Confusing Contactors!

[antonyc]

Hi everyone!

I need a contactor/relay but I'm really stuck!

This is my situation:

I have a solar inverter, mains, and my office. I want both the solar and mains to power the office (but ofcourse not at the same time). I want the contactor to do the following:

If the solar inverter is supplying 240v, then power the office using this, if not, power the office with mains.

This is my understanding:

• I need a 240v contactor.
• The contactor needs a 240v coil.
• The contactor needs 3 output terminals?
• It needs 3 input NO terminals.
• It needs 3 input NC terminals.

I obviously need the solar L and N to be on the coil to energise it.

I also need solar L, N and E on the NO terminals.

I need mains L, N and E on the NC terminals.

Where will the 3 output terminals go?

I have a contactor here by Schneider electric, model number CAD32. How can I wire this up to do what I need?

Thanks in advance, Antony!

 

[DetlefSchmitz]

Sounds a bit over simplistic to me. How do you know that the solar inverter can supply enough power for the office at any given time?

 

[ban-all-sheds]

It also sounds like you're planning to have a switch in the earth connection, which is a no-no.

Is your office equipment going to be happy with the supply being interrupted each time the contactor switches?

 

[antonyc]

Sounds a bit over simplistic to me. How do you know that the solar inverter can supply enough power for the office at any given time?

I know it can power it because I have a 1kw solar system with a 450ah battery bank, including a 2.5kw inverter! The office contains nothing more than a 7w router and a 250w PC including monitors, etc. It can definitely power it!

To add to this, the solar has been powering this for a few months already... But I need the contactor to switch over at night.

 

[antonyc]

It also sounds like you're planning to have a switch in the earth connection, which is a no-no.

Is your office equipment going to be happy with the supply being interrupted each time the contactor switches?

Yes, I was planning on having an earth switch. The reason being is that the solar stuff is in a seperate building with it's own earth. Is this wrong? The alternative is to join both earths together permantly - which I could do. Should I?

The equipment should be fine too. Although without testing it, I'm not going to know for sure.

Antony

 

[DetlefSchmitz]

Sounds a bit over simplistic to me. How do you know that the solar inverter can supply enough power for the office at any given time?

I know it can power it because I have a 1kw solar system with a 450ah battery bank, including a 2.5kw inverter! The office contains nothing more than a 7w router and a 250w PC including monitors, etc. It can definitely power it!

To add to this, the solar has been powering this for a few months already... But I need the contactor to switch over at night.

So, for my interest, how does this work? The 230V disappears from the inverter as soon as the sun goes down, or as soon as the battery goes flat?

 

[antonyc]

Sounds a bit over simplistic to me. How do you know that the solar inverter can supply enough power for the office at any given time?

I know it can power it because I have a 1kw solar system with a 450ah battery bank, including a 2.5kw inverter! The office contains nothing more than a 7w router and a 250w PC including monitors, etc. It can definitely power it!

To add to this, the solar has been powering this for a few months already... But I need the contactor to switch over at night.

So, for my interest, how does this work? The 230V disappears from the inverter as soon as the sun goes down, or as soon as the battery goes flat?

No worries...

To start with, my office is a small brick and block, modern outhouse building. It has a SWA cable which runs underground to the shed (the shed is also my solar power house), where it is plugged into the mains. The office has it's own consumer unit.

Here is the current setup:
In the day, before I go to the office, I look at the battery voltage in my shed, assess the weather and decide which should power the office; the mains or the solar. If solar, I switch on the 125a switch, then switch on the inverter also. I then plug in my office plug into the meter, which is plugged into the inverter. At night or when sun goes down, I do the reverse, then plug the plug into the mains in the shed.

And here is the proposed setup:
The solar inverter will be permanently switched on, but I'm going to have an electronic cut off system in place between the solar/battery input and the inverter. This cut off system basically consists of a low voltage cutoff and an LDR circuit. The cutoff will cut the supply to the inverter if system voltage drops below 24v (prevents excessive battery drain) or if my LDR circuit detects that it isn't sunny enough to allow high drain.

If the battery voltage is above 24v AND the LDR is giving the go ahead, the inverter will be allowed to power up. It will pass through an RCBO and to the contactor. If the contactor senses power on the coil, I want the solar to power the office. If not, I want it to switch to mains.

I'm still looking at this contactor but I can't understand it...

I expect to see something like Load 1, Load 2, Load 3, NO 1, NO 2, NO 3, NC 1, NC 2, NC 3.

 

[Spark123]

Afaict the CAD32 comprises of 3x N/O contacts and 2x N/C contacts.

 

[DetlefSchmitz]

Yeah, that's the best I could make out of the (not very good) data sheet. So you could make 2 changeover contacts from that. If you just switch line and neutral that is fine (two NO and two NC contacts). I couldn't find the data sheet for 230 V coil. But I suppose the OP has found one. Probably that leaves the earth question. I won't make any judgement on this as I'm not really sure. This gets a bit esoteric.

I wouldn't want to use this before finding out if break before make. If not it could be a disaster. (EDIT: Looks like that is guaranteed by the data sheet)

 

[antonyc]

Afaict the CAD32 comprises of 3x N/O contacts and 2x N/C contacts.

It seems as though you're right.

 

[antonyc]

Yeah, that's the best I could make out of the (not very good) data sheet. So you could make 2 changeover contacts from that. If you just switch line and neutral that is fine (two NO and two NC contacts). I couldn't find the data sheet for 230 V coil. But I suppose the OP has found one. Probably that leaves the earth question. I won't make any judgement on this as I'm not really sure. This gets a bit esoteric.

I wouldn't want to use this before finding out if break before make. If not it could be a disaster. (EDIT: Looks like that is guaranteed by the data sheet)

Ok, yes, it seems that 2 pole will do. So 2 NC, 2 NO but I still don't understand where the other two terminals would go. Ok, and well earth, I might just join them together permanently.

Here's the spec document:

http://pdf.schneider-electric.nu/files/partnumbers/CAD32U7_document.pdf

It doesn't say whether it's make/break or break/make.

I've had a look at a few of these contactors and the documentation is shocking!There's another one which seems good but I've scoured the net for an English spec sheet. I'm still looking.

 

[DetlefSchmitz]

If you look at the picture in the data sheet the contacts are kind of labelled. If you get one and have a multi-meter then the connections are fairly obvious. Once you realise that there are three pairs of NO and two of NC. Clue: the outside edges seem to be three pairs of NO. and so on...