short circuit thermostat

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Comments

  • CraziFuzzyCraziFuzzy Registered Users Posts: 19
    Re: short circuit thermostat
    You know quite a bit.

    DC can create a sustainable arc above 15 Volts. It does not require a motor or induction coil to do so. Multiple series interrupts are a way of handling the problem, but they do not eliminate the arc or the possibility it may start a fire.

    One thing is for sure: if the people trying this have any degree of success they will crow about how they know so much more than engineers despite their success being 100% dependent on pure luck. But when they burn the place down they'll never post pictures of the disaster.

    Now if you'll excuse me I'm going to feed my diplomas through the paper shredder and become an Internet Expert.

    While true DC car arc over a gap at even low voltages, the lack of inductive kick means the arc gap is not as high as would be found in a DC motor contactor. You still have to have a switch rated for the DC voltage being switched, or better, just use a SSR that was already discussed.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: short circuit thermostat

    Obviously some serious education and hands on experience needed to prevent fires when switching DC.
    Scary some of the things one reads on the internet. Could very easily lead to disaster. Hopefully (for the victim) the insurance company can be convinced the fire started elsewhere.
    Of THIS you can be sure - - - Caribocoot knows of that which he speaks! Take heed!
  • HandyBobHandyBob Banned Posts: 31
    Re: short circuit thermostat
    CraziFuzzy wrote: »
    No doubt it will work. It won't be very maximized in power recovery though, without something back-regulating panel voltage. That's the purpose of the MPPT circuitry. With that fixed resistance load, at lower sun levels, production will be VERY small. By actually increasing the resistance (that's what the MPPT controller would do in this instance), panel voltage would be allowed to increase, to a point where the actual power produced would be higher. Solar panels are not like other voltage and/or current sources, in regards to I/E curves. Allowing as much current as possible to flow out of them does not necessarily make the most power.

    This is starting to drive me crazy. Your opinion is not correct here and you don't see it. Only if you have experimented for yourself should you be making statements as if they are facts. I see this all over internet forums and it is why I generally avoid them and why when I started out here I asked if anybody has actually tried this. I didn't get anybody telling me they had, so as usual, I had to think for myself. I found an old heating element, measured it, hooked it up to some leads, stuck it in the top of a jug of water and played with it. My experiment proved that the voltage does go up at a resistance element, unlike with a direct coupled battery. MPPT works for increasing battery charging by turning the potential voltage increase into higher charging amps. Here watts are watts, they all get turned into heat. When the voltage increased because the sun came out of the clouds, both the voltage and amperage went up at the element. BTW, a resistance element is 100% efficient. Cold panels during winter ARE going to make for more heating, without any fancy control circuitry. Caution does need to be exercised in matching the amps with the heating element's impedance so that the solar panels are not trying to produce more that the element will accept, and that may need some fine tuning by changing the element, but your basic assumption is wrong.

    It isn't going to be perfect, but close enough. Having the element producing some heat all day will add up and I expect to hardly ever need backup using propane. I bought less than $1200 worth of panels. When I add up everything, my investment will be paid for in less than 3 years. To the guy who couldn't understand why, that is why... It makes sense. Plus, people should stop making assumptions about what solar conditions are like in places they have not seen. We live in the rain shadow of several mountain ranges. Our conditions are much better than you would believe. Yesterday was mostly cloudy, but not heavy clouds. We got over 4KW of charging from our 2000W of panels. That will more than run our house, if I ever get it built.

    Made it to the shortest day of the year without starting a generator... Yippee!
  • HandyBobHandyBob Banned Posts: 31
    Re: short circuit thermostat
    Scary some of the things one reads on the internet. Could very easily lead to disaster. Hopefully (for the victim) the insurance company can be convinced the fire started elsewhere.

    I learned engineering from a great mentor, who had no college education. He taught me many things that are not what is accepted by the general consensus. One of them is that whenever the fire department cannot figure out what caused a fire, they always blame electricity. There is always evidence of arcing and electrical fire, but is that where the fire started? Electricity is not as dangerous as most people believe.

    "A good engineer is not the guy who thinks he knows everything. A good engineer is the guy who knows how to find the answer." Stark Bridwell, the best engineer I ever knew. Stark was taken by Alzheimer's. I miss him.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: short circuit thermostat

    Yep; nothing like an untrained engineer to put wrong ideas in peoples' heads and have them stick there.

    Some of what you 'know' is correct, but some of it is not.

    Good luck with your experiments; you'll need it.
  • solarvicsolarvic Solar Expert Posts: 1,049 ✭✭✭
    Re: short circuit thermostat

    My neighbor has a 40 gallon waterheatert with quanity of 4 300 watt panels. = 2sets of 2 parrelelled to one dc element. The panels are left connected 24/7 and preheat the water to about 110F. The preheated water flows to a conventional 240 volt AC waterheater which heats the water to the higher temp. he wants. He is grid tied so that works for him. That was his first experiment with solar. Now he has a large solar system and still left the waterheater set up connected. Solarvic
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: short circuit thermostat

    If you leave the panels connected to the heating element all the time it eliminates the issue of the DC arc across a thermostat (the original question in this thread). But it also introduces the problem of either having no overheating safety other than the T&P valve or reducing the heating effectiveness to a low level which must be kept in balance (total output from PV can never cause excess temperature rise which in turn reduces the heat gained).

    Everything is a trade-off.
    As Bill and others have said the most effective way of utilizing 'spare' power from PV to heat water is to trigger a standard heater on the inverter when that power is available. The 'losses' with such a system would be minimal compared to other schemes and the heating most effective.
  • ZoNiEZoNiE Solar Expert Posts: 100 ✭✭
    Soooooo, it works, then?


  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    ZoNiE said:
    Soooooo, it works, then?


    Been 10 months now, so we will probably never know.
  • DaveBDaveB Solar Expert Posts: 48 ✭✭✭
    edited September 15 #41
    Youtube video of someone showing their system doing exactly this.  No battery, no controller, PV direct  (no MPPT) to regular water heating element. 
  • NANOcontrolNANOcontrol Registered Users Posts: 87 ✭✭
    That is digging up the past.  Sure it works, solar always works in Arizona.  It just needs twice the number of panels if it isn't done with  a power point controller. I don't see why there aren't $50 controllers coming out of China to do this. It is pretty low tech and would have a high profit margin. People are so slow to adopt technology.  In the early 70's an IEEE award for innovation was the microprocessor toilet. That took 40 years to gain acceptance.
  • jonrjonr Solar Expert Posts: 1,116 ✭✭✭✭
    I agree - it's possible to profitably build a direct PV solar to hot water heater controller board with MPPT (no DC-DC needed) for around $50.   
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