On Fri, 2 Apr 2021 05:34:56 -0700 (PDT), TimR
wrote:
On Tuesday, March 30, 2021 at 5:19:06 PM UTC-4, wrote:
On Tue, 30 Mar 2021 14:08:46 -0400, Pat
wrote:
We had a power outage here last Friday that lasted about 19 hours. (It
was caused by a wind storm blowing a large tree into power lines a few
blocks away). I happen to have four 100 Ah LiFePO4 12v batteries near
my circuit breaker box. (Their normal use is to power my boat during
the summer, but they were just being stored in the basement this time
of year). I also have a 1500 watt 12v to 120 VAC inverter. You can
probably see where this is going... Can I power my
refridgerator/freezer during the power outage using the inverter and
one of the 12v batteries? I thought, why not give it a try?
The refridgerator/freezer is a Sub-Zero brand built-in side-by-side
that is about 15 years old. If you aren't familiar with these, they
have separate systems for the refridgerator and freezer (ie, two
separate compressors). It has a dedicated 15 amp circuit, so it was
easy to pull the breaker and separate the wires from the breaker box.
I did that and then put a regular three prong plug on the end of the
wires and plugged the plug into the inverter socket and gave it a try.
The Sub-zero powered up normally and appeared to run. It drew about
800 watts for short periods and about 100 watts for longer periods.
(For example, 800 watts for 20 seconds followed by 100 watts for 2
minutes ... then repeat). So far, so good. After an hour or so, the
refridgerator section was back down to its normal 38 degrees F, but
the freezer temperature was slowly rising rather than dropping as
expected. Near the time the power was restored, the refridgerator
temp was still at 38F, but the freezer had risen from 0F to 22F. In
other words, the freezer wasn't really working at all. When the power
came back on, I restored the circuit to normal. Within a short time,
the freezer was back down to 0 and everything was back to normal.
So, my mystery is why did the refridgerator run normally off my
inverter but the freezer did not? The inverter is of the sine-wave
variety. I don't have a scope to look at the wave form, but it kept
the voltage up at 114 VAC even under the heaviest load (measured with
a Fluke 87). It was 120 VAC with no load. I would like to understand
this so I can use this setup during any future outages.
Thanks,
Pat
It is possible it just doesn't like 114v. That might be a bit lower
than that by the time it gets to the fridge. My generator puts out 115
under a fairly full load and my newer Whirlpool side by side didn't
like it much. The actual voltage at the plug was 109-110.
I ended up putting this together and it solved the problem.
When I ran it up to around 120 all was well.
http://gfretwell.com/electrical/Henc%20Variac.jpg
If you're unlucky enough to not have a variac, they're pretty easy to build, and no tedious winding of wire is involved.
See he
https://www.youtube.com/watch?v=P9UjxG8sN1c
The "scariac" is NOT a variac - it is a high powered rheostat.
A Variac is a variable output autotransformer and can increase voltage
as well as fecrease it and the output voltage is pretty much unrelated
to the resistance of the load - unlike the "scariac" which is
basically part of a voltage devider network, dropping part of the
voltage across the load and dissipating the rest as heat in the
"cell". The "scariac" will also work on DC - while a Variac is
strictly AC. I have several rangng from 500ma to over 2a amps. I have
one set up in a toolbox that can supply up to 160 volts - either AC or
DC - from a 115 volt AC input and had another set up to supply
adjustable 240 from 115 or adjustable 115 from 240.
I also have a "sstepiac" - a buck-boost transformer which has a 6
and 12 volt secondary connected in series with the primary - either
forward or reversed - to boost or reduce the line voltage by 6, 12, or
18 volts depending on how it is configured - as well as an isolation
transformer made of parts of 2 microwave oven transformers. I used to
have an isolation trandformer made of 2 big fillament transformers
connected back to back for working on "ac/dc" tube radios and TVs
back when I was a kid.
A Variac is NOT an isolationtransformer - both sides of the line CAN
be "hot" on the output!!!!!