[NSRCA-discussion] Internal battery impedance
Gordon Anderson
GAA at owt.com
Sat Mar 15 19:55:07 AKDT 2008
You can measure the cell's resistance by measuring the battery voltage with no
load then apply a load and measure the cell voltage with a load. The difference
between these two voltages divided by the load current in amps is the cell
resistance in ohms. If the cell's behavior is linear (nothing in the world is
linear!) then this value will apply for other load currents.
This value will change with the cell's charge and condition.
--Gordon
-----Original Message-----
From: nsrca-discussion-bounces at lists.f3a.us
[mailto:nsrca-discussion-bounces at lists.f3a.us] On Behalf Of Lance Van Nostrand
Sent: Saturday, March 15, 2008 8:45 PM
To: NSRCA Mailing List
Subject: Re: [NSRCA-discussion] Internal battery impedance
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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