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Relay for 4.5kW Immersion


Johnnyt

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I have a 10kWp array up and working and am awaiting battery and DHW divert to be fitted all to be SolarEdge.

The DHW divert can take up to 5kW resistive load and hence after much searching I found a single phase 4.5 kW immersion  and it is fitted.

It’s only 10ft from the consumer unit and has a direct 4mm feed.

The literature with the immersion suggests a relay to be fitted.

My query is what size relay is appropriate and will this  have any issues when the PV generation is say delivering a lower rated current say if the surplus PV power is 500w to the immersion or anywhere in the range.

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On 19/02/2022 at 16:45, Johnnyt said:

I have a 10kWp array up and working and am awaiting battery and DHW divert to be fitted all to be SolarEdge.

The DHW divert can take up to 5kW resistive load and hence after much searching I found a single phase 4.5 kW immersion  and it is fitted.

It’s only 10ft from the consumer unit and has a direct 4mm feed.

The literature with the immersion suggests a relay to be fitted.

My query is what size relay is appropriate and will this  have any issues when the PV generation is say delivering a lower rated current say if the surplus PV power is 500w to the immersion or anywhere in the range.

I would use a 32A contactor, 25A would work too, but it's only just over 5A greater than max load, I like more spare as the contacts will be better sized.

 

Second question depends on control hardware/software.

 

Some heaters for PV work on a variable input, so if you have 500W it will take 500W, some however wasn't their full rated input all the time in which case you need to spare 4500W. I personally would have gone for a couple of smaller elements and banked them up as power was available, but you could use the variable input control perhaps and mitigate this issue. 

 

 

Edited by Carrerahill
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Thanks for your input.

 

4 hours ago, Carrerahill said:

I personally would have gone for a couple of smaller elements and banked them up as power was available, but you could use the variable input control perhaps and mitigate this issue. 

 

Me too, this was my initial thoughts but the UVC (500l) arrived unbeknowns with only one pocket for an immersion.

Rather than return it with resultant delays, I decided to press on with the knowledge that the diverter could accommodate a 5kW immersion.

Little did I know the difficulting in sourcing same with the correct thread.

I've been in touch with solar edge technical who say the diverter can accept a minimum of 5% of the load rating, so hopefully all should be fine.

Edited by Johnnyt
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