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View Full Version : Eagletree Data - Savage Flux and 5000mah 30C Lipos


fastbaja5b
07-07-2009, 12:28 PM
Just need some opinions on this:

I only had ONE pack hooked up to the logger

http://i212.photobucket.com/albums/cc202/fastbaja5b/fluxrun-1.jpg

Note the drop to 6.42 volts on a 119 Amp spike. Is this too much of a drop?

Pack is a Harris RC 5000mah 30C Lipo from this site:

http://www.harrisrc.com/lipo1.htm

Kostaktinos_mt
07-07-2009, 07:57 PM
based on a couple of peaks, it looks like a ~12mohm battery, which translates to about ~6mohms in this case... not a bad number at all [5-6mohms/cell is a typical value for true 30C cells]. i am not sure if i can see the 6.42v drop in the 119amp spike you mention. there 3 spikes of >110amps and the battery stays above 7v at all 3 cases.

as a comparison, a friend of mine had a maxamps hv-5k 20c, which i measured at 14mohms/cell [practically equals to about a 10c rate]. it did easily hit the lvc at ~80amp peaks.


remember that the internal resistance is subject to change depending on ambient temperature [colder = higher resistance] and charge left on battery.

also, keep in mind that the 10hz sampling rate of the e-logger is insufficient for deep inspections and proper analysis. but it`s good for most 'bashing calculations'.

fastbaja5b
07-08-2009, 02:36 AM
Well it looks to be consistant, I measured my other Harris pack and recorded a drop to 6.2V similar run style, and a Reedy 20C 5000mah pack got down to 5.8! (That reinforces the idea that a 5000mah 20C pack is INSUFFICIENT in the Flux, the same pack later only dropped to 6.89 under 80 Amps load in my Slash VXL)

All spikes around 119 Amps. Keep in mind I am using a 100 Amp logger so perhaps it's a certain margin of area when recording spikes outside the logger sensor's preferred range.

Also the fact that my MMM LVC set at 3.2v a cell didn't kick in makes me inclined to think that's a possibility too.

Still food for thought though, neither pack was even warm to the touch after these runs

Kostaktinos_mt
07-08-2009, 12:41 PM
i don`t think it works that way. the max current spikes are probably recorded at the max acceptable scale, which means that the 120amp spikes could be 150amps [or even more] in reality.
all in all, based on a 100amp logger [with a fluffy 10hz rate] i wouldn`t measure a pack by the max peaks. a typical 1/8 bl system can create peaks higher than 500amps for <1ms. you are not going to see that with the elogger, and honestly they don`t mean a lot on their own.

some of the peaks shown on the above graph are:
7.6v, 65a
7.75v, 42a
7.26v, 90a
these matter most imo. they can tell you [in generic figures] how warm will your packs be after a run, how hungry your system is, how much dangerous it is for the esc to brake hard with any particular packs, how high or low to set the lvc depending on the batteries, etc.


the reason the lvc doesn`t kick in that easily, is because it takes some time [usually a second or something] under the low voltage threshold for the lvc to kick in. it`s not going to kick for 0.1s, etc.

btw, that harris 5k pack looks exactly like a tuneup pack.

fastbaja5b
07-08-2009, 03:22 PM
Good points, it's more a matter of curiosity for me, and after reading some of the "typical" discharge graphs for Enerland cells on their site, I am pretty confident these packs are sufficient for the Savage Flux on 4s. I have plenty of room in case of a voltage surge on brakes (esc rated to 6s) and the packs after a hard 20 minute bash are very rarely above the ambient temperature.


The Reedy pack dropping to 5.89 under load, I wouldn't use in the Savage flux, but that is quite happy in the Slash :)