using the load function

[tecnodave]

Chris,

I still have the standard 6 gallon propane gas heater installed but have added a standard house type 10 gallon water heater which was meant for 120 volts AC but swapped out the element and thermostat with DC units from Missouri wind and solar.  These elements use U.S. Standard 1 1/2" NPT thread so it fit directly.
I have valves on the cold input of each so if I have a real foggy spell I use gas only.....I leave gas off until I know I will not have enough solar power available. In good sun times in need only 400 watts power so a 1 kW array is only needed in foggy times. July thru September.  The water heater element is 600 watts 24 volts DC 25 amps so it is a good fit for the capability of the Kid controller


This is all experimental, this is pushing the Kid to its capabilities.....this is a beta test! 

Soon I will be receiving a second kid and will further this experiment to include refrigeration as well

Notes on these heater elements.......what they really are is stock tank water heaters for preventing water freeze up in the winter so they are really designed for use at 35 -55 degrees Fahrenheit in cattle drinking water tanks...........i do not know how well they will stand up using at 120 -140 degrees Fahrenheit in domestic water use.    There are a number of people doing it this way to save inverter time and use.......they are available in 200, 400, and 600 watts at 12 volts and 24 volts on Amazon, at Missouri W&S and others as well as cattle ( farm)  supply houses.......don't remember exactly......about $65. USD for 600 watt element and thermostat.......don't skimp on the thermostat as these have way beefy contacts that handle the DC or use a relay controlled by the standard AC thermostat.....they will handle pilot duty on DC driving a relay


One other method I am using is I have a 120 volt 1000 element installed into my (factory original) propane gas only water heater.........these are real special elements as they install through the drain fitting on the tank.........they are designed as a retrofit for motor homes only........Kit is made by CAMCO Manufacturing in Tennessee......an RV specialty outfit......kit comes complete with thermostat and remote on off switch.........this has been real marginal and I use that rarely at the DC method is way superior as it runs on solar automatically

The Kid does not divert any power to the water heater element until adsorb stage is reached then it will divert only enough that the battery  gets it set point first.....if solar input is reduced to the point that absorb voltage is not made then diversion will cease until enough power is available

Please note I will not recommend that you use a controller at maximum power all the time.......this is an experimental setup and I will be adding a second kid and more panels in the near future.  Generally I do not want any of my equipment running at more than 75-80 percent of max ratings to preserve life

@Acorn.      Yes the kid will see the voltage going up and sense that the load has shut off and will regulate the voltage when thermostat shuts off.

Hope this info will help...do post questions

td

[Highflyer]

Dave,
Why not use the cheeper AC water heater elements?  They are like $9 at the hardware store.  I am going to dump the heat into 2300 gallons of water and never expect to see more than 80 degrees F in the tank.  The one I am looking at is capable of 3000 watts so I can never overload it even at 48 Volts and all 30 amps from the Kid.  I'll be running at 24 volts.

I suspect I am missing something........ Please help before I mess this up.

[mike90045]

Dave,
Why not use the cheeper AC water heater elements?  They are like $9 at the hardware store.  I am going to dump the heat into 2300 gallons of water and never expect to see more than 80 degrees F in the tank.  The one I am looking at is capable of 3000 watts so I can never overload it even at 48 Volts and all 30 amps from the Kid.  I'll be running at 24 volts.
  I suspect I am missing something........ Please help before I mess this up.

Playing with ohm's law, the 3KW 240VAC heater element would be 19 ohms.  at 24V, 19 ohms passes 1.26A or about 30 watts   Yow !
or did I miss the step where the load triggers a relay to power a 120V MSW inverter connected to the element ? (1500W)

[TomW]

What Mike said.

Plus the AC thermostat will not like switching DC and will more than likely fail with the contacts shorted {ON}.

[Highflyer]

Curses Ohm's law, curses!!!

Okay, I'll see what DC heater I can use.

[tecnodave]

Brian,

I am trying to eliminate any conversion steps......yeah the AC units are more common but now I need to run an inverter at ?88-92 % efficiency at best???probably 60-70 % in reality.......no, I will net way more power at 24 volt DC ......no conversion.........the DC element will have the same efficiency as the AC elements. They are a non-inductive resistor. This also does not cycle the batteries.....excess power is diverted on its way to the batteries.

I don't do a lot of off the shelf work as I have been a commercial electrician for 46 years......my approach is based on my experience, besides always tinkering to make it better.

I have found these same DC elements at several places so they are available.

td

[Westbranch]

what are you suing to switch the power to the DHW tank vs the batteries, other than the signal from the KId?

[tecnodave]

WB,

That is the beauty of the kid design.......built in......set load function to battery, connect diversion load to load terminals..........no relay, the kid does it all. With the Classic you will need a relay or SSR to turn load on or off which is controlled by aux 1 or 2

I do have a 30 amp breaker between load positive and the heater

td

[tecnodave]

Someone has thrown out a question about the difference between an AC and a DC element. It not that it is rated for AC or DC. It's the voltage that it's meant to work at. The DC elements that I am referring to have a much lower resistance than the higher power 120/240 volt elements that are commonly used. Most water heater elements are nichrome wire coated with ceramic. They are not inductive so they behave the same on AC as they do on DC. The only difference is the resistance. I think that mine are .96 ohm. Rated at 600 watts at 24 volts DC.  The original elements in the GE water heater as purchased from Home Depot were about 12.5 ohms, rated 1500 watts at 120 volts AC , would only produce about 50 watts at 25 volts DC

David

<edit>. There is no reason why you could not use a 120 volt AC water heater element on DC if you have a high enough voltage in to get the watts draw you need. I.e. 120. volts DC. The thermostat is entirely a different issue.......DC has a much meaner arc so the DC thermostat has much larger contacts and are probably designed to open at a faster rate than an AC thermostat.

<second edit>. To make a bit more clear about the relationship between resistance and voltage consider this:  If you use a common 2,000 watt 240 volt water heater element on 120 volts AC you will not get 1,000 watts draw.......the voltage is half........so the current is half.........watts is volts times amps......1/2 of 1/2 is 1/4...... You only draw 500 watts......and when you drop the voltage to 1/4.........1/4 of 1/4 is not much at all


Best case 50 gallon heater two 5,000 watt elements, 240 volt, heater rewired so both elements wired in parallel operated at 24 volts will draw 99.3 watts  same 10,000 watt heater at 48 volts will draw 397.2 watts..............thus....... the very low resistance DC water heater elements

Power squares with same resistance when voltage doubles.  Ohm's law!

[Highflyer]

Dave,

Thanks for the explanation.  I understand the process a lot better now. 

My case is more of a one of a kind case than most.  I am trying to capture the extra energy as heat for an indoor overwinter fish tank.  The tank I am heating is 2300 gallons and will be stored in a barn.  I am trying to overwinter Tilapia and can use the heat from mid Oct through Mar.  There is no way the water will ever get hot enough to do any harm, so whenever the kid has power to spare, I am going to direct it to the heater directly unless there is an issue with wiring the heater directly to the Kid's load terminal. 

Again, thanks for the help, The learning curve remains steep.

[tecnodave]

Brian,

Use the load output on the Kid to do this, the Kid will modulate (switch on and off ) the power so the average power will be regulated at what the p.v. System has to spare.  Mine runs from 100 watts or so up to a maximum of about 700 watts or so. I adsorb at a bit higher voltage than normal so I get a bit more power than rated. If you connect such a large load directly to the solar panels without regulating the current in some fashion you will pull the p.v. Voltage well below the maximum power point, resulting in reduced power production. Using a MPPT controller keeps the panels at their maximum power production

Like I have said before, I think I am loading my beta Kid real hard, charging a 400 a.h. Battery set AND diverting at the same time,  with 1020 watts in  I have seen 942 watts out, temp raised to 53 deg. C............I don't walk away from the units when I do things like this. There is an adjustment for maximum output on the Kid,s menu and I set the currents down to 22 to 25 amps both battery charge and load divert to keep heating down.

The Kid is rated to do this but I am pushing the maximum. I have ordered a Second Kid that will share the load on this system as well, target is full stand alone power with water heating and refrigeration as well.......will be approx 1600 watts poly P.V. In with two diversion loads.....one on each kid......600 watts water heating.......AND.......500 watts resistance heating adsorption referigation........I will be posting more on this

In another thread I detail diversion loading the adsorption referigeration...."A different approach to waste not" on this forum.


With your big tank is there a possibility of using multiple heater elements, tied in parallel they will add up, but unless you are like me, just gotta tinker with stuff, try to find low resistance elements.
Mine came from Missouri Wind and Solar but I have seen identical ones on farm supply house websites and there are several dealers on Amazon. I have never seen 48 volt ones though.

Just a thought I will throw out there, there is a major swimming pool heater outfit here in California that makes co-polymeric water heating panels that are a real good bang for the buck.  Fafco Solar of Menlo Park, Ca makes panels that are parallel rows of 5/16 inch plastic tubings edge welded togather to from sheets 4 feet by 8 or 10 feet long with 2" headers. I have been using these panels for years with no fails......they are not suitable for domestic hot water as the difference between ambient temp and hot water is too great but at the temps you are looking at these panels achieve 53% efficiency! with no glazing and no insulation! I have frozen these solid and they expand and are not damaged by this, No Fafco does not recommend this.......seen these used on Craig's list at under $50......was a tech at Fafco years ago......

Have fun tinkering......td

[Highflyer]

Dave,
Thanks for the info.  I appreciate the help from people with your level of experience. 

I'll keep tinkering.  I'll post and I'll look forward to the advise of experts.