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Power supply for stepper control application


#1

I am working on a project that will run a lightly loaded stepper motor continuously for 12 hours. At the beginning and end of the cycle, a servo will activate briefly. During the cycle, the system will periodically check values from a light sensor which may result in another brief activation of a servo. The system will be run in a variety of environments, many of which will not have access to plug-in current, so a battery will provide the primary current source. The control system will be a Simblee bluetooth controller so there will be typical BLE power management in the code. The load will be mechanically balanced and driven through a 90.25:1 ratio gearbox by a 6v, 0.06amp/phase stepper at a single rate of speed.

I’m trying to decide how best to approach the battery and voltage regulator. My inclination is to use a step-up regulator with a single cell or parallel configured LiPo battery pack to maximize energy density and minimize the form factor. I will need 3.3 volts for several of the ICs in the circuit and some voltage level to drive the stepper and the servo(s). Since I’m not looking to get high rpm from the stepper, it seems like driving it at 6 volts (or less) would be sufficient, using something like the DRV8834 and U3V50F6 in combination.

The servos would need to be low/no current drain unless activated, so perhaps they could be driven by a second step-up regulator that could be disabled for low current drain when the servos are not in use. (Or maybe a digitally controlled switch of some sort would be better for this. I’ve located several discussions about the servo issue that include discussion of getting the servo to come back on in the same position it was left in but haven’t read through them yet.)

But perhaps there is a compelling reason to use a higher voltage pack and step-down regulators instead. And just to complicate matters, I’m trying to decide if the battery can just be swapped out and charged outside of the circuit (probably) or if I should include a solar cell or plug-in input to charge it in circuit. In the past, I have used plug-in current alternatively with the battery circuit by switching between them rather than trying to charge and discharge the battery at the same time. I haven’t researched that idea at all yet. But if I can get a battery of appropriate size to reliably run the system, I would like to keep it as simple as possible. So this topic is mainly intended to discuss getting maximum efficiency out of the battery/voltage regulator/stepper driver combination. Any thoughts would be appreciated.


#2

Hi.

For a few LiPo cells, it’s usually going to be more efficient to put them in series rather than in parallel since you won’t lose as much power in your wiring. It would be easiest not to need regulators for your high-power components at all; if you set yourself up with 7.4V, you won’t need any regulator for the stepper driver, and you could look for some servos that can run directly off of that higher voltage. This of course doesn’t take into consideration your charging requirements; if you happen to have a good solution for charging one cell and not two in series, then having to mess around with boosting the voltage might be easier. In general, though, until you get to some voltages that start getting dangerous or harder to work with, higher voltage and lower current is going to be more efficient.

-Claire