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Chinese “1200W” DC-DC Boost Converter DOA Fix

1200W DC-DC Converter
1200W DC-DC Converter

Ah the curse of the Chinese Electronics strikes again. These large DC-DC boost converters have become very common on the likes of AliExpress & eBay, and this time my order has arrived DOA… On applying power, the output LED lights up dimly, and no matter how I twiddle the adjustment pots, the output never rises above the input voltage.

Boost Converter Topology
Boost Converter Topology

From the usual topology above, we can assume that the switching converter isn’t working, so the input voltage is just being directly fed through to the output. The switching IC on these converters is a TL494,

Control Circuitry
Control Circuitry

The switching IC on these converters is a TL494,with it’s surrounding support components, including a LM358 dual Op-Amp. Power for this lot is supplied from the input via a small DC-DC converter controlled by an XL Semi XL7001 Buck Converter IC. Some testing revealed that power was getting to the XL7001, but the output to the switching controller was at zero volts.

Inductor
Inductor

The 100ยตH inductor for this buck converter is hidden behind the output electrolytic, and a quick prod with a multimeter revealed this inductor to be open circuit. That would certainly explain the no-output situation. Luckily I had an old converter that was burned out. (Don’t try to pull anything near their manufacturer “rating” from these units – it’s utter lies, more about this below).

Donor Converter
Donor Converter

The good inductor from this donor unit has been desoldered here, it’s supposed to be L2. This one had a heatsink siliconed to the top of the TL494 PWM IC, presumably for cooling, so this was peeled off to give some access.
After this inductor was grafted into place on the dead converter, everything sprang to life as normal. I fail to see how this issue wouldn’t have been caught during manufacture, but they’re probably not even testing them before shipping to the distributor.
The sensational ratings are also utter crap – they quote 1.2kW max power, which at 12v input would be 100A. Their max input rating is given as 20A, so 240W max input power. Pulling this level of power from such a cheaply designed converter isn’t going to be reliably possible, the input terminals aren’t even rated to anywhere near 20A, so these would be the first to melt, swiftly followed by everything else. Some of these units come with a fan fitted from the factory, but these are as cheaply made as possible, with bearings made of cheese. As a result they seize solid within a couple of days of use.
Proper converters from companies like TDK-Lambda or muRata rated for these power levels are huge, with BOLTS for terminals, but they’re considerably more expensive. These Chinese units are handy though, as long as they are run at a power level that’s realistic.

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Chinese CO Meter – The Sensor Cell

As the CO meter I bought on eBay didn’t register anything whatsoever, I decided I’d hack the sensor itself apart to make sure it wasn’t just an empty steel can. It turns out that it’s not just an empty can, but there are some reasons why the thing doesn’t work ๐Ÿ˜‰

Cell Disassembled
Cell Disassembled

The cell was crimped together under the yellow shrinkwrap, but that’s nothing my aviation snips couldn’t take care of. The photo above shows the components from inside.

End Cap
End Cap

The endcap is just a steel pressing, nothing special here.

Filter
Filter

Also pretty standard is the inlet filter over the tiny hole in the next plate, even though it’s a lot more porous that I’ve seen before in other sensors.

Working Electrode Components
Working Electrode Components

Next up is the working electrode assembly, this also forms the seal on the can when it’s crimped, along with insulating it from the counter electrode & external can. The small disc third from left is supposed to be the electrode, which in these cells should be loaded with Platinum. Considering where else they’ve skimped in this unit, I’ll be very surprised if it’s anything except graphite.

Counter Electrode
Counter Electrode

Next up is the counter electrode, which is identical to the first, working electrode. Again I doubt there’s any precious metals in here.

Backplate
Backplate

Another steel backplate finishes off the cell itself, and keeps most of the liquid out, just making sure everything stays moist.

Rear Can & Reservoir
Rear Can & Reservoir

Finally, the rear of the cell holds the reservoir of liquid electrolyte. This is supposed to be Sulphuric Acid, but yet again they’ve skimped on the cost, and it’s just WATER.

It’s now not surprising that it wouldn’t give me any readings, this cell never would have worked correctly, if at all, without the correct electrolyte. These cheap alarms are dangerous, as people will trust it to alert them to high CO levels, when in fact it’s nothing more than a fancy flashing LED with an LCD display.

Ironically enough, when I connected a real electrochemical CO detector cell to the circuit from the alarm, it started working, detecting CO given off from a burning Butane lighter. It wouldn’t be calibrated, but it proves everything electronic is there & operational. It’s not surprising that the corner cut in this instance is on the sensor cell, as they contain precious metals & require careful manufacturing it’s where the cost lies with these alarms.

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Baofeng Battery Capacity Lies

I’ve had a couple of larger batteries for my UV-5Rs for some time now, and decided to do a quick teardown to see if they’re actually the capacity claimed.

BL-5L Battery
BL-5L Battery

Here’s the label, claiming 3800mAh (3.8Ah) of battery capacity.
These batteries are held together with glue, but a good way to get these kinds of things open is by whacking the seams with the handle of a screwdriver. This cracks the glue without damaging the casing.

Battery Cracked Open
Battery Cracked Open

After a few minutes of cracking the seams, the battery comes right open. The pair of wires link the protection board on the cells to the DC terminals on the top of the pack. The charging terminals are under the cardboard insulator on the right.

Cells
Cells

Here’s the other half of the case, with the cells themselves. These are wired in series for a 7.2v pack, and at a capacity of 2600mAh (2.6Ah) printed on them, the label clearly lies about the capacity.