Scott Autoflow Battery Adapter

This is a 3D-printable adapter to power a Scott Autoflow powered air-purifying respirator (PAPR) using modern, Makita or Milwaukee M18 power tool batteries.

The original Ni-MH battery packs for this older system are prone to failure. The locking mechanism weakens over time, causing them to fall out, and the cells eventually lose their ability to hold a charge. With this adapter you can revive an old Autoflow system.

There is no switch so remove drill battery when storing, otherwise DC-DC converter will drain the battery!

Parts required for both versions :

• LM2596 DC-DC Buck Converter (or a similar module with adjustable output voltage)
• 2x M4 x 15mm Countersunk Machine Bolts
• 2x M4 Nuts
• 2x M4 Washers (approx. 20mm diameter)
• 2x M5 x 25mm Hex or Screw Head Bolts
• 2x M5 Nuts
• 2x Fork or Ring Terminals (sized for M4 bolts)
• Wire (approx. 20-22 AWG, flexible silicone wire is recommended)
• Print scott_adapter_body and scott_adapter_cover
   

Milwaukee M18 adapter:

• 2x 6mm Male Spade Terminals (uninsulated, or with plastic covers removed)
• Print milwaukee_adapter

Makita adapter:

• 4x M4 x 15mm Hex Bolts
• 4x M4 Nuts
• 1x M5 x 10mm Bolt
• 1x M5 Nut
• 2x 6mm Female Spade Connectors (insulated)
• For Battery Contacts (Choose ONE):
  • Option A (Salvaged): An inner terminal piece from an old Makita tool.
  • Option B (DIY): A small piece of 1mm thick sheet metal (steel or brass) to fabricate contacts.
• (Optional) 1x M3 x 15mm Countersunk Bolt
• Print makita_left, makita_right, makita_adapter_extension and makita_terminal_body (if needed)

Wiring

Always check battery polarity (+/-) at each wiring step!

Remember to check output voltage before connecting the adapter to Scott Autoflow! Output should be 5.4 volts.

Wiring Scott Adapter Body

This section creates the electrical contacts that will power the Autoflow unit.

1. Prepare Washers: The M4 washers will act as the power contacts. If needed, use a countersink drill bit to create a slight chamfer on one side of each washer. This helps the countersunk bolts sit flush.
2. Press Washers in Place: Press the two M4 washers into the round recesses on the top of the scott_adapter_body. The spring-loaded terminals inside the Autoflow will press against these.
3. Prepare Wires: Cut two 10cm pieces of wire. Crimp a ring or fork terminal onto one end of each wire.
4. Assemble Contacts:
   1. Insert the M4 countersunk bolts through the washers from the top.
   2. On the underside of the part, place the crimped ring/fork terminals onto the bolts.
   3. Secure everything tightly with the M4 nuts.

5. Wire the DC-DC Converter Output: Solder the free ends of the wires to the "OUT+" and "OUT-" terminals of the LM2596 converter. Match the polarity to the markings molded into the scott_adapter_body.

Choose the set of instructions that matches your battery system.

(Option A) Wiring Milwaukee M18 adapter

1. Prepare Terminals: Remove any plastic insulation from the 6mm male spade terminals.
2. Attach Wires: Cut two 10cm pieces of wire and solder or crimp them to the spade terminals.
3. Install Terminals (Heat-Set):
   1. Use a soldering iron to carefully heat one spade terminal.
   2. While hot, use pliers to gently press it through its designated slot in the milwaukee_adapter part, from the side the battery will connect to.
   3. The terminal should protrude about 8mm from the printed part to make solid contact with the battery.
   4. Repeat for the second terminal.
4. Wire the DC-DC Converter Input:
   1. Feed the wires through the bottom of the scott_adapter_body.
   2. Check Polarity: Use a multimeter on a real M18 battery to confirm which terminal is positive (+) and which is negative (-).
   3. Solder the wires to the "IN+" and "IN-" terminals of the LM2596 converter. Double-check the polarity before soldering!
5. Attach Adapter: Secure the milwaukee_adapter to the scott_adapter_body using the two M5 x 25mm bolts and nuts.

(Option B) Wiring Makita adapter

1. Prepare the Extension: Insert the four M4 nuts into the hexagonal slots on the back of makita_adapter_extension. Attach this piece to the scott_adapter_body using the two M5 x 25mm bolts and nuts.
2. Prepare the Battery Contacts:
   • If fabricating: Cut two contacts from 1mm sheet metal. Use a soldering iron to heat-set them into the makita_terminal_body.
   • Fabrication instructions for the contact:
   • 
   • If using salvaged contacts: Insert the salvaged Makita terminal piece into the makita_terminal_body.
3.  Assemble the Terminal Holder:
   1. Prepare two 10cm wires by crimping a female spade connector to one end of each.
   2. Sandwich the makita_terminal_body between the makita_left and makita_right pieces.
   3. (Optional) Secure the sandwich together using the M3 countersunk bolt from the back.
4. Mount the Terminal Assembly:
   1. Connect the female spade connectors to the metal battery contacts. You may need to bend the contacts slightly to ensure a snug fit.
   2. Attach the entire terminal assembly to the makita_adapter_extension using the four M4 x 15mm bolts.
5. Wire the DC-DC Converter Input:
   1. Check Polarity: Use a multimeter on a real Makita battery to confirm which terminal is positive (+) and which is negative (-).
   2. Solder the wires to the "IN+" and "IN-" terminals of the LM2596 converter. Triple-check the polarity before soldering!

Setting voltage on LM2596

    DO NOT ATTACH THE ADAPTER TO THE SCOTT AUTOTFLOW YET.

1. Attach a fully charged power tool battery (Milwaukee or Makita) to your completed adapter. The LED on the LM2596 should light up.
2. Place multimeter probes on the output washers on top of the adapter (or on the "OUT+/-" terminals of the converter).
3. Using a small screwdriver, turn the adjustment screw on the small brass potentiometer on the LM2596 module until the multimeter reads exactly 5.4V.
4. Now you can test by connecting the adapter to the Scott. If nothing happens, turn the power switch to another position on the scott, remove battery and reinsert. Sometimes it won't start if voltage is applied when the switch is in ON position.