RMweb Premium rab Posted December 27, 2020 RMweb Premium Share Posted December 27, 2020 This one concerns the plug-in transformers which I'm sure I'm not the only one who is accumulating quite a few as smartphones and tablets get upgraded. In the good old days when we played around with batteries for low voltage power, if we needed more oomph we wired them together in series. Can the outputs from these 5V transformers be similarly wired in series? Link to post Share on other sites More sharing options...
AndyID Posted December 27, 2020 Share Posted December 27, 2020 Not if one side of their outputs is tied to mains earth, but that's fairly unlikely. Link to post Share on other sites More sharing options...
WIMorrison Posted December 27, 2020 Share Posted December 27, 2020 for the costs of an SMPS (that is what they are) just but one with the correct voltage - and also check that the wattage is what you need. Link to post Share on other sites More sharing options...
DCB Posted December 28, 2020 Share Posted December 28, 2020 Do you want more volts or more power per se? I never tried series but mine work ok in parallel,. These things don't have overload protection like dedicated model railway power supplies, they aren't supposed to be shorted out. I always recommend a poly fuse in the circuit and quite a low rated one, below the rated output in amps of the supply. They aren't intended to work at high output for extended periods like model railway power supplies are often required to do. Not saying don't use them but be a bit careful. Link to post Share on other sites More sharing options...
RMweb Premium rab Posted December 28, 2020 Author RMweb Premium Share Posted December 28, 2020 TBH it was more a case of seeing the pile of un-needed chargers growing and trying to think of alternative uses for them. Link to post Share on other sites More sharing options...
DCB Posted December 28, 2020 Share Posted December 28, 2020 A Variation of Murphy's law suggests when ever you dispose of a charger within a month you will need one just like it, As an alternative when you're bored you can try playing match the charger to the mobile, its like a jigsaw puzzle but more frustrating. Link to post Share on other sites More sharing options...
RMweb Premium kevinlms Posted December 29, 2020 RMweb Premium Share Posted December 29, 2020 8 hours ago, DavidCBroad said: A Variation of Murphy's law suggests when ever you dispose of a charger within a month you will need one just like it, As an alternative when you're bored you can try playing match the charger to the mobile, its like a jigsaw puzzle but more frustrating. With some of the pieces missing, because it was the power pack that died, or you've already swiped it for something else! 1 Link to post Share on other sites More sharing options...
LimboBrit Posted December 29, 2020 Share Posted December 29, 2020 On 27/12/2020 at 18:39, rab said: Can the outputs from these 5V transformers be similarly wired in series? There are many ways of designing a SMPS so while it may be possible to connect them in series you may not get what you think. Some designs will give you say 5V output but that may be on top of a 230V sine wave that may not be useable in all situations. Generally I would not recommend it and definitely not for some cheap Chinese wall warts Link to post Share on other sites More sharing options...
AndyID Posted December 29, 2020 Share Posted December 29, 2020 50 minutes ago, LimboBrit said: Some designs will give you say 5V output but that may be on top of a 230V sine wave If they were originally supplied, for example, with a phone from a reputable manufacturer that would be highly unlikely. Have you actually seen an example of a SMPS that does not include an isolation transformer? Link to post Share on other sites More sharing options...
LimboBrit Posted December 29, 2020 Share Posted December 29, 2020 1 hour ago, AndyID said: Have you actually seen an example of a SMPS that does not include an isolation transformer? The 230V was capacitively coupled and I’ve even seen this on a Dell laptop adapter. Link to post Share on other sites More sharing options...
AndyID Posted December 29, 2020 Share Posted December 29, 2020 8 hours ago, LimboBrit said: The 230V was capacitively coupled and I’ve even seen this on a Dell laptop adapter. There is always a small amount of capacitive coupling between the primary and secondary in any SMPS and any PSU come to that. Some of it is stray capacitance and some is intentional to limit RF interference. The amount of current it can supply to ground is the critical factor. It should be very small. Link to post Share on other sites More sharing options...
LimboBrit Posted December 29, 2020 Share Posted December 29, 2020 2 hours ago, AndyID said: There is always a small amount of capacitive coupling between the primary and secondary in any SMPS and any PSU come to that. Some of it is stray capacitance and some is intentional to limit RF interference. The amount of current it can supply to ground is the critical factor. It should be very small. Agreed but at the time it was enough to cause a problem on a development project I was working on. Link to post Share on other sites More sharing options...
AndyID Posted December 29, 2020 Share Posted December 29, 2020 1 hour ago, LimboBrit said: Agreed but at the time it was enough to cause a problem on a development project I was working on. I imagine so, but I'm not sure that's relevant to RAB's original question. I don't know for sure but I doubt he was thinking of of using them in a situation where that would make much difference Link to post Share on other sites More sharing options...
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