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Anonymous Poster

Internal resistance of Battery charger

04/15/2007 2:14 AM

I am calculating sort circuit current of 110VDC panels, but I don't know how to calculated internal resistance of batterry charger. Who can help me about that, or any guide about DC sort circuit calculation (the system include battery, battery charger, cable, lamp, dc moter with small power,... for a 110kV substation). Thanks very much !

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Power-User

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Location: Australia
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#1

Re: Internal resistance of Battery charger

04/15/2007 11:24 PM

I'm sorry but you're going to have to clarify your question as I can't make sense of it. I presume you mean "short" circuit current? Where does the 110kV substation fit into all this? I'm also unsure as to what your 110VDC panels are.

I'm sure you'll get plenty of help with what sounds like a basic DC circuit but we'll need to understand more about the question first.

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Power-User
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#2

Re: Internal resistance of Battery charger

04/16/2007 4:57 PM

If I read you correctly, you're looking for the current at the panel
fed by the charger in question.

The manufacturer is your best source for the fault current of the charger,
which will not change regardless of the line available current.
Simply add the short circuit current of the battery and you've got it.

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Guru
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#3

Re: Internal resistance of Battery charger

04/16/2007 10:17 PM

If you hope to know the inner resistance. thats easy!

1] measure the open circuit voltage of the set,

2] apply a resistor on the circuit and then measure again.

3] use ohm law. you get it!

this resistance is am important specific for a power. you would know it.

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Guru

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#4
In reply to #3

Re: Internal resistance of Battery charger

04/16/2007 11:01 PM

I like the approach suggested by Cnpower, but I wonder if a charger is a non-linear type of circuit, so measuring the voltage change between open-circuit and with a load resistor may be misleading. Beyond this, I am thinking that the vast majority of the short circuit current available will be from the battery bank. Cnpower's approach for determining the internal resistance of the charger will work if applied to the batteries, to determine their internal resistance. Perhaps, however, you already have this data. Remember that usually the DC short circuit rating of a circuit breaker is significantly lower than the AC rating. Good luck--JMM

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Guru
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#6
In reply to #3

Re: Internal resistance of Battery charger

04/17/2007 3:48 PM

Yes but note the power of the resisters needed. I did some basic calculations and got my fingers singed. P= V X R2 ouch-er!

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Guru

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#7
In reply to #6

Re: Internal resistance of Battery charger

04/18/2007 12:01 AM

Brainwave--

It looks like your keyboard also got a little singed. Don't you mean P=V2/R? Probably you will still have warm fingers even after you plug your numbers into this equation.

--jmm

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Guru
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#8
In reply to #7

Re: Internal resistance of Battery charger

04/19/2007 10:10 AM

Your quite right my brain must have been in standby when I made my posting. Just cross checked and found the error of my ways. It can also be expressed as W=I2XR.

Thank you for the correction, I'll hit reboot next time.

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There's them that knows and them that just thinks they know, whitch are you? Stir the pot and see what rises up. I have catalytic properties I get a reaction going.
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Member

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#5

Re: Internal resistance of Battery charger

04/17/2007 1:32 PM

S.C. calculation :Suppose it is in the cable-fault between a positive and negative :Calculate the total resistance ofthe cable length upto the fault length+bridge circuit (when currents are coming from an AC source);Otherwise if the source is purely from battery then resistance will be the internal battery res.+cable resistance+ resistance of the charger circuit.

Next you calculate the current =v/r ,must be in KA.

The S.C. may happen anywhere in the total distribution.It is not dependent on a load.

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