18v Makita LXT Power Pack - Cordless to Corded Conversion

OK so this is my first ever instructable so it may be a bit rough round the edges!

I have constructed a 110v / 240v 33A 18v DC corded power supply for Makita's current range of 18v tools.

I own quite a lot of the above tools which includes some of the more power hungry tools like the DHR242 brushless SDS Plus drill and the DGA454 brushless 115mm angle grinder and they eat batteries for fun, so lately I wore out yet another 3ah battery so was faced with the following dilemma:

Splash out good money on yet another battery for an upcoming big DIY home project or source a bunch of bits and have a power supply to offload the stress on my existing batteries when working at home.

Simple, build a supply. Lets rock.......

Prerequisite and warning:

Big power supplies are a totally different beast to laptop / wall mains adapters / small open frame supplies so I can't stress enough the potential to do yourself serious harm if you dont know what your doing. At the very best your going to get a nasty burn off this bad boy so please please be careful. If in doubt, get someone who is proficient in electronics to help you. This is not a comprehensive guide, merely an indication of how I went about it.

Step 1: Parts List - Power Supply

This is an Astec MP4 400w/600w 18v Power supply which runs at 110v as well as 240vac. I picked this up for a bargain on ebay. If you can't find an 18v one go for 24v or 15v and adjust the trim accordingly.

This model puts out 33.3A @ 600W at full tilt. Powers my grinder and SDS drill no problems at all under full load.

Step 2: Parts List - Everything Else

You'll need the following ( tools not listed ):

ABS Enclosure- I went for an IP67 rated one

Dead Makita Battery - Preferably genuine

4mm2 2 Core cable H07RNF - My supply cable is 2.7m long so it should actually be 6mm2 but it'll do me.

6mm2 Red & Black wire - For the battery PCB connections and Anderson plug to PSU connection.

Please note at these amperages anything below 4mm2 is a fire hazard if its pulling high current for an extended period. YOU HAVE BEEN WARNED.

50A Anderson Plugs - Essential for a safe connection

12mm Strain Refief Gland M20x1.5- Supports the cable where it enters the battery

10A IEC Socket, 10A Switch and 10A Fuseholder- For the mains connection to the power supply

12v 50mm PC Fan and DC to DC Buck Board - The power supply needs to be kept cool. Even though the PSU has its own fan I decided to add another case exhaust fan to aid cooling. The Buck circuit changes the voltage down to 12v from 18v

Step 3: Sorting the Battery

Once the batteries had been gutted out of the case I originally soldered the 2 6mm2 wires on, packed it all up and glue gunned it. A quick test revealed that the 18v contacts were good but non of the "starred" tools would work.

This is because theres a third pin on the battery which also has to supply 18v. Check out the picture showing the solder on the PCB and copy the soldering to create a bridge. 18v is now permenantly on the third pin.

Once i'd got a decent solder connection I re-glued every thing and drilled the underside of the battery cover with a 20mm hole saw to accept the gland. Connections from the cable to the battery wires were joined with a 60A terminal block.

Step 4: Case

I cut out a square hole on the underside of the case. This is where the airflow comes in from through a square of filter wool which fits in between the base of the box and the steel frame which the PSU is screwed to.

The IEC socket and switch / fuse holder were drilled with a 10mm pilot hole then filed with a square file until everything fitted.

Step 5: Wiring Up

The supply cables to the Anderson plug are 6mm2. I can always upgrade the trailing flex to 6mm2 at a later date.

I soldered the wires into the pins on the Anderson plugs so I know that theres a good contact.

The connection to the PSU is crimped with 5mm eyelets.

Step 6: Firing Up

I checked that the polarity was correct before connecting any tool the the PSU. A continuity test to the battery terminals was done as well - just to be sure.

You can see that the fan and finger guard is also connected now. The little DC DC buck circuit is heatshrinked and just sits tucked to one side inside the case.

Step 7: Finished

I'm very happy with the results as it powers everything I own with ease.

The air is filtered from replaceable filter wool underneath ( It's raised up with legs) and pulled through the PSu and forced exhausted through the case so it runs nice and cool.

Best of all is that it fits perfectly into a Makita Makpac Type 3 case - Winner