[NSRCA-discussion] Internal battery impedance
Ron Van Putte
vanputte at cox.net
Sat Mar 15 05:41:21 AKDT 2008
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
>>>>>> _______________________________________________
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>>>>>> http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
>>>>>>
>>>>>
>>>>>
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>>>>>
>>>>>
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