backup battery charger

[falconmaster]

Hello all,

Does anyone know where you connect the 12 input for the backup battery charger that FIRST put out the schematics for? If you connect to the breaker panel the battery tries to run the robot electronics. Do we connect it on the battery side? Help!

[falconmaster]

Help!

[kE7JLM]

I would guess it goes on the breaker side, because FIRST would want everything off when the breaker is off.

[jee7s]

The 12 V input to the charger circuit should be attached to a small (20A) breaker from one of the breaker panels. (According to my reading of the wiring rules.)

The output of the circuit goes to both the RC backup input and the backup battery. When you connect this, you'll probably splice into the backup battery connector cable, or attach the backup battery connector cable to the charger board, then the charger board to the RC.

-JEE

[falconmaster]

When I connect it like you said, the backup battery tries to light up the motor speed controllers and spikes. This would drain the battery when you turn the robot off. Has anyone out there actually done this that could help us?

[Alan Anderson]

The IFI-provided circuit has the small issue of powering the entire robot from the backup battery. A simple addition will fix it: just put another 1N5820TR diode in series with the power input. That will prevent the circuit from back-feeding the breaker panel.

[jee7s]

Hmm...Al's on the money. It makes perfect sense both that the charger would try to power the robot, and that the diode will fix it.

I was basing my comments on the schmatic. My team has never used on board charging before. We'll be sure to include this modification.

-JEE

[Tom Line]

Yep. We built the circuit last year, and then chucked it out. You're much better off going to a hobby store and spending $25 on a high capacity 7.2 volt pack for RC cars and a nice charger actually comes with it. Once we did so, we never once had a backup battery issue, even when running with the same battery all day (with camera).

[SuperBK]

We also put a diode on the 12V power into the backup charger to prevent the backup battery from trying to power the electronics. Did that last year and plan to do it again.

[mneary]

It would seem that FIRST should modify the official schematic... where do we send the suggestion?

[d235j]

Originally Posted by mneary

It would seem that FIRST should modify the official schematic... where do we send the suggestion?

A suggestion should be sent to Innovation First (as they provided the original schematic).

[PhilBot]

Originally Posted by Tom Line

Yep. We built the circuit last year, and then chucked it out. You're much better off going to a hobby store and spending $25 on a high capacity 7.2 volt pack for RC cars and a nice charger actually comes with it. Once we did so, we never once had a backup battery issue, even when running with the same battery all day (with camera).

Even with a better battery, there's still the issue of someone remembering to change it periodically. The longer it lasts, the longer between changes... so kids tend to forget.

Having it charged on-board means never having to remember to change it. Granted, without the camera this year, the batteries should last longer....

We built a PCB for the charge circuit and got 3 boards made (just the boards) for $60.

I attached the ExpressPCB scematic and PCB files on this post: http://www.chiefdelphi.com/forums/sh...6&postcount=27

We'll be building a new one this year....