Battery Adaptor for Cordless Tool

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Introduction: Battery Adaptor for Cordless Tool

I had a whole set of 14.4 Volt cordless tools including flashlight, small circular saw and a drill.
First the charger went, then the batteries died, and then before I could buy replacements the company then switched to the 18V format and dropped all product support for the 14.4V line.
I purchased a new 18 Volt drill from another manufacturer in protest but it really wasn’t as good as my old one, the chuck slips when drilling and the drill clutch doesn’t seem to handle torque well.
So how to resuscitate my old tools cheaply?
I had two 18V batteries and chargers from other tools and when I jumped them to the 14.4V tools they seemed to run okay. The challenge then was to convert a 14.4V battery into an adaptor.

Step 1: Step 1 Salvage

Gut the battery, removing the NiCD batteries inside and safely recycle them. Salvage the clips off the battery that serve as the connectors to the Tool.

Step 2: Step 2 Solder Some Bits You Salvaged


Solder on a new wiring as needed for the clips

Step 3: Step 3 , Glue the Terminals Back In

Glue into the battery housing part that fits into the tool.
Note the polarities carefully!!!!!!
I use common plastic seals-everything glue as it’s also waterproof and serves as a good insulator

Step 4: Step 4 Solder in a Clip to Attach to the New Battery

Solder on a clip to attach to the battery. I used a piece I salvaged from inside an obsolescent cordless tool. ( they are good for something) and wirenuts to make sure nothing comes apart.

Step 5: Step 5 Cutting the Base to Fit the New Battery

Use the 18V battery as a template and cut out the oval from the bottom of the 14.4V battery case.

Step 6: Step 6 Reassemble and Glue on Something to Hold Them Together

Reassemble the 14.4V (no longer a battery) adaptor.
Glue on some salvaged hook and loop fastener strapping.
This pic shows the new battery clipped to the adaptor but not yet inserted

Step 7: Step 7 Insert Battery Into Adaptor

Connect the new battery via the clip and insert into the adaptor.
You may need to cut the hole a wee bit wider than than the battery's neck to allow the clip to pass.
Fasten the straps to hold it together

Step 8: Step 8 Polarity Check


Mark what side and what colour wire your polarities are on the adaptor so you don ‘t short out your tools by mistake. I have one 18V battery with the positive and negative the same side as the adaptor and one that is reversed......

Step 9: Step 9 Inset Into Tool

Step 9
Insert into your favourite tool!

Now you can get back to fixing all those things you said you’d get around to if you only had tools that worked.

I haven't run into any problems so far with the difference in the voltage. No guarrentees on that by any means. Matching voltages is preferrable but close will probably work fine. 14.4 and 18 might work okay, 9.6 and 18 will probably melt down but who knows......

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    54 Comments

    Hi ! Once you've fabricated the addaptor, you're replacement battery pack could be wired to a voltage closer to what's needed. Say 9.6v needed... take a 20v battery pack, open it up. rewire your batteries from series to series/parallel; if possible. It depends on what you find after you've opened the battery pack.

    electrics are black magic to me, but i have a 12v dewalt. reckon a similar approach is feasible...or is it too big a jump from 12 to 18?

    Thanks! Hard to believe so many people have looked at this and my other battery hack instructable! Hope they find useful ways to keep old tools working.

    I agree with dendave.joe, I have dropped my Milwaukee drill off the roof, off of ladders and abuse it on a daily basis. I also know for a fact that I can get any part for any of my Milwaukee power tools including batteries. It always pays to buy high quality tools

    2 replies

    yea me too with my dewalts

    I've been using my Hilti hammer drill, Makita drills and impacts & Milwaukee sawzall for 15 years with a few battery pack cell replacements since I purchased them. Hilti, 20 years (corded) Sawzall also corded, 15 years, & Makita Li-on since I replaced my Dewalt Nicd 6 yrs. ago. I've got a Milwaukee 3.6 volt screwdriver which will do darn near everything the Makita will do and is my most used tool. I'm an Electrician destructing, drilling, and screwing for a living. Handy Dave's philosophy is undeniable. You truly get what you pay for and if & when they go down they'll survive homemade batterie's, alternate power sources and an infinite variety of DIY repairs. The additional cost is more than negated when you have no complete tool systems being tossed in the dustbin. My wife doesn't get it or approve but if I allowed her to purchase I'd be pitching Ryobi's once a month.

    Wyle_E suggested (Jun 19)that "You could make a similar adapter ... to run portable tools from a car battery." I tried that with my 12v Black&Decker;, but disconnected it REALLY quickly when smoke came out of the drill's vents! Why would that happen? 12v car battery, 12v drill... Has anyone successfully done this?

    11 replies

    Yes, the drill was 12v and the battery should have been 12v. The drill overheat could have been cause by one of two things:

    1. As someone else here mentioned, car batteries vary in output voltages slightly. The battery could have had an output voltage slightly above 12v. OR...

    2.The wire you used to connect the car battery to the drill was too thin. That drill is going to draw 12v at around 2 amps, (depending on the drill). For this reason, I would guestimate you should use a wire no smaller than 10 Gauge, for both positive and negative leads. If the drill was unable to draw the current needed, this would cause either a voltage drop or increase (can't remember which right off hand) either of which means death to the drill.

    Cars don't put out a consistent 12v. They can jump up or down depending on how fast the alternator is turning. You if you try to use auto power, measure the voltage first (using a multimeter), build a voltage divider circuit, and filter the input power to protect from irregular voltage spikes.

    FOR THE BENEFIT OF QUITE A FEW... Lets put it clear and more or less complete.- Understanding the most basic law of electricity and electronics can help a lot when you want to use electric motors and almost any kind of stuff. The OHM law is not difficult to understand. Imagine a piping circuit instead of an electrical one, that will help a lot. The amount of water that can flow thru a partially open valve will depend on how high the water tank is above the valve, but also on how big the diameter of the pipe is, and how open the fawcett valve is. The VOLTAGE of the circuit source or supply is akin to the PRESSURE of the water inside the piping (think PSI), the CURRENT is akin to the FLOW or quantity of water that flows in a given time (think GPM), and the RESISTANCE is akin to the friction loss or PRESSURE DROP of the piping circuit, either with a pipe that is too small or a valve that is almost closed. Now, using the unit system, the voltage is measured in VOLTS, the current in AMPERES, and the resistance in OHMS. This way is all too easy to fully understand and even predict how the devices will work when the power is applied to the circuit: Let's say we have a car battery with a nominal 12 volts (in reality it could have as few as 11 volts when almost discharged, to a little above 14 volts, when fully charged ans just recently disconnected from the charger!).

    If we connect an electric motor, a small one, it will allow  just a fraction of an Ampere to flow through it, say 250 milliamps or so; because the small wire that is used in the windings will present a comparatively large RESISTANCE of about 48 Ohms.  BUT if we connect a much larger motor, like the Starter Motor of a car, the same 12 V battery will flow a large current, maybe 150 Amperes! because this motor presents a much lower resistance, of around 0.08 Ohms... (its windings are made with a much larger wire gage, just look at the diameter of the car battery cables!).

    POWER is the result of multiplying applied voltage times current, so that a WATT is produced or dissipated when a current  of one Ampere flows pushed by one Volt.  Therefore, power can be calculated from the following simple relations:

    I = V / R, V = I x R,  R = V / I...    P = V x I  or  P = (V) squared / R

    In the case of our friend FINTON above, the small motor must have been defective, most probably having some shorted windings.  This resulted in a too small resistance that caused that the large capacity 12 V car battery  able to deliver several amperes and quickly burned the poor small motor.  If the motor would have been in good condition, it would run perfectly under the light load meant for it.  At the same time, that small defective motor would turn at partial speed when connected to an smaller voltage battery (say, a common 9V alcaline cell), but that small battery would be incapable of sustaining its output voltage when connected to the partially shorted motor, thus not being cappable of burning it!

    Now, most DC (direct current) electric motors can be fed with a higher voltage, above the nominal one it was designed to handle, but  it is a matter of how heavy will it be loaded when operated.  See, the motor presents an electrical load that DEPENDS on the MECHANICAL load it has to move, so that if lightly loaded, common electrical motors certainly can handle say 1.5 times the nominal voltage, if the mechanical load is not far above the design one.  Present day Model Airplane hobbyists use motors designed for say, 12 Volts, with battery packs that can sustain almost double that voltage, but they use it wisely, using the maximum power for brief periods of seconds, like for Take-Off or maneuvers, backing off the electronic throttle to avoid burning the motor.  As this INSTRUCTABLE says, it is "safe" to assume that a Cordless Hand Drill meant for "12 V" nominal, can be perfectly run with a 14.4 V pack.  It will turn faster and will be capable of more power output, BUT WILL ALSO OVERHEAT more quickly if the same Load is applied, so keep this in mind and avoid loading it too much.  BTW, rechargeable cells have an actual voltage that is NOT the nominal one under load, so that the 12V pack is assembled from 10 1.2 V nominal cells, that maintain close to 1.0 volt under load each wired in series, and the 14.4 V pack has 12 such cells, thus achieving only 12V under load.  This applies to Nickel based cells. Lithium cells have 3.7 to 3.8 nominal Volts, so that one can perfecly use a pack of three to four Lithium-Ion or Lithium Polymer cells for that drill, saving a lot of weight and bulk, but then would need a special charger designed for Lithium cells, and also apply ALL the cautions of using Lithium cells!  Good Luck. amclaussen.-

    Oh, OK. In my particular case the car wasn't running, but your point is good to know for when the situation arises. Thanks. Oh, and Criggie: I didn't have the battery in the drill when I tried running it off the car battery. As it turns out, the charger was defunct: the replacement I bought also didn't work! I gave the hardware guy my drill, battery, and the new charger - I just got them all back today with a charged battery, so I guess we'll see if the chargers are at fault or I have a problem in my workshop wiring...

    The NiCD batteries of the drill have more resistance than the car battery. When you run your tool off NiCD it actually gets less than 12 V (the rest is lost in heating up the battery) The car battery has low resistance so the tool gets really allmost all the 12 V You can add something with few ohm resistance in series to the car battery to simulate the resistance of NiCD's. Heat wire from electrical heaters is good for this. Expect it to heat quite much

    Hey 11010010110, I know it's over two years later, but what significance is the number 3372 to you? (your binary username in base 10).
    Still haven't got around to trying your idea with resistance... :[

    hmmm. well the car battery has 12 volts sure, but it can deliver 80 ampere so its about 200W of power. Sure, that enough juice to burn any electronic component.

    that's not how amps works. amps are simply available, it's up to the load to pull them. Your typical home outlet provides 15 amps, but plugging in a .5amp cell phone charger doens't explode anything.

    This is true, but your example isn't really correct. A .5 amp phone charger outputs .5 amps, that doesn't mean the charger *requires* .5 amps from it's source or that it passes on a higher amperage to the phone. The amperage from the socket doesn't pass directly through the phone charger (or shouldn't). If it's stated amperage is .5 amps, it outputs .5 amps (or should) and no more.

    You are right though, amp rating is simply what is available, it's up to the load to pull what it requires. Too many amps won't damage anything unless the voltage isn't fixed. Some (cheap) stuff can increase voltage when the current requirement exceeds it's amp rating, which could damage a device, but it's unlikely.

    The voltage output of a car battery can vary slightly, up to 14 or 15 volts. It would only be this extra voltage that may damage the drill.

    The problem you had could be the wiring. The motor may have drawn more current than it's wiring could handle.

    this was at idle or under a load? it could be that the motor itself also had a problem and was trying to pull more amps than it should have. Black&Decker's tend to have "lowest bidder" parts in them, which is why your chargers keep failing.

    Yes - I used a 14.4 V drill and connected 15 metres of cable to a pair of clamps. Great for using out in the land rover, and a lot more efficient than an inverter+mains drill. The long run of cable induces quite a voltage drop too - the drill only gets around 11.5V Also remember the charging voltage of a car battery is around 14 V, so running the drill with the car motor going is likely to provide a slightly higher voltage than when the motor is stopped.