Re: Home Brew Chargers anyone?

RogerN wrote:
Years ago I started working on what was supposed to be an alternative to the Alpha 4. The basic concept seemed simple enough but I wasn't sure how to get components to handle reverse polarity and short circuits without smoke. About the time other multi-chemistry chargers came on the market, I quit working on it. The interest has been there and over the years I've learned what I needed to know then. Also, now there is more available in free simulation tools, etc.

I've been studying different switch mode power supply topologies. SEPIC would allow you to charge batteries over a wide voltage range but I haven't found very high powered SEPIC controllers. I have found Linear Technologies has Boost controllers that can give 50V at 5A (250 Watts) from a 12V (Actually 10V to 28V) source. Then you can use a buck converter to lower the voltage to what you are charging. Add some analog outputs and op-amps to allow a microcontroller to set the current and analog inputs to read the voltage and current and that should be a pretty powerful charger.

I'm interested in getting something going on this and let the schematics and firmware be open source. That way the software can be improved, features added, or new charging algorithms added as new battery technology comes out. If anyone's interested I can give links to the simulation software and circuits.

I'm not sure on the microprocessor or microcontroller to go with. I want something that anyone interested can program for low cost. Anyway, I've got to get the details ironed out and tested in the analog circuitry first.

RogerN

Why not use a flyback topology, with the battery connected between your +V and the output? It'll give you 0 - whatever volt output, at the cost of having the battery floating above your ground reference. As long as you don't bring the battery + terminal above some magic regulatory voltage WRT ground (I think 60VDC or so is where some regulatory hurdles start popping up in most places) you shouldn't have problems.



.---------------------o----o -battery
| |
| |
| ---
| ---
| |
+12V | ___ |
o----o---UUU----o---->|----o----o +battery
|
|
gate drive ||-+
||<-
o-------------||-+
|
|
===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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See details at http://www.wescottdesign.com/actfes/actfes.html
.

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