Motor Plate only states 400V 3ph - Can I Run It In Delta?

[Owziswurk]

Hello experts,

I got hold of an Optimum Bench Drill - B23 Pro. The motor plate states 3ph 400V 750W 1.5A 50Hz.

So, one would assume it's *not* dual voltage -> would need step up + VFD combo to run from 240V house main.

However, when I open up the motor cover (6 connections), there is a diagram on the back of the cover showing both star and delta configs with 400V under the star wiring diagram and 230V under the delta wiring diagram.

So, my question is this. Clearly, the motor *is* capable of dual voltage, but will it burn out my switches if I change to delta 230V? Why wouldn't it be rated dual voltage on the front plate if it's possible? It's the current being greater (*sqrt3) at 230V that I'm concerned about.

If I get a 1.5KW 1ph 230V -> 3ph 230V VFD and run the motor in delta, will I break sh*t?

My thinking is it will all be fine, no problems. But what do I know? Do they really put lower rated wiring/switches in single voltage 400V models? Especially half decent machines like this - it seems pretty heavy duty.

Perhaps someone with more experience of these oddities could enlighten me?

Thanks!

 

[CHJ]

The more important aspect is that the switch wiring will have to be modified to switch the single phase supply to the VFD invertor, not between the three phases of the VFD and the Motor.


The VFD must have all three connections Permanently Connected to the Motor BEFORE power is applied.

 

[Owziswurk]

Ok, so the switch wiring, emergency stop etc. need to connect into the VFD at the input stage not the output stage in order that the emergency stop actually cuts power to the VFD onwards? If I'm understanding you correctly. That makes a lot of sense. I'll wager there are connections in the VFD contacter array. I'll be reading up on it all as I get to that point.

Thanks for the input.

Any thoughts on the incongruence between motorplate rating and what's actually available under the hood i.e. both star and delta described on the back of the motor cover and the motor wired in star @400V?

 

[CHJ]

Myfordman (R C Minchin ) of this parish is your man for specifics on connections/switch needs.


See his Technical Document on the subject.

 

[Owziswurk]

Thanks, reading now.

 

[Owziswurk]

I'm going to try and answer my own questions...

The motor in my machine, as stated on the external motor plate, is a 750W 3ph 50Hz 1.5A motor.
Under the motor cover is a diagram detailing two wiring schemas. Currently, it is wired in the Star (Wye) configuration. However, the Delta wiring is also available, since there are six (6) connections and a picture detailing it, with 230V stamped below the pictogram.

IMPORTANT - The switchgear (the Start, Stop, Emergency Stop etc.) are also currently wired into the motor connections. These switch connections must be disconnected from the motor array and wired instead to the VFD (input stage, completely separate connections) to allow control of the output stage from the original buttons. This is what CHJ was pushing me to understand in his previous post.

If the switches aren't attached to the output stage, then they aren't going to receive an increased current (*sqrt3) through them. They will instead be wired to either a 12V or 24V control stage at the VFD input. Your VFD manual will contain the details.

Therefore, my plan as it stands is to disconnect all the switchgear from the connection array inside the motor cover, then rewire the motor to its Delta configuration. This will leave the motor requiring 3ph 230V for operation.

My original switchgear will be rewired to the VFD, if possible. Alternatively, new switchgear can be used. These switches will be wired to the input stage on the VFD to control its operation.

The output stage of the VFD, with suitable gauge new wiring, will be connected to the three (3) motor input connections under the motor cover. I'm not sure which way around the three wires will go yet. Details to follow.

Other things I've learnt:
Stick a Circuit Breaker of suitable amperage in BEFORE the VFD stage, whether the VFD says it needs one or not. Don't rely on the VFD's fuses or CB at the input stage. Get a dedicated CB and always place it BEFORE the VFD in the circuit.

NEVER place a Circuit Breaker, or anything else for that matter between the VFD and the motor input connections.

Don't have long connection leads to the motor from the VFD. Try to keep as short as reasonable. A few feet is fine.

Don't bundle the switching wires together with the motor wires in the same loom, have two separate cables/bundles to avoid weird interference.

Check what sort of switchgear you have and confirm its compatablility with your setup. You may need new switchgear.

If a motor can be simply rewired in Delta when you look under the hood (and there is a diagram detailing it), then it is a dual voltage motor whether stated on the motorplate or not.

In conclusion:
My motor *is* dual voltage, even though it's not stated on the motor plate.
I *can* rewire my motor to Delta 230V 3ph but I MUST DETACH ALL THE SWITCHGEAR FROM THE MOTOR HOUSING and either rewire them to the VFD control inputs or just use the VFD front panel controls instead.

Hope this helps someone who finds themselves where I was.

[edited for incorrect motor technical data at start]

 

[Inspector]

If you haven't already decided on the VFD yet, I bought a Powtran through Alibaba. They will also sell direct and will help you pick the model you need and the prices are very competitive. I bought one for my dust collector as I ordered it with a 5hp three phase motor to be able to adjust the airflow to suit the job at hand. (Still setting it all up.) The controls panel comes with a 2 metre cable to allow remote mounting of the controls. You could have the VFD located behind the drill press on the wall and the remote up beside the switch. If the documentation is any indication of quality the manual is 190 pages.
http://www.powtran.com/en/index.html

 

[Turbo]

I'm not sure if you are aware but on most vfd's you can add a potentiometer into the control circuit to vary the output frequency. This is very useful on a pillar drill as it gives you infinitely variable speeds without having to change belts.
Another useful safety feature is you can program in an electric brake to stop the motor quickly if you hit the emergency stop.

 

[Sideways]

Power is power. Your motor is 750 Watts so divide by 230v (I assume single phase) supply = 3.25 Amps more or less if the motor was a simple resistance.
Motors are an inductive load so current and voltage are out of phase to some degree. For this reason your motor rating plate should show a "power factor" or "Cos Phi" it's likely to be something between 0.6 and 0.9. Lets guess 0.7. Divide the current by the power factor to find out the ampere rating you really need. E.g. 3.25 / 0.7 = about 4.5A.
Then allow a bit more for the power loss in the inverter. Say it's 90% efficient, 4.5A / 0.9 = about 5A.
Circuit breakers come in standard sizes so 6A is the nearest one greater than 5. Protect your 230v single phase supply to the VFD with a 6A circuit breaker.
Choose a type C breaker as induction motors can pull a surge current on startup of upto 5x their rated current. A type C breaker will tolerate this startup surge without tripping but protect the fixed wiring if you draw a big enough overload for long enough.
The VFD will really be taking care of the motor. If the VFD instructions say to do something different, I'd follow the manufacturers instructions. If they don't the method above is generic and sensible.
Make sure the circuit you're connecting into is big enough for the (let's assume) 6A breaker.
Oh, and if the motor spins the wrong way, swap any two of the three supply wires from the VFD to the motor around. That will reverse it.

I think you answered your own questions just fine

 

[Owziswurk]

If you haven't already decided on the VFD yet, I bought a Powtran through Alibaba.

I've got one already now but could be a good lead for another, thanks.

I'm not sure if you are aware but on most vfd's you can add a potentiometer into the control circuit to vary the output frequency. This is very useful on a pillar drill as it gives you infinitely variable speeds without having to change belts.
Another useful safety feature is you can program in an electric brake to stop the motor quickly if you hit the emergency stop.

Yes, so I've learnt. Even if you have 3ph power supply, they allow, as you say, variable speed for all sorts of machines. Electric brake well worth looking into, thanks.

Power is power. Your motor is 750 Watts so divide by 230v (I assume single phase) supply = 3.25 Amps more or less if the motor was a simple resistance.
Motors are an inductive load so current and voltage are out of phase to some degree. For this reason your motor rating plate should show a "power factor" or "Cos Phi" it's likely to be something between 0.6 and 0.9. Lets guess 0.7. Divide the current by the power factor to find out the ampere rating you really need. E.g. 3.25 / 0.7 = about 4.5A.

No Cos Phi anywhere, so 0.7 it is. The plate does state Amp 1,5 (note the comma - I think that's European designation of 1.5A?) but that would be in Star (Wye) with 415v.

Then allow a bit more for the power loss in the inverter. Say it's 90% efficient, 4.5A / 0.9 = about 5A.

Circuit breakers come in standard sizes so 6A is the nearest one greater than 5. Protect your 230v single phase supply to the VFD with a 6A circuit breaker.
Choose a type C breaker as induction motors can pull a surge current on startup of upto 5x their rated current. A type C breaker will tolerate this startup surge without tripping but protect the fixed wiring if you draw a big enough overload for long enough.

The inverter has a rating of 8A output but 18A input. Do I rate the circuit breaker for 8A, 18A or the Fuses 30 rating? or the calculated amount above? And type C, right, got it. I've read up on the surge vs. breaker type now, thanks.

Input 4kVA 18A
Output 1.5kW(2hp) 8A
Branch Circuit Protection Fuses 30

Does this mean the VFD can be taking up to 18A (and maybe then some) under full load? And does Fuses 30 mean it needs a 30A fuse i.e. its own section on the house MCB plus a circuit breaker before the VFD?

I couldn't run this VFD on a 10A extension lead from a 13A house socket then?

I think I already know the answer to this. Just means more work before I can test, oh well.

The VFD will really be taking care of the motor. If the VFD instructions say to do something different, I'd follow the manufacturers instructions. If they don't the method above is generic and sensible.
Make sure the circuit you're connecting into is big enough for the (let's assume) 6A breaker.
Oh, and if the motor spins the wrong way, swap any two of the three supply wires from the VFD to the motor around. That will reverse it.

I think you answered your own questions just fine

Thanks Sideways, always open to good advice!

And the wiring, yes. I can see now on the VFD the U,V,W terminals ready to connect to U,V,W on the motor. And the reverse, great! And unplug first, eh?

So, I'm at this stage of wondering whether I need to do some building/electrical work even to test this project? Maybe I need a new MCB fitted by a pro? I realise that's best in the long run for a workshop but is there anyway of limiting the input/output to 10A or less, even, just to see it working? Like, setting VFD max Hz to, say, 15-20Hz?

Go easy on me, I'm new to all this electrical pokery.


Motor 750W

VFD
Input 4kVA 18A
Output 1.5kW(2hp) 8A
Branch Circuit Protection Fuses 30

 

[AES]

Hi,

I don't know much about all this stuff, but just to put your mind at rest re expressing decimals with a comma rather than a full stop. That is standard "continental" practice, definitely so in German, and I'm pretty sure that's true in French, Italian, and Spanish too.

In German one even says "One comma Five" instead of "One point Five" - so "1,5" in German means exactly "1.5" in English. Just one of their many "funny little ways" (like saying "half nine" when they actually mean "half past eight", rather than half past nine). Now THAT is confusing until yer get yer 'ead around it!

HTH. For the rest, your on yer own mate, sorry!

AES

 

[Sideways]

Hi again. It's good to see someone reading stuff up, learning and working through a problem
So you got a VFD that is big enough to handle a motor twice the power of the one you intend to connect to it. No harm in that. You can be pretty sure you won't overload the VFD.
So you have a choice. If you only ever intend to drive that little 750W motor with your VFD, you don't have to wire a supply to the VFD that's twice the size you'll ever need. The VFD will only ever draw a bit more power than the motor. It won't do any harm to connect the input to the VFD to a 13A plug, plug it into a socket and give it a go. The worst you'll do is blow a fuse. Your 13A plug fuse will carry nearly 20 amps for a little while before it gets hot enough to blow. The 20 or 30A breaker in your fuse box will carry more.
This will at least let you run the motor no load and see how it goes.
If you may want to use the full capacity of the VFD in future to drive a 1.5kW motor, or there's any chance of you passing this machine / property along to someone who could see a big VFD and assume they can hook up a bigger motor to it, then best wire in the supply based on the full capacity of the drive.

Watch out for the difference between power in a single phase system = amps x volts and power in a three phase system = ( square root of 3) x volts x amps in any one phase.
On the motor side of the VFD you have current flowing in three wires, on the supply side, you only have current flowing in two (live and neutral) so the current on the single phase side is bigger than the current in any one of those connections UVW that you noticed. The VFD is working it's magic to convert the large single phase current into lesser current but on three phases not just one. The square root of 3 comes from geometry because the currents in the 3 phases are at 120 degrees to each other.

From those VFD specs 4kva / 18A, the cos phi bit has been accounted for. You can tell by the use of VA (volt amps) rather than Watts.
I suspect the manufacturers are assuming a "standard" fuse or breaker will be used for protecting the circuit. That's why they are saying 30A. The bigger fuse will survive the startup surge. Personally I would choose a breaker that is a closer match to the 18A rating. The nearest standard is a 20A breaker but you need a type C to tolerate the startup.

Cheers.

 

[wallace]

The lathe I just finished had 6 leads in the box making it possible to change to 220v, in the past on a previous lathe I did there were only 3 wires. I took the motor to my local winders and they managed to extract the leads from the windings to achieve the same thing. Then I could use the cheaper vfds.