looking for a way to support (local) grid for starting current of motors - Page 1
Forum section: electronics / general

author: grumpydeveloper
author_rank: Newbie
timestamp: December 01, 2024, 04:53:14 pm
content: Hi,let me start with a short description of the current state:I have (mostly) 2 machines with a big motor with their typical start current spike. One 2.2kW air compressor and a ~1kw water chiller, both single phase. Both can't be equipped with a soft start.Incoming supply from grid: 3 phase 230/400V (Germany), seems like very high wire resistance or so.Rental garage place, no touching of electrical before the single 3-phase outlet.Issue: After the rental company did "changes", the starting current brings down the voltage to an unacceptable level, even across other phases. The light (no touchy zone) goes almost out,even running on a different phase.And running both heavy loads at the same time, I'm afraid of damages, even across phases.So my question is:Is there a battery unit (similar to a UPS) that can bridge the power demand for a few seconds in addition to the power from the grid. Something where I can set to ~220V instead of the normal ~240Vso it only triggers and pumps power when the power spike happens. I don't want to back feed into the grid. Manually turned on only when I need the compressor.I can't measure the start power, but assuming it's the normal ~6-8x range, we are speaking about 17kW - 3-4kW or so from the grid. Enough to trigger a 10A class B circuit breaker, class C is fine.I need that only for a few seconds until the grid can handle it again (barely, you can see the light flicker on the peak of the compression).I don't need high capacity, just a short power delivery. 1kWh capacity would be plenty, but the ~17kW peak might be an issue.Any suggestions for devices that don't cost an arm or leg?Moving is not an option, looking for a replacement place for yearsCheers Grumpy

author: Siwastaja
author_rank: Super Contributor
timestamp: December 01, 2024, 05:12:55 pm
content: Really, VFD. Everything else is a kludge.

author: David Hess
author_rank: Super Contributor
timestamp: December 01, 2024, 05:45:27 pm
content: A big constant voltage transformer or online UPS might do it, but will be expensive. I think by the time you get to this level of desperation, it could be less expensive to replace the motors with soft start VFDs and 3 phase motors.Soft start should be possible with capacitor start-run motors, but the reduced torque may stall the motor into a heavy load, like a compressor. More likely you have capacitor start motors which apparently do not play well with soft start systems.

author: grumpydeveloper
author_rank: Newbie
timestamp: December 01, 2024, 05:56:10 pm
content: The compressor is a capacitor type 1 phase motor. I haven't tested a soft start, but since it needs full power from the start, I assume it won't work with reduced torque.The other motor is unknown, new device yet unopened. But I'd assume a AC compressor also does not like soft-starts.I was thinking about adding a second compressor for low air consumption, something in the <1 kW range so the start current is also reduced a lot and only use the big compressor with high air consumption.Maybe I can find a cheap VFD+motor combination somewhere used.

author: nctnico
author_rank: Super Contributor
timestamp: December 02, 2024, 09:48:55 am
content: Quote from: grumpydeveloper on December 01, 2024, 05:56:10 pmA compressor shouldn't need full torque from the start. The good ones blow off the air from the cylinder heads to protect the valves. So even with the tank at operating pressure, the first stroke won't be at full load.Still, my first point of call would be your landlord. You pay for a functional electricity supply. Go talk to them and find out what they think about the situation. What would also help is finding an electrician to look at the electrical installation. Maybe there is a problem like a floating neutral which causes your problem. I find it very odd you also see effects on other phases; that shouldn't happen if the neutral is OK.

author: Marco
author_rank: Super Contributor
timestamp: December 02, 2024, 10:03:37 am
content: Any 17 kW solution would be more expensive than buying inverter/soft-start equipment.

author: grumpydeveloper
author_rank: Newbie
timestamp: December 02, 2024, 12:55:26 pm
content: I'm going to talk to the landlord. It's a garage park with questionable morals.Difficult situation, they raise the rent as fast as legally possible and kick out old renters, because they have a loooong waiting list and the new ones pay a lot more (about 1.5-2 times my price).As soon as someone makes "trouble", they find reasons to kick. Happened to my neighbor.When I rented it, they advertised with images with cars and workshops in it (also the reason for the 3-phase connection), now they only rent as storage, no flammable things,nothing with pressure, no batteries, no working in there, just go there, load/unload and leave. I'm just tolerated with what I do.Lack of competitionAnd sadly I don't have the funds to make one (a few million € needed for that).

author: nctnico
author_rank: Super Contributor
timestamp: December 02, 2024, 04:24:18 pm
content: BTW, one way out would be to convert the compressor to 3 phase. Likely all it takes is a 3 phase motor and new wiring.

author: Siwastaja
author_rank: Super Contributor
timestamp: December 02, 2024, 04:39:14 pm
content: Quote from: nctnico on December 02, 2024, 04:24:18 pmAnd at that point, a three-phase VFD would be cheap and easily available (compared to special 1-phase VFDs).

author: David Hess
author_rank: Super Contributor
timestamp: December 03, 2024, 05:53:23 pm
content: Power banks are available now which can support that kind of load for not too much money. I have seen people using them for 240VAC loads where only 120VAC is available, and have been thinking of doing that myself for a welder.