DC water heater element with front mounted heating element not safe in my opinion

solarvic
solarvic Solar Expert Posts: 1,071 ✭✭✭✭
in General Solar Power Topics #1
About three years ago I bought one of those water heater heater elements that has the thermostat mounted on the front of the element. There is a you tube video about this element on you tube  by Missouri wind and solar.  The video is misleading as he just hand tightens the element. No way to tighten it enough so it will not leak. I used a oilfilter wrench on it and it just twisted off the can that the thermostat is attached to the element. When I sent him an email asking him how to tighten it down and he didn,t return an answer. So I decided to try again with a new experiment to see if I could just wire direct to the element so cut the wire and left a couple foot of the original wire on the element. I tried it on a 20 amp nbreaker and it tripped in anbout 30 seconds. So I connected it to a 30 amp breaker and it didn,t trip. After about ten mit the wire that came with the element got so hot it smelled and I couldnot hang on to it very long. the wire that came on the element looks like about #12. I connected #8 and didn,t heat at all. Just wanted to say In my opion it is not safe and the price I paid was a waste of money. Solarvic
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #2
    Wattage and voltage of element? I asked them some questions and didn't get a reply. In fact I think it was on the wiring! I figured I'd use a AC element on DC, still working on that project.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    #3
    It is listed at 24 volt 700 watt which is about 29 amps. The 20 amp breaker I tryed is suppose to trip at 25 amps which was just an experiment. I knew I needed a 30 amp breaker and it is supposed to trip at 35 amps and it holds ok. The element has a pig tale that is molded into the element and looks like #12 wire which is way to small wire size for 30 amps.  I think I am going to try a regular dc water heater element without a thermostat.  just hooking  direct to the battery as an experiment to see if it is feasible to use a dc element to heat my water. If that works I will control it with a charge controller. I have a fork truck battery that only gets charged with grid power thru inverter and the battery is not getting any use. Thinking of ac coupling which is what I intended to do but it doesn,t work with my pesent inverter. A magnum 4024 AE which I might try to sell in the for sale category then buy a 4024 pae which supports ac coupling. I am sticking with 24 v inverter
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #4
    I'm not sure how you will control "...it with a charge controller". I think there are DC thermostats, but perhaps leave AC current running to your original thermostat and let it run a relay to shut the DC current on and off.

    Thank you for the info, I'm working on doing a direct DC water heater this year. I have seen the DC one temp thermostats, but the idea of running so much current through a 1/4 spade connection is a bit frightening! Mostly only available from MWAS or one of it's cousins in south west Missouri.

    The heating element is a purely resistance load, so I don't mind running DC instead of AC, and would like to take advantage of solar being able to turn off and on without harm. I've thought about running a 48v 1500 watt element directly from the 35 volt VMP of my panels, should be roughly a 750 watt heater and low enough voltage to not worry too much about arcing issues. Arcing is one of the things I worry about the contact very close together in some elements. I have bookmarked some others info, and I'll post it when I am on that computer.

    I see a gap and need for this as solar panel prices continue to be reduced making direct electric DC water heating viable. Particularly in areas where direct solar thermal requires heat exchangers.


    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    #5
    I think you know the heater element I have posted. Besides the wire guage bieing too small you can not use a socket or water heater wrench as the thermostat is screwed onto the front of the element. With about 2 inches of insulation you can not use an open end wrench to tighten the element.  Since I am grid  tied and I just got a new rheem hybrid water heater I could be wasteing my time bothering with the dc element. I was just trying to get more use out of the present geospring hybrid that has a failed heatpump and still heats with the heating elements. At present I want to change my electrical system as it violates my grid tie agreement and I would be up the creek without a paddle if they locked me out. What happened I installed 16 panels to a grid tie inverter so I could ac couple. It wouldn,t work with my present inverter so I just connected it to my service panel inside my home and it has been singing away for 3 years and I over produced more power than I used for the last 3 years. The power company quit using meter readers so now they have a lineman to read my meter and I am getting nervious. I will probably start a new post about the ideas I have,  Whether to get the right inverter I need to ac couple or bury new wires and use a couple charge controlers I already have.
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