Battery Charger Project

I just posted another battery charger with minimum parts count. Both current and voltage regulated, but it is a Non-Isolated design. Can be useful in some applications.

If interested, go to:

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Take care......Gary

Reply to
Gary Lecomte
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Do you think there any danger to the diodes if power is applied at the peak of the line voltage, say 340 volts? The current could be many amps for a short period, but maybe only a microsecond or so. I usually use a resistor in series, but maybe it's not needed?

-Bill

Reply to
Bill Bowden

Hi Bill, It shouldn't be a problem. The 1N4005's have a surge current of 30 amps and the Capacitors Reactance of the 2.2 ufd cap should quite effectively stop any peak currents to a reasonable value. However at 340 Volts, you will need to use a Much smaller Capacitor to get the 100 Ma. in my circuit (About .8 ufd and at least a 400 volt rating)

Take care.........Gary

Reply to
Gary Lecomte

Yeah, right. "Take care", and you have a project that can be deadly.

I have a gizmo that's very similar to your circuit, that looks like the plug on the end of a power cord, minus the power cord. On one end there are the two brass prongs, and on the other end there are the standard snap-on clips for a 9V battery. This device was imported from Japan in the '60s, and was made for charging these batteries. It was downright dangerous, and you won't find such devices nowadays because they _are_ dangerous. If you build one of these circuits, you should enclose the battery under a lid with an interlock switch to shut it off when the lid is opened, so that someone can't touch the contacts when it's live.

BTW, the 470 uF (not MFD) capacitor is of little use in this circuit. The battery dowsn't need filtered DC, and the cap can't charge up to more than the zener voltage.

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Watson A.Name "Watt Sun - the

It should have a 100 ohmn resistor in series with the line, to make a low pass filter. This helps prevent high voltage transients from passing thru the capacitor and damaging the rest of the circuit.

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Watson A.Name "Watt Sun - the

Peak of the line voltage for 120 volts is ~170 Volts. Peak to peak is

340 and a DC rated cap should be 3X higher than the AC line.

The circuit would probably work and last forever, but I'd go with a

100 ohm resistor to limit the inrush current all the same. The current is only limited by the circuit impedance until the 470 uf charges. When the reactance cap is at zero volts, and power applied at the peak of the sine wave, the wire inductance and resistance of the wire and parts are the only limiting factors.

A flame proof resistor will also serve to act as a fuse if the reactance cap shorts. In that scenario, your zener may vaporize or flame and the electrolytic turn into shrapnel. The cost of the resistor is a bargain considering the safety it adds.

Does the circuit really need the electrolytic cap?

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I'm not sure if the resistor is needed or not. When you turn the thing on at the peak of the line (170 volts) the current is limited only by the wire resistance, maybe an ohm or so. This means the diode current will be 170 amps which falls off with a time constant of RC or 2uS. If the time constant is 2uS, the current falls to almost zero in 10uS. So, we have an average current of 85 amps for 10uS which amounts to 850 microjoules of energy if the diode voltage is 1 volt. I don't think a millijoule is much to worry about since some of those avalanche MOSFETS are rated at 500 mJ. This is 500 times less, so I doubt the diode will blow. But the capacitor could be already charged to the full line voltage and switched on at the negative peak which would multiply the problem by 4. Still not much at 4 millijoules. I think I'll try that circuit using a couple 1N914 diodes back to back to see if I can blow them. They should survive.

-Bill

Reply to
Bill Bowden

There is a commercial product, for a cordless power tool, that is a charger that is directly connected to the line. The terminals are deep inside the unit where the battery is inserted.

Reply to
Gary Tait

In article , R75/ snipped-for-privacy@defaulter.net mentioned...

If it's used as a power supply. But for a dharger, I don't believe so.

I've heard that the pulsating DC ripple knocks some hydrogen bubbles off one of the plates, but I don't know if this applies to all types of batteries.

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Reply to
Watson A.Name - "Watt Sun, Dar

A Few Comments:

Yes this circuit can be dangerous, that is why the warnings in my article.

No the 470 Cap isn't needed if you are only charging a battery, but can be helpful if it is also running a circuit at the same time.

As to uf which I agree is proper abbreviation, but back in the 50's when I started in electronics, numerous schematics used various definitions and I picked up some bad habits. Sorry if it offends anyone, but we all have bad habits.

Placing a 100 ohm resistor can be a good idea as it will act as a fuse in the event of a short, however a standard 1/2 watt resistor will constantly fail. If you really want this I suggest a wire wound type resistor or even a 250 ma fuse.

I have used this charger design in a large number of speciality industral products that have been in the market place for over 20 years. These products were all used by "Electric Utility Companies" throughout the world. "They are totally isolated from the user with a plastic case and knobs". No limiting resistor and no problem. I used both Phillips "366 series" and Evox "MMK" caps, both rated at 250 volts. "None of these chargers have ever failed to date". The only thing I did do that is not mentioned in my article was to put a small brass heatsink on the zener. Not sure if it was really necessary but it does reduce some heating.

A number of units were also produced for 220/240 volt operation by simply putting another cap in the neutral line. They were also as reliable.

This design is "definately not suitable for all charging applications", but it can have practical safe applications.

Take care.....Gary

Reply to
Gary Lecomte

In article , snipped-for-privacy@hotmail.com mentioned...

Not a matter of bad habits, but a matter of internationally accepted abbreviation standards. The m or M in MFD, by international standards, means mega if it's capitalized, or milli if it's lower case. So it's a matter of confusion as to what you mean. I and many others remember those days, and also picked up those bad habits, but we had to change to the new standards. It's time you did so, too.

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Watson A.Name - "Watt Sun, Dar

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