Propeller Battery Charger

Philldapill

I'm building a charge regulator for a 28AH deep cycle lead acid battery. It's for a gate opener that does a Smile poor job of charging it from a solar panel, apparently. The solar panel puts out ample juice when I directly connect it to the battery, but if I keep it on, it will boil it. So, I want to make one with the propeller. I have a couple of 14-bit ADC's that I'll be using that are low power and seem ideal for this. The charging seems simple - connect the solar panel to the battery if the voltage falls below X, and disconnect it when the voltage rises above Y. I know there are better charge schemes, like bulk charge, trickle, etc. but this is a first go at it and I'm not going for 99% efficiency.

However, speaking of efficiency, this leads to my next question. I need to devise a way to reduce the power consumption of the whole charger to a minimum. I was thinking using an opamp to watch the voltage from the panel(or current, which ever) and supply power to the propeller when the panel is producing power, AKA during the day. One scheme I thought of was to use a phototransistor to sense ambient light. This would probably be the simplest, but maybe not the most accurate. The other was to sense the voltage from the panel. My thinking is that the opamp won't know if the panel is connected or not to the battery, so if the voltage is ever above 12.6 volts, then there is some power.

Anyway, bottom line, I need to cut the power consumption to a minimum. I'm sure I could do this with an opamp with hysteresis, but my other objective is to be able to log the voltage of the battery throughout the day at around 5 minute intervals or so. That's why I want to use a propeller.

BradC

Why not just power the prop directly from the solar panel? Use a small and efficient switching converter that can cope with the open circuit voltage of the panel (the one I have can kick out nigh on 30v in good sunlight).

You could set it up so when the prop is not running, the panel is isolated from the battery, so the software must be up and running prior to it commencing a charge.
The prop should be up and running well before there is enough juice to commence charging the battery so you can watch the events at the start and end of the day also.

Philldapill

Hmmmm, good idea BradC. You've got me thinking about this a little differently now. You're right about the high voltage of the panels... mine puts out about 36V OC in decent sunlight, as high as 40V in bright sun. Come to think of it, I need to have the propeller on all the time to be able to log the voltage of the battery... Perhaps, for now, I might use an external source such as another battery to power the propeller at night so that it's own current draw doesn't skew my log results. I like your idea though about the prop having to be ON to commence a charge. Kind of a fail safe way of doing it, but at the same time I want to watch the battery voltage and keep time...

Lawson

How about using the Propeller's "sleep mode?" I.e. stop all but one cog, switch to RCslow, and sit in a WAITCNT or other wait insturction 99% of the time. If I remember right this will drop the current requirements to less than a micro amp. (check the datasheet for exact numbers) Just disabling the PLL and running at like 5MHz makes a big difference too. I think it's also possable to switch directly from 5MHz no PLL to 80MHz PLLx16 which is useful if "sleep" is combined with a cog acting as a real time clock.

My 2 cents,
Marty

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Lunch cures all problems! have you had lunch?

Fred Hawkins

Why not use a charging manager·chip like this $4 one? http://focus.ti.com/docs/prod/folders/print/uc3909.html

Then your prop recorder unit can eventually be used for something else.


·