classic 200 with a dc water heater DIY style questions

[shadow44]

So... I know someone has already done this. Why reinvent it. I have 1.2kw of panels, and am wasting 4 hours of sun every day that I get good sun. IF I am not hard on my battery bank, I am full up by 11am. So I want to divert those hours to a hot water tank. So I got me a used electric water heater. Getting a 24v element, my question is, where do i go from there? I know I will need a relay, to divert to it, but not sure how the aux works on the classic. or how to tell it that's what I am doing. I want it to dump excess voltage at 24v to the water heater while in float. how do I accomplish that?  The documentation I can find on the aux relays, is poor to say the least. Then on the water heater, must I replace the original thermostat? a quick eBay search for 24v thermostat did not produce anything, I seen as useful for this. What did you use?

And just in case I had not mentioned it, I LOVE my midnight classic 200! Of all the solar equipment I have purchased, I feel it was the best money spent!

[Vic]

Hi Shadow ..,

Have you seen this Thread:  (?)
http://www.midniteforum.com/index.php?topic=886.0

This thread is mostly (all?) regarding using the inverter's AC output,  rather than PV DC.   Believe that those who have played with this function have found that AC is easier to control,  and throttle ...

The general term that MidNite uses for the skimming of excess RE power is,  "  Waste Not   "

You can use the following search term on Google to help locate additional Threads on this Forum:
waste not site:midniteforum.com

There are a number of Threads here and elsewhere as well.  More Later,  Vic

[zoneblue]

Im also planning on doing a dc waste not implementation over the christmas break.

The plan is thus far a 100A dc SSR, was going to be Aux2, now will have to be aux1 (aux2 taken with WBjr),  30second bursts or something like that. You cant put 60A or whatever through the dc thermostat youll kill the contacts. Use a low voltage signal wth small relay or a couple transistors or something. I dont see any reason why you cant just feed aux1 12v through the thermostat. But i think ill use an optoisolator and an logical and gate, one input from aux1, the other from the thermostat. I think it was dgd who said you can also glue a 60 degree C thermal cut out device onto the cyllinder as an alternative.

At 24v volts youll need good sized wire, and close proximity to the controller.

Good luck, let us know how you get on!

[shadow44]

Well at this point after reading what Vic posted, I am thinking of going another route. But I dont think I like this route. I wanted to spare the classic and inverter the extra load.
take power from the inverter (120v my xantrex 4024 wont do 240v) to a 120v heating element (cheap ) run aux1 to a relay to control the load. I would think the 1000w element would not draw enough to pull the batteries down to cause the relay to chatter. but the classic will still have to convert the panel energy at high amp to 24v then the inverter convert it to 120v. I fell like I am working the equipment UN-nessessarly. So at this point I am just going to think on the matter, and buy some copper tubing, and a cheap 24v pump and get some radiant heat from my woodstove

[zoneblue]

Unfortunately there is no 'ideal' solution. Use ac and you tie up a significant chunk of your inverter capacity. You can use a second cheaper inverter, (and then worry about the thing blowing up). Use DC and lose a heap on wiring loss (and less choice of elements, fuss with getting the element out without damaging the cyllinder). Dgd and some others tap in the PV output direct, which is good if your vmp is up around the 120V mark, because it matchs the element voltage. However you do need to use a blocking diode, leave some current for the controller so it can mppt track, and midnite doesnt really approve of this route, but look in the archives youll see folk who do it.

Its an imperfect world, Shrug. On balance DC is best for us, but thats only because the classic is 3 meters from the HWC.

[laszlo]

Using high voltage DC in a wet environment is extremely dangerous. I understand the ethos -- when it's nice sunny day, the desire is universal to get the most out of it.  But I would never put DC current into a water heater that was not designed for DC.  120V DC causes more extensive damage to the human body than 120V A/C. Providing a safe environment should override any other consideration.

[ClassicCrazy]

Using high voltage DC in a wet environment is extremely dangerous. I understand the ethos -- when it's nice sunny day, the desire is universal to get the most out of it.  But I would never put DC current into a water heater that was not designed for DC.  120V DC causes more extensive damage to the human body than 120V A/C. Providing a safe environment should override any other consideration.

Not sure about DC in water but just saw this AC water electrocution demo video the other day - kind of debunks some of the movie myths  http://www.youtube.com/watch?v=dcrY59nGxBg&feature=share&list=UUJ0-OtVpF0wOKEqT2Z1HEtA

[Westbranch]

here is one on DC,  http://www.youtube.com/watch?v=hp97GjuULX8&list=UUJ0-OtVpF0wOKEqT2Z1HEtA

[shadow44]

 westbranch LOL I would not admit in public I watched that guy, He tried to cook his tongue! Some people.....

[David]

Northern Arizona Wind & Sun sells the 48V water heating elements.  From the comments above it sounded like this was not a great idea to use or what?  I have extra 1/0 copper I can use for the the 30ft distance to the water heater.

[laszlo]

here is one on DC,  http://www.youtube.com/watch?v=hp97GjuULX8&list=UUJ0-OtVpF0wOKEqT2Z1HEtA

LOL, this guy in the video is so funny. I guess a sense of humor is required to get through electrical engineering.

[kitestrings]

I think zoneblue hit on the main pros and cons, but I wouldn't be afraid of using DC elements with some consideration for the right breakers, wire gage, etc.  Obviously it can't go thru the stock thermostats as other have mentioned.

We've been diverting to pre-heat water for a number of years using DC elements and inexpensive (Futerlec?) relays operating off the stock thermostats.  Seems to work well, except our tank could be larger in our case.  A bit dated but I'd bookmarked our write-up and some related discussion from an unnamed competitors forum.  we'll soon be changing the control to the Classic, so they may forgive me here ;>].

I'm also a fan of intentionally overheating the water in the tank (to whatever the tank max T allowed), then bucking it down with a mixing valve.  Just one more way to leverage a bit more storage.  The fuel is free.  Kindly, ~kitestrings

http://outbackpower.com/forum/viewtopic.php?f=29&t=2865&hilit=electron&start=25
http://www.fieldlines.com/index.php/topic,130053.html