thyristorised dc drive

[jidiya]

I want to make project in thyristorised dc drive.....can u pls help to find out the all the detail to control for 1-5 hp dc motor using armature and field control schematics?

 

[goldsmith]

Dear jidiya
Hi
What do you need accurately? do you want to control the speed of a DC motor with an SCR?
Best Wishes
Goldsmith

 

[wa1kij]

"control the speed of a DC motor with an SCR" ...is that even possible? Once triggered, an SCR will pass current until power is removed. SCRs are widely used in AC, not DC, circuits, especially as lamp dimmers, because the polarity reverses 50 or 60 times a second, thus interrupting current flow.

 

[goldsmith]

Dear wa1kij
Hi
It is possible to control the DC motors with an SCR . you should use a chopper network ( with another SCR to turn off your SCR) , to control it , with your command.
Best Wishes
Goldsmith

 

[jidiya]

yes i want to control the speed of dc motor using SCR......i am Done the Rpm measurement part but now i have to done the current control part...so if any help then pls do!!
regards.....
jidiya

---------- Post added at 23:27 ---------- Previous post was at 23:25 ----------

hi goldsmith,
u r in right path dat chopper network is used in this skt....

 

[wa1kij]

You say there is an RPM measurement part. Is it analog or digital?

BTW you say a "1-5 HP DC motor" That's awfully big. I'd start with A smaller prototype!

 

[jidiya]

it's digital..............i am using 1 hp,10.3A motor permanant magnet dc motor,

 

[dselec]

If the motor field works with dc u can use a triac feeding a bridge rectifier and get diff. dc level for your motor.
send motor type ...detail .

 

[jidiya]

1hp,10.3A,16v and 4400rpm + pemanant magnet dc motor......

 

[wa1kij]

Permanent magnet, so you don't have to worry about a field coil. Since your speed information is digital, why not use a microcontroller to generate pulse width modulation? Wider pulses to increase speed, narrower ones to decrease.

 

[dselec]

good then use my option and and limit the triac potentiometer for max speed.
u can also use scr if voltage range up-to 150vdc
good luck
here is the perfect link:

Basic Triac and SCR Projects and Circuits
Basic Triac and SCR Projects and Circuits

 

[jidiya]

Permanent magnet, so you don't have to worry about a field coil. Since your speed information is digital, why not use a microcontroller to generate pulse width modulation? Wider pulses to increase speed, narrower ones to decrease.

yes i m using pic16f877a microcontroller......but right now i have to do currrent sensor and feedback loop....i don't have any idea right now

 

[Tahmid]

"control the speed of a DC motor with an SCR" ...is that even possible? Once triggered, an SCR will pass current until power is removed. SCRs are widely used in AC, not DC, circuits, especially as lamp dimmers, because the polarity reverses 50 or 60 times a second, thus interrupting current flow.

You can turn off the SCR by forced commutation.

 

[jidiya]

hi dselec,
have u any idea to sense the currrent feedbak loop....?????????????

 

[goldsmith]

Hello jidiya
The current sensing is simplest section of your circuit . you have many ways , such as : 1- low value resistor . 2- hall effect sensor . 3- CT ( at your AC line ( before rectifying ) . 4- clamp method . and ....etc.
so in your idea , is price important , or quality or both of them ?
Good luck
Goldsmith

 

[jidiya]

both(price and quality matter)....which one is better according to u?????

 

[goldsmith]

Hall effect sensors are better but not cheap ! and resistor is cheap but it's precision as about 10 ma . CT is cheap and with good precision ( if you make it with yourself will be cheap ) .
SO what is your final current ?
Best Lucks
Goldsmith

 

[jidiya]

@goldsmith,
final current will be 1A.

 

[goldsmith]

Ok the resistor will be ok for current sensing and limitation .

 

[ALERTLINKS]

Before IGBTs and mosfets, scr were widely used for dc motor control. I repaired a 'folk lifter motor controller' with a 48V, 275A DC motor. A 450A thyrister was used as controller unit and a 50A thyrister to generate pulse to switch it off. An optical encoder in accelerator controls the speed. A huge battery bank under the seat.
If you want to control dc motor with ac supply, its simple.
Model 1681 Instruction Manual - Firing Circuits DC SCR Drives
Adjustable Speed Drives (a.k.a. Variable Speed Drives) - Application Information - DC Drives - Principles of Operation