Letter of appreciation

This is a letter of thanks, first to the staff of SILICON CHIP for an excellent magazine. I have been getting it since it first started 12 years ago and enjoy most articles but especially those on Vintage Radio.

Now for my special thanks to Greg Swain and his computer articles. I have recently changed two hard drives in my 486 computer and his article on hard disk upgrades led me through this operation without any problems. When I went to install a 4.3GB hard drive, his article told me to down-load a program called EZDRIVE. Once the program was activated, it did the job for me.

I enjoy the magazine nearly from cover to cover but don’t always agree with Leo Simpson, especially when he knocks valve amplifiers. I have been in the trade now for about 55 years and think valves still make the best outputs. Never mind; we can’t agree on everything.

John Breden,
Te-Puke, NZ.

Pros & cons of the AC/DC controversy

Your editorial in the October 1999 issue returns to an old controversy in the Solar/Renewables/RAPS field that has been going on for some time, whether to go for DC, AC or a combination of both. Thanks to modern electronics most electrical equipment could run on DC, motor drives included.

After all, the only reason for running household appliances on AC has been the historical problem of distribution, voltage increase and decrease, motors and generation, all of which can be overcome these days with the help of solid state physics.

The general consensus in the industry at the moment is that it is less messy to remain with AC and go with inverters on separate circuits. So the basic configuration would be gas cook­ing, photovoltaics, batteries, inverters and AC appliances.

This may now attract more attention in rural areas for water pumping and house power, now that the Federal Government is set to introduce a new rebate on photovoltaic installations this year. I believe this is somewhere in the region of $4000 to $5000 per installed kilowatt (peak) as part of the GST package.

Could this lead to more interest in solar-related projects and articles?

One solution that might be of interest in the situation described in your editorial would involve battery storage for about 18 hours of use, with charger and inverters. The charger would be permanently wired to your off-peak mains circuit and could then run the house entirely from batteries. Here in Queens­land the difference is about 8 cents per kilowatt-hour.

This would result in an immediate reduction in power bills but would need about 30 years to pay it off, if then! You could also add photo­voltaics from time to time to improve the system considering the new rebate.

If this sounds expensive, then what price do you put on the inconvenience of blackouts?

As regards DC appliances and their availability, check out the US website at www.realgoods.com

Geoff Dawson
(via email)

Caution on
PC Powerhouse article

I read the article on the PC Powerhouse in the December 1999 issue of the magazine and have to agree with you, "Why didn’t someone think of this before?" Great project. I built the 6V section (I had a plastic bag full of 7806s on hand) hanging in "3D" off a heavy back plane to power my son’s amplified speakers last night and got rid of the hum from the DC plugpack!

But perhaps I can shed some light on why this idea is not used more frequently. In this example it’s used for a powered set of PC speakers. The ability to use this idea relies on the fact that the negative connection of the DC input socket is connected to the sleeve of the 3.5mm stereo lead, ie, negative earth.

Say a manufacturer from Outer Slobovia decided to connect the positive of the DC supply to the sleeve (ie, positive earth) and the computer power supply is used – then there is a direct short on the PC’s supply. This is not common, I’ll admit, but it is possible, with embarrassing consequences.

With batteries or a plugpack it doesn’t matter but with this project it could. Perhaps you could publish a note to this effect in the "Notes & Errata" section, getting people to check the grounding with their multimeter before connection.

Yes, the article does mention the fact that the centre pin of the DC sockets must be positive and the sockets are to be insulated from the chassis. You also refer to powered speakers with the centre pin wired to the negative rail.

However, merely reversing the leads at the other end of wire does not solve the problem if the manufacturer of the device being powered has connected the positive side of the power socket to the shield of the audio cable which goes to the computer’s earth. This will result in short circuit between the hot of the power wire and the cold of the audio cable. This may blow the 3-terminal regulator and possibly do more damage.

Brad Sheargold,
Collaroy, NSW.

Smart Fastcharger
works well

I own a corporate event business and good batteries are essential for the equipment we run. One week out from an event and I found that 24 of my 35 NiCd batteries had developed severe memory problems. I searched the Internet and found some highly promoted battery chargers from the USA and Europe. Then while checking around the electronics stores I heard about Smart Fas­tchargers, in Devonport, Tasmania.

I was sceptical about their claims but I went ahead and ordered one of their chargers. Within 48 hours I had recovered 23 or the 24 suspect batteries.

Since then our office has gone recharge mad. Someone found an old video camera in our store room. It was at least 12 years old and hasn’t been touched for about eight years. At first, the batteries would not even take a charge but the Smart Fastcharger fixed that and now there are very embarrassing home videos being shot on my time. Everyone’s mobile phone batteries have been reconditioned and the search continues to try and defeat the charger, to no avail.

It is wonderful to see a small Australian company taking on the giants and triumphing, with great products, fantastic service and keeping Australians employed.

Mike Sheehan,
Thunderbird Events,
Chatswood, NSW.
www.thunderbird.com.au