24vdc motor control

[blksmith]

I have a Baldor 24vdc motor rated at 4.4 amps and I am looking for a power supply/motor control that I can build. Is there anyone here that has a schematic and parts list or know of a wep page I can find such a thing?

[Al_The_Man]

It depends on what control you are looking for, i.e. any feedback used?
Servo or just speed controller, or for a spindle etc.
For the simple control, there are many app. notes by National and others.
Al.

[blksmith]

just a simple speed control, I want to use this for a weld positioner.

[Al_The_Man]

If the motor has no tach or feedback, you may get away with something like the National LM12 80w amplifier IC up to 30vdc 10amps.
Look in the national applications also look at the LM12 used in the LM628 app sheet, they show a stand-alone configuration of the LM12 with a couple of diodes, resistors and caps.
On the national site also look at app. AN446
You should also find some on the Motorola site (now Freescale).
Practically all of the Chip manufacturers offer motor control of some kind.
Al.

[NC Cams]

2 stages of a LM324 op amp (configured as a triangular wave wave generator running at 2-3 khz) feeding into a 3rd stage of same to act as a "comparator/driver" of a mosfet will give you a PWM'd speed control.

The 4th stage of this quad amp can be used as a buffer to take a simple potentioment referenced "throttle" that is fed to the "driver" mentioned above.

One cheap IC and a fet and some resistors and capacitors is all that's needed. Developed mine to replace a rheostat based model train controller and it gave very good modulation and efficiency.

Depending on your power source for the LM324, you could use either a IRFZ40 fet (+/-15 for better low speed drive modulation as it is easier to get zero volts to the gate) or an IRLZ44 for a simple 12vdc power source (removing ALL voltage to the gate can be a bit more troublesome - this can cause the fet to run a bit warmer when "off" as it is trying to semiconduct).

If you go 12vdc/IRLZ44, be sure to protect the fet gate with a 10 volt zener.

[blksmith]

Ok that all sounds good now if I could get a schematic I would be in buisiness. I can read a schematic and make a pc board I was just not sure what components to use. can someone draw a rough sketch of how the components connect?

[pastera]

http://www.maxim-ic.com/appnotes.cfm?an_pk=3201

Hook the output to an IR3311, the input to a pot and you're done - well almost

EDIT: looks like IR is dropping the IR3311, use a BTS432 instead

Aaron

[blksmith]

I thank you all for your input, this should get me running

[NC Cams]

If you run Pastera's circuit off of a 9v battery, you could drive an IRLZ44 fet directly from the PWM output of the Maxim circuit. Properly heat sunk, the fet will easily provide 10 amps or more of current.

Just make sure the ground of the control circuit is the same as the ground of the 24vdc power source for the motor and it will run just fine. If you want to run the control off of the 24v power source, regulate it down to 9-10vdc with an LM2940T9 or T10 regulator circuit.

HOwever, tie the fet gate to ground with a 10K resistor to make sure it turns off with dutycycle PWM signals.

[pastera]

The reason I suggested the BTS432 is they are pretty much smoke proof as long as you don't hook them up backwards (OK they'll sometimes survive that too, my tech checked that one out for me ONCE!).
At a max of 24V input, any three terminal regulator would work (7805). Also, if you want to drive a fet directly, use a high output current amp like a TLV4112 for U1C

Aaron

[NC Cams]

BTW: LM2940's offer much inproved performance and durability over 7805's, especially with respect to over volatge, reverse polarity protection and voltage spike protection from solenoid 'dumps'.

The auto industry learned its lesssons re: use of the 7805 and initiated development of the LM2940 when transistor and microprocessor circuits became the rule as opposed to the exception in automotive use.

This IC is a godsend for industrial circuits that may be subjected to solenoid dumps and/or possible reversed polarity insertion and/or other severe service operating environmentals. Check it out....

Hobbyists would be well served by using LM2940's in their circuits as opposed to generic 7805's.

NOTE: if you use 2940's, do NOT BYPASS THEM WITH DIODES AS YOU WOULD A 7805 FOR REVERSE POLARITY PROTECTION. By doing the diode bypass, you effectively negate the other benefits offered by the 2940.

[pastera]

The LM2940 is a LDO regulator - not something to be used if you don't need it. The addition of the low drop out voltage comes with some very strict rules for output capacitance to maintian loop stability. Too much or too little ESR in the output capacitance can send them into oscillation. They also call out tantalum caps, expensive and they fail short (BANG!!!). Do you know why they make fused Tants?

A good old 7805 will be happy with a hundred nanofarads of pretty much whatever capacitance you throw at them - very hobby friendly.

The reverse polarity is a very good feature but can be added with a simple series diode if you can stand the extra drop out voltage.

Aaron