Minimum specs required for an MPP inv to start a 1kw AC pump.

Hey from New Zealand.

I'm planning on building a 24v portable rig to supply a 1kw irrigation pump for a farmer. I was going to use their 3024msxe model but now concerned the surge current may trip the unit. Anyone care to guess if this would happen? They do have a 4kw 24v model but has high volt PV input which doesn't suit the panel configuration. Also could go to 48v 5kw but battery cost is going to blow out and their idle draw current is a bit poos.

P.s. First post, long time lurker, great forum and awesome info, I highly enjoy this place, thanks guys.

Photon_energy said:

Hey from New Zealand.

I'm planning on building a 24v portable rig to supply a 1kw irrigation pump for a farmer. I was going to use their 3024msxe model but now concerned the surge current may trip the unit. Anyone care to guess if this would happen? They do have a 4kw 24v model but has high volt PV input which doesn't suit the panel configuration. Also could go to 48v 5kw but battery cost is going to blow out and their idle draw current is a bit poos.

P.s. First post, long time lurker, great forum and awesome info, I highly enjoy this place, thanks guys.

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Hello! I'd sure want to measure the pump starting amps for a few starts before I picked out an inverter.

I have a 1/2 hp 240V deep well pump and starting surge (1/2 second) is 5000 Watts. The motor has a specification for LRA (locked rotor amps). Some motors have built in starting capacitor to help achieve LRA.

Thanks for the replies.

The claimed starting current for AX motors varies hugely online so it's hard to form any conclusions.

I rang a local supplier for a similar pump and they claimed surge current is 2 to 3 times rated load. Which isn't too bad, the mpp is rated at 6000w for 5 seconds. So I should be ok, ideally if I wasn't being cheap then a LF inv is the better choice.

Don't suppose it is started manually every time it starts?
If so, might get away with an inverter that soft-starts when it starts up.
A spare variac might be handy for a short term solution?
Don't know if you can still get the soft-start kits that put the load through a 10-15 ohm resistor for about a half second before directly connecting it?
Victron and Latronics would have something but it would weigh more (low frequency inverter with a big heavy coil inside).

That's a good idea, a high wattage resistor to offset startup surge, would need to be pretty high wattage ha, though if only for half a second not such a big deal. I'm sure there are some AliExpress options I could play with if it's an issue. However I think the irrigator will be on a timer, farmers are generally to busy to worry about turning sprinklers on and off every day...

I will report back to see if the Mpp unit can cope, I'm sure it would be handy for others to know. We tend to face pretty dry conditions in the part of NZ I'm from and it's dairy central, so probably a bit of demand for this kind of thing.

Contrary to the suggestion of my previous comment, a soft-starter could be automatic if put in-line before the motor.
I guess: inverter > timer > soft starter > motor.
Hopefully the inverter can cope with it as is.

For those who have the time:
https://www.siliconchip.com.au/Issue/2012/July/Soft+Starter+For+Power+Tools
This uses a 10 ohm NTC instead of an outright resistor.

I noticed that "soft starter" on ebay has some ~$375 chinese units (I don't know anything about these.)
https://www.ebay.com.au/itm/264645696845
It looks like they can be fine tuned though.

https://search.abb.com/library/Down...LanguageCode=zh&DocumentPartId=&Action=Launch

I'm intrigued how it controls the 'stop ramp'.
I suppose this would be an easy off-the-shelf solution.

https://www.ebay.com.au/itm/195027637555
Hopefully these would last.
$55 "(Module)SSR-20WA-R (1KW) Single-Phase Two-Phase Motor Soft Starter Aluminum"