Filtering Harmonic Currents

So what your saying is that your working on an avionic system, right? Sorry, but you don't run across 400Hz in everyday trouble-shooting.

And anybody that would suggest any solution to your problem would be foolish with out having the component sitting there on the bench staring them in the face.

Dan

If it's true this is for avionics, then the conducted emission specification he's using is not per any approval authority that requires the use of RTCA DO160(), but I guess a customer (airframer) can make up their own PMA requirements. DO-160F has gotten pretty tight with power factor correction. As well power on surge currents for use with solid state circuit breaker systems.

To the original poster, what are your regulatory requirements for this SMPS?

Please quit foaming at the mouth, and correct three spelling/grammar errors.

I can see your "return to service, "IAW Joe blow/golbalspec/CR4 and found to be airworthy"

I find it fascinating that you refer to the requirements for equipment on on airplane as "red tape and BS" in a post where you are raving under the implication that I would wire something up based only on the word of a forum post and attempt to put it in the air.

If you did know the requirements for air worthiness, you would know that I'm not the only one working on this, and that months of testing lay ahead for any solution that is proposed to ensure the safety of everyone involved.

All I asked for was a clarification of a concept.

I would like to request a moderator to lock this thread. I don't think there is anything useful to be gained here.

Define "...huge (~70mH)". Is there a size/weight issue you need to deal with?

Have you considered active filtering vice passive?

Without the design specifications and schematics to analyze, I would not hazard even a guess how to solve your problem. I will say that 1/4 ampere of passed RMS current should not be a problem. I will say that it is obvious that you possess insufficient theory in filter design. If you did then you would know that the attenuation magnitude of the harmonics will determine how many poles will be needed in your filter design. I suspect that you are inadvertently trying to build a filter with much to high of a Q.

You may also have a coupling problem with the SMPS. If the SMPS is not shielded or the wrong style of inductor are used in it, then coupling to your filter inductors can bypass your filter. (Think of an AM antenna.)

You also should use the wide input voltage range a SMPS gives you to your advantage.

If my suggestions cleared out some cobwebs and reminded you of some skills you have not used in a long time, that's great. I wish you the best in hunting down your problem. If my suggestions baffle you even more, hire an analog designer.

I think your SMPS needs to be redesigned or needs a proper replacement approach, because it seems not to supply adequate or enough quality power. Are you working on the supply itself? In that case please correct me if I say that the filter(s) necessary in a SMPS to just reduce the harmonics are not correctly designed, not for your specific load.

To get involved deeper in your query, more specifics are definitely required: type of load, other instruments on that load, nature of load(s)

Working on filters (behind the supply) will affect the supply itself as is now.

"placing an inductor in series with the power supply clears up the harmonics, however it has to be huge (~70mH), be able to pass more than 250mA RMS without saturating"

You apparently know nothing about inductors. First, 70mH is not huge. second, the larger the value, the more likely to saturate. Third, wire size and core material are the main factors for saturation. If the inductor solves the problem then go with it.

And the inductor good for the 3rd will probably also kill the higher harmonic content.

The inductor parasitic capacitance will also need to be carefully controlled since it will create a resonant circuit.

Lots of luck - you have plenty of experimenting and testing to do.