I had a classic Black & Decker Dust Buster vacuum in my shop for years as they are great for cleaning up table top debris and sanding dust while working on r/c gliders.
About 2 years ago, the vac's RPMs would start to fall quickly after a few seconds even after a full charge. I suspected a failing battery pack, and put this now useless unit in storage even though it had only a few total running hours on it.
I was putting together the shop space in my new house and found the old Buster in a box with other workshop junk. I love to recycle old machines so I poured myself a cold Porter and started to disassemble the unit to check out that old failing battery pack. The Buster says 14.4 volts on the side so I was already thinking of putting in a 4S Lithium Ion or Lipo pack that would match that rated voltage.
The included photos show the internals and the wiring changes I made.
The Buster comes apart easily, (warranty voided!) and I found a huge plastic battery box inside with a 12S 1500mah NiCD pack inside. I knew that some of the cells might be bad, and tested the voltage of each, looking for any reading under 1.1v. Two cells were at 1v, and another was at 1.1v. The rest of the pack was at 1.2v, though I suspected some memory effects had reduced the packs capacity. Total weight of the pack was 19 oz.- 538 grams!
For a replacement battery I picked a 40C rated Thunder Power 4S 2200 Lipo which was no longer flight worthy, but still fine for low amp draw applications. You could use a 4S Li-on or Li-Fe pack for this application/hack as well. This battery had the old TP style balance connector on it and the wires were very short, so I just plugged the balance connector into a spare TP to JST-XH adapter board which I could then plug into any of my Lipo chargers. Total battery weight was now just 10 oz. - 283 grams!
The internal wiring is easy to figure out, there is a DC brushed motor connected to a plastic holder that has traces to the main power switch and the charging circuit. I cut the battery box out, and removed the charging and power LED indicator light and PCB board from the the top of the main body. The PCB board has 2 wires to the motor, just disconnect them. You can keep the PCB board in place as long as you disconnect the wires to the motor, but I wanted to run the charging wires through this hole so I discarded this part.
I next lengthened the two main motor power wires from the plastic holder a few inches with a solder splice which gave me some working slack. The center wire on the plastic wire holder can be cut or disconnected. You can also disconnect and remove the metal charging contact tabs at the bottom of the unit.
The + and - wires need to be spliced into the main battery wire for motor power. I cut a small amount of the wire insulation from the negative battery wire first, then soldered the - motor wire to the - battery wire. Some tape insulated the splice. I then did the same for the + wires. Do each wire separately for safety, do not short the battery wires!
With the motor wired to the battery, you can then test the switch, which should be in the OFF position when soldering power wires. The motor should turn on.
You will need to run the main battery power wires and the charge balance connectors outside the unit for charging. I was lazy and used the hole from the LED light and PCB under the handle to exit the wires. You can cut or drill a hole just about anywhere in the vac's body to exit the wires.
The freshly charged 4S Lipo outputs a solid 16+ volts to the motor, about 1.5 volts higher than the best the NiCds could give. The suction is noticeably better at the higher RPM's and there is no voltage sag or motor over-heating even after many minutes of run time. Once the RPMs start to noticeably drop, its time to recharge, you don't want to drain any Lithium pack to zero. You can use your Lipo voltage checker to check remaining capacity just like with your powered r/c planes.
Dust Buster models vary, but any model rated at 14 volts are likely to have NiCD packs and should be easy to modify with new batteries. Newer models come with Lithium batteries as an option. I recently replaced the 5S NiCd packs in my cordless shop drills with 2S 18650 size Li-on cells and they now run forever without any self discharge. **Use any lithium battery with caution and charge them properly.
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