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Wow, that's some project!  Can you explain the numbers shown in the display please.  I would have expected Solar power to be the sum of House power and Immersion power.  And are there really three CTs in there?  I presume that you're not measuring voltage, just currents.  Are you using the current-only sketch in some form?

So many questions (sorry)

Hi, it's nice to have some questions rather than just typing more and more details into the project page...

The sketch is based on Glyn's 2_Channel_NonInvasive, but updated for 3 CT's - one on the House tail (import/ export), one on the Solar line (generation) and one on the Immersion circuit. The 'normal' control is done using a PID (actually only PI) algorithm based on a target export figure (30W), but when I want an Immersion 'one hour boost' I change the setpoint to be 2500W immersion and use the other CT to achieve it. The PID controller allows easy gain tuning for fast response with stability.

The display photo was taken during an immersion 'boost' (top red LED on), so the readings are Solar 30W (generation nearly over), Immersion 2500W, House 2708W - i.e. my other house loads at the time must have been (2708+30) - 2500 = 238W.

The temperature is copper surface 300mm from the top of the water cylinder - I plan to use this with the immersion thermostat as a back-stop because I find them rather unreliable and I like the idea of using the immersion to get the water 'just' warm enough for my morning shower but then let it cook up through the day on 'free export' power...

I'll post the code up once I get a github logon ;-)

Cheers,

Mike

You will find that the phase angle controller  will produce harmonics and emissions out of spec for emc. Not a worry for DIY unless you listen to old fashioned radio at 198kHz ( am radio 2). If the filter is a standard one or two stage  it will not do anything except very high frequency clean up beacuse it uses a common mode transformer. What you need is to add a large inductor(250uH) in series with the phase angle controller you can make one quite easily the cores are only a few quid. Alternatively UA sell a phase angle filter which incorporates the inductor for about £30. This reduces the harmonics and emc emissions to class A level  (industrial)  which is more than enough for DIY. Unfortunately they don't do one for domestic class B if you want to be squeaky legal. I have done conducted emission tests on standard filters and Choke combinations as well as UA filter . Graphs available if you are interested.  

If you want to heat all of your tank rather than going to the expense of fitting a new tank you could just add a pump, check valve and stat to circulate the water I have done this for the last year and it works well.

I think it depends on the quality of the EMC filter.  When running my Mk1 version in phase-angle mode using a Carlo Gavazzi  AC controller, I wasn't able to detect any disturbance on the radio.

Circulating the water in the tank to encourage more take-up of available power makes good sense.  Wth Mk2's logic, this could be achieved without requiring a second thermostat, and all using free power.  As soon as the primary stat opens, the energy bucket's level will increase to the maximum, and this can cause the secondary pump to turn on.  If that pump draws more surplus power than is available, the bucket's level will start to fall.  Dropping below some convenient threshold could cause the circulation pump to turn off.  This approach should be applicable to most schemes which divert surplus power.

I've often thought of having a pumped return pipe from the kitchen.  After a few seconds' worth of pumping, hot water could then be made to appear straught away, rather than having to run off half a bowlful of cold.  A temperature sensor & display would be a nice touch.

Or, if it has the room you can get a 36in heater to replace a standard 27in one, that's what I did only £20. I do my "topping up" between 8.00 and 9.00 PM (its only needed to do so once) and have the tank stat set to a gnats below what I get on a good day from the solar, I also have the immersion stat set to maximum, the idea being in the morning the water has dropped a few degrees so is more suitable to use in the shower.

Thanks for the replies guys!

I have a Schaffner FN660-20 2 phase filter with inductor that I thought would be appropriate - what do you think? It looks as if it should go in series on the feed from the PAC to the immersion load.

The 36" heater is a great idea, so is the recirculating pump. The funny thing is, I already have a re-circ pump on the circuit to my extension where the shower is to help get the hot water there (bungalow with about 20m pipe run)- I'd been cursing it as a major cause of water heat loss, where in reality what I was seeing was the mixing of hot and cold water in the tank!

I realised it this morning, when I saw the water temp 300mm from top of tank drop suddenly 10 mins before my shower -  this was the pump programmer switching on the recirc. The graph shows the 1 hour immersion 'boost' at 4am, then at 4:50 the recirc pump came on mixing the hot and cold water, then at 5am I had my shower! Rather Big Brother-esque that the whole world can see this data - when I'm at work, I can see when the kettle goes on at home...

The good news in all this is that I can schedule the recirc pump to come on for 10mins in the afternoon so my immersion can do some more work on a sunny day - result!

When you want to "boost" water with your immersion, I wonder why you limit the power to 2500W.  Couldn't you just put it on full whack and save using the third CT?  Or am I missing something?

Good question! I really wanted the third CT so I could monitor the total kWh I send to the immersion. Once I'd decided that, it was easy to switch the PID controller setpoint  to hold it at a desired 2500W. I picked 2500W as I've had to replace burnt out 3kW immersion heaters in the past and guessed they might be a bit more durable at 2500W...