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Old 06-09-2018, 07:06 AM   #1
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Two 120v power sources, automatic switch/relay


hi

my Motorhome developed an issue with the charger, which is integrated within the Magnum ME2012 Inverter. In order to temporarily have to ability to continue using all the Inverted outlets(30a sub panel) until the unit can be repaired(we think it's a defective temperature 'thermistor' which is causing the unit to cut the Inverter on/off rapidly as a 'fault'), I created a work-around that allows everything to work on SHORE/GEN power when parked, or all the inverted outlets when on the Inverter while traveling, for the fridge, of course!

The concern is that I don't want the two power sources to 'accidentally' overlap/feedback, if I should forget to cut off the Inverter when I plug into shore power, or turn on the generator, since both of these 120v power sources, thru the ATS(auto transfer switch) are now run into the same Inverter 'sub panel' 30amp Main breaker, and to it's Inverted 15a outlets, which is for the fridge, and all the 120v outlets.


While it works fine as is now, I would like to add protection from overlapping/feedback by installing a SPST or similar type of simple 'switch/relay'
that will allow any 120v power from the onboard ATS(auto transfer switch) for the Shore Power or Generator to take precedence over the Inverter power.

I will have two INCOMING power connections
(1-Inverter, 2-ATS[Shore or Gen power]),
and one OUTGOING connection to the sub-panel's 30a Main breaker...
there is only the single #10 hot wire coming from the ATS's 30a breaker to the Inverter's 30a subpanel Main breaker.

This unit will 'switch' automatically to the Shore or Gen Power when they are available, leaving the Inverter then 'disconnected' from the breaker.
My understanding is that the Inverter wire will be of the 'Normally Closed' type, and the ATS wire will be the 'Normally Open' type, with the 120v energized relay to operate(switch) when the ATS 120v power is present.

Can you suggest a SPST or similar simple unit that will make this an 'easy' integration? Thanks.
-----------------------------------------------------------
30amp, 120v switch
2 Incoming 120v power sources
1 Outgoing 120v line to 30a sub-panel Main breaker
-----------------------------------------------------------

Last edited by NCmountainCabin; 06-09-2018 at 07:12 AM.
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Old 06-09-2018, 07:39 AM   #2
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Re: Two 120v power sources, automatic switch/relay


A simple three way switch will do the job except I don't think they are rated 30 amps.
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Old 06-09-2018, 10:47 AM   #3
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Re: Two 120v power sources, automatic switch/relay


This should work.
https://www.westwayelectricsupply.co...0-277v-br.html

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Old 06-11-2018, 10:47 AM   #4
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Re: Two 120v power sources, automatic switch/relay


sounds good, but I wonder if there is 'automatic' similar 'relay' that accomplishes the same, with the 'normally closed' side for the 'always on' 120v Inverter power, and then switch to the 'normally open' 120v ATS power(either generator or shore power) when available...

the Inverter will fault to a 'OverVolts' condition if these are not 'separated'...

yes, I can just turn the inverter OFF when I crank the gen, or plug in, but I want to minimize any 'accidental' forgetfulness in doing this...

in researching Relays and Contactors, it's fairly confusing as to how to wire them, or which 'side' is the one that 'energizes' the coil in order to throw the switch to the new incoming power source...
-SinglePole single throw, singlePole double throw
-DoublePole single throw, doublePole double throw
etc!

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Old 06-11-2018, 09:05 PM   #5
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Re: Two 120v power sources, automatic switch/relay


On a relay, the "closed" condition is when the coil is energized (the relay is "pulled in").
The way I'd do it is to connect the shore power to the normally-closed contact on the relay, and the inverter to the normally-open contact. Then, connect the relay coil across the shore power line. This way, the relay will pull in whenever shore power is present, and the shore power will be connected to the output via the NC contact. When the shore power is shut off or fails, the relay goes over to the NO contact and the inverter is connected to the output. This way, shore power will be connected whenever it is present, whether the inverter is on or off.

I see the TE Connectivity 655-KUHP-5A51-120 at Mouser, which looks like it will do what you want, and it's in stock. You'll have to do some work to figure out how to safely connect to your wiring, and how to enclose it.
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Old 06-11-2018, 10:40 PM   #6
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Re: Two 120v power sources, automatic switch/relay


never mind
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Old 06-12-2018, 07:11 AM   #7
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Re: Two 120v power sources, automatic switch/relay


Quote:
Originally Posted by fa_f3_20 View Post
On a relay, the "closed" condition is when the coil is energized (the relay is "pulled in").
The way I'd do it is to connect the shore power to the normally-closed contact on the relay, and the inverter to the normally-open contact. Then, connect the relay coil across the shore power line. This way, the relay will pull in whenever shore power is present, and the shore power will be connected to the output via the NC contact. When the shore power is shut off or fails, the relay goes over to the NO contact and the inverter is connected to the output. This way, shore power will be connected whenever it is present, whether the inverter is on or off.

I see the TE Connectivity 655-KUHP-5A51-120 at Mouser, which looks like it will do what you want, and it's in stock. You'll have to do some work to figure out how to safely connect to your wiring, and how to enclose it.
thanks for your reply, as this sounds very good for my situation...though what I'm finding is that it's difficult to ascertain 'which' of these connections on the device are the ones to 'connect' my wiring to. Some I've found don't have ANY instructions, and some that do are so 'electrically' oriented that it's like reading a foreign language...

my situation is very, very simple.

I have two simple 120v 10awg wires that provide incoming power...
(since these are already fed thru 30a breakers, there is only this single 'hot' wire to deal with on each...)
- one is RED(from Shore or Generator)
- the other is BLACK(from the Inverter)

- a single WHITE wire then exits into a 30a sub-panel breaker(which supplies the power to the outlets in the RV, from either the Shore/Gen or the Inverter)


If someone can provide me a clearer picture of where to attach each of these three wires, I think we'll have this project licked! Thanks
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Old 06-12-2018, 12:09 PM   #8
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Re: Two 120v power sources, automatic switch/relay


Quote:
Originally Posted by NCmountainCabin View Post
thanks for your reply, as this sounds very good for my situation...though what I'm finding is that it's difficult to ascertain 'which' of these connections on the device are the ones to 'connect' my wiring to. Some I've found don't have ANY instructions, and some that do are so 'electrically' oriented that it's like reading a foreign language...

my situation is very, very simple.

I have two simple 120v 10awg wires that provide incoming power...
(since these are already fed thru 30a breakers, there is only this single 'hot' wire to deal with on each...)
- one is RED(from Shore or Generator)
- the other is BLACK(from the Inverter)

- a single WHITE wire then exits into a 30a sub-panel breaker(which supplies the power to the outlets in the RV, from either the Shore/Gen or the Inverter)


If someone can provide me a clearer picture of where to attach each of these three wires, I think we'll have this project licked! Thanks
The attached schematic shows how to wire a DPDT relay to automatically switch between two power sources. Whenever "primary" power is present, the relay coil will activate and the output will be connected to that source. When "primary" power is not present, the relay is not activated and the output is connected to the secondary source (inverter). The wire colors or terminal markings depend on your relay and are not standardized, but all DPDT relays have the same eight terminals: three for each pole of the relay, and two for the coil.

(Note: the "+" symbol indicates "hot" rather than "positive" since those are AC sources. I did not design that confusing schematic symbol.)
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Two 120v power sources, automatic switch/relay-schemeit-project.png  
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Last edited by mpoulton; 06-12-2018 at 12:11 PM.
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Old 06-12-2018, 12:25 PM   #9
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Re: Two 120v power sources, automatic switch/relay


excellent diagram, thanks.... though I only have 3 wires(2 in, 1 out) and therefore the confusion of 'which' of these contacts on the Relay/Contactor I should be connecting them to.
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Old 06-12-2018, 09:08 PM   #10
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Re: Two 120v power sources, automatic switch/relay


Quote:
Originally Posted by NCmountainCabin View Post
excellent diagram, thanks.... though I only have 3 wires(2 in, 1 out) and therefore the confusion of 'which' of these contacts on the Relay/Contactor I should be connecting them to.
Well, you actually have 6 wires... you just may not be thinking about all of them. The inverter has two output wires, hot and neutral. The AC power source has hot and neutral wires too. The output (to your loads) has hot and neutral also. (Grounds don't figure into this - they should all be connected to each other all the time, so I did not mention them or include them in the schematics.)

It is possible to do this using only a SPDT relay (see below), switching just the hot wires and leaving the neutrals connected all the time. That's OK too, although it introduces a minor issue that probably won't ever come up and is too complicated to get into here (the neutral-ground bond in the inverter). The attached diagram shows this arrangement, with the neutrals connected all the time and the relay only transferring the hot wire from one source to the other. If I were doing it, I'd use a DPDT relay and switch both the hots and neutrals - but you do not have to do this. You could use the simpler method shown below.
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Old 06-13-2018, 06:44 AM   #11
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Re: Wiring for 120v 30a simple RELAY - power wires only


Quote:
Originally Posted by mpoulton View Post
Well, you actually have 6 wires... you just may not be thinking about all of them...
It is possible to do this using only a SPDT relay (see below), switching just the hot wires and leaving the neutrals connected all the time...
alrighty! great info, and I think you've narrowed it down for me, as to the device 'type'(SPDT relay), and the wiring scheme.
Yes, I only have 'three' wires to deal with as the Neutrals are all already bonded at the panel.
Now, I hope that I attach these wires at the correct posts on the Relay.

I found this simple, small, enclosed 120v 30a rated SPDT relay, which looks like it really fits my need.
I, though, am still unsure about where MY wires should come and go. Would the 'coil' be energized by an additional 'jumper' from the RED wire(Shore/Gen)?
Maybe if I provide the website link, and their stock 'instructional' picture, you can mark it up for me and show me where my connections should be made.
-------------------------------------------------------------------------------
My wiring:
RED - power in from SHORE/GENERATOR
BLACK - power in from INVERTER
WHITE - to sub panel breakers that I want to provide power to
---------------------------------------------------------------------------------
https://www.auberins.com/index.php?m...roducts_id=250
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Two 120v power sources, automatic switch/relay-r30a2a.jpg  

Last edited by NCmountainCabin; 06-13-2018 at 06:46 AM.
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Old 06-19-2018, 11:46 AM   #12
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Re: Two 120v power sources, automatic switch/relay


here's the successful connections to the SPDT relay:

for Inverter(bk) NC power, or Shore/Gen power(rd) NO power switching.

the gray(gy) leads are from the (rd) power source trigger
White(we) is to the sub-panel breakers/outlet that need to be powerred

so, the INVERTER(always on) powers the outlets when there is no outside power, and the SHORE/GENERATOR outside power provides it when available, thru the triggered 'switch'(coil). Works very nicely, instantaneously, and quietly.
Attached Thumbnails
Two 120v power sources, automatic switch/relay-relay-wiring-inverter-bk-outside-power-rd-triggered.jpg  
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Old 06-25-2018, 08:24 AM   #13
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automatic switch/relay SUCCESS


thanks

we are on our first 'maiden' voyage with the newly installed RELAY to switch power from Inverter(always on) to 50amp Shore Power or Generator.

We've traveled 80 miles on the Blue Ridge parkway from the start(official end) at Cherokee NC to just east of Asheville, where we are now parked at the top of the mountain at the beautiful Campfire Lodgings RV park...what a view!

The relay is performing perfectly, as designed, and is switching seamlessly between Inverter and shore Power, exactly as I had hoped.

I actually leave the inverter ON, but in what's called 'SEARCH WATTS' mode, where it is active, yet does not provide full 120v power UNLESS a device(s) is asking for power, such as the fridge, when the compressor needs to run.
Now, normally when you are in travel mode, it will power the fridge and all other items, operating in 'ON' mode.
When we 'plug in' at an RV park or campground, or run the generator, it will go back into 'SEARCH' mode, since now the rely has switched to the other power source, and the Inverter is no longer sensing anything 'needing' power.
I really only did this since the inverter doesn't need to remain 'ON' all the time we are on outside power, but it is sitting 'ready' for when we unplug, doesn't require the microwave(blinking clock!) and other devices to lose power during the change over, and uses slightly less battery power during that time.
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