We installed a second hand cool room 3mX 3m
(10'X10') the old condensing unit used R12
refrigerant that is no longer available and was
belt coupled, therefore in the interests of
efficiency we installed a new unit, and so the
troubles began.
Our inverter is a Solar Energy Australia
SEAP-24-3K0, a pure sine wave 24v 3 kW
continuous, 4 kW for 10 min, 3.8 kW for
30 min with a 9 kW surge capability. I had every confidence that it was up to the task,
but from the word go the condensing unit overloaded the inverter approximately every third start.
http://www.solaraustralia.com.au/html/everest.htm
A brief explanation of the refrigeration cycle
for those who are unfamiliar (for the purists
this is not a technical tuition).
In the case of this cool room the refrigeration
is in two parts, the evaporator is inside the
cool room with its associated fan(s). Part of
this is the expansion valve, basically an
orifice that drops the refrigerant pressure,
which dramatically drops its temperature,
this is the part the cold comes from.
Outside is the compressor and condenser
(radiator), the compressor takes its suction
off the evaporator return, a gas at this stage,
compresses it to a high pressure. The compressor discharge goes to the condenser
where it is cooled by a fan passing air across the fins and returned to a liquid. This liquid
collects in the accumulator and from there to the expansion valve, and so the cycle begins again.
In order to find the reason for the inverter
overloads I began investigating the power
supply at the source, the batteries. (again for
the purists all problems could probably have
been sorted out in about 3 hours of fault
finding, but I live on site and wanted to know
the cause.)
I checked the DC connections, fuse connections,
AC connections at the inverter, distribution
board, change over switch (this allows me to run the cool room on the generator)
and finally the isolator at the condensing unit. All were sound,
and voltage measurements taken when the unit started correctly showed a drop from 240v to only 238v.
Instantaneous start amps on the refrigeration guy's
digital tongs (instrument for measuring amps by clamping around a cable)
showed 39 amps, my analogue tongs showed 25 amps,
even on those occasions when it would not start.
Run amps for the condensing unit was 4.7 amps.
Next I dived into the junction box on the
unit and two earth wires pulled out of the cheap spade connector
which was part of the refrigeration guy's installation of the thermostat and high pressure switch. All power
to the unit passes through these two devices, so I checked and replaced all his other spade connectors for
"proper" ones.
A test run period showed an improvement but not cure.
So into his other connections on the
thermostat and high-pressure switch, the
thermostat had connections where the wire is captive under an inverted U onto the flat lug.
Yep you guessed it one connection was loose because the U was not aligned the other just not tight.
The high-pressure switch had only one loose
connection. Another test run period revealed there must be more faults.
During this period we were having
relatively high temperatures with many days
in the high 30's and several over 40 deg.C. The inverter specs say it must be dratted
1.25%p/dc. for temperatures above 30 deg C.
So thinking the inverter may be overheating I added an old microwave
oven fan
on top of the heat sink, I also removed a sheet of iron
from the shed to allow more air to circulate, all to no avail.
Now to be fair, refrigeration units need a
period to depressurize after running before a restart. I tossed about ideas about partially blocked
expansion valve, under cooling of condensing unit and raised the
cut in/out temp difference to 10 deg. but could not hit on anything.
So back into the junction box to check out the condenser
fan and what do you know the spade connector's were crimped on the insulation with the bared cable
splayed in all directions, all leads including the earth. You beauty this could be the answer to the hard starting.
Another test run to no avail,
so back into the
junction box to check all spade connectors, and all others were Ok.
Only one thing left, a blue point connector where the refrigeration guy a had looped the active cable
around the thermostat and HP switch, this he had wrapped in
insulation tape so I had not to this point viewed it.
Undoing the tape revealed the culprit all along, one wire simply slid out,
he had made no attempt to twist the wires together before
placing them in the connector making a high resistance
connection at this point.
Bit fuzzy but look hard and you can see below the black tape one red wire and the bared copper.
Since correcting this, the unit has performed
well, even started one morning when the toaster was in use(1kW), it is still necessary to maintain
a high differential temperature but that's fine for our purposes.
Mains, (as the generator can) could maintain the 25 amps required until the
unit started or tripped on
thermal overload, with a lower temperature difference.
To top it all off the refrigeration guy's
parting comment when he presented his bill was "I'm glad you fixed it, I would hate to have
had to return it for warranty since you are on renewable energy",
I could have further enlightened him but.....