Electrical – owenduffy.net

Hitachi DB3DL2 UC3SFL repair

The UC3SFL charger for my Hitachi DB3DL2 screwdriver departed this world after just 8 years with a bang, several parts around the main switching transistor deposited as soot inside the cover.

Above is a view of the underside of the charger board, it is very complex, lots of parts, and there are lots of parts on the topside. Ouch, this is going to be expensive.

Yes, it is the replacement power supply is more than half the price of complete tool with two batteries (~$200)… so that is not on.

Modification / fix

The screwdriver’s LED control board has already failed (probably a low grade Chinese electrolytic capacitor) and had to be removed as it would switch on spontaneously and flatten the battery. The hole left vacant by the removed push button provides a convenient exit for a charger cable. Continue reading Hitachi DB3DL2 UC3SFL repair

Last update: 31st May, 2019, 10:46 AM

Review – Chinese heating / cooling controller ITC-308

The Inkbird ITC-308 is a digital heating / cooling controller with two independent outputs for heating and cooling, and using a thermistor temperature sensor.

Above is the ITC-308 package. Continue reading Review – Chinese heating / cooling controller ITC-308

Last update: 28th February, 2019, 6:26 PM

On Thevenin’s theorem – #2

On Thevenin’s theorem looked at a simple source network to demonstrate some key characteristics and limitations of Thevenin’s equivalent circuit.

The example network used was linear in V,I for all V,I combinations possible. Let’s now look at a network that is not linear for all V,I, but is sufficiently linear over a sub range to be usefully modelled using Thevenin’s equivalent circuit.

Black Box for discussion

For the purpose of discussion, we have a Black Box with just two terminals and is a source of DC voltage and current, and the internal implementation is hidden from us.

A series of measurements is made with different load resistors attached and the voltage and current at the terminals is recorded and plotted uniformly stepped currents.

The V,I characteristic is clearly non-linear, but on closer examination there are two fairly linear regions, from 0.008 to 0.060A and 0.08A to 0.1A. It is a device that is usually used in the region below the knee, and for our application, let us concentrate on 0.008 to 0.030A. Continue reading On Thevenin’s theorem – #2

Last update: 26th December, 2018, 6:18 PM

On Thevenin’s theorem

Seeing another long running discussion on QRZ about transmitters and antennas, and maximum power transfer and Thevenin equivalent circuits prompts some discussion.

Thevenin published his theorem in 1883, the following is an English translation: Continue reading On Thevenin’s theorem

Last update: 26th December, 2018, 5:59 AM

T962 IR reflow oven rework #2

T962 IR reflow oven rework documented rework of the inexpensive T962 IR rework oven. This article reports some tests on various modules.

The solder cream used is cheap Chinese 63/37 tin/lead solder cream that has been in the fridge for a couple of years, so it is past its use by date.

Solder cream was applied to pads using a pneumatic drive of a 10ml syringe with #22 blunt needle.

A U shaped piece of 0.5mm copper wire was placed on the oven drawer tray and the boards placed on the wire. This to isolate the boards from the thermal mass of the drawer tray.

The program used is shown above. Continue reading T962 IR reflow oven rework #2

Last update: 27th November, 2018, 2:43 PM

T962 IR reflow oven rework

This article documents the rework of an inexpensive Chinese IR Reflow Oven for PCB assembly.

The product is widely sold and quite modest price, but is properly criticised for a number for problems that are easily fixed in the hands of a competent person. Continue reading T962 IR reflow oven rework

Last update: 26th November, 2018, 2:41 PM

Hams helping hams

I saw a series of diagrams on a commercial / ham website explaining to hams how to properly power its products.

Above, an example of their explanatory figures for discussion. The red cross is mine, lest anyone think it is less than confusing and dangerous. Continue reading Hams helping hams

Last update: 6th January, 2019, 7:11 AM

A comparo of two bare light dimmer modules

Two bare dimmer modules sold on eBay with identical specification and similar price are compared.

Both claim to have zero hysteresis. Zero hints a lie!

Hysteresis is caused in simple phase control dimmer circuits at low settings because in each half cycle the trigger capacitor starts at a different voltage depending on whether the diac fired on the previous half cycle.

A serious issue with this snap-on effect is that if power is turned off at low power setting and re-applied, the controller may not switch on.

Above is type 1, a very triac basic phase control circuit. The red capacitor and resistor to its left are snubber components, the yellow capacitor, 4.7kΩ resistor to its left and the 500k pot are the phase delay circuit, the diac is just visible above the red capacitor. Continue reading A comparo of two bare light dimmer modules

Last update: 18th January, 2018, 9:21 AM

WBT-4000W 230V AC dimmer / motor speed controller

The WBT-4000W is a triac dimmer selling for upwards of $25 on eBay.

It claims:

AC 0V-220V continuously adjustable, zero hysteresis, zero latency, superior heat dissipation.

The question is, does it deliver these things? Continue reading WBT-4000W 230V AC dimmer / motor speed controller

Last update: 22nd December, 2017, 4:18 PM

A flexible test panel for microcontroller based power control projects – #2

This article expands on A flexible test panel for microcontroller based power control projects with some enhancements and accessories.

A LED power meter that I had ordered finally arrived (slow boat from China syndrome).

Above, the upper rail contains a RCD, the power meter which displays Volts, Amps, and kW, or pf, hours, and kWh, a DIN mount terminal block for mains, and a 40A SSR on a heatsink. A clip on CT can be used for oscilloscope observation of mains current. Continue reading A flexible test panel for microcontroller based power control projects – #2

Last update: 15th November, 2017, 6:10 PM