Auto switchover relay

[lonnie]

Firstly, apologies if this has been answered elsewhere but I couldn't find anything after quite a bit of searching!

I've been considering installing a switch over relay and have found a number of threads on here really useful (esp DBK 's ) and have a question specifically about my setup. I currently have the 2kw invertor feeding two seperate (new) sockets) and all existing sockets are powered from the Elddis power distribution unit.

The biggest question I have seen on this is to ensure that the other items (charger/ fridge/ heating) is isolated so my plan is;
1. Remove the input cable from the 16a sockets MCB and connect these to the NO on the relay
2. Connect the output of the invertor to NC on the relay
3. Cable the common on the relay to the input of the sockets MCB.

Also, I was considering connecting the two 'new' sockets (that would now be redundant) to the output of the sockets MCB - so all sockets are then protected by the RCD.

Does anyone see any issues with this approach please?

TIA, Martin

 

[DBK]

Where are you connecting the coil of the relay to? I'm guessing you are connecting it to the EHU side so when connected to power the relay closes.

You might want to consider swapping this over so it is powered by the inverter output. You then route EHU power through the NC contacts and inverter output through the NO.

The benefit of this if you are on a low amperage EHU you can fire up the inverter and it will automatically switch the sockets over to the inverter. Wired your way you have to unplug the EHU before you can use the inverter. This is the way mine is wired and it isn't a problem but I may one day swap things over.

 

[autorouter]

The MCBs are double-pole, which is correct for motorhome mains wiring. Your idea is basically correct, but needs a double-pole changeover relay, also called a Double Pole Double Throw (DPDT) relay. As opposed to the more common single-pole relay, called Single Pole Single Double Throw (SPDT). This is so that both Live and Neutral can be switched together.

Then you have to make sure the relay coil voltage is 230V, not 12V or any other voltage like 24V which is quite common. The Live and Neutral wires from the MCB go to the NO terminals of the relay, as you say. Run a couple of link wires from these two terminals to the two coil terminals, so that the relay switches when the hookup is plugged in.

That's the usual way to wire a transfer relay, but DBK has described the other way which you could also consider.

In your picture it looks like there is a bit of space in your mains box. You can get a DPDT relay that mounts on the DIN rail like the RCD and MCBs, that would be quite a neat arrangement.

 

[lonnie]

Where are you connecting the coil of the relay to? I'm guessing you are connecting it to the EHU side so when connected to power the relay closes.

You might want to consider swapping this over so it is powered by the inverter output. You then route EHU power through the NC contacts and inverter output through the NO.

The benefit of this if you are on a low amperage EHU you can fire up the inverter and it will automatically switch the sockets over to the inverter. Wired your way you have to unplug the EHU before you can use the inverter. This is the way mine is wired and it isn't a problem but I may one day swap things over.

Great shout, thanks John.

p.s. really enjoyed your 'Two go to' books

 

[lonnie]

Thanks

The MCBs are double-pole, which is correct for motorhome mains wiring. Your idea is basically correct, but needs a double-pole changeover relay, also called a Double Pole Double Throw (DPDT) relay. As opposed to the more common single-pole relay, called Single Pole Single Double Throw (SPDT). This is so that both Live and Neutral can be switched together.

Then you have to make sure the relay coil voltage is 230V, not 12V or any other voltage like 24V which is quite common. The Live and Neutral wires from the MCB go to the NO terminals of the relay, as you say. Run a couple of link wires from these two terminals to the two coil terminals, so that the relay switches when the hookup is plugged in.

That's the usual way to wire a transfer relay, but DBK has described the other way which you could also consider.

In your picture it looks like there is a bit of space in your mains box. You can get a DPDT relay that mounts on the DIN rail like the RCD and MCBs, that would be quite a neat arrangement.

Thanks for the quick feedback and advice on the relay.

I've ordered the relay and socket...

....and like you say, would be really tidy if I can get then on the rail.

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[DBK]

Thanks

Thanks for the quick feedback and advice on the relay.

I've ordered the relay and socket...

View attachment 791804View attachment 791805


....and like you say, would be really tidy if I can get then on the rail.

If you've read my "adventure" on this subject you might remember my problem finding a relay which was rated at sufficient current both closing and opening. Some relays have a high closing rating but much lower opening.

It isn't a problem if you disconnect all loads before turning the inverter off but it is best to use properly rated components.

 

[autorouter]

and like you say, would be really tidy if I can get then on the rail.

I was thinking of something like this:

IK8701.12 AC50HZ 230V | Dold DIN Rail Power Relay, 230V ac Coil, 16A Switching Current, DPDT | RS

uk.rs-online.com

 

[lonnie]

I was thinking of something like this:

IK8701.12 AC50HZ 230V | Dold DIN Rail Power Relay, 230V ac Coil, 16A Switching Current, DPDT | RS

uk.rs-online.com

I like that. Very compact. Thanks for the recommendation.

Hopefully I can return the Finder kit

 

[EuroTrotters]

The late Andy known as Techno detailed a lot on this subject. As did another late member

 

[Googlebot]

There is a thread on this in my signature. Several people really helped me.

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[lonnie]

The late Andy known as Techno detailed a lot on this subject. As did another late member

Thanks, I'll check those out too.

 

[lonnie]

There is a thread on this in my signature. Several people really helped me.

Really helpful too, thanks.

I've also spent the last few minutes reading your other signature threads as I've just fitted a Maxxair and am just about to fit an awning strip!

 

[lonnie]

The MCBs are double-pole, which is correct for motorhome mains wiring. Your idea is basically correct, but needs a double-pole changeover relay, also called a Double Pole Double Throw (DPDT) relay. As opposed to the more common single-pole relay, called Single Pole Single Double Throw (SPDT). This is so that both Live and Neutral can be switched together.

Then you have to make sure the relay coil voltage is 230V, not 12V or any other voltage like 24V which is quite common. The Live and Neutral wires from the MCB go to the NO terminals of the relay, as you say. Run a couple of link wires from these two terminals to the two coil terminals, so that the relay switches when the hookup is plugged in.

That's the usual way to wire a transfer relay, but DBK has described the other way which you could also consider.

In your picture it looks like there is a bit of space in your mains box. You can get a DPDT relay that mounts on the DIN rail like the RCD and MCBs, that would be quite a neat arrangement.

Daft question but can I assume on the Dold relay the link wires will go from A1/A2 to 14/24 (NO)?

 

[autorouter]

Yes, 14/24 for the method I described. Automatic switch to hookup when hookup is plugged in, and back to inverter when hookup is disconnected. Or 12/22 for the other method described by DBK. Automatic switch to inverter whenever the inverter is on, and back to hookup when inverter is off.

 

[lonnie]

Great, thanks again.

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[lonnie]

Yes, 14/24 for the method I described. Automatic switch to hookup when hookup is plugged in, and back to inverter when hookup is disconnected. Or 12/22 for the other method described by DBK. Automatic switch to inverter whenever the inverter is on, and back to hookup when inverter is off.

Well, would you know it? It only bl**dy works

The relay came from RS today and fits perfectly in the space I had left on the rail and the cover. It was cabled as per your suggestion but will be easy to swap to DBK 's setup if I find the sites we (infrequently) visit are low amperage.

So...

• I moved the 16a MCB to the other end so I could snip down the bus bar and feed the relay independently of the other MCBs (I put some heat shrink on the ends to insulate the now bare copper!). These went into 14/24 (NC) along with the link wires from A1/A2
• Inverter output went into 12/22 (NO) with an earth to the bus in the distribution unit
• Common output (11/21) went into the bottom of the sockets MCB
• I also took a an additional lead (earthed to the earth bus) from the output of the sockets MCB into a junction box that fed the two sockets I'd added for the invertor a few months ago.

So everything appears to be working fine and the relay switches seamlessly with a very quiet click when I plug/ unplug the EHU with the invertor on. However, I have a query re the behaviour of the RCD if if that's ok?

I tested the following whilst boiling a kettle! Btw, the results were the same irrespective of whether the kettle was in an original outlet or one I'd installed myself.

	EHU	Invertor	RCD Result
Test 1	On	Off	Trips & stops
Test 2	On	On	Trips and switches to Invertor
Test 3	Off	On	Doesn't trip

I'd be really grateful if you could spot any 'school boy errors' as I don't think this the RCD behaviour is correct

I was going to draw a diagram but a picture paints ... etc

Again, I appreciate any help you can provide, thanks!

p.s. it does look very neat

 

[autorouter]

Is it just when you use the kettle, or is it the same with any other appliance? A kettle can have a slight insulation failure which trips an RCD, but it will work OK on a circuit that doesn't have an RCD.

 

[lonnie]

Having read my post back I realised I've been asking too much of funsters and I need to educate myself more!

I've found a few more threads (that you've contributed to) re the earthing so I just a bit of time to get my head around it .

I'm currently studying about the impact on batteries with inverter usage as the inverter is failing with a low voltage error after less than two minute on the microwave - but that's for another post

Btw, apologies for any confusion but when I was testing the RCD, I was just pressing the test button. I was justing using the kettle as a convenient device I could tell was off or on.

Once again, thanks for the time you've taken to help

 

[autorouter]

when I was testing the RCD, I was just pressing the test button. I was justing using the kettle as a convenient device I could tell was off or on.

In that case it's working as expected. The RCD is on the hookup only, so if the hookup is on it trips when the test button is pressed. If the inverter is not on, the power to the socket goes off. If the inverter is on as well as the hookup, the hookup goes off, so the relay flips to the inverter and the power stays on. If the hookup is off, the test button doesn't trip (it needs a mains supply for it to trip).

 

[Heather Van]

Hello Folks,
Just joined the group, after spending literally hours trying to understand this bit of the puzzle "how to get the power from my inverter into my 240v consumer unit".
This site is full of very clever people.
Thanks everyone

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[Googlebot]

Welcome!

Might be best starting a new thread.

It has to be wired to do so, telling us what vehicle and kit you have will let people know what you need.