<https://forum.allaboutcircuits.com/threads/optimising-modifying-desulfator-design.61257/>
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"Sorry about the topic being so long, I simply wish to be thorough. So many people put up topics with a lack of information making diagnosis difficult. I suspect I may not be one of them. Hopefully I haven't missed anything out.\n \n\n I know a few people on here have made these and I thought this forum would benefit from a discussion about desulfators and how to modify them. This topic is also about my experiment to better understand them and how is has not turned out as expected.\n \n\n It must be almost a year since I got into electronics through a project on here with the idea of making a 36v desulfator. At the time I didn't have the knowledge (in fact almost almost no electronics understanding) to build a 36v one so had to settle for making a 12v one from a thoroughly tested design which has proven to be quite effective. Recently I made another desulfator with the objective of understanding how to optimise the timing of the pulses to gain the understanding I need in order to design a 36v desulfator. Design wise it seems ok and all evidence shows it is working as it should apart from its ability to desulfate being very poor. I hope to find out where I have gone wrong and how to improve the design for my future project. I will also note that due to me using AGM's not flooded cells an equalisation charge would be damaging.\n \n\n http://alton-moore.net/graphics/desulfator.pdf\n \n \n\n It is somewhat based on the above design. I used slightly different parts but most are equivalents. The only notable differences are to L1 which I changed to self wound 70uH for experimental purposes (explained later) and used variable resistors and a 1nF capacitor to get the needed timing from the 555. The cables from the circuit to the battery are 1.5mm^2 mains cables that have been doubled up and some thin cables to a charger that are attached across C4. I have attempted to keep everything low resistance. The timing is set to 2kHz with an inductor charge time of 0.000003465 seconds, less than 1/10 of the original design, which is what I found to be the absolute maximum I could set it to without excessive heat from saturation.\n \n\n Methods I used to test device (I have not yet gotten hold of an oscilloscope) are: Testing the voltage drop across a resistor in my homemade power supply in order to know exactly how much current is being consumed. This has proven to be very accurate. Using a diode and low value capacitor to test the desulfator's peak voltage output. And the old fashioned method of feeling if any of the components are hot.\n \n\n The design itself seems to work, more or less. The output voltage spikes are measured at 61volts and the desulfator consumes about 55mA when the battery is fully saturated and nothing gets any more than warm. I can hear a constant hum coming from the circuit too which I know to be normal from the first one I built which works very well.\n \n\n This is what the desulfator looks like. I made quite a mess of the layout in my attempt to be compact and to get short connections:\n   \n \n\n I gave my design a home wound 70uH inductor, for L1, the idea was to make it work with an inductor that will saturate after an unknown period of time. I also wanted to test if lower inductance and resistance can give more power due to more rapidly charging and discharging the inductor.  I have read about the success someone had with a design that used a 22uH inductor for L1. Since I built this I have read into it some more and quite a lot of what I have read conflicts. Could anyone clear this up for me as this has most likely contributed to my desulfator being ineffective?\n \n\n \n\n Even though L1 is quite small physically and in Henerys it should work more effectively than it does. I read somewhere (can't remember where now) that someone as an experiment put a capacitor across D1 to simulate high diode capacitance and found that it boosted output current but nullified the effects of the desulfator and theorised that it somehow lessened the impact of the pulse on the battery. Could the combination of diode capacitance,130pF according to the datasheet, and relatively high voltage and not massive current be my problem?\n \n\n I have two main theories of what the problem may be, remember this circuit is for experimental purposes for a design that will contain unknowns. Any input and ways of improving the design will be appreciated.\n \n\n A few more notes and questions:\n \n\n I noticed that the mosfet heats up suddenly if I set the pulse width faster than 2 kHz, Why would this be?\n \n\n How helpful are fuses in desulfators? When I first plugged it in the mosfet reached well over 100 degrees C ,to touch, within a few seconds and the fuse did not blow. I am concerned that if something goes wrong with the mosfet or timer I could end up with a house fire.\n \n\n I decided to test to see if it is really worth using such thick wire with these things and the results were that if I use 1.5mm^2 wire to the battery the pulse output is 48v and with 3mm^2 it was 61v. So it does make a difference. It also explains why most commercial desulfators have such a bad reputation as they often use meters of very thin wire in which the resistance would drown out the current pulses. Although with my success I shouldn't be judging. :p\n \n\n Thank you"
<https://forum.allaboutcircuits.com/threads/optimising-modifying-desulfator-design.61257/>