Introduction: Makerspace Power Tool Upgrade: NiMh to Lithium Iron Phosphate

About: Im a Student at RPI in Troy NY. The best part of college is most definatley 'Spelunking' or dumpster diving for parts in the elctrical engineering dumpster.

Did you / your makerspace inherit 12v cordless drills with a dead / unhappy NiMh battery packs? Need more juice and an incredibly high number of charge cycles? Want to safely upgrade to the land of LITHIUM IRON PHOSPHATE GLORIOUSNESS? This is the instructable for you!

Step 1: We Have the Technology

For this project, the replacement battery module is a 12V Lead Acid Replacement Battery, a Lithium-iron battery with a built-in BMS disguised to function like a 'normal' 12 volt battery. This removes most of the issues associated with fancier battery chemistry, charging battery incorrectly and dangerous lithium battery fires

Price/Where to buy:

Price: $125 -

An alternative 12v module is available from K2
Price $139 -

Hm, that's pricey!

Kinda sorta, there's a number of advantages moving from NiMh to Iron Phosphate chemistry:

  • Cycle Life: The number of times the battery can be charged / discharged is significantly higher. whereas NiMh may survive 200 charge / discharge cycles, Iron phosphates can survive ~2000 cycles. If you're using this in a makerspace setting, where it gets used constantly, the 10x increase in battery lifespan will outweigh the 2x increase in price fairly quickly.
  • Flat Voltage Curve: The discharge curve for iron phosphate cells is fairly flat, between 80% full and 30% full, it appears as having a fairly constant voltage. This equates to less 'drooping' during use, it feels like a full charge throughout most of the drill's use.
  • High Current: The battery modules have a lower total internal resistance, and should be able to source more current than the standard NiMh battery module.

Show me the data!

Attached are highlights from each manufacturers datasheets, indicating the cycle life and power ratings

What about the mass?

The lead acid replacement bricks are actually surprisingly lightweight. as listed in the datasheet [pdf link] the modules weigh 1.85 lbs, considerably less than lead acid (~8lb). The stock NiMh batteries weigh around 1lb.

Step 2: Disassembling the Old Battery (NiMH)

In this step we need to take apart the NiMH battery that is standard with the electric drill and salvage a few components.

1 . Dismantle the pack: To disassemble you must remove the screws holding the pack and the connector together.
(Save the Plastic Case of the connector)

2. Disconnect the connector contacts from the battery:
=A= -Cut Wire Leading from the pack to connector
=B= -Cut Metal tab connecting pillar to the pack. (See Photos)
=C= -Cut/bend till separation of the Contact (See Photos)
(Save the plastic top with the leads, we will be re-using this for our own battery)

3. Properly Dispose of the 'pillar' and old battery pack.

Step 3: Wiring Up Drill Connector and Epoxy It to the Connector Housing

This step details wiring and epoxying the components we salvaged in the previous step.

Pre-step: There are a handful of ways to determine which contact is your positive and negative contact, it is important to verify the correct polarity on your drill before continuing.

1. Wire up your two leads, For this model drill, the side pin is Positive and the other pin is Negative (See Photograph)

2. Once wired up, test the fit of the wires and the connector into the Connector housing.
(Note: You can also plug in the connector and test drill with a power supply at this step.)

3. Pre-Epoxy step: (HOT Glue) -Use hot glue to seat and seal our connector to its housing before we epoxy. This allows a barrier to form, and hopefully completely remove the chance of epoxy leaking onto our contacts. Keep an eye on the contacts while the epoxy is being applied, if it starts to seep in clean the contacts.

4. Prepare for epoxying by mounting the connector in a vice or clamp. A 2 part epoxy works well to fill in the gap that once was filled with a NiMh battery cell. Devcon 2 part epoxy was used.

5. Use a vice or clamp to hold connector case roughly upside down and pour in your epoxy. (Make sure wires are in a position to be manipulated and that the connector is completely seated). The wires need to be flat against the battery to make sure the module sits on the charger properly.

Step 4: Attach Connector to Battery Assembly (Epoxy)

This step details prep-work and attaching of the battery to the drill contact/connector assembly.

1. Clean off the bottom of your connector; it should be fairly flat. If there are screw mounts or uneven surfaces try and remove them.

2. Pre-position that connector; It may be useful to plug the connector into the to verify alignment so that it sits in a balanced state when resting.

3. Epoxy the base of the connector and then CLAMP that connector case to the battery case. Make sure to use an intermediary layer between the clamp and the surface, as you do not want the clamp expoy-bonded to the battery.

Step 5: Wire to Battery Terminals (Crimp Connectors)

This step details wiring the connector to the battery contacts using crimp connectors.

1. Strip part of your wires to allow for a solid connection using wire strippers, keeping a small amount of the exposed wire sticking through the metal circle.

2. Crimp the connectors, either using a crimping tool or a pair of pliers, position your wire in the connector and squeeze the metal frame around the wire. This should hold against tugging and some abuse.

3. (Optional) - Soldering the crimp can help make sure it stays in place for longer periods of time. This step is not necessary but increases the connection reliability.

Step 6: Plug Into Your Charger/ and Test

In this step you will test to see if everything works, use electrical tape to temporally hold the battery to the drill. Note that this will be attached in a better fashion below. The battery module has a small ATO fuse, verify the battery is awake (13v or greater) and that the fuse is functional. Testing was preformed at MITERS

Step 7: Reinforce Battery Against Dropping/falling Out

This step details adding rubber to the outside of the battery assembly to reduce shock to the new battery pack when dropped.

Cheap source of adhesive rubber tread - $2.99

1. Measure the sides of the completed module, adding a small amount for overlap.

2. Cut out pieces of roughly those sides. A heavy pair of tin-snips or a bandsaw works well for cutting the thick rubber adhesive strips.
Note: Remember to cut out a small hole/gap so that the fuse on the battery pack can be accessed.

3. Remove plastic off of the back side, and apply the rubber. To increase the contact bonding on the adhesive, ABS epoxy was used [link]. Note that this epoxy is very strong and should be used in an open air environment with gloves.

4. Velcro strap can be used to hold the battery-drill assembly together, and still allow for ease of removal. For this project this [link] was used. Two straps are used to horizontally hold the rubber strips to the batery module, while one vertical strip is used to attach the drill to the battery. A few sewing stitches were used to hold this velcro assembly together, this makes sure the straps do not move significantly.

Check the animated gif for how this looks as a final project.

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