RC Powered on 7.2v backup

[chris31]

I am not an electrical geniuos so I have a question. Is it possible to have your RC powered soley off the 7.2v battery? Or does it want the 12v power supply of the main battery.

[Mark McLeod]

Originally Posted by chris31

I am not an electrical geniuos so I have a question. Is it possible to have your RC powered soley off the 7.2v battery? Or does it want the 12v power supply of the main battery.

The RC needs to detect power from the 12v terminals before it will start up.
After the 12v is disconnected the Master code turns off the RC running on backup alone after a few seconds. Of course there isn't enough power to do more than drive servos.

If it's not for competition there is a way to get the RC to run for about 3 minutes without 12v power using the 2004 version of the Master code, but it still needs a goose to start (we sometimes use a regular 9v battery to jump start it).

[chris31]

So basically you need the 12v battery. My goal was to use the 05 RC for a project I was working on and obviously I want to use something other than the huge 12v battery used for competition. The more I think about it I guess using a smaller 12v battery will work better than trying to power the RC by just a 7.2v battery.

[Mike Betts]

Chris,

Note that, functionally, the VEX controller is almost identical to the FRC controller and needs only the 7.2V Battery to operate.

Mike

[Gdeaver]

Look around for an old 12 volt regulated wall wart power supply. Allot of old ink jets used them. 1500ma are common and some LCD power supplies are 5 amp. Make sure its a regulated supply and mind your pluses and minuses. I bet one is lurking in one of your friends basement in the pile of old electronics that they can't bring themselves to throw out.

[yongkimleng]

Originally Posted by Mike Betts

Chris,

Note that, functionally, the VEX controller is almost identical to the FRC controller and needs only the 7.2V Battery to operate.

Mike

Or try the EDU RC. Runs off 5 to 9 volts.. not sure what would happen if you try anything higher

[BrianBSL]

I'd bet that if you put a 7.2V battery on the 12V terminals it will work. Haven't actually tried it, but I'm pretty sure there is nothing in there that runs on 12v and it is certainly not within dropout range of the regulator.

[chris31]

Originally Posted by Mike Betts

Chris,

Note that, functionally, the VEX controller is almost identical to the FRC controller and needs only the 7.2V Battery to operate.

Mike

Originally Posted by yongkimleng

Or try the EDU RC. Runs off 5 to 9 volts.. not sure what would happen if you try anything higher

Unfortunatly all I can get my hands on is a 2005 FRC FC.

[Al Skierkiewicz]

Originally Posted by BrianBSL

I'd bet that if you put a 7.2V battery on the 12V terminals it will work. Haven't actually tried it, but I'm pretty sure there is nothing in there that runs on 12v and it is certainly not within dropout range of the regulator.

Brian,
The RC has a low voltage detector that shuts down the main outputs and engages the backup when the main input voltage falls below about 7.5 volts for a length of time. This is to insure that the 5 volt regulator has sufficient voltage to keep the main supply at 5 volts.

[Gdeaver]

An old wall wart 12 volt power supply would work. Ones for ink jets are around 1.5 amp and LCD monitor ones can be 5 amp or more. Mind your pluses and minuses. There are some small 12 volt jell cells that are used for alarm system back up. Much small than the First battery.

[Mark McLeod]

Consider using feeding the 12v terminals with a 9.6v NiCd RC transmitter battery from Radio Shack or a hobby store as an alternative.
Regular alkaline batteries in a 9, 10.5, or 12v configuration will work also, but you'd want to look at your expected power drain to see how expensive replacing batteries will get.
As Al said, when the RC/servos pull your voltage below 7.5 you'll have to replace or recharge your batteries.