I will admit to being a little skeptical about the capacitive charger for 2 basic reasons. On the other hand I knew there was a reasonable chance it should work because batteries have a capacitance as well as a resistive factor to them. I knew the resistive chargers worked because I have used them on and off over the past 35 years or so. They have an established track record. Primarily the Reverse Current Charger, the Alkaline charger was simply a new approach with an old design. So I was willing to give it a shot.
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I will admit to being a little skeptical about the capacitive charger for 2 basic reasons. On the other hand I knew there was a reasonable chance it should work because batteries have a capacitance as well as a resistive factor to them. I knew the resistive chargers worked because I have used them on and off over the past 35 years or so. They have an established track record. Primarily the Reverse Current Charger, the Alkaline charger was simply a new approach with an old design.
So I was willing to give it a shot. In part because the capacitive charger also tends to desulphate a battery as it charges. My preliminary battery chosen was a motorcycle battery that had been sitting outside over winter, and was likely 4 to 7 years old and therefore an excellent candidate for sulphated plates.
The charger itself is nothing more than an industrial bridge rectifier I could only infer was a 9 Amp volt PIV as I could not locate a datasheet.
The capacitor was a VAC, 3 microfarad capacitor- non-polarized. That was it. Not counting cord or wires. The capacitor was wired to the line side of the mains power, in the event of a failure, it was the shortest potentially exposed path for AC current in the event of failure.
Ideally in a failure situation it would ground to the metal case I used from an old printer power supply and blow a fuse. At worst, it would hang free inside of the housing. After the initial 90 minutes of the first test, the battery read just over 10 volts. After 6 hours of charging the battery read After about 14 hours it was up to Further charging did not change this, so it is safe to asume one cell likely shorted from dendrites. If it will start lawn tractor, vibration from use might break up the offending dendrite.
Otherwise it may see service powering radios if otherwise healthy. I suspected the shorted cell, due to the low voltage after 6 hours. This was borne out by the final voltage after 22 hours on the charger. The next test will be some golf cart betteries that are so sulphated they will not take even a minimal charge off a conventional charger. As I write this update, the first golf cart battery is under charge.
There is a significant risk of explosion with these due to some unintentional rough handling. There are a number of other batteries in the lineup for testing as well, including potentially some fork lift cells that also sat out over winter. All of these will be updated in posts as the results are known. I may construct a second charger with aproximately 8 microfarads of capacitance just to speed up the charge rate for the larger batteries.
The capacitor is what limits current through the battery. Using larger values of capacitance raises charging current, and reducing capacitance reduces current. In short, the electrolyte level has increased within the cell. In short- the capacitive charger seems to work rather well in the initial test and holds a lot of promise. I do not know how well it would work on European VAC standard which is also used elsewhere in the world like Japan. I do not believe the frequency difference of the two standards is an issue.
In areas where 20 and 25 Hertz AC is in use, I do not know how effective this circuit would be, but I do believe it could still work, and I would be inclined to favor larger capacitor values by a factor of about 2. If hertz AC is the only AC available, a smaller capacitor value should be used, and expect a moderate failure rate of capacitors unless the capacitor is suitable for long term pulse or RF application. I would be inclined to reduce capacitance by at least half or even one fourth.
This is yet another charger style that fools and idiots need to avoid- this one can readily kill you if you do not excercise caution. With all of these, and ideally with any charger, situational awareness will avert most issues that might occur. If you build this, you accept all responsibility if something goes wrong. It is a reasonably safe charger in competent hands.
If you are not a careful individual, do not build this. It is a fast solution that has the potential to be cost effective. The drawback is the inherent danger of being connected to a high enough potential that can easily kill someone who is careless. Lower potentials reduce the energy envelope, but does not eliminate the desulphating ability. It just means a longer charging period.
More battery chargers and desulphaters to come, as well as some other miscellaneous projects as well. Share this:.
Capacitive Battery Charger
Use the Contact page to talk about your project. What follows is a Bad Idea, you could get blinded, burned, electrocuted or have your house burn down. This is not an exhaustive list. Normal battery chargers consist of some kind of regulated DC supply whose voltage is around the final voltage measured across the terminals of the battery being charged. For example, a healthy lead-acid battery has a nominal voltage of 2.
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Capacitive Battery Charger (preview)