motor speed control

[mahmoud shendy]

Dear All..

this is the fourth time I post, sorry but actually I am confused..

my problem is to control the speed of a 4hp DC motor, its rating is

180VDC
20A

I measured the Armature resistance and Field Resistance, both are (0.6 Ohm)

I want to know how to measure the lasting parameters:

Ke and Kt conatants
J (monent of inertia)
B (friction losses)
La and Lf (armature and field inductance)

after determining this parameters, I will be able to model the motor to control
it..



by the way, I need to brake the motor after the rotation, since it still rotates
for about 15 minutes after power of.. AND SO, what is the recommended, series wound
or shunt wound or separately excited?

what is the maximum current can field coil passes without damage, and also the starting
current can the armature passes?

I use external power resistor for Armature and Field, but it runs VERY VERY VERY hot !!!!!

I need your help, thanx a lot, and GOOD BYE
... Shendy

 

[Externet]

Use several series/parallel 230V light bulbs instead of the resistors, and a multi position switch to have several steps of control, or get a treadmill speed control.

Motor Control Boards
Where did that motor come from ?

 

[nxt_]

dc motor control

**broken link removed** , could any one please check this schematic and tell me what is the purpose of putting two 100nf capacitors after the motor. and what is the middle wire between them for?. is the two capacitors for the protection from high start current occur when the motor starts? just smoothing?. if that is right so my question will be what is the middle wire between them?.. onther question. if i want to replace the transistor in the schematic by irf740; how to calculate 'R' base. i know there is arelation between the Drain source currernt ,Gate charge, and temprature. i need standard equation so that i can apply it on any mosfet transistor so that i can reach the maximum possible effecient switching device.

Awaiting Your Prompt Reply,

Thanks To You All.

 

[ronv]

The 2 capacitors are from each brush to the motor frame ground. (also earth ground) They suppress noise created by brush arcing. Often there will be another across the motor as well.
There is not a "magic" number for gate resistance. If you look at the spec sheet the FET will have a total gate charge number (nC). This is how long it will take the FET to turn on if you supply 1 amp of gate drive. So in the case of the IRF740 the nC is 63 which means it will turn in in 63 ns if you have 1 amp of base drive, 126ns with .5 amps 252 ns with .25 amps and so on. Usually faster is better, but may create more noise and may cause ringing in the gate source loop if there is much inductance there. Hope this helps.