AC voltages more dangerous

I wish to bring to your notice a boo-boo in the November 1999 Mailbag letter from Jonathon Waller. He maintains that the danger from a DC electric shock is greater than a shock from the same voltage on AC. He goes on to say that this is because AC tends to throw the person away, while DC tends to paralyse the muscles, making it difficult for the victim to escape the shock.

Now this is a very dangerous boo-boo because it is the exact opposite: DC tends to throw the person off or away and AC paralyses the victim.

Please check on this and you will find I am correct. Now don’t get me wrong; they are both dangerous but AC is more so. Having been brought up on DC power supplies and having had a belt or two from DC, if it has been AC possibly I would not be here today.

The other item I would like to comment on refers to the use of alternative power when connected to the grid and there is a power failure. Do as most rural families do: invest about $1200 - $1400 on a 5kVA engine-driven power plant and you can run the full house from it. Rural areas do have quite a few blackouts, sometimes for days, and the 5kVA plant is the most practical alternative.

Keith Lang,
Esperance WA.

Solar regulators not expensive

I read with great interest your feature on a solar panel regulator in the December 1999 issue of SILICON CHIP. Although I get great pleasure from constructing kits myself, I feel that this project needs some consideration. I wish to point out a few things mentioned in your article that need highlighting.

First, the article says that solar regulators are expen­sive. This is NOT true. The cost of a solar regulator is only a very small part of the overall system cost. Take for example the BP solar panel featured in the article, with a recommended retail price of $795. Although we sell many of these panels, a system usually consists of several of these and sometimes more than a dozen or so. This is expensive indeed, not to mention the cost of quality battery storage, which can be around the same.

Secondly, 5A current capability is all but useless except for the hobbyist, which is probably who you are targeting anyway.

Thirdly, there are no current draw figures for the featured regulator. By using a relay, I guess that it is reasonably high, compared to commercially available units. The reason I say this is because when using solar energy, especially on small systems, such as this regulator would have been designed for, you need to be aware of ALL loads, including the regulator.

For example, if the regulator is drawing 100mA on standby, this will equate to 2.4 Amp-hours per day (24 hours) at 12V. This will require a 12W solar panel just to provide the power to run the regulator during winter, not to mention the relay as well. This could be an expensive regulator if extra power is needed to run it.

Fourth, the regulator provides no equalisation charging, which is required for any system using multiple wet/flooded cells (ie, more than 2V – a 12V battery has six cells). Equalisation charging is required because when cells are discharged and recharged repetitively, they must be slightly over-charged to equalise all cells. This will prolong the battery life substan­tially. Also quality deep-cycle batteries should be charged at 14.1V, not 13.9V as this regulator does, to prolong their life. However, if used with SLA batteries, this regulator will work OK.

Fifth, always check with the battery manufacturer concern­ing their required charging characteristics, as you may void the battery warranty if you are not charging correctly. This should have been explained at the start of the feature, as some compa­nies will not warrant batteries unless they are charged with anything but a quality regulator/charger. I believe this to be very important.

The solar regulator could easily have the current in­creased, if the user does not wish to use the current reading capability of the display, by increasing the relay’s rating and why not use the excess power from the panel/s to do something else, such as run a pond pump or charge a second battery, by removing R1 and dumping the solar power to an outside device, rather than just burning it off with a resistor. You would need a diode in series with the solar panel if charging another battery though, as the second battery may discharge back through the solar array overnight, as well as requiring another regulator.

Another idea: why not make it suitable for charging 32V or even 48V systems, by increasing C10’s voltage rating, and putting in an over-voltage circuit before REG1, using a 47kΩ or 51kΩ resistor (for 48V or 33kΩ for 32V) in place of R5 or R6 and up­grading any other component that may need its voltage rating upgraded (I haven’t looked at it too closely).

The most used solar regulator by us would have to be the P1.20 or P1.40, manufactured by Plasma­tronics, in Melbourne. They consume as little as 8mA, will switch up to 40A current and are programmable with up to four-stage charging, with adjustable set points and time.

They retail for $245 (20A model) and $345 (40A model) plus tax if applicable, so these are not expensive after all, consid­ering the features.

K & C Stork,
Solar Power Consultants,
Bacchus Marsh, Vic.