adjustable DC power supplies meant for systems integration? - Page 1
Forum section: electronics / projects

author: CopperCone
author_rank: Super Contributor
timestamp: May 14, 2018, 01:42:32 am
content: Does anyone sell like adjustable DC power supplies meant for something like DC motor control?I mean something like a Lambda or Meanwell that's fairly responsive and useful for motor control, but with a wide adjust range (i.e. something like 0-24V or 0-90V) and can accept a voltage, PWM, Current or SPI control signal?The idea is if you wanna build a system with a buncha different pumps and motors you can do the signal/control/extra protection electronics yourself but not have to design a bunch of switching regulators and deal with EMI trouble shooting so much.I am looking for some stuff with capacities of greater then 10 A.I don't really care if its DC or AC input, I guess you can get a buncha mean well or lambda fixed voltage supplies to provide the necessary DC rails for power converters.umodules are an alright solution for up to 24V I guess, up to 93% efficient and it just requires ceramic capacitors, you can parallel them too, and it has good EMI behavior, so its not a nightmare to design in I guess. But only 3A... 60$ for 3 of em + alot of capacitors. But you will probably have a hard time beating that loop area.

author: german77
author_rank: Regular Contributor
timestamp: May 15, 2018, 01:45:34 am
content: If the voltage is fixed Meanwell psu can be hacked to output a wider range of voltages, just by changing the voltage divisor. The one connected to the trimpot.I would recommend using an industrial dc motor controller. They are expensive but get the job done.

author: ikrase
author_rank: Regular Contributor
timestamp: May 15, 2018, 05:06:33 am
content: Agreed. If you're just running motors there are purpose built amplifiers, probably more optimal for that purpose.

author: CopperCone
author_rank: Super Contributor
timestamp: May 15, 2018, 02:00:46 pm
content: If its a dc motor then what does a purlose built amplifier do different? Can i get some concrete details in amplifier terminology electronics talk?I can understand ac motors requiring something fairly complicated if you work with slip and torque and everything for a vfd.. But for a dc motor what is there?

author: CopperCone
author_rank: Super Contributor
timestamp: May 15, 2018, 02:04:53 pm
content: Quote from: german77 on May 15, 2018, 01:45:34 amWhat uh downsides are there to doing this? I assume a big hard limit might be something like minimum falling edge speed that makes operation at low duty cycle funky.And how does the slew rate from these look like when used as amplifiers?What are common dangers from misuing fixed voltage dcdc converter designs for amplifier operation?I am looking for hacking rules of thumb for this.I dont think you can make it oscillate from an abrupt change right, since the control loop will have some kinda filter..

author: nfmax
author_rank: Super Contributor
timestamp: May 15, 2018, 02:11:02 pm
content: Yes. They are called "DC Motor Drives' and come in all sizes:https://uk.rs-online.com/web/c/automation-control-gear/electric-motors-motor-controllers-peripherals/dc-motor-controllers/

author: CopperCone
author_rank: Super Contributor
timestamp: May 15, 2018, 02:48:39 pm
content: What do they actually do that makes them wlrth while for a single phase dc motor that can literarly run off a battery?

author: nfmax
author_rank: Super Contributor
timestamp: May 15, 2018, 02:57:39 pm
content: Overcurrent protection, feedback speed control, acceleration profiles, active braking, ...

author: CopperCone
author_rank: Super Contributor
timestamp: May 15, 2018, 03:01:59 pm
content: I see some of the higher end models from that webpage have features like that and some basic protection but most would still require hacking to accomodate control dacs.Are those protection limit settinfs in such servoamplifiers typically analog logic hardwired to the circuit or do theyadjust software constants?I would only be interested in paying for those features if the signal levels generated by the trimpot add dampening or whatever directly to the control loop

author: Siwastaja
author_rank: Super Contributor
timestamp: May 15, 2018, 03:04:56 pm
content: Brushed DC motor controller, in essence, is a CC/CV switching converter (think about synchronous buck) with cycle-by-cycle (or otherwise fast enough) current limit. Then, it has excess parts removed: the motor replaces the output inductor and capacitor!So, if you compare the power section to a decent switch mode converter, the motor driver is simpler! Switching frequency can be lower as well.Although, the software / control part can be more complex, if it implements things like velocity feedback PID loop, accurate torque feedback, regenerative braking control, etc.While you can power some brushed DC motors "directly from battery" (some cannot be powered like this, especially most bigger ones), it's usually of little or no use due to excessive inrush torque, or poor efficiency due to magnetic saturation, and no control over torque. Specifically, a constant voltage source produces ridiculous torque (at ridiculously poor efficiency) at 0 RPM, and then the torque tapers off. Proper controller allows you to run at higher DC link voltage, allowing highger max speed (and meaningful torques at higher speeds) while actively limiting the torque at low speeds.A switching regulator adds current feedback, and if the current setpoint is tuned to the actual sane maximum current for the motor, it reduces the locked rotor current (including startup!) to some sane value, without limiting actual torque much. Extra heating is just removed.Small motors that are inefficient anyway can be usually driven directly from a battery. This is the classical brute force solution, but it doesn't work too well with larger motors. It works for car wipers, for example, because it doesn't matter if the wipers are 30% efficient; the gasoline engine is much worse, anyway.With small, inefficient, highly resistive motors, any power supply will indeed do.When dealing with large motors, a decent motor controller is most likely the way to go. I think decent solutions do not exist at prices comparable to just power supply modules (even though the motor controller power stage is simpler!); I have always rolled my own, application specific.

author: nfmax
author_rank: Super Contributor
timestamp: May 15, 2018, 03:07:24 pm
content: There are a mixture of voltage-controlled, potentiometer controlled, and digitally controlled drives on that page. Delve into the data sheets and see what they do. You know more about your application than I do!

author: CopperCone
author_rank: Super Contributor
timestamp: May 15, 2018, 03:55:26 pm
content: Do you know what the design differences in theamplifier is?What do servoamplifiers do different in comparison to a regular buck converter?Other then the control limit features I mean. Which could be put on anything.

author: german77
author_rank: Regular Contributor
timestamp: May 15, 2018, 07:27:37 pm
content: A servo amplifier is made to run motors and control them. A regular buck converter works better for relative slow changes in load, it's simply not made to be used with motors.I see a problem in here, I can't see what is your goal, problem or limitations. You asked for a adjustable PSU, but you want DC motor control, but you care about signal response.If you want to control DC motors, you have to know if you want an open loop system, or a closed loop system. With DC motors signal quality will be almost garbage as it's full of noise from the brushes, what you care is power handling . An open loop system will be simply a fixed pwm or DC signal changing the power delivered to the motor. A closed loop system will let you maintain fixed velocity or fixed positions.If you want a variable PSU for DC motors. I would recommend using a fixed voltage unregulated PSU with a pwm controller. You simply don't care on how stable it is if you are using motors, you just want power delivery.If you want a variable PSU for system integration, a buck converter for logic stuff will work fine, for power stuff you have to use a another PSU.In order to get to a solution you need to explain your goal and conditions/limits you are going to have. Otherwise we can keep throwing information that will not give you a satisfactory solution.

author: CopperCone
author_rank: Super Contributor
timestamp: May 15, 2018, 07:53:58 pm
content: What specifically is the difference in the regulation of a buck converter meant for fixed voltage operation for say logic vs one that is controlling a motor? Do you have some example circuits that can illustrate?Feedback has to be speed to be useful, any other metric will vary with temperature too much.I mean, I have meanwell power supplies already, on hand, at the correct voltage, it would be effortless to remove a crappy trimpot and connect a DAC or even crude dampened op-amp controller to work with a analog tach signal to maintain a setpoint..Not sure what my requirmeent is gonna be due to not knowing about the motor voltage or the mechanical load.I am just wondering what specifically makes traditional buck supplies ill suited for the job.you said" A regular buck converter works better for relative slow changes in load, it's simply not made to be used with motors."But what will happen?I understand that a motor will turn stuff a engineer considers to be garbage energy into power, but what are the specific downsides other then increased power supply circuit complexity and component count?Can you estimate based on the design of the supply when the control loop time constant will end up causing problems?For instance, we know that you can use a DAC as a modulator by varying the reference voltage, but they will eventually distort, and you get a lower "dac ENOB' (and some dacs are built for this often called mdacs).. I mean the question in the same context here.I ask because these guys can often be picked up cheap, and there are ALOT of applications that you can just deal with a completely ghetto ass response time and hunting while still maintaining good results.. like balls mills, chemistry applications for pumps, rotary platforms, etc I am not trying to make a terminator here,you can skim alot of the cost by doing the mechanical labor yourself, but if you spend 8 hours making the enclosure, painting, bearings, etc, then you add a 200 euro controller plus power supply you start to feel like you probobly shoulda just bought the chinese onemy hunch is, a mean well power supply, might be a pretty damn good motor controller so long your not doing precision robotics but I would still like opinions before I go taking mine apart.ANd quite frankly, I'd feel more confident in the reliability of a meanwell or lamdba power supply connected to some decent home made electronics then some chinese drive.I think a motor of decent size might act as an averaging device too, so even if the control loop goes a bit batty it might not be very mechanically noticeable due to the motors momentum.

author: german77
author_rank: Regular Contributor
timestamp: May 16, 2018, 04:20:33 pm
content: Ok, now I understand you better. The difference between a buck and a motor controller is were you measure, a buck will measure voltage, and a motor controller will measure current. Also a motor controller tends to be over powered in order to handle any anomaly.If you connect a buck converter to a motor it will behave in this way, when you connect the motor the voltage will drop down then it will overshoot, if you have any delicate electronics they will easily will fry when the overshoot happens. The magnitude depends on the motor and the response time of the buck converter.As you, I prefer to make the electronics rather than using Chinese. They simply fail without warning. I usually make my own H bridges to control motors they all depend on the current I want to drive them. For small motors like 100mA I use an IC like L293D, for medium motors like 2A I use power transistor like TIP31/TIP32 in a H Bridge, for higher currents I use Mosfets, and for very high currents I use dedicated IC to power the mosfets. I make sure there is always some kind of isolation between the controller and the H bridge, and put protection and heat dissipation every were.For speed control I usually use an optic transistor with an encoder wheel attached to the shaft of the motor. Then simply count the on/off frequency with the microcontroller and adjust the pwm respectively. If the motor is to fast I decrease the resolution or use a frequency to analog converter and an ADC.If you have already Meanwell PSU at the right voltage use them as they are, don't modify them, don't worry about their voltage stability they will handle it. Instead use the H bridge to control the motor. I like to use above 20KHz frequencies in the pwm signal just to eliminate the noise. But frequencies like 400Hz will work just fine, the inertia of the motor will always smooth their movement even for very small ones.This whole setup usually cost less than 28$ including the microcontroller. The real problem comes when the voltage above 50v, for that I don't break my head, just use the industrial motor controller(not Chinese) as it will save me more time and money in the long run.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 16, 2018, 05:23:57 pm
content: Quote from: CopperCone on May 15, 2018, 07:53:58 pmAnother typical feedback is torque. Which is relatively linear with motor winding current - not much dependent on the temperature. So in many cases, actual torque sensors aren't needed. (Current-torque curve starts to get nonlinear outside the intended (high-efficiency) operating current, when the iron starts to saturate, giving diminishing and finally almost non-zero increased magnetic force for the current increase; resistive losses in windings, brushes, cables etc. just go up).Torque control is super useful, not only for protection, but think about electric vehicles driven by an "electric gas pedal" - that's basically a torque control. Or generating softer ramps, without needing any kind of ramp logic. Analogous to how a current-limited power supply soft-starts its output capacitors without needing a soft start timer.QuoteIf they can supply the current the motor actually takes (which can be ten times the nameplate value!), and if you don't need to limit the torque generated at startup or otherwise, there is no problem.Many PSUs go to hickup or latched fault mode with overcurrent; with these, you need to rate it for the maximum stall current. For motors, constant-current (available from PSUs designed to charge batteries or drive LEDs, or to be generic lab CC-CV supplies) would be more useful, as it would give nice (possibly adjustable) torque limit, instead of you needing to oversize the power supply current rating to avoid the fault mode.QuoteGiven that the power supply can supply the maximum current (rotor stall current), the motor will "kick" with a huge torque peak when connected, but work just fine. Torque delivered will diminish as the RPM goes up. So basically, too much torque at low RPM, too little at high RPM - this curve is often unwanted, but many times acceptable.With small or inefficient motors, especially if the mechanical load is fairly predictable and not too heavy, and the motor is running rather continuously - ie., spin up, do the work around motor nameplate RPM, spin down -, this is usually not an issue.With a lab CC-CV supply, there is no issue. Maybe except that most cannot sink current, which could happen if the motor physically turns at higher RPM than the corresponding open circuit voltage set at the supply. All properly designed power supplies protect from current back flow in this case, unless you exceed maximum ratings.QuoteProbably a total non-issue. Off the shelf power supplies are designed to give either constant voltage, constant current, or both. Feedback loops for both are most likely fast enough, and a motor shouldn't be that difficult. Motors have considerable inductance which guarantees that the current through them doesn't change quickly.

author: CopperCone
author_rank: Super Contributor
timestamp: May 17, 2018, 04:47:41 pm
content: I see. I have never designed an h bridge for an inductive load before, only heaters. I am hoping that it is not too difficult for an dc motor.I would typically be very worried about trying to get a feedback signal from the electricity going into the motor.Do you need any kind of signal conditioning to work with the behavior of the commutating etc? I imagine the arc has content in the scary megahurtz range and can cause all sorts of issues. I was worried that you might need some kind of blanking/discriminator/crude digital filter to prevent weird stuff like saturation of the current measurement amplifier..I certainly imagine that dealing with an opto or well directed (i.e. bifilar/figure 8 wound and sheilded magnetic sense coil) sense method would be much cleaner.Not sure if having a high torque at startup is safe, or good for the motor and gears particularly if stuff needs to warm up to ensure proper lubricant consistancy and what not..Sounds like you would need some sort of gimic like a current limiting resistor that is switched out of the circuit to ensure good startup behavior.All this and brushes and arcing in a lab enviroment makes me thi k i should just figure out how to make a multiphase drive for driving ac motors. I am also guessing electrical feedback is alot nicer on them.Perhaps this merits a seperate thread but how do the noise profiles and power levels look like for dc motors and phase driven ones? I cant imagine arcing is better., then again it is mostly contained by the tank formed by the motor in its enclosure and the filter cap thatis hopefully put againt the motor rails and shielded.

author: german77
author_rank: Regular Contributor
timestamp: May 17, 2018, 06:45:19 pm
content: Sparks generated on DC motors are nothing to worry about, they always happen. If you stay on the specs of the motor it will not fail, they actually can take much more than they are rated. I have seen 5v motors driven with 40v and survive. The driver it's the thing that fails if not designed properly.If you still are worried about the gears, you just program a pwm ramp that will allow a smooth movement. Signal conditioning is needed, like a different supply for the motors, reverse protection diodes and optocouplers. Take a look on the circuit diagram. It has all the protection needed.The reason to use two supply's is to eliminate noise in the logic part that way you don't need any kind of filtering to eliminate them, you just let them be. If for some reason a dual supply it's not posible, using brushless motors will be the way to go as they don't generate high frequency noise.My recommendation is that you are thinking to much, buy two or three different small 5v-12v motor, build a simple h-bridge and play with it. There are lot's of examples in the web for H-bridges that will explain how they work, what to do, what not and design them. If you have an oscilloscope you can see yourself the performance of the H-bridge. Driving a motor with an H-bridge should be as difficult as powering a led.Test them with different loads, pwm, even stall them and see what gets hot and how much torque it has, how do they feel. Get comfortable with the functionality and reliability of the H-bridge.After you are comfortable with the H-bridge try to implement the speed control feedback, there is also a lot of content in the web already.