Immersion Heater - PV electricity

[inie meanie]

The owl on the house load reads about 10% high because it's conversion of the current transformer does not work accurately on non sine wave currents. The meter confirms that over the last three months I have only exported 5%.

Have a look at the AD637 Rms to dc converter. I have ordered a couple as I hope to buffer the house signal then compare the same way with opamp. I hope this will improve the acuracy and reduce any export. I will post as soon as they turn up. Christmas post and all that.

 

[bradburts]

I thought that the B Gas kit is already available.
Its only a relay switched from what I can understand, no phase control.

 

[pmcalli]

Have a look at the AD637 Rms to dc converter. I have ordered a couple as I hope to buffer the house signal then compare the same way with opamp. I hope this will improve the acuracy and reduce any export. I will post as soon as they turn up. Christmas post and all that.

Good luck I have used them in the past and they have limitations on crest factor and sensitivity. rms even if it is derived accurately is only an approximation. to get an accurate imitation of the meter you need to integrate the current over a cycle. interested to see your results when availble

 

[pmcalli]

I thought that the B Gas kit is already available.
Its only a relay switched from what I can understand, no phase control.

I haven't seen any offering yet only press statement about acquisitions and trials.

 

[bradburts]

May be wrong, and have lost the link, but check the company who supply the BG monitors.
They have a control product on their site as well. From memory it was <<£100.

 

[Sunnydaze]

Does anyone have a smart meter yet? I just wondered whether they do actually sense current direction. I can't find any model info / technical specs.

 

[sharpener]

Surely that is exactly what sharpener is proposing, by using an analogue multiplier to multiply the CT output with the voltage waveform?

Correct. The analogue multiplier will multiply the current and voltage waveforms correctly whatever they are. This is a better approach as it uses the actual voltage waveform, rather than a square wave as in synchronous rectification or a synthetic sine wave as the openenergymonitor people do, and so averaged over one cycle gives true instantaneous power.

Also the cost to me is zero because I still have a few AD532s from when I used to use them a lot in laser scanning systems. One of the difficult situations is when the immersion heater is drawing half power, as the current will change sign abruptly at the 90 deg point in each cycle when the triac fires. But with suitable scale factors I expect it to handle this OK as the bandwidth is several hundred kHz.

BTW thanks suntrap for the links to Home | OpenEnergyMonitor, which I am still exploring (using Chrome not Firefox, I hope you approve <g>). I will use a separate winding for the voltage sense input and the transformer will be very lightly loaded, which will I hope avoid the phase shift issue in both primary and secondary. By using true precision analogue computation a lot of the other problems the Arduino community have encountered should be avoided too.

Does anyone have a smart meter yet? I just wondered whether they do actually sense current direction. I can't find any model info / technical specs.

They have to or they would not be able to discriminate between imported and exported power! There is a teardown report on one here Elster REX2 Smart Meter Teardown - iFixit but it is mainly concerned with the physical construction, has anyone got a more informative link?

 

[UKMeterman]

Hi all,
If you have the cash consider puttin a nemo96 in a plastic box and use a Hobut 100A|5A clip on tradional CT

 

[Rogerhillside]

Hi
Have just has 3.55kw PV system fitted. While I have a combi boiler hence no water tank. Intend to fit water tank with 2 3kw immersions and want to buy a controller as outlined in this thread. But would like it to also control a valve for in winter or dull days when the water is cold is uses the combi. Any suggestions?

 

[suntrap]

Are you aware that as this will all be under mains pressure, you can't use a standard hot water cylinder but need an expensive high pressure system? It will take an awful long time to recoup the cost. Also, is the idea of two immersion heaters that you will use them in parallel when you have >3kW spare? This will only be for very short periods in high summer when you're likely to have far more spare capacity than you can use, so I wouldn't worry about a second one. You'd also have to make sure you divert all power to the lower one most of the time (if at different heights) or you won't heat the whole tank.

 

[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?