More on the Capacitive Charger

While searching through some other reference material, I found an Application Note on a “Capacitive” power supplies that is very similar in concept to the capacitive charger. Microchip, http://www.microchip.com has it as note AN954.
If your browser does not show the link the url is below.
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en021083

The note is actually a compairison of a few varieties of transformerless power supplies for use in applications where something like a PIC processor and a couple other low voltage items are used in a circuit, where the rest of the circuit is higher voltage making a transformer a bulky and a more costly addition that can be ommited.

Mind you- the Capacitive charger is a slightly different beast, but you can use the Application Note as a reference to refine the charger and normalize the concept of the capacitive charger. The importance being the calculations. The real notable difference is as a battery charging circuit, the battery is both a load and a capacitance in the circuit, so there is no need for the 470 microfarad capacitor or the zener diode that are shown in the Application Note. The equations provided will also allow for a bit of optimization and also allow those on 50 Hertz/250 volt standards to modify the charger a bit closer to optimal for their area of the world. You can also add the protective devices as well, while not making the charger safer on the ends you attach to the battery because you are not isolating from the mains power, it does make it safer for the AC source.

And remember- this information is presented for educational use- if you choose to construct them, you do so at your own risk. The responsibility is on your shoulders and no one elses.

You can add an ammeter to the output side of the charger, either leg will work, you just need to make sure the meter is correctly polarized. This can help you determine if a battery is okay, or if it has a problem.

You also want to know what the current load rating is on the circuit you are plugging the charger into, you want to size the fuse for the charger at a value less than that current rating.

In that same application note, they also discuss a resistive power supply, and those equations can help you calculate a suitable set of resistances in the “Reverse Current Charger” and the “Alkaline Charger” while maintaining that 10:1 resistance ratio.

This topic will get revisited from time to time as more information turns up.

Additionally, Microchip has a smart charger reference design that will switch between two battery banks, but the circuit is limited to a little over 3 Amps. Someone so inclined could modify the reference design to switch potentially more banks of batteries and at a higher current. PICREF-5

Alternately, the power from the charging cicruit could be used to energize a relay coil for heavier charging rates.

Lastly, there is also an reference design for an uniteruptable power supply with a 1000 Watt true sine wave output. If you are at all familiar with the UPS systems- you can strip the reference design down to just the inverter portion. It relies on a 36 volt buss. With slight modifications it could be utilized on 12, 24, or 48 volts. The reference design as it is has an efficiency of 80% Meaning the 1000 watts is only drawing in the realm of 1200 Watts at total full load from the buss- 1350 Peak output drawing in the realm of a little over 1600 Watts at short term peak from the buss. You do need to tegister with Microchip, but that is no big deal. I do not have an application note or reference design number for this, so you will need to search the site with their search feature.

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2 Responses to More on the Capacitive Charger

  1. email me where you found the template for this site please. Or is this custom?

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