Line Voltage Increases when Air comes on

[campcar]

I have two A/C. With the BR air off when the LR air kicks on the voltage on my line monitor goes from 122 to 124/125. With the LR air off when the BR air kicks on the voltage goes from 122 to 120/119 which is what you would expect. Also I have a surge protector plugged for the TV, DVD, etc and when the LR air comes on and the voltage increases the ground light on the surge protector goes very dim and flickers.

I have spent several hours pinpointing this situation. It only happens when I am on 50 amps.

We are in a two year old RV Park with good power. All sites are 50/30/20. The park has had an electrician check the pedestals for grounding issues, etc. The electrician says the problem is internal to my trailer and I tend to agree.

I have plugged in to two different pedestals in the park which are on different circuits in the park and I have the same increase in voltage issue. However, when I use my 50a-30a pigtail and plug in to either pedestals 30a plug and turn on the LR air the voltage drops from 122 to 120, but if I plug the 50a cord in to the 50a receptacle the LR air increases the voltage from 122 to 124.

I know nothing about electricity or 30a/50a issues but the electrician says it has something to do with unbalanced phases inside the trailer or possibly a grounding issue inside the trailer. This only happens with the LR air, the BR air never increases the line voltage on 30a or 50a.

Any thoughts or experience would be appreciated and do you think I am hurting the Air Conditioner when this happens.

 

[bgscott]

Your problem shouldn't be unbalanced phases, I am new to RV's but my understanding is your 50 amp service is wired as two seperate 120 volt legs instead of a 240 system like in your home. It almost sounds like a capacitance issue, if the air conditioner motor uses a run capacitor you could see a slight increase in voltage due to power factor changes. I have never been inside a unit so I have no idea if this is the case. Your air conditioner motor should be able to handle about a 10% fluctuation in voltage so your probably ok.

 

[bgscott]

Hey Campcar,
If you would like to get to the bottom of this lets run and experiment. While plugged into a 50 amp service locate the breaker that kills your LR air conditioner. Turn off all the breakers on that side of your box, then see what your voltage meter reads. If it still reads hot I have a theory as to what is going on.

 

[campcar]

The voltage is not automatically increased because I have plugged in to a 50a service. I get the same normal voltage reading on both 30a and 50a service.

The voltage only increases while the LR a/c is running while plugged in to 50a service. As soon as the a/c shuts off the voltage drops back. As long as the LR a/c is not running the voltage level is normal.

All of this only applies to the LR a/c. The BR a/c never increases the voltage.

 

[leftyf]

You may have a ground loop. The voltage is not really going up...that leg in reference to ground is changing. Measure each side of the connector to ground and I'll bet you may find two different voltages. You probably have the trailer up on blocks where nothing is touching the dirt. If you remove one of the pads and let the leg touch dirt, I'll bet you may read the same voltage to ground on each leg. Check the ground bar on your switch box, inside the trailer, and make sure all the grounds are tight.

The other thing is you do not necessarily have to read the same voltage on each leg. If you are reading the voltage thru the motor, there is no telling what you might see because of the various electronic components and what they do inside the circuit. Are the makers of your air the same or different, sizewise, and capacity wise? Two volts is nothing to be concerned about.

 

[bgscott]

when you are connected to 50 amps you have two seperate single phase 120v legs relative to ground. these two legs are 180 degrees out of phase with each other, this is what gives you 240 volts phase to phase in your house. In the camper you do not have the ability to put a breaker across both legs so its always two seperate 50 amp 120v legs. when you plug that into a 30 amp connection you are actually using one 120v circuit to feed both busses in your camper. thats why you don't see the difference when you plug up to a 30 amp service. there are several things that could cause you to see the voltage change, my first stab at it above probably is not it. I don't think you have a problem to worry about. If you start seeing 130's or less than 110 start to worry. If you want to check anything pull the cover on your breaker box and make sure your grounds and neutrals are good and tight. Make sure you unplug from shore power before you try this.

 

[leftyf]

Yeah, messing around inside a breaker box can be as shocking experience.

Great explanation, reminded me of things I had completely forgotten.

 

[ct0218]

Mine does the same thing. Each A/C is on a different leg. Lefty is correct-check the voltage at the park box and the voltage is slightly different. Not a problem.

 

[campcar]

Thanks for all of the quick responses but let me reiterate what I see as acting strange. I want to make sure the responses are focused on my problem.

Let me start off by saying that I know pretty much nothing about electricity so checking voltages at breakers and ground wires is beyond my personal capabilities. I hope to ascertain from this discussion if this is something that I need to have a dealer checkout or it is really not a problem since I would not even know it existed if it was not for my line voltage monitor.

Maybe I wasn't clear about how I am monitoring this. My line voltage monitor is plugged in to an electrical outlet inside the trailer. I have plugged it in different areas of the trailer and it always reads the same. I have carefully watched the monitor when any other major electrical appliance kicks on and the needle will dip and then return to normal or just a volt or two below normal.

However, when the LR a/c kicks on the needle never dips and immediately jumps UP 2 or 3 volts and stays there as long as the a/c is running and immediately drops back to normal as soon as it turns off. The other thing is the surge protector that I use for my TV, etc. The ground light on the surge protector which is plugged in to an electrical outlet shows everything OK until the a/c kicks on and then the ground light on the surge protector goes very dim and flickers until the a/c turns off and then it returns to normal.

As I stated in my initial post the rvpark has had an electrician check the voltages on all of the outlets at my pedestal and other pedestals in the park and everything reads 122 volts at the pedestal.

I hope this clarifies what I consider to be unusual. I don't want to beat this horse to death but any additional comments would be appreciated as to why only one appliance in the whole trailer would cause the line voltage to go up instead of down only while it is running and cause the ground light on the surge protector to dim and flicker.

 

[ct0218]

Lefty's comment about the ground loop could be a possibility. You might try grounding a stabilizer or foot to the ground and see if that makes any difference. I'm 450 miles away from my Landmark right now but I think I have wood between every stabilizer and leg so there is no frame to earth contact on mine either. I have never seen a surge protector with a ground light, only a power on light, so I'm a little confused by that. I have circuit testers that have lights for all three, but never have I seen that on a surge suppressor. All of my incoming power runs through a Hughes Autoformer, and I don't have separate surge protectors. I have not tried moving my power line monitor to a different outlet because I think all of mine are on the same leg. I remember shortly after we bought our Landmark I lost power in every outlet, yet other 120V hardwired items, and some inacessible outlets possibly, still worked. Turned out to be a bad main breaker for one of the two 50A legs. Other than that, mines does the same voltage increase now for almost 2 1/2 years and it has created no problems. It does make me want to check all my lugs on the breakers again. I think I checked each one back when the breaker failed, and I did find some loose connections. I can tell you a loose lug or connection anywhere can create problems (heat) and cause weird things to happen and drive you nuts trying to track it down. Just last month it took me a while to troubleshoot my water heater not working on 120V. Backtracking from the heater I finally found a loose neutral at the wall switch inside by the door, all the while thinking that the element had burned out. At least I now have an expensive spare element! Try grounding the trailer frame to earth to see if anything changes.

 

[bgscott]

Campcar,
Your last thread points to what I was trying to test earlier. being new to RV's I don't know alot about the equipment so I didn't know where a voltage monitor was hooked up. your Voltage monitor plugs into an outlet, which uses one leg of the two legs of 120 we were talking about earlier. probably all outlets feed off of that one leg. your probably never seeing a reading on the leg that feeds the LR ac. Anyway, I did check the motor rating on a single phase motor yesterday, they can handle 10% fluctuation. you are ok.

Here is a wild guess at what is happening. There is two wires laying somewhere in your camper parralel to one another, one feeds from a breaker to some load off one 120v leg, the other feeds off of the second 120v leg to another load inside the camper. when you are plugged into a 50 amp service these legs are 180 degrees out of phase with one another, so flux off of the lines cancel each other out. when you add the large load of your ac to one line, the power factor changes on that leg, this causes a slight drop in voltage on that leg, now those two wires laying side by side are no longer totally cancelling out each others magnetic flux. the second leg, the one you are monitoring, actually picks up a couple of volts off of this the phase shift caused by the load on the first leg. this can not happen when you are plugged into a 30 amp service because your actually tying the two legs (busses) in your breaker box to one phase, so there is no way to pick up magnetic flux between those two pesky parralel wires.


or that could be completely wrong!!

Your still ok, two volts variance is nothing.

 

[Shadowchek]

I would tighten all of your connections and then not worry about it. electricity does some strange stuff when you get 2 legs of power out of phase with a common ground and capacitor run motors which your fan motor and compressor both are. If you had a serious grounding issue your gfi would trip. It doesn't take much to trip those things.

Greg

 

[SmokeyBare]

Or.... Tape over that Monitor.... Switch to Bay Watch Re-Runs... and enjoy the View....