AC servo motor help !

[rnr107]

Hi all,
I just bought a new AC servo motor + drive to make a 4th axis on my mill.
Everything looks good and solid, the problem is: It requires 3 phase supply !

I knew the motor was 3 phase but I assumed that the Drive had a 3 phase inverter built in !!!
(The manual says 3 phase 220V supply IN)

So, my questions now are:

1- Is it possible to run this kind of drives of a digital inverter (like a CUB...) ?

2- This servo drives have a Main supply (3 phase) and a control supply (single phase) and on the wiring diagram
it shows the single phase supply taken from the 3 phase supply (Between 2 phases)
Now, I don't think it is a good idea to use only 2 of the phases from an inverter...
So, is this the same as Phase / Neutral supply ?

3- In the manual there is a section saying:
"In peculiar circumstance, the small servomotor, which is less than 750W, can use single phase (L1 and L2
terminals connect to single phase supply. leave L3 terminal alone"
Why would it works single phase if the motor was smaller? What would happen if a 750W motor was used
with single phase supply?

Ta,
Laurent

[m_c]

nobodyknowsanymore

[rnr107]

Thank you for the explanation m_c. All make sens now... Unfortunately this means I can't use this Servo + drive system at all.

Great.... Just wasted 400 quids.....................

[GEOFFREY]

Why is the money wasted? Surely you can still use a 220v single to three phase inverter to power the drive. G.

[rnr107]

Why is the money wasted? Surely you can still use a 220v single to three phase inverter to power the drive. G.

Well, according to m_c (see above) who seems to know what he is talking about, you can't... It has to be proper 3 phase...

[GEOFFREY]

I know that m_c knows exactly what he is talking about, but I think he was referring to using only the L1&L2 connections on the drive. With the inverter I think you can run it as 3 phase using L1,L2&L3. G.

[Gary]

What is the power of the servo motor/driver?
And who is the manufacture /model number?
If you got it from a company, you can return it if it is not fit for purpose.

[m_c]

godonlyknows

[rnr107]

You can't run a servo drive from an inverter, as the servo drive load is not constant, which at best would lead to something faulting out/just not working, and at worse blowing something up.
What you could do if you really wanted to use this servo, is build a rotary converter to produce the required 230V 3 phase, and get the phases as balanced as possible. All that's needed is a suitable 3 phase motor, some capacitors, and a couple switches (plus a relay and contactor if you want automatic starting).

Hi m_c,
Your first reply gave me an idea last night...
I opened up the enclosure of the drive and as you said, the AC from the 3 phases goes to 2 bridge rectifiers and a series of big caps.
So, using L and N single phase would use only 1 rectifier (and therefore geting it over worked...

Now, there is nothing in there requiering a phase shift between the 3 phases coming in....all the bridge rectifiers care about is 240V AC...
So, I decided to connect Neutral, Live, Live where the 3 phase were supose to go (L1, L2, L3)... This way the load is spread over the 2 briges as per 3 phase setup.

Tryed that this morning... All good! Motor happy, drive happy... (all stays cool )


These servo motor are really quiete! even at 3000 RPM ! amazing!


Laurent

[Jonathan]

For peace of mind you could increase the size of the capacitors to compensate for single instead of 3 phase.