Need to keep a relay coil powered for a short time on loss of coil input voltage. (grid failure)

crutschow

Joined Mar 14, 2008
24,966
Can the computer be powered all the time from the inverter so you don't have to worry about it rebooting?

Otherwise, the problem is that a delay on energize without a delay on de-energize may require some added circuitry.
Are you up to building that?
your schematics are pretty cool.
I use the free LTspice circuit simulation program and the schematics were drawn with that.
 
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crutschow

Joined Mar 14, 2008
24,966
Okay, so here's a solution (I think) that uses three relays.
The first coil is powered from the AC mains and the other two are powered from 34Vdc derived from the 24Vac.

So relay U2 has a delay for the main's power when the mains come on, and relay U3 provides a delay for the inverter power when the main's quit.
U1 has a 120Vac coil (or 24Vac), and U2, U3 have (or are wired for) 24Vdc coils.

Note that the main's connections are through U2's NO contacts, and the Inverter connections are through U3's NC contacts.

mF is millifarads or 1000μF.

All three relays can be the RIB2401D since the coils are designed for either AC or DC operation.

(Edit: Corrected schematic error)

1592252337841.png
 
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Reloadron

Joined Jan 15, 2015
5,454
Looking at a few of your drawings you really do not ever want to switch neutral or ground only the hot gets switched. When switching AC mains between utility power and auxiliary power (Inverter or Generator) you normally use a transfer switch designed for the application, Think relays with mechanical linkage to assure that there is no possibility both can supply power to a load at the same time. Each contactor also normally has an aux contact to make sure one can never be powered while the other is powered. You would normally not use a DPDT relay but a pair of DPST relays. They are commonly called an ATS (Automatic Transfer Switch). I am not going to tell you you need to comply with the NEC (National Electric Code) plus any state or local codes, as that is up to you. I am merely pointing out how things should be done or what should be considered.. Again, no matter the road, never ever switch Ground or Neutral.

Nice looking system and panels.

Ron
 

crutschow

Joined Mar 14, 2008
24,966
Think relays with mechanical linkage to assure that there is no possibility both can supply power to a load at the same time.
The only way the circuit in post #22 could connect both to the load would be if either relay U2 or U3 failed (which certainly has a small but finite chance of happening).
The relay he uses has an operating life of 10 million cycles.
 

mcardoso

Joined May 19, 2020
97
I'm going to come in here with an industrial automation perspective. Your needs are pretty typical of industrial control systems, and I would feel more confident in a system built from components that are designed to do the job required.

Bill of Materials:
-(1) Time Off-Delay Relay: Allen-Bradley 700-FEB1TU22 or Equlv. ( something like https://www.digikey.com/product-detail/en/crouzet/SASP10S110AD/966-1637-ND/2240004 might be a less expensive option, you'll have to pick one to suit)
-(1) DPDT Relay, Form C contacts, 24VDC coil: https://www.automationdirect.com/adc/shopping/catalog/relays_-z-_timers/electro-mechanical_relays/square_-z-_cube_relays,_plug-in,_3a_-_15a_(78x-z-_qxx-z-h78x_series)/general_purpose,_3a,_5a,_10a_(ql2_-z-_ql4_-z-_qm2_-z-_qm4_series)/ql2n1-d24 and https://www.automationdirect.com/adc/shopping/catalog/relays_-z-_timers/relay_sockets_-a-_accessories/relay_sockets/sql08d
-(1) 24V power supply with battery reserve: https://www.mouser.com/ProductDetail/Delta-Electronics/DRU-24V10ACZ?qs=MLItCLRbWsy/RzSq%2BWpDig==

The 24V power supply is fed by the mains and has battery reserve to handle the switchover seamlessly. The timing relay monitors the line and holds the output ON, energizing the load relay. When the mains are lost, the DC supply continues to power the system with reserve battery power. The timing relay begins the Off-Delay timer and after a number of seconds switches the load relay off (N.O. contacts open and N.C. contacts close). The nature of the relay contacts means that the N.O. and N.C. contacts can never be active at the same time.

Alternatively, if no time delay is required, but absolute isolation of the two mains is required, mechanically interlocked contactors are the solution.

For example: Allen Bradley 104-C09D22
1592327149837.png
 

Reloadron

Joined Jan 15, 2015
5,454
The only way the circuit in post #22 could connect both to the load would be if either relay U2 or U3 failed (which certainly has a small but finite chance of happening).
The relay he uses has an operating life of 10 million cycles.
I know that and appreciate that. Personally I would be fine with that. Looks like a nice well installed system. My point was merely to point out the NEC. When on occasion bad things happen and insurance companies ask questions before sharing their money I am not going to be the one who said do it this way. I agree with you and your post and circuits are always right on target. I am only pointing out it would not hurt to consult the NEC code for a specific application. I am also the guy who figures sticking a stainless steel nail through opposing ends of a hot dog and connecting 120 VAC across those nails is an acceptable and safe method to heat a hot dog,

Ron

Ron
 

Thread Starter

jeffy104

Joined Jun 11, 2020
14
HI Guys. Whoa. ........I have been so busy working the the farm 16 hours/day that I have not been able to get back here. I’m not supposed to be here now. I sure do appreciate all the thinking you guys are doing. That’s real work- and productive too. I skimmed over things here and am excited to read things over when I’m not stealing time.Lol. There’s about 400,000 individuals waiting on me............
 

crutschow

Joined Mar 14, 2008
24,966
If you can afford it, mcardoso's approach is a more acceptable system from a code point-of-view, and requires no circuit assembly.
Otherwise I think my approach is likely as reliable.
 

Thread Starter

jeffy104

Joined Jun 11, 2020
14
O man. A really long day here and I have not had the time to absorb everything said here. I like the idea of no circuit assembly but I also like the circuit you have come up with. Those 3 RIB2401D’s are more than I can follow right now. There is one thing I am not too tired to talk about tonight and that’s the ground/neutral switching situation. I don’t claim to understand perfectly the business of grounding and bonding but when I wired my home, everything was grounded to rods I put in near the panel. And my panel ground bus is bonded to the panel neutral bus IN the panel box. I was talking to a friend before starting this thread and as result of our conversation I came up with the switching to ground (neutral) that is in my sketch. My inverter has two lines for load coming out of it and one of them has to go to ground. In my sketch, it’s relay contact #3. Tomorrow (or later) I’d like to quote him but I can’t put my finger on his note right now as much as I would like to. That said, I DO remember we talked about the RV industry, shore power, isolated loads, bonding, double bonding, the NEC, and things like that, as well as the fact that if you put 6 people in a room and talk about grounding and bonding, you will likely get 6 opinions, but it’s up to the installer/contractor to decide how to go about satisfying the NEC with respect to that. SO- I just wanted point out that relay contact #3 came about after several days of head scratching, while I determined what the best way was to satisfy the NEC. Yes, this is neutral switching and I believe it has to be done this way to make this an isolated load and..........uh oh...... getting tired- oh man. Well, that’s all for tonight but there’s more I’d like to say when I can think straight. Wondering if both systems we are talking about here satisfy the relay contact #3 in my sketch. Got to be up in a few hours.......honey bees don’t like to be kept waiting. Nothing worse than a sleep-deprived beekeeper. Thanks again guys for all the well-thought-out input. Ok, my dish is not working so I’ll leave this here, close the laptop and seerif I get a connection the web tomorrow morning. Wait. It IS tomorrow.
 

Thread Starter

jeffy104

Joined Jun 11, 2020
14
HI Guys. I suppose it’s the way I think but I’m leaning toward the capacitor circuit. I looked at the links sent for the mechanical devices and it makes me wish that somewhere along the line I had made it my business to learn about electronics. I’m still too busy to spend the time needed to study all this info and am looking to locate someone near me to help with the hands-on part of putting something together. But thanks to you guys, I see the possibilities and I know what I want and how it should work. I think one or more of the local ham clubs can point me to the right person. I remember when I got my ticket at a nearby club that there were guys that had a background in this sort of thing and they seemed to have a good understanding of electronics. They went on to get their extra class license and I was happy the general class. Lol. There are operators (me) and then there are technicians. When things calm down here, I’m looking forward to having a good, safe installation that will save me a lot of time and money.
 
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