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Forum Index : Electronics : High Power Inverter to Start 2HP Pump
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| Solar Mike Guru  Joined: 08/02/2015 Location: New ZealandPosts: 1238 |
One very glamorous device we have on site is a sewerage tank fitted with a large cast stainless macerating pump, about 230 vac 2HP motor, sometimes its difficult to start, we run it direct off a 7.5KVA generator couple of times a week, 10 minutes or less each duration. At times the generator doesn't produce enough grunt to start the pump, it will bog the generator down, flicking the circuit breaker off and on a few times gets it running. Once running draws 10 amps or so. Our main 6 kva 48v - 230vac inverter wont start it either, especially when other pumps are running off it. What I was thinking was build a small 230 vac inverter that can supply 15 kw or so for a few seconds to get the pump running. Because the on time is quite short possibly I could get away with a small iron toroidal core as it would have a long thermal lag before getting too hot. Possibilities might be use 100v dc for the inverter from a small pack of 50 AH lifepo4 cells and dedicate this just for this pump. Or use DC from another source, start the inverter and synchronize with our main inverter power on the site, then turn the pump on, once running disconnect and leave it powered from the site supply. Anyone have any ideas..... Cheers Mike |
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Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1294 |
Interesting, I have a similar problem with a old bench grinder (it used to dim the lights on grid power when starting), would often not start even though the generator was plenty powerful enough to run it, it would kill the generator and the grinder would just start to spin but not pickup before the breaker trips or gen stalls, Big inverter just kicked its backside and it starts every time.  Perhaps lower voltage lower frequency start ramp 2 seconds etc, experiment perhaps. Cheers Aaron Off The Grid |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 3348 |
Lower frequency will almost certainly require a bigger start capacitor as its reactance will be higher at the lower frequency. A bigger start capacitor might be worth a try on its own as some manufacturers use the smallest one they can. A bigger one (or another in parallel) may get it moving quicker. If that results in too much current in the start winding put a suitable PTC thermistor in series with the extra capacitor to cut it out after a second or two. |
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| kentfielddude Senior Member  Joined: 09/05/2019 Location: United StatesPosts: 102 |
Soft Start - Altistart 01 soft start Maybe something like this could work. Edited 2026-08-12 02:31 by kentfielddude |
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| Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1294 |
Be very careful adding a large capacitor over the existing size, it will increase start toque and surge sometimes to s huge amount and has in some multi stage pumps screwed the shaft off from such a violent start, will also use more power and heat the motor, the surge will be shorter. (Can be More difficult for inverter or generator to start it) I have seen a motor take off across the floor even though it was clamped, the start was so violent, it had a different capacitor on the manual compared to a rough stamped nameplate value. Likely know this already.  Edited 2026-08-12 07:20 by Revlac Cheers Aaron Off The Grid |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 689 |
HI Mike, I am guessing the pump is actually in the tank which makes stuff harder. I have an hydraulic wood splitter that my inverter can not start. I drilled a hole in the fan end of the shaft and put a bolt in there, I use a battery drill to spin the motor up to speed a bit then hit the start button. Once the motor gets started it is fine the inverter can run it no problems. Obviously if the pump is a submersible then that gets much harder. I don't know what battery bank you have but I added a 500 farad capacitor bank in parallel with our VRLA batteries to help with starting current. All my power tools and compressor start as if on mains power. It is only the hydraulic splitter that has problems. My system is 24 volt so that makes stuff a bit harder. |
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Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 2205 |
Hi Mike that madboard I made starts everything I have thrown at it and just works  Sometimes my little air compressor will go chug chug then fire into life and sometimes it just starts it normally. With my mig welder I found using 110 amps the brandnew 16 amp circuit breakers tripped so I do need to source some 25 amps ones.My old 8" bench grinder sat for over a decade so I thought I would test it and sure enough the inverter started it and for the first time I saw a 20Kw surge on the readout, now as it has been pointed out the power factor would of come into play but I am very happy with the performance of the madboard which will soon break the 200Kw/h mark. Regards Bryan |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1238 |
Thanks for the thoughts so far, Yes the macerating pump is fully submerged 2M down in a tank of crap buried in the ground, so any change in start caps etc isnt possible. I think so far, a small LF inverter that will run for 5 min without over heating maybe the easiest solution. We have a 900AH 48v bank of lead carbon batteries, prob needs about 15 Kw peak power, that's what about 350 amps to get the pump started. Feel happier with 100v input DC to get the current down, 24v dont think would be possible; I do pull apart old Lifepo4 failed 48v sealed battery banks apart from time to time, they usually have 16 or 32 x 100AH cells in them, the retailer has to dump them as its uneconomic to fix and NZ has no Lifep04 re-cycling. Will see what I can scrounge up... |
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