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Can someone please help me to figure out how to replicate the power you get from a 3.7v Li-Po, but from mains power?

A DC motor, powered directly with a 3.7 V Li-Po battery draws between 400 mA and 1.2 amps (shown on my multimeter), and the motor feels strong, with it taking a bit of force by hand to stall it.

The DC motor has these markings on it:

RC280SY 4238 39DVSSZ
3.7 V 13500 rpm

and I found absolutely nothing on the internet about it.

The motor, when connected via a 5 V, 3 A DC switching supply through a MOSFET on a PWM signal from an Arduino (on the same power supply) seems to run fine, but is much easier to stall. I have put a SEPIC Buck/Boost converter on the supply and boosted the voltage up to 6.8 V which feeds the motor to get it to run nearly as strong, but it still stalls easier. The motor runs faster, but not harder.

I don't have an oscilloscope, but I imagine that the switch mode power supply or Buck/Boost converter is not as efficient as they say? The buck/boost inductors also get very hot after a time with the motor running at full speed, and the voltage starts dropping here and there down to about 4 V. So I believe heat build up is making it less efficient.

Can anyone offer advice in the best way to replicate what the Li-Po does but from the mains? The Li-Po is good and everything, but doesn't last very long. Perhaps I'm going about it wrong.

Do I just need to throw money at it with a bigger supply / higher voltage? I thought a 5 V 3 A would be sufficient, but it seems not, unless I'm missing something about how amps flow from a DC transformer vs a battery?

Thanks to anyone who can help, and perhaps educate me! 😁

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    \$\begingroup\$ How does the Arduino fit into the picture? Can you draw a diagram? \$\endgroup\$
    – Justme
    Commented Jul 28 at 18:04
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    \$\begingroup\$ My guess is the DC power supply cannot handle the peak current of the motor, especially when you stall it. \$\endgroup\$
    – user1850479
    Commented Jul 28 at 18:45
  • \$\begingroup\$ Thanks. I'm thinking it's the supply. The Arduino fits in direct from the same supply at 5v, feeding the 2 pins on the back which the USB would normally feed. There is then 2 wires bouncing from this to the boost converter which feeds power to both motors at higher voltage of 6.8 V. \$\endgroup\$
    – Danny Akuma
    Commented Jul 28 at 22:50
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    \$\begingroup\$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. \$\endgroup\$
    – Community Bot
    Commented Jul 28 at 23:22
  • \$\begingroup\$ I highlighted at the end what I wanted: To replicate the power that a small 3.7v Li-Po gave to both motors just fine, but I want it running off the mains. I tried to provide as much info as possible on how I went about it, sorry if it's confusing. It's confusing me why it doesn't work very well as the current being drawn from the mains seems to be weaker despite the voltage being higher and rated for higher amps. I'm wondering if this is the problem: ebay.co.uk/itm/364016033976 \$\endgroup\$
    – Danny Akuma
    Commented Jul 29 at 8:11

1 Answer 1

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Ok, I figured this out after buying a bench power supply... Seems like the boost converter was being asked to do too much, raising voltage lowered the current, so the amps were not there to provide the power, only the speed.

I also made some of my connections better as I think running 3 amps through it was failing in certain parts. So it turns out the power supply wasn't the issue, just the settings I chose. I replaced the boost with a buck converter to step down the voltage, and now I have stable current everywhere and more torque on the motor.

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    \$\begingroup\$ If the motor is rated at 3.7V, you should run it at around 3.7V. Or you should know the operating range. But not at 5V and more. I suppose that's the reason of your problems. And I suppose that you should control the speed with PWM or regulating the current. \$\endgroup\$
    – Gos
    Commented Jul 30 at 12:09
  • \$\begingroup\$ Could be also that the switching regulator doesn't like the PWM at some high frequencies, because you are disturbing it's switching operation. Could be that above 300Hz is not very stable. \$\endgroup\$
    – Gos
    Commented Jul 30 at 15:08
  • \$\begingroup\$ You might be right about the switching frequency, I hadn't considered that. However I think it was more to do with the limit of the boost converter and power going in, as I ran some tests and saw voltage drop and it get very hot. I have been running a PWM signal the entire time from slow to fast. I replaced with a beefier buck converter and also put a 100mf cap on the supply end and I've not had a single stall since. I found 4v to be about right. \$\endgroup\$
    – Danny Akuma
    Commented Jul 31 at 13:23

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