I could pretty much go off grid when the sun shines and apart from the lawnmower. We learned during load shedding that the lawnmower would trip the inverter every time. So whilst we could run an extension lead to the outbuildings to use the washing machine, and probably could have got away with a suicide plug for the pool pump, the lawnmower was going to bring everything to a halt. So I never went further than the extension lead for the washing machine.

But it's a quiet weekend and I'm bored, so today I used my Kill-a-watt to measure the lawnmower to see just how over the limit it is.

And the Kill-a-watt says it ain't anywhere near the limit. Which surprises me.

KAW says the highest load (start up) is about 2.8 kW. Says the steady load is about 1.0 to 1.1 kW. All of which my Goodwe should be able to handle.

But when I flip the KAW through it's different modes it shows the aforementioned steady load of 1.11 kW, but it also shows a constant draw of about 11A.

Huh?

That's like ... 230 * 11 = 2.53 kW. But the KAW is showing half of that.

Is this then something to do with the power factor? And what sets the factor? The supply side or the load side?

My inverter is rated at 20A. So if that displayed 2.8kW turns out to be a bit more than double the steady load, and the steady load is about 11A, then startup probably does push it into overload territory.

1 hour ago, Bobster. said:

Is this then something to do with the power factor? And what sets the factor? The supply side or the load side?

Inductive load... power factor rears its head...

48 minutes ago, Kalahari Meerkat said:

Inductive load... power factor rears its head...

Thanks. This makes sense then. The limit of that inverter is expressed in amps, not watts. And it is quite likely that the lawnmower is pulling more than 20A on startup.

Kill-A-Watt limitations:

Low sampling rate, RMS averaging,

Cannot capture:

Sub-cycle peaks Magnetic saturation spikes

Non-linear inverter waveform interaction

So when it says:

“Startup 2.8 kW”

What it didn’t show was: 60–80 A (LRA locked rotor amps)instantaneous current, Massive VAR demand, DC-bus voltage sag inside the inverter.

It’s not just power factor — it’s LRA”

5 hours ago, Bobster. said:

Thanks. This makes sense then. The limit of that inverter is expressed in amps, not watts. And it is quite likely that the lawnmower is pulling more than 20A on startup.

It can be over 20A but it will be just a very short period. Have you checked that the lawn mover does not have grass etc or binding bearing that it trips your inverter.

Each time I read your head ache I just wonder why it's tripping unless you have other high loads on. My Deye is set to only discharge at 55A yet even after the 2 bad days before Sat my helper mowed the lawn with grid off and my battery only on 21% SOC and never had it tripping my inverter. Yes I have a 1.8 kW which might be lower than yours. May be I have a kind angel 😀

11 hours ago, Scorp007 said:

It can be over 20A but it will be just a very short period.

I'm guessing that's what it is. The inverter trips when the lawnmower is started on a backed up circuit. It may be that once the motor is spinning it will draw less, and that's what the KAW seems to show.

11 hours ago, Scorp007 said:

Have you checked that the lawn mover does not have grass etc or binding bearing that it trips your inverter

I've kept it serviced. All I myself can do is a manual check.

11 hours ago, Scorp007 said:

Each time I read your head ache I just wonder why it's tripping unless you have other high loads on.

I need to gather more data. On a regular day we usually top out at 3kW. 750ish of that is the pool pump, which is not backed up.

We have a fairly old mower with... Errmm... Unsophisticated technology.

I'm thinking of fitting a slow start device to it.

I have an old fashioned push mower which I bought for load shedding. But now I'm retiring I might decide to mow the lawn the manual way, a section per day.

11 hours ago, Scorp007 said:

My Deye is set to only discharge at 55A yet even after the 2 bad days before Sat my helper mowed the lawn with grid off and my battery only on 21% SOC and never had it tripping my inverter. Yes I have a 1.8 kW which might be lower than yours. May be I have a kind angel 😀

1 hour ago, Bobster. said:

I've kept it serviced. All I myself can do is a manual check.

I had issues using a cut-off saw on start up previously when the battery capacity wasn't looking too great here (old LA batteries...) anyway, the cutoff saw, once running, was no issue, the startup, though... anyway, what helped, was briefly pushing the power on, on the cut-off saw and then releasing it, half a second later, same procedure and rinse repeat 3 or 4 times and then usually the saw was up to speed and I could keep the power button depressed and no issues from the inverter/battery end...

You try the same with your lawnmower, tilt it up on it rear wheels, so the blades are no in contact with the grass, then pulse start it, like I did with my cut-off saw, if you are lucky, buy a lotto ticket you can get the lawnmower to run without tripping the inverter... this may not work for you, but worth a try anyway, I'd think...

14 hours ago, TaliaB said:

Kill-A-Watt limitations:

Indeed, that device has been quite useful and helpful until now. This is the first time I've used it on any sort of large inductive load.

3 hours ago, Bobster. said:

I'm guessing that's what it is. The inverter trips when the lawnmower is started on a backed up circuit. It may be that once the motor is spinning it will draw less, and that's what the KAW seems to show.

I've kept it serviced. All I myself can do is a manual check.

I need to gather more data. On a regular day we usually top out at 3kW. 750ish of that is the pool pump, which is not backed up.

We have a fairly old mower with... Errmm... Unsophisticated technology.

I'm thinking of fitting a slow start device to it.

I have an old fashioned push mower which I bought for load shedding. But now I'm retiring I might decide to mow the lawn the manual way, a section per day.

My mower is now running 35yrs and I only had to change the switch and a few blades. Wheels still running on the original bearings. Also old tech I guess😀

What I do find strange is that it would trip some 20A MCBs but not the old Heinemann type yet it does not trip on a 55A load limit set on the inverter. When running it uses less than 700W for the 1800W motor.

2 hours ago, Scorp007 said:

What I do find strange is that it would trip some 20A MCBs but not the old Heinemann type yet it does not trip on a 55A load limit set on the inverter. When running it uses less than 700W for the 1800W motor.

Yesterday my system shows a peak load of over 5kW - that would have tripped the inverter if I were running the mower on a backed up circuit. The Kill-A-Watt showed a peak load of 4.8kW, but see various comments above: we can't depend on that figure.

Edited December 15, 2025Dec 15 by Bobster.

8 minutes ago, Bobster. said:

Yesterday my system shows a peak load of over 5kW - that would have tripped the inverter if I were running the mower on a backed up circuit. The Kill-A-Watt showed a peak load of 4.8kW, but see various comments above: we can't depend on that figure.

Yes not even using a clamp meter would show you the peak current used. They all use measuring at x times per second. Expensive clamp meter tend to sample more times per second. Just like some inverter Apps as standard sample once per 5min unless one changes it. Each measurement uses data that must be transmitted and time stamped and stored. Storage costs money. Recently I saw banks sending out one SMS for a number of transactions. POS can be in real time. Dt orders once a day.

18 hours ago, Scorp007 said:

Yes not even using a clamp meter would show you the peak current used. They all use measuring at x times per second. Expensive clamp meter tend to sample more times per second. Just like some inverter Apps as standard sample once per 5min unless one changes it. Each measurement uses data that must be transmitted and time stamped and stored. Storage costs money. Recently I saw banks sending out one SMS for a number of transactions. POS can be in real time. Dt orders once a day.

OK... so how dependable are they? I have benchmarked several domestic appliances with my KAW. From what we're discussing here it would seem that over a period of time the figures must be in the ballpark. EG when we got our new deep freeze I measured the old one for 8 hours and got a total for power used over that period of time as well as a momentary high which I took to be the motor on startup. Then I let the new freezer settle get up (down) to temperature and then repeated the test. This showed about 1/3 of the consumption per hour and a peak of just 107W - considerably better than the machine it was replacing.

Old deep freeze: .577 kWh over 8 hours. Peak 1365W
New: 0.192 over 8 hours. Peak 107W

The new machine has a variable speed motor. When it turns on it slowly speeds up, and you can (if you have a boring life) hear it speeding up and slowing down all the time.

I'm telling myself that a single peak reading may not be very helpful, but over a long run you will catch something close to the actual peak.

Edited December 16, 2025Dec 16 by Bobster.
clarity, grammar

1 hour ago, Bobster. said:

When it turns on it slowly speeds up

I had a old very thirsty Air conditioner unit (48000 Btu) that keep on tripping the breaker, electrician fitted a "slow curve breaker" which worked. Needless to say that unit did only one summer duty - too hectic on the pixies!

25 minutes ago, Demo said:

I had a old very thirsty Air conditioner unit (48000 Btu) that keep on tripping the breaker, electrician fitted a "slow curve breaker" which worked. Needless to say that unit did only one summer duty - too hectic on the pixies!

My problem is not a breaker tripping, it's the entire PV system. I can't go to AC/DC and buy a bit that will sort that out.

3 hours ago, Bobster. said:

My problem is not a breaker tripping, it's the entire PV system. I can't go to AC/DC and buy a bit that will sort that out.

Just go and Google SSR-60W soft starter. This has an adjustable power start level and time duration of the starting cycle. A bit expensive but it will pull down your surge current. A member shared the link of Roland on YouTube. If interested I can look for the link and post it here. I do belief there are far cheaper options.

2 hours ago, Scorp007 said:

Just go and Google SSR-60W soft starter

Interesting option... One could also not cut the grass during power outages, or connect a generator to the inverter, or connect an engine to the lawnmower.