[Amps] Transformer guess?

[Ian White GM3SEK]

Manfred Mornhinweg wrote:
>Vic,
>
>> What I want to know is how much DC I can draw from the HV winding
>> with a full-wave CT circuit.
>
>A simple rule for small transformers is that they are designed to have a
>voltage drop of close to 5% in each winding (10% total). This figure can
>vary a little, but not very much. At least it gives a reasonably close
>idea. So, take out your multimeter, measure the resistance of the
>windings, and apply Ohm's Law, using 5% of each winding's voltage. That
>will give you the approximate current rating of each winding.
>
>It might be good to measure both the primary and secondary windings,
>calculate the current for each, and see how well the two power ratings
>match. They should be very close, of course. If there is a large
>difference, you either have made a mistake, or the transformer is poorly
>designed!
>
Or it's a multi-winding transformer, which is exactly the case here.

Also, in windings that are rated for a very low current, the 
manufacturer may use over-sized wire to help avoid breakages, so the 
real-life current rating may be higher than the value specified.

If Vic is not proposing to use the heater/filament windings, he may be 
able to increase the current in the 380V winding without overheating.

As Carl says, the only valid test is to try it on load (and I think I 
know what the load may be :-)   Use the actual rectifiers and smoothing 
capacitors, with dummy load resistors of the correct calculated value.



-- 

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek