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Forum Index : Electronics : transformer widing ration.

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stockleys
Regular Member

Joined: 21/06/2019
Location: United Kingdom
Posts: 54

Posted: 09:55pm 11 Apr 2022

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hi all.

in the process os rewinding the primary on an aerosharp 3kw transformer.
i am building a 24v system.

from what i have read on this sight, i believe i should be looking for a 13-14v primary.
but i was thinking, as i am using lifepo4 batteries and their cutoff voltage is 21v.

would a 13v primary with a 21v source cause clipping? and should i reduce the primary to 11v or 12v to account for the low cut off voltage?

would a 12v primary still be ok with a full charge voltage of 29v?

many thanks

Godoh
Guru

Joined: 26/09/2020
Location: Australia
Posts: 458

Posted: 06:49am 12 Apr 2022

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Hello stockleys, it will depend on what you are using as a powerboard.
I have a couple of home built 24 volt inverters that use powerjack transformers that I changed the primaries on.
I am pretty sure I made mine for 13 volts. Powerjack seem to design them for around 16 for some strange reason.
So I had to use a couple of turns less than they did.
I used 8010 based Sunyima boards and the output voltage is adjustable on them.
So it seems that you just need a high enough output voltage to prevent clipping when the batteries voltage falls off.
If you go for 11 or 12 volt primary and it doesn't work then it is not too hard to add a turn or two.
Pete

Haxby

Guru

Joined: 07/07/2008
Location: Australia
Posts: 423

Posted: 07:17am 12 Apr 2022

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21vdc as a minimum, chopped up will give you 14.85v RMS as a maximum.

Vrms=Vpeak/?2

But there will be losses in the resistance of the winding and in the MOSFETs. So I would wind for maybe 2v less than this. To minimise this loss, you will want to wind a good quality well magnetically coupled, well regulated transformer.

So maybe wind for 13v? You can always add a turn or subtract a turn during your final stages of testing.

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