The element is in a 1 gallon per minute flow of water to hydronics in a 20cuYd cement slab, my 'thermal battery'. There is a 0.1♟ cap across the heater element. them caps change things!įet's are on grd with 4500w element to positive.Īcross fet's is a snubber circuit(here I am very very unknowledgeable) with a 0.1♟ cap & a 3.3k 5w resistor(runs extremely hot). Tried to look at wave form, but with the ringing on top of the 340vdc it shorted my 10x scope probe(now have a 1500v probe 100x) Have run at 5500watts) large heatsinks never get above 120☏. ![]() quan 10(had 4, 2 blew on first fire up(no pun intended). Now my circuit:pwm at 1000hz with a cypress psoc4200 µPC sensing volts from batteries, fet's driven with a 2.5amp opto isolated driver chip and 15dc supply. Using the filtering input as was:Ībout a 2" torroid with bifillar winding from l1 l2Īn iron core choke on each line(several pounds each)Ĥ 35amp full bridge rectifiers on large heat sinkĤ large(8,000♟ 150V) series connected filter caps w/bleed-balance resistors Salvaged 230V input, 54V output at 50amp switching charger frame(2 came with batteries -). ![]() Back as far as 1999 I was bank switching sets of panels when the batteries were charged, to 72V to send to hot water tank element. So many panels to get thru winter with no generator. 15+KW of solar panels(mostly vertical on side of buildings, 48.5° N Latitude. 8000w 230v sine wave inverter(stacked Trace SW4024)(now Schnieder) from the last century. It is currently in service and working great(except for horrid RF noise). Always test behind a 3/4" plywood shield. Retired technician, have been working on the same thing for a long time. If it applies to your meter (and we do not known that), zero-crossing SSR will not help. UPDATE: This document ("Import and export of electrical energy" by "Surendra Jhalora") talks a lot about import/export energy when applied to smart meters:Īccording to it, the import/export is calculated per-cycle. Switching / dimming a high power mains heater Thus, any 20A / 250V SSR (solid state relay) will work. ![]() Your heater takes (3600 watts) / (240 volts) = 15 amperes. The 'zero-crossing' part will ensure the lack of extreme currents and EM interference. I have no idea what this interval is for your meter but if it is at least few seconds, you should be doing low-frequency PWM (with period measured in seconds) and using it to control zero-crossing solid-state relay. It would be stupid for power meter to register it as '40W import + 40W export' simultaneously. This interval cannot be too small - a switcher with no load will have power factor close to zero, and thus 'export' power in one part of AC cycle and 'import' power in another part of AC cycle. In general, the power meters measure total power over some interval, and then determine if it was 'import' or 'export' base on the sign of then total value. The feasibility of the installation hinges on whether I can vary the load to match the generation. If I import power I pay 20 cents per kWh. Eg: when solar power in = 4kW, internal loads = 2kW, I want the HWS to draw 2kW. To do that I need to use as much of the solar generated power internally, while being careful not to import power during a sunny day. ![]() I am trying to minimise the bill to the electricity company. The inverter connects on my side of the meter, but import and export are measured separately. Would an approach like a switching power supply make sense? ie rectify the AC, then chop the current at high frequency, while protecting the supply side with large filters? I suspect this approach would cause EM noise unless carefully designed.Īre there better ways of controlling HWS power? Motivation Ideally, the load should look like a varying resistance. Would a heavy duty phase controlled triac be suitable? Would the large current switches cause problems? I do not know how the metering works, so this per-cycle method may not even register as a smaller average current. Our electricity supplier only pays a pittance for exported power but still charges the full rate on any imported power, so the trick is to control the current to the hot water system (HWS) so that most excess solar power is consumed internally. To use solar power efficiently, I would like to use excess solar power (in a grid-tied arrangement) to heat our domestic hot water. My water heater element is rated at 3.6kW at 240V.
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