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Homemade Lead Acid Desulfator

Do you know what is a desulfator?
It's a little circuit very useful to have a last chance to restore to life a weak sulfated lead acid battery.
But you'll have greater satisfaction using this desulfator (for the quick final job) when used with Ni-Cd AA batteries affected by the so called "memory effect" or crystalline formation that reduces their capacity.
Recently, I connected this little desulfator for two hours to some elements near dead and the batteries seem become like new.

What is sulfation and why it happens?
It's the real consequence of the chemical reaction for the battery discharge, where the lead (Pb) and the lead dioxide (PbO2), reacting with sulfuric acid (H2SO4) during the proceeding discharge, change in lead sulfate (PbSO4). The lead sulfate layer is unable to dissolve in water and this creates a real insulation layer between the battery's tiles and the electrolite. Often lead sulfate forms because the lead battery was forced to rest for months and so there is no way to recover the full charge.

How can the desulfator restore a lead battery? When connected to a "weak" battery for a few hours (sometimes days), simply dissolves the lead sulfate layer (PbSO4) that cover the battery's tiles. Of course this circuit have to be used ONLY if the battery isn't damaged but only sulfated, if the battery is broken, shorted or with collapsed elements, desulfator can't do the miracle.
Over the internet, there are many links that explain life, death and miracles about this, one of the best for me is lead-acid-battery-desulfation.

Here is the schematic I used to homemade my "personal" 12 Volt battery desulfator and the final photos.
The current drain from this desulfator is 32-33 mA.


How to use your homemade desulfator and suggestions: simply connect the desulfator to the 12 Volt battery you need to "cure" and desulfator supplies itself.

In case your battery is completely flat, to run this circuit, you'll need to connect a little 12 Volt power supply in parallel with flat battery. Be careful that, when sulfate will be dissolved enough, there will be a huge current absorption from the battery and you could risk to melt the little power supply, as it was happening to me!

When I need to "desulfate" a few AA Ni-Cd batteries (1 to 4 elements), I put the elements in series with a 12 Volt lead acid battery: this desulfator can run safely till 20 V, so the desulfator works with the Ni-Cd elements and the lead acid battery also.

Be careful: if you leave the desulfator working all the night time, it could happen that Ni-Cd batteries fully discharge and that 12 Volt battery voltage starts to flow inverted inside Ni-Cd elements, charging the AA batteries with inverted voltage and damaging them. So, from time to time, it's better to monitor the Ni-Cd voltage batteries and if the voltage drop to 0 Volt/element, pull out the element or invert the same element, in this way the current will start to charge with correct polarity the Ni-Cd element.

homemade desulfator's side componentshomemade desulfator's side wires

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