Here’s another active balancing circuit for large ultracapacitor banks, this one is designed for a series string of 6, at 2.5v per capacitor.
Based on the design here, I have transcribed the circuit into Eagle & designed a PCB layout.
As can be seen from the circuit diagram above, this is just 6 copies of the circuit from the above link, with screw terminals to attach to the capacitor string.
And here’s the PCB. the MOSFETs & OpAmps are very small SMT parts, so require a steady hand in soldering. This board can easily be etched by hand as there’s only 3 links on the top side. No need for a double sided PCB.
As always, the Eagle project files & my Eagle library collection are available below:
This is the Velleman MK179 Proximity Card Reader, which is supplied in kit form. In the image above you can see the completed kit, the read coil is etched onto the black PCB on the left. Bringing a recognised card close to the coil operates the relay on the main PCB for a programmable amount of time.
Closeup of the main PCB, 12v DC input at top right. Left IC is an LM358 dual Op-Amp, the IC on the right is a PIC12F629 with Velleman’s custom firmware.
Logic power is supplied to the ICs & the oscillator from the LM7805 regulator at the top of the PCB. The relay is a standard 15A SPDT 12v coil relay, with the switch contacts broken out onto the screw terminals on the left.
As it is not provided with the kit, unlike other Velleman kits, here is the schematic for this.
Here is a Bosch 14.4v Professional cordless drill/driver, recovered from a skip!
It was thrown away due to a gearbox fault, which was easy to rectify.
Here is the drill with the side cover removed, showing it’s internal parts. The speed controller is below the motor & gearbox here. The unit at the top consists of a 12v DC motor, coupled to a 4-stage epicyclic gearbox unit, from which can be selected 2 different ratios, by way of the lever in the centre of the box. This disables one of the gear stages. There is a torque control clutch at the chuck end of the gearbox, this was faulty when found.
Here is the drive motor disconnected from the gearbox, having a bayonet fitting on the drive end.
This is the primary drive gear of the motor, which connects with the gearbox.
The motor is cooled by this fan inside next to the commutator, drawing air over the windings.
This is the gearbox partially disassembled, showing the 1st & second stages of the geartrain. The second stage provides the 2 different drive ratios by having the annulus slide over the entire gearset, disabling it entirely, in high gear. The annulus gears are a potential weak point in this gearbox, as they are made from plastic, with all other gears being made of steel.
Here is the charging unit for the Ni-Cd battery packs supplied with the drill. The only indicator is the LED shown here on the front of the unit, which flashes while charging, & comes on solid when charging is complete. Charge termination is by way of temperature monitoring.
Here the bottom of the charger has been removed, showing the internal parts. An 18v transformer supplies power to the charger PCB on the left.
This is the charger PCB, with a ST Microelectronics controller IC marked 6HKB07501758. I cannot find any information about this chip.
Here is a battery pack with the top removed, showing the cells.
This is the temperature sensor embedded inside the battery pack that is used by the charger to determine when charging is complete.