DIY Arduino based solar PV dump controller

[ProDave]

2 minutes ago, dpmiller said:

there's already this for a start?

 

https://www.ebay.co.uk/itm/Solar-Immersion-Diverter-PCB-3-phase-Arduino/123811780800?hash=item1cd3c1d8c0:g:bsAAAOSwjOxavhmH

That looks like just some current transformers but 3 of them for a 3 phase system, to do much the same as my simple device. No mention of the electricity meter chip.  And no mention of code to support it.

 

I think using the electricity meter chip is crucial to a simple repeatable design.

[dnb]

12 hours ago, ProDave said:

Building it and putting it into production comes with all the overheads of certifying it for the EMC directive etc and CE marking it.

Not something I would want to do either. But if we ended up with something that would pass then it remains an option. I have done such things at work for very low volume stuff. There's no wonder defence equipment is so expensive...

 

Definitely an "open" project. But we aren't calling it an "open dump controller"! The idea would be to get a good flexible circuit board made with plenty of the right sort of I/O so that it needs a little work for the particular installation, but the tricky soldering is done so you were pretty sure of getting something that worked. I worked on an open source engine management system a few years ago and this scheme worked out pretty well.

 

12 hours ago, ProDave said:

 

I think using the electricity meter chip is crucial to a simple repeatable design.

Totally agree here. 

 

I'll have a think about a cardinal point specification when I get a few spare minutes. I'm thoroughly worn out tonight after an afternoon of tree surgery. PPE is unpleasantly hot in this weather. But more pleasant than the alternative of course.

[SteamyTea]

Don't most modern electric meters have two LEDs on then, one for imports and one for exports.

If that is the case, then can't you just sense the pulses and divert accordingly.

Easy to count pulses with just about anything.

Edited June 29, 2019 by SteamyTea

[Jeremy Harris]

I thought of doing this, but the need for compliance testing (as @ProDave has mentioned above) and the consequent potential liability from selling stuff to build one put me off.  I did publish my original design and code over on the Picaxe forum years ago, but even then added a caution, because of the risk of somebody getting things wrong.  The version I'm using now is basically the same, in terms of the measurement system and energy bucket principle, but uses a 868 MHz link between the measurement and sensing unit and the 20 A SSR unit that switches power to the Sunamp.

[ProDave]

I am thinking of an addition to this.

 

There are plenty of occasions when the excess PV exceeds what the immersion heater can soak up, so some power gets exported.

 

I am considering dumping some of this "unusable" power to a small electric heater.  In the summer that won't be needed, but now, in the shoulder seasons, a little extra free heat in the house would be useful and even now there is still sometimes some surplus around mid day.,

 

So I am thinking of making a "wireless controlled electric convector heater"

 

We have 3 cheap Glen convection heaters, bought when we were occupying the static caravan.  It seems all I need is a simple wireless on/off transmitter built into the solar pv dump controller, and a wireless receiver built into one of the electric heaters.  Then if the immersion dump power gets to 100% (or any threshold I choose) it could turn on the electric heater to dump more power.

 

And being wireless the heater could be plugged in, in any room where a little heat might be useful.

 

Any ideas therefore for a cheap wireless transmitter and receiver, preferably a receiver that has a volt free relay contact as it's output to switch a small heater?

[Onoff]

1 hour ago, ProDave said:

Any ideas therefore for a cheap wireless transmitter and receiver, preferably a receiver that has a volt free relay contact as it's output to switch a small heater?

 

ESR might do a kit/module?

 

https://www.esr.co.uk/

[Onoff]

I've a busted one of these you could maybe hack? Just the LCD screen busted:

 

https://www.amazon.co.uk/SIEMENS-RDH10RF-Digital-Room-STAT/dp/B00BJ72OIO

[SteamyTea]

https://en.wikipedia.org/wiki/ESP8266

 

@TerryE is the man for these.

 

[ProDave]

17 minutes ago, SteamyTea said:

https://en.wikipedia.org/wiki/ESP8266

 

@TerryE is the man for these.

 

That is probably over complicated.  I want to turn 1 relay on and off remotely, that is all.

[Jeremy Harris]

The HC-11 modules provide a 433 MHz, encoded, control link.  The documentation on them is crap, and most of the time people use them as half duplex serial links, but there is an option to just have the receive end turn something on or off on receipt of a command (I've not tried it though).  There's a not very good data sheet on them here: https://www.elecrow.com/download/HC-11.pdf

 

They are pretty cheap from ebay: https://www.ebay.co.uk/itm/1pcs-HC-11-433MHz-CC1101-RF-wireless-Transceiver-RS232-TTL-the-official-agency/191864666716?hash=item2cac067a5c:g:QWUAAOSwKfVXKx9y

 

The "con" terminal can be used to both send and receive a simple switch command, but first the modules needs to be programmed by connecting it to a serial terminal and setting the channel, baud rate and code.  Once set the modules store the programming in non-volatile memory.  It should be possible to drive a transistor and relay from the output, or it should also be able to directly drive an SSR, which might be simpler.

 

I have a bunch of HC-11s here, so if I get some spare time I might play around with the simple switch control setup, as I've only used them for transmitting serial data.

[ProDave]

I am looking at something like this for the receiver https://www.ebay.co.uk/itm/1-Channel-Receiver-Wireless-Relay-RF-Remote-Control-Switch-Module-DC-12V-433MHZ/272638003210?epid=3006634822&hash=item3f7a7dc80a:g:NHgAAOSwSypY-BkU

 

And something like this as the transmitter

https://www.ebay.co.uk/itm/EV1527-433Mhz-Wireless-Transmitter-Learning-Code-Encoded-Arduino-AVR-ATF/192441280820?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D20131003132420%26meid%3D27344d523a564c628efcd674f40b9953%26pid%3D100005%26rk%3D2%26rkt%3D12%26sd%3D192441468854%26itm%3D192441280820%26pmt%3D1%26noa%3D0%26pg%3D2047675&_trksid=p2047675.c100005.m1851

 

What I don't understand is how I set up the encoding at the transmitter end?

[Onoff]

26 minutes ago, ProDave said:

What I don't understand is how I set up the encoding at the transmitter end?

 

Chap here uses the same chipset as your link:

 

https://www.instructables.com/id/Decoding-and-sending-433MHz-RF-codes-with-Arduino-/

[ProDave]

5 minutes ago, Onoff said:

 

Chap here uses the same chipset as your link:

 

https://www.instructables.com/id/Decoding-and-sending-433MHz-RF-codes-with-Arduino-/

I have hit the buttons on ebay and sported a little under £3 on the transmitter and receiver in my link above. I wanted to avoid just hacking a battery powered keyfob transmitter.

 

My assumption is I set a code using the 4 jumpers on the transmitter, and then press the button on the receiver and it will "learn" that code.  If it is that simple it will do all I want.

 

At the Arduino end, I have power and I just have to turn the transmitter on and off as required.

 

At the receiver end, I just have to mount that inside one of the heaters and use it's relay contact to switch a heating element using the 10A relay on the board.  I also have to  provide a simple 12V power for it.

 

As the heater is in a metal box, I might have to extend the receiving antenna outside the metal box.

 

As usual I now have the 2-3 week wait for these to arrive from the far East.

[SteamyTea]

59 minutes ago, ProDave said:

That is probably over complicated

They are cheap, under 3 quid.

And it does give you the opportunity to do other things as well.

 

Complication is a complex thing. My car is complicated, as are the roads, and the associated rules to use them.

But they get me to the seaside and back, and I can't even now, 15 minutes after the journeys end, remember anything about it.

[Onoff]

21 minutes ago, ProDave said:

 

At the Arduino end, I have power and I just have to turn the transmitter on and off as required.

 

How is the transmitter turned on exactly? Just out of interest. As in how is the TX module switched on?

 

(My adventures in RF stopped at making 2 transistor bugs and and the odd SW receiver etc).

[SteamyTea]

Just now, Onoff said:

My adventures in RF stopped at making 2 transistor bugs

I made a bi stable and multi vibrator, with a couple of trans.

Things were different in the 80's.

[ProDave]

36 minutes ago, Onoff said:

 

How is the transmitter turned on exactly? Just out of interest. As in how is the TX module switched on?

 

(My adventures in RF stopped at making 2 transistor bugs and and the odd SW receiver etc).

Judging by the fact the board only has 2 connections, you apply power and it transmits (turns heater on)  Remove power and it stops (heater turns off)

 

It transmits a code so it only turns on the thing you want to turn on, and not open next doors garage door.

 

If that is correct then that is the level of complexity that I like.

 

A concern is whether it would block the car remote controls from working when the transmitter is on.  I will have to try that and see. I would hope as the car keyfobs are used right next to the car that they would swamp any signal from the heater controller.  But I do have history with such a thing happening before.

[Ed Davies]

44 minutes ago, ProDave said:

A concern is whether it would block the car remote controls from working when the transmitter is on. 

 

Don't the licence conditions for these sort of devices limit their transmit duty cycle?

[Onoff]

52 minutes ago, ProDave said:

 

A concern is whether it would block the car remote controls from working when the transmitter is on.

 

Or worse, it opens the cars! ?

 

[ProDave]

15 minutes ago, Ed Davies said:

 

Don't the licence conditions for these sort of devices limit their transmit duty cycle?

My car one seems to transmit as long as you hold the button.

[Jeremy Harris]

I had major problems with interference on the 433 MHz band when I originally fitted the HomeEasy/Byron wireless light switches.  They used simple ASK receivers/transmitters that were extremely prone to interference.  Any transmission near 433 MHz would just block the receiver and stop them working.

 

The problem was fixed by changing to the Quinetic wireless switches, which use FSK on the same 433 MHz band.  These are immune from interference it seems, and just work very reliably.  The same goes for the 433 MHz data transmissions from both the treatment plant monitor and my energy metering system.  These use FSK, with the small HC-11 modules, and are also completely immune from blocking, it seems.

 

In our case the interference seems to come from a wireless weather station that a neighbour has.  This seems to transmit data pretty continuously, using ASK, and tends to swamp any nearby ASK receiver operating in that band.

[ProDave]

I will let you know if interference is a problem.  I am not so concerned about interference to this heater switch, rather interference from it to more important stuff.

 

Listening on 433,920 there is nothing transmitting continuously here. Just the car key fobs used regularly. 

[TerryE]

Dave, if you want to stick with Arduino, then the simplest method is to get yourself a Zigbee shield.  There are a few marketed and YouTube videos on how to build ZigBee controlling projects.  This way you can use standard Zigbee-controlled plugs.  Less learning curve for you than using ESPs.

[Ed Davies]

2 hours ago, ProDave said:

My car one seems to transmit as long as you hold the button.

 

Looking a bit further: http://www.ti.com/lit/an/swra048/swra048.pdf Table 9.

 

It seems that in Europe in this band you're limited to lower power, narrow bandwidth OR shorter duty cycle. I'd obviously only come across one of those options before. I.e., if you want to use the higher of allowed powers and greater than 25 kHz bandwidth then you're limited to a maximum of 10% duty cycle.

[ProDave]

I won't loose sleep, buying from the quality source I have, I am sure they are all type approved and compliant.