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I have an Arduino project which uses a L298N to control a 12V DC brush motor (with an apparent 1.8A stall current rating). The motor is equipped with an encoder but I don't think that is relevant to my problem.

While prototyping I have been using an ATX PSU for a PC which I modified for a 'bench supply', which provides 5v, 9v and 12v with ample current.

With this PSU, everything is great - no problems, motor is smooth. I thought any old 12V power supply that could provide at least 2A would be sufficient as a replacement.

However, every other power supply I have tried does not perform nearly as well as my ATX PSU; the motor feels weaker but most importantly it sounds like it's having a bad time. It's hard to explain, but the motor makes a whole lot of mechanical noise, especially when under load. I don't mean a PwM whine, but more a noise like it has bad bearings or gearbox or something. The motor jitters/judders/vibrates as it moves instead of giving nice linear feedback/movement.

As it works fine with my ATX PSU, I can only assume this is a power supply issue. Also I think I can rule out lack of current based on the specs of the ones I have tried:

I tried this first: EFISH Power Transformer 12V 2A 24W,AC 100-240V to DC 12V Power Supply Adapter https://www.amazon.co.uk/gp/product/B07KZB5TQX

Then this, as I thought the first one might just be a cheap unit that wasn't as capable as it said: BW High Quality 12V 5A 60W DC Power Supply https://www.amazon.co.uk/gp/product/B00C676JNM/

Finally, I tried this, thinking a more 'dedicated' regulated switched mode power supply would do it: Velain 12V 5A DC Universal Regulated Switching Power Supply Converter, 60W Adapter Transformer https://www.amazon.co.uk/gp/product/B01N0Y5E8K/

Motor specs: Gear Motor 12V-DC 12V Encoder Gear Motor Speed Reduction Pure Copper Coil Motor (500RPM) https://www.amazon.co.uk/gp/product/B07XRDVXRZ/ Rated speed (RPM): 500 Reduction Ratio 9.6 No Load

  • Speed ±10%RPM 620
  • Current A 0.07 Rated
  • Speed ±10%RPM 500
  • Current A 0.3 Torque KG.CM 0.2 Stall
  • Torque KG.CM 0.9
  • Current A 1.8 Rated Voltage 12V

Any help much appreciated.

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  • \$\begingroup\$ It's going to be very hard for anyone to answer this without more specific information about what is happening. For example, if the motor is causing a supply to cut-out at a periodic rate, watching the supply rail with a scope would show that. It's also worth noting that the L298 is (like all darlington drivers) infamously horrible, though that's probably not your issue here. \$\endgroup\$ – Chris Stratton Sep 20 '20 at 1:26
  • \$\begingroup\$ I don't have a scope unfortunately :( It's on my list. I don't think it's causing the supply to cut out though, but what would cause this if so, given the PSUs I've tried have been rated well over the stall current? \$\endgroup\$ – Alfie Sep 20 '20 at 1:30
  • \$\begingroup\$ You might be mistaken about a current, or the alleged supply rating might be a lie; realistically you seem to be describing something that works with one supply and not another, so... \$\endgroup\$ – Chris Stratton Sep 20 '20 at 1:32
  • \$\begingroup\$ Can you attempt to accurate measure the resistance of the motor with it just sitting there? You would likely have to subtract the meter lead resistance. \$\endgroup\$ – Spehro Pefhany Sep 20 '20 at 2:08
  • \$\begingroup\$ Guess the brushes or the collector are just crap or end of live. ATX are quite strong and can deliver huge peaks. Guess your motor produces short cuts while rotating. Do you see brush sparking? \$\endgroup\$ – schnedan Sep 20 '20 at 7:12
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It's a 12 V DC motor which draws 0.07 A on no load, 0.3 A on full load and 1.8 A when stalled.

A single phase, unfiltered DC supply using a 12 V 500 mA transformer and a 1 A bridge rectifier would be good enough to run this motor.

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