Immersion Heater - PV electricity

[Rogerhillside]

Suntrap Thanks for the quick reply
I have bought a direct unvented tank already and only intend using one of the immersions at a time. The lower one from the excess solar and the upper one for occassional warming up. The tank was used so not so expensive and only 140l.
[email protected]

 

[suntrap]

OK sounds good. I suppose in theory you could feed the tank straight into the boiler but that's probably not allowed...

 

[pmcalli]

Suntrap Thanks for the quick reply
I have bought a direct unvented tank already and only intend using one of the immersions at a time. The lower one from the excess solar and the upper one for occassional warming up. The tank was used so not so expensive and only 140l.
[email protected]

I run two vented tanks in series the first tank is an economy 7 tank ie with two immersions the second with an immersion in the top and gas heated coil in the bottom. I run the controller via a daisy chain of relays so it heats the second top of tank first then a std cylinder stat set high on the tank switches via a relay the controller to the top of first tank another stat switches it to bottom immersion when hot. This way I always have the max quantity of hot water if you heat the bottom one first and its a dull day you just get a lot of Luke warm water. The relays cost about £3. I don't see why you couldn't use the same idea with the first relay enabling the combi boiler via the nc contact of the relay.

 

[echase]

This may be relevant. I have a granny annex with its own combi boiler for water heating. I’d like to draw its feed off the solar cylinder in main house but the pipe would be long. I am thinking that best bet may be to install a thermostat half way up the cylinder switching the boiler feed from this cylinder to mains (although one is mains pressure and other loft tank fed). If it’s above a certain temperature, like 40C, it’s a sign that there is lots of hot water higher up the cylinder so there is spare to send to the combi. For short combi runs this hot water may not reach it before run time ends, so is largely wasted. For longer runs like baths it will reach it. But don’t want to use it if little spare in cylinder, so the thermostat prevents this.

In these solar installations you need to consider legionella. Opinion is divided but heating all or at least the top part of cylinder to 60C regularly (daily/weekly) is needed to kill the bacteria. There is the risk that unless a good top up heating system is used this 60C is rarely reached in dull periods.

http://www.solartwin.com/solartwin-...l-to-a-combi-boiler-combination-boiler-geyser partly covers all this. They use a 60C mixing value to stop the water into boiler being too hot.

 

[sharpener]

Can anyone who has used the Crydom 10PCV2425 controller or similar confirm that they are optically coupled so there is complete isolation between the input and output sides? Also, what current does the control input draw at 10V and what are the voltage limits? Some circuits published here seem not to have any overvoltage/reverse voltage protection for the control input!

Lastly can anyone point me at a supplier for the Crydom polycarbonate terminal cover (pictured earlier) and heat sink pad? Farnell have a good price for the controller but don't seem to stock the accessories.

TIA

 

[echase]

RS Components stock a Crydom cover but can't say if it fits that particular SSR model as I don't use it. They list a pad but have not had any in stock for months.

I'd be very surprised if it did not have 1000s of volts of input to output isolation as all their simpler SSRs do. Look up the datasheet for the answers.

 

[sharpener]

Thanks for that. Inie meanie has also been generous enough to provide some answers off-line too.

Look up the datasheet for the answers.

If only it were that easy!

The data sheet says 2500V max signal to load but says nothing about how this is achieved. If I knew what the input configuration was - opto-coupler like the LPCV series? - I could then guesstimate how it would behave and whether I need to protect against voltages <0 and >10. The control input is only specified as drawing 4 mA at 5V, which is not very helpful when you need 10V to turn it on fully. I had hoped to find an application note on the Crydom web site with more details but there is nothing useful there, hence my previous posting.


BTW pmcalli, the analogue multiplier power measurement circuit I described in posting #354 is now working a treat.

 

[suntrap]

If you just put an 11V zener diode across the input, it will protect against both overvoltage and wrong polarity (assuming your source impedance is high enough that the diode can dissipate the excess power) and as it costs a few pence I'd just do that and not worry about the finer details.

 

[sharpener]

Good thinking. Actually I found a 4V7 and a 6V2 in my scrap bin so have put them in series across the feedback resistor in the driver amp, this reduces the power drain and is a bit kinder all round.

 

[thushar]

Just found this 27" 2 1/4" BSP thread 1 kW immersion heater in ebay -
1 kw / 1000 W 27" Immersion Heater - Use Spare Solar Panels Power For Heating | eBay

Hope that will help

 

[bradburts]

A 2 kW immersion heater 2kW Immersion Heater and IMM01 - 2kW Immersion Heater Power Halver and Power Reducer would be as cheap and may prove more flexiable.
I imagine that its just a diode, perhaps some filtering. Its CE marked (for what that is worth) & has a thermal cut out.
You could easily add a relay to switch between 1kW and 2kW

EDIT: Removed link, it won't work!

 

[suntrap]

Interesting thing, that power halver, though I'd wait to see how much the 3kW one is as it would mean the standard/existing element could be used.

Those marine heaters are short (for fitting horizontally in the bottom of the tank) and it doesn't say they're "incolloy".

 

[bradburts]

Yes, the second immersion link is no good.
Was scanning & saw 28 & assumed inches.......
I will remove the link if possible.

 

[pmcalli]

Thanks for that. Inie meanie has also been generous enough to provide some answers off-line too.



If only it were that easy!

The data sheet says 2500V max signal to load but says nothing about how this is achieved. If I knew what the input configuration was - opto-coupler like the LPCV series? - I could then guesstimate how it would behave and whether I need to protect against voltages <0 and >10. The control input is only specified as drawing 4 mA at 5V, which is not very helpful when you need 10V to turn it on fully. I had hoped to find an application note on the Crydom web site with more details but there is nothing useful there, hence my previous posting.


BTW pmcalli, the analogue multiplier power measurement circuit I described in posting #354 is now working a treat.

I have now completed testing of meter behaviour and have very bad news for you. The meter measures true power and your analog multiplier measures apparent power so you will be feeding back uneccesary power. I have now tested using a synchronous demodulator and it correctly follows true power as measured by the meter. The other advantage is the circuit is unchanged whether you use one ct on composite meter tail or two cts on seperate meter tails.

 

[JohnBoyZ]

I have now completed testing of meter behaviour and have very bad news for you. The meter measures true power and your analog multiplier measures apparent power so you will be feeding back uneccesary power. I have now tested using a synchronous demodulator and it correctly follows true power as measured by the meter. The other advantage is the circuit is unchanged whether you use one ct on composite meter tail or two cts on seperate meter tails.

That sounds very interesting, especially if it can give accurate readings with a single ct on the combined meter tails and presumably with import/export direction indication. Are you likely to be posting a circuit diagram as I for one would be very interested to try it out?

 

[pmcalli]

That sounds very interesting, especially if it can give accurate readings with a single ct on the combined meter tails and presumably with import/export direction indication. Are you likely to be posting a circuit diagram as I for one would be very interested to try it out?

Yes it is direction sensitive. I have been testing it by running it at same time as my original and it shows the power factor error. I haven't been able to test it running the immersion heater yet as I haven't been at home when the suns out. before posting I would like to run a proper test to ensure there is no forward meter creep on all loads. If friday afternoon or the weekend is sunny i will do the tests and post the circuit. If you want a preliminary look send me a private post with your email address.

 

[pmcalli]

Can anyone who has used the Crydom 10PCV2425 controller or similar confirm that they are optically coupled so there is complete isolation between the input and output sides? Also, what current does the control input draw at 10V and what are the voltage limits? Some circuits published here seem not to have any overvoltage/reverse voltage protection for the control input!

Lastly can anyone point me at a supplier for the Crydom polycarbonate terminal cover (pictured earlier) and heat sink pad? Farnell have a good price for the controller but don't seem to stock the accessories.

TIA

the cover RS supply fits nearly all the crydom models. Don't bother with the heat-sink pad its runs stone cold without it. I have been using the MCPC2450C because its twice the current rating and 54.36 instead of 72.20 from RS

 

[inie meanie]

the cover RS supply fits nearly all the crydom models. Don't bother with the heat-sink pad its runs stone cold without it. I have been using the MCPC2450C because its twice the current rating and 54.36 instead of 72.20 from RS

Anybody know what the difference between the 10PCV2450 and the MCPC2450C is? They look the same apart from the price.

 

[pmcalli]

Anybody know what the difference between the 10PCV2450 and the MCPC2450C is? They look the same apart from the price.

The MCPC2450C is 50 Amps instead of 25 it has an enable i/p and you have to supply the voltage for the analogue part. I tie the enable and the Vd to 15V. It also has an LED whose brightness indicates control level. It has a better spec for control impedance and there is a lot more max rating specified. data sheet is on RS site. I have controllers running with both types. The control voltage can go to max supply so protection zener is not required but I still fit one as it stops the integrator saturating. Cover fits both

 

[DickiePhitt]

I've been out of this thread for a few months while I followed the Nanode-based control solution that was discussed in earlier posts. I have done the assembly and mimicking and am about to connect to the 5V version of the same controller[FONT=Verdana, Arial, Helvetica, sans-serif] - MCPC2450A[/FONT]

pmcalli, do you have the output filtered? If so what have you used?

 

[suntrap]

I'd use a washing machine mains filter, which have the current rating and can be bought cheap.

 

[pmcalli]

I've been out of this thread for a few months while I followed the Nanode-based control solution that was discussed in earlier posts. I have done the assembly and mimicking and am about to connect to the 5V version of the same controller - MCPC2450A

pmcalli, do you have the output filtered? If so what have you used?

The I/P is filtered to stop fast turn on edge causing interference. I have used a standard emc filter from rs stock number 7024019

 

[DickiePhitt]

Thanks guys.
pmcalli, hope you dont mind but I pm'd you with a more detailed series of queries as I think you've done what I next need to do on my project

 

[sharpener]

I have now completed testing of meter behaviour and have very bad news for you. The meter measures true power and your analog multiplier measures apparent power so you will be feeding back uneccesary power. I have now tested using a synchronous demodulator and it correctly follows true power as measured by the meter. The other advantage is the circuit is unchanged whether you use one ct on composite meter tail or two cts on seperate meter tails.

No, the bad news is the other way round. If you are just doing synchronous demodulation of the current waveform you are not using any voltage waveform information (other than the zero-crossing points), so you are assuming that its waveform is the same as the current. This is only true if you have a pure resistive load, which may not be the case.

As suntrap has pointed out already in posting #388, what I am doing is multiplying instantaneous current by instantaneous voltage and then averaging the result over (at least) one cycle.

That this will work with any load or combination of waveforms to give true rms power is a well-known mathematical result, if you are not familiar with it then read this paper

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.134.5837&rep=rep1&type=pdf

or these articles

Power Measurement Article

Voltage, Current, Power & Energy : Definitions :: Electronic Measurements.

 

[pmcalli]

No, the bad news is the other way round. If you are just doing synchronous demodulation of the current waveform you are not using any voltage waveform information (other than the zero-crossing points), so you are assuming that its waveform is the same as the current. This is only true if you have a pure resistive load, which may not be the case.

As suntrap has pointed out already in posting #388, what I am doing is multiplying instantaneous current by instantaneous voltage and then averaging the result over (at least) one cycle.

That this will work with any load or combination of waveforms to give true rms power is a well-known mathematical result, if you are not familiar with it then read this paper

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.134.5837&rep=rep1&type=pdf

or these articles

Power Measurement Article

Voltage, Current, Power & Energy : Definitions :: Electronic Measurements.

Many applogies I didn't read your post properly I mixed you up with another poster who is using an analog devices true rms device fed from current taps which will only deliver apparent power. Thanks for the links best explanation I've seen. However your statement is not 100% correct. If you synchronously demodulate the current waveform with the voltage zero crossings you do get true power. A simple simulation with sine waves out of phase proves this. What happens with non sine waves I havent analysed. I have been running some tests against my meter which is of the spinning disk type and found firstly that the meter reads 4.6% low yip yip hooray but also creeps at 0.1kwhr when the controller is running the immersion at 2 to 3 kW. In my two ct circuit this can be compensated but not in the single ct without applying a higher offset which is not desirable for winter use. The unfortunate conclusion is that if I had been measuring apparent power then this problem would not occur as the current would be over reported. I suspect my meter is responding slightly to apparent power. Can you remind me which analog multiplier you are using and I will try it out as a measuring device to identify the cause of my creep.

 

[inie meanie]

I found found that to deal with the problem I have had to use two vairiable gain amps wich have allowed me to tune out the problem at the 2 to 3 kw point. I know 0.1 was only a small input but I didn't want to pull anything.

 

[pmcalli]

I found found that to deal with the problem I have had to use two vairiable gain amps wich have allowed me to tune out the problem at the 2 to 3 kw point. I know 0.1 was only a small input but I didn't want to pull anything.

Any idea to the cause. I have stupidly been concentrating on trying to get true power when apparent power would actually have given some margin to this effect. On my systems I see the effect on both a two ct balanced system and a single ct on composite meter tail. In the 2-3 kW range most of the power is resistive so I can only speculate that either the current taps are non linear or the meter reads the composite waveform incorrectly. I will try the suggested analog multiplier but not hopeful as I have had previous bad experience (over 25 years ago mind ) with this device beacuse of non linearity effects of up to 5%?. I will also try my demodulator circuit with added hysteris in the mains voltage squarer this will give a selectable phase shift and hence give the same effect as miss balancing the two ct circuit which was very successful. I am desperate to get a solution to this as I have a queue of people whoose installer used a spare way in the consumer unit making a two ct design difficult to implement.

 

[inie meanie]

I too have been battling with ever changing errors on the export rate. I have built and tested many many variations using different coils and approaches. I have noticed when inductive loads kick in ie. Washing machine and the fridge and freezer loads, these change the way the circuit will compare the power loads due to lag or lead on the current angle. It has all come to a compromise. I have now settled on the circuit that gives me adjustment on the buffering op amps. I have been told. Don’t let perfect be the enemy of good! I have been striving for perfection on the’ no export’, but Unless I spend a lot of money and map all this in a plc ( EMMA ) I am not going to get it. I am now happy to settle with ,< 120 watts export generally and up to 250 if the house has a heavy inductive load running. After all the testing and different approaches I am only marginally better than my original design. But hey it’s been fun. I now have to make some up for my friends who are all nagging me. Without this forum it would have been a lot harder.

 

[sharpener]

Many applogies I didn't read your post properly I mixed you up with another poster who is using an analog devices true rms device fed from current taps which will only deliver apparent power. Thanks for the links best explanation I've seen. However your statement is not 100% correct. If you synchronously demodulate the current waveform with the voltage zero crossings you do get true power. A simple simulation with sine waves out of phase proves this. What happens with non sine waves I havent analysed.

That's OK, no problem, at least unlike the true rms converter your synchronous demodulation will give the direction of power flow. Perhaps I should have said a linear rather than resistive load, because I agree that this technique will cope with sinusoidal current out of phase with the voltage.

But I still think it will fall down if there is any harmonic current. Another way of thinking of it is that your square demodulation waveform contains odd harmonics (1/3 3f, 1/5 5f etc) which are not actually present in the voltage waveform, so if there is any harmonic current at these frequencies it will give corresponding spurious terms in the expression for power. This is probably addressed in the paper above but I confess I have not actually looked it up.

Can you remind me which analog multiplier you are using and I will try it out as a measuring device to identify the cause of my creep.

I have sent you a PM about this as it is not the device I referred to in my original posting.

The I/P is filtered to stop fast turn on edge causing interference. I have used a standard emc filter from rs stock number 7024019.

Is this effective? I have fitted the even more expensive Schaffner multi-stage filter suggested by others, but there is still a 100Hz buzz from the unit, from the immersion heater itself and on AM radio. So I am now trying out an entirely different approach which may also work out cheaper.

 

[pmcalli]

That's OK, no problem, at least unlike the true rms converter your synchronous demodulation will give the direction of power flow. Perhaps I should have said a linear rather than resistive load, because I agree that this technique will cope with sinusoidal current out of phase with the voltage.

But I still think it will fall down if there is any harmonic current. Another way of thinking of it is that your square demodulation waveform contains odd harmonics (1/3 3f, 1/5 5f etc) which are not actually present in the voltage waveform, so if there is any harmonic current at these frequencies it will give corresponding spurious terms in the expression for power. This is probably addressed in the paper above but I confess I have not actually looked it up.

I have found the cause of my 5% error. I originally analysed the effect of crydom current shape but only the up to half power. Up to this point the demodulator gives a higher house power than actual so no problem I am not after 100%. I incorrectly assumed that this would be the peak but having simulated the full range the current shape gives a 7% under power. Limiting the integrator dc gain on a single ct implementation fixes the problem.
The multiplier arrived today and I have tried it out. Performance is as you described. I will be testing it over temperature in the next few days where I expect to have serious problems if its offset spec of 50mV is real. I should be able to compensate the circuit fairly easily. On the single ct after some analysis the scale error of the device will not matter as the peak value is not high when the currents are balanced. I too get a 100Hz buzz but no interference. Even with a multistage filter the current rise time is very high I think a different approach may be required to mitigate this effect.

 

[delleray]

Interesting thing, that power halver, though I'd wait to see how much the 3kW one is as it would mean the standard/existing element could be used......

I have used a single diode out of a MB356 BRIDGE RECTIFIER 35 Amp 600V (£2.79 posted from polarity_electronics_uk on ebay ) to halve my 3Kw immersion load. Its AC input feed is relay switched in with a wireless remote when the output from the PV exceeds fixed amount.

It gets warm but not hot as it's only having to dissipate < 10W so is mounted in a double wallbox with cooker isolating fuse/switch.

A similar unit could be used to half feed a 750W oil filled radiator.

Will try the CT differential phase control technology mentioned elsewhere when I have time...

d.

 

[thushar]

Have found a similar unit to power monitor on ebay : Business Building Kits items in Fair Trade Hub Shop store on eBay!

Hope it will be help to resolve your problem

 

[suntrap]

You mean a lower power heating element? Problem with those is that you then lose the versatility of the high power original if you need it. Advantage over diodes is that it doesn't mess up the mains current waveform.

A tip to delleray: use two diodes in parallel from the bridge (connect both AC terminals together) to reduce heat dissipation and increase reliability marginally.

 

[thushar]

Not the immersion heater. The link ( Business Building Kits items in Fair Trade Hub Shop store on eBay! ) does have an immersion heater control switch, which monitor the output of the PV and turn on the immersion when enough power is available .

 

[suntrap]

Oh you mean this? As you say, it only monitors PV power rather than exported power, so is really not a satisfactory solution because as soon as you turn on a kettle you will start to pay for the immersion heater.

 

[thushar]

Yes. they are good enough to use when the house is in standby - When no one is in the house. Working fine for the last one month with my install. It leaves 500W for the in house use - So will turn on the immersion automatically at above 1.5 kW PV production. I'm getting full tank of 60C ho****er even in feb with this setup- boiler hardly runs.

I have a immersion switch as well, will turn it off during weekend when washing machine is on.

 

[sharpener]

A bigger tip to delleray: it's illegal to do this because it puts a large direct current back down the mains. Someone else has posted the actual permissible limits, but you can be sure an immersion heater exceeds them by a very wide margin.

It's also dangerous for you because ordinary Residual Current Devices (ELCBs) don't work with a large d.c. component to the current, so you and your family will not be protected against electric shock any more.

For both these reasons it is preferable to use a step-down transformer e.g. a 240/110V site transformer to reduce the power to the immersion heater.

 

[bommels]

If you want to go the transformer route, you might want to consider these:
BLOCK Transformatoren-Elektronik GmbH :::: Products :::: Transformers :::: Product Details
Although an autotransformer would be good enough for the job, the price still lies between £130-160. But that is the price for smooth waveforms, I guess!

 

[Plotty]

Hi all,

Found this site via a PV thread: my eyes did glaze over as I waded thru all 44 pages.

I'm not an electrician or an engineer, nor am I interested in this field - I just want to use my free electricity to heat my hot water (apologies to those who think that's not green). However ...

it would seem to me that if a device monitored the pulse on the import meter so that it only switched on the immersion circuit when you're NOT importing, that would allow any excess PV electricity to be diverted to the immersion. (or is that too simple an idea?).

BTW, echase, claims for your system appear interesting, but there's too much secrecy to give me confidence - even your customers on this board are not willing to discuss something a simple as the price??

Would be good to hear about Sparqui's progress with that solution (post 338).

 

[echase]

Hi all,

I'm not an electrician or an engineer, nor am I interested in this field -

BTW, echase, claims for your system appear interesting, but there's too much secrecy to give me confidence - even your customers on this board are not willing to discuss something a simple as the price??
QUOTE]

This forum is mainly for people interested in sharing design ideas for solving this issue. I respect that so don’t clog what is already a very long and interesting thread with adverts for my design and I ask people who have my units not to do so either. Happy to receive Private Messages on it though and give out testimonials that way. I supply people with at least some electrical or electronic engineering expertise. It’s not for the beginner.