John,
See below;
*********** REPLY SEPARATOR ***********
On 3/22/06 at 8:52 AM John T. M. Lyles wrote:
>Back when I was designing broadcast transmitters, I used the tables
>in the old Motorola Silicon Rectifier manual for all of my DC power
>supply designs. Its the green book, mine is dated 1980.
That's a good reference.
>
>It lists transformer secondary rating in VA/Pdc as 1.23 for a single
>phase FWB and 1.75 for a center tapped full wave rectifier. PIV for
>the diodes is of course halved for the FWB also. In another chapter
>it states: "The utilization factor of the power transformer is much
>poorer with the capacitor-input system because of the higher ratio of
>peak-to-average current flowing through the rectifier diode, and
>likewise the diode is less efficiently utilized."
>
>I think this is what you mean, wiht the 1.6-1.8 X factor for
>secondary current to DC current ratio.
Actually, no. I've seen both formulas published for a full wave bridge. A full
wave center tap is lower and is about 1 to 1.2 or so if I recall. These I'm
getting from the Hammond transformer PDF and a few other websites who make
transformers and power supplies. That pdf is there at Hammonds website, but you
have to dig through their webpages to find it, or at least I did.
Is this for RMS or peak
>secondary current (charging the cap?). I didn't see half voltage taps
>on the transformer I found yesterday, it was mounted in the bottom of
>a massive Westinghouse RF generator, using some big mercury vapor
>looking rectifiers and two RF tubes which i cannot remember. Thing
>was as large as a standalone freezer chest. I have no idea what Ed
>would charge for the unit, usually too much. I only would want the
>iron and maybe some insulators.
>
>I also found another nice looking brand new transformer in a wooden
>crate, all it had marked was a single primary for 208 VAC and two
>separate secondaries marked 0 - 1600 with some taps in between. It
>was about 10 x 8 x 8 inch sized, and might have some use somewhere.
>If the secondaries were adequately insulated, they could be series
>wired for 3200 Vrms, but that might be risky.
>
>So going on what you (Will) said, the LS184 UTC transformer would not
>be adequate for a 0.6 Amp DC load, with cap input. Thats about an Amp
>of secondary current.
John, yes. A lot of folks think that whatever the DC current is, is what the
RMS primary current is. The use of those formulas is what you have to use.
They're printed in several amateur radio books, and some books on communication
engineering under their power supply or transformer sections.
>
>73
>John
>K5PRO
>
>
>
>>John,
>>
>>It's according to what type of rectifier circuit you'd use with the
>>capacitor. For a full wave bridge and capacitor input, the secondary
>>current is from 1.6 to 1.8 times the DC current. That variance I
>>don't know for sure where both came from as some formulas I've seen
>>use either. It has a lot to do with the size of capacitor of course.
>>Hammond has a downloadable pdf with these formulas in it, and I'm
>>pretty sure they use 1.6. Ohter transformer manufacturers though
>>I've seen use 1.8.
>>
>>The one you found, didn't the primary have it where you could change
>>the voltage? Most always had this because there are some places
>>using 220/240 VAC.
>>
>>Best,
>>
>>Will
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Best,
Will
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