Immersion Heater - PV electricity

Discuss Immersion Heater - PV electricity in the Central Heating Systems area at ElectriciansForums.net

Hi Paul,thanks very much,I thought the power and size were fixed,a 1 kw 26"from the top would be great.I was looking at the ideas on this thread regarding auto control and Andy appears to have a cracking bit of kit he has made but as I explained to him we use very little hot water, so as much as I would have liked to go that way I could,nt justify the costs, "Gotta use it to save"
Once again many thanks. Ron.
 
mac1 said:
Hi
I noticed this on a website. It might be possible to use it to lower the power of the immersion to match the output of the PV system.
http://www.graham-laming.com/bd/Immersion_Heater_controller.pdf
Click to expand...
This will not work as expected!
If you research the technology you will find that because it 'chops' the sine wave, it will use more than 1kw for a short period of time and then use no power at all for the remainder of the cycle (wasting generated power).
If you are not familiar with the technology principles - then please take my word - it won't work! (but nice try)
 
Hi Millerman,

Please can you forward me more information on your appliance switch you mentioned in your post on 06-01-2011.

Many Thanks
 
Hi Paul
I am interested in your comment regarding the power control. Having just built an opto isolated triac control unit, I tested controling a 3kw kettle via the triac circuit as a test for my immersion heater control. Using a power meter at the plug of the kettle and whilst watching the output of my inverter and the mains input meter I performed vairious tests ranging form 300 watts to 2 kw taking it close to the total spare capacity that I was generating. At no time did my standard electricity consumption meter register any load. Can you provide a link to a paper / information that may cover your thoughts regarding the wave form cutting situation? Using a triac will provide a much more efficient way of heating your water as you will be able to drive the heater from a much lower level. It seems as though lots of people are catching on to the possibilities of using this spare power :)
 
Please see Light Dimming | Micro Basics which shows the principles of how a Triac works and which I refer to below.
You will see that the power is controlled by firing the Triac at a certain phase in it's cycle, thereby reducing the power 'average' through the full cycle.
Now, if we assume (for example) that you are trying to reduce the power of a 3kw heater down to 1.5kw, this will mean that the Triac will fire at 90 degrees at both the positive and negative cycle (as shown on the 3rd diagram down).
You will note that the current flowing as the Triac fires will be the full current of a 3kw load, of which only 50% will be supplied by the invertor, and the rest via the grid supply.

- The overall power reduction is only achieved by supplying full power for 50% of the time.

A further consideration is that in the 90 degrees before the Triac fires, the power flow is zero - which is not making efficient usage of the power provided by the invertor....

It is many years since I studied Triacs, so would be grateful for confirmation from other board members that this is correct.
 
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Hi Paul
Yes I can see the logic of that. I wonder if the short duration of the extra spike is not seen by the input meter, almost like a transient spike. I willl carry out some more real life tests to see if this is what happens. I will get back to you.
 
I'm not sure how the digital input meters work, or how they deal with reactive/resistive loads, phase shifts ect, so can't really help there, but look forward to your results.
Maybe if instead of using a kettle for testing which will only run for a few minutes and be more difficult to measure as the input meters usually record in 1kwh units, you might consider an appliance which can be left running for an hour or so, such as a heater, tumble drier etc.
 
Hi Paul, aquired 1kw immersion heater from source you reccomended and fitted ,works a treat on topping up between boiler firings.
Would you know if there is a remote switching device available (to switch the 1kw 230v heater) trying to save my legs up and down the stairs. I guess that would be 230v x 5amp capacity?

Many Thanks Ron.
 
rondo said:
Hi Paul, aquired 1kw immersion heater from source you reccomended and fitted ,works a treat on topping up between boiler firings.
Would you know if there is a remote switching device available (to switch the 1kw 230v heater) trying to save my legs up and down the stairs. I guess that would be 230v x 5amp capacity?

Many Thanks Ron.
Click to expand...

The only commercially available 'automatic' switching unit that I am aware of is called EMMA - Solar and Wind Applications Ltd but it very expensive and probably not suitable for your needs.
However, there are a number of people who are developing switching units, and it is only a matter of time before an affordable unit is made available.
 
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rondo said:
Hi Paul, aquired 1kw immersion heater from source you reccomended and fitted ,works a treat on topping up between boiler firings.
Would you know if there is a remote switching device available (to switch the 1kw 230v heater) trying to save my legs up and down the stairs. I guess that would be 230v x 5amp capacity?

Many Thanks Ron.
Click to expand...
.....until a competitively priced 'automatic' switcher is developed, you could try something like this 3 Remote Control Mains Plug Sockets & Transmitter which although does not control the heater automatically, it would enable you to switch it on and off from downstairs, saving your legs!!
There are many similar ones for sale - many even cheaper, usually in big supermarkets/diy stores, and this particular one for example will switch 2900 watts, and because the remote control works by wireless (and not infrared), it will work through walls and ceilings, and up to 20 mtrs away.

...just a thought...
 
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Hi again Paul.

Well I have just run some tests using an accurate industrial power meter that shows direction of power flow and power factor as it is referenced to the voltage. I balanced my 3 kw kettle using my circuit running it at various loads depending on power that was available. My consumption meter is divided in 100ths of a kwhr and each digit takes 8 flashes from an led before it moves. I ran the export rate right down to 10 watts with some fluctuations but I kept it pretty level. At no time did the import meter show any input. I have discussed the principal with another electrical engineer who also believes that the power meter will average the consumption over the duration of the cycle. If this was not the case the rather expensive Emma unit would not work either. I am really happy with my tests and will now continue with the rest of the measurement side development. I do understand your principal of why it should bring power in during the cycle, but in real life tests it doesn't seem to work like that.
 
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inie meanie said:
Hi again Paul.

Well I have just run some tests using an accurate industrial power meter that shows direction of power flow and power factor as it is referenced to the voltage. I balanced my 3 kw kettle using my circuit running it at various loads depending on power that was available. My consumption meter is divided in 100ths of a kwhr and each digit takes 8 flashes from an led before it moves. I ran the export rate right down to 10 watts with some fluctuations but I kept it pretty level. At no time did the import meter show any input. I have discussed the principal with another electrical engineer who also believes that the power meter will average the consumption over the duration of the cycle. If this was not the case the rather expensive Emma unit would not work either. I am really happy with my tests and will now continue with the rest of the measurement side development. I do understand your principal of why it should bring power in during the cycle, but in real life tests it doesn't seem to work like that.
Click to expand...
If this is the case, then it opens up opportunities to automatically vary the power supplied to the element from zero up to the full 3kw on sunny days, and of course use 'off the shelf' cheap 3kw elements too.
I was basing my opinion of 'theory' rather than 'practice', but pleased it is working out.
 
Yes it does seem that way. I am going to do further tests at a friends house who has a different type of energy meter. And I do like to make sure of these things so I will be repeating my tests under different day light conditions. I have two tanks both with 3 kw heaters fitted this is what is driving me on as it's all there just waiting to be used. The key will now be to use the correct type of measurement coils and accurately plot the slope. This could either be used on a multi output programmable relay ( changing resistances at steps ) or with more work a method of connecting the op amp output to drive the 555 timer circuit that fires the Triac. Any body had any experience of that type of interface? Or which is the best current coils to try?
 
Hi Mac
Just to put your mind at rest, your idea will work. The usage meter measures rms and gives the average across the cycle and not sub cycle. This means that a spike causing a draw from the grid will not be seen by the meter. I have completed a series of tests that confirmed this, so develop away. I am currently working on my system. When completed I will be happy to pass the details on. Good luck with yours.
 
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inie meanie said:
Hi Mac
Just to put your mind at rest, your idea will work. The usage meter measures rms and gives the average across the cycle and not sub cycle. This means that a spike causing a draw from the grid will not be seen by the meter. I have completed a series of tests that confirmed this, so develop away. I am currently working on my system. When completed I will be happy to pass the details on. Good luck with yours.
Click to expand...
Mac,
inie meanie and myself have been discussing this outside outside of the forum, and I also now agree with inie's version, that the meter will average out the power usage.
So this does look the way forward after all.....
 
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Hi Mike
That would be fantastic apart from the fact that you would have to sit there adjusting the pot. I have just bought a triac control unit that will take 0 to 10 volts to control upto 25 amps. If I can provide that voltage from a comparitor circuit measuring the coils. Bingo! Hope to complete soon.
 
Paul.

"Can you expand on this?
Are you using a 1kw or 3kw element, and if 3kw - how are you limiting it's power dump? "

I am using a my original 3kw element. the unit i have purchsed is a Crouzet controller M3, and a thyristor controller.
The M3 controller measures the current from the grid and solar using CT's, then compares the two.
This then sends a 0 - 10 V DC signal that operates the thyrister controller ( 0 v Dc = 0 watts, 10 v Dc = 3000 watts.

The only down side is the way the solar supply is connected to the house fuseboard (by the contractor). It might have to be changed for this system to work.
 
I have fitted a 26" 1kw element, so the power dump is either zero or 1kw.Most of the renta roof installers don't like to wire directly into the fuseboard, as they like their systems to run completely independently (so anything I do won't affect their system), so I was lucky. I did however have to wire a separate feed for the immersion heater, so it didn't use the immersion power in my unit's calculations.
You could probably simply fit a Henley Block between the meter and the fuseboard, to separate the system.

Was calibration of your system difficult?
 
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Paul,

You have hit the nail on the head. One installer (AshadeGreener) fitted a seperate fuseboard and then linked it to the grid via new meter tails and a henley block(mother's house). When i had my solar panels fitted the installers (Homesun) they went directly into my existing fuseboard. (this was quickly changed) Both methods are correct according to th IEE regs.

This forum is about using the surplus available power and using it in an immersion heater. I have just elected to keep my existing immersion heater 3Kw and use a off the shelf controller to run it.
A 2.5 Kw controller is as little as £50
Plc is about £100
CT's are about £70 Pair (probably find cheaper) need them to be 4 - 20ma or 0 - 10v Dc output

Dont suppose anyone know how i can reduce this cost (CT's) ??
 
Millerman said:
Paul,

You have hit the nail on the head. One installer (AshadeGreener) fitted a seperate fuseboard and then linked it to the grid via new meter tails and a henley block(mother's house). When i had my solar panels fitted the installers (Homesun) they went directly into my existing fuseboard. (this was quickly changed) Both methods are correct according to th IEE regs.

This forum is about using the surplus available power and using it in an immersion heater. I have just elected to keep my existing immersion heater 3Kw and use a off the shelf controller to run it.
A 2.5 Kw controller is as little as £50
Plc is about £100
CT's are about £70 Pair (probably find cheaper) need them to be 4 - 20ma or 0 - 10v Dc output

Dont suppose anyone know how i can reduce this cost (CT's) ??
Click to expand...
Try Current Cost Daisy Chain CT Sensor Jaw pack of two | eBay UK at £16.50p!

I use these and they are quite good.
 
Hi Paul,
I am interested in the used of my free lekky to heat water- can you send me details of the 26 inch 1kw heater- who makes it/sells it please?
 
I'm pleased you have located a supplier of a 1 kW immersion heater.
I wish to load up[ my solar panels in the same way. Could you please let me know which company supplies the 1 kW heaters?
 
Company is called Howden Electro Heating, 01698 573100, and they can supply a 1Kw 27 inch immersion heater for £83.52, including vat and carraige.
Ray
 
hope you dont mind me saying but why pay £83 for a 1 kw immersion heater. I've found a thyristor controller for about £40 and you keep your existing 3 Kw immersion, just need a controller to run it, thats the easy bit.
Use all spare electric up to 2.5 Kw
 
Millerman said:
hope you dont mind me saying but why pay £83 for a 1 kw immersion heater. I've found a thyristor controller for about £40 and you keep your existing 3 Kw immersion, just need a controller to run it, thats the easy bit.
Use all spare electric up to 2.5 Kw
Click to expand...
Are you using a home built Phase Angle Controller or a ready made, off the shelf solution
 
Paul Hi

I'm using an off the shelf unit. It's tried and tested and resonable cheap (2.5 Kw).

There are two units i've considered

0 Kw - 2.5 Kw and the other 0 Kw - 3 Kw

Both are controlled via a 0 - 10 V DC signal and the plc i am using does that fine.

There is a dead band at the lower end but never the less any thing over 500w is used. so if there is 1.75 kw spare, it is used. The unit switches off the immersion, or any other device if any power is taken from the grid. also switches itself back on when there is spare power.

Andy
 
Ray see posts 48, 71, 73, 74, 82, 84

The units are available from RS (Thyristor controller) PLC from Rs or EDC (program for PLC from Me!!!) CTs from Scatterrgood and Johnson. I could do a deal on all of them.

Andy
 
Hi Andy,
Sounds excellent, but I have a confession to make; I am not an electrician, so though I get the gist of what you are proposing, I am not sure that I would have the skills to put it all together and set it up. Am happy to spend the cash if I am able to set it up myself. What do you reckon?
Ray
 
Ray you have my email address, lets coresspond via external means.

As long as the PV system has been fitted a certain way and you can put the equipment in a "box"
(to suit your location) . Not installations have the room to mount everything. The rest is easy.

Andy
 
Hi Andy
I have been looking at the Crouzet controller M3, Did you need to get an extension module to give the 0 to 10 vdc output? Or is there a model that does it all in one? I am at a similar point as I have just bought the coils from Scats and I have a Crydom thyristor 0 to 10 vdc. Would you be able to let me know what the part number is to save me making a possible expensive mistake. Many Thanks. Tony
 
Tony hi,

The part numbers i'm to sure about, need to go home to look at the boxes, but will let you know. The model i used has 1 pwm output node 24 v DC so you need to buy a converter from Crouzet. I do have them in stock although i have to order them from France.

if you give us a ring 07717723352 i will chat directly. Txt first as i don't answer unknown numbers.
 
Millerman said:
Ray you have my email address, lets coresspond via external means.

As long as the PV system has been fitted a certain way and you can put the equipment in a "box"
(to suit your location) . Not installations have the room to mount everything. The rest is easy.

Andy
Click to expand...

Hi Andy
We've just had a PV system installed by Rayotec (commissioned on 9th June) with generation meter etc. in the porch and tails going direct to outside meter box. Like Ray I'm not an electrician but reasonably competent and very interested in assembling and installing the controls you have described in these posts. We have an indirect hot water cylinder fitted with with 3 kW immersion heaters top and bottom formerly controlled by Horstman Economy 7 timer. Would you be able to supply the bits and instructions? Thanks, Brian
 
Like a drill speed controller or light dimmer a phase angle controlled immersion is going to radiate some electrical interference, only worse because of the larger current and long cable between the immersion and fuse box. What sort of suppression is going to be needed to stop interference with say radios and TVs?
 
Well a drill has an arc across the com that is suppressed by a capacitor, but I am not sure that there will be any problem with this. I have been testing my circuit on 3 kw immersion heater with the triac control and have had no problem at all.
 
echase said:
Like a drill speed controller or light dimmer a phase angle controlled immersion is going to radiate some electrical interference, only worse because of the larger current and long cable between the immersion and fuse box. What sort of suppression is going to be needed to stop interference with say radios and TVs?
Click to expand...
This is an interesting article which discusses this aspect http://bit.ly/m1sLDY
I think that it's not so bad with resistive loads.
 
Hi Millerman. Forgive me but burst firing will pull full power for a determined number of cycles. (see Burst firing ) This will then give a draw from the grid and then the cycles shut off for another set period. This is only useful for the power control of a heater temperature not what you need for balancing a load. I have just completed my circuit that measures the two power levels ( current coils, no need to phase reference if you go on output from dist board, several cores can fit through one coil no problem, remember to only use one from each ring circuit ) compares them and provides an output via the triac. It keeps the house just exporting a small amount of power whilst dumping what else is free into any resistive heating load. I used a 741 to compare the two signals, pass this onto another 741 which adds a reference voltage ( zero point ) and adjusted the gain via pot on feedback gain to alter the slope, thus totally analogue and very cheap. No problem with EMC at all. It can only do this by working at a cycle level. Burst mode will cost you power consumption sorry.
 
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