help with transformer secondary voltage reading

Status
Not open for further replies.
Jump to Latest
J

jarthel

Member
Joined 2002
#1
with transformer secondaries, is the voltage reading higher than rated voltage when there is no load?

I measured voltage reading a 12V transformer is around 14.7V without any load. when I connected it to the power supply circuit (linear regulated and again without any load after the regulator), the voltage reading on the 1st cap is 17+V.

thank you for the help. 🙂
 
#2
Hi,

Yes, that is normal. For a true reading, load the secondary down with a power resistor for the rated load. So, if the transformer is rated 2 amps, load the secondary with a 25W, 6 ohm resistor and remeasure.
 
#3
Hi,
the difference between loaded voltage and open circuit voltage is specified as the regulation of the transformer.

Small transformers can give over 30% high on open circuit measurement.
Larger transformers get down to near 4%.

Your one measures out at 18%, if your input voltage was set accurately.
 
#4
The "why" portion...

Both the primary and secondary windings have resistance... so the voltage drops (or appears to) as the current increases. Some of the voltage is being "burned" inside the transformer... half the reason they get warm. The tranny people take this into account... all very normal... Andrew's numbers, as always, are quite correct.

🙂

I am designing a transformer today... hate it, hate it, hate it!

😡
 
#7
Thanks Geek,

But no... I am doing a 60 Hz power transformer. I am trying to learn McLyman's method... which is supoosed to be simple and direct (BS).

😡

I know how to do it the hard way... iterate, iterate, iterate. I am not having such good success.

😡 😡 😡
 
Status
Not open for further replies.
Top Bottom