Is it safe to wire an AC-DC adapter directly to a DC motor? (with this setup...)

Question

I just wanted to check that this setup is safe as I am not an electrical engineer, nor am I experienced...

I am using an AC adapter which outputs 12 volts DC. It has a max current rating of 6 amps. I have wired it directly to a DC motor (rated for 12 volts) using wire rated for 21 amps. The AC adapter has a pin output like on a laptop charger, so I used an adapter which allows me to screw in the positive and negative wires. (Looks like this: https://uge-one.com/image/cache/catalog/catalog/0%20UGE%20JACK%20ADAPTOR%201-550x550.jpg) I intend on using some insulation tape around this to make it safer.

The motor drives a system of pulleys to lower/raise a shelf in a linear motion, so it has some load. I tested the current drawn with this load with some batteries. With 5.9v across the motor, it drew 1.8 amps (with a load).

The eBay listing for the motor (I couldn't find a decent datasheet) states that its locked-rotor current is 3.25 amperes. I assume that this is the maximum current it can draw, although could the starting current exceed this or exceed the max current rating of the AC adapter (6 amps max)? I ask this because the load could increase as it is driving a shelf with items on. I am not sure if this is something to worry about as the item description for the AC adapter says that it does have over current protection, so what's the worse that could happen?

So, my question is, does this circuit sound safe with my current, tested load, and would it be safe if the load were to increase? Is the safety gap between the amps the motor is drawing and the AC adapter rating large enough?

Many thanks in advance!

The AC adapter that I am using: https://www.amazon.co.uk/gp/product/B074HX4GJ3/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

The motor that I am using: https://www.ebay.co.uk/itm/775-DC12V-4500RPM-Motor-D-Style-Axle-Mini-Generator-DIY-High-Torque-Bearing/312542643980

Answer 1

If the motor 3.25 A locked rotor current and the 6 A power supply output current rating are reliable, that should be ok. A lot of power supplies have over-current protection that is quite sensitive and shut down when a motor is switched on.

I would be concerned about the motor current at full speed. Your 5.9 V test would have only driven the motor at half speed. Even the 1.8 amps that you measured may overheat the motor depending on duty cycle.

Answer 2

Stall current is(theoretically) the maximum that the motor will draw, so your power supply should be more than sufficient for your use.

Some power supplies don't use very large output filter capacitors, though, so it never hurts to add an additional somewhat-largish capacitor across the output of the power supply and/or input of the motor, at least a 16 Volt electrolytic at 1000uF or greater, maybe a lower 330uF/470uF or so on the motor if it's current is toggled between the power supply and the motor. Keep in mind that the additional capacitors will require the power supply to attempt to provide slightly more current than normal upon startup than it otherwise would, so low ESR capacitors should not be used as they could be exposed to a still-existing switching-frequency component if the inbuilt capacitors are not ample.