Immersion Heater - PV electricity

[brianboru]

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
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

 

[Millerman]

Brian, See posts 90 and 74 for contact details

 

[brianboru]

Thanks Andy. I'll be in touch.

 

[MBE Contracting]

wow, that sounds like a product that could do very well. Could you please give some more details. Kind regards Mick. MBE solar.

 

[Millerman]

Mick, please contact me via post 90 / 74

Andy

 

[echase]

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?

 

[inie meanie]

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.

 

[pauldreed]

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?

This is an interesting article which discusses this aspect http://bit.ly/m1sLDY
I think that it's not so bad with resistive loads.

 

[Millerman]

burst firing is the way to go no problem with EMC. Talking to a company to develop a unit,,,,, more later

 

[inie meanie]

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.

 

[Millerman]

inie hi

well it must be the way i have it working with my PLC because there is no consumpstion from the Grid.

 

[inie meanie]

You can see how that burst mode by definition will fire at full power for a time period? Have you accurately measured the current at the meter with a scope or with a phase referenced meter? The reason you may have not seen it is because you may have had a generous supply from the pv at the time. You will see a draw from the grid under more difficult conditions i.e. when you only have a couple of hundred watts to spare from the pv and you then load up your immersion heater.

 

[Millerman]

As of yet i have not put my scope on the grid supply and have only set the unit to "work" when there has be 700watts free.

 

[bigbob1]

Tell me more Mr Millerman, don't suppose it's called an EMMA? link me to your website i may be a mass customer. Before you change your tank and mess about with it have you tried leaving your immersion turned on and seeing if it heats up? because you might be surprised that in 6 hours it will be hot enough to have a shower etc that is if you just want a tank full of water. try it.

 

[bigbob1]

note to one's self >> check there's not a million pages after the first one lol

 

[inie meanie]

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?

I have been reading up about this issue. Initially I thought it wasn't a problem but with further investigation the triac requires some form of suppression. The particular model I have chosen turns out to have a built in snubber in the package ( 10PCV2425 crydom I contacted tech support at Crydom today ) this is why I haven't seen any evidence on interference. This happens to be the same unit that the EMMA uses so it has pedigree. :- ) As an update from my previous notes I have decided to fit a Henley block and an extra 2 way dist board to make the current measurements easier as I was struggeling to fit all my wires through the current coil. This will be a much neater installation.

 

[Millerman]

Okay firstly BigBob1 i do leave the immersion switch on. It will not work unless there is enough spare solar power.
Yes some days the tank doesn't get very warm (dull days) but every bit of heat input from the solar reduces the amount of gas needed to riase the water temperature to the desired setpoint. Overall the water temperature has been fine. The unit is not an EMMA similiar but not the same. Give me a ring to discuss further if you wish.(07717723352)send txt message first don't answer unknown numbers.

Quote" As an update from my previous notes I have decided to fit a Henley block and an extra 2 way dist board to make the current measurements easier as I was struggeling to fit all my wires through the current coil. This will be a much neater installation." ----- Its the only way really

 

[suntrap]

Hello - I found this wonderful thread having had the same immersion heater idea and having searched around. I haven't got panels yet but one installer says they always put in a separate RCD-protected consumer unit just for the inverter in order not to infringe on Part P if the existing wiring doesn't comply. A bit more material cost but seems like a good idea, and I've got a Henley block between my meter and CU anyway so it's easy for them. I have an old electric shower feed to the loft which I hope they can use; I would have thought that if it tests out OK then it would be fine, but I am not qualified so I don't know.

I don't think anyone on this thread has mentioned the case of their existing meter being analogue. I know these can theoretically go backwards but I wondered if they had some sort of ratchet to prevent it. My meter was replaced in late 2008 with another analogue one, and the installer said that it would indeed go backwards. Could I really therefore be paid three times for some of what the panels generate? I presumably won't have the trouble/fun of making an immersion heater controller as a result. I wouldn't be surprised if the supplier, when informed of the solar installation, doesn't immediately whip out the analogue meter and replace it with a digital one.

 

[inie meanie]

Hi Suntrap
Yes your meter will go backwards during the day then forwards at night. Unfortunately you are under obligation to inform your supplier and they will change it after a month or so. My next door neighbor has this exact situation. his meter reading at the end of the month is less than when he started. So until it is changed there is no benefit to add a water heater circuit, but nothing like being prepared :- )

 

[suntrap]

Thanks for that - so informing them does more than just "keeping the grid balanced" :smartass:. They would think I'd been bypassing the meter otherwise, anyway. If the inverter has a separate CU, I presume that will make it easier to fit current transformers.

I've noticed someone has written Linux software for getting data from Aurora inverters (RS232/RS485). Their desktop monitor is pretty but very expensive. At some stage I want to play around with plug computers and this could log the data.

 

[pauldreed]

If a Phase Angle Controller is able to restrict the amount of recorded power usage, would a simple series diode result in a 50% power reduction.
ie. does the electricity meter measure power usage over 180 or 360 degrees of the mains cycle??

 

[suntrap]

I would say yes, it records real power consumption, multiplying volts by amps continuously. That's what an analogue one does and a digital one would be designed behave the same or it would be naughty. Non-domestic meters measure VA rather than watts, encouraging customers to correct their own power factor/current waveforms.

 

[inie meanie]

I am very pleased to say that I have completed my system. I have heated the top part of my tank very quickly. ( only as deep as the length of the immersion heater ) I raised water temp 10 deg before the solar water system had got up to temperature and started to circulate. This was important as some people have said this system won’t work quickly enough and this proved it is much faster than the water type system. Also to confirm that I have had NO interference generated by the triac effecting either the radio or tv (10pcv2425 contains a snubber circuit ). This system, just to confirm doesn’t use an expensive plc and follows the spare power level in an analogue way NOT waiting until there is a spare 1,2 or 3 kw before switching on in steps and thus wasting potential energy. It runs as soon as there is a spare 100 watts and continues to feed all the way up to full power 3kw. All it contains is a small comparison circuit made from 2 opamps ( 741, 75p each ). I triac crydom 10pcv2425 ( just bought one on eBay for £12 ) . A power supply that provides -12 0 +12 vdc, 2 current coils from LEM model AT20B10 ( £ 54 inc vat for the two ). I have fitted and extra dist board with a Henley block to separate the measurements. I now need to find a nice box to put it all in and maybe add a couple of voltage meters form eBay just to make it very easy to see what power is being supplied. The future improvements would now be to add another heating element to the bottom of the tank and a relay circuit to switch between the elements once the top one is up to temp. I hope this will encourage some of you to develop your system. It just goes to show there are several routes to achieve free hot water. :- )

 

[Andy_WSM]

Following this thread with interest as I am also on the look out for a device to divert my spare PV energy to my hot water tank.

 

[suntrap]

Well done on getting it going and it would be great to see a circuit diagram. However, one thing concerns me slightly:

Also to confirm that I have had NO interference generated by the triac effecting either the radio or tv (10pcv2425 contains a snubber circuit ).

I believe a snubber network is primarily to prevent the triac being damaged by high voltage ringing when it switches off. It is not sufficient to provide proper filtering of electromagnetic interference - for this you need a series inductor at least, as contained in light dimmers. You might not get interference on FM radio or TV, but you are very likely to hear it in MW or LW transmissons and it may become apparent on FM and TV when the wanted signal is weak.

 

[inie meanie]

Well done on getting it going and it would be great to see a circuit diagram. However, one thing concerns me slightly:



I believe a snubber network is primarily to prevent the triac being damaged by high voltage ringing when it switches off. It is not sufficient to provide proper filtering of electromagnetic interference - for this you need a series inductor at least, as contained in light dimmers. You might not get interference on FM radio or TV, but you are very likely to hear it in MW or LW transmissons and it may become apparent on FM and TV when the wanted signal is weak.

Yes this might be the case but IF there is some interferance I will add a circuit to resolve it. SO far so good :- ) No problems.

Hey Suntrap have you actually experienced any problems with interferance? As I havent seen any thing yet.

 

[suntrap]

I have experienced problems with interference from cheap switch-mode power supplies imported straight from China, which don't have input filters fitted - they wouldn't be allowed under EU emissions regulations. I haven't built anything like this yet so can't comment, but it may be that you are causing interference to your neighbours' equipment which you don't know about and which your neighbours won't know the source of. It could disrupt ADSL communications as this uses the lower frequency range. I can imagine that your circuit may severely disrupt power-line networking equipment, but that is very controversial with radio amateurs because it causes interference problems of its own!

 

[inie meanie]

Hi Suntrap. Well today I had the tv on the radio and my wireless router. No problem at all. I understand your concern and I will watch it very carefully. Do you have any suggestions for adding some protection? I would be happy to add it even if it wasn't required just to be on the safe side.

 

[suntrap]

I guess you'd look at circuits for light dimmers and see what they use. Unfortunately you'd need quite a hefty inductor to handle 13A though.

 

[Millerman]

Hi Suntrap
. Unfortunately you are under obligation to inform your supplier and they will change it after a month or so. :- )

My parents have had their system since last december. the electricity board came out and installed an isolator on the instructions given to them from the solar company. As of now they still have the old analogue meter good luck to them.