Transformerless power supply for PAROT

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.

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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

Variac refurb

I purchased a Yokoyama 5A Variac quite some years ago which was unsafe as purchased (with a current Test’nTag tag) and boxed up for repair / restoration.

It is needed for a current project, so time to fix it!

variac01

Above is the terminal block of the Variac. The defects include exposed input active and neutral terminals, exposed single insulated conductors, and the earth terminal has no spring washer or like and the screw also secures the resilent plastic P clip so it does not provide a reliable low resistance independent connection to the frame. There is no sign that there was ever a cover for this terminal block. It is noted that the terminal markings have been somewhat defaced.
Continue reading Variac refurb

An Emergency Stop switch for the mill

In a non-thinking moment, I had an accident with the mill because the head had not been clamped fully. I found myself fumbling for the power switch and the incident reinforced the need to fit an emergency stop button. I had procured parts for this a long time ago, it was time to put them to use!

ES01

Above is an inexpensive emergency stop button from eBay, about $6 including the box. This switch had NC and NO contact sets, for this application only the NC set is used.  A gland is used in the bottom of the box to let a 3 core 1mm^2 flex into the box. Continue reading An Emergency Stop switch for the mill

Ultrafire XML-T6 LED torch – a fix for the dysfunctional mode memory ‘feature’

On review of the Ultrafire XML-T6 torch, I found the mode switching / mode memory so dysfunctional that it rendered the torch useless in my evaluation.

XML-T6This article describes a work around  that makes the thing usable (IMHO). Continue reading Ultrafire XML-T6 LED torch – a fix for the dysfunctional mode memory ‘feature’

Fridge / freezer setup

The operating temperatures of refrigerators and freezers used for food storage is important to safe storage of food and to minimisation of energy costs.

The US FDA recommends the refrigerator should be set to 40F (4.4°) and the freezer to 0F (-17.8°).

Temperatures vary inside the cabinets, and they vary over time with opening and closing doors, and introduction of warmer goods for storage.

Many spot temperature checks are helpful but they don’t provide a very complete picture, and opening the door to make measurements disturbs the very thing being measured. Continue reading Fridge / freezer setup

Chinese 18650 Li-ion cells – Ultrafire capacity test

I purchased a torch (flashlight) on eBay recently. It was described as using CREE T6 LED array, and supplied with two 4200mAh 18650 Li-ion rechargeable batteries with charger for A$25 inc post.

Ultrafire18650Above, the cells are clearly marked 3000mAh, way short of the advertised 4200mAh… but what is their actual capacity.

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Above are the results of discharge tests, the first digit is the cell number and the second is the test. The first test is charged with the supplied charger, the second test is with my charger. Continue reading Chinese 18650 Li-ion cells – Ultrafire capacity test

Panasonic NCR18650B Lithium Ion cells on eBay

Further to 18650 Lithium Ion cells on eBay I purchased a pair of Panasonic NCR18650B cells, nominal 3400mAh, from an Australian supplier for about A$22 posted.

NCR18650B

Above is a pic of a cell.

NCR18650B02

Above is a zoomed in view of the same pic with increased contrast. The feint quality control code printed on the underlying steel container is visible. It is usually visible through the jacket on genuine Panasonic cells.

It is always hard to know whether the product is genuine, the Chinese are better at copying the looks than the internals.

The cell was charged, then discharged at 1C on a battery analyser.

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Above is the first three discharge cycles, the cell achieved just under 3000mAh to 2.8V, about 93% of datasheet rated capacity of 3200mAH, 85% of the advertised nominal 3400mAh capacity.

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The actual discharge curve is fairly similar to the 1C curve from the datasheet.

These cells look more promising than the GTL red 5300mAh cells previously evaluated.

18650 Lithium Ion cells on eBay

I have been intrigued by the huge number of sellers of very low cost 18650 Li-ion cells on eBay.

Could they be any good?

As a reality check, Panasonic cells around 3000mAh sell through traditional channels here in Australia for around A$20 per cell, there are Australian eBay sellers selling cells advertised as Panasonic for around A$22 per pair posted.

GTL01Above, the GTL red LS18650 5300mAh Li-ion cell purchased in a lot of five for $1.30 each (inc post from China).  The rated capacity is more than 50% higher than the maximum from brand name products. Continue reading 18650 Lithium Ion cells on eBay