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Noisy power from typical backup generators
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Johnny B Good:
 I have a feeling that the 140W figure I'd quoted for our home fridge might have been the immediate reduction a second or so after the 1KW surge since I can't shake off the memory of figures of 72W and an 'average' figure of 36W.

 It looks like I'll get a chance to measure the fridge's startup and running demands in the next day or two. The missus told me today that she's going to see her friend tomorrow or Thursday, probably landing up at their favourite garden centre or some such for lunch.

 That'll give me a chance to set up the generator to test its capacity to handle the fridge compressor startup surge which might well be significantly higher than that almost 1KW peak reading I saw on the MetraWatt's 1000W scale (5A 200V settings). I might even try repeating these tests with the chest freezer if I have enough time. Hopefully, I'll be able to report the results of these tests in another day or two.
james_s:

--- Quote from: Johnny B Good on April 20, 2021, 10:54:34 pm --- I have a feeling that the 140W figure I'd quoted for our home fridge might have been the immediate reduction a second or so after the 1KW surge since I can't shake off the memory of figures of 72W and an 'average' figure of 36W.

 It looks like I'll get a chance to measure the fridge's startup and running demands in the next day or two. The missus told me today that she's going to see her friend tomorrow or Thursday, probably landing up at their favourite garden centre or some such for lunch.

 That'll give me a chance to set up the generator to test its capacity to handle the fridge compressor startup surge which might well be significantly higher than that almost 1KW peak reading I saw on the MetraWatt's 1000W scale (5A 200V settings). I might even try repeating these tests with the chest freezer if I have enough time. Hopefully, I'll be able to report the results of these tests in another day or two.

--- End quote ---

I've measured my fridge before, once it starts up, the consumption increases steadily for a bit as the head pressure builds up, then it levels off at around 140W steady state until it shuts off. This varies ambient temperature, which doesn't really vary much inside my house. US fridges are typically quite a bit larger than UK fridges though.
Johnny B Good:

--- Quote from: james_s on April 20, 2021, 11:31:00 pm ---
--- Quote from: Johnny B Good on April 20, 2021, 10:54:34 pm --- I have a feeling that the 140W figure I'd quoted for our home fridge might have been the immediate reduction a second or so after the 1KW surge since I can't shake off the memory of figures of 72W and an 'average' figure of 36W.

 It looks like I'll get a chance to measure the fridge's startup and running demands in the next day or two. The missus told me today that she's going to see her friend tomorrow or Thursday, probably landing up at their favourite garden centre or some such for lunch.

 That'll give me a chance to set up the generator to test its capacity to handle the fridge compressor startup surge which might well be significantly higher than that almost 1KW peak reading I saw on the MetraWatt's 1000W scale (5A 200V settings). I might even try repeating these tests with the chest freezer if I have enough time. Hopefully, I'll be able to report the results of these tests in another day or two.

--- End quote ---

I've measured my fridge before, once it starts up, the consumption increases steadily for a bit as the head pressure builds up, then it levels off at around 140W steady state until it shuts off. This varies ambient temperature, which doesn't really vary much inside my house. US fridges are typically quite a bit larger than UK fridges though.

--- End quote ---

 That doesn't surprise me. :)

 I still haven't had a chance to run that fridge compressor start up surge load test on my little 1KW rated inverter genset. My missus didn't get the chance to meet up with her friends that week as I'd hoped would allow me the opportunity to run the test free of domestic discord. In fact, all further opportunities to do so have failed to materialise ever since to this day. :(

 However, shortly after announcing my intent, I realised it would be more instructive (and quieter!) to make up a current probe for the SDS1202X-E I'd used to determine the PM alternator's pole count and let it capture the event using the same one shot trigger technique. That would give me a more accurate measure of the peak current surge than the camera on a mini tripod setup I'd previously used to record a movie of the analogue wattmeter to estimate the strength of this start up surge current.

 All I can report at this stage is that I'm still formulating the best way to make up a suitable current transformer module that I can plug into the outlet which I can then plug the fridge into to generate a sensor signal to feed to the DSO. Unfortunately, I've had a few other distractions to content with - it isn't just my penchant for procrastination that has delayed things this time.

 Once I've captured a few of these startup events with the DSO, provided the peak amperage readings don't exceed the generator's 5.2A overload limit (1200W for 30 seconds max), I'll repeat the test using the generator. Obviously, if the start up surge demand peaks much higher than the 1200W limit, there won't be much point in testing with the generator (I already know how it reacts to a 1250W overload - instant shut off!). In either event, I'll make a follow up report when I do eventually make up that current sensor module and have some test results to share.
james_s:
Why not just make things simple and cut straight to testing with the generator? If you overload an inverter generator it just shuts down the output, nothing will be damaged. The only test result that really matters is real world behavior.
Johnny B Good:
 If the opportunity arises to avoid the domestic discord over running the generator before I get the current transformer sensor adaptor made up, I'll do just that. I'm not worried about burning out the genset since I already know the inverter overload protection works quite well.  :)
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