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posity
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Join Date: Oct 2013
Posts: 12

Estimation of Rectifier Capacity

10/31/2013 8:43 PM

Above is our simplified battery charger drawing.

Battery charger output rating is DC 125V, 1600A, input voltage is AC 480V, 3ph.

For selecting incoming CB, how can I estimate the charger capacity.

Previously I thought 125V x 1600A => 200kVA.

But in the manufacturer's drawing, is was almost 300kVA.

Anyone who could advise me about above and what I did wrong?
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lyn
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#1

Re: Estimation of Rectifier Capacity

10/31/2013 8:58 PM

Do some research on your own!

Power factor - Wikipedia, the free encyclopedia

Capacitor Smoothing Circuits & Calculations :: Radio-Electronics.Com
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Tornado
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#2

Re: Estimation of Rectifier Capacity

10/31/2013 9:30 PM

Output < input, for one thing.

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posity
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#3

Re: Estimation of Rectifier Capacity

10/31/2013 9:43 PM

Lyn, Tornado, I do appreciate your help.

Of course I know PF, Efficiency.

However, this doesn't seems to do with PF, only with Eff.

Cuz, Apparent Power S = U x I

(P = U x I x PF)

In conclusion, 300kVA(U) = 125V(U) x 1600A(I) / Eff(66.6%)

We can estimate the efficiency of Rectifier is 66.6%??

Then anyone knows typical recitifier efficiency for estimation of rectifier capacity?
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SolarEagle
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#4
In reply to #3

Re: Estimation of Rectifier Capacity

10/31/2013 10:17 PM

Found this....

http://www.brighthubengineering.com/consumer-appliances-electronics/96645-efficiency-of-ac-rectifiers/

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posity
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#5
In reply to #4

Re: Estimation of Rectifier Capacity

10/31/2013 10:36 PM

Thanks a lot for the source.

This and following helped a lot.

http://www.controlledpwr.com/whitepapers/input_calculations.pdf
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dvmdsc
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#9
In reply to #3

Re: Estimation of Rectifier Capacity

11/01/2013 2:14 AM

66% for rectifier is VERY low, how do you get to that thought?

You have a 125 volts system and lose in the worst case 1.3 volts over the bridge.

Is the system switched? With PWM? ( a good charger should run more than 88%)

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dvmdsc
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#6

Re: Estimation of Rectifier Capacity

11/01/2013 12:15 AM

Your drawing is too simplified. I see no 3 phase bridge nor 3 phase feed.

P= U X I X 1.73 (√3)

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posity
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#7
In reply to #6

Re: Estimation of Rectifier Capacity

11/01/2013 1:56 AM

Becuz, this is simplified Single Line Diagram.

But we can see incomer CB is 3P and CT is also 3.

More over S = U X I X 1.73 (√3)

P = U X I X 1.73 (√3) x cosφ (PF)
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dvmdsc
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#8
In reply to #7

Re: Estimation of Rectifier Capacity

11/01/2013 2:04 AM

Cos φ is indeed part of the equation. No info given about type of charger.

Most transformer chargers have no bad cos φ. Only chopped ones can surprise you.

At the end also your ripple counts. How big is that?

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posity
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#10
In reply to #8

Re: Estimation of Rectifier Capacity

11/01/2013 2:26 AM

Here I send you detailed drawing

(Uploaded picture getting blurred all the time, any solution? )
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vsar
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#12
In reply to #10

Re: Estimation of Rectifier Capacity

11/02/2013 8:29 AM

In your drawing, the transformer rating is rated at 300KVA, why are you using that as your basis of the rectifier's capacity? The transformer has its own losses to be considered.

Is it not better and will be more accurate if you use the rated specifications of the rectifier used in the unit as the basis for its capacity?

The KVA rating is only good and only applies to the transformer only. After that device, the power capacity will be in watts, which is quite different..

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beentheredonethat
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#11

Re: Estimation of Rectifier Capacity

11/02/2013 2:03 AM

Allow for inrush current to the transformers.
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beentheredonethat (1); dvmdsc (3); lyn (1); posity (4); SolarEagle (1); Tornado (1); vsar (1)

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