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2 posts

Wannabe Geek


# 254309 6-Aug-2019 10:41
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So I want a big lathe. Just because... Proper big lathes are typically 3 phase power.

 

I don't have 3 phase. I know I can get 3 phase, but it's a fair amount of money.(I had a quote to do it when I built the house, but I was over budget already, so didn't do it. And I'm regretting it.)

 

The other option is to use a variable frequency drive.  

 

So I know I can use a VFD to run a 3 phase motor on single phase. Basically it takes single phase, converts it to DC then uses ....magic to create 3 output phases.

 

AFAIK the single phase input current for a given HP motor on a VFD is less than what it would be if you had 3 phase and ran the motor directly. It also gives you a lot of control over the motor speed.

 

 

 

What I have been unable to find out is if my max input current is limited to <20Amps. What is the largest 3 phase motor I could run? If this motor size is too small, or the VFD required to run it is too expensive, getting 3 phase to the shed may be the less expensive option.


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Uber Geek

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  # 2290867 6-Aug-2019 12:26
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Not a direct answer to your question, but if the VFD path does not work out, a petrol/diesel 3 phase generator *may* be more cost-effective than permanent 3 phase power if the installation and line rental costs are high, and it gives you an emergency power option to keep the fridge running in an outage.





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99 posts

Master Geek


  # 2290877 6-Aug-2019 12:41
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Without getting too nerdy with the maths, you are looking at around 3.5-4kW depending on the power factor of the motor and the losses from the VFD.


 
 
 
 




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Wannabe Geek


  # 2290896 6-Aug-2019 13:10
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TheMantis:

 

Without getting too nerdy with the maths, you are looking at around 3.5-4kW depending on the power factor of the motor and the losses from the VFD.

 

 

righto. The ballpark number I came up with was 5.5HP/4kW too.


929 posts

Ultimate Geek


  # 2290930 6-Aug-2019 13:47
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A motor-generator is another way to make 3 phases from 1.

 

! think VFD has the advantage of being smaller (no floorspace required anyway)  and maintenance free.


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  # 2291075 6-Aug-2019 17:19
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Friend looked into this for an outbuilding that only had single phase out to it at their business (was offices in the past)

 

Basically the motor needs to be able to be rewired to take 230v 3 phase instead of 400v 3 phase like is what comes from the road here.

 

And that means it cant be a simple socket that you plug any tool into, since its now not able to plug into a normal 3 phase outlet with the rewiring.

 

Also doing it legit was going to need specific wire between the motor and the VFD, it had to be close to it, started and stopped from the VFD (not the controls on the machine) - or the controls on the machine rewired back to the VFD to start and stop it.

 

Ended up not suiting them since they had several machines they wanted to run in that building and it was cheaper to take 3 phase out to it.





Richard rich.ms

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  # 2291098 6-Aug-2019 17:47
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Adoom:

 

So I want a big lathe. Just because... Proper big lathes are typically 3 phase power.

 

I don't have 3 phase. I know I can get 3 phase, but it's a fair amount of money.(I had a quote to do it when I built the house, but I was over budget already, so didn't do it. And I'm regretting it.)

 

The other option is to use a variable frequency drive.  

 

So I know I can use a VFD to run a 3 phase motor on single phase. Basically it takes single phase, converts it to DC then uses ....magic to create 3 output phases.

 

AFAIK the single phase input current for a given HP motor on a VFD is less than what it would be if you had 3 phase and ran the motor directly. It also gives you a lot of control over the motor speed.

 

 

 

What I have been unable to find out is if my max input current is limited to <20Amps. What is the largest 3 phase motor I could run? If this motor size is too small, or the VFD required to run it is too expensive, getting 3 phase to the shed may be the less expensive option.

 

 

 

 

What you are asking is do-able, BUT... the 1 phase to 3 phase VSD's are 240V phase to phase, not the 400V that your lathe will have.

 

you may find that the motor can be changed internally for 240V phase to phase, but you will need an electrician with industrial motor exp. to check and advise you (don't ask a domestic electrician as it will typically be out of their league).

 

You may find it more cost effective to swap the motor for a big enough single phase motor or simply buy a new lathe as the cost of the VSD can be quite expensive and typically more suited to the really small 3 phase 240V motors rather than the bigger 3 phase lathe motors.

 

 


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Ultimate Geek

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  # 2291558 7-Aug-2019 11:19
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You can get phase converters that will do 240V 1-phase in, 400V 3-phase out but they're expensive, probably >$3,000 for 5 kW. You could try calling Fastec Ltd in Wellington - they may be able to suggest an alternative.





McLean


 
 
 
 


226 posts

Master Geek


  # 2292629 8-Aug-2019 22:17
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mclean:

 

You can get phase converters that will do 240V 1-phase in, 400V 3-phase out but they're expensive, probably >$3,000 for 5 kW. You could try calling Fastec Ltd in Wellington - they may be able to suggest an alternative.

 

 

Can they handle the inrush current of a DOL motor though, or would you need to massively oversize?


929 posts

Ultimate Geek


  # 2292803 9-Aug-2019 10:29
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Tracer:

 

mclean:

 

You can get phase converters that will do 240V 1-phase in, 400V 3-phase out but they're expensive, probably >$3,000 for 5 kW. You could try calling Fastec Ltd in Wellington - they may be able to suggest an alternative.

 

 

Can they handle the inrush current of a DOL motor though, or would you need to massively oversize?

 

 

I imagine a lower-cost unit would have limiting and call it soft start lol.

 

High start current not such a requirement for a lathe anyway, more interested in getting up to and staying at speed.


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