# Worth Upgrading To Inveter Rated Motor 1340gt?



## marcusp323 (Nov 30, 2016)

Been going back & forth on whether to buy one for a while. The stock 3 phase hasn't given any trouble or anything, but just want to hear from people who have done it & whether they think the $$ were well spent.
Mark


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## davidpbest (Nov 30, 2016)

I replaced the stock 3-phase motor with a Baldor as part of a VFD conversions.   I actually never used the stock motor, so I can't compare the two, but I will say the Baldor is dead quiet and vibration free and has amazing torque at the low end.   The Baldor I bought (on eBay NOS) fits in the space of the old motor, and the only mods required were to shorten the shaft on the unused end, and drill two new mounting holes in the stock PM1340 mounting bracket.


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## marcusp323 (Nov 30, 2016)

Curious where you bought your replacement pulley too. I can't seem to find any that really run very true!


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## davidpbest (Nov 30, 2016)

https://www.amazon.com/gp/product/B003N17PSI/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1


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## Alan H. (Nov 30, 2016)

I have had good luck with Surplus Center on pulleys.  I must say that I use their printed catalog versus their website.  The catalog is easier to deal with.


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## marcusp323 (Dec 1, 2016)

Tried a couple from McMaster-Carr & was sorely disappointed. Used to getting quality stuff from them but not so much in that area evidently!


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## jbolt (Dec 1, 2016)

marcusp323 said:


> Curious where you bought your replacement pulley too. I can't seem to find any that really run very true!



When I did the conversion on my PM-1440GT the only manufacturer that had the size pulley I needed was Gates. I found the best price to be from Motion Industries. It has a small bit of run-out due to the slip fit on the motor shaft but once the belts are properly tensioned (using a belt tension gauge) it has no adverse affect and runs very smooth.


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## mksj (Dec 1, 2016)

The stock motor works well, I would say the major limitation is that I would not push the motor beyond 90Hz since the Hp will probably fall off, and low/high speed cooling could be an issue with continuous use. An inverter rated motor (Marathon BlackMax, BlueMax, Baldor IDNM, etc.) are usually rated to 120Hz with no Hp drop off, and usually are good to much higher RPM with full Hp  (5000-5500). By going to 120 Hz, you can run the lathe off of a single pulley from ~50 RPM to a top end of between 1800-2000 RPM depending on the motor pulley. Something like a 2.7" (2.5-2.9") on the motor and the larger drive pulley works well, you need the next size longer belt (like a BX25).  Most of these type of motors are TENV, so built with a lot of iron/metal to dissipate the heat and are rated at all RPMs with no additional cooling needed. Mine gets almost to hot to touch with continuous use, but these are rated to withstand temperatures to around 300F. They are pretty bullet proof and very quiet without the fan.  An inverter/vector motor can be pushed to higher overloads for short periods (180-200% for a minute), so with the a better VFD they can be pushed harder and can handle a very wide speed range.  The motor offers a bit tighter control over the RPM under load (a few RPM difference) and maybe better controlled braking, but we are talking small  differences. 

I do not think it pays to run out and buy a new motor, but they do come up routinely on ePay for as low as $100 plus shipping for new 2Hp Marathon inverter rated motors (reasonable price range is 100-300). If you get a great deal and have a few extra $, than it may be worthwhile. 
http://www.ebay.com/itm/Marathon-Black-Max-Motor-2-HP-60HZ-230-260V-5-400RPM-1-7-AMPS-/381869088167


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## tmarks11 (Dec 1, 2016)

If you do get an inverter rated motor, don't get Leeson's.

I was very disappointed to pay extra money to get Leeson's wattsaver inverter duty motor with a "made in China" label on it.


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## marcusp323 (Dec 2, 2016)

Sounds like my pulley foray, a disappointing tag to find, attached to far too many labels one used to consider high quality stuff. Not that the Chinese aren't capable of making good products, just that it's a lot of hit or miss in my experience.


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## Ulma Doctor (Dec 3, 2016)

unless you are continuously operating above 90 hz or below 30 hz, you will gain little to no advantage by purchasing an inverter rated motor.


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## tmarks11 (Dec 3, 2016)

Ulma Doctor said:


> unless you are continuously operating above 90 hz or below 30 hz, you will gain little to no advantage by purchasing an inverter rated motor.


If his purpose is to avoid making speed changes with his gearbox, then there would be an advantage.  If he is just going to adjust it up or down a few Hz to get an exact rpm, then not much advantage.


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## Ulma Doctor (Dec 3, 2016)

tmarks11 said:


> If his purpose is to avoid making speed changes with his gearbox, then there would be an advantage.  If he is just going to adjust it up or down a few Hz to get an exact rpm, then not much advantage.


i think you missed my point, we have already established that the motor will be vairiable speed.
my point is that it is not necessary to spend the extra $$$ to get an inverter rated motor UNLESS He'll be operating under 30 hz or over 90 hz continuously


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## mksj (Dec 3, 2016)

Agree with Ulma Doctor, the main advantage is a wider speed range, traditional 3 phase motor's performance tend to drop off above/below this range, although sensorless vector as opposed to V/Hz VFD setting allows you to go lower with little performance loss of torque (Hp drops off in a linear fashion below the base frequency).  Most newer 3 phase motors are rated for use with VFDs, and have a constant torque ratio of around 10:1 so they should be good to 6Hz with sensorless vector http://www.marathonelectric.com/docs/017-020VariableSpeedInfo.pdf . It is still not wise to operate a TEFC motor below 30 Hz for any extended amount of time because of cooling issues, 30-90Hz is a reasonably acceptable range for this application.

There are various versions of "inverter rated motors" some have insulation that are more tolerant of inverters, others are of the "vector" type that are designed to work over a very wide speed envelope. These typical inverter/vector motor have CT ratios of 1000:1 or greater, so full torque down to around 0 RPM and maintain full Hp up to 2X their base speed in the 1-5 Hp range. You can also jack up the short term overload parameters on these motors. The main advantage  is the the higher (and lower) maximum speeds, you do not need to do a belt change if this is part of the equation, if single belt speed than this is moot. By spinning the motor over 60 Hz, you are delivering more Hp to the spindle, and approximately the same torque, relative to a fixed speed motor that is geared up for the spindle speed. This is calculating the applied spindle parameters when you account for the gearing ratio changes required of  a fixed frequency motor.

Bottom line, the stock motor on the PM1340GT works very well, I was never able to not have enough power or see any appreciable speed change with it with the WJ200 VFD. The inverter/vector motor did allowed me to not have to deal with belt changes and operate the speed range routinely from 15-120 Hz on the fly. Essentially I use two gears H and L in the headstock gearbox for general speed ranges, there is no issues with cooling, it stops frighteningly fast to the same exact position with an electronic stop.

On pulleys, I really have not seen an issue. I use a Maska pulley which is a Baldor brand (they are made in different countries) but seem to be well made.


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## tmarks11 (Dec 3, 2016)

Ulma Doctor said:


> i think you missed my point, we have already established that the motor will be vairiable speed.
> my point is that it is not necessary to spend the extra $$$ to get an inverter rated motor UNLESS He'll be operating under 30 hz or over 90 hz continuously



And I think you missed any point as well.  I was agreeing with you.

If he keeps using the gear box to change speeds and only adjusts a little with the VFD, go with the non-inverter duty motor.  If he wants to adjust speed solely with the VFD (i.e. 20 Hz up to 120 Hz), not the gear box, get the inverter duty motor.


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