Good and even branded hair trimmers such as Remington are relatively cheap such that they can be replaced once the batteries inside have been dried out which seems to be the intended usage. The Remington HC363C for example does not even have a trap door to be able to swap out batteries.

When the trimmer / clipper is dismantled, two lithium batteries are found on the inside that are soldered in series and connected directly to the PCB of the trimmer. From what can be determined, the PCB contains a regulator for charging the batteries and a control circuit via a switch for turning the trimmer on and off. Similarly, the whole trimmer is rated at digital levels with the charger also being rated at , such that working with the circuitry on the inside is relatively easy.

So, the process of getting the trimmer working again involves opening up the case, replacing the batteries and then closing the case back up again.

• Remington HC363C (by today's standard, very cheap, maybe even second-hand throwaway),
• 18650 Lithium battery, rated at 3.3V,
• mini motor controller with a minimal range requirement of ,
• mini USB charger PCB, the smaller the better,
• small USB port breakout, Type-C preferred,
• JST sockets and cables

Opening up the Remington reveals two AAA batteries that care coupled in series by being soldered together that float on the inside of the Remington. Disconnecting the AAA batteries involves desoldering the wires that connect them to the PCB but after that the can be just lifted and tossed away.

Initially, the idea was to follow the original design and, as pictured, to replace the blue Remington AAA batteries with AAA counterparts with the exact same size. Replacing the batteries was done by using some conventional AAA batteries and then using some copper wire to connect the contacts on one end, and then connect the wires on the other side at the terminals on the other end in order to achieve a total of that powers the motor.

After a short test, with the case open, it seems that the Remington is successfully repaired, due to the motor engaging and the charger lighting up the LED on the PCB when connected to the trimmer.

However, after closing the case, it was noticed that the trimmer did not start up when using the power button to turn the Remington on. After some investigation, it turned out that while the AAA batteries are sufficient in terms of voltage and total capacity, the discharge rate does not seem suitable to drive the motor. Power motors does not only require a lot of power, as a total product of amperage and voltage, but also the instantaneous drain capacity of the batteries is important. Another interesting feature is that motors generally do not have an involved circuit and consist in just a coil that can be overclocked slightly by increasing the voltage.

That being said, an 18650 vaping battery rated at was purchased and the Remington was opened up again to fit the battery. The first problem is that the Remington chassis is really designed only for two AAA batteries but the bottom case can be modified to sand down some of the support struts that are meant to hold the batteries.

Using a Dremel, with a small grinding head, the horizontal support struts for the batteries are eliminated, thereby making room for the very large 18650 vaping battery. Now fitting the battery inside the case works well and the screws can be placed back to fix the PCB.

Assembling the trimmer back again and then attempting to start the trimmer without the charger now seems to work perfectly, as well as having made the Remington HC363C powerful enough to shave an entire mob of sheep, or your pet llama, if necessary. And, we're not even kidding, it seems that the coupled with the high discharge rate of the 18650 battery, makes the Remington oscillate much faster, moving the front teeth much faster and thereby reducing the probability that the Remington will clip hairs or pull them instead of cutting them properly. A mod, that makes the object better than the original!

While this works to some degree, the board is not really appropriate for charging the 18650 that would rather need a lithium trickle charger. Clearly, the battery is being charged but it is not an ideal solution compared to what it should be and the idea of carrying around a mains line charger for a hair trimmer modernly is a bit counter-intuitive given that such a small device could easily be charged via an USB port. Additionally, it also seems clear that the PCB is "from a different era" given how the components are mounted and the aspect of the PCB itself, so perhaps the board could be reworked into something better.

The PCB shape looks simple enough so a new custom PCB should be fashioned by cutting one up to match the same size. This is not too difficult and using a Dremel for precision, the exact same shape can be achieved.

The PCB should at the very least host the charger circuit for the battery and a good avenue to explore is to use a TP4056 due to its cost and size. The small PCB itself of the charger is then mounted on the newly cut PCB. Of course, the USB port is removed and the problem of actually powering the lithium battery charger is left for later.

The circuitry on the bottom of the PCB is ported over in order to make the slide-switch work. All that the slide-switch circuit requires is two aluminium pads that are made out of solder and then sanded down to size. When the Remington switch commutes, a small aluminum bracket makes an electrical connection between the two pads and current then flows through the circuit.

On top, the lithium charger is soldered to the custom PCB and a small USB port mounted on its own PCB is placed right where the charger socket was before. The small USB PCB is an USB breakout board that can be mostly found in bulk at any electronics store. We hesitated between a micro-USB and an USB Type-C port but settled for the Type-C because the newer USB port format has more tensile strength than it's antecedents which suits the idea of a hair trimmer or clipper perfectly given the usage patterns.

Everything is then wired back up - note that we used small JST sockets to connect every single stage of the new Remington. The USB breakout is connected to the main PCB using a socket, the motor is connected to the PCB using a socket and the battery is also connected via a socket. This is a great design if you have further modifications in mind because every component can be individually removed without requiring solder.

It turned out that the Remington became a lawnmower with an 18650 that was both overclocking the motor a little due to its increased voltage compared to alkaline AAA batteries as well as supplying ample current to make the motor spin extremely fast. In order to resolve the issue a motor controller would be ideal and an interesting thing to experiment because it would give another control to the hair trimmer / clipper by allowing the user to change the speed of the motor on the fly.

The motor controller is a large-voltage-domain controller allowing the input of to by using a solder jumper on the board. Given that the 18650 battery is rated at about , the motor controller is ideal. Also, the controller is phenomenally cheap for what it offers allowing up to to pass through, which is a great realization considering that comparable boards sometimes go for ten times the price.

The only downsides, but truly just relative to the Remington hair trimmer project is that the components on the motor controller are large. However, clearly the potentiometer will be have to be relocated and the wire terminals will be removed completely in order to directly connect the wires, such that overall it does not matter too much.

Interestingly, one side of the PCB contains the small power regulator and other smaller ICs that do not protrude too much while the other side contains just one single component so an idea is to move all components from one side to the other.

Now, it's a matter of fitting this additional PCB into the Remington. One idea is to place it on top but given that the Remington shell has been scooped in order to permit a 18650 battery to fit, it seems possible to fit the new PCB right next to the one that was cut to size.

Doing so also provides a stopper for the battery to not move around and seems like a more compact solution. The circuit itself is very simple; the USB port is connected to the input of the lithium charger and, in turn, the lithium charger is connected to the DC motor controller. The two boards are then glued together by using two-part epoxy glue and a pair of pliers to hold the PCBs up while the glue dries.

It takes about a day for the glue to cure with some adjustments to make sure that the PCBs are lined-up properly.

The result looks pretty good and sufficiently compact to fit inside the Remington shell. JST ports are mounted on the motor controller as well to ensure that everything can be removed for a revision.

All the components fit well inside the shell and some testing is done to ensure that the two parts of the Remington can be closed without additional pressure. What remains to be done is to find a place to put the removed potentiometer. First however, for some fun, here is some testing of the whole assembly by connecting a potentiometer and varying the speed of the motor.

The initial idea was to place the potentiometer on the side but that is encumberent given that there will be shaft sticking out of the case on the other side. Even though the spae seems tight with the new assembly, it seems that a good fitting place for the potentiometer shaft would be right through the top part of the case. The bottom part of the potentiometer will then fit between the motor and the PCB assembly - but only partly, because if the potentiometer is screwed all the way into the top shell then there is lots of clearance at the bottom.

Some thoughts come to mind along the lines of applying some custom paintjob, logos and prototype names along the lines of "Mantis" or "Bumblebee" with "Bumblebee" being the favorite so far given how the clipper sounds when it's on along with some imagined image of yellow and black paint on the shells. For the time being, the Remington is assembled together in order to assess how it all fits together.

The result looks great!