testing a 3 phase motor with meter

[clueless77]

One for the sparkies, I have a couple of bench drills with 3 phase motors, both have only 3 connections at the motor. just tested one of them through the pins of the 4 way plug. I meggered at 1000v from earth to each pin and got 4.2 meg on each one. continuity between earth pin and chassis of drill is 0.1 ohm. Testing from pin 1-2 I got 100.5 ohms. pin 1-3 I got 98.0 ohms and pin 2-3 got 94.5 ohms. I know nowt about 3 phase motors so do these readings mean it should run? ( not tested the other drill yet). Any advice welcome. p.s I don't have a 3 phase supply to plug into so can't test that way, just want to test with meter before buying an inverter or whatever the right name is to run both drills off. Cheers.

 

[wheresmejumper]

are they 400v or 230v 3 phase?if 230v connect live and neutral to 2 contacts,spin motor by hand and turn on.should get it going

 

[piman]

Hello Clueless,

nothing untoward there. You only need to test between earth and one other pin to check insulation resistance as the three phases are all one circuit.

Alec

 

[clueless77]

The one in the first post is 415v. I just tested the second drill which is 400/440. The readings on that were similar for insulation and earth continuity but testing 1-2 I got 82 ohms, 1-3 82 ohms and 2-3 82 ohms. How does that sound. And could I run both drills off the same inverter if it's programmed for each drill. I'm new to this 3 phase/inverter malarkey by the way. And thank you for the replies by the way, social skills not my strong point.

 

[piman]

Hello Clueless,

yes that should be possible, ask whoever is supplying your inverter for the best way of doing it. Are both motors of a similar size?
There are plenty of single phase to three phase 220v inverters but you'll need a 230 to 415 three phase inverter which is usually more expensive unless your motors are dual voltage , i.e., 440/220 which will mean a change of wiring in the motor terminal box, star or delta respectively. In star three of the terminal posts will be connected together with the feed cable to the other three, delta has the three pairs strapped individually.

Alec

 

[wheresmejumper]

maybe a pic of the motor data plates and connections would help

 

[clueless77]

Don't think they're dual voltage motors, when I work out how to work the digital camera i'll upload some pics. There only seems to be 3 terminals inside the motor casings on both motors. The plate on the first one says: LDC Lancashire Crypto 3ph. 0.25hp. rated cont. speed 2850. 50 hz. 415 volts. amps 0.68. size 3AD1B. The plate on the second says: Merlin Brooke Motors 50 hz. type prot. rating cont. 3ph. 1420 rpm. 0.64 fl amps. 0.33 hp. 50 deg c rise. Hope that helps. ta.

 

[clueless77]

After doing some research it seems my options are, a digital phase converter as they aren't dual voltage motors, a package including dual voltage motors and an inverter or just change the motors for single phase ones and just use the single phase supply. A lathe is somewhere on the horizon and unless I go the hobby machine route it will probably be a 3 phase ex industry machine probably a chipmaster or bantam. With the digital phase converter I could put a ring main in my garage that would supply 3 phase and possibly supply all 3 machines (not at once) and maybe in time a milling machine but sounds like it could be expensive. Has anyone gone down the digital phase converter route with ring main and if so how well did it work out and does it need deep pockets? The drills didn't cost much off ebay and i'm starting to see why, one's a fobco star bench drill cost about 70 quid, the other is a jones and shipman bench drill that cost about 40 quid. My head hurts.

 

[wheresmejumper]

a rotary converter would power a whole workshop,or just a couple of drills.
you could make your own cheaply

 

[clueless77]

I wouldn't trust a home rpc if I made it. Looks like a couple of single phase motors would be the cheapest option. Even if I got a converter, the jones and shipman drill would still have a motor from the 1930's so who knows how long it would last and maybe even ****** up the electronics in the phase converter if it went pop. There's no rush, so i'll ponder a while longer. Cheers.