How to build a PAPRa m12 Battery Controller (Aug 2021)

How-To guide for building the Tetra PAPRa m12 battery controller (August 2021 version).

Quick Synopsis

The Tetra Powered Air Purified Respirator requires power to function, and the m12 battery controller provides that power for these models. The controller consists of internal circuitry, a potentiometer to adjust fan speeds, a cable to connect to the fan box, and a port for a Milwaulkee M12 Battery to be inserted.

This build differs from the v1 version in that it uses a custom-built circuitboard to remove many of the difficult steps of the build, add a battery charge indicator, and a separate power port for use in a car. If you cannot get the custom board, then please refer to the v1 version of this guide.

WARNING: we provide no warranty, implicit or explicit, that this device will work up to an N95 specification, when built outside of a facility rated to do so. The only way to truly test one of these devices using something like a Portacount under controlled conditions.

Parts Required

This build will require printed parts, purchased parts, and several tools. Here is a picture of all the components used in this build:

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And the assembly diagram can be found here. Note that this assembly calls for version 0.7 of the board.

Bill Of Materials

You will need these components. Prices fluctuate, and so are not included here. Alternative versions can be sourced, and we welcome edits for tested alternatives.

Table 2. Table Bill Of Materials (BOM)
CountDescriptionURLNumber in Package


Circuit board (v0.7)



2Pack Upgraded 3.5Ah M 12 Battery for Milwaukee 12V Battery Lithium XC M 12B Batteries




Should come with the board




Should come with the board


Recommeded Tools

These tools are recommended. URLs are for tools purchased and used in the building of the prototypes:

Table 3. Table Tool List

4-3/4 In. Bent Long Nose Pliers

A hex screwdriver for the m4 screws

X-acto knife

A deburring tool

A 10mm socket wrench

Build Instructions

Building this version of the controller is more a matter of ensuring that the Controller Box was printed cleanly and all support material is properly removed.

Attach the light pipe to the board:

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You may need to use the bent-nose pliers to get the pipe in place:

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Seat the board into the board housing:

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Place the washer over the power port, and then finger tighten a hex nut over the same power port to hold the Plate in place:

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Repeat for the potentiometer knob:

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Put the battery housing over the board housing, with the power plugs going through the spaces in the battery housing:

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Place square nuts into the square nut sockets on the battery housing:

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Screw in the screws into the board housing to secure the board housing to the battery housing:

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Use the bent-nose pliers to attach the nut to the DC jack in the battery housing:

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Use the socket wrenches to secure nuts onto the various ports:

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Attach the potentiometer printed knob onto the potentiometer knob:

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When the battery is in the housing and the potentiometer turned on, a battery life indicator should turn on:

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Congratulations! You have built a Tetra PAPRa M12 Controller Box v4 (August 2021)!