PhotographyIntelligent digital battery charger
Once upon a time, sifting through the scrapheaps at work, I scavenged a circuit board from a power supply of a portable, battery operated device (LMS Pimento 1) that was obviously not functioning properly. The charger part, recognizable by the Linear LTC1325 chip, seemed to be in working order. So I separated that part, and decided to use it as a universal battery charger for NiCd, NIMH, and lead acid batteries. It'll be controlled by the all-time favourite PIC16F628, readout will be from an all-time standard 2x16 alphanumeric LCD, and heck, I still have a rotary encoder lying in the junk box. So it'll be thrown in as well.
This is the circuit board:
The board contains the LTC1325 charger chip, which is capable of controlling charging current with a switched current source, read out battery voltage and current, connects to 2 temperature sensors and more. It'll have to be slightly modified to enable charging battery packs of 12 volts or more. In the image you can clearly see the charger chip and the discharge and current sense resistors, as well as the energy storage coil for the switching current source.
I have the schematic for this circuit board. But because of copyright issues, I'm not allowed to publish it. I'd be in breach of contract with my employer, so I'm not risking anything, I hope you'll understand. However, having said that, the schematic is almost identical to the base circuit in the LTC1325 datasheet, so if you're tech savvy enough, you'll be able to figure things out and build this charger yourself.
The charger chip is for experienced designers only (I consider myself experienced 
). This is simply because the chip is only a power interface with no ready-made charging algorithms on-chip. The algorithm is determined by the software in the host microcontroller. This way, you can set up this charger in any imaginable way you want, but you'll have to know your stuff to do it properly. The host communicates with the charger through a serial link and can read the A/D converters and temperature sensors, and control the charging current and the discharge output. Because of this versatile setup and because of the switching current source, you can charge any number of cells and any chemistry type, though this has limits, of course.
Update: well, there goes another great idea. I got a MAHA MH-C9000 multi-function charger/analyzer. It only takes separate AA and AAA batteries, but that's all I'm using anyway.
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2011-06-25 Martin Catudal
Are you able to find a small charger like that for a Lithium Ion batteries?
Martin Catudal
CEO Abicom Inc
mcatudal@abicom.ca
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