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uses of dc and ac relay in an inverter

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Apr 20, 2015
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How can I connect DC and ac relay to my inverter for auto switching.


a relay has a coil and contacts.

If you want the relay to switch, then you have to connect the voltage to the coil connections. Usually there is a printing on the relay what voltage and wether AC or DC to use.

Connect the relay contacts to wires of your inverter wherever you need it.

If you expect a more specific answer, then you need to give us more specific informations first.


get a big power relay with a 120 vac coil. Like a 4PDT 35 amp relay

When the inverter comes on, have it energize the coil to swtich the relay.

For example here each contact point can handle 35 amps AC 120v. this one will give you 4 poles double throw.
You could gang them together to get 70 amps for a hot and neutral transfer switching. Most inverters though, will not be such high powered.

So you have inverter and grid power as inputs, and the output goes to the desired circuit.
Just remember, in a home electric panel, neutral and ground are joined at the distribution panel, so to use this relay as an auto transfer switch, the inverter in a home must be able to have a grounded neutral.
An RV or boat does not have a grounded neutral, so you can use an inverter with a floating neutral with 60vac on the white wire, 60 vac on the black wire.

You can also cascade two of these relays together so that you can have automated switching of three sources, grid, inverter, generator feeding the distribution panel as an outlet. Each additional relay would add another source, so you could switch from as many sources as you want.

Here for example, I made this box and setup two relays to switch between gen, shore, inverter.
I actually drive the AC relay coils using 15 to 17 vdc from wallwarts. Makes them totally silent no buzz. And I added several lockout relays to absolutely make sure a power relay cant possibly come on when it should not, not that it would ever interconnect.
Even a stuck relay will not allow two sources to interconnect at the same time. Not that they stick, but if it dd stick one way, then when the relay coil changes to on or off, the relay arm would not move. What my additional lockout relays do, is if the gen tries to run, it turns off the power to the relay coil for inverter - gen switching, breaks the relay coil circuit, so auto selects for gen power, even if the inverter is on.

If the grid power switch is on, it also prevents the inverter from powering on the right side relay, it breaks the coil circuit.
So the right side relay switches between gen and inverter, and the left side relay switches between shore and the right sided relay's output.
It all works very well.


This relay box lets me do automatic and manual switching between three power sources and twin 30 amp shore power inputs on the boat.
I have various switches up at the helm to turn on and off relays. these relays switch hots and neutrals together.

- - - Updated - - -

Adding some more as I keep thinking of how I did this.

These relays switch hots and neutrals together, two entirely separate power circuits of hot and neutral.
I ganged together the inverter and the gen so that they energize both sides hots and neutrals are shared, those being single sources. The shore power cables though being twin 30 am discrete sources dont share them.

I did recently add a DPDT switch to join the 2 hots and 2 neutrals on the output of the left power relay. This because my current marina I only have single 30 amp power. So then the entire electric distribution panel can work with a single input from a single shore cable. I have to keep one of the 30 amp circuit breakers for the other 30 amp shore power input off, otherwise the prongs inside the covered outlet would have live power on them. The switch I used is a 30 amp DPDT with a pullout key. The shore line breaker box is lockable, so it is securable against mischief of someone fiddling with the power arrangement.
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