General > General Technical Chat
Noisy power from typical backup generators
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PaulAm:
There are also soft start devices for large compressor appliances like heat pumps.  I had one on my geothermal unit that took a 100+A starting surge down to 30A.  It made my backup generator a LOT happier.
james_s:

--- Quote from: Renate on April 20, 2021, 12:23:04 am ---And for that fridge, just use a nice Dometic water/ammonia/hydrogen thermal cycle fridge, nice and quiet.

--- End quote ---

Quiet and very dependable, but aren't they horrible in terms of efficiency? I remember my grandparents had one in their old motorhome and it put out a ferocious amount of heat. It could run on either propane or electricity and the energy to feed the cycle entered in the form of heat.
Renate:

--- Quote from: james_s on April 20, 2021, 02:25:05 am ---I remember my grandparents had one in their old motorhome and it put out a ferocious amount of heat.
--- End quote ---
They have a chimney flue for the heat.
Unless you put your hand under the flue cap you can hardly notice the heat.
The flame is like a disposable cigarette lighter goosed up to about twice the flame.
It runs me about 7.5 US gallons of propane a month ~$30 with tax (in an expensive area).

You've got me thinking though.
It does have 120 VAC switchover, but no 12 VDC switchover
There are certainly times where my solar panels are throwing electrons to the wind.
I'll have to consider that.
james_s:

--- Quote from: Renate on April 20, 2021, 02:44:03 am ---
--- Quote from: james_s on April 20, 2021, 02:25:05 am ---I remember my grandparents had one in their old motorhome and it put out a ferocious amount of heat.
--- End quote ---
They have a chimney flue for the heat.
Unless you put your hand under the flue cap you can hardly notice the heat.
The flame is like a disposable cigarette lighter goosed up to about twice the flame.
It runs me about 7.5 US gallons of propane a month ~$30 with tax (in an expensive area).

You've got me thinking though.
It does have 120 VAC switchover, but no 12 VDC switchover
There are certainly times where my solar panels are throwing electrons to the wind.
I'll have to consider that.

--- End quote ---

Well the motorhome was a 1965 model and the refrigerator was original, it's possible things have improved since then. This was also 25 years ago so my memory could be a little fuzzy. At one point they made domestic refrigerators using the same process that burned kerosene using an Aladdin mantle lamp burner. Never saw one in the flesh, I only came across them when I was looking for parts for my oil lamp.
Johnny B Good:
@Renate

 Regarding VFD compressor fridges, when I checked what was available here in the UK about a year back, there wasn't a single one. Even looking for high spec (overpriced) fridge/freezers I could only find one (maybe two) VFD compressor models. Needless to say, this was all in aid of eliminating the 1KW or so (measured with an analogue MetraWatt power meter) startup surge of our under counter fridge to save that cheap inverter genset from tripping out to a 1200W plus overload.

 Once the fridge compressor had kicked in, the loading swiftly dropped to 140W. At the time I was testing the compressor startup surge and running loading, it was maintaining temperature on a one hour run with one hour off cycle, averaging 70W consumption. I didn't bother testing the chest freezer since I could probably run it on a daily schedule with the thermostat turned to a lower temperature to allow it to remain safely shut off for 18 to 20 hours per day, allowing me to pick the best time of the day to minimise loads before disconnecting the generator from the SmartUPS2000 to concentrate all of its energy on starting the freezer back up before reconnecting to a lightly loaded UPS.

 You can't really manage a fridge this way like you can a chest freezer which can safely keep its contents frozen through a 24 to 48 hour mains outage depending on the thermostat setting and how often you feel the need to extract items of frozen foodstuff from it.

 I haven't actually tested whether the inverter genset can actually start the fridge compressor, in part because of it lacking a priming bulb pump but mainly on account I'd have to wait for it to cut out on the thermostat to avoid disruption to the temperature regulation and allow a half hour or so for the compressor to cool down enough to allow a normal restart before firing up the genset for another half hour of run time for the 'stat to restart the compressor in the usual way with my missus giving me earache over the noise disturbance to our neighbours.

 Also, since it was late Spring / early Summer, it was low down on my priority list and could wait for when she wasn't around - as per usual when a job is put on the back burner, the test never got run. However, since fitting that priming bulb pump has removed all the hassle I'd originally suffered with starting the generator, I'm a lot more inclined to take advantage of her absence next time she's visiting friends or family, given a dry weather day.

 Even if the generator can only cope with no other loads connected, I can always rig up a load shedding relay to dump the UPS load for the half minute required to ensure the compressor startup surge has been overcome as a work around solution to keeping the fridge running during an extended Winter outage (the only time I'm concerned with due to the increasingly marginal UK grid capacity at that time of the year).

 If it can't cope, then there's no point in rigging up such a work around. If it's a severe winter outage we'd probably do just as well by using the fridge as a "Coolbox" fed with cooler packs chilled by exposing them to the outside freezing temperatures.

 Aside from the increasing risk of winter outages, loss of mains supply is very rare in urban areas of the UK. We've only ever witnessed one actual loss of supply some thirty years ago as a result of a fault in the locality which was cleared just four hours later. My family think I'm wasting my time in making some token gesture of preparedness against what they can only see as an extremely unlikely event, hence all the flak from my ever loving' wife. :(

 We'll probably never see any winter blackouts, especially now I'm prepared to a limited extent to mitigate such events, due to Sod's Law. That's fine by me since the hundred quid investment in the generator is chump change in the larger scheme of things anyway.
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