Immersion Heater - PV electricity

[pauldreed]

Haha - those cheap power supplies, battery chargers etc you get from the likes of DealExtreme don't have any filter components in them.

That's probably why they are on DealExtreme!!

 

[inie meanie]

Haha - those cheap power supplies, battery chargers etc you get from the likes of DealExtreme don't have any filter components in them.

Well it must depend on their design.If they don't use a triac then they dont need any thing I suppose. Just a regulated output via a FET etc they won't have that problem.

 

[chriswarhurst]

Hello all,

New to this and picked up a google search thread - my company has developed a 240v low power immersion heater for domestic installation that incorporates 2 elements a 250w and 500w into one immersion heater. The idea is that it compliments your solar PV array and heats your water tank up slowly throughout the day. Starting at 250w, switching to 500w, then switching both on which gives you 750w then back to 500w then 250w later in the day. It works really well - we received the prototype last week and it works really well on its own connected to a simple timer. If you have developed a switching system tied to the inverter then I would be really interested in talking to you about it. contactable on [email protected]

 

[pauldreed]

Hello all,

New to this and picked up a google search thread - my company has developed a 240v low power immersion heater for domestic installation that incorporates 2 elements a 250w and 500w into one immersion heater. The idea is that it compliments your solar PV array and heats your water tank up slowly throughout the day. Starting at 250w, switching to 500w, then switching both on which gives you 750w then back to 500w then 250w later in the day. It works really well - we received the prototype last week and it works really well on its own connected to a simple timer. If you have developed a switching system tied to the inverter then I would be really interested in talking to you about it. contactable on [email protected]

Hi Chris, what length is the element(s)? and does it have a inbuilt thermostat?
... oh, and how much money!!

 

[chriswarhurst]

The immerser is made from Incoloy - 11” long with a standard 21/4 inch BSP thread. 240v TWIN element version 1 x 500w and 1 x 250w including two 7” stat pockets and two TSDR stats. If its a one off purchase its £110 + VAT if you are looking at bulk we can come down in price. Got to say the figures it producing so far are fantastic - effectively it is raising the water temperature high enough so that the boiler is currently switched off - and for free as the power it is drawing is within the output of the 3.8 Kw Solar Array. Watching the performance closely as we head into the winter months. Hope this helps

 

[suntrap]

Well it must depend on their design.If they don't use a triac then they dont need any thing I suppose. Just a regulated output via a FET etc they won't have that problem.

No, they are standard switch-mode designs (power supplies, not power controllers) which all need mains filtering. Their PCBs have positions for filtering components but these are all missing!

 

[suntrap]

it works really well on its own connected to a simple timer

Unfortunately, connecting it to a timer is a very inefficient way of maximising your use of solar power whilst minimising (or for most, preferably eliminating) your draw from the grid - the difference between output when the sun is shining and on a dull day is easily a factor of ten and a timer cannot predict this.

If you have developed a switching system tied to the inverter then I would be really interested in talking to you about it.

Read this thread and you will see that there are several such systems, one (sadly, only one) of which has had all its details published and made available on a royalty-free basis.

 

[pauldreed]

The immerser is made from Incoloy - 11” long with a standard 21/4 inch BSP thread. 240v TWIN element version 1 x 500w and 1 x 250w including two 7” stat pockets and two TSDR stats. If its a one off purchase its £110 + VAT if you are looking at bulk we can come down in price. Got to say the figures it producing so far are fantastic - effectively it is raising the water temperature high enough so that the boiler is currently switched off - and for free as the power it is drawing is within the output of the 3.8 Kw Solar Array. Watching the performance closely as we head into the winter months. Hope this helps

Chris, this sounds very much like an element designed for boats - not domestic hot water systems, and for the majority of this thread's readers would be unsuitable for the following reasons;
1) As suntrap has commented, using a timer is inefficient as on dull days, the power would be drawn from the grid, therefore a more complex switching solution should be sought.
2) Hot water rises to the top of the tank, therefore if top mounted (as is the norm) then this element would only heat the top 11", leaving the majority of the tank cold (would work OK if it could be bottom fitted).

 

[chriswarhurst]

Its an adaption of a standard immersion heater that uses two low power 240v immersers - we can do an 11 inch or 27 inch for larger tanks. The timer I agree is a crude mechanism balanced against a 3800 w Solar PV system. The array puts out 400w on the most cloudy rainy day so 250w from 0900 till 1500 hrs is background power consumption. The 500w element kicks in at 1130 till 1330 so still well within average power tolerances. You are right in that the switching mechanism is suboptimal but I disagree with the word inefficient it depends on the cost basis. A simple electronic timer costs £38. A bespoke emma unit is over £1000 so the cost benefit analysis over time against a viable use of the energy in heating hot water actually makes it very efficient.

As far as the tank is concerned - this is designed to sit in the top third horizontally so it only heats up the top 100 Ltrs or so. That means it is not wasted in trying to heat the whole tank up - something that it just does not have the power to do. 100 Ltrs of water is enough for average normal domestic use. Modern mains pressure systems have the immerser mounted horizontally in the top third of the tank. This system is not designed to sit vertically at the top of the tank as is common with older HW cylinders. Its not perfect but it is working and producing free hot water. Hope this is of use

 

[pauldreed]

...The array puts out 400w on the most cloudy rainy day..

Yes but how much power is being used in your home... fridge, freezer, etc, offset home consumption against your 400W, and there won't be a lot left for the immersion heater.

... but I disagree with the word inefficient...

IMO inefficient is an accurate description! if you put the washer on, boil the kettle, dishwasher etc. where does the power come from to power the immersion heater? The grid of course, which is kWh chargeable.

...A simple electronic timer costs £38. A bespoke emma unit is over £1000 ..

You havn't grasped the concept of this thread!
We are trying to develop cost effective control systems, albeit in different ways, which cost far less than £1,000 and nearer the £38 mark.

 

[chriswarhurst]

Let me know when you have developed one - i will be very interested

 

[suntrap]

He already has - and all the information about it has been published. Look through this thread if you want to know.

 

[DickiePhitt]

I've been working my way through this thread for days. Really interesting and a credit to the contributors. Its taken days because I'm a chartered (mech) eng so can only deal with things that can be measured in buckets. No, I've 16th Ed and did hobby electronics years ago so I think I have the skills, if not the electronics knowledge, to have a go at building a simple,safe, economical controller for an existing 3kw Immersion heater.

Was surprised at how little the potential savings were, though. Checking the gas meter these past few weeks without heating on, converting to kWh, and plugging in the cost per unit I reckon about 50p per day on HW. In summer its likely HW will max out on the temp stat part way through the day and in winter it'll struggle to put much surplus into the HW tank. So maybe 1/3 of the annual cost will be saved - say £60 - which is worth having but limits options - yeah I know its a crude calculation but probably not wildly out.

Can I just ask a few questions ,which I hope are not too stupid, asked on the basis of 'will it work' not "is it the perfect solution"?
I want to use the Arduino (no experience, I'll have to learn) as it seems to be a well supported, flexible platform for development and communicating. Am I right that 2 suitably sized LEM CT's will hook up fine to the inputs? Think I read here somewhere that something else was needed but cant see where and cant think why.

The Crydom and filter (at the right price) + fuse & MCB looks the proprietry, proven way to control the 3kW load. Since it doesn't like PWM I thought a suitable compromise might be to use an R-2R ladder and an Op-Amp to double the voltage.

Digital to Analog converters (DAC), using R/2R netwroks

Suitably programmed the Arduino would step the output voltage applied to the Crydom which would raise or lower the immersion heater power. Not perfect DAC but a good 80:20 pereto solution I thought.

If this is totally out of court can someone please suggest and illustrate / point me to a suitable way of achieving this? I would need to be taken through Triacs, etc as they came after my hobby days.

 

[methley]

I'm building one right now with an Arduino Uno board which is perfect for this job. For the output, the R-2R ladder uses too many outputs. As the Arduino supports PWM outputs all you need to do is filter the output of a PWM pin and add a voltage doubler to drive the input of a Crydom. The Crydom takes away any difficulty in driving a Triac. It's all there in one package, and is fed simply with a 0-10v input.

For the inputs from the LEM's you'll need to half the voltage, using a simpler resistor potential divider. Note the minimim load on the output of the LEM is 2MOhm.

 

[pauldreed]

My Arduino based device is here if you are interested.
The first version was built with a Arduino Uno, but my current one uses a £4 Arduino chip (Atmega 328PU) along with a few support components, and runs the same software.
The credit however must go to these guys.

 

[DickiePhitt]

Methley, have you successfully got the Crydom working via PWM and filter? Crydom advised me "The analogue DC input is sensed by a micro-controller, a PWM input would either not be recognized or falsely interpreted. The PWM signal would have to be converted to DC signal." which led me to doubt that a filter would give a clean enough input, and as a result might damage or overheat it.

Paul, I've been impressed with the development you've put into this, as witnessed by this thread and others. I'll read up the links and try to get some understanding of what you and these guys have been doing. Might be a bit advanced for me I fear :-(

 

[pauldreed]

Methley, have you successfully got the Crydom working via PWM and filter? Crydom advised me "The analogue DC input is sensed by a micro-controller, a PWM input would either not be recognized or falsely interpreted. The PWM signal would have to be converted to DC signal." which led me to doubt that a filter would give a clean enough input, and as a result might damage or overheat it.
(

I too spoke with Crydom some months back, the problem with PWM is inherently the speed of the sampling rate is too fast for the Crydom Thyristor circuit to recover, and therefore would not work.
I think Methley has taken the PWM output through a capacitor/resistor circuit to smooth and average the peak value, similar to this.
The input would be clean enough, but there is a lot of debate around the switching harmonics/distortions caused by the thyristor.
As for being 'Advanced', this was my first project for over 30 years when valves were the norm, so if I can, so can you, just take your time and if you get stuck there is plenty of help in the forums :->

 

[suntrap]

Was surprised at how little the potential savings were, though. Checking the gas meter these past few weeks without heating on, converting to kWh, and plugging in the cost per unit I reckon about 50p per day on HW. In summer its likely HW will max out on the temp stat part way through the day and in winter it'll struggle to put much surplus into the HW tank. So maybe 1/3 of the annual cost will be saved - say £60 - which is worth having but limits options - yeah I know its a crude calculation but probably not wildly out.

That sounds very plausible and does make it less attractive if you are offsetting the cheapest fuel - mains gas. Same problem there has always been with solar water heating: loads in the summer and not enough in the winter. And you could also argue that offsetting gas consumption with electricity is not very environmentally friendly. I did ponder the idea of overriding the freezer thermostat to reduce its consumption from the grid at night, but of course that's a fairly small fixed load and has the additional complication of not liking to be short cycled.

 

[suntrap]

an Op-Amp to double the voltage.

There is a 5V version available.

 

[pmcalli]

I have now built and tested two immersion controllers so thought I would share the results.

the first solution used a PID controller crydom and true rms ct's which as people here have pointed out is a very expensive solution.

results
The true rms CT's are loaded by the PID controller this does not affect the operation but is undesirable.
the response time of the true rms cts is 300ms so the PID integration time had to be long
very small grid feed in with large load changes otherwise results good.

the second solution uses some inexpensive ops amps the crydom controller and a couple of owl ct's.

results
the cost is very low the owl ct's are obtainable for about £6 each op amps and other components are less than a £1. crydom is about £70 filter £25 power supply £10
response time is set at 100ms and no grid feed in or consumption is measurable.

As there has been many posts on how the inverter and phase controller work to ensure no grid consumption. I have run an experiment whose results may lead to some other solutions.

while my controller is running using an oscilloscope with line trigger and a spare CT I have measured the current from the inverter and the current going to and from the grid.

the result is the inverter delivers current evenly over the whole mains cycle. this means that if the load from the immersion heater is phase controlled then the part of the mains cycle that it is on the current is drawn from the inverter and the grid if the inverter is not generating enough. On the part of the cycle that the crydom is off the inverter feeds into the grid. Over a cycle the net result is zero. the meter response time is more than a cycle and therefore does not record that you borrowed some power and gave it back before the end of the cycle. measuring the current going to and from the grid confirms the result. measuring the meters response time is more tricky as I would have to burst fire a SSR over an increasing time until the meter recorded if i get around to it I will post the results but I expect it will vary with meter type.

I shall be laying out a PCB ( currently on vero board ) and am happy to share the circuit diagram/component list/PCB layout with anybody who wants it.

incidentally I also ran the controller without the i/p filter and I am unable to Bluetooth to my inverter due to the interference showing that an input filter is absolutely essential.