Jump to content

Is the SFT 240 an fully automatic switch


GordonT
 Share

Recommended Posts

 If you really think about it. Should we not be using a relay instead of a change over switch as this could be wired so that the relay wound be fully automatic switching between mains and inverter and would require no human intervention. 

Link to comment
Share on other sites

34 minutes ago, GordonT said:

 If you really think about it. Should we not be using a relay instead of a change over switch as this could be wired so that the relay wound be fully automatic switching between mains and inverter and would require no human intervention. 

Sure! But grid tie inverters do this automatically..

If you don't have one of these then you need to do the control. How would yo do this??

Link to comment
Share on other sites

1 hour ago, GordonT said:

 If you really think about it. Should we not be using a relay instead of a change over switch as this could be wired so that the relay wound be fully automatic switching between mains and inverter and would require no human intervention. 

That's something I don't have complete clarity about. In principle, all that is required is that your changeover must be interlocking, that is to say, it must be impossible for both sides to be engaged simultaneously. A contactor (which is a heavy duty kind of relay) with two NC (normally closed) and two NO (normally open) contacts, usually would be sufficient. The physical separation makes it difficult for both sides to be engaged simultaneously, and if a contact were to weld close, it would be impossible for it to release and engage the other side.

With that said however, most of the examples I've seen of building changeovers with contactors use two contactors, wired in such a way that it is electrically interlocked, but also with a physical lock-out. See here for example, this is for using contactors to reverse a three-phase motor, but the principle is still the same. If you look around a bit you will find a similar method for star/delta 3-phase motor starters. So I have a gut feeling there must be a reason for using two and not just one...

But what @Richard Mackaysays is true as well. Most inverter/chargers have a changeover switch built in already. But if you lack this, then you'll either have to throw some contactors at it, or buy a dedicated unit. In all cases, make sure it has the required IEC/SANS rating.

Link to comment
Share on other sites

Thanks Richard........ I had forgotten about the built in switch or relay that comes as standard on a Axpert 3kva King inverter so what i think you saying to me is that the SFT 240 change over switch  really only needs to be used if you have problems and do not want to feed power back into the grid.  Is my thinking correct or is it up the Creek...

Link to comment
Share on other sites

2 minutes ago, GordonT said:

SFT 240 change over switch  really only needs to be used if you have problems and do not want to feed power back into the grid

The changeover is simply so that the inverter can be bypassed. It moves the loads away from the inverter and back into the grid. This allows you to work on the inverter, do maintenance, replace it even, etc... without the wife and the kids asking every 5 minutes when the power/internet will be back on...

(Honestly, it is amazing how modern man cannot go 5 minutes without such luxuries... ).

🙂

 

Link to comment
Share on other sites

 Many thanks Plonkster and Richard for your input.......  I  am all for the safety of the installation of an inverter and will make sure it is in compliance  with all IEC/SANS ratings and that a certificate of compliance is issued on completion of the installation.   I actually have another question.   That I sure you guys can help with. My mains Db board has only got the sans type circuit breaker mounting brackets and want to know if i can mix the din type switch mounts on the same board..  

Really appreciate your advice and input.

GordonT

Link to comment
Share on other sites

2 hours ago, GordonT said:

If you really think about it. Should we not be using a relay instead of a change over switch as this could be wired so that the relay wound be fully automatic switching between mains and inverter and would require no human intervention. 

That is what I done, I have a contactor doing the switching between Eskom or Solar, so no need for manual switching just push a button on phone or set the timer on my phone to switch it.

 

2 hours ago, Richard Mackay said:

Sure! But grid tie inverters do this automatically..

If you don't have one of these then you need to do the control. How would yo do this??

I don’t have grid tie but just a clone Axpert and had to make it work automatic, I managed to wire it automatic with a contactor and managed to still maintain a manual change over switch as-well for if the auto system might fail than I can flick the hager C/O switch and still use Eskom or Solar, I would not recommend this system as it requires quite a bit of control wiring, but if your budget can’t go the grid-tie way with all the bells and whistles it can be done.

I have a red section that is my essential stuff and can switch on its own and the yellow section is non-essential that can also be switched on its own to solar or Eskom. Than the green is Eskom only as my heavy stuff is on there till I get more batteries. You can see the two contactors in the red and yellow sections.

CB4E40B8-838D-453A-8D31-306488B29222.jpeg

Link to comment
Share on other sites

1 hour ago, plonkster said:

The changeover is simply so that the inverter can be bypassed. It moves the loads away from the inverter and back into the grid. This allows you to work on the inverter, do maintenance, replace it even, etc.

Agreed! And a very useful facility for sure. But I'm sure a lot of off grid systems need to be switched back to the grid when they can't supply power (or you don't want it to run off the battery etc.

Link to comment
Share on other sites

1 hour ago, plonkster said:

(Honestly, it is amazing how modern man cannot go 5 minutes without such luxuries... ).

🙂

 

Not only do we have an expectation of 'mains' power always being available, we have also got an addiction to permanent internet access!

I try to help with this by providing Mini UPSs for router backup during power outages. When going to somebody's home I have learnt to ask first before shutting down the internet so you don't upset the online bridge game or the kid's streaming of whatever.. :(

 

Link to comment
Share on other sites

1 hour ago, phil.g00 said:

It looks impressive depending how it will be used, with a switching time less than 50ms. I think it might be able to switch over without interrupting the supply acting like a ups you might see a slight flick in the lights when it switches. Another benefit is, it is a “stay put” until a signal is applied which mean it won't draw current while switched to any position but it can be a disadvantage because sometimes you want it to drop out when supply is lost like with a contactor.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...