Battery Charging per TU #9

[Al Skierkiewicz]

Team update #9 addresses charging robot batteries while connected to the robot.
"Running the control system while recharging the battery:
We do not recommend simultaneously charging the battery while using it to power thecontrol system.
Teams should only power the robot control system components from a battery. Using bench power supplies or a battery charger/battery combination (in an attempt to recharge the battery while running the system) is not recommended, and it may cause damage to components or unsafe conditions."

To insure that teams realize the gravity of this response it is important to know what takes place during charging. It is and always has been against sound engineering practice to charge a battery on the robot and in particular while connected to the robot control and electrical distro. Many modern chargers not only produce current in pulses that exceed the terminal voltage of the battery, they often perform battery tests while in the charge mode to determine state of charge and define charge current parameters. In addition, during the charging mode, batteries may vent some gas pressure and or in the event of a failed charger or defective battery, it may actually leak some of the sulpheric acid used in the battery. Connecting a bench supply to power the robot and charge the battery also can produce spikes and currents that are destructive to system components.
Please charge batteries off robot using approved 6 amp or less chargers. Take the time to replace the alligator clips on your battery charger with an Anderson battery connector as suggested in several threads here on CD.

[writchie]

Al's comments are well worth heeding!

It is certainly possible to engineer systems that can operate while charging but this requires a lot of extra effort and extensive testing, especially with lithium ion batteries where the changes in voltage and current into the battery (and temperature) need to be closely monitored to determine when to change charge modes. The current draw from the operating device can mess this up unless fully accounted for.

While lead acid chemistry is much more tolerant, as Al pointed out most chargers today operate in switch mode and while the battery does a good job at filtering them at it's end, the high frequency pulses from the charger can find their way into the power supply of the PDU causing catastrophic problems. You don't want this kind of headache. Stick with powering from the battery and re-charge it when it drops below 11 volts. Learn to manage your batteries now - not during competition.

While we're at it - don't let your underclassman carry batteries by the wires. They can't resist this for some reason. This of course weakens the connections at the terminal and the damage can be hidden by the required insulating tape. The problem will show up as a voltage drop during heavy loads and you don't want to find this out on the competition floor. Remember, we're dealing with 100 amp loads.

[Gdeaver]

Also note that the jags probably will not like a stiff power supply. The battery soaks up surges from the back emf. Don't run them from a bench power supply. The whole system would be best powered from batteries.

[EricVanWyk]

I'll add my two cents in an attempt to flog this thoroughly (though correctly) dead horse.

The PD was not designed to work with a benchtop supply. It was designed to prevent damage if a benchtop supply was attempted.