Backup Battery Charging Circuit

[David55]

I have a question from the electrical team:

They built the custom circuit needed to charge the backup battery using the main 12V battery (found here). The output voltage to the RC is 8.8V instead of 7.2V. Is it still safe to connect the circuit to the RC? If not, what do you suggest we do? (we used the exact parts that are written in the diagram).
BTW, the output to the battery is 9V instead of 8.7, so we assume that's OK.

Thanks in advance,
"Steampunk" #1577 electrical team

[Dad1279]

Check the other threads, there has been alot of discussion on this circuit. The condensed version is that the circuit works, but always charges (overcharges) at about 100mA. If we use the camera, we will use this circuit, but use a spike to switch it on and off.

[Al Skierkiewicz]

David,
It sound as if you don't have a backup battery installed. Ths charger is desinged for the backup battery to be installed on the robot.

[natis]

where do you find the parts for the backup battery circuit?

Please reply soon. Thank You

[pheadxdll]

Bateries are usually charged at a voltage slightly higher than their capacity. Our circut puts out something like that.

We found most of our parts at Radioshack and for the few we couldn't get we orded them from Digikey.

[oddjob]

Mouser.com has all the parts, although some might need to be cross referenced to equivalent part numbers. The diodes were the hardest to find, but Mouser does have them.

[Rapt0r9]

Last year one of our engineers made a schematic to charge our back up battery. I am not sure if he knew that ifirobotics had one, but we built the circut and were going to use it to charge the battery for use with the camera, but when arriving at Trenton, we found the bot to be 20 pounds overweight, so the camera got the boot and along with it the need to charge the back up battery. We never got to test the circut, but I am pretty sure all of the parts are avalible from radio shack's parts cases.

Yes it is normal for a charger to outut at a higher volatage than the battery. Otherwise it would take a very long time for the battery to charge.

[dlavery]

Originally Posted by Rapt0r9

Last year one of our engineers made a schematic to charge our back up battery. I am not sure if he knew that ifirobotics had one, but we built the circut and were going to use it to charge the battery for use with the camera, ....

Better be careful with that. It is a violation of Rule <R56> to use any circuit other that the one specified by IFI to charge the back-up battery (last year it would have been a violation of 2006 Rule <R53>). As of Team Update #13, you can use alternate chargers to charge the battery off-board of the robot. But you only have one option for on-board charging.

-dave