A simple approach to radiator fan switching

I read with interest your article on the automotive temperature switch in the January 2007 edition.

I recently upgraded a 1986 car to electric radiator fans to improve fuel economy and make the engine quieter. The way I got the fans to turn on and off was simple. I attached a circuit breaker (Altronics S-5595) to the radiator and used that to toggle a standard 12V automotive relay (Altronics S-4339). The circuit breakers come in different temperature set points and have built-in hysteresis.

Rob Clark,
via email.

Comments on the Intelligent Car Air-Conditioner Controller

I liked the Intelligent Car Air-Conditioner Controller project in the January 2007 issue. My suggestion is to add an extra function that switches on the air-conditioner every now and again during the winter months when the air-conditioner is not being used

I have been told that the air-conditioner should be switched on for short periods during winter to ensure that the rubber seals don’t dry out and then leak. This extra feature may then save you the cost of replacing the seals and recharging the refrigerant gas.

Other than having to change the software to add this feature, the circuit would also need to be changed so that +12V power would be connected to the NO contacts of both Relay1 and Relay2. The NO contacts would need to be connected to the connection between the air-conditioner Fuse and the air-conditioner relay (or switch).

Roderick Wall,
via email.

Source for cartridge styli

I noted that Rodney Champness was having difficulty sourcing styli for the Philips RF5 Stereogram (Vintage Radio, January 2007 issue). He could try www.garage-a-records.com. They have just about every component for any turntable. I use them for the occasional turntable repair.

Pudney & Lee in Wellington, NZ, may also be able to help.

Ian McPherson,
via email.

Partner wanted for electronics development

I am a Mechanical Design Engineer and my business/hobby is the development of new ideas. I currently have one about to be commercialised and several on-going.

One idea under development involves programming a chip and displaying information on a screen for an exercise device. The concept has a novel twist and can be used on most exercise machines and I have been lent one by a local manufacturer/importer, who is interested in incorporating the idea into their machines.

My knowledge on this subject is limited, so I’m looking for a partner to develop the electronics, so that we can produce it. A brief search suggests the idea is novel (ie, patentable) and development would be on the basis of their part ownership and income from sales at a later stage.

If you live around the Tea Tree Gully area in South Australia, have the skills and this project interests you, please email me tony.rossiter@voice.net.au and I will outline the idea to you personally, under a confidentially agreement, so that you can decide.

Tony Rossiter,
via email.

Holden airship is actually a balloon

The article on the Holden/display airship in the December 2006 issue was very interesting. I have been a keen follower of lighter-than-air ships ever since I was a kid back during WW2.

There are three basic kinds. First, there are dirigibles, which have a complete frame with the gas bags inside and an outer skin over the frame. Zeppelins and the US Navy’s Shenandoah-Class airships were of this kind. Then there are the blimps, which have a half-frame in the lower portion of the torpedo-shaped body. The most famous of these are the three Goodyear blimps.

Then there are balloons which have no frame at all. Examples are the Montgolfier Brothers’ pioneering balloon, one of the very first to fly, then the hot air balloons of today and of course, the famous barrage balloons which flew over cities in wartime. These barrage balloons were large and tethered by strong cables and were there to interfere with low flying aircraft.

Contrary to the statement in the article indicating it was either a dirigible or a blimp, the Holden airship is actually a balloon. It has no internal structure or frame and the gondola is attached in the standard balloon manner, suspended by a set of cables from the gas bag. The main difference between a barrage balloon and this airship is the rigid tail fins with control surfaces.

I was quite surprised at the statement that the gondola was built on a steel frame, as this would be nearly twice as heavy, for the same strength, as aluminium/magnesium alloy fram-
ing. I don’t know of any other lighter-than-air vessel with steel in the structure except where its use is unavoidable; eg, as support for the engines. And in many designs this too is made from forged aluminium alloy.

The Montgolfier balloon was lifted by methane, which is only one third as dense as air (but easily available in those days). Helium is 1/10th and hydrogen 1/20th as dense as air.

The only suitable lifting gas for dirigible airships is hydrogen. The US Navy’s attempts to use helium in their dirigibles saw all five quickly lost in storms at sea – all of them came down with the loss of all life. Helium is simply too dense to lift that kind of weight.

Blimps have a limited weight-carrying capacity, even with only half the frame of a dirigible, due to the limitation of using the higher density gas, helium.

Pure hydrogen is perfectly safe; it cannot explode unless contaminated with oxygen (as will all flammable gases) and will just burn if there is a fire. No Zeppelin other than the famous Hindenberg ever crashed or was lost.

The Zeppelins were truly huge. Their scale was unimaginable – they carried many fully furnished cabins, a ballroom, dining room, galleys and nearly everything an ocean-going luxury cruise ship would have. It was – even built of aluminium – a massive amount of weight but was lifted with lots of capacity remaining by hydrogen-filled gas bags which at cruising altitude occupied less than half the interior of the ship.

Too bad that since the Hindenberg’s destruction, hydrogen is not preferred for lifting airships, even though it is not really a serious danger or problem – in fact it is easier to contain than helium, the "escape artist" of the gases.

Bear Stanley,
Atherton, Qld.

Audio tones can cause clocks to gain time

With respect to the letter in "Ask Silicon Chip" in the December 2006 issue, the writer is quite correct in that AFIC (Audio Frequency Injection Control) tones which are used for off-peak, street light and tariff switching can affect digital clocks.

This usually happens when the tones exceed 20V and the clocks race due to multiple zero crossings during the tone burst. This can be from minutes to hours, depending on the level. The injected level is usually set to between 3V and 10V superimposed on 240VAC. The signal rises, usually due to the area in question being supplied by a feeder that consists of a long length of overhead cable with an underground subdivision at the end. This can create a resonant circuit at the control frequency which then acts as a voltage doubler.

John O’Brien,
via email.

Remote Telltale for Garage Doors

I have a comment regarding the microswitch arrangement for the top & bottom limits on the door track shown on the inset photo on page 59 of the Remote Telltale for Garage Doors in the January 2007 issue. The arrangement shown assumes that the door is going to stop in the same position each time it reaches its upper and lower limits, which is not always the case, particularly if the door is manually raised and lowered.

A better arrangement would be to orientate each switch at 90° to the inset shown whereby the switch activator points towards the door and a sprung follower is attached to the door to activate the microswitch. An even better arrangement would be to install a magnet and reed switch which requires no mechanical contact.

If your house has a security system that protects the garage doors, the door magnet could activate the additional reed switches when the door reaches its upper or lower position.

Mal Land,
via email.

Comment: we did not envisage that this project would be built for a door that was manually operated. However, your comments on manually-operated doors are quite valid.

RME equipment search

I would like to hear from anyone who used to work for a company called RME that used to be in Sydney and made broadcast equipment for radio stations.

Specifically, I am looking for the plans/PC board layouts, or even original boards, for the 451M1 LED Level Monitor they used to make. Ultimately, if someone has a complete unit, I would be most interested in buying it but board layouts would be the next best. Please contact me at happydayradio@hotmail.com.

S Williamson,
via email.

Safer method for discharging microwave oven capacitors

I read with some awe the description of how to discharge a high-voltage capacitor in the December 2006 issue, on page 94. A dead short on a fully charged capacitor is foolish, very frightening and almost as dangerous as leaving it fully charged. The correct way to deal with it is much less spectacular: a resistor of about 1kΩ, well insulated (eg, contained within a plastic box), connect one side solidly to ground (as one side of the capacitor is usually grounded, through the transformer secondary winding and often a high-voltage fuse), and connect the other side to each side of the capacitor in turn.

Use something like a high voltage screwdriver as pictured in the article, and tape a good quality multimeter probe to it. There should be a small arc if there is any charge in the capacitor.

Be aware that if the high voltage fuse has blown, you will need to connect directly across the capacitor but try the ground method first. This is MUCH safer and then you can go directly across the capacitor. Refer to the WES components Microwave Oven Servicing Manual for further information. There are 2¹/₂ pages of safety notes, quite a few of which are applicable to those recycling the bits.

I service electric fence energisers and need to discharge the dump capacitors, typically 30μF to 120μF charged up to 900V through a mains doubler or tripler circuit. I use a simple pair of multimeter probes with eight 560Ω 0.5Ω resistors in series within the probe bodies (four in each). The probe tips are long enough that I can short them together after about five seconds, just to make sure the capacitor is discharged. There is enough energy in these capacitors to destroy the tip of a screwdriver.

With regard to microwave transformers, it is easy to cut off the existing secondary (with a hacksaw and cold chisel combination) and wind a new low voltage secondary on it. OK, maybe it will not be pretty or 99% efficient but the primary winding is generally well protected and it is a big impressive-looking heap of iron.

David Walters,
David Walters Electronic Services,
Dubbo, NSW.

Not all battery-less torches are fakes Your correspondent Roger Forsey (SILICON CHIP, January 2007) must have been unlucky with his battery-less torches. I have bought three of them in various sizes but from auto parts shops. They have all worked well, with the larger one holding its charge and being able to shine its light at the push of the switch and with no further shaking. In all of them, the "magnet" worked remarkably well, to the point where it would hold a teaspoon in mid-air despite the thickness of the torch case through which the magnetism had to work. Indeed, I cautioned my grandsons to keep the magnet away from credit cards! A Google search under "battery-less torches" will reveal several battery torches, all modestly priced. The best that I have found, and a friend brought me four back from Hong Kong, is the compact, hold-in-the palm-of your-hand model which is operated by just squeezing the pistol grip on the underside. This model holds its charge well and is much easier to operate than those wind-the-handle things. I gave up on the solar panel jobs; you can’t recharge them if they are in the glove box or in the bedside table drawer. John Richardson, West Pymble, NSW.

Adjustable hysteresis for Battery Controller I read the article in the December 2006 issue on the 12/24V Battery Isolator with enthusiasm. Over the years I have made up many of the original EA 1992 Low Voltage Cut-Out kits for myself and fellow campers. That kit is reliable and solves the problem of over-discharging the battery. However, I have always been troubled by the fact that it draws a constant 70mA or so for as long as the relay is energised. With devices like refrigerators becoming more efficient both in terms of the current drawn and how much of each hour is taken up with the "on" duty cycle, that current drawn by the cut-out is becoming more significant, even if only psychologically so. As you correctly observe, every microamp is indeed precious. This new controller could be just the bee’s knees as a superior replacement, not only because of its negligible current drain but also its robust current capacity. However, it appears that, in the low-voltage protection mode, it has almost no hysteresis. If set to drop out at say, 10.5V, it would cut back in again at 11.1V. Even with a modest load of 2A or 3A, the device would cut out at 10.5V and the battery voltage would almost immediately drift up to considerably more than the 11.1V cut-in voltage. It would cycle thus, with possible bad effects on the fridge etc, until the battery was finally drained enough to not drift up much. This is a problem we experience with the standard cutouts found on some 12V refrigerators over the years. The EA kit has an adjustable hysteresis, so you can have the controller cutting out at 10.5V to 11.5V and the cut-in happening at say 12.9V. This is an effective solution. Can we add this capability to the new controller? John Keitley, via email. Comment: we referred this question to the designer, Branko Justic, at Oatley Electronics. His reply is as follows. The hysteresis of the voltage sensing comparator of the L4949 IC is around 8%, which corresponds to 0.8V at a battery voltage of 10.5V. As pointed out, this may not be sufficient in practice. A simple way to increase the hysteresis would be to add a series resistor and diode combination between the input pin of the comparator (2) and the open collector output pin (7). With this in place, when the battery voltage is high the open-collector transistor is off and the voltage is pulled high (+5V). The additional diode is reverse-biased so this network would not have any effect on the voltage at the voltage-sensing comparator. However, when the battery voltage falls below the lower set limit, the open-collector transistor is turned on and the series resistor/diode combination would add extra loading between the comparator input pin and ground. This means that the battery voltage would have to rise to a higher figure before cut-in, amounting to increased hysteresis. With a series 1N4148 diode and 43kΩ resistor combination connected between pins 2 & 7 of the L4949 IC and with the cut-out voltage set to 10.5V, the cut-in voltage was 12.9V. We will modify our PC boards to make provision for these components and include a note with our kits. Branko Justic, Oatley Electronics Pty Ltd.

3-phase motors have excellent torque

I’ve worked extensively with the application of 3-phase induction motors in industry and I don’t agree with the comments of correspondent Jeff Jones (December 2006 Mailbag) who says they have poor start torques. Induction motors started direct on line (DOL) have excellent start torque characteristics – typically locked rotor start torques are more than twice the motor full load torque. This start torque remains reasonably constant until the motor approaches its running speed, where the torque delivered by the motor reduces to match the load.

I agree that reduced voltage start methods decimate the starting tor-que (start torque varies as the square of the voltage).

Even with DOL starting, high-
inertia start loads can trip you up. A classic example for us was the application of centrifugal blowers. They often have a small aerodynamic load due to low air volumes but a high mechanical inertial load due to a large diameter but narrow rotor.

Motor size is traditionally established from the aerodynamic load and this means the run up period to full speed can be long – and with a typical start current draw of 5-7 times the full load current, they had a tendency to trip their thermal overloads. This was usually solved by using electronic overloads with an adjustable run up time.

I like your editorials which take an honest and straightforward look at the state of things. There is an eye on waste and sustainability which is good. So why the extensive feature on the airship in the December issue? It may be technically interesting but is an unnecessary and an expensive waste of resources for no real purpose other than to serve as a floating billboard.

If you believe we need more invasive exposure to advertisers then I’ve misjudged you. I frankly don’t see any point in its existence. You lead the way in asking why car manufacturers now add frills and not enhanced performance and economy to their cars and yet in the same breath laud this thing.

I read your article on cheap battery drills and like a man enlightened I rushed out to purchase new batteries for my favourite (and ailing) drill. Now repacked, I look to the smart charger and well . . . phew! It’s pretty clever but isn’t it really applying a hammer to crack a nut?

Why not just charge the drill at the trickle current and leave it at that? OK, it takes 20-30 hours to fully charge but if you can leave it on all the time then it is likely to be fully charged and ready when you need it. So it goes flat part-way through that job? If you are like me, I wouldn’t wait even three hours for a drill to recharge, I’d curse, go to the garage and drag out a lead and power drill and finish the job.

OK, that wouldn’t suit a tradesman but they wouldn’t use these cheap drills anyway. I’m talking of the home handyman.

The extensive kit development you do for cars is fascinating but the thought of dissecting my car’s dash facia to fit any of them is scary.

Andrew Buchanan,
via email.

Comment: we agree that we don’t need any more advertising but we thought the technical story of the airship was of interest.

We realise many people would be reluctant to break into their car’s wiring but we believe that we should show what is possible.

Electrical licensing is still a bureaucratic mess

I’m writing in regard to the electrical wiring license debate which will very soon raise its head once again. As a frequent magazine buyer, I read many of the responses a few years ago from SILICON CHIP readers and can only agree with the readers and look in disbelief at the unreasonable electrical licensing rules, especially those in Queensland.

As you may be aware, 2007 could be scheduled for a review of the Electrical Safety Act in Queensland which was last written in 2002, since it has been five years since the last publication.

I’m writing to give an indication to you and the other readers as to the difficulty in becoming a licensed electrical worker in Queensland from my own experience.

Throughout my university studies, completing a Bachelor of Electrical & Computer Engineering, I was working part-time at a small TV radio repair shop as an electronics technician repairing TVs, consumer electronics and audio-visual equipment for around 20 hours per week. This work was supervised by an experienced and restricted licensed technician and has continued on a part-time basis despite having a full-time engineering position since completion of my studies.

When I first began my engineering position I was required to confirm my ability to perform some wiring. My position does require me to construct prototypes and test electrical components for use in designs which involves a disconnect/reconnect licence.

Prior to approaching the ESO in Queensland about a licence, I had read the current Safety Act and noticed a clause which is still current, stating that a person does not require an electrical license for the performance and supervision of electrical work as part of practising the person’s profession as an electrical engineer.

I contacted the ESO to confirm my understanding of the clause. I obtained many varying responses which did not give me any confidence in my understanding of the clause before I eventually spoke to the head of licensing at the time who I explained my position and work to and was informed that the work I was doing is covered by the clause although the clause would not cover my second job as a technician.

This led me to apply to obtain a restricted electrical license in order to continue the technician work. Applying for a license requires completion of forms which require details, evidence of a trade or calling requiring an electrical license, JP-signed evidence of CPR qualifications and paying the prescribed fee for processing.

Several weeks passed without a response before eventually getting a letter stating that an electrical engineer is not a trade or calling that requires an electrical license and that my application was rejected. I then obtained a number of letters from my employer as evidence of my requirement to perform electrical work and resubmitted my application.

Many weeks passed before getting another lot of paperwork from the ESO containing a training permit stating that I would have to complete at a relevant TAFE college a number of courses and sign-off from an electrical worker of my competence to perform the required electrical work. My electrical engineering degree, according to the ESO, means nothing for the purpose of obtaining a license.

I eventually found a TAFE college that permitted me to sit for the relevant
exams and practical competency tests, saving me around $1600 norm-ally required in fees to enrol in the appropriate courses. After eventually having completed all examinations for the license, a completion statement of my competence in electrical wiring was sent to the ESO for me to obtain the license. The ESO managed to lose the relevant documentation several times, delaying the process by a further two months before I finally obtained a licence.

As you may appreciate, the pro-
cess for obtaining a licence is extremely difficult and frustrating. I believe that electronics technicians should be issued with the license as part of their trade and that electrical engineers should have a complete unrestricted electrical work licence.

Don’t get me wrong, I do not believe some electrical engineers after completion of their studies are competent at performing wiring but . . . they should be. Punishment should be on unsafe wiring rather than based on relevant licensing.

The ESO appear to have the rules in place for ensuring business and economic growth for electricians and have no regard for electrical engineers, electronic diploma graduates, technicians and DIY hobbyists that simply want to construct electronic circuits for their own use.

The unrealistic stand the ESO has taken on licensing and the unbelievable difficulty in obtaining a license is unacceptable. I very much hope that some serious changes are made to the Electrical Safety Act before the next amendment is published.

Name and address supplied but withheld at the writer’s request.

Comment: the Queensland bureaucracy continues to amaze with their ongoing stupidity with regard to electrical licensing and safety. The other states are not much better.