 |
Search Sci.Electronics.Basics |
|
|
|
|
|
|
 |
|
|
Sci.Electronics.Basics -> Looking for some ideas for DC motor control
There are 4 messages in this thread.
You are currently looking at messages 1 to 4.
|
Author: Eric R SnowDate: 19:49 25-08-06
|
|
Greetings All,
I'm working on a device to pull wire for welding. The mechanical part
is done and now I'm trying to figure out how to do the motor speed
control. I thought that a PWM speed control would be best because the
motor torque will be close to constant. However, there are only two
wires available to turn on the welder, power the motor and turn the
motor on. this is because there two wires to the wirefeed gun. These
wires are meant to turn on the welder. My idea is to instead use these
wires as power wires for the motor. Once power is flowing I could also
put a relay coil in series with the motor power wires with the relay
doing what the switch in the handle is supposed to do. I can turn on
the PWM motor speed controller at the welder. Then the switch in the
gun is used to complete the circuit from the PWM to the motor. But
since the current will be pulsing I can't see how it could also be
used to power the coil in the relay. I'm afraid that if I can get the
relay to operate at the lowest average current being delivered to the
motor then it will overheat when the motor is being supplied with the
highest current. I also don't know if the PWM speed controller will
like having the load switched on and off or if the relay coil in
series will cause a problem.
Any Ideas?
Thanks,
Eric
|
|
|
|
Author: Mr. J DDate: 20:02 25-08-06
|
|
Eric R Snow wrote:
> Greetings All,
> I'm working on a device to pull wire for welding. The mechanical part
> is done and now I'm trying to figure out how to do the motor speed
> control. I thought that a PWM speed control would be best because the
> motor torque will be close to constant. However, there are only two
> wires available to turn on the welder, power the motor and turn the
> motor on. this is because there two wires to the wirefeed gun. These
> wires are meant to turn on the welder. My idea is to instead use these
> wires as power wires for the motor. Once power is flowing I could also
> put a relay coil in series with the motor power wires with the relay
> doing what the switch in the handle is supposed to do. I can turn on
> the PWM motor speed controller at the welder. Then the switch in the
> gun is used to complete the circuit from the PWM to the motor. But
> since the current will be pulsing I can't see how it could also be
> used to power the coil in the relay. I'm afraid that if I can get the
> relay to operate at the lowest average current being delivered to the
> motor then it will overheat when the motor is being supplied with the
> highest current. I also don't know if the PWM speed controller will
> like having the load switched on and off or if the relay coil in
> series will cause a problem.
> Any Ideas?
> Thanks,
> Eric
I am thouroughly confused by your description of the problem. If you
are just trying to "steal" the wattage from the welder line, you could
use this for the relay as well as the PWM. The output of the PWM does
not really interfere with the power source it is using, please explain,
or perhaps offer a schematic.
|
|
|
|
Author: Eric R SnowDate: 11:42 26-08-06
|
|
On 25 Aug 2006 17:02:43 -0700, "Mr. J D" <JedOs86@gmail.com> wrote:
>
>Eric R Snow wrote:
>> Greetings All,
>> I'm working on a device to pull wire for welding. The mechanical part
>> is done and now I'm trying to figure out how to do the motor speed
>> control. I thought that a PWM speed control would be best because the
>> motor torque will be close to constant. However, there are only two
>> wires available to turn on the welder, power the motor and turn the
>> motor on. this is because there two wires to the wirefeed gun. These
>> wires are meant to turn on the welder. My idea is to instead use these
>> wires as power wires for the motor. Once power is flowing I could also
>> put a relay coil in series with the motor power wires with the relay
>> doing what the switch in the handle is supposed to do. I can turn on
>> the PWM motor speed controller at the welder. Then the switch in the
>> gun is used to complete the circuit from the PWM to the motor. But
>> since the current will be pulsing I can't see how it could also be
>> used to power the coil in the relay. I'm afraid that if I can get the
>> relay to operate at the lowest average current being delivered to the
>> motor then it will overheat when the motor is being supplied with the
>> highest current. I also don't know if the PWM speed controller will
>> like having the load switched on and off or if the relay coil in
>> series will cause a problem.
>> Any Ideas?
>> Thanks,
>> Eric
>
>I am thouroughly confused by your description of the problem. If you
>are just trying to "steal" the wattage from the welder line, you could
>use this for the relay as well as the PWM. The output of the PWM does
>not really interfere with the power source it is using, please explain,
>or perhaps offer a schematic.
I often have trouble making myself clear. I guess the ability to get a
point across clearly is what makes great authors. So I'll try again.
The welder cable terminates in the "gun". The welder cable is
actually a braided copper tube, like the sheild in some types of coax.
Inside the tube is a liner that the welding wire passes through. A
shielding gas is also directed through this copper tube. A pair of
insulated wires run on the outside of the braided copper. And a
rubber insulating sheath surrounds it all. Where the welding cable
terminates inside the the gun the two insulated wires are brought out
and connect to a trigger switch in the gun. So the braided copper
carries the welding current with the welding circuit being completed
by a groung cable from the welding power supply. The two wires
connected to the trigger switch only turns on the welding current and
the drive motor which pushes the welding wire through the welding
cable. I want to add a motor to the gun to help pull soft aluminum
welding wire through the welding cable. And I am hoping to be able to
use the two wires already there to power the pull drive motor. These
wire would be disconnected from the welder and connected to the PWM
motor power source and a relay. The relay takes the place of the
trigger switch. So I will not be "stealing wattage" from the welder
power supply. The motor will have it's own power supply which will
powered by the 120 volt mains.
Thanks,
Eric
|
|
|
|
Author: ehsjrDate: 13:20 28-08-06
|
|
Eric R Snow wrote:
> Greetings All,
> I'm working on a device to pull wire for welding. The mechanical part
> is done and now I'm trying to figure out how to do the motor speed
> control. I thought that a PWM speed control would be best because the
> motor torque will be close to constant. However, there are only two
> wires available to turn on the welder, power the motor and turn the
> motor on. this is because there two wires to the wirefeed gun. These
> wires are meant to turn on the welder. My idea is to instead use these
> wires as power wires for the motor. Once power is flowing I could also
> put a relay coil in series with the motor power wires with the relay
> doing what the switch in the handle is supposed to do. I can turn on
> the PWM motor speed controller at the welder. Then the switch in the
> gun is used to complete the circuit from the PWM to the motor. But
> since the current will be pulsing I can't see how it could also be
> used to power the coil in the relay. I'm afraid that if I can get the
> relay to operate at the lowest average current being delivered to the
> motor then it will overheat when the motor is being supplied with the
> highest current. I also don't know if the PWM speed controller will
> like having the load switched on and off or if the relay coil in
> series will cause a problem.
> Any Ideas?
> Thanks,
> Eric
Piece of cake - I think. :-)
Use a current sense resistor tied to a comparator.
When the trigger is pressed, current flows in the
resistor creating a small voltage drop, which the
comparator senses and operates the relay. The
comparator circuit can be installed at the welder.
Put your PWM controller in or on the gun where you
mount the feed motor. The trigger will connect the
+12 to the PWM circuit as shown below. The comparator
diagram is below this one.
View in Courier font
+ 12 --+
|
[1R]
|
+------> To comparator Vin
|
o
\ < Trigger
o
|
+------------------------------------------+
| |
[D1] |
| |
+------+---+----------+ +-----+
| | | | | |
| | | | | |
| [1K] | ---------- [D3] [Motor]
| | | | 8 | a| |
| | +-----|4 | | |
| / | | +-----+
| 25K \<---+----|7 555 | |
| / | | | /
| | a| | 3|---[150R]---| TIP31
| [1K] [D2] | | \ e
| | | | | |
| +----+----|6 | |
| | | | | |
| | +----|2 5|----+ | Diodes: 1N4001
|+ | | | | |
[C1] [C2] ---------- [C3] |
|470 | .1uF | .01uF |
| uF | | |
Gnd ---+------+-------------------------+---------+
+ 12V ---+------+-----------------+------------+-----+
a| | | | |
[D1] | +-------------|-----+ [D2] [Relay]
| | | |\ | | a| |
| | | | \| [1meg] +-----+
Vin --------------------[1K]---|- \ | |
| | | | \ | c/
| / | |324 }---+---[100]---| NPN
|+ 5K \ | | / e\
[C1] /<--+--[10K]---|+ / |
|470 \ | /| |
|uF / |/ | |
| | | |
Gnd -----+------+-----------------+------------------+
For the comparator, adjust the pot so that the relay
actuates when the trigger is pressed.
I don't know what the contacts of the relay will carry.
You need to size the relay contacts to be able to
handle the same (or more) current & voltage than the
welder trigger switch. I also don't know if the voltage
that the welder puts in the gun will create transients that
upset the PWM.
Ed
|
|
|
|
1 |
|
|
|
|
Contact | Electronic Portal
|
|
|
