Amperage Differences - Star vs Delta

Looking for opinions please. My electrical theory knowledge is not extensive.

I've recently taken on an Astra Elite AR5-E tool and cutter grinder.

Motor nameplate states ratings for 440V:

0.75HP

50Hz

1.15Amps

2800 rpm

There are six motor leads plus earth. The instruction manual gives directions for wiring the motor for 220V 3 phase. I've wired up a VFD and the motor runs nicely, but struggles to get going when changing the pulley to the two spindle high speed settings. According to the VFD display, no-load current draw at 50Hz is 0.4 amps ( this is with the 1:1 pulley belt attached, rpm check with an el-cheapo tachometer is 2550 rpm)

Q - When configured in 220V delta, will the motor require additional current compared to 440 star? I've heard it mentioned but wanted to confirm this is the case. If so, I'll cautiously increase the VFD current parameters from the nameplate rating. I don't want to fry an otherwise decent motor.

Also, would anyone know how many poles is motor likely to have?

Thanks all.

Edited By Stuart M on 14/11/2020 12:20:03

Its a 2 pole motor if its running at 2800 rpm

perhaps the motor will pull about 2 amps on 240v wired in delta/mesh

increase your vid current to suit

2800 rpm = 2 pole

Dual voltage motors usually have 2 current ratings - one for 400/415V & the other for 220/240V - and the lower voltage will have a larger current. Could you post a photo of the rating plate ?

Nigel B.

Yes the motor will take more current and it is a 2 pole motor.

Andrew.

Edited By Andrew Tinsley on 14/11/2020 12:25:44

Nominal speed for 50Hz, 2 pole is 3000rpm, 4 pole is 1500rpm. What are the instructions for wiring in delta like? It is possible that one coil is reversed if the wires are not clearly colour coded or the three that are connected to the star point are not clearly identified.

What is the VFD ramp up speed set to? It may need shortening.

In both star and delta configurations the same voltage should be applied to the coils so the currents should be similar.

Martin C

Thanks for the replies. All six motor wires are clearly labelled (I presume from the factory) - U-V-W-X-Y-Z. The instructions are very clear (with diagrams) so I don't think there is any error in the connections.

The namplate doesn't provide any additional information apart from the motor and machine serial numbers.

I've yet to change ramp settings, so this could help. I've noticed the motor will start more easily on a lower Hz when the spindle is on one of the higher rpm pulleys.

WRONG Quote deleted

Edited By Robert Atkinson 2 on 14/11/2020 13:07:10

While the current through the coils will be the same, the current per phase drawn from the VFD will be higher with a Delta connected motor. The delta phase current will be1.723 (square root of 3) times the star current.

The VFD current limt should be set to 2A for the deta connection (1.15 x 1.72 rounded up)

Robert G8RPI

You have not said how the motor is wired or wha the VFD inputs and outputs are.
From a current of 0.4A I deduce that the motor is wired for Star (440V) and the VFD is 240V single phase input and 240V 3 phase output.

If this is the case you need to re-wire the motor to Delta (240V) to get full torque (and current)

Robert G8RPI.

The motor is wired to Delta as per the manual instructions. VFD is 240V single phase to 240V 3 phase output. U-V-W VFD outputs connect to U-V-W motor connections.

I just ran the motor with no pulley attached and the VFD reports 0.2 amps at 50Hz.

With no load any motor takes less current as it has no work to do, just overcoming internal friction and ineficiency. The rated current is only taken when running at full load which will be when you ar taking a heavy cut and can take more in an overload or stall condition. Start up also is equivalent to high load as it has to accelerate itself and the lathe.
The VFD is designed to protect itself and the motor so has various current/power limits which you will have to find and set high enough for the starting and load currents. The soft start ramp up features also help but will need some experimenting.

If you visit "the inverter drive supermarket" and look at their three phase motors, the amperage for star and delta are listed. Star is 440V and delta is 230V.**LINK**

If you visit "the inverter drive supermarket" and look at their three phase motors, the amperage for star and delta are listed. Star is 440V and delta is 230V.**LINK**

That link takes you to 0.7Kw 6 pole motor & the OP has a 0.75Hp ( 0.55Kw) 2 pole motor

Interesting that modern "high efficiency" .55Kw 2 pole machines all show a higher FL current, though that is at 400V rated not the 440V of the OP,s motor.

Can't say I have come across a dual voltage motor that doesn't show both sets of information on the rating plate before - first time for everything, though the plate looks quite old.

As said, turn up the maximum amps, set a couple of seconds for the acc & dec ramps and see how it goes.

Nigel B.

That link is irrelevent and may be misleading. For any 3 phase load motor, heater whatever, if the coils. elements etc are changed from star to delta wiring the current will change by a factor of 1.73 (root 3) if the voltage remains the same. Current is higher in Delta
Note that 240 x 1.73 is 415, the UK nominal single and 3 phase voltages. The power remains the same for a given load if wired star on 415V or delta on 240V.

Robert G8RPI.

They also sell 2 pole ones, that was just a link to their site.

I remember when single phase mains voltage was 250V, things change with time.

Edited By old mart on 14/11/2020 18:10:56

Thanks for all the replies and advice. I’ll increase to 2 amps and investigate the VFD ramp parameters. I’d like to actually get a wheel on the machine but I first need to make hubs for the various wheels I’ve got.

Edited By Stuart M on 15/11/2020 19:56:43