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Thread: portable system, pure sine inverters vs modified sine, MPPT vs PWM

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    Default portable system, pure sine inverters vs modified sine, MPPT vs PWM

    I have built a portable solar system and recently constructed a portable gold mining wash plant that uses a 5000gph 120VAC submersible water pump. As I'm a long way away from any gold mining country I've only had the wash plant in action one time for 4 days, several hours per day. It works great but it was cloudy most of the time so could not get an idea how efficient everything was running. Ended up powering off the vehicle alternator much of the time. Such a lousy feeling to be testing a system 300 miles from home and having cloudy rainy days 3 out of 4. Testing with a Kill-A-Watt meter the pump draws 270 watts off the grid power. 330-360 watts with modified sine wave inverter. I'm hoping to improve the efficiency with a pure sine inverter. Today I ran a simple test with the mod sine inverter using a small 120 VAC heater as a load, a 12V 50A shunt and multimeter to measure 12VDC consumption and found 242 watts into the inverter for 205 watts out. Does anyone know if the Kill-A-Watt meter is accurate measuring a modified sine wave? Would a pump motor run more efficient on pure sine wave AC power? What would be a good estimate on the 12VDC wattage required for a pure sine inverter to get 270 watts of 120VAC. The thought of precious solar electricity being consumed to heat creek water makes me a bit ill. I'd like to try to get the most power out of my 280 watts of panels as possible and wonder if the expensive shorter lived MPPT controllers are worth it. I'm using a single 12V 100ah deep cycle battery. May have room to pack another 100 watt panel with the gear but need a Tetris game expert to come pack my truck for me.
    I'm also questioning how would a 100ah deep cycle battery handle 300+ watts of charge? Is this too rough? Thanks for any input.

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    Modified sine wave will do two thngs in this case. One you already saw in increased draw on the battery when using the motor on the inverter vs the grid. This is caused by a low power factor which is only seen with motors and some electronics. The current you saw on the heater takes into account the inverter losses only as there is no power factor to be concerned with in a straight resistance load.
    You do not have nearly enough battery or panel to run that load.
    Find your intended location and the insolation and plug the loads into this
    Off grid calculator excel 97 version (2).zip

    You may want to consider a small 2000W honda generator that sips gas and will be much more reliable than what you currently have.

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    Thanks Rich. I've thought about just buying a gasoline engine water pump as that is what everyone else uses but that would be failure to me. I dislike the sound, the exhaust, and the dependency on fossil fuel. Building things is just a hobby as is the gold mine and I want to be fully solar. I have already purchased a pure sine inverter, a 1500 watt model from Royal Power. I have a problem with it right off the start. It's defective and has a direct short somewhere internally and blows all the fuses as soon as it is hooked up to 12V. I'm not getting very good customer service on this issue but that's another story. I'm still waiting for authorization for return and replacement 4 days after contacting them about it. I'm assuming the 12V consumption using the pump will be just over 270 watts as it's supposed to be 97% efficient. for curiosity sake I'll set up the pump on the modified inverter with the shunt and see how much 12V power it's drawing. I do plan on adding another panel or two so there should be little draw off the battery as long as the sun shines. I'd like to be able to operate it for a few hours before lunch. Take a break while the battery recharges, run again for a few hours. I would like to keep the battery in the 20-85% charge range understanding there wont be enough time in the field to fully charge.

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    Quote Originally Posted by Element 79 View Post
    Thanks Rich. I've thought about just buying a gasoline engine water pump as that is what everyone else uses but that would be failure to me. I dislike the sound, the exhaust, and the dependency on fossil fuel.
    Sorry but that is reality. At 270 watts used 24 hours per day would be a complete nightmare using solar especially in your location. The batteries alone would weigh in just over 2000 pounds and cost upward around $7000. Then in just a few short years you get to replace them.

    Solar panel wattage required will drain your bank account compounded by your location. You would be looking at a 10,000 watt system, and if operated at 12 volts, 5 very expensive 80 amp MPPT charge controllers at $800 each. By the time you acquired all the equipment required you are staring at $25,000 to $40,000.

    There is a very good reason everyone is using generators, it is the only way to get the job done. If you are going to do this buy you a good quality diesel power generator.
    MSEE, PE

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    Quote Originally Posted by Sunking View Post
    Sorry but that is reality. At 270 watts used 24 hours per day would be a complete nightmare using solar especially in your location. The batteries alone would weigh in just over 2000 pounds and cost upward around $7000. Then in just a few short years you get to replace them.

    Solar panel wattage required will drain your bank account compounded by your location. You would be looking at a 10,000 watt system, and if operated at 12 volts, 5 very expensive 80 amp MPPT charge controllers at $800 each. By the time you acquired all the equipment required you are staring at $25,000 to $40,000.

    There is a very good reason everyone is using generators, it is the only way to get the job done. If you are going to do this buy you a good quality diesel power generator.
    Actually it only runs for a few hours a day

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    Thank you Rich. I ran a test today. From the modified sine inverter the pump was drawing 320-330 watts. 12VDC into the inverter was 370 watts. I also tested all the panels directly into the battery while the pump was running and the battery was at 12.7 volts. All 4 panels rated at 280 watts total was inputting 200w on full sun aimed directly, at 2:30pm. I'm hoping that adding an MPPT controller and a pure sine inverter the numbers will improve.
    Thanks

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    switching from a PWM controller to a MPPT will make a big difference.
    Say you have 280 watts of 12 volt panels with a VMP of 18V
    So max power at 18 volts is 280W/18= 15A With a PWM controller the most you would ever get to the battery is 15A x12V=180W a loss of over 100W .
    With MPPT you would get 280-5% /12 =22A

    Big difference

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    As long as you are getting a MPPT controller, wire your PV panels in series, to increase voltage (within the MPPT controller limits) and let the MPPT downconvert the voltage, and reduce your losses.

    If you want the delux 12V inverter - look at the Morningstat Sure Sine 300W inverter. It's quite efficient, and the pure sine will let your motor run normally without overheating. If you mounted it to a aluminum plate to act as a heatsink, you should be able to run continuously without reaching the thermal shutdown.

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    Thanks guys. I had an MPPT controller last week. EBay purchase "from Canada". A 25A model with LCD display. It came from China directly and the dealer in Canada never touched it. I tested it for a week and decided it wasn't working right. The maximum power input it would display from 280 watts of panels was 174w. It would also occasionally shut itself off. Even when the battery was less than 50% charged and would not start again without disconnecting the panels for at least a minute. I've sent it back. Since then have borrowed a shunt to test current with the multimeter. Yesterday got 200 watts from the panels with no controller, 80% charged battery with the 370 watt load. I've been reading other posts about how MPPT is no better than PWM especially in warmer climates and would be better off just buying another panel instead of the expensive MPPT unit. I built the main power unit with large wheels so it can be rolled around easily and also use it with a 14" electric chainsaw. works great with the 2kw inverter. I've tested the chainsaw with the Kill-A-Watt and it consumes 750-1300 watts depending on how hard you cut into a log. Would this be too harsh on a single 100ah deep cycle battery? Only on for 3-30 seconds at a time. I did not consider setting up the panels in series and don't think this would be the way to go with this system. I'm currently adding banana jacks to the main unit to quickly plug in up to 4 more panels if needed. Normally it will just use the single 40 watt panel built in as the lid. Another concern is that I have both 40 and 100 watt panels in parallel and read that MPPT controllers don't perform well with mismatched panels. I did not notice this in testing last week and as additional panels were plugged in the power input increased to about what was expected from the erroneous display on the controller. Would this only be for panels in series? Can anyone confirm and explain this? Thanks for the input. I'm glad to have run across this forum.

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    Quote Originally Posted by Element 79 View Post
    Thanks guys. I had an MPPT controller last week. EBay purchase "from Canada". A 25A model with LCD display. It came from China directly and the dealer in Canada never touched it. I tested it for a week and decided it wasn't working right. The maximum power input it would display from 280 watts of panels was 174w. It would also occasionally shut itself off. Even when the battery was less than 50% charged and would not start again without disconnecting the panels for at least a minute. I've sent it back. Since then have borrowed a shunt to test current with the multimeter. Yesterday got 200 watts from the panels with no controller, 80% charged battery with the 370 watt load. I've been reading other posts about how MPPT is no better than PWM especially in warmer climates and would be better off just buying another panel instead of the expensive MPPT unit. I built the main power unit with large wheels so it can be rolled around easily and also use it with a 14" electric chainsaw. works great with the 2kw inverter. I've tested the chainsaw with the Kill-A-Watt and it consumes 750-1300 watts depending on how hard you cut into a log. Would this be too harsh on a single 100ah deep cycle battery? Only on for 3-30 seconds at a time. I did not consider setting up the panels in series and don't think this would be the way to go with this system. I'm currently adding banana jacks to the main unit to quickly plug in up to 4 more panels if needed. Normally it will just use the single 40 watt panel built in as the lid. Another concern is that I have both 40 and 100 watt panels in parallel and read that MPPT controllers don't perform well with mismatched panels. I did not notice this in testing last week and as additional panels were plugged in the power input increased to about what was expected from the erroneous display on the controller. Would this only be for panels in series? Can anyone confirm and explain this? Thanks for the input. I'm glad to have run across this forum.
    I've got four chainsaws, one gas and three dif sizes of electric but don't bother with any of them for cuts as you describe. My solar charged 18V reciprocating saw will do an incredible number of cuts on a single charge and I need not haul out hundred+ ft of cord.
    Think about it.... 280 watts of panels, controller, the 200AH battery you should have with that, inverter, less all the fudge factor and what do you have left to work with using a 14" elect chainsaw. 1300 watts (almost 110amps) seems a huge amount to pull out of a true deep cycle 100AH battery even in 30 sec bursts. I suppose you have a hybrid, rated w/CCA?
    anyway... back to your fun project.... I checked fleabay for 25A MPPTs and found the cheapest there are $130? You might check into the (I'm sure Asian) 15A MPPT for $44 w/ free shipping from 'LA', USA. hahaha, could be the state or city but delivery time is fairly quick whichever. They will take 200W @12V but better yet can do 400W @24V. I bought one, found out it actually works so bought nother for back up. A very basic MPPT, no temp control and their 'four stage charging' has nothing to do with equalization. Does give me a couple extra amps out of my 145W panels tho.
    Extension cords are cheaper.

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