Thanks that sounds like an excellent idea, I'll have to try it next
time. Do you have any tricks on how to achieve neat side by side turns?
73 John
On 17/09/2011 00:19, Manfred Mornhinweg wrote:
> Hi John,
>
>> Thanks, for your excellent review of transformer design. Coming down to
>> a more practical problem that has bugged me in the past when I've tried
>> to rewind the secondary of a transformer is how to deal with the last
>> two laminations.
> A good question! I used to have that same problem, until I found the
> solution! ;-)
>
>> It doesn't seem to matter
>> how much you clean up the laminations the penultimate one usually goes
>> in with a bit of a struggle with the aid of a blunt instrument but then
>> the last one ends up bent and useless.
> Cleaning any varnish off the laminations is the first step, but you have
> that right. And here comes the trick:
>
> When you assemble a core, you normally put in the E's from alternate
> sides. That's fine, but next time you assemble a core, ocassionally put
> a PAIR of E's in from THE SAME side, that is two neighboring laminations
> going in from the same side. Do this a few times, so that you end up
> with enough such pairs distributed throughout the height of the stack.
> Now, when you are reaching the end, and it starts becoming hard
> inserting the last E's, insert each of the remaining ones BETWEEN two
> E's that point the same way. These two E's will guide the third one, so
> that you can get it in without applying so much force that you bend it!
> I usually push them in using a block of wood between the lamination and
> my hands.
> Inserting these last laminations at one end of the stack, where they
> chafe against the bobbin, is hopeless, but between two E's they will
> slide in!
>
> So you end up with a few groups of three neighboring E-s looking to the
> same side, but that's not a big disadvantage. In any case it's better
> than leaving some laminations out.
>
> When you insert the I's after that, of course you need to look where you
> need two or three I's together.
>
>> So far the transformer I've done this with seem to work OK despite
>> missing one lamination
> Yes, usually it's not too terrible to end up with one or two fewer
> laminations. It just eats away a little of the saturation headroom. The
> worst problem actually is that the stack will end up too loose inside
> the bobbin, and might vibrate, causing audible hum. So it's always good
> to get those last laminations in!
>
> Manfred.
>
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> http://ludens.cl
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