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I need to power a stepper motor in a handheld device. I'm currently using a 9v battery, which has flawed long term usage. The problem I am finding is that the 9v battery is: (a) expensive; and (b) has a short life. Once the battery falls below 7V, the voltage is insufficient to drive the motor. This occurs after around 150 button presses (activation of the motor). A single activation of the motor lasts less than one second, as it is only stepping it 1/8th of a step. However, I'm more concerned about the cost and time associated with replacing the battery. Are there better battery operated solutions out there? Something rechargeable would be ideal.

The battery is powering a bi-polar stepper motor for tiny bursts. The battery is currently connected to an ATTiny85 and EasyDriver v4.4. The stepper motor is from Alibaba. It is rated for 3.9V and .6A. The datasheet can be found here.

The mechanism of operation is as follows.

  1. Switch turns circuit on
  2. Capacitive switch actives circuit
  3. Circuit drives motor which performs a 1/8 step.
  4. Switch turns circuit back off

Note: The motor is most likely at the maximum load each time it activates.

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    \$\begingroup\$ Hi Hugo, welcome to eesx. Your question as is is quite unclear, and will probably be closed. Please try to better state your problem: which model/make of motor are you trying to drive? For how long? Will it be used continuously or just in short bursts? What driver circuit are you employing? Why exactly are you not satisfied with the 9V battery solution? Please also note that 'dissipate a high voltage' does not make sense, particularily in this context. \$\endgroup\$ Sep 27, 2016 at 7:14
  • \$\begingroup\$ Apologies, that was naive.. Edited. \$\endgroup\$
    – Hugh
    Sep 27, 2016 at 7:28
  • \$\begingroup\$ And how long does your battery last? Also, this easy driver is a ready made circuit? Can you provide a link to it as well? \$\endgroup\$ Sep 27, 2016 at 7:31
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    \$\begingroup\$ I'm confused about how you powered the motor: You're using 9V battery and the motor needs 3.9V. EasyDriver needs 6-30VDC for powering itself, so I think you apply 9VDC directly to EasyDriver's supply. According to the schematics, EasyDriver is an A3967-based motor driver and the LoadSupply pin of the chip goes directly to the supply input of EasyDriver. If I'm wrong, please correct and clarify. Maybe the problem comes from this point. \$\endgroup\$ Sep 27, 2016 at 8:01
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    \$\begingroup\$ I smell a fatal flaw: He's microstepping (1/8 step) which requires power all the time. If he's powering-down between steps, where does the motor relax to while it gets no power? \$\endgroup\$
    – glen_geek
    Sep 29, 2016 at 14:25

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it appears what you need here is a 2 cell lithium battery. Li-po(nominal 7.4) or li-ion(nominal varies, but more than lipo) would probably both work. Worthy of note though, is that adding a lithium battery to a project safely adds quite a bit of complication. Unlike other battery chemistry, these do not drop to 0V at discharge, but are considered "discharged" when there is still over 3V at the terminals. Discharging the battery farther will cause damage to the battery and most chargers will refuse to recharge it. That being said, as long as this isn't an autonomous project, any method of checking the voltage will work. The vast majority of modern RC cars use 2 cell lipos, so they can be had for resonably cheap. http://www.hobbyking.com/hobbyking/store/__6540__ZIPPY_Flightmax_2200mAh_2S1P_20C.html You also need specialized charging circuitry as well.

If all of this is too complicated, you should be fine with 6 AA batteries. You can buy whichever rechargeable brand you like. That will give you approximately 4X runtime of your current setup and requires no voltage monitoring.

With regards to power supplied to the stepper: Most steppers don't care much about the voltage supplied to the terminals, as the insulation is rated for much higher voltage than you could apply with simple batteries. What they do care about is amperage. More specifically heat If the motor is getting too hot to old onto chances are you are on your way to burning it out. Steppers are 2 phase brushless DC motors, and the permanent magnets inside will become permanently not-magnets if they get too hot. Looking at the easydriver website, it appears there is a current limit setting on the driver. Set that somewhere under the maximum rating for that motor and you're good to go regardless of input voltage.
Cheers.

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  • \$\begingroup\$ If the OP would use 6x AA rechargeable cells, cycle life can be significantly improved by voltage monitoring. NiMH cells can withstand short periods (like hours) of being at zero volts, and they can withstand momentarily getting reversed by a short current spike (like fractions of a second), but die quickly if you slowly over-discharge them. In a stack of 6 cells, it is common for one cell to be the first to be empty, while the other cells still have enough voltage to force a current through the discharged cell. \$\endgroup\$ Sep 27, 2016 at 15:54
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    \$\begingroup\$ Maybe the question was edited, but as the OP does only single steps (and powers the whole system down in between), heat should not be a major concern because of the thermal inertia of the stepper motor. Too low current on the other hand means that the motor doesn't step so it makes the system fail. 9V block batteries are known for their awfully high impedance, especially if not fully charged, so the focus should be on getting more current into the motor, not worrying about too much current. Paralleling the battery with a cap (4700uF, 10V) might significantly improve battery life. \$\endgroup\$ Sep 27, 2016 at 16:02
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    \$\begingroup\$ I agree that the chances of OP burning out a stepper on a battery pack is low, But if he goes the lithium route it is a distinct possibility. That is a tiny tiny stepper. Capacitor trick is neat but he did specifically ask for a non-9v solution. \$\endgroup\$ Oct 4, 2016 at 0:45
  • \$\begingroup\$ That's correct. If a the OP uses a beefy 3S lithium pack and holds the switch down for several seconds, it might actually damage the motor. It's quite interesting that in a first approximation, the heat depends only on the current of the motor, even if you raise the voltage to counter the back EMF at higher speeds. (The extra voltage is converted mostly into mechanical power, nor heat) \$\endgroup\$ Oct 4, 2016 at 16:13
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    \$\begingroup\$ Please clarify exactly what is meant by "only stepping it 1/8th of a step". Does that mean you are micro-stepping? Else that statement is incomprehensible. The size and power of the motor seem completely incompatible with a wimpy power source like a 9V battery. It would be marginal even with 4-6 AA cells. The basic premise seems questionable. \$\endgroup\$ Oct 29, 2016 at 15:21

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