How to build a Tetra PAPRa m12 Battery Controller (v1)

Describes how to build the October 2020 version of the Tetra PAPRa m12 battery controller component.

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.

If you can build or buy custom circuitboards, then the v2 version is much more straightforward to assemble. The plans can be found here: https://github.com/tetrabiodistributed/PAPRA-PCB

Parts required

3D Printed Parts

These parts should be printed at 0.2 spacing:

Table 1. Table Printed Parts
PartQuantityMaterialSupports Required? STL File Location

The Controller Body

1

PLA

No

https://github.com/tetrabiodistributed/papr-print-files/blob/15d2646571625c84bc1cf04a3f13bcbb808990b3/STLs/M12%20Controller%20Body.stl

The Controller Lid

1

PLA

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

1

Onyehn DC Motor PWM Speed Controller3V 6V 12V 24V 35V Speed Control Switch Mini LED Dimmer 5A 90W

https://www.amazon.com/gp/product/B07GP72BWV/

2

1

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

https://www.amazon.com/gp/product/B082WW688D/

2

2

Baomain Male Spade Quick Splice Crimp Terminals 6.3mm Crimp Connector Non Insulated

https://www.amazon.com/gp/product/B01MQ332R6/

100

2

TOTOT 30 Pack 5.5mm x 2.1mm 3 Pin Female DC Power Jack Panel Mount Screw Nut Kit DC Socket Electrical Plug

https://www.amazon.com/gp/product/B077YC457J/

30

6"

BNTECHGO 20 Gauge Silicone wire 10 ft red and 10 ft black Flexible 20 AWG Stranded Copper Wire

https://www.amazon.com/gp/product/B01AAX64EC/

120

6"

20 awg Solid wire kit Electrical wire Cable 7 colors 23ft each spools 20 gauge UL1007 Tinned Copper Hook up wire kit breadboard wire for DIY

https://www.amazon.com/Electrical-colors-spools-UL1007-breadboard/dp/B083DNGSPV/

276

Heat shrink connector covering (optional)

Recommeded Tools

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

Table 3. Table Tool List
DescriptionURL

Iwiss SN-48B Pin Crimping Tool

https://www.amazon.com/gp/product/B00OMMZ502

4-3/4 In. Bent Long Nose Pliers

https://www.harborfreight.com/4-34-in-bent-long-nose-pliers-63819.html

Soldering iron

https://www.amazon.com/gp/product/B01MD12DYT

A hex screwdriver for the m4 screws

https://www.amazon.com/gp/product/B007ICWAJC

Flush cutter

https://www.harborfreight.com/micro-flush-cutter-90708.html

X-acto knife

https://www.amazon.com/Xacto-X3201-N0-Precision-Knife/dp/B00004Z2TQ

A deburring tool

https://www.amazon.com/gp/product/B01L2XR4P2

#0 Phillips head screwdriver

https://www.homedepot.com/p/Husky-8-in-1-Screwdriver-with-LED-Light-232360016/301959976

Build Steps

You will need these components on hand:

  1. Battery Case ("Controller Body")

  2. Battery lid ("Controller Lid")

  3. Crimper

  4. Needle-nose pliers

  5. Soldering iron/solder/soldering tools

  6. 2 red jacketed stranded wire ~2-3 inches (7-10 cm) long

  7. 2 black jacketed stranded wire ~2-3 inches (7-10 cm) long

  8. Heat Shrink (to protect wire connections)

  9. 2 Male Spade Quick Splice Crimp Terminals

  10. Flush Cutters

  11. Wire stripper

  12. Deburring tool

  13. Philips head screwdriver

Prepare the wires

Cut the wires to size.

To do so, you will need to cut them down to their lengths (our build used ~3 inch/10 cm lengths). We prepared all six wires (4 stranded and 2 solid) to be basically the same dimensions: ~3 inches/~10 in length, 0.5 cm insulation stripped from both ends.

Tin the stranded wires.

Video describing the amount of wire to be tinned:

Photo showing tinning of the wires:

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Crimp a red and black tinned wire each into the spade connectors

How to crimp:

Here’s a photo for bad crimping:

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and the video explanation:

Attach remaining red and black tinned wires to the power socket

How to build the power socket with tinned wires:

Attach remaining red and black solid wires to the power socket

How to build the power socket for the fan box with solid wires:

Final prepared wiring looks like:

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M12 controller circuitry

Snip a portion of the spade connector

A video describing this step:

Clean the M12 battery holder spade ports

On the inside of the printed M12 box, there are two slots where the spade connector should fit in. These slots may have some extra plastic around them due to print quality issues, so use an x-acto knife to clean those slots:

Insert the spade connectors into the M12 box

These spade connectors should be inserted with red on the left, black on the right. The snipped connector should slide in place and prevent the spade connector from coming back out again.

Tab to hold the spade connector in place:

Wire orientation:

Test the spade connectors are in place:

Install the board into the M12 box

This video captures the entire process:

Essentially, these steps are followed:

  1. Remove the knob and nut from the control board

  2. Install the power plug into the box

  3. Connect the knob and spade power wires to the board (red to plus, black to minus, spades to DC in and power plug to motor control)

  4. Place the board in the box

  5. Screw the nut and motor control knob onto the board from the outside of the box

  6. Check the connection by turning on the power knob and looking for the red LED on the board to light up

  7. Close access to the circuitboard using the M12 Lid

You may need to deburr the edges of the hole:

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The final board:

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Congratulations, you have completed the assembly of the power box for your PAPR!