Wiki: Power Tools: Battery Conversion

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Craftsman V20 Power Tools Battery Interface

Craftsman's cordless power tool web sites states: "*20V MAX battery, maximum initial battery voltage (measured without a workload) is 20 volts. Nominal voltage is 18."

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Craftsman V20 Battery Pin-Out

The photo below shows the pin-out on the battery:

  • B+ stands for battery positive terminal.
  • NTC stands for Negative Temperature Coefficient. This connector most likely connects to a NTC thermistor temperature sensor for battery safety.
  • ID. It's unknown what Craftsman power tools use the ID connector for. If you have an idea, please share it with us.
  • B- stands for battery negative terminal.

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Craftsman V20 Charger Pin-Out

The photo below shows the pins on the Craftsman V20 charger. Apparently, the charger interfaces to all four pins on the battery.

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Craftsman V20 Power Tool Pin-Out

Like the charger, the Craftsman V20 power tool interfaces to all four pins on the battery. But does it really take advantage of all four pins?

In order to figure out how the tool operates with the battery, we ripped up a piece of paper to cover the NTC and the ID pins in turn (see photo above). We tried it on three different Craftsman V20 power tools: a drill, an impact driver, and a heat gun. We determined that the Craftsman power tools operated fine with the ID pin covered (making us wonder the purpose of this pin).

On the other hand, the Craftsman V20 power tools will not operate with the NTC pin covered (shown in the photos above). The drill and impact drive will rotate for a split second, the LED light will turn on, but they shut down right after that.

So if you want to interface to the Craftsman V20 power tool with other battery source, you'll have to fake out NTC pin. The question is how to fake it out?

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Inside of a Battery Adapter

To answer the question from the previous section, we purchased the DeWALT 20V MAX Battery Pack to Craftsman V20 Power Tool Adapter on Amazon. Then we took it apart to see what's inside.

Inside the adapter, there is a very simple circuit board (see photo below). It consists of one surface-mount resistors--1002--that ties the positive terminal to the NTC pin.

Using the SMD Resistor Code Calculator, we determine that the resistor values is 10000 ohms, or 10 kilo-ohms.

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