterfeit Mosfets from China.
Go forth and desulfate
Mark

I have corrected my stupid mistakes. I have made a png of the table of components. Can you check for stupid errors again please. I have kept the redundant protection diod as I need the trace to go through it I could replace it with a 0R I guess.

I cannot be certain of the inductor without physical examination, as the suppliers website does not really indicate much.

[edit] I have changed the images to reflect the latest pcb version. Our local supplier does not have any current rated inductors except one 0.1mH, which from what you [Mark] have written may be large enough. What is the part number of the tiny little inductors in the first post. They look good. I fear that the high voltage nova caps wont cut it. I think I need to build a rig to measure ESR, which doesnt look easy. Detecting bad caps is not so bad, but measuring ESR looks a bit tricky. If anyone could look at http://www.emcesd.com/tt020100.htm and http://repairfaq.ece.drexel.edu/sam/captest.htm to help me find a method to determine the ESR in ohms using a square wave genreator and a scope, it would be much appreciated. (I can see the hint of it ,but dont quite get it yet...)

Cheers.

Jasper

Here's a new twist guys:
There seems to be efficiencies to be gained using a transformer run direct drive with a half wave voltage doubler front end.
http://www.creative-science.org.uk/multipliers.html
Because of the ac sinewave we dont see high inrush currents into the caps thus we can eliminate the current limit resistor.
Further the voltage doubler means we only need half the supply V from the transformer => lower transformer resistance losses. I calc. that with a transformer that uses 14 gauge wire at 10" per turn needing 16 turns secondary wire (for 16VAC RMS) we should see around .04 Ohm secondary resistance. Add that to perhaps .04 Ohm for a 15000uF Low ESR cap as the first cap in the doubler circuit => .08ohm total. Thus for a given current draw of say 3amps we have a power loss of i*i*r = 3*3*.08= .72 Watt. Compare to say a 3 ohm "limit" resistor we get 27 Watts lost! An improvement of 97%!!!.
With 16VRMS the voltage doubling works out to about 38VDC. (32*1.4 peak) - (6V Cap charging losses). This is as simulated in Proteus ISIS with a 4000uF secondary cap.
For the second cap I used a 4000uf .01 ESR ....annd estimate about .03ohm for the MOSFETS and wiring losses and .01 for a 13V desulphated batt. This still delivers up to (38 -13)/.05 = 500 Amps per pulse at a 60Hz frequency, 10us pulse.
If the 38V peak pulse bottoms out around 25V (based on pulsewidth), avg energy delivered is : 0.5 * capacitance * V *V = 0.5 *.004*(38-25) *(38-25) = 0.338 Joule per pulse. At 60Hz => .338*60 = 20 Watts into the .05ohm load! or 20/5 = 4Watts of pulse energy into the batt!!
For a heavily sulphated batt of perhaps .1 ohm Int Res. We have a pulse of (38- 13)/.14 = 178A. And a larger pulsewidth = 200usec due to slower discharge. This simulates to a peak of 38V and a base of 29V (on a 13V batt) for a 9V change.
Energy = .5*.004*81= .162Joule per pulse = 9.72 Watts into the .14 ohm load => .1/.14 * 9.72 = 7 Watts into the batt!!!

I have completed assembly of your Voltage Doubler Desulfator Pulsor and have it connected to a healthy battery rated at 435 CCA. I have also connected a voltage adjustable 2 amp battery charger with amp meter to this battery. The voltage is set at 13.5 volts. Current draw with both pulsor and battery connected is 590 ma. The battery alone is 90ma. The control circuitry operating behind a 100 ohm register at 12.6 volts draws 93 ma. The output voltage measured on the + and - bus at the output terminal of the PCB is 20.98 volts. Voltage measured across battery terminals is 15.47 volts. The output voltages were measured thorougha peak detector circuit consisting of a 1N4148 diode and a .05 ceramic cap. The frequency measured off pin 3 of the 555 timer is 947 hz. I am sorry to say I do not own a scope. Some day maybe. I constructed this circuitry on a 4" x 6" PCB which provides a generous amount of space for components and traces. The traces on the power side are 3/8" wide and two of them are 3/4" wide. I hope this is adequate. What do you think? If not I can lay solder wick along them. These wide traces are about the limit for a 25 watt soldering iron. The leads from the PCB to the battery consists of #12 stranded wire 6" long. Heat sinks purchased from Radio Shack were placed on both the mosfet and diode D2, thankfully.
The following is the list of components I used:
Mosfet - IRFB3307
Diode D2 - Schottky Power Rectifier, MBR40250, 250 Volts, 40 Amp, DigiKey #MBR40250GOS-ND, I hope this was a good choice.
Diodes 3,4 - Schottky Rectifier, 5Amp, 50SQ080.
Inductors - Pulse Electronics PE-53120NL, DigiKey #553-1588-5-ND.
Capacitors - 4 @ 35V, 3300uf, low ESR .013, Nippon Chemi-con, KY series.
NE555N
Mosfet Driver IC -TC4426CPA, DigiKey listed 3 series of these, EPA, CPA, AEPA, I flipped a coin, came up C. You get the picture. DigiKey #TC4426CPA-ND.If this was not the bestchoice, it is easily replaced and fairly cheap. I later looked at the 2 data sheets. AEPA may be the latest edition, I am not sure.
First let me say that I am not an electronic engineer. I have some basic skills, but thats about it. I am not new to kit building nor new to battery desulfation. However, the last couple of months have been my first attempt at building my ownbattery desulfator. This will be my third one. The first two appear to be successful, at least one battery thinks so. My test equipment consists of two DMM's, A Fluke 27 and a Fluke 179. The 179 along with the normal menu will read frequency, temperature and capacitance. I built this desulfator with the hope of obtaining more desulfation power. The first two were to slow slow slow.
My observations: The circuit appears to be operating, but less than optimal. The mosfet became very hot. Temp reached 150 deg F.I had to blow on the heatsink to keep it cool to finish taking measurements. I hooked up an 80mm computer case fan to cool it. The temp went down to 95 deg F. Very nice. I thenchecked the voltage drop across Diode D2, it was .039 volts. That concerns me, because not much current flowing.Voltage on base of mosfet is .096 volts. Whats going on here? This circuit is drawing approximately 400 ma, but not much output to battery. Problem could be in the timing circuit not properly turning on the mosfet.I will replace both ic's in timing circuit. I hope the problem is not with the mosfet or diode itself. Mark, what do you think?
Mark, I want to thank you and others like yourself who contribute so much knowledge and help to others on this forum. I have read a good portion of the posts on this forum and am amazed at the willingness to help.
Thank you,
Cyber Guy

Richard
The basic circuit will work very well with only minor changes at 24 Volts.
- You do not need the 7812 regulator. A 12V .5 watt zener diode works well at 24 volts with a 500-600 ohm .5 watt series resistor.
- The IRF 540 is a bad choice. It will get very very hot due to its high on resistance. An IRFB4110 is a far better part. You can start with the IRF540 and change later. Watch the temperature with the 540.
- D4 appears to be in backwards and has no reason to be there at all. If you must use a 7812 regulator change D4 to a resistor, 200 to 400 ohms .5 Watt.
The original simple circuit works very well at 24 volts with only component changes. Change the series resistor that feeds the zener diode and change the Mosfet to a IRFB4110. And of course you will need C5 and C6 to be rated at 30 Volts or above.
Simple is better. Please do not hesitate if you have more questions.
Mark

I use the big blue cap (51,000uF), a power supply and low ohm resistors to simulate a battery. This is much more stable than using a real battery,and I can change the "internal resistance" very easily.

These are all the same parts we are use to using. The 555 timer circuit is right out of a kick back design. The TC4426 replaces the PNP transistor Mosfet driver. (You can replace the TC4426 with the PNP Transistor or an inverting totem pole driver if needed.)

Heres how it works.
When the Mosfet is off, the two caps are charged up to the battery voltage (13V) through the inductors. When the Mosfet turns on the capacitors are now in series, generating a high current 24 volt potential that discharges into the battery. It is a pretty simple design and generates a lot of current. The desulfating pulse voltage will always be double the battery voltage minus resistive losses (ESR, on resistance,etc.) As the battery voltage rises so will the output of this circuit.

The following photos were measured under the following conditions:
- Pulse width = 7 microseconds
- Pulse rate = 1700 Hz
- Battery internal resistance = .25 ohms
- Battery voltage = 13 volts

This shows 22 volts peak (9 volts above the battery voltage)

This shows 34 Amps peak current pulse (measured with a pearson current transformer)

The equasion to calculate the peak current (with no losses) is as follows:

Vin X Iin / (Vpeak - Vbat) X DF = peak current

Vin = Input voltage to the circuit (13 volts)
Iin = Average input current to the circuit (.371 amps)
Vpeak = Peak voltage seen across the battery (22 volts)
Vbat = battery voltage (13 Volts)
DF = Duty factor (.000007 X 1700 = .0119)

This means that the calculated peak current with no losses should be 46 amps.

Another way to calculate peak current is: (Vpeak - Vbat) / battery resistance= peak current. This formula yelds 36 amps.

Recap of peak current measurenents and calculations:
Calculated no loss - 46 amps
Measured pearson CT - 34 amps
Calculated from voltage and current - 36 amps

So far I am thrilled with the performance and the simplicity of this circuit.
More details in the next posts