Need advise on eliminating 60 Hz ripple after tranformer brick coming into laptop

[wandir]

I'd like to eliminate the 60 Hz noise on the DC power supply coming into my laptop as it leaks into my data acquisition. I know this is the source because if I unplug the transformer from the laptop so that the laptop is running on the battery alone most of the 60 Hz noise goes away. There is, parenthetically, no chance of a ground loop, I made sure of that. Running the laptop unplugged is an option for short periods of time, but the equipment supposed to be idiot-proof. In the end I would like to keep the laptop plugged in while making the measurements in question.

Obviously the main offender would the transformer brick, but the ripple from the wall source ground before it gets there might be a factor too. Is there a preferred way to eliminate the ripple after the transformer to get a nice clean DC signal into my laptop? Should I just build a connection box with a passive low-pass filter, or is there some better way? I'm sure this issue comes up in audio equipment (which I know nothing about) since 60 Hz noise can be heard, and is ever present.

 

[Papabravo]

You could run the laptop from a laboratory power supply, a custom DC power supply, or from deep cycle marine batteries. Those laptop bricks are not designed for your application period. You can try to put lipstick on the pig, but I think it will be a waste of time.

 

[Diver300]

The noise isn't likely to be 60 Hz. It is more likely to be 120 Hz, as the input power is full-wave rectified first.

There may also be some much higher frequency noise coming from the switching part that runs from the DC link.

If the laptop power supply is marginally rated, it might be struggling at 120 V. It is probably rated up to 240 V so you could try running it from 240 V to make sure that the DC link voltage is always adequate.

 

[Papabravo]

I understand that the OP is trying to do this job on the cheap. Using a laptop and and its power supply for a purpose that it was not intended for has consequences. Get an industrial power supply and ruggedized industrial components and try again. I know the components are more expensive, but compare that to the cost of a line shutdown.

 

[wandir]

You could run the laptop from a laboratory power supply, a custom DC power supply, or from deep cycle marine batteries. Those laptop bricks are not designed for your application period. You can try to put lipstick on the pig, but I think it will be a waste of time.

I had originally written that "all these bricks are crap" but edited it out.

 

[wandir]

I understand that the OP is trying to do this job on the cheap. Using a laptop and and its power supply for a purpose that it was not intended for has consequences. Get an industrial power supply and ruggedized industrial components and try again. I know the components are more expensive, but compare that to the cost of a line shutdown.

No, I am not trying to do anything on the cheap, on the ignorant possibly, but not on the cheap. Currently I am using a custom made brick with UL medical-grade isolation that cost about 4 times what a typical laptop brick would cost. But I will see what effect trying new external power supplies has on the problem. The measurements I am making are being corrupted by a few MICROVOLTS of ripple on the ground line. I'm not using the power supply to power anything other than the intended laptop. The signal amplification and acquisition are powered by a separate battery, but there is a common ground to make DA conversion possible.

 

[crutschow]

You could also try plugging the brick into a good 1:1 power isolation power transformer with a grounded shield between the primary and secondary.