Hi, I wonder if someone could help me with this application please.

I have a hot water cylinder powered by 230v mains (U.K.) from a fused spur with a timer. It's timed to come on at the low rate electricity feed overnight.

I also have solar panels and a device (designed for use with H/W cylinder elements), which can feed a resistive load with any excess solar production, if there is any (so no output from this device on cloudy days or if the house load is using all the solar production).

What I'd like to do is connect the h/w load to the solar device during the day if it's sunny, or to the mains supply directly if there's no sunlight.

So it's a mains switching application and my expertise is in low power DC electronics and programming microcontrollers. I'll set up a sunlight detection circuit which will provide a TTL output and I'll use that to switch a MOSFET driver which can switch the high power circuitry.

Could anyone point me in the right direction for the a.c. switching? Is there an off the shelf device I should search for which will switch a load between two supplies?

I'd like to use SS technology for preference and I think I'll probably need to switch at the zero point of the sine wave ?

Thanks for any help,
Paul

 

You need a contactor, and you need to switch both live and neutral, because otherwise you will trip the RCD as the current may return through the wrong neutral, and because you need to be able to isolate the immersion heater safely as it could possibly be supplied via two different MCBs.
Use a changeover contactor (double pole n/o and n/c) and supply the coil from the output of the solar device. An ordinary relay would not have a large enough contact gap to count as isolated when it is off.
No solid state solution would satisfy safety requirements For isolation.

 

You need a contactor, and you need to switch both live and neutral, because otherwise you will trip the RCD as the current may return through the wrong neutral, and because you need to be able to isolate the immersion heater safely as it could possibly be supplied via two different MCBs.
Use a changeover contactor (double pole n/o and n/c) and supply the coil from the output of the solar device. An ordinary relay would not have a large enough contact gap to count as isolated when it is off.
No solid state solution would satisfy safety requirements For isolation.

Thanks very much for this, I'll have a search and see what I can find.

 

So I've found a modular contactor at a well known long standing UK parts supplier. It's specified as 25A 4, pole, with NO contact gap >= 3mm, double break, continuous duty for coil and contacts. Could I just check I am going to wire it as per the attached image, where A1 and A2 is the contactor coil power (specified as 230V a.c for this contactor) and the load will be my thermostatically controlled hot water cylinder coil.

Sorry for a naffish diagram.

thanks,
Paul

 

So I've found a modular contactor at a well known long standing UK parts supplier. It's specified as 25A 4, pole, with NO contact gap >= 3mm, double break, continuous duty for coil and contacts. Could I just check I am going to wire it as per the attached image, where A1 and A2 is the contactor coil power (specified as 230V a.c for this contactor) and the load will be my thermostatically controlled hot water cylinder coil.

Sorry for a naffish diagram.

thanks,
Paul

Yes - that's right.

 

Brill, thanks for the advice.

 

On second thoughts. . .
if you swap N/O and N/C and power the coil from the E7 timer, then the contactor only changes state twice a day, and only once under load (presuming that the thermostat has turned off the power by 7am), whereas the other way round, it has to switch on and off every time a cloud goes over.
Also, it would work with a solar output that uses proportional control to match the water heating with the amount of surplus power.

 

On second thoughts. . .
if you swap N/O and N/C and power the coil from the E7 timer, then the contactor only changes state twice a day, and only once under load (presuming that the thermostat has turned off the power by 7am), whereas the other way round, it has to switch on and off every time a cloud goes over.
Also, it would work with a solar output that uses proportional control to match the water heating with the amount of surplus power.

Thanks for this, I am just creating a circuit diagram and description by way of documentation for those who may follow after me , so this is a nice variation.

 

Warning label stating “This equipment has two supplies, isolating one supply does not make it safe for maintenance” might be appropriate.

 

Good point, thanks for that.

 

Hi Paul,

Here's the schematic.



Nandu.

 

Hi, I wonder if someone could help me with this application please.

I have a hot water cylinder powered by 230v mains (U.K.) from a fused spur with a timer. It's timed to come on at the low rate electricity feed overnight.

I also have solar panels and a device (designed for use with H/W cylinder elements), which can feed a resistive load with any excess solar production, if there is any (so no output from this device on cloudy days or if the house load is using all the solar production).

What I'd like to do is connect the h/w load to the solar device during the day if it's sunny, or to the mains supply directly if there's no sunlight.

So it's a mains switching application and my expertise is in low power DC electronics and programming microcontrollers. I'll set up a sunlight detection circuit which will provide a TTL output and I'll use that to switch a MOSFET driver which can switch the high power circuitry.

Could anyone point me in the right direction for the a.c. switching? Is there an off the shelf device I should search for which will switch a load between two supplies?

I'd like to use SS technology for preference and I think I'll probably need to switch at the zero point of the sine wave ?

Thanks for any help,
Paul

Hi

Im also interested in doing just this
just never got around to it !!!

Whats the contactor you have found please ?
I have the old wattson optimiser,
still works, but a pain going into the meter box to press the button on the controller,
when I need to boost the water heater...
would be great to have a bypass .
My "fix" / "bodge" at the moment, I known its horrible
is I put a 13 amp plug on the water heater / thermostat , and a socket on the output of the optimersion
and swap as needed !

 

Hi

Im also interested in doing just this
just never got around to it !!!

Whats the contactor you have found please ?
I have the old wattson optimiser,
still works, but a pain going into the meter box to press the button on the controller,
when I need to boost the water heater...
would be great to have a bypass .
My "fix" / "bodge" at the moment, I known its horrible
is I put a 13 amp plug on the water heater / thermostat , and a socket on the output of the optimersion
and swap as needed !

https://www.ledcontrols.co.uk/nc1-2...1kw-5060hz-ac3-2-no-2-nc-4p-4-main-poles.html
if you buy a small empty consumer unit, you can fit it in there, with perhaps another MCB, or a two-pole isolator on the output so you know for certain it is switched off if you need to change the immersion heater.
Many consumer units come with a 2-pole isolated already fitted.

 

Hi

Im also interested in doing just this
just never got around to it !!!

Whats the contactor you have found please ?
I have the old wattson optimiser,
still works, but a pain going into the meter box to press the button on the controller,
when I need to boost the water heater...
would be great to have a bypass .
My "fix" / "bodge" at the moment, I known its horrible
is I put a 13 amp plug on the water heater / thermostat , and a socket on the output of the optimersion
and swap as needed !

The contactor I found with a good spec is this

Finder 22 Series Contactor, 230 V ac Coil, 4 Pole, 25 A, 4 kW, 2NO + 2NC

I also have an electronics box which uses a c clamp in the house mains tails. This box detects if there is surplus solar being generated, so as Ian0 described, by using this, a contactor and a fused mains spur, it's possible to use surplus solar to heat the water cylinder, from the mains overnight and from solar during the day. Where I live in South Wales, we don't get much solar between end Nov and end Feb, so we need the mains for that period.

 

I note that the contactor I have found is 'DIN rail' fitting and I think I'll probably need an enclosure of some kind, but there seem to be different DIn rail sizes. Could anyone advise on a suitable enclosure please and whether they come fitted with DIN rails?
thanks.

 

thanks, I have managed to sort the DIN rail and enclosure aspect

 

I have completed the installation, and it seems to work ok from an electrical perspective, but the contactor emits a fairly loud buzzing noise when the solenoid is activated. Is this normal for these devices? If so, are there any devices which would be quieter? Just got to think about being able to sleep at night