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Step 8Update:
It's been over a month now and I'm happy to report that my desulfator circuit is working well! My battery now charges to over 13.4 volts after a full charge. Before desulfator treatment it would not rise beyond 12.7 volts. This is a very good sign meaning that the plates are now much cleaner, the electrolyte is now contacting their full surface area, and that full electricity production has been restored. I kind of wish I could verify this visually but I can't due to the battery being a sealed type. For now, I'll have to be satisfied with just reading the improvement in my voltmeter.
Some notes:
1. During testing I found that my charger has no real trickle rate mode and instead stops the charge entirely when it decides that enough charge has entered the battery. Call it an idle state instead of a trickle rate. If left like this, after a full charge the battery voltage will slowly drop to about 12.2 volts within a week or so (further if I let it), which I assume is a reflection of the battery's natural decay rate plus the amount of charge being consumed by the circuit itself. I therefore, every few days, top off the battery by turning the charger's power switch off, then on again to restart the high charge rate. A few hours later I make sure that the red LED has turned off and the green LED has turned on meaning that the charger has finished the charge and gone back to its idle state. The desulfator is then free to do its thing without interference from the charger.
2. There is a marked drop in pulse peak voltage from about 50 volts, measured at fuse F1, to about 36 volts measured at the battery. This is due to losses in the cabling going to the battery. You can limit these losses by keeping the cables as thick and as short as possible. 12 or even 10 ga wire is not too thick as long as you can solder it and it is flexible enough to not make the circuit unwieldy. If you use thinner wire just know that the circuit will still work but that the reduced voltage at the battery will take longer to recondition it. My thanks to DRZCYY for bringing this to my attention.
3. Use of wire loops to hold down the two coils can simulate a shorted winding in the coils and result in slightly reduced output. It's best to use plastic or nylon tie wraps for this purpose. My thanks to EDTEK for this tip.
I'm working on some improvements to the design and hope to offer a printed circuit board in the near future. Check back here for further updates.
Some notes:
1. During testing I found that my charger has no real trickle rate mode and instead stops the charge entirely when it decides that enough charge has entered the battery. Call it an idle state instead of a trickle rate. If left like this, after a full charge the battery voltage will slowly drop to about 12.2 volts within a week or so (further if I let it), which I assume is a reflection of the battery's natural decay rate plus the amount of charge being consumed by the circuit itself. I therefore, every few days, top off the battery by turning the charger's power switch off, then on again to restart the high charge rate. A few hours later I make sure that the red LED has turned off and the green LED has turned on meaning that the charger has finished the charge and gone back to its idle state. The desulfator is then free to do its thing without interference from the charger.
2. There is a marked drop in pulse peak voltage from about 50 volts, measured at fuse F1, to about 36 volts measured at the battery. This is due to losses in the cabling going to the battery. You can limit these losses by keeping the cables as thick and as short as possible. 12 or even 10 ga wire is not too thick as long as you can solder it and it is flexible enough to not make the circuit unwieldy. If you use thinner wire just know that the circuit will still work but that the reduced voltage at the battery will take longer to recondition it. My thanks to DRZCYY for bringing this to my attention.
3. Use of wire loops to hold down the two coils can simulate a shorted winding in the coils and result in slightly reduced output. It's best to use plastic or nylon tie wraps for this purpose. My thanks to EDTEK for this tip.
I'm working on some improvements to the design and hope to offer a printed circuit board in the near future. Check back here for further updates.
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You can also check the voltage in each cell by attaching your meter probes to short lengths of stiff wire and placing them in the acid of each adjacent cell, one at a time. The wires should just touch the acid and not the plates to avoid shorting them with the wire. Do this at each of the six fill holes to measure each individual cell voltage. Any cell that reads 0 volts or slighty more is shorted. Any cell that reads less than 1.7 volts is too far gone to be worth your trouble.
If you don't have a voltmeter you can still do this, but you'll have to use a hydrometer and measure the acid's specific gravity. You're on your own there as I don't have one and prefer to use meters when possible.
By the way, batteries will self discharge and sulfate at a much higher rate if they are left uncharged in a high temperature environment. My internet sources tell me that for batteries in temperatures over 77 deg F (25 deg C), the rate of discharge and sulfation doubles for each 18 deg F (10 deg C) rise in temperature. My best advice here is to try to find young batteries that have not been sitting outside a vehicle or left uncharged for more than a month or two to have any success in desulfating them. And remember, there are LOTS of things that can go wrong inside a battery. A desulfator can fix a lot of them but it is not magic. You'll find many batteries that, for one reason or another, simply won't take to the process.
Follow the steps in Smoke Test 1 to maximize your pulse output. Turn up R2 until an AC ammeter shows about 0.7 A. If you don't have a meter then you'll have to use the heat given off by coil L2 (the smaller, but hotter of the two) as your guide, but don't let things get too hot to burn either you or the circuit. Start by turning R2 up slowly until you just barely hear the tone, wait 1 minute, then SNIFF the coils. If your nose detects heat, or a burning lacquer smell, then L2 is too hot. If you don't smell anything then touch L2, D2 and C4. If they're still cool you can turn R2 up another 5 degrees. Wait 2 minutes more, then give the sniff and touch tests again. When you can leave the circuit running for 30 minutes without smelling the components, and the coils, D2, and C4 are warm but not hot to the touch, then you're at the maximum operating point for your circuit.
The coil core shapes are not critical but toroids give the most inductance in the smallest size. The secondary of a small step-down transformer can probably be used, or the ferrite core of an old AM radio antenna rewound with thicker wire might work, but they would be much bigger. I imagine several large steel washers coated with lacquer and wound like a toroid might even work, though be prepared to do some experimenting.
we are 2 amazed friends of your project working with renewable energies in nicaragua.
the lots of wastebatteries that are piling up made us looking for a solution.
the problem we are facing here is that almost noting of the parts used an be buoght in a store.
we have taken all the parts so far from pc-boards and the coils from power-supplies of computers.
here are some questions which we thank you if you would answer to us:
1. we only have found toroid coils with a yellow plastic coating, do you have any suggestion about how manny windings and what wire diam. could work?
2. there are no LOW ESR capacitors to get here, not even from old boards.
can we prevent overheating using 2 or 3 normal electrolitic capacitors in parallel??
3. without osciloscope, how can we determine the pulse voltage?
thanks again for your tips
martin and karl-gunnar
Read the comments under the instructible if you haven't already. In one I describe the coils in detail and how to make them. It's more important to get the wire size large enough to handle the current than it is to get the inductance values exact though they shouldn't be too far off the values listed. You should strive for a ratio of roughly 4:1 for L1:L2. They're pretty easy to make using used coil or motor wire of about the right diameter. Google "toroidal winding tutorial" to help you with the wire lengths and calculations.
The value for cap C4 is also not critical but it will get hot if the pulse width is too wide. The best advice here is to try several of about the right value and see if they work. Two or three in parallel will give greater surface area and allow better heat dissipation but you'll probably need a larger enclosure than an Altoids can to fit them all. You can also try heat sinking them (press-on TO5 transistor heatsinks will fit the little caps in the instructible perfectly). The Fast-Recovery (FRED) diode is fairly critical, however you can often find them in used computer power supplies. They too, can be doubled up for better heat dissipation.
As for testing the pulse voltage without a scope, that's hard. Just make sure your coils sing their 1K Hz tone, the output LED is on telling you pulses are present, and nothing is overheating and you should be well on your way. Good luck!