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First of all I'm a hobbyist so please assume I know very little.

I have a broken battery-based drill and I'm transforming it to be wall mounted, without batteries.

The motor has a label saying RS 550S-14.4V. I tried to supply it from a 12 V, 3 A wall-mounted transformer and it worked, but the transformer was not mine, so I bought another.

I bought a 14 V, 2600 mA wall-mounted transformer and it cannot stay on. If you press the trigger too fast the drill stops.

I thought it was too much consumption in peaks and that the cheap Chinese transformer could not handle it, so I got an ATX power supply. According to the label it can provide 19 A at 12 V, which should be PLENTY. I fooled the PSU to start (PS_ON - GND, Pwr_OK - 5 V) and it started.

But then the same happens: if I press too hard or too fast, the power supply cuts itself off. The PSU fan stops, so I know the problem is the PSU and not in the drill mechanism.

What am I missing here? I cannot provide anything more powerful than the ATX's 19 A.

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  • \$\begingroup\$ Is it an ATX power supply, or ATX-12V? \$\endgroup\$ Jan 29 at 20:14
  • \$\begingroup\$ I've no real clue. I bought it second hand. All i see here is HP5188-2627 LITEON. Output 300W ATX HP. How can I check ? \$\endgroup\$
    – javirs
    Jan 29 at 20:39
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    \$\begingroup\$ I found a photo of one. It seems to have the 4 pin 12V connector which would make it ATX-12V. Most ATX-12V supplies will run with no load on 5V, while most ATX supplies won't. However you may still find putting a load of eg. 1A (5 Ohm 10W+ resistor) on the main 5V output will help it deliver higher current at 12V xdevs.com/doc/Standards/ATX/… electronics-tutorials.ws/blog/… \$\endgroup\$ Jan 29 at 21:10
  • \$\begingroup\$ I dont have a power resistor at hand but added a toy motor in the 5v rail, it spins like crazy but nothing changed. Am I right assuming the motor more or less should do the same as the power resistor ? \$\endgroup\$
    – javirs
    Jan 30 at 19:31
  • \$\begingroup\$ Without a load the 'toy' motor will probably draw much less than an amp. \$\endgroup\$ Jan 30 at 19:56

1 Answer 1

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The motor may take a lot of current when it is started.

ATX power supplies are turned on by connecting PS_ON to GND, but the PWR_OK is an output signal and so it's completely wrong to connect it to 5V.

And ATX power supplies are not magical devices intended to power arbitrary loads. They will not generally work very well if you only load the 12V output and have no load on the other outputs. Some supplies won't even start properly with no load at all, and the motor takes no load until you start it. And the motor may still take a lot of starting current which the ATX supply can't provide and the overcurrent shutdown trips. Also if the motor does start, when you suddenly stop it, thee ATX supply may not handle that too, and the output voltage rises too much as suddenly there is no load, and the voltage may rise too high and trip the overvoltage protection.

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  • \$\begingroup\$ Would it help adding a dummy load in the 5v rail? Or the fact that it starts demonstrates that this particular PSU does nos need that ? \$\endgroup\$
    – javirs
    Jan 29 at 20:41
  • \$\begingroup\$ The fact that a power supply turns on without load is irrelevant. I would not know if adding dummy load on 5V and/or any other rail helps. But increasing load on one rail means it might raise voltages of the unloaded rails and it may shut down due to overvoltage on the unloaded rails. The ATX specs also mandate that you can't add and remove a load instantly, there must be a certain ramp how fast the current is brought up or down in some unit of amperes per microseconds. And the add or removal of load must be within specs as well, a jump from 0% to 100% or 100% to 0% may not be within specs. \$\endgroup\$
    – Justme
    Jan 29 at 21:32
  • \$\begingroup\$ I did further investigation and hooked a meter for the amps. Started slowly and rubbed my finger opposing resistance to the movement, the amps moved up slowly and near to 1A the PSU goes off. That's like super early. It is rated 19A. Ara all cables connected to the main power line or maybe they are connected to different sources and I need to merge them to get the actual 19A ? \$\endgroup\$
    – javirs
    Jan 30 at 13:13
  • \$\begingroup\$ The problem is not the wiring. Some supplies have single 12V output rail, some have multiple, so unless you know you can connect all yellow wires together or not, you should not. The problem is also not that the ATX supply can't provide 19A, it most likely can if the load is a computer, but it is unreasonable to expect it to succesfully power a motor, if it is the only load on the supply. \$\endgroup\$
    – Justme
    Jan 30 at 13:35
  • \$\begingroup\$ So what would you recommend? Adding fake loads for compensation? Or just ignore this option at all ? \$\endgroup\$
    – javirs
    Jan 30 at 14:20

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