Wall charger transformer leads

Thread Starter

OrionV

Joined Jul 3, 2016
22
Hello. I wanted to use a wall charger transformer to step up some voltage but it has 7 leads on it - 3 on one side and 4 on the other. I have no idea how to connect it, if anyone can tell me which lead does what that would be great.
Thanks.
 

Hypatia's Protege

Joined Mar 1, 2015
3,226
It's from a regular, cheap mobile phone charger. A tiny tranformer, kind of like this one:
http://sc01.alicdn.com/kf/HTB13JztH...transformer-tesla-transformer.jpg_200x200.jpg
The image appears to be that of a ferrite core transformer of the type commonly incorporated in SMPS units --- Such transformers are generally comprised of a primary, an (often tapped) secondary and, occasionally, a feedback/auxiliary winding... Please perform a continuity 'scan' of the leads such that we may be of further assistance.

Best regards
HP:)
 
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Hypatia's Protege

Joined Mar 1, 2015
3,226
Thank you for the answer but I don't know how to do that. I'm not even sure I know what it means...
I apologize for my over-cursory treatment of the subject in my first post:oops::(...

You may perform a continuity scan via use of a resistance indicator (e.g. A DMM set for resistance ['Ohms'] measurement) to measure and record inter-lead resistances...

For instance, you might arbitrarily number the leads 1 through 7 then connect one test prod to lead #1 and with the other measure and record the resistance to each of 2,3,4,5,6,7 -- Then move on to lead #2 and record the resistances to each of 3,4,5,6,7 and so on until all (21) measurements have been recorded:cool:

Very best regards
HP:)
 
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MrAl

Joined Jun 17, 2014
8,123
It's from a regular, cheap mobile phone charger. A tiny tranformer, kind of like this one:
http://sc01.alicdn.com/kf/HTB13JztH...transformer-tesla-transformer.jpg_200x200.jpg
Hi,

I dont think you can use that like an ordinary wall wart transformer. That looks like it is from a switching regulated wall wart, which use higher frequency transformers. The only way you could use that is if you knew the specs of that transformer or just needed some light current perhaps.
In any case, you have to use a higher frequency switching signal to power it, not directly from the line. I dont know if you want to do that or not.

Back when they made regular wall warts they would consist of just a 60Hz line transformer and rectifier diodes and a filter cap. These days they make regulated wall warts that use a special switching IC chip that pulses the primary of the transformer and also regulates the output to stay within a certain percentage of the target voltage, such as 5v. These newer kinds have completely different kinds of transformers so they have to be used in a switching circuit.
 

Thread Starter

OrionV

Joined Jul 3, 2016
22
That is the result from the "continuity scan", I think that between 6th and 7th lead is the secondary, but I'm not sure about the primary. Any thoughts?
Thanks.
 

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Thread Starter

OrionV

Joined Jul 3, 2016
22
Hi,

I dont think you can use that like an ordinary wall wart transformer. That looks like it is from a switching regulated wall wart, which use higher frequency transformers. The only way you could use that is if you knew the specs of that transformer or just needed some light current perhaps.
In any case, you have to use a higher frequency switching signal to power it, not directly from the line. I dont know if you want to do that or not.

Back when they made regular wall warts they would consist of just a 60Hz line transformer and rectifier diodes and a filter cap. These days they make regulated wall warts that use a special switching IC chip that pulses the primary of the transformer and also regulates the output to stay within a certain percentage of the target voltage, such as 5v. These newer kinds have completely different kinds of transformers so they have to be used in a switching circuit.
I'm not sure if I undertood you correctly but I'm using only the transformer for stepping up voltage. The higher frequency required for that to work doesn't bother me, I'm trying to use a 555 oscillator with a 9v battery, so changing some specs in the schematic should increase the frequency.
Thank you for your answer.
 

Hypatia's Protege

Joined Mar 1, 2015
3,226
That is the result from the "continuity scan", I think that between 6th and 7th lead is the secondary, but I'm not sure about the primary. Any thoughts?
Thanks.
The 'equidistance' of the tapped winding (i.e. 1,2,3) is curious:confused: --- I can but assume such owes to the indicator's precision limitations -- What does the instrument show when the prods are 'shorted' together?

Please give me a moment that I might compose a diagram:)

Best regards
HP
 
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Hypatia's Protege

Joined Mar 1, 2015
3,226
I'm not sure if I undertood you correctly but I'm using only the transformer for stepping up voltage.
In that case 6,7 is a good choice for the secondary - bear in mind, however, that higher resistance does not necessarily = greater number of turns (though, in this case, I feel same is a safe assumption).

You may use the tapped winding as the primary in a 'half bridge' arrangement -- however, owing to the very low resistances, the configuration of said winding must be determined by other means (e.g. an LCR indicator or merely exciting the transformer with ≈ 40kHz while measuring the 'drops')

I'm off to work up the diagram -- Pleas stand by:D
 

Hypatia's Protege

Joined Mar 1, 2015
3,226
Here's the (putative) schematic of the transformer -- Inductance values would allow calculation of turns/impedance ratios, etc... -- That said, I feel this should supply a good starting point -- Should you wish to use a single-ended driver, I suggest 4,5 as the primary (for its higher resistance [and, presumably, impedance] with respect to 1,2,3) -- On the other hand, 1,2,3, once 'mapped' would likely lend itself to more efficient design (used as the primary)...

It may behoove you to consider 40kHz the minimum frequency of operation...

Best regards
HP:)

xfmr.jpg
 

Thread Starter

OrionV

Joined Jul 3, 2016
22
The 'equidistance' of the tapped winding (i.e. 1,2,3) is curious:confused: --- I can but assume such owes to the indicator's precision limitations -- What does the instrument show when the prods are 'shorted' together?

Please give me a moment that I might compose a diagram:)

Best regards
HP
It reads 0.4 ohms. It isn't the most expensive and high quality multimeter on the market :D . As for a "half-bridge arrangement" I assume that means using only the first two leads instead of the first and second?
 

Thread Starter

OrionV

Joined Jul 3, 2016
22
Stated plainly it means applying power to the center-tap and alternately switching the 'outer ends' to ground:cool:

Best regards
HP:)
Okay, sorry to bother you again :D but just a small final question: wouldn't it be even more efficient if I just connect 5 and 6 together and use 4 through 7 as a single coil for greater inductance?
 

Hypatia's Protege

Joined Mar 1, 2015
3,226
wouldn't it be even more efficient if I just connect 5 and 6 together and use 4 through 7 as a single coil for greater inductance?
First off - Please don't assume the phasing is shown correctly! - Such was not determined via resistance testing! --- But to the 'gist' of your question, you could do that (assuming you will be using 1,2,3 as the primary) howbeit it would offer only a modest increase in secondary EMF - whether or not such would be more efficient will depend upon the impedance of the load...

Please feel free to ask should you have further questions or require clarification:)

Best regards
HP:cool:
 

Thread Starter

OrionV

Joined Jul 3, 2016
22
First off - Please don't assume the phasing is shown correctly! - Such was not determined via resistance testing! --- But to the 'gist' of your question, you could do that (assuming you will be using 1,2,3 as the primary) howbeit it would offer only a modest increase in secondary EMF - whether or not such would be more efficient will depend upon the impedance of the load...

Please feel free to ask should you have further questions or require clarification:)

Best regards
HP:cool:
Thank you very much for your help, you are awesome. Have a great day! :)
 

MrAl

Joined Jun 17, 2014
8,123
I'm not sure if I undertood you correctly but I'm using only the transformer for stepping up voltage. The higher frequency required for that to work doesn't bother me, I'm trying to use a 555 oscillator with a 9v battery, so changing some specs in the schematic should increase the frequency.
Thank you for your answer.
Hi,

That sounds good then. Probably 10kHz or higher should do it.
 
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