Need help with my DIY transfer switch!

Thread Starter

alexrace

Joined Apr 17, 2020
9
Hi, instead of buying the package sold by Go power or Progressive dynamic, I bought a simple AC relay (30A) with a 120 VAC coil to switch current between shore power and inverter in my RV. I connect the coil with the black and neutral wire of the shore power to switch the AC power when the shore power is plugged. The problem is that the relay is chattering when I use it with some particular load. For example, when i use my heat gun at medium power, it chatter a lot, but It doesn't when I use it at high power ??? I remove the relay from my rv to make some tests and it looks like when I use two differents circuits (from two differents breakers) for the coil and the main, it works fine. What can i do to prevent chattering when I plugged the coil and the main with only one circuit as what it is possible in a RV ? Thank!
 

crutschow

Joined Mar 14, 2008
25,680
I'm a little confused when you refer to "shore power" with an RV (so I assume no boat is involved?).
Post a diagram of exactly how every thing is wired.

It sounds like there is excessive voltage drop to the relay coil from a high resistance somewhere in the circuit.
How large are all the wires?
 

crutschow

Joined Mar 14, 2008
25,680
From your diagram it would seem that the Shore power wiring or plug contact resistance is too high so that when you apply a load, the voltage drops below the relay drop-out voltage.
Do you notice any dimming of the lights when this occurs?

So you might try to use a voltmeter to determine where the voltage drop is occurring.
 

sghioto

Joined Dec 31, 2017
1,561
I remove the relay from my rv to make some tests and it looks like when I use two differents circuits (from two differents breakers) for the coil and the main, it works fine. What can i do to prevent chattering when I plugged the coil and the main with only one circuit as what it is possible in a RV ?
This part is confusing to me. What two breakers are you speaking about? In the RV???? Or the panel where the AC cable for shore power is plugged in?
 
Last edited:

Tonyr1084

Joined Sep 24, 2015
5,258
First, I'm assuming 120VAC single phase (not split phase) since I would assume shore power comes from a single plug (according to your drawing). You state that when you use two breakers (assuming RV panel) the relay chatters. There's still a lot of uncertainty. However your drawing looks like it should work. I've simplified it a little, see if this helps. (below)

The only conclusion I can come to is that though this is how you intended to wire it - something is not right. When you use your heat gun on High the relay doesn't chatter but it does when you use it on Medium (assuming Low as well). Verify you've wired it correctly. For the relay to chatter either the current is dropping WAY low, causing it to chatter OR you've used the wrong sort of relay. The coil must be rated for 120VAC (Alternating Current), not DC. I'm no relay expert, but my first thought is that something is not wired right.

1603389033281.png
 
What are you using for a shore power cord and how long is it? This sounds similar to using too small of an extension cord with a portable air compressor. They will struggle a bit until they get to speed then work fine until the end of the cycle and struggle again on the next start cycle (if it gets that far to begin with)
 
I remove the relay from my rv to make some tests and it looks like when I use two differents circuits (from two differents breakers) for the coil and the main, it works fine.
Using separate power for the coil and main also leads me to the cord line of thinking, or maybe even upstream of where you connect to power.
 

Tonyr1084

Joined Sep 24, 2015
5,258
Haven't been camping much, but aren't those outlets regulated to limit the amount of current?

But what isn't making sense to me is the heat gun thing. On high the relay doesn't chatter, but on medium it does. Cord? Maybe. But I still suspect something is mis-wired. A drawing is great. But the actual building of the circuit - that is another thing. I still suspect something is wrong in the wiring. Less power shouldn't result in more drain.
 
I'll admit I don't know myself, but I would imagine a current limiting device would open up the door for man made brown outs that in the long run would lead to more problems than they are worth. Obviously a standard circuit breaker (or fuse) would be in the mix as well as probably some sort of GFI.

I was thinking the medium setting may have something to do with the fan itself and how it is drawing power. At higher speeds it may draw power more consistently than a slower speed which may have more of a spiked draw that in the long run is actually less power overall. Needless to say I don't know for sure and may be totally wrong, but in my head it works.
 

Lo_volt

Joined Apr 3, 2014
123
Definitely worthwhile checking the size (wire gauge) of the cord and the length. Too small wire size or too long a cord will cause problems.
alexrace can you measure the voltage at the relay while you run your heat gun? Also, let us know what the relay voltage does when it starts to chatter.
One last suggestion is to get a watt-meter, something like a Killawatt. Measure the power you are drawing while running your equipment. This will help us recommend the proper wire size for your cord.
 

Tonyr1084

Joined Sep 24, 2015
5,258
I'll admit I don't know myself, but I would imagine a current limiting device would open up the door for man made brown outs that in the long run would lead to more problems than they are worth. Obviously a standard circuit breaker (or fuse) would be in the mix as well as probably some sort of GFI.
My brother, when I was quite young, lived in a condominium. A couple times he couldn't pay his bill so since it was winter the power company was prohibited from shutting people with children off. So they put a device that would limit the amount of current he could draw. It was enough power to run the heat and lights and maybe some cooking apparatus but nothing big power.

When people rent campsites with electric hookup there must be some way of controlling how much power is being used by a camper/RV. I don't know - I've never rented a campsite with electricity. Never even looked into it. Still, I don't think that's the problem. Some are suggesting wire size, which WILL make a difference. Others suggest the plug itself may be a poor connection. While all that is valid, I still don't see how using less power can make the relay chatter as opposed to using more power. That's what I'm hung up on.
 
My brother, when I was quite young, lived in a condominium. A couple times he couldn't pay his bill so since it was winter the power company was prohibited from shutting people with children off. So they put a device that would limit the amount of current he could draw. It was enough power to run the heat and lights and maybe some cooking apparatus but nothing big power.
Interesting. I guess it is possible. It seems overkill in a way, but also smart in others for a camp site, park, or whatever. It wouldn't be hard to add enough cushion in the rent to cover a little more than normal electricity. I've just personally had more issues with under voltage situations than anything else that I can remember.

The low / high power thing is odd for sure, but pretty much in the end a voltmeter and some time will be worth a lot more than our guesses.
 

sghioto

Joined Dec 31, 2017
1,561
Just for the record the electricity at most RV sites is normally included when staying for just a few days. Longer stays usually by the month are metered just like at your home.
 

Thread Starter

alexrace

Joined Apr 17, 2020
9
From your diagram it would seem that the Shore power wiring or plug contact resistance is too high so that when you apply a load, the voltage drops below the relay drop-out voltage.
Do you notice any dimming of the lights when this occurs?

So you might try to use a voltmeter to determine where the voltage drop is occurring.
Yes, that's what was my first thought but the heat gun thing make this hypothesis not right. Why the relay chatter when it is working at low but it does not when it is working at high? That's confusing me. Also, why when I use one 110V circuit for the coil and another 110V circuit for the pole (with their own breaker), all is working fine. I ask myself if there was not a electronic part that I use to make it work only with one circuit as it in my RV. Thanks!
 

Thread Starter

alexrace

Joined Apr 17, 2020
9
First, I'm assuming 120VAC single phase (not split phase) since I would assume shore power comes from a single plug (according to your drawing). You state that when you use two breakers (assuming RV panel) the relay chatters. There's still a lot of uncertainty. However your drawing looks like it should work. I've simplified it a little, see if this helps. (below)

The only conclusion I can come to is that though this is how you intended to wire it - something is not right. When you use your heat gun on High the relay doesn't chatter but it does when you use it on Medium (assuming Low as well). Verify you've wired it correctly. For the relay to chatter either the current is dropping WAY low, causing it to chatter OR you've used the wrong sort of relay. The coil must be rated for 120VAC (Alternating Current), not DC. I'm no relay expert, but my first thought is that something is not wired right.

View attachment 220335
Yes, the relay that I am using has a 120VAC coil. The heat gun thing is very confusing. What I'm saying is that when I use one 110V circuit to energized the coil and one 110V circuit for the pole of the relay all is working fine, but this configuration is impossible in a RV as I have access to only one 110V circuit outlet to plug into my RV. I was wondering if there was a part that I could put between the "shore hot line" and the hot pole of the coil to make the voltage more stable to remove the chattering in all situations. Thanks!
 

Thread Starter

alexrace

Joined Apr 17, 2020
9
This part is confusing to me. What two breakers are you speaking about? In the RV???? Or the panel where the AC cable for shore power is plugged in?
This part is confusing to me. What two breakers are you speaking about? In the RV???? Or the panel where the AC cable for shore power is plugged in?
No, I mean I tested the relay outside my RV with one 110V circuit to energized the coil and one 110V circuit for the "pole switch"of the relay and all was working fine in all situation. This configuration is impossible in a RV as you have access to only one 110V cicuit.
 

Thread Starter

alexrace

Joined Apr 17, 2020
9
I'll admit I don't know myself, but I would imagine a current limiting device would open up the door for man made brown outs that in the long run would lead to more problems than they are worth. Obviously a standard circuit breaker (or fuse) would be in the mix as well as probably some sort of GFI.

I was thinking the medium setting may have something to do with the fan itself and how it is drawing power. At higher speeds it may draw power more consistently than a slower speed which may have more of a spiked draw that in the long run is actually less power overall. Needless to say I don't know for sure and may be totally wrong, but in my head it works.
That is a good remark. Do you know if it exist a electronic device to stabilize the voltage to the coil to eliminate any chattering. I know that the transfer switch made by Go power come with a cicuit board install between the shore line and the pole of the coil. I don't know what are they made of, but it says that the device is use to imply a delay when you plug a gas generator to make it start before drawing any power. May be this circuit board include a device to stabilize the voltage given to the coil pf the relay?

1603413225009.png
 

sghioto

Joined Dec 31, 2017
1,561
and all was working fine in all situation. This configuration is impossible in a RV as you have access to only one 110V cicuit.
Depending on the park I suppose. I've seen some with seperate breakers for 50,30 and 20 amp outlets but I know that will not always be the case. Just a thought, what if you tried a 12 volt dc relay powered by a 12 volt adaptor on the same breaker as the mains.
 
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