# Getting Voltage from a Linear DC Motor

Thread Starter

#### NW_4wheeler

Joined Apr 6, 2006
2
I have a linear DC motor. It has a rod with permanent magnets inside and the rod moves through the coils. Normal operation is applying 320V to three windings and the rod moves depending on the phase of the input. An output sensor tells the position of the rod. I want to move the rod mechanically and capture the power coming from the three coils (hence the generator). I want to then regulate the power. I understand the lower the resistance of the load the more force required to move the rod. My rod will not move continuously (it will stop for moments at the end of each travel), but I want to create a circuit that will help regulate the output. I don't care what the voltage out is, I only care that what I get out gets regulated enough to power some LEDs or something. Thanks.

#### Papabravo

Joined Feb 24, 2006
16,180
Originally posted by NW_4wheeler@Apr 6 2006, 03:21 PM
I have a linear DC motor.  It has a rod with permanent magnets inside and the rod moves through the coils.  Normal operation is applying 320V to three windings and the rod moves depending on the phase of the input.  An output sensor tells the position of the rod.  I want to move the rod mechanically and capture the power coming from the three coils (hence the generator).  I want to then regulate the power.  I understand the lower the resistance of the load the more force required to move the rod.  My rod will not move continuously (it will stop for moments at the end of each travel), but I want to create a circuit that will help regulate the output.  I don't care what the voltage out is, I only care that what I get out gets regulated enough to power some LEDs or something.  Thanks.
[post=15907]Quoted post[/post]​
Use a 3-phase transformer, some rectfiers, some capacitors, some optional filters, and some regulators. What is a moment, and what is your problem or question?

Thread Starter

#### NW_4wheeler

Joined Apr 6, 2006
2
Originally posted by Papabravo@Apr 6 2006, 12:59 PM
Use a 3-phase transformer, some rectfiers, some capacitors, some optional filters, and some regulators. What is a moment, and what is your problem or question?
[post=15908]Quoted post[/post]​
I have many questions. First though, a moment will be a up to a few seconds.

1. The force constant is 22.1 N/A rms. What does that mean to me?

2. The back EMF is 18.0V pk/meter/second. Saying I can move the rod 3 meters per second what is the expected output power I might see?

I cannot relate these numbers to any electronics equations that I am familiar with. I have been told to expect somewhere around 150 watts peak. I feel this is way to high. I have also been told to use a switching circuit to switch between coils but I feel I can get the voltage by connecting the three outputs through a rectifier.

3. You think I should connect the output to a 3 phase transformer?

4. What kind of storage caps do you think it would take?

#### Papabravo

Joined Feb 24, 2006
16,180
Originally posted by NW_4wheeler@Apr 6 2006, 04:58 PM
I have many questions.  First though, a moment will be a up to a few seconds.

1. The force constant is 22.1 N/A rms.  What does that mean to me?

2. The back EMF is 18.0V pk/meter/second.  Saying I can move the rod 3 meters per second what is the expected output power I might see?

I cannot relate these numbers to any electronics equations that I am familiar with.  I have been told to expect somewhere around 150 watts peak.  I feel this is way to high.  I have also been told to use a switching circuit to switch between coils but I feel I can get the voltage by connecting the three outputs through a rectifier.

3. You think I should connect the output to a 3 phase transformer?

4. What kind of storage caps do you think it would take?
[post=15909]Quoted post[/post]​
1. N stands for Newton, a unit of force in the MKS system. Even a noob should know Newton's(same guy) 2nd Law that
Rich (BB code):
F = m * a

Where F is the force in Newtons
Where m is the mass in Kilograms
Where a is the acceleration of gravity in m/sec^2
2. Don't know about the power yet but the back EMF at 3 m/sec will be 54 Volts peak, which will subtract from the power out.

3. I think you should use a transformer to avoid working with high voltages and currents, especially if you don't know what you are doing.

4. The capacitors most people use are electrolytic, in the 1000 uF to 100,000 uF range. The larger the capacitor, the less ripple. Problem is large capacitors that can withstand large voltages are expensive and hard to acquire. That is why you need to lower the voltage out of the generator. High value capacitors can give you a nasty shock and a painful burn after the power is turned off if you are not careful.

Can you do this successfully? I have no bleeping idea!