Saturday, March 17, 2012

I have hardly been out today.

I've been a busy boy inside - piles of paperwork that all needs completing by Tuesday and so there's no time like the present to do it even though I'm not really in the mood.

Apart from that, I had to change the batteries over in the outside temperature gauge and that meant moving the dustbins with the sawdust and the kindling, and a huge pile of wood fell over that was propped up there and so all of that had to be repositioned.

Such is the exciting life that I lead.

But in other news, the dump load was registering off the end of the temperature gauge as early as 14:00 and there was that much power going through the dump load controller that the heat sink was positively boiling - and I had a few papers and a plastic fuse holder sitting on top. I'm surprised that the whole thing didn't go up like Joan of Arc.

This dump load is clearly to small for summertime use - it needs more than 25 litres of water. But if I do that, then there will be not enough useful heat in the winter. What I need is two tanks therefore, each with its own water heater element. But the overload controller only handles 60 amps, and each water heater element is rated at 500 watts, which (at 13 volts) is about 40 amps or so, and so it won't handle two. And anyway, imagine how hot the heat sink would be.

The clue for this might well be twofold, and as I don't know the implications of what I'm talking about, I'll write it here and invite comments. Basically, I could have two elements and have them both wired to the battery circuit, but have them wired via relays that are powered from the overload controller. After all, the relays that would drive the heater elements need just enough power to overcome the resistance of the spring, namely a few milli-amps or so. That way the heat sink wouldn't be so hot.

 But a refinement of this is to have the second relay wired to a heat switch that is attached to the side of the water tank that is heated by element number one. If the switch was set to close at, say 65°C, then when the water in the tank was heated to that temperature and the heat switch detected it, it would switch on the second relay to heat the element in tank 2.

What would happen then though would be that the current would be split 50/50 between the two elements, so that would mean that the temperature in tank 1 would continue to rise as the temperature in tank 2 was continuing to warm up. So supposing I had another heat switch on the side of tank 1 - this time a switch that opened at say 70°C and wired to the element in this tank. When the water in tank 1 reached 70°C the switch would open and this would cut off the supply to the element in tank 1 and stop the temperature rising. Without heat the temperature in tank 1 would slowly fall and when it fell to 65°C it would cut the supply to tank 2 and restart the heat at tank 1.

This all sounds thoroughly complicated to me, but that's the way that it would have to work. I just wish I knew enough to work out what the pitfalls were in all of this.    

Tomorrow I'm going to be heading to Montlucon if I'm up early. I need a bulk shopping session seeing as how I haven't been there since January, and I need a pile of stuff from Brico Depot.

1 comment:

  1. Build yourself a shower shed with several water tanks on top, all thoroughly insulated. Use some of the solar power to pump water into the tanks from your rain-water collecters.

    Have two ot three hot tanks and one cold. You'll need to put a thermal switch in the hot tanks and also a level switch so that the element doesn't burn out if the tank is empty.