Would it be better for the performance and long term battery life if the 7.2V batteries were periodically run all the way down and then recharged? If so, does anyone have any suggestions for how to quickly run the batteries all the way down? I’ve been trying to think of a device the (middle school) students could build that would run a battery down without needing a lot of monitoring but also not risk tripping a motor PTC and have a bunch of time wasted.
Good info here:
1.) Don’t overcharge batteries (Hence the reason I hate the VEX chargers, they do a poor job at this).
2.) Don’t drain them all the way down.
A good example is how Toyota manages battery charge level in their Prius, which uses NiMH batteries as well. The Prius computer management system will never let the battery go below 40% charge and only charger it to approximately 85% capacity. By doing this they are sacrificing a large amount of amp hour capacity but their batteries also last easily over 10 years in their cars. (I own a 8 year Prius with a perfectly healthy OEM battery)
Well if you really wanted to drain them you could just do what our freshman team does and forget to turn off their robot…
Thanks for the replies!
When you say this are you talking about charging them over 7.2 volts?
IF so, you are loosing a large part of potential power from the battery. The way the motors work is by turning them selves on and off very quickly, as you increase the power value in robotc, the % that the motors are on increases. Because of this, if you only have a battery at 7.2 volts the robot will perform very different from a robot that uses the standard vex charger, and charges them to >8. As the voltage increases the motors will perform slightly better, hence partially why you are required to use VEX chargers.
Sorry for going so far off topic.
Also, thanks for the link to the battery care website it was very informative!
No, thanks for pointing that out. A charged 7.2v NiMH battery should read about 8.2-8.4 volts. Anything over 8.4 volts is probably overcharged and may cause long term damage to the battery.
Umm OK, this doesn’t really help at all considering that VEX Batteries aren’t Lipos and won’t be until they are MUCH more safe