Immersion Heater - PV electricity

[Trader9]

Hi Peter

Can you send me a private message (PM) with your email address.

I am also working on a system to track the solar without any steps but the step system works so well I would be loath to change it. What most people don't realise is that you don't need to chase every watt as by midday your thermostat has switched off.

However, the new system will use the same interface but replace the relay board with a LED and LDR (Light Dependant Resistor) or as it is not commonly known a Vactrol. However, I had problems with oscillation which I may have found the cause.

Anyway PM me, and then get a Arduino with a printer lead to connect to your PC and get a screw shield for the Arduino too as this will enable you to connect wires easily to the Arduino. A screw shield I found on ebay for less than £5.00. If getting a 5V 8way relay board from ebay get one with terminals for input and output, they are available if you look around, as this will make the connections easier.

I will be in touch.

Regards, Trader9

 

[runthangs]

Hi runthangs

187Vac is way to high, as that is 1821Watts. You are never going to get that much spare solar on a regular basis, even in summer. What you need is a system that starts low, say 43.8 Vac for a 100W load and then increase as the solar increases. This is the only way you will get any power in the winter. It would be better to get 100W all day than 1821W for ten minutes.

I think if you do use an ebay 3800W dimmer, then I would increase the heat sink size and ensure good ventilation and don't put it in the immersion heater cupboard.

Thanks for the tips, you said 187W minimum in your previous post (I misquoted it as 187VAC), which I think is low enough. I think anything lower than 800W would take too long to heat up.

I was thinking my megaflo's metal cylinder could be used as a heatsink or one of the cold water pipes in the airing cupboard.

I've also ordered an energy plug monitor to measure the actual usage once I set the dimmer up. Only thing to complete my project is a decent way (i.e. no PCBs/soldering/re-wiring) to measure the actual house consumption - the british gas supplied ct wireless monitor records both consumption and generation so is pretty useless.

 

[runthangs]

How is the dimmer meant to be wired? Presumably whether the live or neutral is connected it doesn't matter? But which side is input vs output?i tried live in via the connector closest to the scr/heatsink, it worked for a few seconds then a bright spark and now nothing no matter which way or which wires I connect!

It says 220v only, whilst my supply is 240v so wonder if that's an issue?

The whole thing feels a bit unsafe so I might have to opt for a £50 site transformer if nobody has any other suggestions?

 

[echase]

What happened to all the other pages of this thread? Used to be 50+ and now down to 22. Or are there just more posts per page now?

 

[Fronius]

What happened to all the other pages of this thread? Used to be 50+ and now down to 22. Or are there just more posts per page now?

I'm puzzled too. I have this page saved as no. 69 ?

 

[Trader9]

Hi runthangs

Unfortunately you wired it up wrong I reckon.

I normally take the switched and fused live wire to one side of the immersion heater and the neutral back from the immersion goes to one terminal on the dimmer and the other dimmer terminal goes to neutral. Basically the heater and the dimmer switch are in series. If you prefer you can put the dimmer in the live side, but that is not how it is wired in most of the diagrams I have seen. Also it is good practice to have a fast blow fuse in the circuit to protect the triac. Rapid electronics do a do a DIN rail fuse holder that takes high speed fuses.

Good job those ebay dimmers are cheap, as it sounds like you need a new one.

Regards, Trader9.

P.S. If you are going down the transformer route make sure it is twice the size of the load you intend to supply as those transformers are not continuously rated i.e. a 1kW load will need a 2kVA transformer. Also you may have problems with you B type circuit breaker tripping when you switch it on, due to the inrush current. If so you will need to change your circuit breaker for a type C one. All adds to the fun.

 

[runthangs]

Hi runthangs

Unfortunately you wired it up wrong I reckon.

I normally take the switched and fused live wire to one side of the immersion heater and the neutral back from the immersion goes to one terminal on the dimmer and the other dimmer terminal goes to neutral. Basically the heater and the dimmer switch are in series. If you prefer you can put the dimmer in the live side, but that is not how it is wired in most of the diagrams I have seen. Also it is good practice to have a fast blow fuse in the circuit to protect the triac. Rapid electronics do a do a DIN rail fuse holder that takes high speed fuses.

Good job those ebay dimmers are cheap, as it sounds like you need a new one.

Regards, Trader9.

P.S. If you are going down the transformer route make sure it is twice the size of the load you intend to supply as those transformers are not continuously rated i.e. a 1kW load will need a 2kVA transformer. Also you may have problems with you B type circuit breaker tripping when you switch it on, due to the inrush current. If so you will need to change your circuit breaker for a type C one. All adds to the fun.

So, I discovered that it wasn't dead after all. The solder/copper on the pcb had been burnt away from the sparks, so the connection wasn't being made. I sorted it by running some wire over the burnt out joints, it has been running fine today, but I don't keep it on for more than 20mins without a short break because the small heatsink gets very hot. I ran the live through it, I can try neutral but not sure it makes any difference at all?

I have found my old soldering iron and solder so will solder the wire on properly, also have found a long slab of aluminium to extend the heatsink with.

Weird thing I found is that the solar pv inverter buzzes a lot louder now when the triac is running (which also hums a lot) vs when the triac isn't on. Normally the inverter buzzes more when the sun gets brighter - i hope this won't play havoc with my solar generation or electricity usage meters??

The last "bad" thing is that my electrical tester screwdriver shows that the body of the potentionmeter is live, and so is the heatsink. There are no live wires touching either though!?

 

[Trader9]

Hi runthangs

That is why I always use the neutral, as it is safer.

I also suggest you get a bigger heat sink and even consider a small cooling fan. I did some tests the other day on a 25A SSR VA (25A variable output solid state relay) which came mounted on a commercial size black heat sink and I was surprised just how hot hot it got in just a few minutes. If I are using this I would fit a fan.

I have been working on an automated system using an Arduino microprocessor to replace the potentiometer with varying resistance as more solar is available, but have failed, as once the triac comes on the harmonics (your buzzing) cause the Arduino current sensor to read much higher current than the theoretical load should be. Which then increases the resistance thinking the load is now more than the solar. Then the solar tries again and so on.

Been driving me nuts all week.

If it makes you feel any better I actually drilled a 110mm hole in the bottom of my 3.3kVA transformer casing, then mounted the transformer off the base and fitted a mains fan underneath to supply cooling up around the transformer and out the top. As even though my max load is only 1,320W and the transformer is contunuosly rated at 1,6500W it still gets very hot after being on for ten hours.

Regards, Trader9.

 

[echase]

There is something seriously wrong with your design if it's coughing out that much heat. A good design will not do this.

 

[Trader9]

Hi echase

Were you referring to the triac dimmer or my transformer system.
Even with no load after the thermostats have switched off the transformer still runs warm. My guess is that it must be drawing at least 30W with no load.
My system only switches 160W, 320W, 660W, 820W or 1,320W, so at no time do I ever get near the 1,650W continuos rating. But on a long sunny day it got hotter than I liked although the thermal trip has never operated. So I decided to add cooling for those long hot summer days. Ambient temperature's in my garage are normally less than 20 degrees.

As for the SSR getting hot after a few minutes testing with a 19.2 ohm resistive load, this was unexpected, as the heat sink was substantial and I had added heat transfer paste to ensure max heat transfer. The max load was 12.02 amps so less than half the 25A rating and for only how long it takes to take reading at every half amp.

Incidentally, the Arduino I was using for the testing was always showing about 2A higher currents than the Fluke meter or calculated currents from the voltage readings, but at maximum voltage all the currents more or less agreed. I suspect the triac switching is is creating a lot of harmonics which are effecting the current transformers. But have no answer as to why the SSR got so hot so quick. The SSR is controlled by input resistance between 0 - 500k from a potentiometer, so not a lot you can do about that design.

I did try adding a mains filter but it had no effect on any of the readings.

Any ideas would be more than welcome.

Regards, Trader9

 

[echase]

Hi echase


As for the SSR getting hot after a few minutes testing with a 19.2 ohm resistive load, this was unexpected, as the heat sink was substantial

I am not familiar with your design as not read all the thread but a SSR should drop about 1.2 V. So for every 1A flowing it is dissipating 1.2W which means a 3kW heater causes 14W of dissipation in SSR when fully on. That is not a lot but it does need a small heatsink of a few square inches. I get the impression that yours is dissipating more than that but I don’t know why.

 

[suntrap]

I also have some of the SSR-25 VA that Peter mentioned and that is a far better bet as it goes down to low voltages and comes mounted on a better heat sink and all for only £9.99 from Hong Kong. Lower input current too.

Do you have a link for this please? I can only find them much pricier. Thanks.

By the way, I've suggested before that you ought to be able to use a washing machine filter to reduce EMI - they are a lot cheaper than the specialist filters.

 

[Trader9]

Do you have a link for this please? I can only find them much pricier. Thanks.

By the way, I've suggested before that you ought to be able to use a washing machine filter to reduce EMI - they are a lot cheaper than the specialist filters.

Hi Suntrap

Open Ebay and search using SSR-25VA Resistance Type Adjustable SSR Solid State Relay 25A w Heat Sink

The cheapest in the list was £8.39. Bigger heat sinks are also available for about £4.00.

I will look again at washing machine filters.

Regards, Trader9.

 

[suntrap]

Ah thanks - I was expecting Fotek-branded which is why my search wasn't coming up with anything.

They are incredibly cheap - I wonder why? Are they definitely isolated? Does the pot have a constant current flowing through it?

 

[echase]

Some of the stuff on eBay from HK and China is OK but some not. I bought a simpler SSR for <<£10 from one such firm and it behaved in a very strange manner, so you might be lucky and might not. It will probably be opto isolated but maybe not with as high an insulation resistance as is really safe.