@robl Did your can of propane contain Butane as well? also, do you have link to where you got it and the regulator please.

The propane was pure, just R290 - in fact just search R290 in ebay. I got it from ebay uk, they called it: "Embraco compressor R290 gas 370 GRAM REFRIGERANT CANISTER CYLINDER BOTTLE"

The regulator was also from ebay uk, and it was called: "Fridge Freezer gas R290 R600a BOTTLE ADAPTOR service Valve"


Pic shows items that look identical to mine. Nb: my regulator was supplied in the ON state, and I should have turned the regulator OFF before fitting it. Oopsy.

Thanks Robl, it was just a thought. Another question how did you 'do' the co2 bit tank and regulator ?

I started off with a fire extinguisher that somebody gave me. Don't do that though, it was a mistake on my part - there's all sorts of other rubbish in fire extinguisher gas, so it doesn't completely stop oxides from forming when you braze. Get a CO2 or a N2 bottle intended for brazing/welding, and a regulator for it. Annoyingly, all the bottles have different threads, so I needed another regulator for the CO2 can too.
I got a CO2 welding can and regulator from toolstation (UK).
The other bit of invaluable kit is the manifold gauge, which comes with a few HVAC pipes, which you'll likely need anyway? To braze, I went from CO2 bottle+reg-> manifold gauge -> system I was brazing. I needed a tiny amount of CO2 bled through continuously - too much and I couldn't get the piece hot enough.
Good luck, whatever you're up to!

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.

I have tried an addon beefy 200J 10R NTC to decrease the startup inrush, to prevent my fuse from blowing again. And the behaviour was really not what I would have predicted. I actually have 2 notionally identical 2nd hand compressors - as they're cheap I got one of them as a spare - and to vacuum down during the build. Turns out one has a relay +80uF cap to start it up, the other is simpler with a PTC in series with the startup winding. Anyway, they behave very differently. After a lot of startups and measurements...

PTC compressor startup 16A rms for 230ms, I^2t = 59A^2s
PTC compressor +10R NTC startup 12A rms for 429ms, I^2t = 62A^2s

Relay+80uF cap startup 17A rms for 79ms, I^2t = 23A^2s
Relay+80uF cap +10R NTC startup 11A rms for 19ms, I^2t = 19A^2s

Conclusions:
The version I am using, is the wrong one. I installed the cheapie inferior startup one.
The relay + 80uF cap version is MUCH easier to startup, with 3x lower I2T. This extends the expected life of the fuse type I am using to >1million startups :thumbup:
Adding an NTC to either drops the peak current to below 13Arms, but oddly hardly affects I2T.


There are forms to fill in in the UK if the ASHP/GSHP has a startup of >13A, so swapping over will both save the fuse, and also means I'm vaguely legit:-) I think I can just swapout the elec bit - it's just a plug in object + solder on the cap, no need to change the actual compressor, no brazing needed.
There is a subtlety - I will add a 60kR 5W 500V resistor in parallel with the 80uF startup cap. Otherwise by default it stays charged, and there is nasty DC available down the power cables after power is removed. 60K will dissipate <1W, and should decay to 60V in <10s.

Attached are some pics, the scale is the same every time. One shows the PTC style compressor startup plus a schemtic of the compressor, the other the relay style, both have with and without an addon series 10R NTC.

Looking harder at the compressor datasheet, it has 3 possible starter configurations. And one of them is slightly higher efficiency - not a lot, but I'm chasing anything I can get here! This new starter configuration almost turns off the starter coil after a few seconds - but then it leaves a 4uF cap in series with it forever. I guess it lowers the effective drive resistance?
The datasheet says for our typical 35degC deltaT, the COP increases from 4.29 to 4.5 by doing that. Not too shabby! For a cost of £2, I should get get a 5% heating bill reduction. The heating bill is tiny, but it's the principle of it :-)