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Technical - Voltmeters

Last Changed 2/28/2011

We had an interest problem each time we used our generator.  Our generator is rated at 7KW which means it can drive about 30 amps on each of the two Power Legs.  The problem comes that when we turn on the generator, when the automatic transfer switch (ATS) connects the trailer wiring to the generator output, the Inverter/Charger starts to restore energy to the batteries.  The normal setting for the Inverter/Generator is 50 amps, meaning that there is 50 amps available for the Inverter/Charger to use for charging.  The Inverter/Charger pulls more current than the 30 amp breaker on the generator that feeds that leg. 

There are no indications because the other leg of the generator is providing power and the Inverter is proving the leg with the flipped breaker.  No indications unless the batteries drop to a level where the Inverter stops providing power.

LED AC Meters Our first solution was to tap the ATS with two fused leads, one to each Power Leg.  These leads were connected to two 120 volt rated LED panel indicators that we position is a visually convenient location next to the LP detector.

That solution served us well for a few years until the brightness of the LED indicators would only be visible when we were right on the LEDs.

One day looking around eBay, we found some AC Panel meters at a very low cost.  The meters we choose had the feature of being self powered, i.e. the meter gets is operating electricity from the two wires attached to the AC source.  Most meters need a DC source for the meter circuitry.  Providing DC voltage wouldn't have much of an issue but we wanted the meters that  uses the AC source and the power because the lack of power would be indicated by no display.  With a DC powered meter, the lack of AC would be a display of "0".

LED AC Meters The size of the meters was just a little larger than the rectangular switch/receptacles used in home.  We choose a nylon plastic plate and enlarged the holes.

We used a surface mount box that attached to the trailer wall and the cover plate was attached to the box.
click on images to enlarge
LED Nightlight A side benefit the pair of meters is an indication of the differences between the power legs.  We found the low cost meters were a few volts lower than the more expensive Progressive EMS or the Good Governor indicated.  That is okay as the first purpose of the meters were just to indicate whether the Power Leg had any voltage.
click on images to enlarge

With the two voltage indications together, we can see if the is a wide difference.  We have run into a condition is a couple of RV parks called floating Neutral.  Normally, the Neutral is tied to Earth Ground somewhere in the park.  That holds the Neutral at Earth Ground and the two Power Legs will have a relatively equal voltage reading.  If the Neutral is not tied to Earth Ground well, when current from one Power Leg flows back through the Neutral, the Neutral will rise in potential and the voltage reading between the Power Leg and Neutral will lower.  At the same time, the voltage difference between Neutral and the other Power Leg will increase.  If the current flow from both Power Legs were equal, the voltage differences would be equal.  But the typical current draws are not equal.  If the current draw in one Power Leg is more than enough than the other Power Leg, the low current Power Leg voltage difference to Neutral becomes high enough to caused the Progressive EMS to shut down on a over-voltage condition.

The EMS protects us from a floating Neutral condition when the current draw is enough.  With no current draw, there is no problem.  By observing the two voltage meters, we can see an impending problem is the two voltages are several voltages apart.

Disclaimer: The information in this site is a collection of data we derived from the vendors and from our personal experiences.  This information is meant as a learning guide for you to  make your own decisions  Best practices and code should always be followed.  The recommendations we make are from our personal experiences and we do not receive any compensation for those recommendations.
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