After about 100 days of operation, and around 2000 startups, the 5A input fuse blew. The compressor takes a lot of current on startup, almost 30A peaks(pic), and I calculated an I2t of around 65A2s, while similar fuses are rated at ~135A2s.
From the logs, it blew when heating hot water with a temp of 50C rather than actually at startup. There would have been around 4A rms flowing at that point, while most of the time it runs at 32C out with 3A rms. From a bit of internet searching, it seems that some older or cheaper fuses use Zinc wire as the element, and repeated high I2t startup events fatigue the fuse so it is a bit "tired" and more likely to fail. Better silver or copper fuses apparantly don't suffer this fatigue at all.
Littlefuse give an expected number of I2t events versus magnitude (pic). I've no idea who made the 5A fuse I used, it was just what I had, likely off ebay some time back.
I'm trying to avoid uprating the current rating, as some of the pre-existing cable run is awkward and only 6A rated. I'll buy a branded fuse, see how it goes.
Has anybody any experience of putting an inline NTC resistor, with a reciprocating compressor? While this would reduce peak currents, I note the compressor has 2 winds, one is a starting wind that runs briefly then is turned off - so I expect a series NTC would affect the startup somehow.
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