"bob prohaska" wrote in message news:sp5fti$69s$1...@dont-email.me...
Does anybody have experience with soft-start circuits for domestic
refrigerators? The goal would be to minimize the size of inverter
or generator needed to run a fridge during an outage.
That's the sort of thing I experiment with, though not with changing the
operation of the compressor because I don't know how much starting torque
margin they have under all conditions, especially after a very brief outage
when pressure is still high, and don't want to stall and burn out one.
I capture the starting surge with an AC current probe and a digital storage
scope after other methods gave very inconsistent readings. The surge on a
small fridge that draws 60~80W running was 12A for about 600mS. My APC1400
UPS (900W, 1400VA) starts it until the battery is nearly drained. The APC
also starts a compact 4.3 cubic foot Magic Chef refrigerator without
If you can live with the small capacity a compact refrigerator may be the
most cost-effective solution. Mine was $160 on sale. Its capacity was
adequate for me until Covid forced me to stock up with more food less often.
I also have a small Alpicool C20 to use in the car, which became my backup
freezer with an extra week of food. It's shut down for every type of soft
fault mentioned in the Amazon reviews but so far always worked again after
I'm presently checking out an Alpicool T60 fridge and/or freezer that runs
on 12V or 24V DC. Their inverter compressors, similar to the Danfoss/Secop
BD35, soft start without overshoot. For a solar+battery system they have the
advantage of not needing a true sine AC inverter with its significant idle
power consumption. A KAW EZ shows the T60 as a freezer costing $2.28 per
month at $0.187 per KWH. For reference the Magic Chef costs less than $3 per
month in winter and around $5 in summer, at room temps between 75F and 80F.
60 liters is 2.1 cubic feet. Since the food is in wire baskets it can be
more tightly packed than on shelves, assuming you choose containers that
nest together well like mayo in flat squeeze bottles instead of round jars.
The C20 and T60 power connector appears to be an IEC C11, which ARB and
other makers of twice-the-price portable DC refrigerators also use. The
supplied cord drops several tenths of a volt and I couldn't find a bare
connector to wire so I made snug-fitted socket pins from 3/16" brass tubing
flattened to 2mm inside, and wired them to Anderson PP45s.
You would have to suffer long and frequent outages for the cost of gasoline
to approach the price of another generator or refrigerator.
My Honda EU1000i is rated to run 3.9 hours on its 0.61 gallon tank at full
load, 900W, and the ECO setting. That's .156 gallons/hour, $0.69 per KWH at
$4 a gallon. The cost is around $10 to recharge my 2 KWH battery bank daily
for a week of outage each year. That's the maximum, we don't have week-long
outages every year and in sunny weather I don't need the generator at all.
My appliances are sized within the capacity of the APC inverter and low
consumption from a generator is just an added bonus. For me these are hobby
and educational expenses, I'll never recover the costs of "free" solar power
if I store it in batteries. The Alpicools allows me to use solar electricity
as it's generated to replace grid power but the savings is hardly $1 per
month. Their value is versatility and convenience, I can stock up during
sales and shut them off after using the contents. The C20 is a 0F freezer
right in the car.