# Voltage stabilization

I have several motors, and a microcontroller. The microcontroller sends 3.5v signals to the motors, which are powered by a separate 5v source. (The microcontroller also runs off the 5v.) Problem is, it seems like the power supply is insufficient. When the motors start up, or when they're all trying to move, they often behave strangely, and the microcontroller sometimes resets. If I increase the voltage, they behave better - but I have to increase it to like 6v, and I'm worried about pushing it much farther, since the microcontroller and motors are only supposed to get 5v. Looks like the motors draw up to half an amp, collectively - which is a fair amount for small motors, but not THAT much. With a multimeter, I've seen the voltage drop by over a volt. I've tried two variable power supplies and a set of 4 AA batteries, and they each show significant voltage drop. (One of the supplies was supposed to provide up to 3A. Note that both supplies seem fairly inaccurate in the voltage they claim to be producing vs the voltage they're actually producing.)

How do I get the voltage to STAY at 5v? (Or at least within 50mv of, say, 5.5v?) Is there a particular style of power supply I need, or a special intermediate box, or do I just need a massive stack of batteries in parallel? I wasn't measuring voltage AT the battery tips, merely at a convenient spot a little further downstream; only wires/connectors in the way - maybe the wires were adding some resistance??

Here's a video demonstrating the setup, and the problems. Demonstration video

Here's a diagram of the connections:

• What are you using for a power supply? A good power supply will give its rated voltage up to its rated maximum current. A poor power supply will not. Commented Feb 21, 2021 at 3:31
• You state in the second sentence that there is a separate 5V source but then you go on to say that it is the same source. Can you provide a picture or schematic of your setup? Commented Feb 21, 2021 at 3:55
• @RonReiserer I mean that the microcontroller and the motors are powered by one 5v source, and the microcontroller only provides control signals (which are at 3.5v). I can make a diagram, if you still want one. Commented Feb 21, 2021 at 3:58
• @MathKeepsMeBusy A Yihua PS-1501S, a QiYe-32430, and 4 Meijer Powercell AA alkaline batteries. Link for the first: ebay.com/itm/…, link for the second: en.aliradar.com/item/… Commented Feb 21, 2021 at 4:01
• I'd try without a breadboard and thicker wires. That might help a bit. Commented Mar 14, 2021 at 17:57

Sounds like you have at least one of two possible issues or both. The first possibility is that your 5-volt DC power supply is undersized or cannot supply the current demand. The output of the 5-volt power supply must be 5 volts at full load current, not 4.9 volts or something lower.

The second issue is the plague of all low-voltage circuits: IR voltage drop on the distribution. At 120 volts, maintaining a 3% voltage loss is easy, as you have 3.6 volts to work with. At 5 volts, you don’t have much to work with and likely need to throw more copper into the equation to limit IR losses on the distribution.

Here is a real example from practice. You must deliver two power circuits, one at 12 and one at 120 volts. The one-way circuit length is 50 feet, the load is ten amps on both circuits, and limit voltage drop to 3%. What gauge of wire is required?

The 120-volt circuit requires #14 AWG, and the 12-volt circuit requires #4 AWG. Low voltage is inefficient and costs a lot more to distribute and utilize.

• With moderate experience gained in the intervening years, this was probably my problem, indeed. I haven't gone back to try it again, but improving power distribution would be my first fix for this. Commented Jul 10 at 19:09

Based on the question you said the motor requires 5v thus you need a source that can provide 5v with a lot of current, I'd recommend you get a 6v SLA battery, it may be 6v but it's still safe to be used on 5v applications yet at the same time SLA batteries have a very low internal resistance thus there barely will be a voltage drop when you connect the motors and the SLA battery provides a lot of current. So try a 6v SLA battery, with a diode in series to keep it within the 5v requirement

• The absolute maximum rating for a 5v0 microcontroller is typically either 5.5V or 6V; in both cases it's definitely exceeded by a 6 V SLA battery (a single cell of an SLA battery has a voltage of 2.1 V, making the total stack as high as 6.3 V) Commented Feb 21, 2021 at 6:21
• But a series diode can fix that Commented Feb 21, 2021 at 6:44
• Then you should update your answer to indicate that a series diode ought to be used. Commented Feb 21, 2021 at 15:28