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Author Topic: Switch between Two Immersion heaters powered from PV panels  (Read 4422 times)
Gareth J
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« Reply #15 on: October 14, 2019, 08:40:47 PM »

I built exactly this setup for my boost.

It's a bit "outside of the box" and does mean that a relay is in the "energised" state when the water is cold but it works well, especially spring/autumn when diverted energy is a bit less.



You need a NO/NC relay which aren't that easy to find (think mine was a 20A garo one) which flip/flops between the top and bottom tank.

Or you could buy an boost+ which has the functionality built in and will be a lot easier to install.
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ecogeorge
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« Reply #16 on: October 14, 2019, 09:58:59 PM »

I used a very similar thing but in reverse.
Bought a NO/NC contactor.
Wired top immersion through NC contacts so always heating with no coil load/consumption.
Used thermostat with NO/NC contacts -when temperature satisfied NO switches to closed and provides power to contactor. This then energises and closes NO circuit heating the bottom immersion (or another tank).
The benefit of this is that the contactor is only energised when the first immersion is satisfied ,thereby minimising power consumption.
George
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Gareth J
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« Reply #17 on: October 15, 2019, 11:48:24 AM »

Interesting. I would have liked to (and still would like to) have it the other way round so the NO/NC relay is only energised when top tank is hot. Not so much for energy consumption, the power draw is pretty low, bit it seems a better, safer way about things.

The only thing is I couldn't think of a way to use the top thermostat to energise the relay when it's hot. The nature of the thermostat is that it opens when the tank is up to temperature so how to get it to energise the relay once it is open?

The system's downfall has come about this autumn as the iboost has the functionality to heat just the top tank with mains (e7) and ignore the bottom tank. I'll scratch my head again but think I've lost that functionality now.
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Countrypaul
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« Reply #18 on: October 15, 2019, 02:22:02 PM »

Interesting. I would have liked to (and still would like to) have it the other way round so the NO/NC relay is only energised when top tank is hot. Not so much for energy consumption, the power draw is pretty low, bit it seems a better, safer way about things.

The only thing is I couldn't think of a way to use the top thermostat to energise the relay when it's hot. The nature of the thermostat is that it opens when the tank is up to temperature so how to get it to energise the relay once it is open?

The system's downfall has come about this autumn as the iboost has the functionality to heat just the top tank with mains (e7) and ignore the bottom tank. I'll scratch my head again but think I've lost that functionality now.

Surely what ecoGeorge has posted is exactly what you are describing as your desire. That is the contactor is only energised when the first immersion is satisfied - ie. the water is hot.

Getting the right thermostat as EcoGeorge has described (one with both NC and NO contacts) is the only non standard part to me.

Not sure how well it would work with an iBoost as at low power levels the contactor might be switching too often, unless it has some sort of delayed action.
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Gareth J
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« Reply #19 on: October 15, 2019, 05:47:31 PM »



Getting the right thermostat as EcoGeorge has described (one with both NC and NO contacts) is the only non standard part to me.


Ah, that's the missing bit in my understanding, I wasn't aware that a NO/NC thermostat existed. Will have a google around.

Just surmising if I can (safely) make just the top tank boost overnight.
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pj
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« Reply #20 on: October 16, 2019, 03:25:56 PM »

I used a very similar thing but in reverse.
Bought a NO/NC contactor.
Wired top immersion through NC contacts so always heating with no coil load/consumption.
Used thermostat with NO/NC contacts -when temperature satisfied NO switches to closed and provides power to contactor. This then energises and closes NO circuit heating the bottom immersion (or another tank).
The benefit of this is that the contactor is only energised when the first immersion is satisfied ,thereby minimising power consumption.
George

This can be done passively without a contactor or relay. Some tank thermostats with NC/NO outputs will also switch 16A (3.8kW) directly through those contacts, thus fine for a 3kW immersion.

So, using two separate thermostats, one at the top and one lower, feed the diverter output to the CO (common input) of the top thermostat. Take the top thermostat NC output to the top immersion. Take the top thermostat NO output to the CO of the lower thermostat. Then take the NC output of the lower thermostat to the lower immersion.
Job done.
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Gareth J
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« Reply #21 on: October 18, 2019, 07:28:13 AM »

Anyone got a link a NO thermostat? I can't seem to find any.
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pj
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« Reply #22 on: October 18, 2019, 10:44:41 AM »

Try googling Salus CT100
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TT
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« Reply #23 on: October 18, 2019, 01:17:12 PM »

It's the relay that need the N/O and N/C connections
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Countrypaul
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« Reply #24 on: October 18, 2019, 01:53:47 PM »

It's the relay that need the N/O and N/C connections

I think you've missed part of the thread, they are looking at a solution without a relay now.
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pj
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« Reply #25 on: October 18, 2019, 02:10:58 PM »

It's the relay that need the N/O and N/C connections

I think you've missed part of the thread, they are looking at a solution without a relay now.

That's right. The thermostat itself contains the change over switch, there's no need for a separate relay.
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TT
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« Reply #26 on: October 18, 2019, 04:48:27 PM »

https://www.myson.co.uk/static_files/my/media/downloads/MCT1_Installation_Instructions_V3.pdf

Link to another stat with No/Nc connections
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pj
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« Reply #27 on: October 19, 2019, 06:33:52 PM »

And three more...

https://www.tlc-direct.co.uk/tcl/search?query=cylinder+thermostat&Submit=Search

Horstmann, Sangamo and Timeguard. All changeover types, 16A resistive.
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Gareth J
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« Reply #28 on: October 20, 2019, 06:14:36 PM »

Brilliant! Nice one, thanks.

I'd not considered that type - only the slide in probe type but should work if I decide to rearrange things.
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Countrypaul
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« Reply #29 on: October 20, 2019, 11:35:14 PM »

You can alwaya leave the slide in one in place to act as a safety overheat limiter in case the external one fails in some way for example someone knocks it loose
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