Author Topic: SIMPLE Auto Power Diverter switch suggestions.  (Read 834 times)

glort

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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 »

glort

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Re: SIMPLE Auto Power Diverter switch suggestions.
« Reply #2 on: January 23, 2018, 12:16:04 PM »

You are indeed a man on the ball Bruce.

I want to set up one ( of my several) arrays and inverters to backfeed my spinny meter.
When the AC comes on, I want to stop back feeding the spinny meter and divert the ( limited) output to the leg of the 3 phase AC with the electronic meter.
I believe that pulls around 2KW (which I'll have to check with a clamp meter) so the idea is to feed that leg with a 2 KW inverter is the draw is say 2.2 KW or a 1500w inverter if it pulls say 1800W.  I don't want to over feed it although If I did feed it 2000W and it only pulls 1800W i'd only be billed for 200W so probably not much difference.

When the thing turns off I want it to go back to feeding the other phase.

As you can see the the 2 feeds must never connect as they will be 120o out of sync.

It won't be perfect as I'll have to wait for the inverter to reboot after every switching event but I will look at maybe tapping off the evaporator fan for the switching rather than the compressor or maybe even the cooling fans.

If I can take the majority of the load off the grid power and use as much of my own generated power as possible, that will save me a lot I think.
Obviously at night when there is no solar there will be no input from the panels so the power feed will be as normal.

I'll cool the place down freezing or hot as hell during the day and hope it carrys over to the night.


Is this going to do the trick?

https://www.ebay.com.au/itm/LY2NJ-220V-AC-Coil-10A-240V-Power-Relay-DPDT-Led-Lamp-New/132005868726?epid=510076760&hash=item1ebc29b4b6:g:hsUAAOSwOyJX-20X

BruceM

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Re: SIMPLE Auto Power Diverter switch suggestions.
« Reply #3 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 #4 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 #5 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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glort

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Re: SIMPLE Auto Power Diverter switch suggestions.
« Reply #6 on: January 24, 2018, 10:05:27 AM »

Thanks Guys.
This is exactly the sort of info I was after.  The other places I asked meant well and I have no doubt their electronic soloutions would work better  however if they are over my head and the people suggesting them aren't around to build them for me, not much use I'm afraid.
Electrical I'm better with than electronic so this is a much more practical and workable solution for me.

I think you are spot on with the delay Bruce. I notice if I am playing with the inverters if I disconect the AC side and reconect, it re engages straight away.
That said, how would it know where the phase was in it's cycle? Would it have some inbuilt timing or would it have to just do a very quick Sync and then re connect and start feeding?
I'm thinking to use something other than the compressor power feed as that is going to kick in and out pretty often I think and I'd loose a lot of input with the inverter resetting.  OTOH, If I am feeding when the compressor is off, that is going to register as a charge on the meter.
I there a way to 2 stage the power feed? ( now I'm getting complicated!)
Say a 500W input for the fans and a 2KW feed when the compressor kicks in. This would keep the Inverter synced while ever the AC was on but not backfeed.

I'm starting to see the value in these electronic devises.

I'll look for contactors and time delays.  Pretty sure I have a couple of little time delay boards here already. I bought a lot of misaleanious board last year for thing I thought I might do.  These China boards are so cheap but take a while to arrive so I try to keep a stock and replace them as I use them.
Not too many days when we don't get a Fleabay package.

I followed the Amazon link Bruce and got :

ERROR
The request could not be satisfied.
The Amazon CloudFront distribution is configured to block access from your country.

I hate effing Amazon with their " We can't sell it to YOU being outside the US" crap.  I believe they have an AU site now. They can stick it fair up their nether regions far as I'm concerned, I'll never buy squat from them. Thing is, my mate in Texas can buy anything and have it shipped to me which he has done in sympathy / generosity a couple of times. What's the difference if he buys it and sends it here or I buy it and have it sent here?

The other ones you mentioned I'm not aware of.  I have tried some other places like bangood but find I can get the best prices and the same stuff in fleabay.

Thinking about it, My mate in AC can probably get me some used contactors and delays.  He gets heaps of old electrical and AC stuff and I know he has just done a HUGE refit at a private hospital.  His biggest job so far, half Million bux! But there is a ton of stuff he has.

Forgive my ignorance but are contactors like relays, DPDT or is there a specific type I'd need?

Every time I type "Contactors" auto correct wants to make it CONTRACTORS.
 If I got a contRactor, I wouldn't need a time delay, it would be built in and come with guaranteed delays!!  ::)

BruceM

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Re: SIMPLE Auto Power Diverter switch suggestions.
« Reply #7 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.











glort

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Re: SIMPLE Auto Power Diverter switch suggestions.
« Reply #8 on: January 26, 2018, 05:02:28 PM »

Mate is Doing an Uninstall on some equipment this week and has said he will save me the contactors.
Have ordered a time delay board.


I discovered there is an AU version of mouser. Have to look through that some more and become familiar with what they have.


BruceM

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Re: SIMPLE Auto Power Diverter switch suggestions.
« Reply #9 on: January 26, 2018, 10:16:34 PM »
Glad you found a good electronics supplier there in Au.  That will make things easier.