I intend to use the relay to "cut in" and "cut out" the charging circuit depending on a) the state of the battery, and b) the state of the solar array. Let's say for instance it's early morning, and my panel which in full sun open circuit puts about 21v output, is putting out about 13.5. This would be indeed a case where a boost circuit on input charging power would be beneficial, which my "theoretical circuit" does not currently provide for. It does however try to use the solar array power on "load inputs" to reduce the battery output during low light conditions.

I guess one of the things I would like this circuit to do is use whatever renewable power (stationary bike output, solar output, wind output etc) is available to a) charge the battery (if necessary), and b) provide any leftover power directly to the load, taking some of the "pressure" off the battery array. c) report all the specifics on input and output power levels via a pc interface (usb, serial, i2c etc)

I've been working for about 2 years to whip together a relatively simple / low cost solution to manage using solar panels (or other input sources) in a renewable system. I would consider myself an "intermediate level beginner" in terms of my electronics knowledge, PICBasic programming knowledge, if that makes any sense.

What I'd really like to do is get a bunch of us talking about a reasonably scalable low cost circuit that accomplishes a) charging 12v Sealed lead acid batteries (like the ones in UPS units) b) over voltage / under voltage cutoff (maybe with boost, maxim?) c) USB/SERIAL voltage / current status monitoring (vb system tray interface?) provided by a 18F4550 or equivalent and a couple (very small) MAX4172 ic's.

I would be happy to scarf up and share some vb software to interface the whole thinger to a Winblows box (which would use the melabs usb dll, legalities?).

I'm not an electronic engineer, nor do I wish to be (at the moment). I think if there's other's working on similar tasks that we could all benefit from joining forces.

I realize my posted diagram is not a full blown schematic and lacks some passive components.

So far in the course of my electronics projects I've been able to a) setup a 18F4550 to do usb and use a/d inputs b) use max4172's to acquire current measurement. c) use the a/d inputs to aquire voltage via a voltage divider, d) write vb code that uses the melabs easyhid dll to communicate with the usb device.

Anyways let me know if anyone wishes to collaborate or has suggestions as to how to develop a reasonable circuit.