lies – Experimental Engineering

Posted on April 1, 2018March 18, 2018 by The Engineer — 3 Comments

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

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.

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,

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.

The 100µH 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).

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.

Posted on February 9, 2016 by The Engineer — Leave a comment

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 😉

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.

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

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.

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.

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

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

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.

Posted on September 2, 2015 by The Engineer — Leave a comment

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.

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.

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.

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.

Posted on July 25, 2015July 28, 2015 by The Engineer — Leave a comment

Stock Baofeng Antenna Problems

Recently I’ve noticed my usual mobile rig, the Baofeng UV-5R, has had very poor receive, and non-existent transmit.

I did a power test on the radio, and confirmed it was still outputting it’s rated RF power. Trying another antenna proved that the radio was fine.

Time to tear down the antenna & see if it can be fixed!

Here’s the antenna, just the factory rubber duckie. As with all these antennas, they’re a compromise between size & their efficiency.

Giving a gentle pull to the antenna sheath while it’s attached to the radio allows it to come apart. The quality actually doesn’t look to bad. It’s very similar in construction to my Diamond X-30, just on a much smaller scale.

At the bottom of the antenna is the matching network, an inductor & ceramic disc capacitor. Here lies the problem with this antenna.

Here where the capacitor joins onto the feedpoint from the SMA connector, the solder joint has come away. This was a very poor joint to start with, and the solder hadn’t wetted the capacitor lead at all

After cleaning the joint, and applying some flux, a new joint was easily made with some Real Solder.

Here’s the joint freshly repaired, the antenna is now back to full working order. It even seems to work better than the others I have 🙂

Posted on March 16, 2011March 16, 2011 by The Engineer — Leave a comment

The Truth About DWP Cuts From A DWP Worker On The Front Line

A bit of a shift from my usual content, but I thought this deserved a place for people to see. Only relevant for people of the UK though.

“I’m a DWP worker sticking his head above the parapet and hoping not to get shot…

I work in a busy Jobcentre and my customers are those 25+ who’ve been out of work for 13 weeks or longer. Probably 60-70% of the one hundred or more people I see every week [who] are evidently not fit for work and yet, in theory, it’s my job to whip them through the same hoops as everybody else, persecute them, attempt to stop their benefits and generally shame them into applying for all manner of wholly unsuitable jobs that they’re never going to be able to do.

In reality, what I do is tell them the system sucks and advise them of ways they can stay beneath the radar, or suggest they sign off JSA and move onto ESA and do whatever I can to make the transition as trouble free as possible.

On the other side of the office to me are the Pathways team, who deal with customers on ESA. We all know that over the coming months most of them will be forced to migrate over to the JSA bods like myself and we won’t be able to cope with either the numbers or the particular problems that this customer group represents.

The point of all this waffle is that the policy makers have embarked upon their catastrophic journey without consulting the frontline workers who, without exception in my experience, KNOW that the planned changes CANNOT work.

I would advise people worried about a forced transition from ESA to JSA to be brave and try not to lose too much sleep about it… It’s just not do-able in the real world, there’ll be a horrible mess and people’s lives will face some awful but shortlived disruption and then it’ll be business as usual.

Also, for those who face the indignity of having to venture into a jobcentre from time to time, please be assured – the majority of those who work in them are actually on your side, and have probably less faith in our political masters than you do, and just as much awareness as yourselves that all their vitriolic guff about benefit scroungers and feckless layabouts is simply empty, venomous scapegoating…”

Please feel free to copy and paste this to your own notes/blog, etc. Spread the truth.