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Janma

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Janma last won the day on May 6 2016

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About Janma

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  1. Janma

    Inaccurate energy meters

    @Plonkster : The sampling frequency may be low and that could cause a error. That does not explain why Hall effect current sensors under estimated the energy and why Rogowski coils greatly over estimated the energy. (Both would make use of similar integrator circuitry) I suspect problem is in the frequency response of the sensors and the approximations they use to calculate the energy. Rogowski coils gives a voltage output that is proportional to the strength of the current and its frequency (Integrate over dI/dt). I think the designs they use assume that the frequency will only be around 50Hz, but that is not always the case. LEDs, Energy saving Light bulbs, electric motors, dimmers and switch mode power supplies all inject much higher frequencies (Harmonic distortion) into the grid. These harmonic distortions, because they are at higher frequency cause the approximation they use to fail. The approximation they most likely use is Vsensor = K * Irms * F or Irms = Vsensor/(K*F) Where K = a constant specific for the sensor F = 50 Hz (assumed) This approximation works well if the frequency is 50 Hz, but it over estimates the current contributed by the second harmonic by a factor of 2 and that for the 10th harmonic by a factor of 10! In the old days this was not such a big problem because there were no LED, Energy saving light bulbs or switch mode power supplies etc. The big electrical energy consumers in a household were Geysers, Heating elements, stoves, incandescent light bulbs etc. none of which inject any significant harmonic distortion. Things have changed though. Take my home for example, I've replaced all the incandescent light bulbs with LEDs. I use a solar geyser and gas stove. Other than the kettle and toaster almost all appliances in my home either have an electric motor or switch mode power supply, all of them inject harmonic distortion to some extent. I'd be interested to measure the harmonic distortion at my home, just to see what the impact of this would be if I were to move from the mechanical rotating disk meter to a new electronic prepaid meter.
  2. This morning I came across this interesting article : https://www.sciencedaily.com/releases/2017/03/170303180139.htm I effectively have to energy meters at home. The old disk type meter (municipal meter) and a grid tied limiter and I've noticed that their measurements don't always match 100% At first I thought it was a calibration issue. From the study it seems a much bigger problem. I wonder how pervasive this problem is with the energy meters in SA, especially with the increase in popularity of LED light bulbs.
  3. Janma

    Panel Earthing

    Hi Chris, I agree. You are talking about a ground loop. These can pose a serious problem. You do not want multiple paths to the ground which will cause a loop. Yes any lightning strike close to it would cause a current to flow in the loop, frying any equipment in attached in the loop. Lighting will induce a current in any conductive loop within the magnetic field flux. In my case I have a rater large irrigation system with a central controler. There are wires running from the controller to all the irrigation valves. These + & - wires form loops from the controller to the valve and back, very narrow ones but still they are loops. Any magnetic field flux through that loop will cause current to flow through it. But there is a trick, if you twist the wires around each other and you look at them from the side you'll see that that some places the + wire is on top and the - at the bottom, then other places the - will be on top and the + at the bottom. This will work like small loops. 50% of the loops will have the + wire on the top and the - wire at the bottom and 50% of the small loops will have the - wire at the top and the + at the bottom. Depending on the direction of the magnetic flux it will cause a current to flow either clockwise through the loops or anti-clockwise. But since the 50% of the loops are one way round and 50% the other way round the current cancel each other out. They use the exact same principle in Ethernet cables (twisted pair) to minimize interference of induced currents.
  4. Janma

    Panel Earthing

    We all know that in SA there are two types of electricity supply. Single phase and Three phase. What most people don't know is that when it comes to how the "earth" is supplied there are also different ways. (All legal and above board). One of which is tapping a wire off the neutral and supplying it as a earth wire to the consumer. When you have a 3 phase power supply you will have 4 (or 5 wires) coming from the municipality. 3 of them are the live phases, one of them is Neutral. The three phases (live wires) will have 230 Vac relative to the Neutral wire. Remember Voltage is always measured between two points. In this case a Live phase wire and Neutral. In the distribution network the Neutral is always considered as the reference voltage (0V). But by convention the Earth (the planet) can also be used as a reference voltage 0V. It would be a very bad thing if the Neutral wire would be at a much higher voltage than the earth... So what Eskom does is they earth the neutral wire that come out of the generator. They also earth the neutral at various points in the distribution network. This is to ensure that the voltage difference between neutral and the real earth is very close to 0V. So in theory there is nothing wrong with splitting the Neutral wire into two, one they give you is labeled earth and the other is labeled neutral. (This is fine because the neutral is suppose to be earthed further up stream in the distribution network.) In an ideal world this would be the end of the story.... but.. Here's a little test you can do. Take a volt meter and switch it to measure mV. Now take the two leads about a meter apart and see what it measures. It will most likely never be 0V. The further apart the two points you measure the higher the voltage can be.. Depending from how far you are from the point where they earthed the neutral and how well its earthed you may find that there is a voltage difference between the Neutral and the real earth at your property. Typically this should be a small voltage difference. The thing that really mess things up is when they steal cables.. If they break the neutral cable before they break the live cables you can potentially get hundreds of volts on the neutral wire and serous voltage differences between a given live and neutral wire! This is because breaking the neutral cable they've effectively disconnected it from the ground. In many cases (such as yours) the earth wire that you get from the municipality is nothing other than the Neutral wire. In addition to them bonding it to the earth, it is also connected to all the metal fittings in your house and all the other houses, all these fittings are connected to the earth really, so they all pull down the voltage of the neutral/earth back down to 0V relative to the earth. The problem comes in when its not done this way and the neutral is not bonded to earth properly in the distribution network... If your sparky picked up that there is a high voltage between the earth/neutral supplied by the municipality/eskom and the real earth it could point to a wiring fault on the local distribution network. If I were you I'll contact the municipality and ask them to check it out. Normally your appliances (inverter, fridges etc) would not be affected. They only really use the live and neutral to operate, they only care about the voltage difference between those two wires. The problem comes in with the earth wire you get from the municipality, if its connected to the metal casing of the fridge for example and you touch it you might not like it very much. In theory the earth you get from the eskom/munisipality should be at very close to 0V relative to the earth and it should be perfectly acceptable to use it in your DB and for grounding your PV panels etc. It should be okay to connect it to your own earth spike as well. In your case I would not do that until the municipality had a look at why the earth/neutral is at high voltage.
  5. Janma

    Panel Earthing

    Jaco I would suggest doing both. Have a wire running from the panels directly to an earth spike then have a separate wire connecting the earth spike to the AC earth in your DB as well. Nope, I would not do that unless the inverter/charge controller's documentation explicitly instruct you to do so.
  6. Janma

    Panel Earthing

    When it comes to lightning there are more than one way that it can damage equipment and people. I think all of us know about the direct strike between the clouds and the top of trees/houses or whatever. The reason there is a strike is there is a potential/voltage difference between two points (the cloud and the tree). Normally air is a very good insulator that prevents current from flowing, but there comes a point where the voltage difference is just to big that even air can't prevent the current from starting to flow. The amount of current that flows when this happens is enormous! You are talking kilo/mega amps flowing for a fraction of a second and then stops. When current flows it causes an magnetic field to build up around it (this is what happens in a transformer). Now imagine how strong that magnetic field is when such a large current flows. The closer you are to the actual lightning bolt the stronger that magnetic field. If you have a conductor in that magnetic field and the field does not change nothing will happen, but when the magnetic field changes in strength or direction, it will induce a current/voltage in any conductor in side the field. This is how a transformer works. The current through the primary winding changes (AC) and that causes the magnetic field in the transformer core to change. The changing of the magnetic field causes a voltage/current to flow in the secondary coil even though its isolated from the primary coil. (Induced current will flow). Those old iron core transformer based welding machines is a very good example of how strong an induced current can be - we weld metal with it... Now lets see what happens when you have two earth circuits in your house that are not bonded together. The first is your normal AC earth that is connected to the grid earth. The second consist of an earth spike that has a wire running up to your PV panels. The key here is they are not connected. Now lets assume there is a lightning strike very close to your home, it causes a very strong magnetic field for a brief moment. This induces a voltage across the AC earth wire as well as a voltage across the PV panel earth wire. The voltages will NOT be the same (magnetic field is not the same everywhere and the wire lengths are not the same either). There may be quite a big difference between the two (anything from a couple of volts to a couple of thousand volts or even higher). If someone were to touch the PV panels and the AC earth at that time, they may not be able to tell you how about how it felt afterwards... The same applies to an inverter or charge controler that is in close proximity (electrically speaking) to the AC earth and the PV panel earth. If the induced voltage difference between the two earth systems is high enough it may find/make a path from the one to the other. That path can be via a cutter, inverter, or a person. Connecting the PV Panel earth, to the AC earth gives induced lighting voltages a controlled route through which to dissipate. Its better for that induced current to run via the wire connecting the two earths than through you or your equipment. That is the reason why you should ALWAYS make sure all the various earths are connected. If it was a direct strike, you most likely would not have survived it. I might have been an induced strike as I've described above. The fact that you were wet (just out of the pool) and you were sitting on a metal chair made you a good conductor. If a lighting strike were very close it would have induced a current flowing through you and the chair. You were very lucky!
  7. If you don't mix the panels in the right way you will loose a lot of power. Here's why Lets take the case where you have two types of panels 300W and 200W that you want to place in the same string. Lets assume the following is true for the two types of panels: V open circuit300W = V open circuit 200W V max power300W = V max power 200W Then it follows that I max power300W > I max power200W But since you put them in series, the current that will run though both of them will be the same. The MPPT will search for volt and amp combination that will produce the maximum power for the string. So what would happen is that the I max power string will be somewhere between the I max power300W and the I max power200W In other words not optimal for either of the two types of panels. The 300W panel will never produce 300W and the 200W panel will never produce 200W Now if you put the 300W and 200W panels in separate strings (parallel). The voltage over both strings will be the same. The 300W strings will then contribute I max power300W and the 200W strings will contribute I max power200W. So both strings will run optimally. There is one other way it can be done in the case were the following is true: I closed circuit300W = I closed circuit200W I max power300W = I max power200W Then it follows that: V max power300w > V max power200W If the above is true, then you should mix the 300W and 200W in the same string. Make sure each string has the same amount of 300W and 200W panels (the strings must be symmetrical) The problem comes in when the panel's specs do not match up on the Volts or the Amps. Then it becomes quite difficult to ensure maximum power out of the strings.
  8. I have a 3kw grid tied inverter with 13 x 255W panels = 3315kW. The Voc of the string is lower than the Vmax of the inverter. Most days I get arround 2500W max but it has gone up to 3000W. I've had no issues. As long as the string volts is never higher than the Vmax of the MPPT/Inverter don't think it should be a problem.
  9. Janma

    Modified Sine Inverters

    @plonksterI have a MicroCare Grid Tied Inverter with grid tied limiter. Yes its using a RS485 communications cable to link the inverter and limiter. I've not been able to get much information about the protocol they use. When I have time I'll start playing around to figure out how it works. (Not really into M$ stuff, mostly C on Linux) Being grid tied it switches off at night so there is very little losses at night. It only powers on when the voltage on the PV input rises above a certain value. The drawback is I draw from the grid the moment the sun sets. But it is still cheaper to buy electricity from the municipality than putting in batteries. But this does not mean I don't have batteries. The garage doors, gate motors, alarm system all have batteries. So in a sens they can already act like separate small systems. All that's needed is to replace the batteries with some deep cycle (lead crystal) ones and then switch off the AC supply to them at night. They all plug into normal wall sockets so it should be easy enough just to put them on a timer plug. (I only thought of that while reading this thread...) I also have the option of putting in one or more bi-directional inverters with their own batteries. For example have a small one in the lounge that just runs the TV and entertainment equipment. Another maybe just running the light circuits. They would all use AC to charge the batteries (during the day) when the GTI produces power. Effectively an AC coupled system. You can couple as many bi-directional inverters/UPSs to your system as you like. One per device or one big central one or a combination. @edmundp Since its grid tied it does not limit the amount of power I can draw in the house. If the wife switches on the microwave, kettle and washing machine the GTI will still provide what it can and the shortfall (up to 60A ac) can still be drawn from the municipal feed. Thus preventing the "emotional downward spiral" :-P
  10. @Boeriemore Have a look at the liter per minute that the unit can give you. The smaller units can heat the water but at a lower flow rate. If you use it for a shower it should be fine but if you use if for a bath it may take a lot longer to fill up.
  11. Hi Boeriemore, I would advise getting an electrician to have a look after you install it. (Or maybe chat to one before you start, it may save you time and money). Ask the electrician to give you a COC after the inspection. If somethings goes wrong and the insurance company find out it was due to an electrical fault and you do not have a COC they will not pay out. About plugging in the 5KW water heater into a normal wall socket, its dangerous! The wall socket is only rated at 16Amps and a 5KW element will pull more than 20Amps. If you are going to do the work yourself remember the following things (The list is a LOT longer but there will help) A Circuit Breaker is there to protect the wire. In other words if the wire is rated to 15 Amps max, then you need a 15 Amp (or less) circuit breaker. This will prevent the wire from carrying more current than it should and will prevent it heating up/starting a fire. The Earth Leakage (Residual Current Device) is there to protect people. Isolators are there to switch circuits/appliances on or off. They do not do the same thing as Circuit Breakers (they will not trip). Typical wall sockets are rated at 16 Amps and some standard plugs are only rated at 15 Amps. If you have an appliance that draws more current than that it would be best not to use a wall socket. Instead of a wall socket you can put in a two pole isolator switch and wire the appliance directly to it. Be careful in a bathroom. There are a lot of rules/regulations around where and what you can and can't install in the bathroom. If unsure speak to an Electrician before you start installing something. Run the wires in a conduit (except if its in the ceiling,but even so, there is no rule against using conduits in a ceiling). If its metal, earth it! This includes metal conduits, junction boxes etc. etc. If an appliance has a earth wire or a place to fix one, do it! If you want some reference document regarding the size and current capacity of the different types of wire have a look at this link : http://www.aberdare.co.za/sites/default/aberdare_cables/files/brochures/649/brochures_649.pdf For short lengths of cable you should be able to use the specifications in that document. For larger lengths the voltage drop play a part so go for one size bigger.
  12. There are special regulations for geyser, and I asume the same would apply to instant hot water systems. For one, it has to be on its own circuit. Secondly it not only has to have a dedicated circuit braker in the distribution board, but also a two pole isolator switch within 1 meter of the appliance. If I remember correctly it also has to be protected with an earthleakage device ( residual current device) typically in the db. As for the wire size, I'll have to look it up, but it depends on the length of wire. The regulations specify the maximum voltage drop of 5% between the point of supply and the point of consuption. Thinner wire will have a bigger voltage drop per meter than thicker wire. The type of wire used also has an impact on the required thickness. How long will the wire between your db and the instant water heater be? What type of wire are you using, surfix? Is it in a conduit or loose on the ceiling in the roof? Typically it would require a 6 sq mm conductor or more. i would not recommend a breaker less than 32A in the db. Also remember that when an element is cold it will draw more current than when its hot. So even if the element is rated at 7kw it may use slightly more until it heats up ( this does not take too long though).
  13. Janma

    Grey Water System

    I'm also investigating ways to make use of grey water. I have an old house on a large property that I am in the process of renovating. I spend a small fortune on water to irrigate the garden. I've fixed up both bathrooms already. As part of their renovations I've split the main sewerage line into two. One carrying all the back water and the other all the grey water. These two lines merge quite some distance from the house just before they exit the property. My plan was to cut the grey water line and put in a "sump" with pump and level switch. The sump would be below ground. That pump would pump the grey water out into a small jojo tank. I've also split the main water supply line at the point where it comes into the property into two separate lines. The one goes directly to the house (drinking water), the other one is for irrigation only. The irrigation main line runs in a loop around the property. All the irrigation valves/zones are fed from this one line. The irrigation line has a non-return valve and a valve just after the split from the main line. This is to prevent irrigation water from flowing back into the drinking water line. Also, to be able to isolate the irrigation line if I need to. My plan is to use the valve to isolate the irrigation line and then use a second pump to pump the grey water into the irrigation line from the jojo tank. It should be easy enough to just cut into the irrigation line and and hookup the pump. I'll use a relay that's triggered by the irrigation controller to start the pump. I'll also install a simple ball valve in the jojo tank to ensure that if there is not enough grey water it will top up using drinking water, thereby preventing the pump from running dry. But... What I've been able to gather is that you have to do some kind of filtering of the grey water before you can put it though a pump. Shower/bath water contain hair that can clog up the impeller of the pumps. It also contains beard stubble/shavings that will nicely clog up your irrigation nozzles. I have a couple of old cast iron enamel baths that came out of the old bathrooms. So I'm thinking of filling one with a combination of gravel, sand and landscaping cloth to make my own filter. The cloth will be on top and between the layer of sand and gravel. Hopefully the top cloth will catch most of the solids and should be easy enough to clean. Fortunately for me both bathrooms' floor level is about 50cm higher than the ground level outside the house. I would be able to reroute the PVC drain pipes of the baths, showers and basins to empty into the bath/filter outside. Then connect the bath/filter drain back into the grey water sewage line via an existing gully trap. From there the grey water will flow to the "sump" and then pumped up into the jojo tank. I've not done this yet so I don't know how well it will work...
  14. Janma

    Solar Pool Pump

    I have a 100 000l pool that use to have a 1.6kw pool pump that ran for about 6 hours a day. It added quite a bit to my electricity bill each month. I also looked at solar pool pumps with panels but it was really expensive. Also, since its a DC pump its quite expensive to replace if it breaks, not to mention the fact that you can't just run down to the local hardware/pool shop to go and get one. Then one day I was strolling through Builders Warehouse and saw the Speck Eco Touch pool pump for about R2500 (I suspect it was priced incorrectly). http://www.speck-pumps.co.za/badu-eco-touch.html It has a variable speed drive so it does not have a high surge current at startup. It has 3 speeds (low, medium, high). I run it on low all the time so it uses less than 400 watts . At first I was concerned that it would be under powered to run the Kreepy Krauly. I was pleasantly surprised to find that the Kreepy Krauly actually ran better on the low setting than it use to run on the 1.6Kw pool pump! I have a 3Kw grid tied system so all I did was change the pool timer to run during the day.
  15. Janma

    Measuring kwh on different places

    Hi George, I know of a couple of products out there that you can evaluate Efergy monitor: https://engage.efergy.com/ http://www.ellies.co.za/energy_monitoring/efergy/Elite-Classic-Energy-Meter/FSEME They have a number of products that can be used to do monitoring. All of them only monitor the AC current that run through a wire. It uses that to approximate the energy consumption (KW). They have two types of stand alone monitors, the Elite Classic and the E2 Energy monitors. They look very similar. They both just monitor one circuit at a time. The difference comes in that the one (E2 Energy monitor) comes with an USB interface that you can plug into a laptop/pc and download the monitored data, where as the other only provides current, daily totals, monthly totals etc. They do not monitor voltage or frequency or power factor so they are not 100% accurate, but they do give you a pretty good idea as to what is going on. They also have a HUB system. This allows for up to 5 circuits to be monitored. The HUB system normally include 1 current sensor for one circuit. It you want to monitor more you will have to add either a E2 Energy monitor or a Elite Classic monitor per circuit you want to monitor. The HUB system records the data to the cloud and they provide you with a Web interface to look at the real time and historical data (including graphs). You can also download the data from in CVS format. They also have a smartphone app that you can use to monitor 24/7 from anywhere in the world. The HUB systems does requires an Ethernet Internet connection. So if you do not have and ADSL connection or something similar at home then you can not use the HUB system. You can still use the Elite Classic monitors or E2 Energy monitors. Ellies distribute them in SA and I know Builders Warehouse stock them. Owl energy monitors : http://www.theowl.com/products/energy-monitors/ Owl monitors are very similar to the Efergy E2 and Elite Classic monitors. It also just measures the current flow but not the voltage, frequency, power factor. Some models include a USB interface that you can hook up to a PC and download the data. Exsolar energy monitor : http://www.exsolar.co.za/products/monitoring-devices/advanced-energy-monitor-exsolar-em502/ This monitor can be used to monitor up to 3 circuits. Its much more accurate than the previous two monitors as it monitors both volts and amps and give you power factor figures as well. Open energy monitor (EMON) https://guide.openenergymonitor.org/ This monitor is also more accurate than the Efergy or the Owl monitors because it can also monitor voltage and frequency. They have various components that you can add to monitor as many circuits as you like. This is open source hardware and software you you can change it if you have the skill & time. I don't know of anybody selling this in SA so you would have to purchase it in the UK and let them ship it to you.
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