Author Topic: High Volt/ Amp DC Switching hacks.  (Read 1165 times)


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Re: High Volt/ Amp DC Switching hacks.
« Reply #15 on: May 23, 2018, 12:15:56 AM »

I agree with Bruce, a bigger pre heat tank would be better.
You actually don't want the thermostat on the pre tank cutting out because the water is all hot. That's inefficient.  More water even if not as higher temp will have the same energy/ saving imparted to it as less water hotter.
For me, would be better to have 100L @40o than 50L @ the cut out point of 70. 
I would also allow for summer. Your inlet temps will go up ( quite a bit here I noticed) and you will get more concentrated and longer sun radiation.

There is one other thing with using an over sized pre heat tank..... You could do away with all controls completely.
If you know the capacity of the tank is beyond that of the heater and it will never catch up to full temp,  there is no need to have a thermostat and switching at all.
If you go away or stop using the water to the point it may catch up, just switch it off all together. In any case, if it does overheat it will just trip the safety valve and dump some water so not a lot to worry about. Done that a load of times in my oil fired heater.

IF you are using gas, it may be possible to turn that off over summer.  I Imagine a black drum in the sun especially with a reflector behind it and in a transparent fronted and insulated Cabinet would warm significantly.  Put that pre heated water into a tank that was electrically heated and I think you'd be bouncing off the thermostat pretty easily. You'd probably get enough  heat either side of the summer months for a bit to get by on as well.

I'm hoping to get a tank off the neighbour later in the week. He said his element blew in his and it's rusty round the bottom. Thing apparently does not leak  but he wants to install a new one before this one fails.  I asked if he throws it out to throw it over the fence for me which he was more than happy to do.
Pretty sure I saw a service guy in there yesterday but didn't see any new tank in his wagon.  Maybe neighbour just put in a new element.  They certainly aren't expensive.

In any case, I have been thinking about water pre heating only with my gas heater and an oil burner.  Still a couple of weeks away from mid winter but all my solar has just been breaking even. I check my meters several times a day when I'm home.  Morning we are down from electric stove, AC and lack of solar feed.  Water heater has been kicking in mid morning.  Mid afternoon we catch up and when I do my 4pm reads we may be slightly ahead depending on how cold it was the night before and how long Daughter decided to give herself the wrinkled prune treatment.  That said I haven't been exactly quick to jump in and out lately either.  I have the water pretty hot and it makes my aches and pains fell better.
We have had pretty much perfect weather so its been a best case scenario so far.  When the crappy weather hits as it has to do sooner or later, I won't be making the power I need and want.  If I used the gas tank with the oil burner, I'd probably free up another 5 + KWH day on the hot water tank.
Tank I have is only 1/4 size the main one and I do keep a casual eye out for a full size tank.

I'm thinking of just batching the heating every day with a passive updraft burner.  Work out how much fuel it's going to take to raise the water temp where I want it, add the required amount of fuel and let it go.  People think these things have to be drip fed but that is incorrect. The passive pot design works fine in batch mode. I put over 4L in my old one very regularly and it burnt fine from start to finish but it seems to have been lost/ chucked out in the move.
Went to the Charity warehouse shop yesterday and they had every type of pot, pan, tray and cooking vessel imaginable BAR the one I wanted.
Just a big stainless or enameled  Pot with a lid that wasn't glass.

I could do a dedicated Solar fed pre heat as I have more panels but maybe the novelty is wearing off. I know I can do it now, rather than put more panels up just for a water heater I may as well just incorporate them in to the rest of the arrays.
That said, will be OK in winter but in summer I'm starting to get to where I have to be careful.  I'm getting up to the limit on not so much my wiring but the power co's coming into the house.  Likely in summer I'd have to switch a good amount off so maybe dedicated Hot water might be a better idea after all?