Articles describing how to make a Return Loss Bridge are pretty common, but they don’t often spell out component values that are critical to accuracy.
Above is a schematic for discussion. It is somewhat simplified, but it is complete and will work. Continue reading Return Loss Bridge – some important details
I purchased a kit to convert a oyster luminaire to single colour LED on eBay. The kit was nominally 18W, supplied with the 5730 LED plate and driver module for about $10 incl shipping.
A cautionary note: do not play with these things unless you have the necessary competencies.
The thing was packed in nothing more than a plastic mailing bag and was bent in several places in transit from China. It was not usable in that state and some LEDs were not working so my money was refunded in full (after the usual tug-o-war eventually resolved with eBay intervention). It had to be straightened to be usable, but at the risk of damaging LEDs and possibly cracking or compromising the insulation layer.
Above, after flattening the back plate, nearly half the LEDs are not working. Continue reading Conversion of oyster luminaire to LED
When I was a student at TAFE in 1970, a teacher, Milton Moore, explained why the lab power supplies that were used, Perini & Scott 30V 2A, were the largest power supplies given their modest capability.
He explained that they were almost student proof. He went on the classify students in three categories, the average students constituted the bulk, then there were the quite inept who damaged the best equipment by doing things that no one could have anticipated, and the very bright who sought to understand equipment and expose their weakness.
Milton explained that they tested these power supplies using the rat tail file and hacksaw blade test. One output terminal was attached to the rat tail file and the other to a hacksaw blade, the voltage and current were set to max and the rat tail file and hacksaw blade were rubbed together yielding a shower of sparks… and possibly smoke from the DUT.
At the time I was very interested in overcurrent protection of linear regulators, so this was especially interesting.
ua723 – the darling of power supply designers of the time
Lets look at the issue with the ua723, recently released at that time and appearing in lots of designs.
Above is a schematic from the ua723 datasheet. Rsc is the current sense resistor and it is chosen to develop 0.6V at the current limit, so for instance in a 20A power supply it would have a value of 0.6/20=0.03Ω. So, the current sense circuit presents a Thevenin equivalent circuit of Vth=Rsc*I and Rth=Rsc. Continue reading Milton Moore’s power supply test
This article documents a simple test to ascertain whether the current regulation dynamics of are good enough to use for testing strings of LEDs as found in much modern lighting
The APS3005S is a linear bench top power supply 0-30VDC at 0-5A with adjustable voltage and current regulation… so called constant voltage and constant current modes.
A pair of 900mm long small gauge (0.5mm^2) hook up leads were used to apply a short circuit to the power supply, and current was set to 0.1A. The resistance and inductance of these leads will to some extent limit the peak current.
The short circuit was removed and the power supply set to 30V out.
The short was reapplied and the current captured with a current probe. The current probe calibration is 1mV/10mA.
Above, the peak current is 6680*0.1=66.8A, that is 668 times the set value. Continue reading Current regulation dynamics of Atten APS3005S
This article describes a 230V AC power utility box containing a 6 function 20A LCD power meter, a 4000W rated phase control dimmer, fitted up as a 230V 10A device.
The power meter has displays 6 metrics:
- (real) power
- power factor
- energy (kWh)
Continue reading Power meter + dimmer
This article describes the programming sequences for a common Chinese 315/433MHz remote relay which works with the common EV1527 transmitter.
The EV1527 should not be confused with high security protocols, the transmitter has burned into it four fixed supposedly relatively unique codes (in a space of 1 million code possibilities) and sends the burned in code associated with the transmitter key each time it is operated. This should not be confused with rolling code systems such as KeeLoq. This information is not usually disclosed by sellers.
These are usually supplied with little or no instructions, or bad online translations that are quite misleading. I dare say sellers have refunded money in lots of cases due to user confusion about programming them or compatible transmitters. This information might assist owners to find a working solution.
Above is an example remote relay (~$3 on eBay), they are available with a number of channels and may look physically different but use the same or similar firmware. Note that though the relay on this one is rated at 10A AC, that rating is for resistive load and it is rated at 5A AC for an inductive load (PF=0.4). Continue reading Programming a certain type of Chinese 315/433MHz EV1527 compatible remote relay
I bought a little wattmeter / power analyser with SB50 style plugs on it on eBay for about $20.
These devices have been common in the RC market for many years, and I have found them useful for a number of things but note that the input -ve lead is NOT directly connected to the output -ve lead, you cannot use them where the input -ve and output -ve are common.
Above is the promo pic. Of course they are not Anderson plugs, but clones. Continue reading Chinese wattmeter / power analyser fix
The HRD-831 (AKA HDR-831) is a low power mini FM stereo transmitter out of China.
The device appears to have FCC approval under the model HRD-831, but is sold out of China in a configuration that may not have FCC approval. Continue reading HanRongDa HRD-831 FM transmitter – configuration and review
The recent article Soldering iron – temperature control failure gave a plot of V’rms vs conduction angle for a simple full wave phase controlled AC waveform, and I have been asked to explain the derivation.
The phase controlled switch turns on at some delayed time from the zero crossing of the AC waveform, and conducts until the next zero crossing.
With the simplest circuits, there is a practical limit to the achievable stable range of conduction angle, and a minimum of about 50° to a maximum of about 160° is typical.
The RMS voltage is the square root of the mean of the square of the instantaneous voltage. We can write an expression for the normalised RMS voltage as a function of conduction angle θ. Continue reading Normalised RMS voltage of a full wave phase controlled power waveform
I wanted to modify a soldering iron to insert brass threaded inserts into holes drilled in plastic parts, and for this application looked to eBay for an inexpensive temperature controlled soldering iron that could be adjusted down to around 200°.
Well first check was of its temperature when set to 200°.
Ouch, that is a fail. The Chinese cheats have supplied product that does not comply with its description. Continue reading Soldering iron – temperature control failure