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Power supply for small 12v motors

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  • #16
    That's true. But the OP self identified as being not familiar with anything electrical. It may not be perfect but it at least would not require him to putz around with line voltages.

    By the look of his later reply though he's comfortable enough to work on using an old computer supply as a power source and hooking up the motor controller. So all is well.
    Chilliwack BC, Canada

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    • #17
      You can get a 12V 3A external laptop computer power supply for about $6, and 6A for about $12:

      https://www.mpja.com/12-Volt-Adapter.../products/567/

      There are many 12V switching supplies available on eBay. I bought a 30 amp supply for about $16 including shipping:

      https://www.ebay.com/itm/Universal-5...t/312597839731

      If you have a car boost starter, you can use it as a 12 VDC source. Many of them have an accessory outlet you can plug into. For any of these, you should use a properly rated fuse or circuit breaker.

      The adjustable bench supply is ideal for testing small motors, as they are also current regulated and have displays of voltage and current. But for actual use in a project, a battery or switching supply with a PWM motor controller is best.

      http://pauleschoen.com/pix/PM08_P76_P54.png
      Paul , P S Technology, Inc. and MrTibbs
      USA Maryland 21030

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      • #18
        Computer power supplies often require a 'turn on' lead to be connected- you will have to know this for whatever power supply you might try to use.

        Most 'small' dc motors won't draw more than about 3 amps- something like a windshield wiper motor might want about 10 amps to start up, sometimes a bit more. Some switching power supplies (like a computer power supply) will limit the current at some level, but will continue to operate- others will enter a shutdown mode, which will restart when the load is removed. Since motors draw the maximum current at startup, you can find that some supplies won't be usable. You'll have the best chance with one that has a higher current rating, say 20 amps. If you use a pwm controller, they often have an input capacitor, which acts as a short until the input voltage charges it up. This is a headache for some power supplies. But those controllers are great for varying the speed of motors- some have some form of speed regulation built into the circuit, others simply output a variable pulse width and that's it. Even the simple ones are quite workable, especially with a permanent magnet motor which self-regulates due to back emf.

        Some of those circuits are called speed controls, but have no means of regulating a motors rpm. Still, they can often control the motor satisfactorily in many circumstances. I have one of those cheap Banggood pwm controllers, and it works fine.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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        • #19
          Often times I find that the best power supply is the old fashioned 'brute force' transformer, rectifier, filter approach. The older battery chargers are made this way, and often have regulating circuitry which would get in the way of it being used as a power supply. If you can get rid of that circuitry and use the rectified voltage straight from the filter cap, you can have something which isn't going to shut down on you as you draw a starting surge current. But usually the voltage is up around 20 volts or so at no load condition, so now any kind of voltage control is going to need a regulator of some sort. This is my favored type of power supply- a transformer, which might weigh 5 to 20 lbs on its own, a bridge rectifer, and as large of a filter capacitor as I can find in my collection. Then I will add a linear regulation circuit which will have voltage control, plus a two step current regulation system. One step is simple current regulation where current will continue to flow- even if you short the output- and the other is where the current flow will stop when the current flow reaches the adjustable point. This is really handy if you short the output leads- the power supply doesn't sit there cooking itself, or the circuit it's powering. It shuts off, and a light tells you it's in cutoff mode.

          And talking about power supplies- a really handy feature is an output which is current limited at 10 milliamps. You can quickly test any led without having to worry about a certain value of resistor in series. This output is also great for checking zener diodes since they are usually rated at an operating current in about that range.

          What else are you going to use the power supply for? Checking car stereos, perhaps, maybe tail lights and headlights? It needs to be good for 10 amps if you're going to check a headlight.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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          • #20
            I found that some of the generic switching supplies dont like to drive motors. The startup current triggers a fold-back function that results in the motor running in short bursts with about a 1 second period.

            Ed
            For just a little more, you can do it yourself!

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            • #21
              I didn't have to do anything special with the power supply but find the 12v feeds. I had found a you tube vidio that the person set up a motor and just did as he suggested and it has been working fine. If you want I can try to find the vidio for you.
              John From Slinger, Wisconsin

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              • #22
                OK so I did look up the vidio is at https:youtu.be/xboLavMBVxs and he will explane how and what to do to set it up. As I didn't know how to post the link you will have to copy and post in a new tap to get it to run Sorry. And like I said I have been using this setup for awhile with a window reg. motor and a ring light with no problems.
                Last edited by Old School; 11-21-2020, 10:04 PM.
                John From Slinger, Wisconsin

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                • #23
                  Originally posted by ed_h View Post
                  I found that some of the generic switching supplies dont like to drive motors. The startup current triggers a fold-back function that results in the motor running in short bursts with about a 1 second period.

                  Ed
                  For those, a smallish resistor that in combination with the motor does NOT trip the protection would work. Start up with resistor, cut it out (short it with a switch) when the motor has come up to the slower speed with the resistor, which should be just a second or two.
                  1601 2137 5683 1002 1437

                  Keep eye on ball.
                  Hashim Khan

                  If you look closely at a digital signal, you find out it is really analog......

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                  • #24
                    Better link. ... Here




                    John Titor, when are you.

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                    • #25
                      A cheap 12 volt supply, like a cheap 12 volt battery charger! Just try one that will provide the required current and ignore that it might be 1-2 volts more than needed.

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                      • #26
                        In case I was not clear, I was not recommending a switching power supply. I was recommending a motor control that uses switching as opposed to one which just varies the DC Voltage like a pot would. Lower Voltage to the motor can result in very little torque at low speeds. Most uses for a motor controller do not want that. Motor speed controls that use a switching type control (pulse width modulation if you want fancy words) will still send the full Voltage to the motor and preserve the torque a lot better at low speeds. This isn't perfect, but it is a lot better than a variable Voltage control.

                        As for the type of power supply used, most of the inexpensive supplies that are available are of this type. One reason for this is due to the "green" movement: switching supplies are more efficient. They waste less energy than conventional power supply designs that use linear components. Also if a transformer is required, then a switching supply can use a higher frequency which allows smaller transformers to handle the same power. Less copper and steel equals lower cost. But I was not saying he should use a switching supply. He probably should, but I just was not saying it. And if he has a motor controller between the switching supply and the motor, I suspect he will have no trouble.

                        If you are trying to run a motor directly from a switching supply and have problems, you were probably trying to run the motor on a supply that was too small. If your running current is, say 2 Amps and you just have a 2 Amp supply, then it can not supply the surge current that the motor needs to start up. For a motor that needs 2 Amps while running, you probably need a 4 or 5 Amp supply or some large filter capacitors on the output of the supply to provide that surge current.



                        Originally posted by ed_h View Post
                        I found that some of the generic switching supplies dont like to drive motors. The startup current triggers a fold-back function that results in the motor running in short bursts with about a 1 second period.

                        Ed
                        Paul A.
                        SE Texas

                        Make it fit.
                        You can't win and there IS a penalty for trying!

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                        • #27
                          my car window motor is rated at 40w and has a no load current of 1.5 amps. theres plenty of 5 amp supplies on ebay for around $7.

                          https://www.ebay.com/itm/12V-40V-10A...oAAOSwzDFb5P-D

                          depending on what im doing i find the handiest supply often is a small battery. i have taken out the lead battery from a tire compressor that i havent used for ages and its still good. good idea to have it fused, though.

                          interestingly i dont see a single transformer on ebay.
                          Last edited by dian; 11-22-2020, 07:13 AM.

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                          • #28
                            There was a saying years ago about people in the electronics field who 'enjoy enmeshing themselves in yards and yards of copper wire'- referring to winding your own transformers, etc. I guess that's me- I can only guess at how many transformers I've had apart and rewound to my own specs. It's time-consuming, but a bigger problem now is finding a donor transformer, and one which can be taken apart. Copper wire is becoming harder to source locally as well. I'm not suggesting anyone go this route these days.

                            What I have done in the past is wind a transformer to give a no-load output voltage (after rectifier and filter) of about 13.5 volts. No regulation, just accept a voltage drop as significant current is being drawn. The bigger the transformer, the less the voltage drop. Simple system, almost bullet proof. For something similar, look for an old charger from a motorhome- one that runs the 12 volt system from ac when that's available, and keeps the battery up too. That will be something a bit more 'skookum' than a typical battery charger that you might find that is not so electronic that it's unusable as a power supply. Pretty much all battery chargers now want to test the state of the battery before they will power up- to make a power supply out of one of those requires butchering it, and some electronic knowledge.

                            Something which might work for you is to find an old yard lighting system, one which has you spreading a number of 12 volt bulbs around and wiring them to the power pack. I've had a couple of those- they're pretty straightforward, and can put out about 3 amps or so.
                            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                            • #29
                              I'd like to thank everyone for their responses. When I get to the USA next time (probably in January) I'll try to order some of these items that were recommended.
                              VitŮŽria, Brazil

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