Voltage variations and Surge cut off.

[joelc]

We are hooked up to 50A service. I just recorded the voltages at different areas and I will note them below. I have a Progressive EMS/Surge suppressor hard wired in just before the breaker box. It has always worked well and has saved the coach several times at CG. My problem is it seems, there is a voltage rise on one leg at night, about 3 a.m. and when the heat pump goes on the EMS cuts the current. Both legs are high, but one is about 130V.

Taken 11 A.M. today
1. Voltage at post. Both legs 121 V
2. Inside at input to EMS Leg 1 = 128V 0 A Leg 2. 127 V 0 A
3. With Air on
Leg 1 130 V o A Leg 2 121 18A
4. With A/C fan on only
Leg 1 129 0A Leg 2 125 V 8A
5. With Heat Pump on.
Leg 1 130V 0 A Leg 2 122 V 17 A

The A/C voltage does drop during the day with no problems. If I shut off the electric water heater, there are no problems running the heat pump on heat during the night.
As you can see, there are voltages differences between the post and the EMS input. That is why I feel something in the RV is raising the voltage. ANY IDEAS WILL BE APPRECIATED.

By the way, I do not have a generator and I am sure that on my unit there was no transfer switch installed unless you had one.

[joelc]

Got a call back from Progressive Industries today and I guess I did the right thing. I noted to him what my voltage readings were and how I did them and told him neutral was fine. The display board on the EMS does signal the EMS when the voltage peak is either too low or high to disrupt the voltage. It is not there just to display the voltage. He indicated the pots might have swayed due to age. Should it happen again, I could replace the board.

Thanks for all your help.

[Jframpey]

I,own a small RV. Park. I received a complaint from one of my campers - 130 volts on one leg and 110 on the other... checked with my voltmeter, and called the power company. Sure enough it was a poor neutral - squirrels like to sharpen their teeth on overhead wires!

[CA_Traveler]

Checked the neutral how? One check is to place a heavy load on L1 and then L2 while measuring both voltages and the voltage from ground to neutral. Ground to neutral should be just a few volts.

You may/may not find anything depending upon the problem and/or it may be dependent upon what is happening in the CG. Your best test may be another CG.

[joelc]

dougrainer:
What you have mentioned is absolutely correct. I just checked the Neutral and it is good. All other aspects are true and working properly. Since I adjusted the pots the voltage is concurrent with the VOM readings. All seems good at this point. When we get some cool weather again and I can turn on the Heat Pump, I will be able to tell if there are still problems.

What I do not understand is how the pots got out of adjustment.

Thanks all for your help. I am confident we are on the right track. Will keep you up to date.

[dougrainer]

1. Get a GOOD voltage reading with a regular Multitester/voltmeter. Do not trust the EMS system.
2. On TRUE 50 amp service, you have 100 amp available with the required supply wiring to the CG 50 amp plug. So, you should NOT see such a voltage variable between the 2 legs if the CG is wired correctly.
3. As others have mentioned. I would have the NEUTRAL wire and connection checked at both the CG pole plug and in your EMS connection and in your RV inside 50 amp breaker box. Loose/burnt Neutrals can create havoc and problems in a 50 amp RV.
4. On REAL correctly wired 50 amp service, you should have NONE of the problems you are experiencing.
5. You do show double the line voltage which shows out of phase 120 supply(which is correct), but that will not show if the supply wiring to the CG 50 amp plug is the correct gauge for true 50 amp service. IF the wiring is undersize, you will get voltage drops as you experience. Doug

[SoundGuy]

time2roll wrote:
My amp reading always seems high. Is there a trim pot for amperes displayed?

Not that I know of.

[time2roll]

My amp reading always seems high. Is there a trim pot for amperes displayed?

[joelc]

I decided not to try to trip the voltage by adjusting the pot. What I did was kept the post voltage on and shut off all power to the RV by way of the main RV 560A breaker. I then used my VOM to check the voltage incoming and outgoing to the EMS to be sure they were the same. Being said, I then adjusted the pots to the incoming voltage of both poles L-1 and L-2 to the same as the VOM dictated.

I then opened up the main breaker to be sure all areas of measurement were the same. I will wait to see what happens now. If Progressive calls me back I will ask questions. I also recorded the voltages before I made any changes in case I have to put anything back.

[SoundGuy]

joelc wrote:
I shall also bring it to 132V to see if it plays any role in cutting the voltage or if it is merely for information purposes.

And how would you do that? :h To do this properly one needs some sort of variable voltage source (Variac) ... during my professional years I used one many times but now that I'm retired I no longer have access to one. In lieu of this the best I can do is use the EMS's input trim pot to reduce input voltage to the circuit board that senses and eventually triggers low voltage cutoff. However, that won't allow the voltage to be adjusted upward beyond what the source may be, say 120 vac ... ergo, the need for a Variac.

[joelc]

Now that I know I will do no harm and I can put them back where they were, I will experiment by adjusting them to my VOM and then see what happens. I shall also bring it to 132V to see if it plays any role in cutting the voltage or if it is merely for information purposes.

[SoundGuy]

joelc wrote:
Soundguy:

You are correct. I do have two adjustment pots above the display. I was not sure what their function was so I did not touch. Do you happen to know if the display board is just for display or if it plays a roll in cutting the power should it go above 132 V? D currently have mine pulled and I am reading the same voltage before the EMS and after the EMS.

Obviously I'm not privy to an authorized schematic of these EMS units but from what I can tell the readout display is just that - reads out the voltage inputted to the EMS circuit board. Adjusting the trim pot(s) adjusts the input voltage down (or up) but the low voltage cutoff threshold of 104 vac is fixed. In other words, if you adjust the voltage down using the trim pot(s) the voltage display will drop accordingly and when it hits just a hair below 104 vac the unit will disconnect. I've not tested the high voltage cutoff as I'd need a Variac (which I don't own) as a voltage source but I'd assume it's functionality would be the same. I wouldn't touch these trim pots though without having a calibrated meter on hand since there's no point in making any adjustments unless they're accurate. My EMS was originally reading about 1.4 volts high compared to the actual voltage being inputted to the unit, now it tracks very closely with my calibrated DVM and as luck would have it with my Kill-a-Watt meter. :B

[joelc]

Soundguy:

You are correct. I do have two adjustment pots above the display. I was not sure what their function was so I did not touch. Do you happen to know if the display board is just for display or if it plays a roll in cutting the power should it go above 132 V? D currently have mine pulled and I am reading the same voltage before the EMS and after the EMS.

[SoundGuy]

joelc wrote:
This leads me to think that the LED display on the EMS is giving false voltages.

I read your original post several times and didn't quite understand your concern until you posted the above which indicates you're questioning the accuracy of your EMS's monitor panel readout, not it's ability to accurately connect or disconnect to power. Since you originally referred to your unit as being "hardwired" into your rig I'll therefore assume what you have is a Progressive Industries EMS-HW50C, essentially the same as my own EMS-HW30C. If so, open the EMS and you'll likely find a couple of trim pots similar to the single trim pot I have in my 30 amp version ...



Yours being a 50 amp may have 2 of these trim pots. This trim pot adjusts the voltage readout on the monitor panel but does not affect low voltage or high voltage cutoff thresholds. I trimmed my own against a known calibrated DVM but it's a bit of a guess since the EMS's readout only reads to full volts, not tenths. That said, I did manage to get mine to track quite closely to my calibrated DVM. All this said, it's hard to believe your EMS could be reading as far off as you claim - a volt or two I can see but anything more than that I'd wonder why.

A series of 10 pics of my own EMS-HW30C starts here.

[joelc]

I did some measurements this morning again. I think I noted that for some reason the voltage is lower in the morning. But anyway here is what I got:
Voltage at the EMS
Before Both l1 and l2 121 V with 244 across
After the EMS. L1 and L2 121 V with 244V across
The reading on the LED was L1 128 and L2 127

The voltage at the circuit breaker box was 121V on each circuit with 244V across

This leads me to think that the LED display on the EMS is giving false voltages. I do not know if the display has something to do with cutting off the power or not. So I removed it and am still getting all same voltages.
I have a call into Progressive to find out additional information. If the problem occurs next time the heat goes on, ( I tested it and it was OK) then I will switch over to 30A until I get the problem resolved. No problems with 30 A.