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.
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
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".
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
click on images to enlarge
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
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
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.