AC to DC motor conversion - Page 1
Forum section: electronics / beginners

author: rthorntn
author_rank: Frequent Contributor
timestamp: August 08, 2024, 06:11:00 am
content: Hi,I have a 3HP single phase AC motor on a tool and I want to change it to DC for speed control (to be able reduce speed and keep torque)... the motor size isn't important.So I see a 180V 3HP ZYT110-30 on eBay & AliExpress, is this an option?If such a motor is an option, how would I safely drive it with speed control, I'm looking for an off-the-shelf solution?Budget is $1000 AUD, that's why these treadmill motors look appealing, its a home project.Thanks!

author: BennoG
author_rank: Frequent Contributor
timestamp: August 08, 2024, 07:44:52 am
content: Why not a 3 phase motor with a frequency inverter in front of it.This is all off the shelf.Benno

author: rthorntn
author_rank: Frequent Contributor
timestamp: August 08, 2024, 08:51:23 am
content: Thanks, do you mean a 3PH motor paired with a vector drive?

author: Zero999
author_rank: Super Contributor
timestamp: August 08, 2024, 09:09:37 am
content: Quote from: rthorntn on August 08, 2024, 08:51:23 amYes, I'm pretty sure he's talking about a three phase motor and a variable frequency drive. It will be more reliable than a DC motor, as there are no brushes to fail. Most small three phase motors can be connected to either 400V in star Y configuration or 230V Δ configuration.https://www.electrotechdrives.co.uk/product/electric-motor-2-2kw-3hp-2-pole-2800rpm-three-phase-90-frame-teca-90l1-2/https://www.amazon.co.uk/Variable-Frequency-Drive-Single-Phase-Controller/dp/B07TVSYQ72/ref=asc_df_B07TVSYQ72/?tag=googshopuk-21&linkCode=df0&hvadid=696285193871&hvpos=&hvnetw=g&hvrand=17570945388077428865&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9047010&hvtargid=pla-2281435177178&psc=1&mcid=4bc9a4d322af3e748d30bacad65b9f03&hvocijid=17570945388077428865-B07TVSYQ72-&hvexpln=74&gad_source=1

author: rthorntn
author_rank: Frequent Contributor
timestamp: August 08, 2024, 09:37:24 am
content: I should add that I occasionally want to have good torque at 2% of the motors rated speed, I think that has to be a VFD capable of vector control or DC...

author: Zero999
author_rank: Super Contributor
timestamp: August 08, 2024, 10:57:54 am
content: Then, yes you do need vector control. Another thing to consider is over-rating the motor, in order to give the required torque at lower speeds.

author: BennoG
author_rank: Frequent Contributor
timestamp: August 08, 2024, 11:29:24 am
content: and if you add a encoder feedback in the mix then you will have constant speed regardless the load on the motor.Benno

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 08, 2024, 04:00:01 pm
content: A VFD with integrated support for encoder feedback would be a very nice option indeed, but I don't know if that's COTS for a reasonable price.You can close the loop yourself by adding a small uC in the loop but where is the fun in that?And what does this mean:Quote from: rthorntn on August 08, 2024, 09:37:24 amDC motors are exceptionally good for high starting torque and overload peaks as long as the motor does not overheat (That will take time).Brushed DC motors are often seen as a cheaper alternative for induction motors, but I don't understand why. Adding all that copper in the rotor, and the commutator and brushes should all add to the cost. I guess the main difference is that COTS induction motors are designed for industrial applications and last 50+ years while treadmill motors are designed to burn up after a few years so you buy a new treadmill.I also had a short peek at Aliexpress for a "2kW Servo motor". These are PMSM motors, and 2kW costs well below EUR 500, and that includes controller and cables. These motors are designed for accurate RPM and position control. Just add some ball spindles, add LinuxCNC with a suitable interface and a bit of steel and you've got a decent CNC machine. Although for axes control, a 500W motor is probably plenty.Horses are obsolete and PH has something to do with liquids.