Electronic – the difference between “medical” grade and ordinary AC-DC power supplies

powerpower supplysafety


My wife and I are expecting a baby soon and a family member has given us their previously-used, thoroughly cleaned electric breast pump. The pump came from the vendor with a "medical grade" 120V AC to 9V DC power supply (i.e., a "wall wart") that powers the pump's motor.

Based on the size and weight of the power supply, it appears to be a transformer-based linear power supply. It is marked "120V only". This is a problem, as my wife and I now live in Europe were 240V AC power is the norm.

The pump itself is fairly simple and does not seem to have highly sensitive electronics: there is an electric motor powering a peristaltic pump and a potentiometer that varies the pumping speed. My multimeter indicates that the internal electrified components are isolated from the user and the fluid being pumped, as expected.

I've tested the pump with an off-the-shelf regulated 9V switching power supply (UL-listed and CE marked) that operates on 120/240V power and which can supply more than adequate current for the pump and the pump works normally.


What is the difference between a "medical grade" AC-DC power supply and a more common, non-medical one like one would find accompanying an ordinary piece of consumer electronics?

Would a medical-grade power supply offer additional voltage stability, less ripple, greater isolation, and/or greater reliability than a standard wall wart meant for electronic devices?

While I understand that higher-grade power supplies would be important for critical life-support systems, is there any reason why a common, non-medical-grade power supply that meets the voltage/current needs of the pump would be inappropriate?

Best Answer

Medical grade power supplies have supposedly been tested to specific standards. In particular, the maximum leakage current between the hot and isolated sides will be very low. There are also other internal requirements, like a large creapage distance accross the isolation barrier.

The medical-grade requirements are to make the supply more safe, even if the isolated side is connected to a human more closely than thru ordinary skin. Some of the requirements are to reduce the chance of failures, and to decrease the chance that any one failure could electrocute someone.

All this costs money, so medical grade power supplies are significantly more expensive than ordinary ones. The volumes are less, which again drives the price up.

These extra specs have nothing to do with voltage stability, ripple, current rating, and the like.