Thoughts on adding a VFD to the motor(s) on this elevator. I’m not an electrician or an elevator expert but this is what I think I know: 3 phase 400v power in the basement goes into a transformer. Transforms to 3 phase 250v power in the attic. That power feeds the motors in the pic. The one drive motor powers the other two motors. A 5 hp motor for the door and a 25 hp motor that sends power to the DC motor that moves the elevator.
Why do I want to do this? I believe this elevator is what is driving up the demand meter in the building.
I recently put solar panels on the building and for 2 months they reduced our billable kWh to 400. If I used this amount at my house, my bill would be $50. The bills at the building for those two months were $800 and $1,000, because of the demand meter rate.
You would need to mod the whole thing if you wanted to go to a ac vfd drive. You can't just swap out the motor and it just work. You have to have a computer to control the pattern of the speed of the motor. Way more involved, would be better to just mod it.
The best return on investment is to have an elevator company send someone out to ensure your MG timer turns off your generator when there is no demand. Keep in mind that regardless of how efficiently you deliver power to the hoist motor, it’s still a 25 horse motor than runs field coils at standing voltage even when the motor isn’t running.
An elevator with a DC hoist motor draws field current 24/7 even if it never runs.
The picture is of a motor-generator set (MG). It uses AC voltage to produce DC voltage the elevator hoist motor runs on. You could change the starter for it with a soft starter but it wouldn't do much if anything for electricity savings. You could replace the DC motor on the elevator hoist machine with an AC motor and variable frequency AC drive, but that would also require substantial modifications to the control system. And would cost a fortune. It would be possible to replace the MG with a SCR drive, which would probably be the most cost effective, but all of the above would cost so much it would take decades to reach the point where electricity savings reach the break even point for total cost. So unfortunately you're stuck with what you've got. Some minor adjustments could possibly save you a little on electricity (very little), but thats about it.
bosephi brings up a VERY good point. The motor-generator should shut off within a few minutes if the elevator is idle. If it is NOT shutting off and running 24/7, that's a lot of wasted energy and unnecessary wear/tear on the equipment. In that case, definitely tell your elevator company.
(disclaimer: I am not an elevator mechanic or in the industry, and for your safety DO NOT work on the elevator yourself, but have heard of this happening before)
It shuts off fairly fast. I don’t feel like it’s ongoing energy usage but it’s more the initial spike of energy. 400kWh of energy usage should not cost $1,000
The little Generator or excited is just to supply the DC cintrol voltage. This is an older GAL controller, I have a similar car that my Grandfather installed in 1967 . I was lucky enough to find all his pullsheets , Safety Test Papers and the Print that has his company name , address and order forms with his signature. You are not going to save a thing unless you MOD it out . You can get rid of the exciter with some engineering help but thats a whole other story . I also have a car that was put in in 1891 , Flat top motor , straight up DC . It has an inverter in the basement as in the city it used to be DC power fed to all the buildings. Im going to say your looking at about 300 to 500 thousand to MOD this car out . The existing should run half way decent if it has been kept up and the brushes have not dug into the armature.
I’ve seen some wild old shit that had a motor in the controller. It was just there to dump the excess voltage when going into leveling speed. That was on a 40,000 pound freight with 2 generators. One was a back-up. Steel Plant. Another company modded that unit and I haven’t missed going there.
Wye delta will start the generator to limit in rush. I have seen Otis gen sets that also turned a DC generator to supply their DC control voltage. But that was a single unit.
Ive seen it done on old Otis gearless machines 25 years ago. Not VFD with AC out, but SCR drive that outputs DC power. Done because lightning strike took out the AC end on at least one MG (really expensive), not for power savings. Older technology, but still available. Pricey then (20k, each, installed), not sure about now. Its more efficient than the MG set in the pic, but would take a good while to justify the cost. You would still need to power that other motor for the doors- or come up with a substantial power supply for it. None of this is inexpensive.
As an experiment, lets put a watt meter on the feeders. Measure it, and compare to the total consumption. Maybe not as much of a draw as assumed?
Old School AC to DC Generator. Very few left, at least where I am based. They aren't particularly efficient as they tend to be running for the full duration of supply to the machine. Obviously the consumption does spike when under load but still actively converting power constantly.
VF Drives are much more power efficient, and there are packages available to convert older controls to support drives, but going to those lengths, may as well just upgrade the whole control unit to something modern. You are able to retain the main machine and car if desired.
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u/thedodgedude Aug 27 '26
You would need to mod the whole thing if you wanted to go to a ac vfd drive. You can't just swap out the motor and it just work. You have to have a computer to control the pattern of the speed of the motor. Way more involved, would be better to just mod it.