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Wiring 3 phase motor

Bob Korves

H-M Supporter - Sustaining Member
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Jul 2, 2014
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Doesn't say it is rated for over speed. You will be the test pilot, please use sensible safety precautions and be ready and willing to replace it and/or other machine hardware if/when there are failures, and reconsider the modifications. Personally, I will not push my older 3 phase motors beyond 20% over speed, they were not designed for it. If I wanted to go faster than that, I would get an inverter rated motor, which would still require that all existing machine parts being raised beyond design speeds also be carefully considered, tested, and monitored. I do not see many reports of exploding parts with inverter speed increases, so either they are working pretty well, or failures are not being reported by the builders. Again, please be careful (What could possibly go wrong???)
 

markba633csi

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Apr 30, 2015
Messages
4,682
The motor may get too hot at higher frequencies than 60 Hz and may lose power also
 

ErichKeane

Making scrap at ludicrous speed.
H-M Supporter Gold Member
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Aug 3, 2017
Messages
785
Thanks, its running on my VFD. Would 120hz be ok with that motor?
There are only two things to be concerned about when setting the frequency higher than the rating:

1- Whether the bearings are capable of the increased RPM
2- Whether the cooling fins are capable of cooling sufficiently at the higher RPM.

If the manufacturer has a very similar motor that is 3500 RPM, they likely use the same bearings for both, so #1 ends up being OK. For the second, it depends on what you're doing. That is a continuous-duty motor, which means it is designed to run for extended times*. If you up the frequency, you could very likely change the duty down the chart in the link below. For a hobby machinist, this is likely OK.

For example, I run my milling machine at higher frequency because I know I'm only running for a few minutes at a time. I'd be much less willing to do so if I was a production shop, or in need of a higher duty cycle.


* https://myelectrical.com/notes/entryid/106/understanding-motor-duty-rating
 

Superburban

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Jan 2, 2016
Messages
1,330
Besides all the good info above, you also need to look at the end speed of the motor, and everything down the line. You are talking about doubling the speed, so you will be doubling the centrifugal forces. Are the winding's going to stay in place? Since you are starting with a 1735 RPM motor, you will likely be ok at 3450. If you started with a 3450, then I would have some concern. Now look down the line, what are you driving? A spindle that runs at 2250, with the 1735 RPM motor, will be looking at 4500 RPM. will the spindle and bearings hold up? Since you do not mention, I can only give an example, and hope that you and others contemplating the same move understand, and take a look. When things turn faster then they were designed and can withstand, the results can be deadly. Looking at the whole picture, and applying common sense goes a long way.
 

martik777

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Apr 19, 2011
Messages
642
Tested at 100hz for 30 mins, temp rose from 75F to 78F. This is 25 mins more than I would ever run it on the mill.
 

ErichKeane

Making scrap at ludicrous speed.
H-M Supporter Gold Member
Joined
Aug 3, 2017
Messages
785
Tested at 100hz for 30 mins, temp rose from 75F to 78F. This is 25 mins more than I would ever run it on the mill.
The real key is testing under load. Any motor should stay reasonably cool without any resistance.
 
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