[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Wiring a Transformer.....Help!!



Original poster: "BunnyKiller by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bigfoo39-at-telocity-dot-com>

Tesla list wrote:

>Original poster: "Chris by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<chrislj-at-earthlink-dot-net>
>
>
>Let s say I have a suitable sized core to wind a transformer on. If I wanted a
>5kw transformer
>
>with a 100:1 winding ratio and an output of 15000v. How many primary turns
>would it need to
>
>be able to handle that amount of power? Is there a type of formula for
figuring
>out how much copper needs to go into the primary? How do you know when you
have
>enough turns?
>
> 
>
>Chris
>


Hi Chris...

to start with ...  a 1:100 ratio will need 155VAC input to reach 15KV 
out (you will need a few extra volts to cover core losses and wire 
resistance).  to use 120 VAC to achieve 15KV will require around 1:125 
ratio.

to handle 5KW worth of power , the primary winding will have to be able 
to handle that amount of power ( heat disapation factor) , this leads to 
the decision on choosing wire gage, insulation type and winding 
technique( close wind or air gap wind).

there is also the choice of voltage supply ,  120VAC or 240 VAC ...  the 
240 VAC will allow you to use a "lower" amperage factor in design.   
example ...   if you use 120VAC for 5KW unit , the primary will pull 
approximately 40 amps when the secondary is fully loaded for that power 
setting. In a 240 V senario, the primary will pull approximately 21 A.

Core size is another thing that has to be considered, too small of a 
core and saturation will occur ( which leads to a runaway current 
condition )   A general rule of thumb for core size ( center leg sqr " 
area measure) is about 3-5 amps capacity per sqr inch of area to keep 
saturation out of the equation.  Core window size will limit the amount 
of wire that you can put onto the transformer ( thus limiting  the power 
desired or output voltage ) .

soooo...    lets do a sample core...   240 VAC in  15KV out   -at- 5KW   
...  full amp draw will be 21 A .   primary wire could be #8 with THHN 
insulation ( this could be over kill... #10 could be substituted but 
heating may become an issue and insulation may breakdown)   need to keep 
the turn to turn voltage near 1-2vac ( lets do 2 v) ...  so we will need 
125 ( minimal) primary winds.   for 15KV the secondary will need a 
minimum of 1:63 ratio.  Sooo...   125 X 63  = 7875 turns on the 
secondary  ( or you can use half as many turns on 2 core legs and series 
the windings) .   Ok..  now for core size ( center leg which the primary 
is mounted on) ...  20A current yeilds about a minimum core size of  4 
sqr inches ...  7 sqr inches would be better.

Wire size for secondary...    15KV out at 5KW = approximately .3 amps   
a #22 or 24 wire will work here just fine.. probably could go even 
smaller ( 26-28) ...

things to consider when winding your own HV trannie...

insulation factor on the secondary side..   wrap core with insulation. 
either saturate the secondary side with a liquid insulator ( glyptol 
etc) or use a film wrap about every 5 layers ( minimum)   the wires 
coming "off" of the secondary side will be seeing the full voltage, sooo 
 an additional sleeve type of insulation is advised. Keep the secondary 
wire away from the primary ( to decrease arc over).


just some insight in core winding....

Scot D