Introduction: Cordless Power Tool Conversion 18VDC to 120/240VAC

Necessity is truly the mother of all inventions....and my case was no different.  About a year ago, I found myself with a dead battery for my Ryobi 18V cordless tools and no means of getting a new one as I was working overseas. So I came up with a setup to run my tools off AC (household current) safely and with no worries of my tools dying halfway into the job.

Now I enjoy all the benefits of battery operated power tools just as much as the next guy....They're convenient, flexible, and you can usually get quite an assortment of tools that run off the same battery.  Then the inevitable get the dreaded blinking set of lights on your charger and the batteries die out almost instantly. Your faced with two options.....Drop $50-$100 on a new set of batteries or try rebuilding them yourself.  Neither one of those two options appealed to me nor did I have the time to order the parts from overseas.  As anyone in my situation might do, I scoured the internet for an alternative solution.  I found guys connecting car batteries to their drill...ummmm no thanks.  Then I came across the idea of using an old laptop power supply in place of the battery.....The voltage seemed right, but alas the wattage was too small.  Even at 180 watts, the biggest pc power supplies couldn't provide enough to overcome the start-up current of my battery operated circular saw or angle grinder. 

The principal of the pc power supply was sound, I just needed something bigger.  After a little more research I found that the common everyday laptop power supply is what they call a "switch power supply".   Turns out, switching power supplies are very common everywhere in the world, affordable and come in a variety of voltage and power ratings... I eventually chose a 350w AC/DC power supply produced by a reputable company called Meanwell with a voltage range of 15-18volts DC.

Wiring of the power supply to a dead battery is very straightforward, but the following instructable goes through the details step-by-step.

Step 1: Electrical Warning

Before starting please understand you have a power supply capable of discharging 20Amps.  Although the setup is fairly simple, if you are not comfortable working with electronics, please seek professional help on this Instructable.

The cable exiting the battery and connector of the DC outlet from the power supply are made from an standard 120VAC wall plug.  The plug and cable was selected for ease of availability and to allow me to use a standard extension cable if needed.  For my case, I will be the only individual using this setup.

Under no circumstances would I plug an AC powered appliance, tool or otherwise, into this power supply.  If you choose to make this setup please think ahead who might be using it.  If there is the remote possibility of someone not trained to using this setup, I would suggest using a different type of connector and cable.  Something more unique but capable of handling the amps. 

One recommended cable is that of a twist lock generator plug. 

Step 2: Tools Needed

• (1) dead 18v Ryobi battery
• (1) 15v 350w AC/DC switching power supply
• (1) IEC C14 electrical receptacle (for incoming AC power)
• (1) standard 120vac receptacle to be used as the DC output or a twist-lock generator receptacle
• (1) computer power cable (has the mating connector for the C14 receptacle
• (1) 16-18awg extension cord (male connector is needed or a male twist-lock generator plug)
• (1) small toolbox (big enough for the power supply and to store the battery)....a 50cal ammo can works really well too.

• small Philips screwdriver
• needle nose pliers
• wire cutters
• hot glue gun
• 2 part epoxy
• soldering iron
• razor blade
• hacksaw blade
• drill
• multimeter

Step 3: Gutting the Battery

1. Using the Philips screwdriver, remove the 6 screws at the base of the battery (special thanks to my lovely 5 year old)
2. Separate the two halves of the housing and pull out the battery pack
a. Save the (2) yellow square buttons and the mating steel spring
3. Cut the leads from the battery to the terminal block
4. Save the plastic terminal block and the positive (+) and negative (-) terminal strips

Step 4: Don't Mind the Wire..."doctor's Orders"

1. Using heavy gauge power cord (16 awg) cut off the female receptacle end.  The length of the cord is up to you.  Remember this cord is going to be connected up to your power supply, but you can always use an extension cord if your tool will be far from the power supply. I find 3-5 ft of cord is sufficient.
2. Routing the wire....There are 2 options

Option A: Drill a hole in the battery cover the diameter of the outer jacket of the wire.  The location of the hole is your choice.  You can even add a rubber boot over the wire as it exits the battery cover to act as a strain-relief.

Option B: Install a swivel adapter I've designed and will be making available on in the near future.  This swivel adapter allows the cable to pivot from the front of the battery pack to the rear anywhere within the 180deg angle.  The remainder of this tutorial will be using the swivel adapter.  I've also uploaded the stl files onto under the title of "18V Battery Swivel Cable Lock" if you have access to a 3D printer.

3. Cut back about 6" of the outer jacket insulation from the cable
4. Strip and tin about 1/4" of the leads.
5. The swivel adapter consists of (3) parts
    (2) clamp halves
    (1) swivel base
6. Make sure the clamp halves can completely encircle the OD of the outer jacket of the cable
7. Sand the ID of the clamp halves until you get a snug fit around the jacket

Step 5: Start Cutting

1. Mark out a 1/2" wide path on the bottom of the battery cover to be cut off.
2. Using a 1/8" bit, drill a series of holes along the path long enough to get a hacksaw blade to continue the cut.
3. There will be two standoffs from the original screws on the inside of the bottom cover along the path of where you will be cutting.....cut them off.

Step 6: Break Out the Epoxy

1. Feed the wire through the slot of the bottom cover
2. Using some "Super Glue", attach the clamp halves to the edge of the outer jacket
3. Assemble the swivel adapter to the clamp halves, feeding the stripped wires through the small slot of the swivel adapter
4. Epoxy the swivel adapter to the inside of the bottom cover

Step 7: Fire Up the Soldering Gun

1. Cut off about 4" of the exposed 8" of unsheathed wire
2.  Strip the about 1/4" of insulation from the wires and solder them to the positive and negative terminal strips (see the attached image for the polarity of the cable)
3. Re-assemble the terminal block and install it into the top half of the battery cover
4. Use a hot glue gun to fill the cavity where the terminal block sits
5. Attach wires from the top half cover to the bottom half cover using wire nuts or cable lugs.
6. Reassemble the top and bottom halves of the battery cover using 4 of the 6 screws.  Remember to install the yellow side buttons and springs.

Step 8: Box It Up

Now its time to make the housing for the power supply. 
1. Arrange the power supply in the box to allow room for the battery adapter and the AC inlet plug and the DC outlet plug
2. Make a template for the four M4x6 mounting screws of the power supply to transfer the location onto the box.  Drill holes in the box to mount the power supply.  But don't mount it just yet.

Step 9: Laying Out the Connectors

1. Locate where you want to mount the incoming AC and outgoing DC receptacles on the box.  I prefer mounting one at each end and dressing the wires under the power supply.
2. Solder (3) 12" 16awg gauge leads to the IEC C14 electrical receptacle for incoming AC power on the positive, neutral and ground leads.
3. Solder (2) 12" 16awg leads to the standard 120vac receptacle for outgoing DC power on the positive and negative leads.
4. Make a couple of templates of the receptacle profile and transfer the outline to the box.  Using a sharp utility knife, make several passes until you cut out the holes for the two receptacles.
5. Attach the receptacles either by screw, glue or snap fit; whichever it was designed for
6. Apply some hot glue over the leads on the receptacle to protect the exposed terminals

Step 10: Final Connections

1. Attached the leads of the connectors to the indicated leads of the power supply.
2. Install the plastic protective cover over the terminals of the power supply
3. Make sure the selector switch on the power supply is set for your country's voltage, either 120 or 240VAC.
4. Plug in your portable power supply using a standard computer cable for the AC receptacle.
5. Plug in the battery adapter into the DC receptacle.
6. Turn on the power supply with the switch located on the IEC C14 electrical receptacle
7. Using a multimeter, check the polarity of the battery terminals and adjust the pot on the power supply (small plastic philips screw to the far left of all the terminal connectors) to above 18VDC.
8. Once confirmed everything is reading correctly, mount the power supply within the box and dress the wires neatly under or behind it.
9. Plug in your battery adapter into your favorite 18V CORDLESS tool and enjoy continuous use.

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