Category: Electrical

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

I have used Toshiba alkaline cells in several sizes for many years (decades) and had not encountered one leaked cell… however in the last few months I have found 8 AA cells that have leaked in different devices.

The leakage has always had the same failure.

Above is a view of the -ve end of the battery, ground through to expose the inner structure.

The failed batteries have leaked corrosive electrolyte, and they have all split around the circumference of the battery in the region indicated by the red arrow above. The split is common half way or more around the cell, the green seal and remnant of the rolled over case is  there, split away from the main case and covered in corrosive electrolyte residual.

This is not a failure of the green seal material, but rather the case fails.

It fails either due to internal corrosion, os weakness of the forming process. It is not clear that this area should be exposed to electrolyte anyway, so the corrosion might result from some other internal failure that releases electrolyte.

Enough reason to remove them from all devices and NEVER use these cells again.

This article documents an implementation of PAROT (Power Amplifier Run On Timer) using Transformerless power supply for PAROT.

This PAROT uses a 230V AC relay for 230V mains switching and includes PTT switching using an FOD852 opto coupler.

The intended application is to control power to a valve PA, providing programmable heater delay, and cool down delay of power off.

Above is the electronics built on a small piece of Veroboard. This one uses a 0.47µF cap as the power supply current requirements are a little lower than for the SSR. Continue reading PAROT with transformerless power supply and 230V AC relay

This article documents an implementation of PAROT (Power Amplifier Run On Timer) using Transformerless power supply for PAROT.

This PAROT uses a 10A SSR for 230V mains switching and does not include PTT switching, but space exists for a FOD852 opto coupler for PTT switching.

The immediate application is to control my main station power supply so that if it has been in use, is hot and fans are running, the PAROT provides in this instance a 5min cool down before powering down.

Above is the electronics built on a small piece of Veroboard.

Above is the copper side of the Veroboard. The layout is designed to accomodate another implementation using a small Triac to switch a 230V AC relay. The board has been given a heavy coat of acrylic PCB lacquer to improve voltage withstand.

The PAROT is assembled inside a small die cast aluminium box with stick-on rubber feet.

Above is a view of the interior of the box. A 430V MOV is connected across the SSR output terminals, it is not clear whether the device has internal protection (Chinese product, very brief data). The LED / momentary switch on the right is the only control and indicator for PAROT operation. Note that because of the transformerless power supply, everything inside the box is potentially at mains voltage… a fact that must be kept in mind when working on it. An isolation transformer is a worthwhile tool for working on these type of things. Continue reading PAROT with transformerless power supply and 10A SSR

Power Amplifier Run On Timer (PAROT) (Duffy 2013) reported some measurements of the voltage withstand of Veroboard. Voltage withstand between tracks was observed to be just over 1400Vpk.

This article reports some further measurements of genuine Vero strip board.

Above is the test piece. Continue reading Voltage withstand of Vero strip board

This article documents design of a capacitive transformerless power supply for operating low voltage, low power logic from power mains. The intended application is PAROT (Duffy 2013), though it has potentially wider application.

(Microchip 2004) gives a method for design of a capacitive transformerless power supply for operating low voltage, low power logic from power mains. The equations seem simplistic for a circuit whose apparent simplicity belies the complexity of an optimal design that properly tolerates supply voltage and load variations. For that reason, a SPICE simulation was used to refine a design.

The immediate application is for the PAROT chip driving a 40A SSR.

Above is measured characteristic of a Fotek 40A SSR, it seems typical of several similar types on hand. It appears that much smaller SSRs in the 2A range require fairly similar current. Continue reading Transformerless power supply for PAROT