20% over nameplate
20% over nameplate
(OP)
I have a 24Vdc 1/4hp motor PM-4 pole, that runs max efficiency at 10A. I have installed it is an evaporative cooler driving and propeller blower. I currently have 2-pully options, the first draws 9.5A, the second draws 12A. Now that is 2*24= ~50W over nameplate, maybe not optimum for the motor, But it sure seems to be better from a "system", btu-cfm standpoint.
By the way, I have hear (JB) the term "motors are constant KVA devices" This surely does not apply to DC motors with variable supply,does it? These seem to increase speed with voltage.
Sofar I donot have a problem with the extra 20%, nameplates were not etched by god, only some tech in the factory. besides, it resides, inside a cooler.
any comments?
By the way, I have hear (JB) the term "motors are constant KVA devices" This surely does not apply to DC motors with variable supply,does it? These seem to increase speed with voltage.
Sofar I donot have a problem with the extra 20%, nameplates were not etched by god, only some tech in the factory. besides, it resides, inside a cooler.
any comments?





RE: 20% over nameplate
And no, kVA and kVAr obviously don't apply to a DC motor because they are AC quantities.
The nameplates might have been etched by a technician, but I bet the numbers he etches onto the plate were determined by the motor design engineer. Whether you heed the nameplate depends on whether you know more than the designer does about the motor and the application it is going in to!
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RE: 20% over nameplate
RE: 20% over nameplate
If your particular application can remove more heat from the motor, probably you could overload it. You must monitor the temperatures until the motor reaches a steady rise.
As Skosgurra mentioned, no motor is a constant VA machine, including DC motors, the electric power input (VA) changes mainly with the load and the voltage too since the efficiency is affected.
RE: 20% over nameplate
At 24 volts, the rules are probably different, but how will water-saturated air affect winding-insulation life?
RE: 20% over nameplate
Is the unit (TENV). The humidity factor in the evaporative cooler does not seem to be an issue. I have had this motor running in a squirrel cage evaporative cooler for at least 5, maybe 7 years.
Funny thing, I never bothered before to acurately measure the current in the old set-up. The ~10A is an aqward current to measure with a dvm. I am using a current shunt now.
I have the eff/hp/rpm/amp vrs. tourque curves for the motor that indicate the efficiency holds flat at around 76%, the Hp goes up linearly with the current. Since I am not losing efficiency and the unit is located in a region on airflow ~4-5000 cfm, I will just run it for a while to see hot hot it gets, I have a new spare, just in case
RE: 20% over nameplate
Various electrical power system modeling software actually demonstrate the above statements.
RE: 20% over nameplate
RE: 20% over nameplate
1. Shunt
2. Series
3. Compound
4. Separately Excited
The DC Series motor (e.g. compensated series motor operating on alternating current) phasor diagram showing current locus will reflect the terminal current increasing with voltage increasing and speed decreasing up to certain culmination point. This point determines how much of power can be processed by the motor magnetic circuit design. If the motor is designed physically for 10HP max, there is not much more the magnetic circuit (iron) can process HP-wise. There is no such thing that one would purchase 10HP motor and run 20HP load (would not this be nice for Wall Street investors?).
Once, the Series motor reaches the culmination point in Terminal Voltage, Et, terminal current, It, plane, then further increase of the motor current will cause reduction of speed and reduction of Et up to a point where the motor speed becomes equal to zero, the motor will draw maximum current and there will some smaller terminal voltage Et.
Other types of DC motors Et, It loci are left for exercises since the original posting does not address a specific type of DC motors.
RE: 20% over nameplate
RE: 20% over nameplate
http://zone.ni.com/devzone/conceptd.nsf/webmain/FFB03CC27F0408FC0625683F00762B2B
for: DC motor details
http://www.ecmweb.com/ops/electric_direct_current_motor/
for: Basics
http://www.pdma.com/DCmotor.html
for: DC motor analysis and troubleshooting
etc. for more info
RE: 20% over nameplate
RE: 20% over nameplate
RE: 20% over nameplate