Thermostat + Timer

If you are doing this for a fun project, yes, that will work.

If you want to create a good, dependable system, look at timers made for high current loads, such as swimming pool filter systems. Or use that relay (which you will need for your fun project anyway).

KISS--Keep It Simple, Small.

I have built and programmed a battery backed clock chip and a PIC16F628, attached to a RS-232 serial port.

I am sure this can be modified to add a relay driver.

Let me get the docs together sometime this weekend.

don

don Inscribed thus:

Thanks. I'll take any help I can get.

--
Best Regards:
                Baron.

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View in Courier:


     +----------+
     | C O------|-----+
     |   |   NC |     |
     | > |--+-|      |----+  +---+             |
       |      |           |          NO |
       |      |         [COIL]- - -| --+-|      |-----------+        OC
     | +------+                    |
     |                          [HEATER]
     |                             |
     +-----------------------------+

Doesn't the hot water heater already have its own thermostat?

Thus all you would need would be ON/OFF.

Has anyone tallied up power consumption for such an ON/OFF, COOL-DOWN/WARM-UP type of operation?

I have recirculating hot water here... big loop around the house and back to the water heater, pushed by a pump (Bosch). So you get instant on hot water. And also big heat losses in the underground loop. Since the water heater is well-insulated, I'm tempted to simply turn off the pump (with a timer) in off hours. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
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I love to cook with wine.      Sometimes I even put it in the food.

On a sunny day (Thu, 15 Oct 2009 13:46:48 +0100) it happened baron wrote in :

You can make a nice zero crossing power switch for 240 V with a MOC3041, driving a TIC263M triac, that one can do 25 A continuous (use heatink). The MOC3041 needs 15 mA, PIC can drive that, the MOC3042 10mA, and the MOC3043 needs only 5mA. Just did one last week. What sort of temp sensor are planning to use? Immersed in the water?

needs only 5mA.

Alternatively, you could buy a 25a solid state relay with ttl compatable isolated control input for around $10 from Ebay. Did exactly that for a small lab heater a year or so ago, driven from a omron temp controller with a pt100 sensor.

Don't actually need the 0.1 degree accuracy, but it works just fine...

Regards,

Chris

Is this a domestic hot water heater to 60-70C stock or a boiler to 100C? Most electric immersion heaters usually have some thermostat built in.

You can buy CH timers that could be easily subverted to doing this job but check the contact ratings carefully.

But you would probably be a *lot* better off wrapping 10" of fibreglass insulation around it (preferably the easy handle stuff in a plastic tube with a mirror finish on the outside), or the mirror finish bubble wrap if space is a problem. The water in the low loss hot tank in our Village Hall is still warm enough to be useful the next morning. Uninsulated it would go cold overnight.

Regards, Martin Brown

John Fields Inscribed thus:

Thanks John. Your circuit is exactly what I had in mind. Its the timer and temperature sensing circuits that I want to create electronic versions of.

The timer only needs to be accurate to a few minutes but needs to be settable for any span within a 24 hour period. This is why I thought that a PIC, with its programmability might be suitable.

I have a rigid rod thermostat probe, but its way too coarse between its on/off switching points. Something around 12 - 18C between them. I would hope to obtain a couple of degrees of hysteresis over say 50 to

85C range.

I was thinking diode or thermistor clamped to the bath to measure the temperature more accurately.

--
Best Regards:
                Baron.

Hi Jim, How about a flow sensor on the cold in side of the water heater that turns on the pump for five minutes. You want hot water, you turn the tap on, turn it off, and a few moments later you have hot water. That way the pump only runs when you need it.

Charlie

Jim Thompson Inscribed thus:

No ! Just an over temp non reseting cutout.

I would imagine the losses could be quite large unless the pipes are well insulated.

--
Best Regards:
                Baron.

Jan Panteltje Inscribed thus:

Hi Jan, That heatsink would be live I guess ! I wouldn't want to compromise safety at all. The temperature sensor I was just going to clamp to the bath lip or I could clamp it to the heater fixing.

--
Best Regards:
                Baron.

They're not insulated at all :-(

At some point in time I should re-tile the house and, in the process, re-pipe will suitable insulation and containment (for easier repair). ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

On a sunny day (Thu, 15 Oct 2009 17:07:29 +0100) it happened baron wrote in :

Well I hope you mount the heatsink in some double isolated housing. You could use temp_pic:

as a temprature sensor if you keep it dry, and drive the opto triac from it. And you can monitor temperature on the PC if you want. Only an 8 pin PIC... You will need a 5 V supply too. Could all be a very small box. I use temp_pic as room thermostat at the moment.

1 PIC 12F629 1 opto triac MOC 3041 1 power triac TIC263M 1 78L05 5V regulator some resistors, some capacitors, a small met heatsing, and a poly box. You could even feed it with a series C+R+bridge, and do optional RS232 out with an optocoupler, no transformer needed.

\\ Well, in our new house, they ran all the supply plumbing overhead, but it is that flexible plastic pipe, like small, high pressure hose. I 'think' that the house insulation surrounds it, but it isn't really well insulated.

Of course, in the summer, our 'cold' water is more like 100 degrees, since the water filter out in the garage gets to that temperature, as well as the water in the overhead. We don't use much hot water for showers in the summer, just the washer and dishwasher...

Charlie

Same here, but it's all under-slab (and copper :-( ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Ouch ! Big losses there.

--
Best Regards:
                     Baron.

That looks interesting ! Thanks:

--
Best Regards:
                     Baron.

I had not given a thought to central heating timers...

I'll have to investigate those !

I agree. My hot water tank will stay hot for about 24 hours, certainly enough to have a shower before the off peak comes back on. I've only got 3" of foam insulation around that.

--
Best Regards:
                     Baron.