Hi, I wasn't sure where to ask for help and thought I'd try here - I need some advice on a 3 Phase motor that's running slow - I've got an old woodworking combination machine that's fitted with three small 3 phase 2.2kW motors. I tried to use the table saw earlier today but the motor's running slow and has practically no power/torque - the blade stopped when I tried to rip some 2"x2" softwood - it used to rip 9"x4" oak. The machine's been standing unused for about five years and everything was working fine the last time it was used, although I do remember working it quite hard on a dull blade - but just had to get the job done. All wiring connections are okay, I've tried swapping motors over, but it still ran slow. I'm guessing I need to find a replacement, or get it rewound - I'd just like to know what has caused it lose power so I can avoid it happening again. Many thanks in advance.
3 Phase motor running slow
- Thread starter fuzzytrifle
- Start date
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Are you on a real 3 phase supply or using one of those converters from a single phase supply? Have you metered from phase to phase and each phase to neutral and phase to earth?
Is it running slow without any load? Does it drive through a gearbox? Is any gearbox and bearings in working condition?
If you've swapped the motor and it's still running slow, then as above, what's supplying it? Phase converter, VSD? VSD will have lost its settings after 5 years off.
If you've swapped the motor and it's still running slow, then as above, what's supplying it? Phase converter, VSD? VSD will have lost its settings after 5 years off.
Thank you for your responses - yes it's a 3 phase supply, the machine is connected to the 3 phases and earth, there's no N connection, and there's no gear box. The three motors are identical with varying sized drive pulleys. I don't know how to test from phase to phase - swapping motors, changing the wires from like to like is about all I'm capable of/willing to do on a 3ph supply. I've swapped the supply, which comes from the machine's function selector switch, to the other two motors in turn, and both run at full speed on that supply. The faulty motor runs slowly (at about half speed) on all three supplies from the function selector switch.
I had something similar happen to a planing machine some time ago, the machine ran at about half speed for a minute or so before stopping completely. The electrician found that the thermal overload switch had failed, I sold it for parts as the cost of a replacement motor and switch was more than the price of a used machine - this was before the availability of cheap invertors and nobody wanted small used 3ph machines.
I had something similar happen to a planing machine some time ago, the machine ran at about half speed for a minute or so before stopping completely. The electrician found that the thermal overload switch had failed, I sold it for parts as the cost of a replacement motor and switch was more than the price of a used machine - this was before the availability of cheap invertors and nobody wanted small used 3ph machines.
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Sounds like the motor may have developed shorts in the windings if the other motors run up to speed on the same supply.
What size and speed motor is it? Anything below 11kw is usually binned and replaced by rewinding companies as it is the cheapest option unless it is a specialist motor.
Do you have a rewinding company near you? If so they can test and best advise. They may also be willing to source you a replacement unit much cheaper than going direct to a supplier yourself.
What size and speed motor is it? Anything below 11kw is usually binned and replaced by rewinding companies as it is the cheapest option unless it is a specialist motor.
Do you have a rewinding company near you? If so they can test and best advise. They may also be willing to source you a replacement unit much cheaper than going direct to a supplier yourself.
It's only a 2.2kw, 3HP motor, I've found the same spec motor on ebay for less than £150. So, considering the amount of use it's going to get I'll probably go for that, although I'm not sure what the quality will be like at that price.
It's possibly a used item but a lot of people strip down machinery and sell as spares because they can generate more money that way.
Does the seller give any guarantees? Second hand is usually about 3 months whereas brand new should be at least 12 months.
Does the seller give any guarantees? Second hand is usually about 3 months whereas brand new should be at least 12 months.
Second hand motors can be good, they can also be a waste of money.
If this motor is the right type then you would be getting a good quality motor, costs more but zero risk of disappointment
https://uk.rs-online.com/web/p/ac- motors/1879870/
Companies like this http://www.renu-electrical.com/ can supply motors with a sound guarantee.
If this motor is the right type then you would be getting a good quality motor, costs more but zero risk of disappointment
https://uk.rs-online.com/web/p/ac- motors/1879870/
Companies like this http://www.renu-electrical.com/ can supply motors with a sound guarantee.
I'd rather buy from a reputable company like RS, but can't find a motor with the correct overall combination of power, speed and dimensions.
Assuming that the details are correct, this motor on ebay is an exact replacement - even though there are 2 different motors pictured:
https://www.ebay.co.uk/itm/2-2KW-3-...00-RPM-2-Pole-2-2KW-3HP-400V-NEW/183996423869
but feel it's a bit of a gamble at £106.
Assuming that the details are correct, this motor on ebay is an exact replacement - even though there are 2 different motors pictured:
https://www.ebay.co.uk/itm/2-2KW-3-...00-RPM-2-Pole-2-2KW-3HP-400V-NEW/183996423869
but feel it's a bit of a gamble at £106.
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Seller appears to be
LEVER & WOOD LIMITED
19 Stirlin Business Park,
Sadler Road,
Lincoln,
Lincolnshire,
England, LN6 3RS
LEVER & WOOD LIMITED
19 Stirlin Business Park,
Sadler Road,
Lincoln,
Lincolnshire,
England, LN6 3RS
Indeed. Given the preceding post from the OP, are you intending to imply that it is (or is not) a "reputable company" - and, if so, which?
Kind Regards, John
The company may sell direct and give a better price than if bought through Ebay.
All 3 phase, 2 pole, 2.2kw motors will run at the same speed. The speed is determined by the number of poles and the frequency of the electrical supply.
Most 2.2kw motors will have the same frame size and the relative dimensions from the feet to the motor output shaft are standardised.
We buy quite a few motors (around 50 a month) and pay about that price (inc VAT) for a decent quality, 4 pole, chinese manufactured, 2.2kw motor.
Links in this post may contain affiliate links for which DIYnot may be compensated.
Has the OP not "covered all those bases" with ....
Kind Regards, John
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