3 phase motors

[Huge]

I'm considering buying a vehicle lift, but most of the second hand ones on eBay require 3 phase. I assume this is because they have 3 phase motors? Would it be possible to swap that for a single phase? I know you can get 1 -> 3 phase converters, but they seem expensive...

(I know exactly nothing about 3-phase, so be gentle with me!)

[Bob Minchin]

Depends on the motor power. Up to 3hp no problem, 4hp you might have to look a little harder and 5hp you will need a good high current capacity circuit to start that on a domestic main. In all cases a separate circuit is recommended with a suitably rated typeC breaker rather than the more usual type B. You will possibly need a sparky to fit the type C as it imposes greater requirements on the earthing of the installation.

You may or may not find this useful:-

specifically targetted at your problem but maybe some useful background.

Bob

[Andrew Mawson]

bolts

Often single phase motors of the same physical size do not produce enough torque, particularly when they have to be reversable as in a car lift

OK - running three phase 415v motors on single phase 240v can be done several ways:

a/ Static converter - generates a phase shift through a capacitor using the motor inductance - usually incorporates a 240 to 415v transformer b/ Rotary converter - same principle as a static one but incorporates a motor which is usually also the transformer c/ Inverter - takes in 240v mains, converts to DC, electronically chops the DC to form 3 phase but at 240v

If your motor is relatively modern it can be re-wired from 415v 'star' configuration to 240v 'delta' configuration - (older ones have the 'star point' embedded in the windings which makes it rather harder). If yours can be set to delta then an inverter is probably the easiest way to go - they are quite cheap on ebay. For motors in delta it is possible to generate the third phase using a suitable capacitor and run off single phase mains, but the starting torque will suffer.

A few years ago I set my neighbours car lift up using a 415v invertor to drive his motor but fed it from a 240 to 415 transformer - still working as far as I know (moved 3 yrs ago)

AWEM

AWEM

[dom]

That's very good advice on using an inverter.

I used one to convert a three phase bandsaw to single phase - very pleased with the results.

I bought an Omron unit through ebay, and found the manufacturer's guide very comprehensive.

You *may* need to be a bit techy to get everything working well. e.g. my bandsaw had a contactor with momentary start and stop buttons used in an unusual configuration (which I can no longer recall) as well as an emergency footbrake and safety microswitches on the doors - so it took a bit of ingenuity to get all the safety features to work correctly with the inverter (inverters use low voltage control signals and the 3-phase power output *must* be connected directly to the motor load - no circuit breakers allowed).

Inverters can also do clever stuff to start and stop motors smoothly by ramping the output frequency - not something I've used - but as a car ramp will start and stop under full load, may be useful to you.

[Me Here]

Item 130418999843 is what I used to have. The motor only drives the pump, so can easily be changed for a single phase one. Gravity drop and power lift. Excellent and parts still around. Even managed to get the company that services them to do a proper service and check.

[John]

Good article.

[Huge]

Thanks for that. I shall keep an eye open for "Bradbury" lifts.