[NSRCA-discussion] Internal battery impedance

Gordon Anderson GAA at owt.com
Sat Mar 15 20:41:52 AKDT 2008 

Agreed, in fact if you have a precision 1 ohm resistor (with high enough power
rating) the cell resistance is very easy to determine, its equal to ((Unloaded
cell voltage)/(Loaded cell voltage) - 1).

--Gordon 

-----Original Message-----
From: nsrca-discussion-bounces at lists.f3a.us
[mailto:nsrca-discussion-bounces at lists.f3a.us] On Behalf Of Ron Van Putte
Sent: Saturday, March 15, 2008 9:26 PM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] Internal battery impedance

That's true, you do need to know the current.  I should have said that you don't
need to measure it.  Most people who have an inexpensive digital multimeter have
one that measures voltage, not current.  Using a precision resistor allows the
determination of the current with an inexpensive multimeter.

Ron Van Putte

On Mar 15, 2008, at 11:17 PM, Gordon Anderson wrote:

> In general you do need to know the current. The fact is measuring 
> voltage across know resistance is measuring current. i.e. 1 Volt 
> across a 1 ohm resistor is 1 amp. So using known resistance and making 
> voltage measurements will allow the measurement.
>
> --Gordon
>
> -----Original Message-----
> From: nsrca-discussion-bounces at lists.f3a.us
> [mailto:nsrca-discussion-bounces at lists.f3a.us] On Behalf Of Ron Van 
> Putte
> Sent: Saturday, March 15, 2008 9:06 PM
> To: NSRCA Mailing List
> Subject: Re: [NSRCA-discussion] Internal battery impedance
>
> You don't need to know the current.  Knowing voltage and resistance is 
> enough.
> It is very simple and just as you described,  It does require 
> precision resistors.
>
> Ron Van Putte
>
>
> On Mar 15, 2008, at 10:44 PM, Lance Van Nostrand wrote:
>
>> This sounds like a way to do each cell, but don't you need the 
>> current?  If one were to measure the voltage across the battery and 
>> the current through any resistor whose Ohmage is known then V=I * (R 
>> + internal resistance).  or is this just too naive.
>> --Lance
>>
>> ----- Original Message -----
>> From: "Ron Van Putte" <vanputte at cox.net>
>> To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
>> Sent: Saturday, March 15, 2008 8:40 AM
>> Subject: Re: [NSRCA-discussion] Internal battery impedance
>>
>>
>>> I'd forgotten Earl had the plans.
>>>
>>> The Lipo Doc is a very simple device that is mostly a rotary switch 
>>> and a couple of precision resistors.  You measure voltage on the 
>>> cells of a lithium polymer battery in an unloaded condition, with a 
>>> 10 ohm load and a 1 ohm load.  The results are put in a spreadsheet 
>>> and the internal resistance of each cell is determined.
>>>
>>> Ron Van Putte
>>>
>>> On Mar 15, 2008, at 5:25 AM, Earl Haury wrote:
>>>
>>>> Lance
>>>>
>>>> I use the "LiPo Doc" built from plans I got from RVP.
>>>>
>>>> Earl
>>>> ----- Original Message -----
>>>> From: "Lance Van Nostrand" <patterndude at tx.rr.com>
>>>> To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
>>>> Sent: Friday, March 14, 2008 11:23 PM
>>>> Subject: [NSRCA-discussion] Internal battery impedance
>>>>
>>>>
>>>>> Earl,
>>>>> How do you measure the battery impedance?
>>>>> --Lance
>>>>>
>>>>> ----- Original Message -----
>>>>> From: "Earl Haury" <ejhaury at comcast.net>
>>>>> To: <chad at f3acanada.org>; "NSRCA Mailing List"
>>>>> <nsrca-discussion at lists.nsrca.org>
>>>>> Sent: Friday, March 14, 2008 10:10 AM
>>>>> Subject: Re: [NSRCA-discussion] Batteries
>>>>>
>>>>>
>>>>>> Chad, you have a point, however it's important to factor in that 
>>>>>> the 1P packs are also generally higher C rating. My view when 
>>>>>> considering batteries initially was that higher cell count 
>>>>>> provided more failure opportunities, both as individual cell 
>>>>>> failure and connections. I've disassembled a number of  "failed", 
>>>>>> or no longer pattern suitable packs, and measured individual cell 
>>>>>> characteristics.
>>>>>>
>>>>>> Generally, the cells in a lower C pack tend demonstrate an 
>>>>>> increase in impedance, resulting in lower voltage output for a 
>>>>>> given current draw over their lifespan until no longer "pattern 
>>>>>> viable". During this time capacity diminishes - but most cells 
>>>>>> with high impedance will still retain
>>>>>> 80+% of
>>>>>> their original capacity. Even though these things generate more 
>>>>>> heat than the higher C packs - they tend to handle abuse (as 
>>>>>> you've found) partly because of the retained capacity and partly 
>>>>>> because of "performance limiting" impedance. Post flight 
>>>>>> imbalance doesn't change too much as these packs age - suggesting 
>>>>>> a similar "aging" of the individual cells.
>>>>>>
>>>>>> Conversely, the high C packs demonstrate very low impedance 
>>>>>> initially and that appears to be retained throughout their life.
>>>>>> However, the cell capacity appears to drop pretty early and 
>>>>>> continue to do so over the pack life. I've measured some of these 
>>>>>> with an average capacity loss of 40% after 50 flights - that 
>>>>>> means a 5000 mAh pack is now a 3000 mAh pack.
>>>>>> Even
>>>>>> worse -
>>>>>> there is often a good deal of variance from cell to cell. Their 
>>>>>> low impedance will provide little warning (as loss of power) 
>>>>>> until a cell is injured, real easy to do if you try to take 3500 
>>>>>> mAh from the now 3000 pack.
>>>>>> Often one will notice the post flight imbalance increasing as 
>>>>>> these packs age and it will be greater at higher depths of 
>>>>>> discharge - a sure sign some cells are getting weak. OTOH - for 
>>>>>> blazing power the high C packs are the way to go - but there's a 
>>>>>> price to pay in life, weight, & $$.
>>>>>>
>>>>>> These observations have led me to surmise that a pack with a high 
>>>>>> enough C rating to minimize impedance losses (and accompanying
>>>>>> heat) and a low enough C rating to allow good capacity retention 
>>>>>> should provide the best value for pattern. I have no idea just 
>>>>>> what construction parameters / chemistry defines these 
>>>>>> characteristics. I chose to try the FlightPower F3A packs because 
>>>>>> they are mid-C rating and 5350 mAh capacity. So far they provide 
>>>>>> good power and generate no more heat than the high C packs I've 
>>>>>> used. I expect that the extra capacity (above 5000) offers a 
>>>>>> little buffer if there is a capacity decline over their life. I 
>>>>>> see little balancer activity with these packs regardless of depth 
>>>>>> of discharge (say 3000 mAh vs 4000 +) so far, time will tell - 
>>>>>> we're all still learning.
>>>>>>
>>>>>> Earl
>>>>>>
>>>>>> Team FlightPower
>>>>>>
>>>>>>
>>>>>> ----- Original Message -----
>>>>>> From: "Chad Northeast" <chad at f3acanada.org>
>>>>>> To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
>>>>>> Sent: Friday, March 14, 2008 8:22 AM
>>>>>> Subject: Re: [NSRCA-discussion] Batteries
>>>>>>
>>>>>>
>>>>>>> I think a huge part of the 5300 Prolites ability to deliver 
>>>>>>> under extreme abuse (I should know! :) ) is in large part due to 
>>>>>>> a 4p config rather than 1p as in the current packs.  In a 1p 
>>>>>>> when that cell gets weak its over, in a 4p when a cell gets weak 
>>>>>>> the other
>>>>>>> 3 in the 4p can help it along for quite a while before they all 
>>>>>>> get weak.
>>>>>>>
>>>>>>> I am really convinced that a move to 1p config packs has brought 
>>>>>>> with it lower useful cycle life.  I feel you need to be a lot 
>>>>>>> more cautious with the 1p packs than the 4p's, or they will not 
>>>>>>> last you very long :)
>>>>>>>
>>>>>>> Chad
>>>>>>>
>>>>>>> mike mueller wrote:
>>>>>>>>  Chris Moon and I have bought the new TrueRC 5000 packs. He has 
>>>>>>>> been testing them for the last 2 months. They seem as strong if 
>>>>>>>> not stronger than his FP 5350 pack. The cost is only $110 a 5S 
>>>>>>>> pack. I've bought 4 packs and I'm hoping that they are as good 
>>>>>>>> as initial testing has shown. I also have 2 brand new TP V2 
>>>>>>>> Extreme 10S 5000 packs. All the packs at the 10S configuration 
>>>>>>>> weigh in around 42oz's with all the connectors.
>>>>>>>>  The True RC packs have a lower C rating but this may be a good 
>>>>>>>> thing.
>>>>>>>> The higher C ratings seem to come at the cost of lower pack 
>>>>>>>> life. Look at the TP Pro lite's many have exceeded the 200 
>>>>>>>> cycle barrier and still have a decent pack. The TP Extreme's 
>>>>>>>> V1's were dying in 50 flights and I have yet to see much better 
>>>>>>>> than a hundred flights from the FP's. From my observation the 
>>>>>>>> older TP Prolites deliver plenty of power for our setups. So I 
>>>>>>>> think the TrueRC offerings are going to do the trick. Dan from 
>>>>>>>> True is claiming over 200 cycles on them. I hope that I can get 
>>>>>>>> 100. At the $'s he's getting it will be a huge bargain.
>>>>>>>> Mike Mueller
>>>>>>>>
>>>>>>>>     The link is www.flightpowerusa.com <http:// 
>>>>>>>> www.flightpowerusa.com/>
>>>>>>>>
>>>>>>>>     I need to buy some packs myself.  Anybody know if they will 
>>>>>>>> be at
>>>>>>>>     Toledo?
>>>>>>>>
>>>>>>>>     Bob Kane
>>>>>>>>     getterflash at yahoo.com
>>>>>>>>
>>>>>>>>
>>>>>>>>     ----- Original Message ----
>>>>>>>>     From: Verne Koester <verne at twmi.rr.com>
>>>>>>>>     To: NSRCA Mailing List <nsrca-discussion at lists.nsrca.org>
>>>>>>>>     Sent: Thursday, March 13, 2008 6:58:32 PM
>>>>>>>>     Subject: Re: [NSRCA-discussion] Batteries
>>>>>>>>
>>>>>>>>     Hi George,
>>>>>>>>     I'm in the same situation and have decided to go with the 
>>>>>>>> FlightPower
>>>>>>>>     5350's. Even when the 5300's were fresh, I occasionally 
>>>>>>>> felt like
>>>>>>>>     I could
>>>>>>>>     use a little more punch, particularly on humid or windy 
>>>>>>>> days. I've
>>>>>>>>     competed
>>>>>>>>     with a number of guys that had both the TP 5300's and FP 
>>>>>>>> 5350's
>>>>>>>>     who would
>>>>>>>>     switch to the 5350's when they needed the extra power. My 
>>>>>>>> plan is
>>>>>>>>     to use the
>>>>>>>>     FP 5350's and change props for different conditions.
>>>>>>>> Nothing is
>>>>>>>>     free however
>>>>>>>>     and you'll pick up 2 ounces in the process. I considered 
>>>>>>>> the 5000
>>>>>>>>     mah 10S
>>>>>>>>     packs from both TP and FP but can't afford to gain 4 ounces 
>>>>>>>> in
>>>>>>>>     either of my
>>>>>>>>     existing planes. The FP 5350's are the best solution for my
>>>>>>>>     situation. Mine
>>>>>>>>     just arrived this week and won't be flown until the snow 
>>>>>>>> melts so my
>>>>>>>>     recommendations come from observations rather than 
>>>>>>>> experience at
>>>>>>>>     this point.
>>>>>>>>     I bought mine directly from FlightPower
>>>>>>>>     http://www.flightpower.com <http://www.flightpower.com/
>>>>>>>>>  .  Hope
>>>>>>>>     this helps.
>>>>>>>>
>>>>>>>>     Verne Koester
>>>>>>>>
>>>>>>>>
>>>>>>>>     ----- Original Message -----
>>>>>>>>     From: <glmiller3 at suddenlink.net 
>>>>>>>> <mailto:glmiller3 at suddenlink.net>>
>>>>>>>>     To: "NSRCA List" <nsrca-discussion at lists.nsrca.org
>>>>>>>>     <mailto:nsrca-discussion at lists.nsrca.org>>
>>>>>>>>     Sent: Thursday, March 13, 2008 12:26 PM
>>>>>>>>     Subject: [NSRCA-discussion] Batteries
>>>>>>>>
>>>>>>>>
>>>>>>>>> Hi All,
>>>>>>>>>
>>>>>>>>> I've been flying with Thunder Power Prolite 5300 packs for a
>>>>>>>>     while now and
>>>>>>>>> they are getting very tired.  As they poop out, I'm trying to
>>>>>>>>     decide what
>>>>>>>>> to replace them with.  From what I've seen, the Flightpower
>>>>>>>>     "FAI" packs
>>>>>>>>> are probably what I'll go with, but if anyone has any other
>>>>>>>>     suggestions,
>>>>>>>>> please sing out.  Also, any suggestions as to a source would 
>>>>>>>>> be appreciated.
>>>>>>>>>
>>>>>>>>> TIA,
>>>>>>>>>
>>>>>>>>> George
>>>>>>>>> _______________________________________________
>>>>>>>>> NSRCA-discussion mailing list
>>>>>>>>> NSRCA-discussion at lists.nsrca.org
>>>>>>>>     <mailto:NSRCA-discussion at lists.nsrca.org>
>>>>>>>>> http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>     _______________________________________________
>>>>>>>>     NSRCA-discussion mailing list
>>>>>>>>     NSRCA-discussion at lists.nsrca.org
>>>>>>>>     <mailto:NSRCA-discussion at lists.nsrca.org>
>>>>>>>>     http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
>>>>>>>>
>>>>>>>>
>>>>>>>>
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