Ditching gas, going electric immersion only, a wee project

Heedtheadvice

I should maybe have worded my warning regarding serial ssr connection a bit stronger.!

I am guessing your idea of suck it see is a good way forward. If that is the case then can I suggest you do a bit more research first?

To explain further:

SSRs come with a few internal circuit configurations but the ones you will be considering will usually be the ones with back to back thyristor rather than triac configurations.

These have three main types Zero crossing ( switch only at  waveform zero crossings); Random on when commanded even mid cycle (  switch off at end of cycle unless tretriggered); and proportional (Zero switching for variable number of cycles depending upon analogue control voltage).

All are only designed to work with substantially resistive loads where voltage and current are approx in phase. Out of phase V vs A is an issue.

The type  you need is Zero crossing as you do not need fine power control just on or off. Random in series will cause problems. - those Zero crossings! - for serial connections.

Eddi. I do not know how the Eddi works internally but suspect it is either based around a random SSR type of circuit (phase control) or more likely a high frequency chopper action to enable the variable power aspects. Irrespective of this it will be expecting a sinusoidal waveform as input or resistive load as output (unless like the Immersun it has a mech relay option output and you use that).

It could be that the current drawn by the Eddi is thus effectively chopped and thus has loads of extra Zero crossings for current, not in phase with supply voltage. So an SSR  feeding it does not get an expected waveform maybe causing issues.

If the control of that SSR chatters then the Eddi might not like it getting frequent resets.

If the SSR follows the Eddi is it too going to get a waveform with lots of high frequency chops on and off?

These I cannot answer as it depends upon each item internal design but conceivably could result in damage and thus not high reliability.

Could be too no issues when all on or all off! But a risk for you. Devices like the Eddi being expensive, if available!

Nevertheless you should employ fast acting fuses to provide protection to each SSR in use..

If you feel like understanding more there is plenty on the net such as https://m.youtube.com/watch?v=J0vi5TqqCyw&t=29s with type differences depicted at about 5mins 30.

Solarchaser

Thanks for the video, quite interesting. 
The ssr's are indeed zero crossing, I researched the data sheet.

The eddi... according to their tech support varies voltage rather than current but keeps same phase, and uses standard neutral, so in theory the input to the eddi should be in the form of variable current but same phase and voltage.

I'm still of the suck it and see mind,  but will monitor closely for first few hours/days/weeks, bearing in mind the one through eddi should be a failsafe and so technically should never be needed, so if I see eddi switching off (it shows data loss due to signal loss in the app, any time I've actually switched it off) I will remove the ssr.
There will be nothing after eddi, only the failsafe before it.

Heedtheadvice

Fingers crossed all will be well. At least you are now aware of some possible issues and can monitor. Glad your ssr types were not the Random ones!

Still suggest the very fast acting fuses though will admit not that easy to get hold of cheaply. However if they protect your SSRs thay can maybe be positioned for easy access?

Remembering your desire for high reliability that has put you off electromechanical relays....

Solarchaser

Yes definitely good advice.
Thank you 👍

Solarchaser

Going to be wiring up these pid's today as I've finally removed the 10mmt&e that was powering one of the showers and now moved it to under the house to power the consumer unit that will power the 4 heating elements in the tanks.

I've probably mentioned already, but I was removing my 2 electric showers and replacing them with thermostatic showers run off the hot water.
My reason for doing this is with the 4 tank elements running its 48A or 12Kw
Add to that my batteries charging at 28A or 7Kw and now I'm using 19Kw of a 25Kw mains fuse.
Add in a 9 or 10Kw shower and I blow the fuse (in theory).

So plumbed in the shower (1 of 2) last week, it's a fairly involved thing as its taking down a partition wall to get to the plumbing and replumbing, so anyway one done.
I have to say I'm loving the rainfall shower, it's pretty great, and also the hand held has easily double the pressure of the electric which is great too.

However it somehow completely escaped my mind that if the electric showers were on 3-5 times a day using say 1.5Kw at a time, then by plumbing that into the tanks, I now have a further 6Kw of heat required from the tanks every day that I never accounted for in my calculations. DOH!!!

Add to that, due to thermal transfer in the coils we have found this week that for the showers to still feel as hot,  the water temperature in the tanks really needs to be around 50C or more, otherwise the shower feels cooler.

What does this mean?
It means that my planned 36Kwh of heat (12kw elements over 3 hours) has virtually no chance of being enough to run on just the cheap period, and my observation that the radiators running with the tanks at 40C still warming the house is meaningless as the tanks need to be 10C higher than that for showering.

I need 6kw of heat extra than the calculations I based everything on.

The one tiny bit of light is that if I'm no longer using electric showers, then the batteries no longer have to discharge to cover those showers, so there is a possibility I can use the batteries to run 1 or 2 of the elements for an hour or two during the day as a top up, but I think even then I'm going to run a bit short.

Worst case, as has always been true, if it gets to the stage of needing to heat during the normal rate instead of the cheap rate, then that will just have to be what happens. 

70sbudgie

If Go doesn't give you enough hours, could E7 be an option? Not as cheap as Go, but cheaper than peak import. 

I'm currently analysing my import data to try to understand whether Go over winter (including sacrificing my Agile export) would be a cost saving for our energy usage. I don't have a complete answer yet, but it is closer and not the way around that I expected. (E7 is cheaper with the high level assessment. So I'm now going into the detail to understand the impact of variables in my data)

Solarchaser

Right now I'm still on go faster 3 hours at 4.5p, and since I use a pretty tiny amount of on peak, it's making good sense to stay on it just now.
When it comes renewal time (feb) I'll maybe move onto normal 4 hour go but keep the same start time as 20:30 is a good time to catch alot of evening use, better for my household useage than the 00:30 normal start time.

You can rest assured though I will definitely be considering all available options including E7.

Solarchaser

Solarchaser said:

The eddi... according to their tech support varies voltage rather than current but keeps same phase, and uses standard neutral, so in theory the input to the eddi should be in the form of variable current but same phase and voltage.

I'm still of the suck it and see mind,  but will monitor closely for first few hours/days/weeks, bearing in mind the one through eddi should be a failsafe and so technically should never be needed, so if I see eddi switching off (it shows data loss due to signal loss in the app, any time I've actually switched it off) I will remove the ssr.
There will be nothing after eddi, only the failsafe before it.

Theories are theories, but facts are facts.
Wired everything up today and within 10 mins the Eddi had reset itself twice with power to Eddi going through one ssr.
So that's a dead duck.
Another of the PID's kept dropping power to the ssr.  (Swapped wiring back and forth to confirm it's the PID at fault)
So I have 1 running after a weekend of wiring work, which is akin to me running one off an extension,  so not much further forward at the moment.

On the plus side the zone valve opens when the destrat pump is on and the temperature in tank 2 is above 45C, so that's progress.
Overflows are piped to outside now also, so if the heaters run away and boil, the safety valve will flow outside under the deck.

Solarchaser

Just a minor update.
Been running 3 weeks at full power. 
Found the PID controllers are no use for me as PID, but do work quite well as a thermostatic switch, which is essentially just switching off the PID part.

October wasn't the coldest month on record,  but CH was on every day for at least a few hours and several times the heating was on all day, and did the job 👍

A problem I've noticed is that with the 500L tank, elements are on the bottom and so heat from bottom to top, however the 300L tank has the elements on the top, and so they are heating the top half of the tank really, and so are doing it very quickly.
When the PIDs were as PIDs they were heating in pulses even when over temperature and so although I'd set them to stop at 80C, they were still heating in pulses to over 92C, and rather annoyingly the 95C overtemp valve decided to open at 92c, and now wants to open at around 85C, I guess like a safety valve on a compressor, once you test it, you weaken it and it blows earlier.
The overflow piping has ensured no puddles though, little mercies!

So I have a situation where the top of the 300L is at 85C and the bottom is at 65C.

I had planned a destrat pump to move the water around the tank to keep the coils heated, and the destrat works well on the double delay timer when CH is running, however I now realise I need to run it a couple of times during the 3 hour heating period so as to get all of the water in the tanks heated to the same temperature. 
This will require another relay so that I'm not activating the central heating at the same time.
That's a job for this weekend. 

It's been great that the family can shower at any time of the day and I don't have to buy any peak rate electricity as I normally would with the electric showers.

The month of October cost £50 in electricity, thats both heating the tanks and charging the batteries. At the 4.5p rate. (Inc standing charge)
Octopus gas rate is now 10p/kwh, so I'm definitely saving vs gas at the moment. 

Overall I'm very pleased the tanks are working and keeping the family warm, still some niggles to sort, but a good 90% there

michaels

The element position is annoying.  We are doing something much smaller scale running the immersion in our 180l tank during our off peak electricity period (4.5p per unit).  Even though we are using the lower of the two immersions I reckon it is still 15-20% up the tank so depending on how much water conducts heat the heat capacity of the tank is not fully utilised.

Related question - if the immersion heater with integrated stat is at the bottom of the tank and is set at 75 degrees, might the top of the tank get much hotter than this?