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Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd may edit and has the right to reproduce in electronic form and communicate these letters. This also applies to submissions to "Ask SILICON CHIP" and "Circuit Notebook".

Banning electric hot-water systems is silly

In regards to Publisher’s letter in the January 2012 edition, a further example of the energy needs being in the hands of clowns would be the new restrictions on the use of electric hot-water heaters. Apparently you are no longer allowed to install standard electric hot water heaters in new houses, town houses etc and soon existing installations will not be able to be replaced with a similar system.

Replacement systems have to be solar, gas or heat pump. The logic is that the standard type of heaters produce a large amount of greenhouse emissions. However, as far as I can see, most of these heaters are on “off peak” and are therefore using electricity that has to be generated anyway.

The stupid part is that, assuming you do not have gas and live in a unit or townhouse where the heater is situated internally and therefore cannot fit solar, to replace it with a heat pump type means that you end up with a unit whirring away in your laundry 24 hours a day at normal power rates, putting further loads on the system at peak times. Then there is the purchase cost and reliability issues of the heat pump systems. How is this reducing power demands, saving the environment and lowering power costs?

Rob Leplaw,

Oatley, NSW.

Comment: virtually all small hot-water systems in home units and industrial premises are electric but not off-peak. In most of those situations, gas is not available and since they are small units, heat pumps would be over-kill. Unless these systems can be exempted from the ban, they will be in limbo.

Solar tracker needs better limit switches

The Solar tracker featured in the Circuit Notebook pages of the January 2012 issue looks interesting and will go into my “ideas” folder but I have a couple of comments regarding the so-called “limit” switches.

The switches S1 and S2 described as “limit” switches appear to be there for the sole purpose of signalling IC1 when travel extremities have been reached. I assume this is so IC1 can drive the unit back to the starting position ready for next day operation. This is OK for this application.

The text then states that in the event of a fault they will prevent the motor over running and causing damage. In this case this is not the way to go about “limiting” travel.

Faults of this nature usually are Mosfets turned on permanently by some means or shorted and there is nothing IC1 is going to do about this. Limit switches used to prevent such situations must remove power to the motor.

In fact, manufacturers of commercial devices such as PLCs etc emphasise the fact that safety interlocks and limit switches must not be dependent on said controller’s correct operation and should be hard-wired.

Bob Rayner,

Willow Vale, NSW.

Comment: limit switches for the motor itself (ie, instead of being monitored via the PIC) will solve the problem should the Mosfets fail. But the limit switches will then have to carry the full motor current including starting current. These too can fail by welding shut if they are not sufficiently rated.

In any event, they should be placed to operate only when the panel moves past the original S1/S2 limit switches monitored by the PIC.

Swimming pool sanitisers can be helpful

I refer to your response to B.C.’s letter published on page 100 of your January 2012 edition concerning copper/silver (Cu/Ag) swimming pool sanitisers. You have published several analyses of products whose promoters make false or misleading claims; such analyses help readers such as me to understand and add to the list of good reasons for buying SILICON CHIP.

I consider that, despite its length, your response to B.C. oversimplifies the information presented in the APVMA reference. Nevertheless, thank you for bringing the APVMA reference to my attention. If the SILICON CHIP staff consider that the Cu/Ag sanitisation is too problematic to be featured in the magazine, fair enough, say so, but please don’t over-simplify; that just adds to the flood of misinformation threatening to drown us all.

I have no connection with any promoter of such products, apart from use of one of these systems, which I purchased 20 years ago. I have found that chlorine to at least the minimum recommended level is necessary when the pool is in use and “normal” chlorine levels are necessary when the pool is being used by multiple people. However, the Cu/Ag keeps the pool reasonably clean without chlorine, when the pool is not being used.

The APVMA article does not discuss the issue of the persistence in solution of Cu/Ag ions versus chlorine but its website shows the product I use as registered “For the control of algae in swimming pools and spas”.

Would I recommend such a system? I have been asked just that question by other pool owners and people contemplating getting a pool, all of whom seem to have been attracted by the “no chlorine” spin. My answer has always been highly qualified because my experience has been that the system I purchased did not meet my expectations but it did have some effect which I judged useful for me, there are many factors to consider and I could not find accessible, comprehensive explanations as references – no thanks to the pool industry on that.

So far as I am aware, none of those who asked my opinion subsequently purchased a Cu/Ag ioniser.

SILICON CHIP often carries articles with a technical focus other than pure electronics. Perhaps you might even consider a technical article on aspects of the use of electronics in sanitiser products. If the promoters of these products are willing to engage in demonstrating that the products are useful and discuss their limitations with a respected technical journal, this would be an opportunity to increase their credibility, rather than just relying on the usual lifestyle magazine advertising hype. If not, then that speaks for itself.

Peter Bennett,

Macarthur, ACT.

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