[AMPS] Transformer Current ratings

[Michael J. Tubby B.Sc. G8TIC]

----- Original Message ----- 
From: "Bill Smith" <ko4nrbs@yahoo.com>
To: <amps@contesting.com>
Sent: Friday, December 14, 2001 6:31 PM
Subject: [AMPS] Transformer Current ratings


> 
> I have been given a large number of used transformers.
>  Haven't checked the secondary voltages yet but some
> of them are know to be 2kv or more.  I want to build a
> stable 2 amp power supply at 2 to 2.5 kv.  What would
> be the lowest transformer currenting rating I should
> settle for?
> 73,
> Bill 
> 
> =====
> Bill Smith KO4NR
> 

Do you mean 2A peak or continuous 100% duty cycle?

What recitifier and smooting configuration?  As Rich hints
if the transformers have a significant secondary resistance
(impedance) it is likely that they're intended for choke
input smoothing.

If they're are very low resistance then they're probably good
for simple capacitor smoothing. Assuming full bridge rectifer
(single output winding, four diode legs) and capacitor bank
then the rule-of-thumb Vdc = 1.414 * Vac (off load) and
Vdc = 1.2 * Vac (onload) with Idc = 0.62 * Iac is a good
place to start (assuming modest capacitors).

For my 8877 amplifier on 6m I had a transformer made which
is 2750VAC rated at 1.6A continuous. It was specified to
be low resistance and for use with full-wave capacitor input
smoothing. It'll run all day at full output without breaking a
sweat... mind you picking it up is another thing! It cost GBP
200 (about USD 290) two years ago.


Mike G8TIC/M0VHF






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