| Electronics > Projects, Designs, and Technical Stuff |
| "over current" use of a Pulse transformer - ( or an alternative ) |
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| mrpackethead:
--- Quote from: T3sl4co1l on December 23, 2018, 11:52:39 am ---Mrpackethead has been deeply involved in PoE applications (I don't know how obvious this is from the OP or his posting history), and as far as I know this is a standard application, for which there are such transformers as linked above, as standard off-the-shelf components. :) Yeah, differential data passes by, common mode power is drawn through the CT. Everything is transformer-isolated so there should be no balance issues outside of insulation/conductor failures. Nice name change..? :o Tim --- End quote --- The difference between current flowing in each side of the transformer should only be minimal. The cable connecting each side is the same guage, and it will be the same length, ( with a few mm ). This is no differnet from any transformer that is being used for this application. My gut feeling says that the limitations here, are thermal, and that the device was only ever tested to 600mA because thats what was requried for POE+. |
| cdev:
You're probably right about them never needing to carry more so likely being able to handle it. But suppose it did get too hot, would there be any technical reason you could not use two with their windings simply *in parallel* with one another? - I suppose then you would lose the size advantage, though, so not worth it. Are all of these POE-ready pulse transformers all rated at the same 600 ma because of the rating being that? --- Quote from: mrpackethead on December 21, 2018, 10:22:45 am ---https://product.tdk.com/info/en/catalog/datasheets/090007/trans_alt4532p_en.pdf TDK have these small pulse transformers which look really useful, as they have a very small footprint which makes them useful for tight packs. they are rated for POE+ or 600mA. I want to run run at 900mA, which is what the 802.3bt standard for POE can go to. --- End quote --- |
| mrpackethead:
--- Quote from: cdev on December 24, 2018, 06:48:17 pm ---You're probably right about them never needing to carry more so likely being able to handle it. But suppose it did get too hot, would there be any technical reason you could not use two with their windings simply *in parallel* with one another? --- Quote --- I'm not sure if there is not.. --- Quote ---- I suppose then you would lose the size advantage, though, so not worth it. --- End quote --- yes. --- Quote ---Are all of these POE-ready pulse transformers all rated at the same 600 ma because of the rating being that? --- End quote --- There are transformers rated at 1000mA such as coilcrafts ETH1-460L, theres other parts from Wurth, and no doubt from other manufacturers such as HanRun.. However they are all large. --- End quote --- --- End quote --- |
| cdev:
If you find it runs hot and its potted I guess you could slap a heat sink on it although it might look funny-that would likely help. |
| mrpackethead:
Worst case, at 100m, you 12.87ohms vs 12.13. total current = 900mA.. this would result in 463mA in one conductor and 437 in the other 26mA. Its unclear if this difference will be enough to cause saturation of the core. It will need to cope with 18mA unbalance if its going to run at 600mA. The articale you reference while interesting is to do with the inblance between the pairs, this particular problem is related to a single pair. |
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