We use external table top power supplies with our products. One problem is when they go obsolete and we replace them we end up retesting the entire system for EMC compliance. The power supplies are all compliant with the standards and carry UL and CE markings. Is there some design strategy or justification that will allow us to avoid all this retesting?
Thanks
Sell the external power supply separately from the product, or not at all by suggesting to the customer where one cna be obtained.. I believe that makes the compliance of the resulting "system" the customer's problem
Suggest you deal with OEMs who don't obsolete the supplies so often.
That sounds great. And EN61326 says that lab equipment does not have fixed equipment and therefore it is reasonable to not test every possible arrangement, but you must realistically simulate the test conditions. I'll see if we can swing it.
Thanks
Yep. The other problem EMC-wise is that similar-looking PSUs can have very different performance - they all meet the regs for emissions and immunity, it's a question of by how big a margin. Unless the vendor publishes the full test report you don't get to see any of this stuff. We had to ditch one manufacturer after they refused to fix the nasty big 55MHz emissions spike from their product. Add a bit of system cabling with a resonance near this point and a minor bit of noise from our own product and it nudged over the limit.
After being burned once we rented a measuring receiver and characterised half a dozen different supplies, it was surprising how many name-brand PSUs had the same innards and were just re-badged. There was a 4:1 spread in prices for what was basically the same product.
We currently use Elpac, I think they were acquired by some other vendor recently but their product line is pretty stable and their PSUs are nice and quiet, there was a big improvement in the system's immunity to transients etc too. The only downside is that they are about 3x the price of the old one, but having a product you can't ship is a lot more expensive...
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