SparkFun 5V/1A LiPo Charger/Booster Hookup Guide

Contributors: MTaylor
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Using Multiple Charger Boosters

5V may be fine for microcontrollers, addressable LEDs, and servos, but with motors sometimes some extra kick is required. With electric motors, speed is proportional to voltage, and torque is proportional to current. So if we want robot acceleration we'd want a high torque motor (low resistance), and if we want to go fast we'll need to supply a large voltage. This section shows how to use multiple boosters and what that means for the voltage levels.

The boosters have bypass diodes placed across their outputs. This means that if a negative voltage is presented to the output, it will conduct rather than apply negative voltage to the rails.

This allows the boosters to be placed in series to create voltages larger than 5, with a couple of caveats.

Running with one dead battery: For each booster/charger that is not generating voltage in the stack, 0.5V will be subtracted from the sum of running boosters/chargers.

The following two diagrams show how two chargers in series interact. With both chargers on and supplying 5V, the output runs at 10V, and 1 amp is driven through the booster circuit (shown as an ideal supply).

Two Charger/Boosters in Series

Two active booster circuits working together to produce 10V

When one booster stops producing voltage, it's still in the current loop and must pass the 1A that the other booster can provide. The protection diodes allow the current to slip by, but at the cost of a diode drop. For these B340A Schottky diodes, that's about 0.5V. The output voltage is now 4.5V.

Two Charger/Boosters in Series with One Booster On

Picture of boosters with one dead battery

Increasing Current

Life gets a little trickier if more current is needed. By supplying your own diodes and "diode OR-ing" the outputs, you can get increased current at the cost of a diode drop, or somewhere around 4.5V. You may get away with just connecting up the outputs but run the risk of back-feeding one output with the other.

Output Voltage: The voltage of the combined boosters will be at a diode drop below the output regulated voltage.

Two Charger/Boosters in Parallel with Diodes

Two supplies in parallel can source more current, but external diodes are required.