How to calculate Burden Resistor ??

[andybarrett1]

Hi thank you for reading.

I have the enclosed circuit using a 100Amp / 5Amp CT ... Bridge Rectified and smoothed.

After searching internet on how to calculate the Burden Resistor I would appreciate some help.

I am looking for 0-10V IP from 0-100Amp




Anybody .....????

Thank You.

[MichelJasmin]

I never used a current transformer but I suggest you place the burden resistor before the bridge.

Then you CT is 100:50 = 20:1

@100A on the primary you'll have 5 amps on the secondary, so 2ohms will give you 10VAC rms.

The bridge has a 1.4V drop you must take in account. Also, AC voltage fully rectified with a capacitor and no load will give you a peak voltage of (v * 1.4142) (1.4142 = square root 2).

So for a 10VDC max:

(10/1.4142) + 1.4 = 8.47VAC on the secondary.

8.47VAC / 5A = 1.694 ohm. Good luck to find one.

My suggestion: pick a standard value < 1.694ohm and then compute the results. Finally, use a good multimeter to caliber your system.

HTH

[andybarrett1]

Thank you for that…

2R is the answer I got to…. I also worked out the Wattage of the resistor needs to be > 50Watt (Large and Hot)

Possible temperature drift !!!!

[MichelJasmin]

Yep! Lot of power! What about shorting the secondary and measuring the current with a current sensor like this:

http://www.allegromicro.com/en/Produ...Cs/ACS712.aspx

on a breakout board:

http://www.dx.com/p/acs712-5a-curren...7#.VLRjedKG_CY

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[amgen]

if you have way to calibrate and check linearity......

[andybarrett1]

Yep! Lot of power! What about shorting the secondary and measuring the current with a current sensor like this:

http://www.allegromicro.com/en/Produ...Cs/ACS712.aspx

on a breakout board:

http://www.dx.com/p/acs712-5a-curren...7#.VLRjedKG_CY

[Board Admin: I'm sorry for the ad , I'm sorry! I'm sorry!]

I like this.....

Also a 30Amp Version.... Might not need a CT !!!

Thank you

[andybarrett1]

Thank you Amgen

Nice Idea.... but pot Wattage needs to be decent size. (More power) ?

[amgen]

ok check these..... http://amploc.com/

[andybarrett1]

Thank you

The sensors all ready exist.. I am attempting to use the output for my purpose.

But will prob look at those in future.

Thank you again

[amgen]

From my experience working with CT's, putting a higher value resister across ct secondary will lower the secondary current by some factor but the voltage still has some relation to the primary current...... that's why a 100 ohm or 1000 ohm resistor will not create that much heat. My guess is that a 100 ohm load resister will probably drop the secondary current to less than 1 amp with 100 amp thru CT.

don