Introduction: DIMP (Desulfator in My Pocket)

Mikey Sklar created the DA PIMP ("Power In My Pocket") versions 1 and 2 based on George Wiseman's paper "Capacitive Battery Charger" and generously released it to the open hardware community.

It is capable of charging and desulfating/rejuvenating just about any rechargeable battery of any type, so long as the battery is not totally unrecoverable.

I took just the battery desulfator portion of the DA PIMP 2, which is essentially George Wiseman's circuit, and designed a PCB and BoM for it that is focused on improving safety. It is called DIMP ("Desulfator In My Pocket") in honor of Mikey's DA PIMP.

This Instructable goes through the assembly steps for DIMP. All that is required is soldering and some drilling, filing, and cutting of a plastic project housing. Time to complete is about 0.5 hours for the soldering and 0.5 to 1.5 hours for the fitment of the plastic housing, depending on how careful you are filing the holes.

DANGER: The DIMP exposes lethal voltages to the operator via the output leads. It is still not perfectly safe, even with the improved safety features. Do not buy or build or use DIMP unless you take full responsibility for the safety of yourself and others nearby. Only adults with a proper understanding of the risks may attempt to use DIMP. I recommend that you do not buy or build a DIMP or DA PIMP 2 if you have young children in the home, as they might plug it in and turn it on without knowing the dangers.

If you accept the lethal danger, here is how you build the DIMP.

Assembly requires drilling and filing the housing so that some parts will be exposed to the user. You might need four (4) #4 x 0.25in pan head self-tapping screws to mount the PCB to the enclosure before you start drilling the housing. You can substitute sheet metal screws if you can't find self-tapping screws. If you are patient enough to fit the enclosure together with tight tolerances, you can forgo the self-tapping screws, as the enclosure can essentially clamp the PCB in place.



The PCB is here, sold in ProtoPacks (1 Protopack = 10 +/- 1 PCBs). When you order, change the Size to max 10 x 10 and the Thickness to 1.6mm. You can also change the PCB color. I recommend dark colored PCBs so that the neon lamps are easier to see. Keep the other settings unchanged (FR4 proto, 2 layer, HASL coating, 1oz copper, no stencil).

(If you have questions or problems with your PCB order, please contact the seller DirtyPCBs for help.)

You are welcome to sell the spare PCBs on ebay if you like.

The BoM is here:

(If you have questions or problems with your parts order, please contact Mouser Electronics for help.)

Please note that the BoM does not include the output leads because you will want to choose the right ones for your batteries. Choose a red and black pair of test leads that have 4mm banana plugs (preferably sheathed and stackable) on one end and the clip type that will fit your battery terminals. They must be able to handle up to 250VDC and 5A. Make sure the clips you choose are safe and fully-insulated, exposing as little metal to the operator.

Also note that 220VAC to 240VAC mains users should substitute two 0.5W 430K ohm to 500K ohm resistors to protect the neon lamps from the higher current. The original 220K resistors are meant for 120VAC mains. Use this formula for your local mains voltage: (Mains_Voltage – 90) / 0.0003 = Maximum_resistor_value


soldering iron with medium conical tip

paste or liquid solder flux


soaking wet sponge for cleaning the soldering iron's tip of carbon residue

wire cutters or flush cutters

Phillips screwdriver

3/16in drill

flat file

square needle file

half-round file or round file or Dremel with small sanding drum


hot glue gun

Step 1: Test Fit PCB

Test fit the PCB in the Hammond 1591XXMTBU enclosure. The PCB should fit in the "bowl" easily and the four mounting holes should line up with the plastic bosses in the bottom of the bowl.

Then test-fit every part into the PCB.

Now is your chance to find pin 1 on each of the switches and on the diode bridge. It's also a good time to make sure you have every part.

Step 2: Install SW1

First, install the two L202031MS02Q slide switches, SW1 and SW2. Note that these switches are a bit shorter than we would like. We'll have to elevate them a bit so that the actuator sticks out above the lid far enough to be operated with fingers. If the switches are soldered flush with the board, they can be operated with a screwdriver.

Let's start with SW1.

On the bottom of SW1 are two plastic feet with an off-center notch cut in each foot. The notches are closest to pins 1 and 3. Ignore the number that might be molded on the bottom of the switch. It does not appear to be a pin number.

Match the notches up with the silkscreen on the PCB, then while holding the switch so that it's as high off the PCB as possible and parallel to the PCB, solder in pins 1 and 6. A Helping Hand tool or a second person holding the PCB and switch makes this easy. Alternately, you can insert a plastic shim underneath the plastic feet of the switch and remove the shim later.

If the switch is not level, adjust pins 1 and 6, resoldering them until the switch is parallel to the PCB. Allow enough time between resolderings for the pin to cool down to avoid melting anything inside the switch.

When the switch is level, solder pin 2. GENTLY slide the switch and test with a multimeter to make sure that it shorts pins 1 and 2 when on and breaks the short when off.

Solder the remaining three pins.

Step 3: Install SW2

Repeat step 2 for switch SW2, putting it at the same height as SW1.

Step 4: Solder the Diode Bridge

Next, solder the diode bridge D1 in place.

D1 is a D3K package. It's asymmetrical with the pins on the back side. Align the bridge with the silkscreen and holes on the PCB. Look for the semicircular notch on one side to locate pin 1.

IMPORTANT: If you accidentally flip the bridge around backwards, the red and black outputs will be reversed, and that is very dangerous for your batteries and the user! Double-check the + and - markings on the body of D1 and visually confirm that the + lead is pin 1 and that the trace goes to the RED side of the board.

Step 5: Solder SW3

Solder the A8L-21-12N2 rocker switch SW3 in place, as low as possible on the PCB. This switch does not need to be elevated like SW1 and SW2.

This switch has markings on the body to indicate the pin numbers, and it also has a the | and 0 sides marked. Align the switch with the silkscreen and solder all four pins in place. Test continuity with a multimeter while flipping the switch off and on.

Step 6: Glue and Solder AC Power Inlet

Because the AC power inlet is designed to snap into 1.4mm thick PCBs and this is a thicker 1.6mm PCB, the snaps will not engage.

Get some hot glue, apply it to the snaps on the inlet, then quickly insert it into the holes and press it flush with the PCB. Do not solder it yet. Let the glue dry, then solder it.

Step 7: Solder the Fuse and Fuse Clips

Carefully insert the fuse into the two fuse clips such that the legs point downward.

Insert the legs through the PCB and solder the fuse clips into the PCB.

Step 8: Solder the Remaining Parts

Solder all the remaining parts in place. Start with the shortest, smallest components. It might be a good idea to hot glue down the small 2mm test jacks.

Pay attention to put the red jacks on the RED side of the board and the black jacks on the BLACK side of the board. There are + and - signs on the bottom of the board near the solder pads and RED and BLACK are clearly labeled on the top.

Be sure to insert the capacitors as low as possible on the board.

Step 9: Mark the Width of the Notches at Both Ends

Put the PCB on top of the bowl part of the enclosure with the components facing up. The 4mm jacks and the AC power inlet will prevent the PCB from dropping into the bowl. Keep the PCB centered over the mounting holes.

Get a marker and mark the edges of the power inlet on the enclosure. This is where you will cut a rectangular hole in the enclosure. The marks should be 21mm apart. The rectangular hole will be at least 15mm tall to start; you will file further to fit. Try to keep the tolerances tight, as a tight fit will help support the AC power inlet when you insert and remove the power cord.

On the other end, mark the edges of the 4mm banana jacks. The marks should be 28mm apart and centered in the middle of that end of the enclosure. The rectangular hole will be at least 14mm tall to start; you will file further to fit. This hole can be W-shaped or U-shaped if you prefer, to fit the silhouette of the round banana jacks.

Step 10: Cut a Starting Notch at the AC Inlet End

Get a coarse flat rasp or file and cut a shallow 1mm to 2mm deep notch that is purposefully less wide than the marks at the AC power inlet end. The idea is to properly center the PCB and work up to the minimum width necessary to fit the inlet.

As you file, confirm that the PCB is correctly centered over the mounting holes below it. You can use long, thin dowels to check the alignment.

Gradually widen the notch, filing each side as needed. Eventually you will widen the notch and be able to fit the inlet in the shallow notch such that the PCB is properly centered.

Step 11: Cut a Starting Notch at the Banana Jack End

On the end with the 4mm banana jacks, start cutting a shallow 1mm to 2mm deep notch, also purposefully undersized. Because the banana jacks are round, this side should be undersized by a larger margin.

Step 12: Mark and Cut Deeper AC Inlet Notches

Using a thin hobby saw or Dremel cutting wheel, cut out 13mm-deep V-shaped notches at the AC power inlet end to form a W-shape. You'll file the bottom out later.

Step 13: Mark and Cut Deeper Notches at Banana Jack End

On the 4mm banana jack end, cut out a rounded W-shape. You'll file out the sides and bottom later.

Step 14: Continue Removing Material From Both Notches

Continue removing material from the holes until the PCB is able to fit all the way down on the mounting bosses. Alternate between the ends so that the PCB stays level as you gradually lower it into the bowl.

When done, the top edge of the AC power inlet and the capacitors should be roughly flush with the top edge of the bowl

Step 15: Mark and Drill 2mm Test Jack Holes

Look through the translucent plastic and mark where holes will have to be drilled for the two 2mm test jacks in the sides of the bowl.

Remove the PCB from the enclosure and drill the holes. They must be at least 2mm in diameter but can be slightly oversized if you like.

Step 16: Mark and Drill the Rocker Switch Hole in the Lid

Now for the lid. Place the PCB in the bowl and hold the lid over the PCB. There is a small alignment tab on the lid that should be positioned at the AC power inlet end. Make sure the screw holes are centered over the threaded inserts. If you have some long 4-40 machine screws, those can be used to keep the lid aligned over the bowl.

With a marker, mark the locations of the rocker switch. Use a bright light source if necessary to see the switch through the translucent case. The outline should be no more than 21mm wide and 15mm high.

Drill through the lid leaving plenty of extra material around the final edges of the hole. You will use a small file to work your way up to the final edges for the best fit and finish. File the rectangular hole leaving about 1mm on each edge. You will finish after cutting the rectangular holes for the slide switches.

Step 17: Mark, Drill, and File the Holes for the Slide Switch Actuators

Keeping the lid aligned over the bowl, mark the positions of the actuators of the slide switches. It helps to shine a really bright light from the side of the bowl so you can see where the actuators are through the lid. You will have to slide the switches to both positions to determine the full extent of the rectangular holes.

Be aware that the actuators can tilt somewhat, so you may need to adjust the markings.

Using a small drill bit, drill through the center of each marked hole. You should use a small drill bit because the bit will probably not end up near the final center.

Using the square needle file, start opening up the slide switch holes gradually so that they fit over the actuators and allow the actuators to be slid to both positions.

Step 18: Cut Small Notches for the Tops of the Banana Jacks and AC Power Inlet

When the slide switch holes are done, the lid should now fit lower over the bowl, but it will not be able to fully close because the thin edge around the enclosure's lid will be blocked by the tops of the 4mm banana jacks and the AC power inlet.

File down the lid's lip so that there is clearance for the 4mm banana jacks and the AC power inlet. The lid should now fit all the way down onto the slide switches' actuators and rest on the lip of the rocker switch.

Step 19: Finish Filing Holes to Fit

Finish filing the hole for the rocker switch to match the size of the rocker switch's lip. It should be easier to see where the final edges should be now that the lid is resting on the lip of the rocker switch.

Finish filing the holes for the slide switch actuators.

Step 20: File the Notch in the Lid at the AC Power Inlet End to Fit

Finally, there is the matter of the two thin lips separated by a gap on the lid at the AC power inlet end. You'll have to cut notches of different depths in each lip. Because the AC power inlet is itself stepped, with two different heights on top, the inner lip of the lid will touch the lower portion of the inlet, and the outer lip of the lid will touch the uppermost portion of the inlet.

Step 21: Fit and Close the Enclosure

The lid should now fit all the way down on the bowl such that you can close the enclosure snugly. If not, complete any final filing to make it fit, and then use the four 4-40 machine screws that came with the enclosure to affix the lid to the bowl.

Step 22: Final Testing and Usage

Now for the electrical testing. We did not do this earlier because it is dangerous to touch the exposed circuitry. The enclosure offers more protection.

Before testing, tape a warning label or write on the housing:


These are the general steps for safely using the DIMP for one charge-rest cycle, start to finish:

  1. Place the DIMP and the battery on a fire-resistant, non-conductive, stable surface where it can rest safely for the entire duration of the charging/desulfating.
  3. Set the two slider switches based on the current needed to charge the battery. For the lowest current (for AA batteries), slide both switches down (towards the rocker switch). To increase the current to medium, slide one of the two switches up. To increase the current to maximum (for most power tool batteries and car batteries), slide both switches up. It is generally better to use less current (and thus take more time per cycle), so if you have the option to do so, use less current.
  4. Insert the output leads into the DIMP's 4mm banana jacks.
  5. Attach the output leads to the battery, making sure the black lead goes to the battery's negative terminal and the red lead goes to the battery's positive terminal. Reversing the leads will result in damage to the battery and possible fire/explosion/personal injury.
  6. Optional but highly advised: insert the test leads from your multimeter into the 2mm test jacks on the sides, red to red and black to black. Turn on the multimeter in voltmeter mode and observe the voltage of the battery.
  9. Plug in the AC input cable into the DIMP and then into the wall.
  10. Turn on the rocker switch and watch the voltage change. At least one of the two neon lamps will light up while there are lethal voltages in the DIMP (see the note below for what the lamps mean).
  11. If the voltage jumps way up and doesn't come down, the battery is almost certainly totally unrecoverable. A moderately sulfated/passivated battery should jump up quickly, then drop down almost as quickly under its nominal voltage, then gradually rise as it charges/desulfates. A badly sulfated battery will jump way up immediately and then take longer to drop down (hours or even days) towards the nominal voltage of the battery. This is because if the sulfation/passivation is really thick, it takes a long while to "chip away" at it with the pulsing.
  12. Monitor the battery temperature and the voltage as it continues charging/desulfating. Heat is bad for your battery. Lithium batteries must be monitored constantly, as they can enter thermal runaway and catch on fire. ALWAYS KEEP A FIRE EXTINGUISHER READY WHEN CHARGING/DESULFATING LITHIUM BATTERIES. Lead acid batteries can off-gas and shoot acid out their vents--you want to avoid this by turning down the current. Some clever guys have used ice packs (the kind that you can buy at a pharmacy that comes in a cloth pouch) or coolant baths (non-conductive liquid!) to keep the battery cooled. You can also buy thermostats that have a temperature probe you can attach to the battery and that turn off the AC mains when the temperature hits the threshold you set (set it slightly above room temperature).
  13. Turn off the rocker switch when the voltage reaches about 110% of the nominal voltage. NiCd and NiMH battery packs for power tools typically take about 15 minutes to half an hour to reach this point. Lithium batteries charge quickly but vary widely depending on capacity. Lead-acid batteries take the longest, often hours. The voltage should drop and then find a steady value. If this value is above the nominal voltage, you are done and can continue with the next step. If the voltage drops below the nominal voltage, you can try another pass this cycle, but it is possible that the battery cell or battery pack might not be completely recoverable.
  17. Then, double-check that the rocker switch is still off and the neon lamps are still dark.
  18. Remove the output leads from the battery.
  19. Remove the multimeter leads from the DIMP.
  20. Remove the output leads from the DIMP's banana jacks.
  21. Allow the battery to rest before attempting another cycle. Rest periods are crucial so as to not do permanent damage to the battery by overheating it, AND resting allows the charge to spread evenly throughout the battery.

There are much more detailed instructions out there on how to best charge and maintain the different battery chemistries. I've only provided a highly-simplified set of instructions per charge-rest cycle. I encourage you to search and read more on the topic of desulfation/depassivation so that you get the best results.

NOTE: DIMP features two neon lamps to improve safety. They are not a guarantee of safety--it is still possible to get a nasty shock if the lamps are off, and if one of the lamps is broken, there is the potential for lethal shock. Always keep clear of the output leads whenever the AC mains are connected.

NE2, the lamp near the output end, turns on when these potentially lethal conditions are met:

+ DIMP is connected to AC mains. + Rocker switch is turned on. + Output leads are not connected to anything OR the battery is offering too much resistance.

In these conditions, there is lethally-high voltage at the output leads.

If there is no voltage at the output leads but NE2 is lit, the fuse is either blown or loose in the fuse clip. Treat the output leads as if they are still exposing lethal voltages to the user, because a loose fuse might suddenly start conducting. Turn off the rocker switch and disconnect the AC mains before handling the leads or opening up the DIMP to check on the fuse.

NE1, the lamp near the AC mains port, turns on when these potentially lethal conditions are met:

+ DIMP is connected to AC mains. + Rocker switch is turned on. + Output leads are connected to something offering low resistance, which could be a non-broken battery being charged or desulfated. The potential danger is if the output leads are connected to the wrong thing, such as a person or a metal rod or each other.


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