Here’s mine ..

 That’s the high pressure line over the amps line.  

regards

robert

Here is the last 24 hours for my heat pump with amps added to the plot. Note that I do not have solar or batteries or inverters, just mains electricity:

But the steepness is very dependent on zoom level. I can flatten the apparent gradient by zooming in to an hour (either side of the bigger spike just before 2200). The actual gradient is of course the same, but it looks far less: 

Amps look OK, what is more interesting to me is why, after running in steady state at the start of the hour, it suddenly starts cycling for no obvious reason.   

Here's the 11th Jan with -4 degrees OAT in the early hours:

Looks rather alarming, however if I zoom in to one of the worst hours:

Again, the amps, though high (max 23-24 amps, but it was very cold, COP was terrible, and it needs those amps to get sufficient output), aren't spikey. The cycle starting at 0610 is a defrost cycle, and it interesting to see how long it affects output: 20 minutes. Not so good.

There is absolutely no doubt in my mind that defrost cycles are a major problem. Others have asked the question before, but I don't think I've ever seen an answer: how do our friends in Europe with colder climates deal with this? Have they found a fix, or do they just put up with it?  

some better resolution graphs for you S gatorator  🙂

If your talking about inrush current I suspect non of our monitoring systems are capable of capturing the resolution needed for that?

Posted by: @irmartini

↑

If your talking about inrush current I suspect non of our monitoring systems are capable of capturing the resolution needed for that?

That is indeed possible, but if there is an inrush it must be very short (and so does it really matter?). I sample every minute, @ivanhoew samples every 30 seconds, and @s_gatorator every second. Also it is surprising that a sample never happens during an inrush (if they do occur, but we always miss them).

What we appear to have here is three different makes of heat pumps, none of which show start up surges in current. I'm not sure that is that surprising, isn't that what modern inverter driven pumps are supposed to do?

Posted by: @cathoderay

↑

That is indeed possible, but if there is an inrush it must be very short (and so does it really matter?)

Just because it is short doesn't mean it doesn't matter!

Running on mains it probably doesn't matter, but if your running on an inverter supplied by a battery only maybe it would?

I'm not knowledgeable enough to know either way, I'm just aware we might not be seeing the whole picture. 

If these modern heatpump motors don't have any inrush then great 😀 it doesn't matter.

Posted by: @irmartini

↑

I'm not knowledgeable enough to know either way, I'm just aware we might not be seeing the whole picture. 

I agree, always be sceptical, always question whether what you think you see is what is actually going on. I think another pertinent question here is how exactly does an inrush current do harm? I can see that sustained overloads might do harm, but a short inrush? Isn't that what happens every time internal combustion car starts its engine using a battery? 

Edit @transparent may have something to add here.

@cathoderay 

I do try and question everything and have learn't a lot from forums like this by doing that, however I often don't have the knowledge to ask or know to ask the right questions.

A Cars battery is designed for starting a a cars engine, it has a CCA rating in the hundreds of Amps and so can provide that very high current for a short periods.

I believe if your system what ever it is is not capable of providing the current being drawn even for a very short period the consequence is the voltage drops and this can effect if devices start-up cleanly or can negatively effect electrically sensitive devices that are already running.

A quick bit of googling does seem to suggest that modern ASHP have soft starts and so don't have large inrush currents but that is generic info not specific to any makes and models.

Posted by: @irmartini

↑

I do try and question everything and have learn't a lot from forums like this by doing that, however I often don't have the knowledge to ask or know to ask the right questions.

Someone after my own heart. We do try to stick to the 'there is no such thing as a stupid question, the stupid thing is not to ask' way of doing things here.

I agree car batteries have high CCA ratings and so are suited to their tasks. What I am hoping is that @transparent (the source of much light on these matters) can tell us a bit more about the actual damage that occurs from high start up currents. Is there a scrapyard somewhere full of dead ASHPs killed off by high start up currents? Or is it more of a theoretical risk (like for example Legionella)? 

I agree most modern heat pumps advertise themselves as being soft start devices. But, as you say, there may be exceptions (and we can be pretty sure they won't advertise the fact!). 

Posted by: @cathoderay

↑

What I am hoping is that @transparent (the source of much light on these matters) can tell us a bit more about the actual damage that occurs from high start up currents. Is there a scrapyard somewhere full of dead ASHPs killed off by high start up currents?

🤣

No.

I'm raising the issue due to the problems it creates for the grid...
or for ensuring that an inverter can deliver a sufficiently high current to allow a heat-pump to start.

There's no 'damage' caused to the heat-pump.
It will quite happily take whatever current it needs.

From the viewpoint of the grid, the major headache for DNOs is a demand-surge that occurs when

• they re-energise a sub-station following an outage
• ASHPs in a locality all experience freezing fog and switch on their defrost cycle

How do I know that?

• because a senior DNO engineer told me
• because I can see the switch-on surges when I look at sub-station current data

That graph shows averaged data.
The actual switch-on surge is much higher than shown here.

Posted by: @cathoderay

↑

Again, the amps, though high (max 23-24 amps, but it was very cold, COP was terrible, and it needs those amps to get sufficient output), aren't spikey. The cycle starting at 0610 is a defrost cycle, and it interesting to see how long it affects output: 20 minutes. Not so good.

There is absolutely no doubt in my mind that defrost cycles are a major problem. Others have asked the question before, but I don't think I've ever seen an answer: how do our friends in Europe with colder climates deal with this? Have they found a fix, or do they just put up with it?  

Hi @cathodeRay , aren't all of the cycles in your chart defrost cycles? The clue I'm seeing is in the OAT graph, which has a small spike just after the compressor stops, presumably due to your outside temperature sensor being near the external unit and it getting some heat from the warm air at the end of the defrost cycle when the fan restarts. I have the same think on ours.

If the temperatures are lower, as in Europe, the moisture freezes out of the air and it looks like frosting does not occur below -7C or above 5C (quick internet search). Otherwise, here, I agree, it's a problem.