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Author Topic: SIMPLE Auto Power Diverter switch suggestions.  (Read 2763 times)

guest22972

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SIMPLE Auto Power Diverter switch suggestions.
« on: January 23, 2018, 04:48:48 AM »

Been asking on some electronics forums and getting some way complicated answers which is no good to me so I'll try the practical brains trust here.
I'm not going to give many details purposeful so not to confuse the issue as they aren't relevant.

I want to take a supply of AC power which will be nominally 240V, single phase , 10A.
I want to have it going to a load until there is demand from another load which can be sensed when a 240V line becomes active as it will have another supply.  This must be isolated from the other load until it has changed over.
When that other load fires up, I want to have something ( simple as possible) that will disconnect the first load and direct it's power to the 2nd load.
When the second load switches off, the power will go back to the first load.

I'm thinking some sort of contactor, switching relays Etc. Maybe there is a fleabay electronic board I could wire up? Just wouldn't know what it's called and guesses have proven futile.  Maybe a boiler plate ardiuno sketch a beggier could follow?
 So far suggestions have been all manner of complicated and expensive ways of doing it but in my ignorant mind, there must be a simpler, straightforward way of doing this.

Any suggestions appreciated.




BruceM

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Re: SIMPLE Auto Power Diverter switch suggestions.
« Reply #1 on: January 23, 2018, 05:42:21 AM »
A double pole, double throw relay  can do the switchover; that's the easy part.

The issue is how is the the second load sensed.

"I want to take a supply of AC power which will be nominally 240V, single phase , 10A.
I want to have it going to a load until there is demand from another load which can be sensed when a 240V line becomes active as it will have another supply.  This must be isolated from the other load until it has changed over.
When that other load fires up, I want to have something ( simple as possible) that will disconnect the first load and direct it's power to the 2nd load.
When the second load switches off, the power will go back to the first load."

If the second load going on results in a 240AC signal with enough current to activate the 240V relay coil of a double pole, double throw relay, then that is all you would need.  You would have to pick up this "active circuit" signal from somewhere internal to the appliance... it would drive the coil of the relay, which would switch the contacts to the new panel supply.  The contacts are open before change - there would be no contact between the two loads, ever, even if the relay fails.  The relay coil takes very little current and has no connection to the load contacts whatsoever.

I'm guessing that the power being switched is the grid tie inverter output going to another panel???
 


Alternately, if the second (highest priority) load is something on a different panel, and you are trying to shift your grid tie inverter ouput to cover it, it can be sensed with a current detector switch added to that circuit after the breaker. That switch can switch the double pole relay coil current on so that the inverter output is now applied to the second panel.

If you can be more specific about your design concept (a rough sketch perhaps?)  I'll try to help you come up with something specific with a wiring diagram to smoke test. ;) 





« Last Edit: January 23, 2018, 05:59:45 AM by BruceM »

BruceM

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Re: SIMPLE Auto Power Diverter switch suggestions.
« Reply #2 on: January 23, 2018, 04:02:11 PM »
OK, good explanation. 
Yes, that relay is the type you need (double pole, double throw or DPDT, 220/230v coil) but I would  suggest using one with at least a 50% higher current rating than your operating current.

I do have some trepidation about switching the inverter quickly between the two different phases; I don't know the specific grid tie inverter design and don't know how the inverter will cope with this.   I think I'd add a time delay relay  to have the inverter first be disconnected from the analog (spinning) meter for a few seconds before connecting it to the the digital meter circuit.  That gives me more confidence that the inverter circuitry will recognize the situation as a power outage and then will sync up to the new phase timing as opposed to a fast relay switch over to the different phase.

If you don't mind blowing an inverter you could try the simpler direct switchover via relay...with a fast blow fuse or breaker on the inverter output. To do it via time delay requires a cheap relay time delay controller and a second DPST relay.

The time delay relay controllers are cheap:
https://www.gamut.com/p/time-delay-relay-600-sec-time-delay-1.5-a-contact-rating-NzY1ODg3?utm_source=google&utm_medium=cpc&adpos=1o6&scid=scplp654U023&sc_intid=654U023&gclid=EAIaIQobChMI-_Oj1sDu2AIVSpV-Ch22fQAFEAYYBiABEgLJKPD_BwE&gclsrc=aw.ds&dclid=CJ-V4-bA7tgCFYqSYgodpRIP_Q

I've used these before on a friend's electric boiler elements and they do work nicely and reliably.

The time delay approach would use two relays  The fan circuit output would immediately open the DPDT relay which normally has the inverter connected to the analog meter, and activate the time delay control to a second relay (DPST) which would connect the inverter (through the aforementioned DPDT relay) to the digital meter circuit after a few second delay.  By having the DPDT contacts feed the DPST relay, no type of failure can ever cause connection between the two different meters and phases.  The time delay is only to give the inverter time to recognize a power outage and so initiate syncing up with the new meters phase when it is connected.

I can sketch this up for you if needed.
« Last Edit: January 23, 2018, 04:46:19 PM by BruceM »

BruceM

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Re: SIMPLE Auto Power Diverter switch suggestions.
« Reply #3 on: January 23, 2018, 04:50:13 PM »
Do you have something equivalent to Digikey, Mouser, or Allied there in Au?  That would make helping with part selection easier.  Digikey has such good selection here in the US I rarely go elsewhere. 


EdDee

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Re: SIMPLE Auto Power Diverter switch suggestions.
« Reply #4 on: January 24, 2018, 07:44:30 AM »
Hey Guys,

Rather use two contactors criss-crossed with the N.C. control contact in series with the coil of the opposing contactor to do the switching... DPDT relays are notorious for arcing under heavy load disconnection and burning contacts closed etc... (Had that on the DEK btw Glort, put in two contactors and now much better)... Also, the couple of cycles delay in switching time for one to drop out and settle the control contact then the other to pull in once enabled is a bit kinder to the inverters I reckon....

Another thing, high current relay in za cost lotsa $$$ while contactors are dime a doz at the scrappies...

Just a thought...

Cheers
Ed

Edit: use the relay/sensing relay/time delay unit/whatever to control the contactors....Let the contactors do the heavy switching work, light current carried by the supervisor circuit...Much greater reliability and cheaper long run too...
« Last Edit: January 24, 2018, 07:49:28 AM by EdDee »
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BruceM

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Re: SIMPLE Auto Power Diverter switch suggestions.
« Reply #5 on: January 24, 2018, 03:56:41 PM »
There is no electro-mechanical difference between a relay and a "contactor".  They both have a magnetic coil and contacts. It's just terminology.  Contactors are the name often used by electricians for the larger motor starting relays and such, and you will often fare better, as Ed says, searching for "contactors".  Thanks for that helpful suggestion, Ed.

There isn't a simple solution for limiting the inverter backfeed current to match a load, without building some elaborate high power circuitry to limit the PV input side to throttle output to a level matching the sensed load current on that digital meter.   It would be more practical  to have a switchover to an off grid inverter...which could have very small capacity batteries since it would only be used to independently power those digital meter'd loads...the meter would not see them at all unless switched back to meter power due to lack of PV power. 

Regarding the time delay requirements and internal sync-up to grid phase:
Grid tie inverters have a microprocessor to manage it's anti-islanding and grid monitoring circuitry.  I read up a bit on those anit-islanding circuits and there are more than 4 different popular approaches and they can be implemented in a myriad of ways. I don't have experience with these products and so suggest doing initial testing on a unit you can afford to destroy.  They must detect a power failure, so a longer time delay would be the safest and most likely to have it "start from scratch" and sync up with the new power phase instead of continuing on it's internal time base. Reading the manual on the unit and how it handles brief grid outages might give me some idea if you send me a link.  I'd start at about 10 seconds.











BruceM

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Re: SIMPLE Auto Power Diverter switch suggestions.
« Reply #6 on: January 26, 2018, 10:16:34 PM »
Glad you found a good electronics supplier there in Au.  That will make things easier.