CONNERLABS

Tag: chinesium-mine

  • Bluetti AC50B review and teardown

    [In this episode of The Chinesium Mine we can’t resist the urge to dismantle the new power bank]

    During my stay at Container Labs I got a Bluetti AC50B in the Black Friday sales. It was very useful as a kind of bucket of electricity that could be charged at home and used to recharge the main batteries on site.

    I liked the Bluetti because it was cheap, used the safer LFP chemistry, and would accept a 230V AC input directly, unlike many other brands that need an external power brick to charge off mains. During my time at Container Labs it worked reliably and appeared to meet its advertised energy, power and runtime specs (700W, 448Wh) just fine.

    As usual I couldn’t leave it alone and had to mess around with it.

    AC UPS functionality

    I checked out the behaviour when used as a UPS, by hooking up oscilloscope channels 1 and 2 to the live and neutral outputs from the front panel AC outlet, and connecting and disconnecting the mains input.

    This scope shot tells us a lot about how the unit works inside. Even before taking it apart, we can see that it must use a bidirectional inverter/charger to transfer power between the AC side and the battery.

    When AC mains is connected, it is passed through to the front panel outlet, and the inverter/charger charges the battery. The changeover of the front panel outlet from inverter to mains is seamless, as it synchronises to the mains frequency/phase before toggling the relay.

    When the mains is disconnected, it quickly switches over to inverting mode. The switch back to inverter on loss of mains entails an interruption of about 20ms, a bit more than a dedicated UPS, but I’d be surprised if any load would be upset by this. I tried it several times and chose the worst looking transfer for my scope shot.

    So overall it’s quite usable as a UPS. And they even used a double pole relay to change over both live and neutral. Some cheap UPSs only change over the live, and can feed voltage back into the neutral pin of the plug after it’s pulled out of the wall.

    1 point for UPS functionality and not needing a power brick.

    Other AC trivia

    The output frequency is selectable as 50 or 60Hz in the Bluetti app. As I tested software in a previous life, I tried setting it to 60Hz before plugging it into our 50Hz mains. The unit wasn’t bothered, the frequency simply ramped down to 50 as part of the synchronisation process, and remained at 50 the next time mains was disconnected.

    The power quality is decent, like most “true sine wave” inverters the waveform looks closer to a sine wave than the actual mains supply. (though again like most inverters, it’s easy to mess that nice waveform up with a nonlinear load)

    With the inverter turned on but no load, the runtime displays as 41 hours. We can infer an idle power consumption of about 11W.

    I also had a look at the current drawn from the mains when the unit is charging. Not the most sinusoidal, and a bit noisy, but it’s definitely making some kind of effort at power factor correction. (blue trace is current, yellow trace is mains voltage for reference, at 275W charging power)

    Charging from the Lister diesel generator was also a success. It would drop out when a heavy load was removed from the generator, but always restarted.

    Teardown

    Next I took it apart. 1 point for not having any “warranty void if removed” stickers 😀

    The build quality seems surprisingly good. The battery proper is in the bottom of the case. It looks like a bunch of large cylindrical cells.

    Most of the power electronics is on this PCB. Below the 2 large heatsinks we can see the circuitry for the inverter, which matches my earlier guess of a bidirectional inverter/charger.

    On the left heatsink we can see 6 XNF20N60T IGBTs from Shenzhen Invsemi. (£0.53 each if you buy 50.)

    4 of these IGBTs function as the inverter H bridge when inverting, and rectify the incoming mains when charging. The remaining 2 function as diodes when the unit is inverting, to rectify the high frequency output of the DC-DC stage. When charging, these act as a half bridge driver.

    On the right heatsink we can see a full bridge of 4 low voltage MOSFETs that drive the DC-DC stage when inverting. They must work as a rectifier when charging, but I didn’t figure out if they went to the extra hassle of synchronous rectification.

    The DC-DC topology is probably a LLC with the inductance integrated in the transformer, and resonant capacitors on the secondary side.

    I believe the vertical PCB above the MOSFET heatsink is the MPPT for the PV/DC input.

    A better view of the DC-DC converter transformer. Our old friend triple insulated Litz wire is doing most of the work here as usual. I couldn’t make out a part number for the MOSFETs.

    I found exactly one microcontroller in the whole unit. An Artery AT32F415RBT7. This is an ARM Cortex-M4 with 32K of SRAM, 128K of flash, a 2MS/s 12 bit ADC… Yours for $0.99 in quantity 50.

    (It wouldn’t surprise me if there was another controller chip of some kind on the underside of the power board, but I didn’t dismantle that far.)

    I was fairly sure everything in this unit would be Chinese, but Artery are actually Taiwanese. Their chips seem heavily inspired by the STM32.

    Smart functionality

    We can also see a Bluetooth module in this pic. The Bluetti smartphone app works fine, but there’s absolutely no security or pairing process. You just install on your phone and connect to any Bluetti within range.

    Minus one point for cybersecurity. I’m sure if I took this to a seriously nerdy event like EMF it would be hacked and remotely self-destructed in 5 minutes. Todo: figure out how to add a switch that disables the Bluetooth.

    Direct battery output?

    I couldn’t resist trying to draw power directly from those clearly marked BAT+ and BAT- terminals.

    It worked, I was able to max out the electronic load and the Bluetti didn’t complain. At 22.3 volts, we can guess the battery must be 7 LFP cells in series.

    The output power display showed 0 and the runtime remained at 99.9 hours the whole time, but the SOC display started to decrease. Half a point for “expandability” 🙂

    Only half a point because I suspect something awful would happen if these terminals got shorted out or the battery was drained completely through them.

    DC inputs and outputs

    The DC/PV input is an XT60 connector. Bluetti supply two adaptor cables: a cigarette lighter plug, and a MC4. I tested it with 12 and 24V power supplies and it measured up to the rated 8.5A and 200W. I didn’t actually try it with a solar panel.

    The 12V cigarette lighter output is 12.0V exactly and has pretty much no overload capacity. It trips off just above 10A even for short pulses. of current draw. This is to be expected considering that it’s derived from a 24V battery with a DC-DC converter, and I haven’t had any trouble with it in practice: the highest powered device I have that plugs into a cigarette lighter outlet is a 12V air compressor, and it ran that.

    The USB ports work as expected. The USB-C ones will run a laptop and charge DeWalt tool batteries.

    One point for comprehensive DC connectivity, and for not having any barrel jacks (aka DC5521)- arguably the worst DC power connector in the world!

    DC UPS?

    Would it work as a DC UPS to power Raspberry Pis and the like from the USB ports? I can’t say for sure that it doesn’t have some evil quirk that would stop this working, but I didn’t see any issues.

    It can charge from AC or DC while powering DC loads. There is no float stage to the charging. The charger toggles on and off and the battery micro cycles between 98 and 100%. Or maybe it was 95 and 100%. Either way it seems like a reasonable charging algorithm, given that lithium batteries don’t like being held at high voltage indefinitely.

    I also didn’t observe any overzealous auto shutdown of the DC outputs if the load didn’t draw current for a long time.

    Conclusion

    All in all, this is a perfectly good power bank. The only thing that leaves a slightly cheesy taste in my mouth is the “Power Lifting” feature, which is claimed to allow the unit to run appliances rated up to 1000W. It does this by simply letting the output voltage sag to about 200V under heavy load, so a resistive load that would draw 1000W at 230V only draws 700.

    So as an engineer I feel cheated, but as a human being, I got coffee and porridge from this 1000 watt travel kettle (drawing 715W as you can see) Grudgingly then I give it an extra half point for the “Power Sagging” feature.

    The final verdict: with 4 points this is

    🀄️🀄️🀄️🀄️ Reactor grade Chinesium

    A genuinely innovative product developed in China. The Chinese might not have invented the portable power station genre (that credit probably goes to the American founders of Goal Zero) but they surely have designed some nice units.

  • What’s the frequency, Temu?

    [In this episode of The Chinesium Mine we summon the ghost of Jim Williams to help reverse engineer some very bad frequency meters]

    Back when I had the Lister diesel generator I spent some time looking for a frequency meter for it. I eventually settled on the “D69-Hz” digital panel meter from a questionable eBay store.

    I bought 2 of these meters and was rather disappointed, both examples seemed very sensitive to temperature. And I wanted to use them to measure small changes in frequency in a location that sees big changes in temperature. Bother. The proverbial chocolate teapot (also useless because of excessive temperature sensitivity)

    Out of curiosity I decided to dive a little deeper to figure out just why they were so bad.

    The obvious way to make a frequency meter is to use some kind of timer/counter algorithm to count cycles of the unknown frequency against a stable reference. But that was too obvious for our Chinese designers. This meter uses a frequency-to-voltage converter bolted onto the front of a digital voltmeter.

    The F-V converter is a monostable made from a 555 timer chip, that generates a narrow pulse for each zero crossing of the input. These pulses are then averaged by the digital voltmeter chip. Everything runs off a single 3.3V rail, and the 555 timer used is of the CMOS variety, a LMC555.

    As the legendary, late Jim Williams explained in his writeup of the “zoo circuit” (see figures 23-16 to 23-18) the output stage of a CMOS digital IC is made of MOSFETs that switch cleanly from one supply rail to the other. There are no Vbe voltage drops like with bipolar transistors.

    Williams was talking about a CMOS logic inverter chip, the 74C14, that he used to squeeze some more performance out of his “zoo circuit” V-F converter. But a CMOS 555 timer chip has the same output stage as a 74C14, and the designers of our Chinese F-V converter used CMOS here for the same reason: to eliminate the error due to the temperature dependency of those Vbe’s.

    I scoped the output of my so-called “LMC555” and discovered that it was only putting out about 1.8V peak-peak with its 3.3V supply, and the output increased when the chip was warmed up.

    Hah! a fake! A common or garden bipolar 555 timer remarked as a more expensive CMOS version. By far the most likely explanation for the missing 1.5V of output is two bipolar transistor junction voltages at 0.7V each. The 555 timer internal schematic on Wikipedia shows a Darlington pair for the high side of the output stage, so that would be our two Vbes right there. The low side is a common emitter, which would only drop a few hundred millivolts.

    I yeeted the counterfeit chip out of there and substituted a TLC555 (which happened to be the cheapest CMOS 555 timer in Farnell’s online store at £0.66)

    C3 is the monostable timing capacitor, I had to change it from 5.6nF to 3.2nF to reduce the pulse width in compensation for the increased output voltage of the new 555 chip.

    Having done this, R12 was tweaked to read 50.0Hz with a mains frequency input at room temperature. Most Chinese meters I’ve seen so far have a “fortune trimmer” like R12 that can be twiddled to give almost any answer you want. I don’t think I even want to know the tolerance or tempco of this part.

    My modified D69-Hz seemed much more stable, so I put it in the Hayburn Labs environmental chamber alongside an unmodified one and a thermometer.

    The environmental chamber is not a precision instrument (actually it’s a freezer from a charity shop) but it’s still incredibly useful for freezing and boiling prototype circuits to discover any temperature-related quirks before the customers do.

    The mains frequency varied by more than I expected during this experiment, due to those meddling wind turbines. I had to go and look up the actual National Grid frequencies corresponding to the photo timestamps.

    At 23C the meters read 49.7 and 49.9. National Grid official value was 50.111Hz so our modified meter is reading 0.211Hz low.

    After refrigerating to 0C and allowing some time for temperature to equalise, the stock meter gave a reading of 47.9 and the modified one 49.6. Actual mains frequency was 50.041Hz so the modified meter has an error of -0.441Hz.

    Stewing at 40C for 20 minutes produced a result of 51.6 for the fake 555 and 49.7 for the TLC555. Actual mains frequency was 49.881Hz so the modified meter error is -0.181Hz.

    So over the 0-40C temperature range, we have an error of 3.7Hz (7.5%) for the unmodified meter and 0.26Hz (0.5%) for my modified one.

    Conclusion: When I originally tested the Lister diesel, it gave a frequency of 51.25Hz unloaded and 50.00 on full load. And the temperature in Container Labs varied from below zero, to over 30C. The error with temperature of the unmodified meter would be more than twice the generator’s actual change of frequency, so it would have been completely useless.

    By replacing the fake 555 chip, we reduced the temperature sensitivity by a factor of 15. But the error still works out as 20% of the frequency range covered by the Lister diesel.

    As a check I got out the same Fluke meter that I originally used to test the generator. It agrees with the National Grid website to within 0.01Hz.

    (National Grid official value was 49.854)

    (National Grid official value 50.034)

    With this level of accuracy, I guess Fluke’s budget must have stretched to an actual quartz crystal in there somewhere, to give an accurate reference for a frequency counting algorithm. Our poor D69-Hz meters probably have a RC oscillator for the clock.

    You can still buy the D69-Hz on Amazon, if you’d like a more laborious way of wasting money than simply setting fire to a £10 note. Believe it or not, I don’t earn a commission if you buy through this link. 😀

    The 5.6nF capacitor and phoney “LMC555CM” are visible in the product photo, so I’m pretty sure it’s the same Shenzhen Chocolate Teapot Industries product.

    Rating: 1 Zhong out of 5

    🀄️Depleted Chinesium

  • Diesel never work

    [But it did. Extending your diesel heater control panel]

    When I moved into Hayburn Labs, the diesel generator had to go, but my trusty (ish) MaxpeedingRods diesel heater came with me. I thought it was worth keeping as the running cost is about half of an electric heater.

    There are dozens of brands of these devices, all Chinese clones of the Webasto air heater, priced at about one-fifth of the real thing. The real Webasto and Eberspacher heaters are sold as bare units for permanent installation in a vehicle, with the combustion air inlet and exhaust routed directly to the outside. But some Chinese entrepreneur came up with the idea of mounting the whole system together with its fuel tank into a portable box, with the combustion exhaust through a short length of pipe to nowhere in particular. This package proved quite popular and it’s now even possible to buy a European made version, the Autoterm Travel Box 2.

    Mine must be one of the better clones as it hasn’t caught fire or gassed me with carbon monoxide. Yet.

    For now combustion air is drawn from inside the building, and the exhaust pipe is poked through a hole in the wall. As I’m doing the place up (and making it more airtight) I plan to relocate the heater outside for safety, and it would be nice to extend the cable that connects the heater to the control panel. I haven’t seen much information about this online, so I’m documenting my experiments here.

    According to the intertubes, all of these heaters have a 3 wire connection with a low-speed digital data link similar to the automotive LIN bus.

    On opening the control panel, sure enough I found 3 wires marked +, R/T, and G, which I guess are positive supply, a bidirectional data line (Receive/Transmit?) and ground. Real LIN uses 12 or 24V for both power supply and signalling, but according to the manual, this is 3.3V. (yes it has a printed manual in legible English)

    You can see from the PCB that it has both Bluetooth and 433MHz wireless remote functionality, and it came with a remote that works, so why am I even bothering to extend the wire? Well the temperature sensor for the thermostat functionality is on this board. Probably “NTC1” in the top right corner. So I think it makes sense for it to be in the main work area.

    I unsoldered the three wires from the control panel PCBA, snipped a Cat5 patch cable in half and attached the two half-cables with the following colour code:

    Signal nameMXR wireCat5 wire
    +RedOrange, orange/white
    R/TBlueBlue
    GBlackAll other wires

    As a Cat5 has 8 cores, I had 5 left over so I used several in parallel for the positive supply and ground. I thought this would help with voltage drop and noise pickup if it really does use 3.3V levels.

    I plugged the two ends together with a RJ45 coupler, and the panel lit up and still seemed to work. So for my next test I interposed a 15m Cat6 Ethernet cable.

    It still worked…

    Discovering what happens when the control panel is unplugged with the heater running is an exercise for the reader. A reputable manufacturer like Webasto would of course have tested this and made sure it went through its normal cool-down and shutdown sequence. I wonder if the Chinese clone makers have that much attention to detail.