[NSRCA-discussion] Internal battery impedance

Gordon Anderson GAA at owt.com
Sat Mar 15 20:17:24 AKDT 2008 

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
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>>>>>>>     http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
>>>>>>>
>>>>>>>
>>>>>>>
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