Here’s a nice little feature-packed USB power meter, the UM25C. This unit has USB-C along with the usual USB type A connectors, along with a bluetooth radio for remote monitoring of stats via a Windows or Android app. Construction is nice, it’s a stack of two PCBs, and polycarbonate cover plates, secured together with brass posts & screws.
The back cover has the legend for all the side connectors, along with the logo.
Down the sides are the user interface buttons, and here the Micro-B input connector. The 4-pin header is visible here that takes serial data down to the bluetooth section.
The other side has the remaining pair of buttons, and the USB-C I/O. I don’t yet own anything USB-C based, but this is good future proofing.
Removing the top plastic cover plate reveals the small 1″ TFT LCD module. This will be hot-bar soldered underneath the screen. There’s an unused footprint next to the USB input connector, judging by the pin layout it’s probably for a I²C EEPROM.
The underside of the top PCB has all the main components. The brains of the operation is a ST STM8S005C6T6 microcontroller. It’s at the basic end of the STM range, with a 16MHz clock, 32K flash, EEPROM, 10-bit ADC, SPI, UART & I²C. The main 0.010Ω current shunt is placed at the top left of the board in the negative rail. A couple of SOT-23 components in the centre of the board, I haven’t been able to identify properly, but I think they may be MOSFETs. The large electrolytic filter capacitor has a slot routed into the PCB to allow it to be laid flat. Providing the main power rail is a SOT-89 M5333B 3.3v LDO regulator.
The bottom board contains the bluetooth radio module, this is a BK3231 Bluetooth HID SoC. The only profile advertised by this unit is a serial port. There’s a local 3.3v LDO regulator & support components, along with an indicator LED.
For a while now I’ve been attaching terminals such as Molex KK Dupont, & JST PH to wire ends with a lot of patience & a very fine soldering iron, however this method takes a lot of time, and with terminals like Dupont types, the terminal won’t fit into the connector body properly unless it’s crimped correctly. Official tools from the likes of JST or Molex are hilariously expensive, (~£250 for the Molex KK tool), and each tool only does a single connector series, so these are out of the picture. The cheapest available tool (~£40) for these types of terminals is the Engineer PA-09:
These are simple crimping pliers, with no niceties like a ratchet mechanism, but nonetheless they work very well for the cost. The PA-09 can handle terminals from 1mm-1.9mm, there is another tool, the PA-21, which crimps terminals from 1.6mm-2.5mm. The fit & finish is good – proper steel (S55C high carbon steel according to Engineer), not the steel-plated-cheese that most cheap Chinese tools are fabricated from, the handles are solid & comfortable.
The rubber handles are press-fit onto the steel frame arms of the pliers, and don’t slip off readily.
The dies are well formed in the steel, and seem to be machined rather than stamped on a press, however the black oxide finish hides any machining marks. The smallest 1mm dies do seem to be a little fragile as they’re so small, so wouldn’t take much abuse without shearing off.
Here’s a Molex KK pin that’s been crimped with the PA-09. The insulation crimp has pierced the insulation slightly, but this isn’t much of a problem. The conductor crimp is nice & tight, and everything is small enough to fit correctly into the plastic connector body. The trick with these tools is getting a feel for when the crimp is done – squeeze too tightly & the contact deforms, not tightly enough & the wire will just pull out of the terminal. The official tools also crimp both the conductor & insulation at the same time, and they also hold the terminal in place while the wire is inserted. In these cheaper tools, the crimps are done separately, but they do hold on to the contact securely enough for the wire to be inserted properly with your spare hand.
With some recent upgrades to the boat’s heating system, the hot water circulation pumps we’ve been using are becoming far too small for the job. After the original Johnson Marine circulation pump died of old age (the brushes wore down so far the springs ate the commutator) some time ago, it was replaced with a Pierburg WUP1 circulation pump from a BMW. (As we’re moored next to a BMW garage, these are easily obtainable & much cheaper than the marine pumps).
These are also brushless, where as the standard Johnson ones are brushed PM motors – the result here is a much longer working life, due to fewer moving parts.
The rated flow & pressure on these pumps is pretty pathetic, at 13L/min at 0.1bar head pressure. As the boat’s heating system is plumbed in 15mm pipe instead of 22mm this low pressure doesn’t translate to a decent flow rate. Turns out it’s pretty difficult to shove lots of water through ~110ft of 15mm pipe ;). Oddly enough, the very low flow rate of the system was never a problem for the “high output” back boiler on the stove – I suspect the “high output” specification is a bit optimistic.
This issue was recently made worse with the addition of a Webasto Thermo Top C 5kW diesel-fired water heater, which does have it’s own circulation pump but the system flow rate was still far too low to allow the heater to operate properly. The result was a rapidly cycling heater as it couldn’t dump the generated hot water into the rest of the system fast enough.
The easiest solution to the problem here is a larger pump with a higher head pressure capability. (The more difficult route would be completely re-piping the system in 22mm to lower the flow resistance). Luckily Pierburg produce a few pumps in the range that would fit the job.
Here’s the next size up from the original WUP1 pump, the CWA50. These are rated at a much more sensible 25L/min at 0.6bar head pressure. It’s physically a bit larger, but the connector sizes are the same, which makes the install onto the existing hoses easier. (For those that are interested, the hose connectors used on BMW vehicles for the cooling system components are NormaQuick PS3 type. These snap into place with an O-Ring & are retained by a spring clip).
The CWA50 draws considerably more power than the WUP1 (4.5A vs 1.5A), and are controllable with a PWM signal on the connector, but I haven’t used this feature. The PWM pin is simply tied to the positive supply to keep the pump running at maximum speed.
Once this pump was installed the head pressure immediately increased on the gauge from the 1 bar static pressure to 1.5 bar, indicating the pump is running at about it’s highest efficiency point. The higher water flow has so far kept the Webasto happy, there will be more to come with further improvements!
CWA-50 Pump Teardown
Above is a cutaway drawing of the new pump. These have a drilling through the shaft allows water to pass from the high pressure outlet fitting, through the internals of the pump & returns through the shaft to the inlet. This keeps the bearings cool & lubricated. The control & power drive circuitry for the 3-phase brushless motor is attached to the back & uses the water flowing through the rotor chamber as a heatsink. Overall these are very well made pumps.
Here’s the impeller of the pump, which is very small considering the amount of power this unit has. The return port for the lubricating water can be seen in the centre of the impeller face.
Inside the back of the pump is the control module. The main microcontroller is hiding under the plastic frame which holds the large power chokes & the main filter electrolytic.