Power supply – panic

[Speedy Builder5Participant @speedybuilder5]

[Speedy Builder5Participant @speedybuilder5]

Bought a 36 volt power supply for a stepper motor, also using a buck converter to make the 12 volts for the Arduino. The 12 volts was working OK, but before wiring to the stepper, checked the PSU o/p which showed a voltage of 100v DC, tried adjusting it down, but it stayed at 100.

Was getting to think about contacting supplier (China) and left disconnected on the bench overnight. Next day, re-checked and O/p voltage was now 38 volts and could be adjusted OK.

Could the supply have been tested at source leaving a capacitor well charged up ?.

[John HaineParticipant @johnhaine32865]

Was it designed for driving LEDs by any chance?

[Speedy Builder5Participant @speedybuilder5]

Ps – and yes, it was set for 240v input (not 110).

Driving LEDs – It was advertised for Stepper motors.

[John HaineParticipant @johnhaine32865]

Could you post a photo or link? I have tried an led supply (for leds) and its regulation was terrible. Ended up using a proper little smps from RS.

[HowiParticipant @howi]

Posted by Speedy Builder5 on 18/02/2021 07:56:59:

Ps – and yes, it was set for 240v input (not 110).

Driving LEDs – It was advertised for Stepper motors.

A power supply is unlikely to be made specifically for a stepper motor, personally I have found laptop power supplies to be great for steppers and can be found in various voltages, I have found 19v more than adequate for even a quite large stepper on my lathe and not expensive.

[Anonymous]

Was the buck converter unloaded during the measurement? It's common for simple switchmode power supplies to lose regulation on light loads, or no load.

Andrew

[SillyOldDufferModerator @sillyoldduffer]

Posted by Andrew Johnston on 18/02/2021 10:23:57:

Was the buck converter unloaded during the measurement? It's common for simple switchmode power supplies to lose regulation on light loads, or no load.

Andrew

I was thoroughly confused by the switch mode power supply in a work-light, providing 12V to a car headlamp bulb. It misbehaved due a an intermittent connection. Unloaded, the PSU appears almost completely dead, barely twitching the needle on my multimeter's 0.5V range. With a 55W bulb correctly fitted, bursts into life – 12V. Deliberately or by accident the power supply doesn't work unless it has a load.

On the subject of stepper power supplies, I use the LED type because they're cheap and easy to find. They're not ideal because a stepper likes lots of volts and quick bursts of current. An ordinary unregulated PSU is more suitable because a voltage stabilised power supply might have trouble keeping up with the motor's wild demands, and because starting pulses with a high voltage is an advantage. In practice, I've not had any trouble with LED PSUs and they are easier to buy than old-fashioned unregulated PSUs with an expensive transformer.

Dave

 

Edited By SillyOldDuffer on 18/02/2021 11:25:09

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