Electronics simple compact battery charger/regulator/display?

this summer i will be making a electric skateboard, and since batteries always die at the most inopportune time (there was an earthquake here in '89, guess who's radio batteries died during the power outage?) i was thinking how simple it would be to carry a power cord in my pocket or make a little holder for one, with a small charger built on to the batteries. since i need the batteries to be regulated at 12V, i figured i could just combine both onto one PCB. I have a Li-Ion regulator for another project i've kinda shelfed for a while, but it's an SO-8 (read: very tiny SMD) package, and its for a different voltage (3.3V). i was also thinking a few LED's (red, yellow, green) to show charge would be nice.

does anyone have a link to something like this? or (if it is possbile) three seperate schematics so i could tie them together?

thanks

 

I guess they are normal lead-acid cells?

It's harder to make a charger for those new maintainance free cells since you need to go below a current specified in the data sheet for the specific battery to avoid gas buildup. But otherways it's the same principle.

You just charge with a given current and have a voltage regulated charger, when the voltage hits somewhere around 14-14.5V, you cut the charge current.

Remember that those cells need to be standing upright when charging to prevent acid from leaking out in case of unintended gas buildup. They have safety valves, but those only work properly if the battery is standing upright.

Allso, stay away from "motor" or "starter" batteries (car and MC batteries), what you need is "deep discharge", "hobby", "caravan" or "UPS" batteries that don't take damage from being emptied like normal car batteries do.
Edit: what was i thinking? Emptied? Should be "completely discharged"...

 

Discover Circuits has umpteen circuits, I've been looking for a good NiMH charger but there are loads of lead-acid ones.

 

Li-Ion, I always forget something important.

 

motorized skateboard? So essentially one of those scooter things without the handle and with 2 extra wheels? Hmmmmmm...

 

no, E-Manual.

basically, i am building the e-unicycle mentioned in the first paragraph, but with a 4DOF (4 degrees of freedom = rotation on the X and Y axis (side to side, front to back) and acceleration along the X and Y axis) gyro board. that board has been harder than circus peanuts in december to copy into Express PCB.

i am thinking about using those 11Ah Li-Ion batteries to make something like a 33Ah battery pack at about 30V, so i'll need both chambers along the side for batteries. maybe i'll have to go with a 22Ah pack.