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# Practically converting AC voltages

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#### Scubasteve

##### New Member
Hey everyone,

I have a centertapped transformer which is generating 6.3VAC@1.3A ( X 2). I need one of the secondaries to generate necessary voltage for an array of LEDs. I need the other secondary to generate ~25-26VAC to drive a 24Vdc motor that I have.

This motor doesn't draw more then 150mA max.. I want to be able to convert this 6.3VAC 1.3A to 25-26VAC. I know I can use another transformer, but I really want to keep this design efficient. I don't want to convert it to DC and use a boost regulator, it seems a bit much for what I want. Initially, I was thinking of using a higher voltage transformer and using a switching power supply from national semiconductor to create a voltage specific to the voltage drop on my LEDs. This seemed like a good idea because some of the devices had current limiting, but when I looked at the simulation, there is a starting peak current which could blow out my 60LEDs.

I know I can use a transformer for this, but which one? I don't want to spend a lot of money. Is there a way I could wind a coil for this? I have a few ferrite rings and a lot of magnet wire. I am not sure about some of the guidelines to do this though, but if anyone has any advice, I would really appreciate it.

Thanks !,

Steve

How about rewinding the transformer ?

Remove the clamp assembly or whatever method is used for mounting the transformer, so you are left with just the core and bobbin assy.

Disassemble the ( the hardest bit!!), then detach one ned of one of the windings, and unwind it, counting the number of turns, so you know the turns per volt.

Next take some ecu, of a suitable rating( use tables to find the AWG to current size) and rewind the secondary(ies).

Viz, if you had 5 turns per volt, then for 6v=30 turns, so for 25v =125t....

Re assemble and job done.......

Rewound many a transformer, to get what I wanted...........

DO NOT ATTEMPT TO CHANGE ANYTHING ON THE PRIMARY!!!!

Above all have fun 8)

how about if you dont need much current use 2 diodes and 2 caps to double the ac voltage and another circuit like this to double it again, this was you have 4 times the voltage, but the more current you need the greater the caps..for 150mA i think that 1000uF will work fine. maybe even 470uF.....then use a btridge rectifier and you get continous at 4times the voltage. i used this to power a 12V/4W lamp from 6V a.c. transformer and it worked fine. i used 1000uF caps.

Your 6.3V@1.3A (X2) suggests a 12.6 volt secondary. As suggested in one post, a voltage doubler may be a simple solution.

Ditto the suggestion to "have fun!"

Here is a diagram that is probably familiar to many.
Bogdanfirst suggests a bridge rectifier,
for that just join the AC legs together,
and treat it as two diodes.

John

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Thanks very much!! I haven't had time to thank you guys for your help..

I am using a quadrupler from the 6.3V.. With 1000uF caps in the stages and across the output, I can acheive around 17.5Vdc@50-75mA. This is acceptable for the design. I need the other winding free, so I cannot load it in any way.

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