• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Ideas to suppress inrush current seen by my electric meter??

Not open for further replies.


Thought I might throw this out to see if anyone has some good ideas here. Basically I am moving to an area where I only have single phase power. No biggy, I build rotary phase converters and know how to get around most of their pitfalls. However, a major issue is the power company ALSO dictates they do no want any more than a 10hp motor on the line. Now, they do not go into any more detail than that. Even VFD controllers, soft starts, etc.

With the day of smart meters, they will be able to see my inrush, and I need to be able to run a couple 30HP motors, on VFDs. Since I will have 600A of power, technically I have enough current, it just comes down to their inrush issue. Now, I could ramp the motors up slower and they would never see it, but the motors need to accel/decel a LOT and I want to get things done.

Bottom line is I would certainly exceed the inrush of a typical across-the-line start of a 10HP motor. I am looking for a way to sink or tank power up, or otherwise snub the inrush that the poco sees. I considered adding additional capacitors in the VFDs, which WILL work, but when I calculated the acceleration rate I need, and estimated current, the qty of capacitors and costs got to be simply insane. like 100 capacitors at a cost of about $10k! That does not seem like a solution.

Before anyone metions just paying for 3Ph power, it simply is NOT available for any less than 6 figures.

At this point, I am almost open to building my own power station, running a huge genset, etc. I will need this power a LOT and I know a genset will be loud, inefficient, etc, etc.


Well-Known Member
Most Helpful Member
What about adding electronic clutches to the motors so they don't have to start and stop?


Well-Known Member
Most Helpful Member
Tough problem. I'll throw out motor-generator with flywheel. That was how my University's computing center was powered.

30 HP Eek!

So, you COULD get the motor-generator up to speed slowly and hopefully the flywheel would remove the hiccups/

Not sure if this http://ieeexplore.ieee.org/document/218864/ paper would help or not.

A solution seems very expensive.

Beau Schwabe

Active Member
The motor-generator with flywheel seems like it would be the most straight forward approach to maintain the power levels that you want on startup where the flywheel would maintain an average power once it was up to speed.... that said it may not need to run continuously once your 30HP motor is up and running unless there are frequent stop starts.

If you can sacrifice startup speed, then an inrush current relay or series of them might work if designed properly where the "open contacts" still provide a significant load but limited with a dummy load in series with the 30 HP motor. 30HP on an induction motor is about 45 to 50 Amps ... which is within the capabilities of an inrush current relay.

I did a similar design with a heater element to keep it from tripping the breaker box. The heater element was on a machine that can accept 110V or 220V, however operation under 110V cause the heater to take 4 times as long to heat. I had a boost circuit when 110V was detected that supplied 190V to the heater ... the inrush current draw was about 30 Amps, but because it was a heater element, the "startup speed" wasn't much of an issue... just that it was faster than nothing at all under 110V operation.


Well-Known Member
Most Helpful Member
Not open for further replies.

Latest threads

EE World Online Articles