[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

[NC Cams]

I believe that the 2940 app note says that the capacitance can be increased with little concern which is something we did to deal with voltage fluctions that we learned can be endemic to some circuits. They happen and stuff resets for no reason. With extra capacitance, they seem to remain immune to momentary drop out issues.

When we used the 2940, we did NOT use tantalums. We used electrolytics and never once had an oscillation problem. However, the one up stream of the regulator was ALWAYS bigger than the one downstream.

In our most sensitive circuit, we ran a CMOS based pwm controller IC and sample and hold chips off of a car battery. The car battery was still used to power/start the auto even though the battery charger was charging batteries for R/C cars at the same time. You can't believe the ugly stuff that the voltage spikes from the starter and althernatory were causing during/immediately after starting the car.

We we ran into all the issues that any automotive appication ran into - these were clearly outlined in the 2940 app note as well - we stumble across and started using the 2940. The extra cost of the LDO 2940 saved us way more in fried circuits that we had from the diode protected 7805 that the EE who designed the circuit had initially spec'd out - and he knew that the thing was going to be used in an automotive environment.

Sadly, his traditional "diode protection of the 7805" scheme didn't protect squatt when/if the charger got hooked up backwards which it did far too often. THe 2940 flat stopped the problems that dumb outs like this caused.

The LDO feature of the 2940 isn't a pre-requisite but when you are shooting for the use of an LM2940T-10 and the car battery starts dipping to 12vdc (does so while cranking), the LDO comes in real handy.

Since then, I've replaced a lot of 7805's with the 2940 and have not had any of the problems that you illude to. Then again, I"m an ME and ascribe to the hummingbird logic of electronics.

Namely, hummingbirds can't fly and I don't know that 2940's shouldn't be used where I use them - but I do and I've never had one not work. Regarding capacitance, I use extra amounts as they served us well with our charger circuit and in many others since them.

[pastera]

If your "EE" put in a "traditional" diode in parallel with the input- you're right it would protect the circuit for the few milliseconds it would take to melt! I have seen this method for battery operated devices and all it does is short the battery out.

As far as oscillations, have you hooked your circuit up to a good spectrum analyser? They may not bother you because they are generally low amplitude but will kill a sensitive receiver. I have a few pieces of equipement that I had to go into the power sections because of issues like this, out in the market barely working well enough to sell. Reverse the design to find they simply cut and paste from datasheets they never read!

By the hummingbird logic, if the smoke stays in it's good enough!

Aaron

BTW: Do you have any recommendations for a regrind or billet cam on a Ford 3.8L supercharged? SC heads (mild short radius work), 15PSI, automatic and primarily street driven.

[NC Cams]

When we did the experimentation with the 2940, we did look at the DC buss with an oscilloscope - that's how we found that the 7805's were dropping out. We also found other goofy stuff from solenoids firing on circuits that were also being fed by the car battery that was feeding the nicad charger that used the 2940.

BTW, the 2940 was something we stumbled across as a resulf of reverse engineeriing some automobile focused microprocessor circuits. Seems that car circuits, due to noise, environmentals and external dumbouts from tow truck drivers need to be as robust a circuit as some aircraft/aerospace stuff. Besides, the automotive durability requirements are not "mission critical" but will pizz you off if the car quits in the middle of nowhere.

Even without a potential for LDO, the 2940 seems to provide exception protection for bizarre/spurious voltage excurusions that crop up/into circuits. I know of an EFI circuit that was 7805 fed and would do all sorts of wierd resets, and other stuff that shouldn't have happened as the 5vdc buss was supposedly "solid". THey bypassed the 7605 with diodes and also had zener protection upstream of he 7805. Even so, dropouts, problems resets and general havoc mysteriously happened for "no apparent reason".

Against the wishes of the EE who designed the circuit, I had one troublesome unit refitted with 2940's and had the diodes/zeners and other "traditional protection stuff" pulled. WE did do a pre-filter of the 12v to the 2940 with a diode followed by a 500 uf filter cap followed by 2940 with a 250 uf cap on the 5v buss. Result: all wierd problems SOLVED.

The diode prefilter actually served as a charge pump and the 12.5-`13.5 vdc recorded at the battery was now 15 after the diode at the 500 uf cap that fed the 2940. The 5V buss downsteam of the 2940 was FLAT as if it was coming from a battery as opposed to an alternator fed circuit.

The circuit would run even when cranking voltage pulling the system down to 7.5- it wouldn't run at that cranking voltage with the 7805.

Also, the spurious drop outs (finallly traced to a suspect alternator diode bridge that wasn't providing pure DC), totally eliminated. We suspect that the diode in concert with the caps and 2940 provided a "cushion" and the 2940 then provided the voltage spike and reverse polarity protection that 7805's can't won't do and zener's won't survive long under.

Besidse, if Ford, GM and Chrysler found the 2940 to be preferrable to a 7805 for their computers and stereos, who am I to disagree.

Yes, on a sensitive reciever citcuit, hummingbird and shade tree mechanic electronics may not suffice. But for hobby, automotive and a lot of industrial circuits, the protection that comes for free in the 2940 package (and its bretheran) are hard to pass up/ignore.

[pastera]

When you start talking about zeners in a reverse protection, I see where you get your low opinion of EE's.

If you want a clean bus during a crank, you definately won't get there with a 7805. The 7805 is good for a quick and dirty 5 volt bus and not much more as technology has passed it years ago.

With 500u on the output, you're not going to have a whole lot of ESR to worry about - the only issue would be over temp but if you don't have a problem it isn't a problem. Nothing like hitting it with a sledge hammer - 500u that's a lot of capacitance - I would love to have that kind of space to spare!

Aaron

[NC Cams]

It was actually:

battery+diode+500uf+2940+250uf

We ended up with 250 and 100 in place of 500 & 125. Didn't use tants' but rather 'lytics as the tants' were too pricey.

The charger became a technological success but a businss failure/nightmare. After a bit of time, and ventures into ano the business, I got into CNC. Interestingly, some of the same issues that we faced with our nicad charger (well regulated sources of 12vdc, 9vdc, 5vdc) were found in a lot of the industrial circuits that we ran across. Where have we fixed THAT before???

Added to the fact that you're using PWM and PMDC motors and even servo's and or solendoids (steppers are BIG solenoids in my estimation), it should not be surprising that/if/when all sorts of noise mysteriously gets dumped onto EVERYTHING.

SO, we simply figured that 'severe service' auto IC's won't know the difference if they are rolling down the highway or sitting in a hot CNC cabinet - same thing as an underhood environment and less chances of a front end collision.

To the DIY'ers out there who use/need TTR's (three terminal regulators), you can do much worse than the LM2940 or LM2931 and/or other derivative automotive grade TTR's. After seeing what a 2940 et al do as compared to 7805's, I wouldn't used '05's if they were given to me for free....

In fact, they may solve/prevent some lurking problems/gremlins that you don't know you have or haven't run into yet.

[pastera]

I took a look at the 2940 - does pretty well.
To tell the truth, I don't use 78xx regulators for anything but very gross regulation - when I need a quiet supply, they are still too noisy.

I mostly use switchers because of heat and discrete regulators when absolutely needed. That said, with a drawer full of 78xx's, I'm not against pulling one out for a quick and dirty prototype.

You'll do well to stay away from tants anytime you have something that will charge them very fast, they don't like that much and will often reward you with a nice flamethrower of molten sh_t out the side.

Aaron