Electronics > Beginners

110 AC DPDT latch relay

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PetrosA:
If you're in the US, I can't think of anything in the NEC that would allow you to do this for less than a few hundred dollars  - legally, that is. When you power mains fed loads from a transferred battery powered source, it's what's called a Separately Derived System (the same as a permanently mounted generator). If you intend to do this, you better read up on the requirements for SDSs. It will mean installing separate grounding electrodes, panels, transfer switches, etc. Big money if you want to do it and have insurance cover a loss if something goes wrong.

bilko:

--- Quote from: Jimmy on October 12, 2011, 04:04:50 am ---
Then when your circuit gives power to the relay it will change to inverter power. This way if your circuit breaks you will have mains power lights. This would act like an automatic change over switch. If wired correctly there is physically no way you can back feed power into the grid.


--- End quote ---

Have you ever seen relay contacts weld ?
That is why I suggested the method in the previous post and then scored through. I would suggest that the OP speaks to his insurance company because if his house burns down or if a utility worker gets electrocuted then he will be in big trouble.
Not wanting to pour water on the idea but there is a right way and a wrong way of doing things.

Jimmy:

--- Quote ---Have you ever seen relay contacts weld ?
--- End quote ---

Yes I have seen many relay contacts wield together. About 8 years ago I had the pleasure of replacing about 80 relays in a 240v emergency backup system that failed to operate correctly. This did not create a fire only incorrect operation.


--- Quote ---I would suggest that the OP speaks to his insurance company because if his house burns down
--- End quote ---
That is why I suggested replacing it with a 12v system. In most places you can burn your house down if you get a permit.

 
--- Quote ---if a utility worker gets electrocuted then he will be in big trouble
--- End quote ---

It a utility worker gets electrocuted form this it is his own fault for failing to isolate all sources of supply and failing to test before you touch. If the contacts on the wield together and the power goes out the inverter will not start supplying power to the grid only your lights. It will only supply back to the grid if there is a short circuit which would quickly blow the fuse in the inverter.

Zero999:

--- Quote from: Jimmy on October 13, 2011, 11:58:35 pm --- That is why I suggested replacing it with a 12v system. In most places you can burn your house down if you get a permit.
--- End quote ---
Why on earth would a 12V system be less of a fire risk?

That makes no sense. In reality a 12V system will probably pose a greater fire risk than the mains. Batteries can catch fire and hydrogen gas can cause explosions. You may also need to replace the wring and switches. The current in a 12V system will be 20 times greater than the equivalent 240V system, causing the power dissipation in the cables to increase 400 fold which may cause a fire if the cables aren't suitably rated. Fortunately the cable in most modern installations is suitable overrated but you should check it, just to be safe. You could also increase the voltage to 48V to reduce the current four fold.

As far as regulations are concerned, in the UK the fact that it's ELV will not absolve you from abiding by the wiring regulations which also cover wind power, battery and PV installations, regardless of the voltage. You still need to use suitable fuses or circuit breakers and the correct cable. The only really difference is you don't need to use an RCD if it's 120VDC or 50VAC.

NiHaoMike:

--- Quote from: PetrosA on October 13, 2011, 02:54:14 am ---If you're in the US, I can't think of anything in the NEC that would allow you to do this for less than a few hundred dollars  - legally, that is. When you power mains fed loads from a transferred battery powered source, it's what's called a Separately Derived System (the same as a permanently mounted generator). If you intend to do this, you better read up on the requirements for SDSs. It will mean installing separate grounding electrodes, panels, transfer switches, etc. Big money if you want to do it and have insurance cover a loss if something goes wrong.

--- End quote ---
If a plug in solution would work, a UPS nearly does just that. You'll need to somehow hack it to use the mains as a backup.

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