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Got a technical problem? Can't understand a piece of jargon or some technical principle? Drop us a line and we'll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097 or send an email to silicon@siliconchip.com.au

Large solar panel for lighting system

The Solar Power Lighting System (SILICON CHIP, May & June 2010) is a great project but what if I want to use a solar panel larger than 5W and a larger SLA battery?

The reason I ask is that my site is alpine and winter is horrible for solar energy – shade and clouds. So I believe I would need, say, a 10-20W panel and larger SLA battery to get through “a bad week”. (A. C., via email).

• The components in the charger could be used for a 20W panel if inductor L1 is changed to 100µH 5A, the fuse to 6A, and diodes D1 & D2 to MBR20100CT. The 470µF low-ESR
capacitors should be paralleled for a total of three in parallel for each. The 0.1Ω 5W resistor should be 0.05Ω, obtained by parallelling two 0.1Ω 5W resistors.

A 100W solar charger was published in February 2011.

Damage to 230VAC
10A speed controller

I recently bought a kit for the 230V AC 10A Full-Wave Mains Motor Controller (SILICON CHIP, May 2009) for my Makita router. Its specs are: universal motor 8.2A, 1850W, speed 22000 RPM. I assembled the PCB with all components, checking all resistors with a multimeter, polarity of all diodes and capacitors etc.

On power up with the router in circuit and advancing the speed control VR1 the router motor jumped forward slightly then advanced smoothly up to full speed. Varying VR1 up and down changed the speed smoothly for a short time.

On turning on the router a second time, the motor failed to start, then after several tries the motor started again and seemed to operate normally. I then adjusted VR2 when the motor started to oscillate slightly which fixed the problem.

After another try the motor suddenly went to full speed; no speed control!

I then followed your fault-finding procedure as per the magazine article, connecting a 12V DC power supply to D3 & ZD1 and checking voltages on the relevant ICs and all seemed normal. On checking Q1, the collector and emitter pins were shorted (consequently no speed control).

I contacted Jaycar who supplied me with another IGBT. On installing this new part the circuit seemed to work normally until suddenly the router went to full speed and no speed control. Checking the IGBT I found the gate, emitter and collector shorted.

Have you experienced this problem before or could you suggest a reason why the IGBT would fail? This circuit has the latest modifications as per your website “Notes & Errata”. Is there an equivalent IGBT other than the “Fairchild” brand?

Should I be looking at IC2, Q2/Q3 maybe? The 10Ω resistor and ZD2 seem OK. I would certainly appreciate some help as I have run out of ideas. (J. M., via email).

• Possibly IC2, Q2 and Q3 were also damaged. With such a large router, the motor should be started with the control wound fully anticlockwise and then wound slowly up to the required speed. Starting the router with the control wound up will cause a large starting current that’s well over the rated 10A.

The IGBT should be parallel and tightly connected to the side of the box (but must also use the insulating washer) to ensure the device is adequately heatsinked. The IGBT should be rugged enough for the application.

Partial cure for the Ultra-LD Mk2

The quiescent current of the Ultra-LD Mk.2 Amplifier (SILICON CHIP, August & September 2008) I have built seems to drift up and down, gradually increasing to possible thermal runaway.

The only solution I could come up with was to solder a 100Ω thermistor across two of the four bias diodes, mounting it on one the output transistors. The quiescent current is now stable at 50mA. Would this cause distortion in the output stage or is there another way of solving this problem?

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