How to build a PAPRa m12 Battery Controller (v1)
How-To guide for building the Tetra PAPRa m12 battery controller (October 2020 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.
If you can build or buy custom circuitboards, then the other version is much more straightforward to assemble. The plans can be found here: https://github.com/tetrabiodistributed/PAPRA-PCB
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
3D Printed Parts
These parts should be printed at 0.2 spacing:
| Part | Quantity | Material | Supports Required? | STL File Location |
|---|---|---|---|---|
The Controller Body | 1 | PLA | No | |
The Controller Lid | 1 | PLA | Yes |
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.
| Count | Description | URL | Number in Package |
|---|---|---|---|
1 | Onyehn DC Motor PWM Speed Controller3V 6V 12V 24V 35V Speed Control Switch Mini LED Dimmer 5A 90W | 2 | |
1 | 2Pack Upgraded 3.5Ah M 12 Battery for Milwaukee 12V Battery Lithium XC M 12B Batteries | 2 | |
2 | Baomain Male Spade Quick Splice Crimp Terminals 6.3mm Crimp Connector Non Insulated | 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 | 30 | |
6" | BNTECHGO 20 Gauge Silicone wire 10 ft red and 10 ft black Flexible 20 AWG Stranded Copper Wire | 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:
| Description | URL |
|---|---|
Iwiss SN-48B Pin Crimping Tool | |
4-3/4 In. Bent Long Nose Pliers | https://www.harborfreight.com/4-34-in-bent-long-nose-pliers-63819.html |
Soldering iron | |
A hex screwdriver for the m4 screws | |
Flush cutter | |
X-acto knife | https://www.amazon.com/Xacto-X3201-N0-Precision-Knife/dp/B00004Z2TQ |
A deburring tool | |
#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:
Battery Case ("Controller Body")
Battery lid ("Controller Lid")
Crimper
Needle-nose pliers
Soldering iron/solder/soldering tools
2 red jacketed stranded wire ~2-3 inches (7-10 cm) long
2 black jacketed stranded wire ~2-3 inches (7-10 cm) long
Heat Shrink (to protect wire connections)
2 Male Spade Quick Splice Crimp Terminals
Flush Cutters
Wire stripper
Deburring tool
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.
Follow this guide here: https://www.thespruce.com/tinning-stranded-electrical-wires-1152893
Video describing the amount of wire to be tinned:
Photo showing tinning of the wires:
Crimp a red and black tinned wire each into the spade connectors
How to crimp:
Here’s a photo for bad crimping:
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:
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:
Remove the knob and nut from the control board
Install the power plug into the box
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)
Place the board in the box
Screw the nut and motor control knob onto the board from the outside of the box
Check the connection by turning on the power knob and looking for the red LED on the board to light up
Close access to the circuitboard using the M12 Lid
You may need to deburr the edges of the hole:
The final board:
Congratulations, you have completed the assembly of the power box for your PAPR!
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Last modified April 5, 2024: rename V1.0 to jun-2022 and moved to past build guides (53d8640)