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Paul Drahn

On 6/29/2013 12:08 PM, wrote:
I recently replaced a couple of electrolytics in a flat screen TV for a customer. The caps were in the power supply and were of course rated for 105 degrees C. So this brought to mind a question. Could this possibly be an operating temperature? Or is it a storage temperature? Or perhaps it's an internal temperature? It would seem like it would have to be a very high frequency component to ever cause an electrolytic to ever approach anything like this. Could one of these parts rated as such actually get this hot and remain operational? Would this actually be within prudent design parameters for the device? In theory if the caps are not actually operating at even 85 degrees C then why wouldn't you be able to use a lower rated temperature cap for that application?

It would seem to me that if a piece of equipment were designed to run a capacitor that hot or even at 85 degrees C for whatever reason then in my mind that would certainly constitute a very poor design. I have been repairing TV's for many years and the only capacitors I've ever seen get too hot to touch were bad ones. Could someone please explain this rating to me? Thanks, Lenny
As the owner of an electronic assembly service, I can help you with
this. It has nothing to do with design and everything to do with price
and availability. The manufacturer may be using the cap in another
product and got a good price for buying 50,000 of them. Or, the lower
temperature cap may have had a long lead time, so, with engineering
approval, the purchaser ordered these so the production line was not
shut down.

We fight engineering all the time when they design a product with
several different sizes of SMT resistors, or several capacitors of the
same value, but different tolerances. This adds quite a bit to the
manufacturing cost because each component has to be ordered and
inventoried and used in a separate feeder on the pick-and-place machine.

When engineered for manufacturing efficiency, a single sized resistor
could do the job for all circuits needing that value and wattage. A
single capacitor with a low tolerance will work in all the other
circuits and cost the same in quantity and need only a single item
order, inventory and p-p feeder.

Paul