New Motor Design

[drax]

General Question from a mechanical engineer:

I have a motor that I have been using for many years and now is being discontined. I have a source in China that I sent the motor too to duplicate. Recieved the new one but it does not electrically function the same. One of the technicians sent them the following electrical data to duplicate:

Universal wound AC/DC
no load speed= 10,000 RPM
load speed= approx. 7400 RPM
load current at 7400 RPM= 6.5A
rated voltage= 230V

duty rating is intermittent
130C thermal rating.

Is this enough info. to design a motor? I don't think so.
What is critical for electrical design, rotor lock current?

I got back the following info from the supplier before he shipped us the prototypes:
Apparantly, my technician approved these values. Looks alot different to me although only a ME.

No load speed= 10,000-12,000 RPM
output power without load= 250W
load speed= 7400 RPM
load current at 7400= 1.5 A instead of 6.5A
output power with 7400 RPM= 180W

Here are some tested differences between old and new

old:

100% voltage (220V) 3.26 amps
100% voltage and no load: 1.51 amps


new:

100% voltage (220V) 2.41 amps
100% voltage and no load: 1.05 amps

Help please?

 

[Skogsgurra]

Not easy to say anything without seeing the machines. What I do not understand is the "output power without load= 250W" spec. How can you have output power if you don't load the motor? I think that you have to find out what the different test conditions are before being able to compare data.

Is it possible that the new data are for continuous duty while the original data were for intermittent duty? What duty factor were you using the original motor in?

The tested curent consumption is also confusing. Is the new motor consuming 2.41 A when loaded while the old motor consumed 3.26 at the same load and speed? If that is the case, I would say you got yourself a much better motor now.

Do you have excessive arcing (more than before) with new new motor and at full load? If not, you can relax and feel very comfortable.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[BobM3]

You would want to include:

At a minimum, specify output torque at some speed and a certain duty cycle (be more specific than "intermittent"). You may also want to specify the maximum allowable temperature at certain points that can be measured in the armature, field and commutator. You may also want to specify the grade of the insulation and the hipot test it must pass.

Additionally you may want to specify maximum locked rotor torque and amps, how well it commutates, and maximum runout of the motor shaft.

 

[drax]

He mentioned that the motor is energized for 1/2 second per breaker closure, with a max. of 2 closures per minute.

How would I measure the output torque of the old motor, under its load?

 

[Skogsgurra]

A simple torque measuring device can be made with a pulley and a belt braking it. Tension the belt more to brake more. Either mount motor in a cradle and measure reaction torque or measure difference in force applied to brake belt ends and multiply with pulley radius.

You may need to cool the brake if running for an extended period. And you always have to be very careful so you do not hurt yourself or anyone else.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[aolalde]

Yes you are missing the "power" rating at operating speed (7400 rpm).
Althogh the current does not necessarily follows a proportional rate to the power, 6.5 amps on the original motor are far appart from the 1.5 amps that the new motor will handle. Aparently the new motor has only 25% of the original power.

 

[BobM3]

Does the vendor of the old motor have a speed/torque curve for it?

 

[drax]

This site is great, thank you all for your help. I did find the original specs for the motor. Mechanically, the motor I recieved looks great, just a matter of power. I found this table. Is this all I need to insure that I have a duplicate?

I have a table listing the amps, watts input, rpm, and torque oz. in and HP, watts out at 190V

Sample:

190 amps .90 watts(rdg.23) watts (corr.115) rpm 15350 torque 0

190 vac amps 3.52 watts 620 rpm 7000 torque 68ozin hp .47

this table covers about 9 lines with different current results.

 

[drax]

This is the actual table:

Volts Amps In RPM Torque (oz/in) HP Watts Out Efficiency
190 0.9 MAX 0 0 0 0.0%
190 1.75 10000 20 0.1985 147.7 46.8%
190 2.78 8000 45 0.357 266 53.2%
190 3.52 7000 68 0.472 352 56.7%
190 4.35 6050 88 0.527 394 52.5%
190 4.45 6000 90 0.537 400 52.5%
190 5.35 5000 118 0.586 437 49.0%
190 6.25 4000 148 0.587 437 43.8%

 

[davidbeach]

If you use the "Code" TGML feature, you will get fixed pitch spacing and tables will look much better:

Volts Amps    RPM    Torque  HP      Watts   Efficiency
       In            (oz/in)          Out
190    0.9    MAX     0      0        0        0.0%
190    1.75  10000    20     0.1985   147.7   46.8%
190    2.78   8000    45     0.357    266     53.2%
190    3.52   7000    68     0.472    352     56.7%
190    4.35   6050    88     0.527    394     52.5%
190    4.45   6000    90     0.537    400     52.5%
190    5.35   5000    118    0.586    437     49.0%
190    6.25   4000    148    0.587    437     43.8%

(OK, I also fixed up the column headers a bit too.)

 

[itsmoked]

Nice tip David.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com