Help! > Mistakes, muckups, and dangerous behaviour

Chinese power supply gotcha


Stan Stocker:
Hi Folks,

Had an quirky thing happen while building a motion controller.  Had a 48V 10A switching power supply.  It has a lovely large yellow sticker by the rectangular slot on the case warning you to check 115 or 240 V switch setting.  Even has HUGE arrows at each end of the case slot labelled 115 and 240.  So it would seem if the red slider is at the 115 end of the slot it's set right.  Hook up a temp AC cord to verify output voltage.  All is good, nice adjustment range, set to 46 volts just to have a wee bit of margin for Chinese cheap stepper drivers.  Power up completed controller, power supply can't maintain regulation with more than one driver connected. Crap.  Replace with 36V 16A supply on hand and move on.

Well, I got wondering about the 48V supply, opened it up, thought I might luck out and find something.  Sure enough, the slot is larger than the switch.  A lot larger... In normal shop light I could see clearly the red part of the switch was at the 115 volt arrow on the case sticker.  In bright light with the case removed on my nicely lit electronics bench I saw the cute little faint white "220" legend on the switch.  Turned out the case slot was much larger than the switch itself, and as soon as any load was applied to a power supply set for 220 with a 115V input the thing folded back.

Not sure whether to be be embarrassed, amused, or ticked off, but if your eyes aren't still those of a 20 year old, don't trust the stickers on the exterior of Chinese power supplies, grab the bright flashlight and double check.

Once set to the 115 V setting (also in very faint white printing), loaded with a nice 10 ohm 250W resistor, it maintained regulation just fine and dandy.  Well who didn't know that?

It sure is nice being able to use one hand to lift a 48V 10A supply rather than with two guys to slide a similar linear into a rack for sure, but there are the occasional downsides to our new global world supply chain too.

Hopefully this is a source of useful info or a bit of gentle amusement in these strange days!

Stay healthy, keep laughing,

Thanks for that heads up - will watch for that in future when using new electrical bits.  :cheers:

Hello Stan,

You were lucky with the switch setting. It was a kind of fail-safe setting.

I dead to think what would have happened if it were set to 115V and 240volts was applied.  :zap: :zap:

I will certainly check that switch setting in future with new stuff from China, as we live in a 240volt country 


I inadvertently ran one of these at 110 when it had 220 selected. It worked just fine when I was testing, but when I asked the steppers it was driving to do some work, the fuse blew.  I checked and subsequently replaced all of the power diodes and it has been fine since.

Dual voltage supplies always come from the factory set at the highest voltage. The only time it is not someone has screwed up or it was used before.
Keep that in mind when using them.

Regards Don


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