BroMikey's Capacitor Dump Circuit

[SeaMonkey]

Excellent analysis and suggestion to sustain current flow
through the duration of the pulses.

[Farmhand]

Well all I need to do is to program the picaxe chip to pulse with narrower pulses and faster and then I get a squarish current wave form if I go narrow enough. Then the capacitor is only partially discharged so current flows the whole time if the pulses are narrow enough.

Anyway I think bromikey was under the impression his caps were fully discharging, and he may have a slow turn off. The residual current flow I think is through the inductor anyway. If I was doing it my way I would use a smaller capacitor and pulse at some kHz. I think with his resistor there is always residual current flowing no matter how long his discharge time is, and if his mosfet is not turned off fast he will heat it up.

If I used smaller caps and faster narrower pulses then I would not need to worry about using an inductor even, I only did that to get the dump cap voltage down at the end of the dump. A MOT primary would work better with 250 mH inductance and thick wire.
A low loss current limiter for a moment.

SeaMonkey I have only 100 nF caps across my driver chips on that board, I need to add the 10 uF caps as well yet. The driver supply is regulated to 11.95 volts so the chips need more reserve energy.

The coil I used had way too much resistance and not enough inductance and the caps were too big to get a voltage rise from the resonant charging circuit. After an hour or so the coil was so hot I could not pick it up, I waited 30 minutes so I could pick it up and used it for a pocket warmer, it's a bit cold here now.

I charge my batteries with a 6 amp dual output solar system, I only pulse batteries to keep them in good condition or rejuvenate them. And never excessively. I treat them usually with only 1000 uF discharges from about 22 volts and at random frequency the cap discharges when the desired voltage is reached and pulses to keep 17-18 volts on the panels, max power voltage.

All my batteries are in good condition and are kept charged and used, with the exception of the motorcycle battery, it doesn't get much use, but I keep it charged.  Motorcycle batteries fail at the drop of a hat, they are too compact to be long lasting.

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[TinselKoala]

Shortening the pulse will square off the top of the current trace all right... by preventing the capacitor from discharging. Don't forget that _energy_ is the time integral of power. So if you shorten the pulses, all else being equal, you will be delivering _less energy_ per pulse. Is there a tradeoff? More pulses per second, but less energy per pulse.... or a capacitor that isn't discharging as far so it takes less energy to recharge it back up....   There will be an optimum pulse width and frequency that transfers the most energy -- corresponding to the highest average power -- I think.

[Farmhand]

Here's a couple more shots one at 400 Hz 10% duty and one at lower frequency, at 400 Hz it pulled the dump cap voltage down due to the MOT primary's 260 mH inductance. I should have tried 200 Hz, at 400 Hz it was pulling 90 Watts out of the wall without the CSR and driving the battery voltage up like mad but also warming up the mosfet just a bit, not hot just warm. At the lowest setting it pulls a fluctuating 20 to 35 Watts and makes the voltage bounce.

Haha at 400 Hz it punching rectangles of current into the battery at a rate of over 10 amps a shot for 260 uS.

I think rather than paralleling mosfets a better way might be to use ie. four mosfets switched in turn so that each one has one 1/4 of the total work to do. Time to cool.

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Well I guess at 10 Amps @ 10% duty it is giving a 1 Amp charge to the battery.

[MileHigh]

Farmhand:

Assuming that you have complete control over the pulse of current into the battery, the next logical step is to use that to maximum advantage.  Without any direct experience myself, you can make a reasonable assumption that you get diminishing returns as you increase the amperage.  Eventually at some high current level the battery will act like 99% resistor, 1% recharging battery.  Also, presumably, standing and charging voltages well in excess of 12.6 volts are also not healthy for the battery.  It's because the EMF potentials set up by the molecular action are supposed to be at 12.6 volts (for the cells in series.)  So in my opinion, you get some kind of "brain fry" going on when the battery is at say 16 volts.  I am sure I have read in a few places how these excessive voltages do damage or reduce the life of the battery, etc.

I am not suggesting that you are doing any of these things, I am just pointing out the limits of going to extremes.

Anyway, the fun part would be to find the "sweet spot pulse regimen."

I am willing to get you that better battery chargers use a microcontroller to do something like this.  You can develop software to sense the battery's condition and adaptively charge it.  I remember reading the information about a pulsing battery charger from a Big Box store a few years ago and reading stuff like that.  I also read about a system that did the same for extracting power from solar panels.  Depending on the illumination level, the impedance match for extracting the maximum amount of power from the solar panel will change, and the microcontroller in the charger/interface to the solar panels would dynamically adapt.  I stumbled there because the Bedini "high tech" solar charger was out.

Finally, charging batteries or extracting the maximum amount of power from a solar panel is a perfect fit for for solving the problem with the application of "fuzzy logic" using a microcontroller.  So I bet you that there are fuzzy logic solutions out there but I doubt they use that term in the marketing.

MileHigh