[NSRCA-discussion] Internal battery impedance

[Ron Van Putte]

I am going to forward this to the LiPo Doc's inventor and ask for his  
answer, but I suspect it's to see what happens to the cells' internal  
resistance with varying loads.

What say you Monk?  Please send a response back to me so I can post  
it on the NSRCA Discussion List.

Ron Van Putte

On Mar 16, 2008, at 7:42 PM, Lance Van Nostrand wrote:

> Thanks for all the posts. I understand the piece of the puzzle I  
> was missing.  Actually pieces.  bob's point is important but the  
> basic approach is to start with a resistor of a known resistance  
> that will give you the current where you want internal impedance  
> measured.  Let's say I have a fresh 2S pack measuring 8v unloaded.   
> I buy a heavy duty resistor of 1 ohm that actually measures exactly  
> 1 ohm (for example only).  Under load it measures 7.2v across the  
> resistor and is therefore pulling 7.2A (I = V/R)
> The voltage drop is due to internal resistance so 7.2a = 8v / (1 +  
> internal impedance)
> internal impedance = .11 ohm
>
> Is the idea of measuring at 1 ohm and 10 ohm a way to find an  
> average number?  If so, I think just finding a resistor that is in  
> the neighborhood of your worst case situation may actually be more  
> representative.
>
> --Lance
>
> ----- Original Message -----
> From: Bob Richards
> To: NSRCA Mailing List
> Sent: Sunday, March 16, 2008 6:54 PM
> Subject: Re: [NSRCA-discussion] Internal battery impedance
>
> The resistor does not really need to be a precision resistor, you  
> just need to know precisely what the resistance is. :-)  And, if  
> you are comparing or matching cells, the measurement only needs to  
> be relative and the accuracy may not important.
>
> I do agree that the measurement will probably not be linear, IOW  
> the cell impedance may vary with large changes in current. If I  
> normally run 30 amps, I would want to make a measurement at 30 amps  
> and probably 25 and 35 amps as well, comparing the differences in  
> voltage at the three currents. This would be more meaningful to me  
> than comparing the unloaded voltage with the voltage at 1 amp.
>
> Just M2CW.
>
> Bob R.
>
>
>
>
>
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