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I have a tiny DC motor directly connected to this power supply. The motor starts just fine when the supply is set to 4.5V. I can then change the voltage to 6V and it continues to run just fine. However, if I try to start the motor at 6V it only runs in pulses (for about 100 milliseconds once every second). Also, if the motor is running at 6V and I apply significant load, it begins pulsing until I lower the voltage. I'm guessing both cases are explained by the larger current required to start the motor at a higher voltage, and to keep it running under load.

I have a few questions:

  1. What is actually happening to cause the pulses? Is my power supply overloading then "resetting" once every second?
  2. Is there something very simple I can add into the circuit to allow it to start at higher voltages (a momentary current spike)?
  3. Is there something very simple I can add into the circuit, perhaps a better power supply, to allow it to run under sustained load (a constant current increase)?
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  • \$\begingroup\$ I'm just wondering how you measured that "100ms once every second". What you say is very strange to me, but I have this wild guess: maybe your cables are not well secured and if you start it too fast the torque moves the motor, disconnects it, then it returns to rest place and gets connected again, and so on. \$\endgroup\$ Aug 8 '14 at 17:31
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    \$\begingroup\$ Or at 6V the power supply is seeing the motor as a short circuit (it's pretty close to a dead short while starting!) and shutting down for a second... \$\endgroup\$ Aug 8 '14 at 17:40
  • \$\begingroup\$ What motor are you using? \$\endgroup\$
    – Phil Frost
    Aug 8 '14 at 17:45
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    \$\begingroup\$ @Vlad It's more likely that the motor is tripping the current protection circuitry on the power supply when it's starting up. Then the power supply resets and all starts again generating the pulse effect. I've expecienced that once and what I did to work around it was to replace the wall-wart by an equivalent set of AA bateries. They usually let you draw a few amps at start up without any limiting circuitry to get in the way. \$\endgroup\$
    – Ricardo
    Aug 8 '14 at 17:48
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    \$\begingroup\$ @Ricardo I've got my darwin when I opened a disposable camera because I wanted to understand how the flash works. Luckily enough I had already learnt to use only one hand, keeping the left behind my back. I discharged the cap with my right index, it was hella painful... But I learnt to be extremily careful, always. I then hooked a long wire to the flash switch with a spst uswitch and used the camera to surprise family members hiding it on shelves and firing the flash at random. I was about 10, 10 to 12 I'd say. \$\endgroup\$ Aug 8 '14 at 18:17
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I'll turn our comments into an answer.

  1. What is actually happening to cause the pulses? Is my power supply overloading then "resetting" once every second?

It's likely that the motor is tripping the current protection circuitry on the power supply when it's starting up. Then the power supply resets and all starts again generating the pulsing effect.

2.Is there something very simple I can add into the circuit to allow it to start at higher voltages (a momentary current spike)?

3.Is there something very simple I can add into the circuit, perhaps a better power supply, to allow it to run under sustained load (a constant current increase)?

In his comments, WhatRoughBeast suggests you get a bigger power supply.

I've expecienced that once and what I did to work around it was to replace the wall-wart by an equivalent set of AA bateries. They usually let you draw a few amps at start up without any limiting circuitry to get in the way. In your case, 4 AAs in an appropriate battery holder will do the trick.

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  • \$\begingroup\$ Is there any solution for my question #2? Perhaps a capacitor or something I can add to handle the momentary current spike? \$\endgroup\$ Aug 18 '14 at 14:51
  • \$\begingroup\$ Both WhatRoughBeast and I meant that a bigger power supply or AA batteries are the simplest thing to add to the circuit to make it start at higher voltages. That's the answer to both questions #2 and #3, but probably not the answer you want. I don't know any other way to make the motor start. But I'm not knowledgeable enough for you to take it as an expert opinion... \$\endgroup\$
    – Ricardo
    Aug 18 '14 at 15:21
  • \$\begingroup\$ Understood. I guess I'm very curious to know if there are any other options besides a larger power supply for #2. \$\endgroup\$ Aug 18 '14 at 18:18

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