leki switch ! !

[1958steveflying]

Hi Guru's, please bear with me here I will try to explain where I need help ! ! !

.

[Keef]

Just rambling here, but it sounds like you need some sort of relay on your second supply that 'makes' by power from your first supply but 'breaks' when the first supply is cut.

Can you get relays that can handle 2kw?

[photoman290]

2 kw at 240 volts is only 9 amps so no problem finding a relay. not sure that is the best way to do it though. the problem is how you power the relay. a transfer switch is the proper way to do it but they are expensive.

[knighty]

you can easily do it with a single relay

one like this would do it...

http://www.ebay.co.uk/itm/AC-CONTACTOR-4kw-240V-COIL-3-POLE-1N-C-AUX-CONTACT-STARTER-CHINT-NC1-0901-240V-/272457680296?hash=item3f6fbe45a8:g:vfsAAOSwzchXRYZI

it has 3 normally closed contacts and 1 normally open

if you look at the pic of it you'll see they're numbered 1, 3, 5 and 21 along the top, then 2, 4, 6, 22 along the bottom

there's a coil built into the base of it, give it 240v ti switches the contacts on/off (think of it like a big 12v car relay)

normally 1, 3 and 5 do nothing, 21 is connected to 22

then when you power it on, 1 connects to 2, 3 to 4, 5 to 6, and 21/22 disconnect


the contactor is switched by contacts A1 and A2, positive and negative (doesn't matter which one is which)

you need to connect your backup/constant positive into no21

and your other supply into no1

your on/off supply also connects to A1 to switch the relay on/off

join A2 to negative

join numbers 2 and 22 together and connect your load to them


then join all the negatives together (only need to switch the live)

:-)

EDIT:

rough picture to explain it better than I can with words





only thing I can think you might want is a little time delay relay, so it waits 30sec when you're on/off supply comes back on before it starts to use it ?

[photoman290]

he still has thr problem of how to power the relay coil. is the back up supply always powered,such as A mains or B genny. if A then no problem, if B how  are you going to power the coil? if it is a genny on B you need the relay coil to be always on when on mains. if the mains  drops out the relay switches to the back up supply. B in this example.

[knighty]

he still has thr problem of how to power the relay coil. is the back up supply always powered,such as A mains or B genny. if A then no problem, if B how  are you going to power the coil? if it is a genny on B you need the relay coil to be always on when on mains. if the mains  drops out the relay switches to the back up supply. B in this example.

the coil is powered by the on/off supply

when it's not powered, the 21/22 are connected, so you get power from the always on supply :-)

Still getting my head round it but yes that looks like it will do just what I need. cheers loads..

no worries, any questions just ask :-)


that contactor is like 2 relays, when one is on the other is off  :-)

[knighty]

yeah, that's the same

wires up the same way too, it's physically identical, just numbers are printed on different :-)



p.s. if you want extra things powered up from the on/off supply, which are only powered by that one, you can use some of the extra contacts for those... so you could have your normal reactor heater or whatever powered from the mains, then when you're on the on/off supply you could have 2 heaters powered up to make better use of the on/off supply

[knighty]

no probs :-)