Dump Backup Battery

[Jack Jones]

Many are missing the point that the keyword here is backup. Any electronics added to replace the NiCad and yet store enough juice to power the RC (ETC.) during brownouts is sure to be less efficient than the NiCad.

That is, you can't get something for nothing! Instead of having a pre-charged NiCad, you use power from the main battery, which is a net loss of power available at the start of the match. You'd also gain weight!

[billbo911]

Originally Posted by BrianBSL

Huh? What is preventing you from doing it with an IC based buck/boost converter? Small surface mount IC plus an inductor and a few resistors is all I could see that would be necessary.

Originally Posted by Billbo911

The only way to do this and still get 7.2v out of it even when the main battery drops below 7.2v would require a circuit with weight and size that exceeds that of the backup battery it's self.

Again, the only advantage I could imagine would be gained by elliminating it would be a reduction of size and/or weight. I don't think it is possible to achieve both requirements based on what you are describing. (I don't mind being prooved wrong, it wouldn't be the first time.) The trick would be to have it supply enought power to keep alive all the devices that may be drawing from it when the input voltage drops to say 5vdc.

Originally Posted by BrianBSL

Not that I would say its worth doing it, stick with the backup battery. If you are really worried about size/weight, there are plenty of suppliers of smaller premade 7.2V battery packs.

Now your talking. Just make certain it has the capacity to power all the devices that run off the battery.

[Al Skierkiewicz]

We can't really answer this for a particulr robot but let us remember that there are robots (many robots) that have inefficient designs that do run the main battery down to nothing in a single match. I have had teams that were actually proud of the fact that they killed a battery every match. With that being said, a power convertor fed from the main battery is still going to fail when a current demand on the main battery causes it to go to a couple of volts during a shoving match. Even with boost buck convertors, a 10 volt swing on input will not reliably keep the backup power up at 7.2 volts. In this case, two voltage sources are the best solution.