(Probably) another silly question from me

[rab]

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?

[AndyID]

Not if one side of their outputs is tied to mains earth, but that's fairly unlikely.

[WIMorrison]

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.

[DCB]

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.

[rab]

TBH it was more a case of seeing the pile of un-needed chargers growing and trying to think of alternative uses for them.

[DCB]

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.

[kevinlms]

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!

[LimboBrit]

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

[AndyID]

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?

[LimboBrit]

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. 

[AndyID]

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.

[LimboBrit]

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. 

[AndyID]

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