A few years ago I wrote this:- https://www.electro-tech-online.com...atic-miller-system.100563/page-7#post-1309053
I now think that using loads of capacitors and a voltage sensitive relay to run a three-phase motor like that is not the best way of doing it.
The lift had got some water in it, leading to condensation in the electrics, and it was tripping the ELCB, so I decided I had to move the control gear. I would need a large box to house the capacitors, so I looked up how much an inverter would cost.
I found that an inverter was only around £80 from Amazon. https://www.amazon.co.uk/gp/product/B07M7NMCVH/
That was a lot less than I paid for the 20 capacitors that I had needed to run the vehicle lift before. When I bought the capacitors, I don't think that I had understood how much inverters had come down in price. The last one that I had bought was around 30 years before, when I paid around £1000 for a < 1 kW inverter.
The inverter is now on the wall and working. I had changed the plastic housing of the control box before I had screwed it to the wall and clipped the cables in place. The contactor in the control box is only used to switch the low voltage control signal to the inverter. The inverter is powered as soon as the control box is switched on, and runs when it gets the control signal.
And here is a car on the lift:-
It has the additional advantage of having a soft start.
Previously, as mentioned here https://www.electro-tech-online.com...atic-miller-system.100563/page-7#post-1333975, the arrangement took lots of current. With the inverter it takes far less. I guess that the power factor is better. I have also slowed it down to 40 Hz instead of 50 Hz, in which brings the current down further, and I'll be changing the isolator to a fused spur in due course.
The house lights no longer dim as the lift starts up. All in all, it's a huge improvement on what I had before. I should have fitted an inverter from the start. There will be few applications where using lots of capacitors is in any way better than using a VFD.
The setup is not perfect. The cheap inverter has a very small but noisy fan that runs whenever it's turned on, whether the motor is running or not, but most of the time that I'm using the lift, it'll be turned off. The inverter also takes a few seconds to turn on.
Before the motor would run, there was a lot of setting up to do, with a very badly translated instruction book, and a terrible user interface. I had to set the normal motor frequency, in this case 50 Hz, in one of the parameters, and that was set to 400 Hz to start with. At that setting, it wouldn't put more than about 25 V on the motor and it didn't run. Initially the ramp rate was set really slow in both accelerating and decelerating, so those had to be changed as well.
I now think that using loads of capacitors and a voltage sensitive relay to run a three-phase motor like that is not the best way of doing it.
The lift had got some water in it, leading to condensation in the electrics, and it was tripping the ELCB, so I decided I had to move the control gear. I would need a large box to house the capacitors, so I looked up how much an inverter would cost.
I found that an inverter was only around £80 from Amazon. https://www.amazon.co.uk/gp/product/B07M7NMCVH/
That was a lot less than I paid for the 20 capacitors that I had needed to run the vehicle lift before. When I bought the capacitors, I don't think that I had understood how much inverters had come down in price. The last one that I had bought was around 30 years before, when I paid around £1000 for a < 1 kW inverter.
The inverter is now on the wall and working. I had changed the plastic housing of the control box before I had screwed it to the wall and clipped the cables in place. The contactor in the control box is only used to switch the low voltage control signal to the inverter. The inverter is powered as soon as the control box is switched on, and runs when it gets the control signal.
And here is a car on the lift:-
It has the additional advantage of having a soft start.
Previously, as mentioned here https://www.electro-tech-online.com...atic-miller-system.100563/page-7#post-1333975, the arrangement took lots of current. With the inverter it takes far less. I guess that the power factor is better. I have also slowed it down to 40 Hz instead of 50 Hz, in which brings the current down further, and I'll be changing the isolator to a fused spur in due course.
The house lights no longer dim as the lift starts up. All in all, it's a huge improvement on what I had before. I should have fitted an inverter from the start. There will be few applications where using lots of capacitors is in any way better than using a VFD.
The setup is not perfect. The cheap inverter has a very small but noisy fan that runs whenever it's turned on, whether the motor is running or not, but most of the time that I'm using the lift, it'll be turned off. The inverter also takes a few seconds to turn on.
Before the motor would run, there was a lot of setting up to do, with a very badly translated instruction book, and a terrible user interface. I had to set the normal motor frequency, in this case 50 Hz, in one of the parameters, and that was set to 400 Hz to start with. At that setting, it wouldn't put more than about 25 V on the motor and it didn't run. Initially the ramp rate was set really slow in both accelerating and decelerating, so those had to be changed as well.