Q: What is the difference between 120 volt and 240 volt?
A:There are two common misconceptions about the difference between 120 volt and 240 volt circuits. One is that an appliance run on a 240 volt circuit will use less electricity than one run on a 120 volt circuit. The other is that 240 volt circuitry is more dangerous than 120 volt circuitry. Both of these notions are false.

The notion that running an appliance on a 240 volt circuit will save energy is based on a misunderstanding of how power companies charge for the use of electricity. The voltage makes no difference at all to power companies because they charge by kilowatt-hour units. One kilowatt-hour unit equals 1000 watts of energy running for one hour. Since the wattage of your lamp doesn’t change when you switch from 120 volts to 240 volts, neither will your electrical bill.

The notion that running an appliance on higher voltage increases the danger in the event of a short circuit or electrical shock is actually backwards. The thing that will hurt you if you get electrocuted is amperage, not voltage. The simplest way to explain all this is to consider the simple formula that applies: W/V=A. Wattage divided by Voltage equals Amperage. This means that doubling the voltage of your circuitry will cut your amperage in half, making it half as harmful if you should accidentally get zapped. In other words, the higher the wattage and the lower the voltage, the more dangerous the circuitry. Please note that most HID lights run enough wattage to be very dangerous in the event of electrocution, even when run at 240 volts. If you aren’t an electrician, please don’t try to rewire any of your indoor gardening appliances yourself.

Q: What is the difference between EC and TDS?
A:There’s a lot of disagreement over the relative merits of measuring Electrical Conductivity (EC) as opposed to Total Dissolved Solids (TDS), so I’ll do my best here to explain the debate in the simplest terms possible. Both measurements are used by indoor gardeners to determine the strength of a hydroponic nutrient solution, and either one can deliver the information a gardener needs to make adjustments and corrections in the reservoir.

The source of all the trouble is that while the information gardeners need to optimize plant growth is the TDS of the nutrient solution in Parts Per Million (PPM), no method exists to measure TDS directly. Every meter out there only measures the EC of a liquid, usually in milliSiemens (mS) or microSiemens (µS). “Hey, wait a minute,” you say, “I’ve got a TDS meter, and it works great!” Well, that may be, but really that instrument is measuring EC, and then converting it into TDS using a standard algorithm. “So why wouldn’t I want that?” you ask. This is where it starts to get a little tricky.
The problem is that different elements change the EC of a solution to different extents. A 1200 PPM solution of one element may have an entirely different EC than a 1200 PPM solution of another element. This means that an instrument that delivers readings in PPM has to make assumptions about what it is it’s measuring. There are two different conversion scales that are common in the hydroponics industry. One is the 442 scale, which assumes that the solids in solution are 40% sodium sulfate, 40% sodium bicarbonate, and 20% sodium chloride – some folks say this scale is the closest approximation of what is actually in a hydroponic nutrient solution. Then there’s the NaCl scale, which assumes that the solids in solution are 100% sodium chloride – other folks say this is the closest thing to a hydroponic solution. Neither conversion scale is inherently better than the other; which one will give you a more accurate estimate of your TDS probably depends on the specific composition and brand of nutrient you’re using more than anything else. But while the NaCl conversion is approximately 510 x EC (in mS), the 442 conversion is approximately 750 x EC (in mS). So a TDS meter dipped into a solution with an EC of 2.5 mS could give a reading of 1275 PPM or 1875 PPM depending on the algorithm chosen by the manufacturer.

So how should we deal with all of this as gardeners? Well the only truly accurate and scientific method I can think of is to get an EC meter, call the manufacturer of every nutrient and supplement you’re using to get information from them on how their products affect EC, and then develop your own conversion algorithm. . . good luck! But most of us just use the nutrient manufacturer’s suggested usage rate as a starting point, find out what works well for us, and then use an EC or TDS meter to maintain a consistent level of concentration.

Q: How should I care for my pH electrode?
A:All pH electrodes eventually fail. Unfortunately, this is a fact of life. All pH electrodes work by comparing the electrolyte ion concentration of the solution being measured to that of a silver chloride reference solution in the probe itself. Over time, two things happen that can cause pH electrodes to deteriorate. Firstly, the electrolyte ions in the reference solution (which is usually a gel or polymer) are very slowly depleted with use. If this were the only factor affecting a pH probe’s performance, its lifetime would be long enough to meet most folks’ expectations. Secondly, the electrolyte ions in the solution being measured can either corrode the electrode’s wire or contaminate the reference solution. When this happens, the probe may begin to respond slowly, erratically, erroneously, or not at all.
Here’s what you should do to minimize problems with your pH meter:
     1) Make sure to buy a meter with a replaceable electrode. Meters with replaceable probes cost a little more than those that don’t allow you swap out the probe, but you’ll recuperate the difference in less than two years for sure, and possibly less than one.
     2) Look for a pH meter with a “double junction” electrode. In double junction electrodes, ions in the nutrient solution take much longer to come into contact with the electrode’s signal wire and internal pH reference electrolyte. Instead of having to pass through only one junction, contaminating ions must first cross the outer junction, then build up a concentration in the buffer cell of potassium chloride electrolyte, and finally pass through the second junction before damaging the reference solution. This increases the life of the probe dramatically. Many manufacturers include a standard single junction electrode with their meters that can be upgraded to a double junction when it fails.
     3) Calibrate your meter regularly and make sure to leave the electrode soaking in a cleaning and storage solution when not in use. This will slow down the rate of contaminating ion buildup.

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