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What size power supply for motor.

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  • What size power supply for motor.

    I've got a motor from a 2001 Jeep Cherokee window and am wondering about

    using it to power some kind of project. It is very geared down for slow turning

    and looked like it could be useful. I tried a power supply with only 1 amp of current

    and it wouldn't turn. How many amps should I have? Any help out there?
    Vitَria, Brazil

  • #2
    Is that a permanent magnet motor, or a wound field motor? The first type would probably like about 6-10 amps for good power, and the second type can require up to 20 amps. These are similar to windshield wiper motors, but often power window motors are rated for a very low duty cycle, needing lots of current for a short time.

    Chances are it's a permanent magnet motor- I don't know that there are any wound field types still being used, but who knows-

    The other problem you could have is if your power supply is a 'smart' battery charger. Those usually won't give out any voltage unless there's at least 10 volts coming in on the output wires. That's to prevent hooking up a shorted battery and damaging the power supply.

    Any of the little flat-sided motors that I've had anything to do with in the last 10 years have been able to run on 1/2 amp or so with no load- 1 amp or more to make it turn over seems high, but as I suggested it could be a motor designed for very intermittent use such as a window motor. Not all window motors need that much juice to turn over.
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

    Comment


    • #3
      If the supply is only capable of 1amp then the voltage may have collapsed, the motor only draws the current needed, dependent on load.
      Feed it from your automotive battery for a test.
      If it is a window motor they are fairly beefy and generally in the auto are fitted with a automatic breaker that comes in to play at the end of the window stroke as they draw a hefty current when stalled.
      Max.

      Comment


      • #4
        Well, without any load at all, it would turn with the 1 amp supply. But

        it was not able to turn the reduction gear it is hooked to. I'm guessing it needs more amps.

        The label on it says "12 volts" and then there is the number 6 but nothing saying that this is amps.
        Vitَria, Brazil

        Comment


        • #5
          It should have at least tried to turn even if very slow. Try on a car batter to see if its even good. These motors will draw pretty heavy on amp and the gear drive will not cause it to draw anymore, at least no amount important. Loaded I would say it could draw an easy 10 amp and more close to 20amps would be more like it.


          The thing is the motor will only draw what it needs, so unloaded should be very low. Your power supply may be kicking in some kind of protection circuit when you try it, or the motor may be bad.


          Jess

          Comment


          • #6
            or the gearbox may have a problem.......

            But I'd expect it to draw more than an amp.

            The wound field ones may have a protector inside to open up if it gets too hot..... The one I took apart for someone had the wires cooked so thoroughly they were black, and that was after the varnish burned off.

            It had a thermal protector.
            1601

            Keep eye on ball.
            Hashim Khan

            Comment


            • #7
              Most window motors are wired with a 10-25A fuse or breaker. It depends on the application and motor. I would guess a small motor would draw about 2-3A unloaded just from the drag of the gearbox. And as already mentioned, they aren't continuous duty like a wiper motor. The window motors heat up pretty fast and the reason they're usually thermally protected.

              Comment


              • #8
                On my 2001 Olds, the four window modules are fed from a 30a breaker and each motor module has an electronic breaker due to the stall that occurs on window extreme up or down travel.
                Never seen a wound field motor on an automobile (except the starter), not recent vintage anyway.
                Max.

                Comment


                • #9
                  I doubt that the motor pulls much more than one amp with no load .. I'm betting 5 or 6 under
                  load.

                  But as Max and the others have said .. current draw is commonly misunderstood. The motor or
                  load requires a certain amount of amperage. If the power supply can not supply that .. it will
                  blow a fuse .. or over heat the supply. Conversely .. If I had a GIANT generator/supply .. capable
                  of supplying millions of amps of current .. and I hooked it up to a tiny little itty bitty light bulb .. the
                  light bulb would be totally safe .. and just ... light. Current is sucked .. not .. pushed.

                  but ...

                  The little geared motors really do get your inventor juices flowing though .. huh ?
                  John Titor, when are you.

                  Comment


                  • #10
                    I got a couple of window motors from a buick riviera at one point- they were wound field, and needed lots of amps just to turn. They got hot very quickly.

                    Lately, I picked up a couple similar motors- not sure but I think they are power seat motors. With no load they will run with about 300 ma. They have a worm wheel with a square hole that goes right through from side to side of the housing. I think these would make good retrofits for operating lead screws. I would add a final drive ratio of about 3-1, and incorporate a clutch within that so you can easily go manual when you want to. A toothed belt drive would be good here.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                    Comment


                    • #11
                      It seems like the consensus is that 20 amps would work.

                      Any sources for a cheap source for such an animal?
                      Vitَria, Brazil

                      Comment


                      • #12
                        You need around 250Va supply, a simple solution would be a 120/240 to 12-18v control transformer, followed by a 50amp bridge rectifier.
                        You could go to a 24v secondary if you have some kind of controller between supply and motor.
                        Max.

                        Comment


                        • #13
                          It seems like the consensus is that 20 amps would work.

                          Any sources for a cheap source for such an animal?
                          Vitَria, Brazil

                          Comment


                          • #14
                            One of the challenges in getting several amps of dc current at around 12 volts is in finding a suitable transformer. The most common device with the capability to produce several amps is a battery charger. But often you can't use the circuitry because they are 'smart'. But if you take the voltage straight from the secondary winding you can usually get 15-20 volts dc. You may be able to use the existing rectifiers, and you would probably have to add a capacitor, but you are ahead of the game in the sense that the transformer already has an enclosure, power cord, switch, etc. You could buy a suitable transformer, but then you'd have to add all that, and wire it up correctly as well.

                            I don't think you'll need 20 amps- a 10 amp charger would most likely be all you need. Depending on how you'll use the motors, you may be fine also with the higher voltage. That voltage will drop a fair amount at a draw of 10 amps, so it's unlikely that any motors will become damaged. Voltage rating on dc motors is usually specified for some particular rpm- it's not a maximum rating for the motor by any means. A 12v motor in a car is often getting 14 volts anyway- another 2 or 3 volts isn't going to make much difference- the motor will run a certain percentage faster on the higher voltage. Unless you load it down in a continuously running application, nothing bad will happen.

                            At any rate, if you are needing to vary the rpm you would need either an adjustable regulator (switching or analog) or a means of varying the raw output voltage. Any transformer based power supply would need this addition, unless it's already an adjustable power supply.

                            One of my bigger concerns with power supplies is the heat they generate. Many will run fairly cool with no load or a light load, but some will get hotter and hotter the longer they are left running. Some battery chargers would be like this, many in fact, but some will run fairly cool when not loaded down to any extent. First thing I do if I've selected a transformer for some application is to hook up the primary and let it run for awhile. If it gets more than warm after a couple hours of running, I tend to not use it.

                            Where else can I go with all this- Ok, technically a switching power supply uses a transformer, but so far I've been talking about the brute force approach, which is an iron transformer of about 5-15 lbs, and which is what almost every battery charger would have. This is the most basic thing which you could modify to make it do what you want. You could go the switching power supply route instead, and then you might start to look at computer power supplies. Often these days, the 12v output is rated at several amps, and they are regulated to 12v. Some will give you 12 amps, 16 amps, or more. You would have to do a simple mod or two to make the power supply come alive and regulate properly, but these things are not difficult to do. Basically you either ground the appropriate lead, or hang it onto one of the voltages to 'power up'. The other thing that's often needed is some minimum load on one of the voltages. This is probably going to be your simplest and cheapest way to get a regulated 12v output.
                            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                            Comment


                            • #15
                              Originally posted by mikeamick View Post
                              I doubt that the motor pulls much more than one amp with no load .. I'm betting 5 or 6 under
                              load.

                              But as Max and the others have said .. current draw is commonly misunderstood. The motor or
                              load requires a certain amount of amperage. If the power supply can not supply that .. it will
                              blow a fuse .. or over heat the supply. Conversely .. If I had a GIANT generator/supply .. capable
                              of supplying millions of amps of current .. and I hooked it up to a tiny little itty bitty light bulb .. the
                              light bulb would be totally safe .. and just ... light. Current is sucked .. not .. pushed.

                              but ...

                              The little geared motors really do get your inventor juices flowing though .. huh ?

                              Well, yeah, as long as your Giant power supply was the right voltage.....

                              Comment

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