Electronics > Beginners

Transformer question

<< < (5/6) > >>

xavier60:
The "V (Avg) D.C. = 0.90 X Sec. V A.C." isn't really a mistake.
It is stating that full wave rectified AC voltage averages 0.9 x RMS voltage.
It isn't referring to the capacitor voltage at all, so it's just irrelevant to the  FULL WAVE BRIDGE Capacitor Input Load. And misleading.
 

Benta:

--- Quote from: ArthurDent on February 03, 2019, 02:36:13 am ---So far you’ve questioned Triad and Hammond (who have been making transformers for ages) about their transformer application knowledge. Perhaps reading other explanations about reducing transformer ratings for use with different rectifier setups might help you understand. The ratios may vary depending on the transformer design used but the principles are the same. 
https://www.powervolt.com/how-to-determine-page-25
https://www.nutsvolts.com/questions-and-answers/transformer-ratings

--- End quote ---

Apparently you completely missed the "Resistive Load" part. The transformer is specified for resistive load (for complex loads you need reduction factors, of course).
Please explain to me why voltage and current need to be multiplied by 0.9 when inserting a rectifier bridge between transformer and resistive load.

soldar:
Maybe I did not explain it well. Yes, we have all understood by now that in a sine signal RMS value is 0.707 of peak and average value is .637 of peak and therefore average is 0.9 of RMS. It has been explained, understood and accepted by all (I think).

My point is that, further to that, most uses are for rectified and capacitor-filtered power and many people do not understand that a transformer specified as 10 A secondary, that means 10 A RMS, 9 A average, into a pure resistive load but much less than that through a rectifier bridge and capacitor. Many people seem to think that if they need 10 A dc out of the unregulated power supply all they need to order is a "10 A" transformer.

Benta:
Soldar, we understand perfectly.
But really, no one uses average for anything at all, it's a useless measure.
If you want to calculate transformer power loss, RMS is the variable, and yes, with capacitive storage after the rectifier, you need to take crest factor into account, which is considerable when calculating power dissipation in the transformer.

That still doesn't explain why Hammond uses a 0.90 factor for a resistive load.
I'm still waiting for an explanation from Hammond or ArthurDent.

soldar:
Well, I can't say as I have not seen the original or the context. It could just be a plain mistake and I wouldn't give it much importance. Mistakes creep in in any work with more than a few pages. It is inevitable. I go over anything I write several times and later I still find mistakes. It happens in the best regulated families.

Some fifteen years ago I downloaded a document from Texas Instruments and it had so many mistakes I felt compelled to email the author who quickly replied with a tirade telling me I got it for free and had no right to complain. I emailed TI and they quickly replied with an apology and I guess they told the author of the document to STFU because that was the end of it.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod