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Post by Deleted on Oct 21, 2008 2:05:35 GMT -8
Dear All, I still in my design problem:
I have a DC motor ( Field and Armature ), both Field and Armature Resistances are 0.8 Ohm.
The motor has a label written on it:
180VDC
8Amp (20Amp)
7200rpm
Now, I need to control the speed of this motor and brake it after power off
where it takes about 15 minutes to stop rotation.
What is the best way to such control?
Shunt or Series wound recommended?
How to overcome the Extremely Large starting currents?
By the way, I know much about power electronics and switching devices such as MOSFETs
and made many times PWM control for DC motors but NOT in such ratings.
I need your advice, many thanx..... SHENDY
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rmeyn
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My primary interests are electronics, sailing, bowling, and camping
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Post by rmeyn on Oct 21, 2008 4:34:28 GMT -8
It seems to me that if you have previously built PWM control circuits, you should be able to design this one. Proper Mosfets, paralleled, and with large heat sinks should do the job. There are plenty of tutorials available to help you design the Mosfet part of the circuits. Here's one that I have been working with: homepages.which.net/~paul.hills/SpeedControl/MosfetBody.htmlThe braking problem to me seems simple. Purchase a large wattage braking resistor that can bleed off the generated power while the motor is still turning. You will have to determine the correct ohmage / wattage configuration. A breaking resistor is often used in Photovoltaic or wind generation applications. You could use a relay to turn it on, or a hand operated switch. And be careful when working around 180VDC. It's dangerous. rmeyn |
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Post by Deleted on Oct 21, 2008 5:27:31 GMT -8
thanx a lot rmeyn for your help
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rmeyn
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Post by rmeyn on Oct 21, 2008 19:09:55 GMT -8
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Post by Deleted on Oct 22, 2008 1:52:13 GMT -8
thanx again rmeyn for your help and advice.... SHENDY
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rmeyn
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My primary interests are electronics, sailing, bowling, and camping
Posts: 163
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Post by rmeyn on Oct 22, 2008 5:23:18 GMT -8
Shendy, I don't plan to build such a PWM controller for your motor, but I would find it fun to
help design one. The application note I showed you clearly shows how to set up a high
voltage device driver for the MOSFETs. But we still have to determine what PWM circuitry to
provide the variable duty signal to fire the device driver. There are many scenarios for this.
The 555 timer seems to be a popular one. It cannot stand VDC in excess of 18V. We would
need to power the 555 someway. Perhaps a DC/DC stepdown convertor? What Power
supply voltage are you running the motor on? I would like to help design a circuit with my
spice simulators. Perhaps Gary, if he has time, would help us with the PWM circuitry.
rmeyn
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Post by Gary Lecomte on Oct 22, 2008 7:06:09 GMT -8
Shendy, I don't plan to build such a PWM controller for your motor, but I would find it fun to help design one. The application note I showed you clearly shows how to set up a high voltage device driver for the MOSFETs. But we still have to determine what PWM circuitry to provide the variable duty signal to fire the device driver. There are many scenarios for this. The 555 timer seems to be a popular one. It cannot stand VDC in excess of 18V. We would need to power the 555 someway. Perhaps a DC/DC stepdown convertor? What Power supply voltage are you running the motor on? I would like to help design a circuit with my spice simulators. Perhaps Gary, if he has time, would help us with the PWM circuitry. rmeyn There is already a PWM control on my site that will work. But As Stated by you, You will need to reduce the 18 volts to about 12 volts to run the 555. That May be Simple, If he is starting with AC and Rectifying it to the 180 VDC. |
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Post by Gary Lecomte on Oct 22, 2008 9:26:58 GMT -8
As an Added note to the Above:
One of the problems in controlling a motor with PWM is the motor tends to reproduce the Tone of the Frequency used, just like a loudspeaker.
This can be anoying to some people.
Using a Resistor/Capacitor on the Mosfets Gate, can Modify the Square wave, so its Not such a sharp spike. This reduces that noise, But now you get More Heating in the Mosfet, requiring a bigger mosfet/heatsink.
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rmeyn
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Post by rmeyn on Oct 23, 2008 5:44:19 GMT -8
Thanks Gary, From what I read the simplest solution is to set the frequency above the human
audible range, maybe 20KZ. Modifying the square wave would probably help as well. The real gist of the situation is that this circuit must be carefully designed, and some math is going
to be necessary.
rmeyn
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Post by Deleted on Nov 2, 2008 5:18:00 GMT -8
Dear All, I still in my design problem: I have a DC motor ( Field and Armature ), both Field and Armature Resistances are 0.8 Ohm. The motor has a label written on it: 180VDC 8Amp (20Amp) 7200rpm Now, I need to control the speed of this motor and brake it after power off where it takes about 15 minutes to stop rotation. I need your advice, many thanx..... SHENDY I would use a DPDT switch. wired to run the motor with the switch in one position . Wire a load to the motor with the switch in the other position. Add a POT to the load to adjust the speed of de-acceleration. Gary why am I being shown as a "New Member"?  |
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Post by Gary Lecomte on Nov 2, 2008 6:28:53 GMT -8
Gary why am I being shown as a "New Member"? No Idea Why. And I can't change it. |
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rmeyn
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My primary interests are electronics, sailing, bowling, and camping
Posts: 163
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Post by rmeyn on Nov 2, 2008 17:42:51 GMT -8
You don't become a Junior member until you have 50 posts, Senior member at 100 posts.
rmeyn
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