Inside the YHDC SCT013 current transformer

The YHDC SCT013 series is very popular for use in energy monitor projects.


Warning, the core is VERY hard, but VERY brittle, don’t hit it with anything hard, don’t grip in with pliers, don’t drop it on a hard surface.

The coil and half core are held in the lower housing by two obvious catches which click over the bobbin. Removal means pulling the assembly upwards gently whilst releasing the catches and feeding cable into the housing. One of the catches will probably catch on the slot in the bobbin, be prepared to release it.


An ideal tool for the purpose is an ordinary $2 DIP chip puller which can be used to get purchase on the two ears on the bobbin that can be seen in this pic. Push a little cable into the housing, pull upwards while releasing the catches, then feed more cable and the assembly is pulled upwards from the housing.

Above is the PCB detail. This one has a TVS (the black component) and no burden resistors. There is a place for two parallel 0806 burden resistors on the board.

The PCB floats on two plastic pin extensions of the bobbin. You may obtain benefit in securing it with two very small fillets of hot melt adhesive as above, small enough so as to not interfere with the guide rails in the enclosure.

Burden resistors

So if you wanted to add a burden resistor for 0.333V out at 50mA secondary current, R=0.3333/0.05=6.6667. You could do this with 1% resistors in the E12 value series, 12Ω and 15Ω will give the desired resistance. Likewise for 1V out, 22Ω and 220Ω in parallel will give the desired value of 20Ω.

If you wish to remove existing burden resistors, they can be removed with specialised tooling but small SMD resistors will usually melt the other side solder moments after melting the first side. Position a toothpick with one had to push the resistor sideways, with the other and use the soldering iron to eat one side to melt, move the soldering iron to the other side and push the resistor sideways with the toothpick as soon as both sides melt.


A CT that has no load could develop extreme and damaging voltage within the secondary winding in the presence of primary current. If the CT assembly does not have an integral burden resistor, it is wise to install a TVS or pair of inverse series 9V Zener diodes to prevent excessive voltage lest the external load be disconnected.


SCT-010-000 current transformer protection

The YHDC SCT-010-000 clip-on or non-invasive current transformer is widely used in DIY energy monitor applications, and is readily available on eBay for A$6 including post.

A key issue with current transformers is that current in the primary winding will cause excessive voltages in the secondary winding unless the secondary winding is suitably loaded. The broad rule of thumb is NEVER disconnect the output connections whilst current flows through the primary.


YHDC’s website is typical of Chinese web sites, and I could not find a datasheet for information on the internal circuit and possibly internal protection.
Continue reading SCT-010-000 current transformer protection

Review of Hantek DSO8102E hand held oscilloscope

This article is a brief review of some issues that were found with initial testing of a Hantek DSO8102E two channel 100MHz hand held oscilloscope.

The DSO8102E is a member of the DSO8000 series (DSO8060, DSO8070E, DSO8100E, DSO8150E, DSO8200E), and shares most specifications across the series.

The specifications are very impressive, and price at just under $1000 for a Chinese brand seemed reasonable (hand held oscilloscopes are expensive compared to bench oscilloscopes).

The test scenario was a practical application, observation of the data traffic to/from a DHT22 temperature and humidity sensor in the project ESP8266 IoT DHT22 temperature and humidity – evolution 2. Continue reading Review of Hantek DSO8102E hand held oscilloscope

The fraud of energy efficient lighting – LED lighting

Having been pushed into CFLs due to conservationist action that removed incandescent lamps from the shelves before mature reliable product was available, I ventured into LED lighting because of the failure rate of the CFLs.

The LEDs are about the same power consumption as the CFLs they replace, the hope was that they had a longer life (you have seen the claims of 100,000 hours).

Two years after cutover, it is time to review their performance.

Of some 25 11W LEDs installed, most would not be used for an hour a month, but 11 are used every day for an average of around 4 hours per day.

The pic above shows the failures of two years operation, 5 of 11 have failed. The average life of the lamps that failed is less than 3000 hours. probably in the region of 2000 hours, certainly a long way short of the claims of 50,000 to 100,000 hours. Continue reading The fraud of energy efficient lighting – LED lighting

Modifications for Jasic 200A TIG welder and pedal

In about 2009 I purchased a Uni-mig Jasic 200A TIG welder (though these are sold under many brands).

The welder came with unusual 2 and 5 pin connectors for the torch trigger switch and an optional pedal. The optional pedal was quoted at around $500, probably partly as the seller had locked the market up with the unusual connectors. (I note that the XS12K2P etc connectors are now available on Aliexpress.)

There is no standardisation of these connectors, but the pedal internals are pretty common. A quite common configuration is a 2 pin Foster (microphone) connector for the trigger switch and 3 pin Foster (microphone) connector for the current pot.

A further usability issue is that the pedal varies current from 5 to 200A, it is not possible to set the maximum current when the pedal is fully depressed. Continue reading Modifications for Jasic 200A TIG welder and pedal

Earth electrodes in parallel

I came across an article giving guidance to hams about antenna / station grounding, presumably for lightning protection.

The question is, what is the ground resistance improvement of one electrode over the two shown above. Let’s ignore the issue of earthing conductor size and deal only with the issue of parallel electrodes.

We don’t know the soil type, and we need to guess the spacing… it appears to be one house brick which is 9″ or 225mm in a lot of the world, perhaps that applies to the pic.

By way of an example, let’s make some assumptions that are likely to apply in lots of practical implementations. Continue reading Earth electrodes in parallel

AU ordinary power plug, plug packs and extension cord sockets

Electrical items personally imported to Australia (eg eBay purchases) commonly do not comply with some basic mandated safety features that can be checked with a cursory visual examination.

10A Extension cord sets (AS/NZS 3120)


Extension cord sets sold in Australia for more than a decade must have two ‘new’ features as in the pic above:

  • insulated live pins (active and neutral); and
  • shrouded socket;

Plug tops at less than 20A (AS/NZS 3112:2011)

Plug tops at less than 20A must have insulated live pins (active and neutral), and the earth pin if fitted should be longer to make contact first. Continue reading AU ordinary power plug, plug packs and extension cord sockets

LED lighting woes

Pressed to replace working lighting with so-called ‘energy efficient’ lighting by well-meaning but narrow sighted conservationists, I recently replace about 25 CFL lamps with 12W LED MR16 lamps.

They have started failing now after a couple of years of service, perhaps a few thousand hours of service. So much for the claims of 100,000 hours… clearly preposterous.

In an effort to identify which of the switched mode power supply or LED assembly was the problem, I tried to substitute LEDs to different power supplied.

That was not a good idea, lets look at the anatomy of your typical Chinese junk MR16 LED.

Above is the complete 12W MR16 lamp with GU5.3 bipin connector on the back. Continue reading LED lighting woes