Hitec RDX2 200 AC/DC Multi-Function Smart Charger

Features:

• User-Friendly Interface
• Balance, Standard, Storage and Cycle Modes for All Lithium Battery Chemistries
• Battery Resistance Meter
• Terminal Voltage Control
• Re-Peak Charge Mode and Delta-Peak Sensitivity for NiMH/NiCd Batteries
• Capacity Cut-Off Limit
• Smart Ventilation Fan
• Built-in Power Supply Function for Powering Devices up to 27V @ 10A

Internal Resistance in FTC

One of the reasons this charger is “smart” is that it can tell you the internal resistance (IR) of a battery. A battery’s IR increases over time, and batteries with a higher IR are likely to reduce a robot's performance. Competitors in the First Tech Challenge (FTC) can use their knowledge of a battery’s IR to evaluate if that battery is still ready for the ring or if it should be relegated to practice.

The effect of batteries’ IR values on robot performance is clarified by a small, but essential, piece of electrical theory. Voltage is calculated by multiplying current by the resistance (Ohm’s Law, written as voltage = current X resistance). As a result of this relationship, when a robot draws current, the IR will cause the voltage drop. Higher IR values produce greater drops in voltage, and voltage drops result in reduced performance.