# VFD minimum motor size?



## John_Dennis (Feb 4, 2020)

I have 2 Allen Bradley VFD motor drives that convert 220 to 3 Phase  The smaller one is rated at 1HP and the larger at 2 HP  I want to use these on a bridgeport I just bought that has a 1 HP motor and a 1/8 HP feed motor.

Will these VFDs work on a motor that is significantly smaller than the rated capacity?

I also found an even smaller VFD which is rated for 1/2 horsepower 110 volts to 3 Phase that I might purchase


161S-AA 04NPU Series B 1hp 220v

161S-AA 07NPU Series B 2ho 220v

161S-DA02NPU .5 hp 110v want to buy?

Thanks
-John


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## ddillman (Feb 4, 2020)

the 1 or 2hp ones would work. the power feed on mine is 110v that plugs into a wall plug separately from the motor


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## John_Dennis (Feb 4, 2020)

I may be misremembering but I was thinking that there was a minimum horsepower for these VFDs  Allen Bradley does not offer support unless you have a maintenance contract.


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## Superburban (Feb 5, 2020)

I tried to get an answer on that, when I searched for my first VFD (Before I found this crowd). Getting answers both ways, that basically made it a wash. I went with double the HP of the motor they are driving. So all my 1 hp motors have a 2 HP VFD, My 2 HP, has a 4 HP VFD, and the 5 has a 10. My thinking, is that I am only going to use half the capacity of the capacitors at most, hopefully extending its life.


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## mksj (Feb 5, 2020)

I do not see parameters that are specific to the motor properties (like RPM, poles, tuning, etc.) which are more common with newer VFDs, but b12 does select for the motor full load amps from 5/120%.. Since these are both single and 3 phase input rated (so no derating is required) the VFD can be sized to the motor Hp/amp rating, so assuming your 1 Hp mill motor is rated for something like 3-3.5A 3 phase you can use the 161S-AA 04NPU which has a 4A output rating. There is parameters b12, b13, b21, b22, b23 that are specific to the motor amperage characteristics. You would set b12 to the name plate amps and b22 to the current overload limit, probably 120% of the name plate amps. If you used the 161S-AA 07NPU, it would appear that with the b12/b22 parameters you should be able to reduced  to the smaller motor amp parameters.

The feed motor would need a separate VFD assuming it is 3 phase 240 VAC, I am use to these drive motors being DC with a separate DC drive. If it is  3 phase 240 VAC 1/8 Hp, you should be able to use your a 0.5 - 1.0Hp VFD to run this size motor. You should be able to power up the VFD and check these settings.  I did a couple of VFD controlled drive motor installs, one was a 1/8 Hp gear motor and I used a Hitachi WJ200 0.5Hp and adjusted the motor settings. I previously tried a KB VFD and it had poor motor control and braking, the WJ200 was much better and not that expensive. I did use an external braking resistor so the drive would stop quickly.

If these VFDs have been sitting on the shelf for a long period of time (like more than a year) you want to power them up on a variac and slowly bring up the voltage not running a motor. This can reform the capacitors to some degree and not result in catastrophic failure.

Manual is attached.


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## Cooter Brown (Feb 5, 2020)

I am running a cheap Chinesium 2HP VFD on my bridgeport and I have a 1 1/2 HP 3PH motor on it that runs with no problems.....


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## ttabbal (Feb 5, 2020)

My Bridgeport has the old feed motor as well. I used 2 Chinese 2HP VFDs. They work great. I did have to tweak a setting for the spindle motor. The motor frequency I believe. I set the spindle for variable speeds with a remote control panel. The feed is fixed so that the IPM label works.


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## tazzat (Feb 5, 2020)

cheap Chinesium  5,5kw on a 2,2kw motor, no problems..


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## Reddinr (Feb 5, 2020)

Here's an outlier:  I'm using a 150 HP Yaskawa F7 drive I rescued free from the scrap heap.  It took a chain-fall to lift it up to mount to the wall.   It has the over-current and other setpoints adjusted to match the "tiny" motor and it has been running my lathe for a few years now.  I disconnected its fans because I think the drive barely notices the load.


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## John_Dennis (Feb 5, 2020)

mksj said:


> I do not see parameters that are specific to the motor properties (like RPM, poles, tuning, etc.) which are more common with newer VFDs, but b12 does select for the motor full load amps from 5/120%.. Since these are both single and 3 phase input rated (so no derating is required) the VFD can be sized to the motor Hp/amp rating, so assuming your 1 Hp mill motor is rated for something like 3-3.5A 3 phase you can use the 161S-AA 04NPU which has a 4A output rating. There is parameters b12, b13, b21, b22, b23 that are specific to the motor amperage characteristics. You would set b12 to the name plate amps and b22 to the current overload limit, probably 120% of the name plate amps. If you used the 161S-AA 07NPU, it would appear that with the b12/b22 parameters you should be able to reduced  to the smaller motor amp parameters.
> 
> The feed motor would need a separate VFD assuming it is 3 phase 240 VAC, I am use to these drive motors being DC with a separate DC drive. If it is  3 phase 240 VAC 1/8 Hp, you should be able to use your a 0.5 - 1.0Hp VFD to run this size motor. You should be able to power up the VFD and check these settings.  I did a couple of VFD controlled drive motor installs, one was a 1/8 Hp gear motor and I used a Hitachi WJ200 0.5Hp and adjusted the motor settings. I previously tried a KB VFD and it had poor motor control and braking, the WJ200 was much better and not that expensive. I did use an external braking resistor so the drive would stop quickly.
> 
> ...


I don't have access to a variac, is there a good substitute?


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## mksj (Feb 6, 2020)

You can pick one up for around $70 on eBay, but then new VFD start at not much more. I am not sure if it would work, but you may be able to power up the VFD on 120VAC and let it idle for 30-60 minutes, then switch it out to 240VAC and let it idle for 1-2 hours, then repeat it in a day or two. Below is the directions for the Yaskawa drives, generally when attempting to reform capacitors you slowly step up the operating voltages and let it marinate for awhile. Since the VFD rectifies the incoming AC, one can use a variac for AC or a DC power supply, although the latter is even more uncommon at the current required.








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## KevH (Feb 26, 2020)

If its the original feed motor it should run off the 110v side of the transformer.  You would need the VFD wired direct to the main motor and a single phase supply to the transformer in the control box


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