Pages: [1]   Go Down
Author Topic: Switching load between two sources.  (Read 904 times)
0 Members and 1 Guest are viewing this topic.
0
Offline Offline
Full Member
***
Karma: 0
Posts: 151
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I need a mains switch that can switch a load between two input sources.

Any thoughts?
I'm thinking something like the on / off / auto switch, but it only needs two positions (off peak, normal), and allow for the load to be switched between either of the two.
It'll want to be a 32A 240V rating (or thereabouts).
« Last Edit: April 09, 2013, 08:01:55 am by tocpcs » Logged

Offline Offline
Edison Member
*
Karma: 58
Posts: 2078
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Search Ebay for ssr-60da or ssr-90da. Two of those. For 9 dollars each.
Logged

Left Coast, CA (USA)
Offline Offline
Brattain Member
*****
Karma: 361
Posts: 17263
Measurement changes behavior
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

As standard AC SSRs are in effect SPST switches you can't totally isolate the two voltage sources from each other to one output load, the neutrals would have to be wired together which would only work if the two sources are is perfect phase with each other. So draw up your proposed switching circuitry and post jere before committing to purchasing parts and building it.

So requirement questions:
Does the transfer have to be instantaneous with the load not missing even a single half cycle of power?

Does switching have to by just a one time event or after switching from primary source to secondary source and then primary source returns does the circuit have then switch back to the primary source?

What is the phase relationship between the two voltage sources?

Lefty
Logged

London
Offline Offline
Edison Member
*
Karma: 46
Posts: 1368
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

As standard AC SSRs are in effect SPST switches you can't totally isolate the two voltage sources from each other to one output load, the neutrals would have to be wired together which would only work if the two sources are is perfect phase with each other. So draw up your proposed switching circuitry and post jere before committing to purchasing parts and building it.

He could use 4 SPST relays, two for the live side and two for the neutral side. Then there would be no problem with phase differences, assuming that all four relays switch at the same time.
Logged

Left Coast, CA (USA)
Offline Offline
Brattain Member
*****
Karma: 361
Posts: 17263
Measurement changes behavior
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

As standard AC SSRs are in effect SPST switches you can't totally isolate the two voltage sources from each other to one output load, the neutrals would have to be wired together which would only work if the two sources are is perfect phase with each other. So draw up your proposed switching circuitry and post jere before committing to purchasing parts and building it.

He could use 4 SPST relays, two for the live side and two for the neutral side. Then there would be no problem with phase differences, assuming that all four relays switch at the same time.


That gets pretty expensive pretty quick, and as two SSRs (for each voltage source) will be operating in series with the load I'm not even sure that would work, it's a pretty unusual arrangement. Again without knowing the phase relationship of the two voltage sources it's hard to propose a good solution. A single normal electromechanical relay would be pretty simple, a DPDT should meet the requirements with the proper sensing circuitry of course to drive the relay coil. That however would not be a 'bumpless' transfer.

Lefty
« Last Edit: April 09, 2013, 10:16:56 pm by retrolefty » Logged

0
Offline Offline
Full Member
***
Karma: 0
Posts: 151
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I think it's a single phase in from the street.

One is just a controlled load.
I realise I posted this on a microcontroller forum, but I'm not fussed with manually switching it.
The idea is that the element in the hot water heater may get power directly when we wish, else it's controlled by the utility controlled load signal.

What I am missing is the name of such a switch (i.e. 3 terminals, load, source 1, source 2).
Logged

Left Coast, CA (USA)
Offline Offline
Brattain Member
*****
Karma: 361
Posts: 17263
Measurement changes behavior
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I think it's a single phase in from the street.

One is just a controlled load.
I realise I posted this on a microcontroller forum, but I'm not fussed with manually switching it.
The idea is that the element in the hot water heater may get power directly when we wish, else it's controlled by the utility controlled load signal.

What I am missing is the name of such a switch (i.e. 3 terminals, load, source 1, source 2).

You really need a six terminal switching device, called double pole double throw (DPDT). This can be either a manual switch or a DPDT electromechanical relay device depending on if you want just manual or automatic switching capabilities. The two common contacts wire to the load, the two normally closed contacts wire to line and neutral of voltage source #1 and the two normally open contacts wire to voltage source #2.

http://www.khazar.com/academics/portal/ucsc/2010fall/art22/images/symbol-dpdt.png

Lefty
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 6
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The best thing to use would be what is called a Solid State Contactor. They contain multiple solid state relays along with circuitry to insure they switch at zero crossing. Depending on the specifics, voltage, current, etc., they can quickly get into the multiple hundreds of dollars.
Logged

Earth
Offline Offline
Edison Member
*
Karma: 52
Posts: 1762
My browser no longer is binding static IP, Floating is the way to go.
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I will vote "SSTS" (solid state transfer switch).

The SSTS is an electrical device that allows instantaneous transfer of power sources to the load.
There are SSTS in the market, but all for high voltage and 3 phases. for OP need, OEM or ODM is needed by ask SSR guy.
« Last Edit: April 10, 2013, 09:42:15 pm by sonnyyu » Logged

London
Offline Offline
Edison Member
*
Karma: 46
Posts: 1368
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I think it's a single phase in from the street.

One is just a controlled load.
I realise I posted this on a microcontroller forum, but I'm not fussed with manually switching it.
The idea is that the element in the hot water heater may get power directly when we wish, else it's controlled by the utility controlled load signal.

Your water heater draws 32 Amps (~8kW)? Are you heating an Olympic swimming pool?
Most UK domestic 'immersion' heaters draw no more than 16 Amps (~4kW), many much less.
Logged

Earth
Offline Offline
Edison Member
*
Karma: 52
Posts: 1762
My browser no longer is binding static IP, Floating is the way to go.
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
I realise I posted this on a microcontroller forum, but I'm not fussed with manually switching it.

Reliance Controls 100 Amp Utility / Generator Transfer Switch, from HomeDepot  $139.99
This one is for US voltage, You need to get same type but UK one.

http://arduino.cc/forum/index.php/topic,152330.msg1144293.html#msg1144293
Logged

Pages: [1]   Go Up
Jump to: