Immersion Heater - PV electricity

[suntrap]

Yes, it helps if no-one's there to mess up the consumption during the day! A diode will of course not do wonders for the current waveform but I agree is a very easy way to halve the heater's consumption.

 

[bradburts]

Do you have a link to the inverter with the relay?
Its sounds a good solution.
The diode would seem a lot simplier/cheaper than changing the immersion coil (which is where this thread started).
Does the inverter allow other power settings at which the relay switches? 1.8Kw seems quite a high threshold, I only go over 500W when the kettle goes on....
Would there be the problem with chopping out half the wave within a house?

 

[echase]

Hi,

Looking back at earlier suggestions; a light dimmer board was thought to be a simple solution, having all needed interference protection etc, but was rejected through having a potentionmeter control.
It may help to note that you could use digipots, digitally controlled potentiometers, to replace the light dimmer potentiometer. You would have to use a microcontroller to control the digipot of course but to my way of thinking the microcontroller circuit has got to be the best way forward with its meter, display and perhaps wireless control capabilities.

I will research and post suitable devices and provide programming examples if converting a light dimmers make electrical sense!

The device I have designed and am now selling does all this. Send me a private message if interested.

 

[echase]

I too am interested in getting an extra current transformer for my OWL, as I noticed the transmitter has three sockets on it (unless that's just for three phase supplies?). I haven't investigated it further yet, though.

I checked with OWL some weeks ago. It’s for 3 phase, but it just adds the 3 powers together and displays one figure so you can’t use it to display 2 or 3 different things like PV generation and export. Plus it has no idea of the direction of the current so an import and export read the same. The trick in any immersion control device is to discriminate them and my device does that.

 

[pauldreed]

Hi All, as I posted a few days ago, I have been working on version 2 of my solar controller, and it is now complete and fitted, so I thought that I would post a few photos.

The PCB contains the input filter and protection components, as well as the main processor and power supply stabiliser. The LCD display is recycled from an old alarm keypad.

Fitted it all into a small 'Maplins' project box after sawing a few holes in the lid and sides.

All wired up to the power supply and CT's, the first display screen shows the current power state, ie. how much power is being used within the home, and also how much solar power is being generated.

By pressing the button on the front, I can select different screens. This one shows how much power has been used/generated in kwh's. This total is culmative and resets every midnight.

Another screen displays the instantaneous mains voltage and power factor. This works very accurately, and is mostly within the tolerance of 1v to that recorded with a professional test meter.
The voltage measurement is what makes the power calculations much more accurate, instead of assuming that the mains is 240V AC.
As you can see here, it is currently 247V, but sometimes drops to just over 240V.

The small LED just above the button lets me know at a glance what the unit's status is;
1) flashing every 4 seconds - indicates that the unit is functioning, but not enough solar power to activate either relay.
2) steady but lit 25% - indicates that 500w is being unused, and activates relay 1, with a diode in series to limit the load to 500w (yes it does work, I've done the sums on the leccy meter!)
3) steady and lit brightly - 1kw power is now available, so relay 1 is deactivated, and relay 2 activated switching the 1kw load.

The device also provides a 0 - 5v variable output, which could feed a 'Crydom power controller' for progressive power control, which I may purchase at some stage.

 

[suntrap]

Fantastic. You must have spent ages doing that!

You could make the LED flash with every fraction of a kWh produced by the cells, like an electronic meter. Watching the LED flash beats TV any day of the week! When the relays are on, it could inverse flash (flash "off").

Pedantic note: your "w"s (watts) should be capitals :stuart:.

 

[pauldreed]

Pedantic note: your "w"s (watts) should be capitals :stuart:.

You are correct of course, amended accordingly!
The building time wasn't long compared to the learning curve, see post Immersion Heater - PV electricity - Page 3 and you will see that it's developed from that point forward with a lot of help from others, especially Home | OpenEnergyMonitor who have written most of the coding and been inspirational and confidence builders.
With the explosion of renta roof solar installations, similar devices are much in demand and I would encourage interested others to buy a Arduino Uno Arduino - HomePage and have a bash! they are great development circuits, and code is loaded directly from your PC without expensive programmers.
However, 240v is a very different matter, and is best left to the experts.

 

[Andy_WSM]

I am very pleased to say that I have completed my system. I have heated the top part of my tank very quickly. ( only as deep as the length of the immersion heater ) I raised water temp 10 deg before the solar water system had got up to temperature and started to circulate. This was important as some people have said this system won’t work quickly enough and this proved it is much faster than the water type system. Also to confirm that I have had NO interference generated by the triac effecting either the radio or tv (10pcv2425 contains a snubber circuit ). This system, just to confirm doesn’t use an expensive plc and follows the spare power level in an analogue way NOT waiting until there is a spare 1,2 or 3 kw before switching on in steps and thus wasting potential energy. It runs as soon as there is a spare 100 watts and continues to feed all the way up to full power 3kw. All it contains is a small comparison circuit made from 2 opamps ( 741, 75p each ). I triac crydom 10pcv2425 ( just bought one on eBay for £12 ) . A power supply that provides -12 0 +12 vdc, 2 current coils from LEM model AT20B10 ( £ 54 inc vat for the two ). I have fitted and extra dist board with a Henley block to separate the measurements. I now need to find a nice box to put it all in and maybe add a couple of voltage meters form eBay just to make it very easy to see what power is being supplied. The future improvements would now be to add another heating element to the bottom of the tank and a relay circuit to switch between the elements once the top one is up to temp. I hope this will encourage some of you to develop your system. It just goes to show there are several routes to achieve free hot water. :- )

Hi all,

Been liaising with Tony (inie meanie) and purchased a PCB off him for the control circuit he describes here. 2 current coils and crydom triac later and I too have a "spare power recovery" hot water system. I fitted the kit on Tuesday morning and haven't used the immersion heater at premium rates since. Today is a dull, cloudy, intermittent sunshine kind of day - I only have a spare 800w being generated, so to heat my water now would normally cost me 2.2kWh from the grid + the 800w generated locally. By using this cct I can just dump the 800W in for longer until the tank has reached temperature, then any surplus goes to the grid. I've really enjoyed this little project and will continue to enjoy the financial benefits it will bring

 

[echase]

Fantastic. You must have spent ages doing that!

You could make the LED flash with every fraction of a kWh produced by the cells, like an electronic meter. Watching the LED flash beats TV any day of the week! When the relays are on, it could inverse flash (flash "off").

Mine does that and also has an override to turn the immersion on if you want a top up on a sunless day. Some LEDs or an LCD are useful or else you don't know if the unit is working properly.

Looks like we have at least 3 viable solutions here. My one achieves the same aim as the others but I use cheaper components that are just as effective. The Crydom 10pcv2425 is pretty expensive (around £100) unless you find a cheap one somehow, as inie meanie did. So I went for a different approach that does not use such an expensive relay but provides the same function. My whole component cost including the box, current transformer, fuses, relay, processor board, etc. is less than just the 10pcv2425. On the other hand I am charging a modest cost for the design and for assembling it, as I don’t have the kit version available at the moment. My making them up saves you the potentially hazardous work of dealing with the mains side (but some of you are electricians so you don’t mind that).

I don't currently supply an LCD but am providing the connections for one as I do connect one to test and calibrate the units. I’ll make them available later for retrofitting when I get around to writing the full LCD software. LEDs provide much of the info that an LCD could supply.

 

[echase]

2) steady but lit 25% - indicates that 500w is being unused, and activates relay 1, with a diode in series to limit the load to 500w (yes it does work, I've done the sums on the leccy meter!)
3) steady and lit brightly - 1kw power is now available, so relay 1 is deactivated, and relay 2 activated switching the 1kw load.

Have you established that all electricity meters can cope with this half wave rectification? For the positive half cycle you will be importing from grid and exporting for the negative half cycle, or vice versa. As long as the meter successfully averages out the power over a few cycles this is OK but if not it will register an export or import when none really exists (apart from the error between the 2 discrete steps and the real power available for export).

 

[pauldreed]

Have you established that all electricity meters can cope with this half wave rectification? For the positive half cycle you will be importing from grid and exporting for the negative half cycle, or vice versa. As long as the meter successfully averages out the power over a few cycles this is OK but if not it will register an export or import when none really exists (apart from the error between the 2 discrete steps and the real power available for export).

I have only tested it with my meter which is a Ampy 5235 and it uses exactly half the full load.
The Ampy, as with most modern meters is fitted with a flashing LED, which flashes every Watt/hour recorded by the meter, so it is easy to check.
Simply count the flashes over 6 minutes and multiply by 10 to give you kWh's.
It's not as good a solution as using a linear power controller such as the Crydom, but it's a safe option (doesn't get hot and is well isolated from the low voltage side via opto isolators), and costwise, a 6A 400V diode costs 99p from Maplins, and a double relay module at £3.99 2-Channel 5V Relay Module for Arduino PIC ARM AVR DSP | eBay

It's great that we have got some solutions to this, albeit different routes, and hope more come on board!

 

[Mark Gee]

Great to hear there are 3 viable solutions.

Am having panels installed (tomorrow!!) and I'm not an electrician (although I dabble). I have a second CU that is already being used off one circuit to power an outside office/garage/studio

Am I correct in assuming that what I need to to 'future-proof' my system (for adding an immersion later) is to get the guys to do is
1. Install another CU (I won't do that)
2. Fit a Henley/Henly block

Is that all...if so I'll get down to Screwfix for the CU this afternoon! That's after I use the scaffolding (going up now) to mess around with the chimney stack and aerial...a bodgers work is never finished ;-)

 

[suntrap]

As I said in my posting, I'm OK with using the existing CU because there is enough space inside it to clamp a current transformer on a single core of the cable where the cores are split.

 

[pauldreed]

Great to hear there are 3 viable solutions.

Am having panels installed (tomorrow!!) and I'm not an electrician (although I dabble). I have a second CU that is already being used off one circuit to power an outside office/garage/studio

Am I correct in assuming that what I need to to 'future-proof' my system (for adding an immersion later) is to get the guys to do is
1. Install another CU (I won't do that)
2. Fit a Henley/Henly block

Is that all...if so I'll get down to Screwfix for the CU this afternoon! That's after I use the scaffolding (going up now) to mess around with the chimney stack and aerial...a bodgers work is never finished ;-)

Mark, who is the installer? is it a renta roof system (like mine).

 

[echase]

1. Install another CU (I won't do that)
2. Fit a Henley/Henly block QUOTE]

No, my system requires no wiring changes. It is useful if the immersion is on its own MCB in any of the CUs, rather than having other devices hanging off that MCB. But not essential.