LiPo Safe cell voltage?

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LiPo Safe cell voltage?

Postby takilara » Tue Aug 03, 2010 9:07 pm

Not really a beginner, but I consider this a beginners question.

What is the actual "danger zone" when it comes to cell voltages for LiPo batteries? I have heard 2.5V, 3.0V, 3.3V and 3.4V as the "don't ever go below, or your battery is ruined..." Seems that 3.0V is the most frequent that i have seen.
Also I would assume that this limit is "while loaded". But someone say that it is the "no load" voltage that is important...

My initial question is as stated, what is the voltage one should never be below.
A followup question is, is there any ways to check if the battery is ruined? I.e. can one determine anything from its voltage drop with a given amperage? (i.e. if i discharge it in the charger with 5A, can i see anything on the voltages that would indicate ruined battery?)
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Re: LiPo Safe cell voltage?

Postby RCModelReviews » Tue Aug 03, 2010 10:54 pm

I don't think there's a *hard* minimum voltage -- basically the lower you go the more damage you risk so higher is better.

I generally don't take lipos below 3.2V and although this may short-change me a little on the useful capacity, it does mean that mine last an awfully long time. I've got some packs that are nearly 4 years old and still have 75% capacity.

Others may like to chime in with their experiences and opinions.
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Re: LiPo Safe cell voltage?

Postby takilara » Wed Aug 04, 2010 5:54 am

Thanks!
Is this 3.2V under load (as determined by onboard sensor), or 3.2V no load (multimeter on ground)?
The ESC i use in the TREX600 has a preset limit to reduce output at 3.2V, and this has to be while under load (would have been hell of an autorotation to measure the noload voltage :). It has a hard cutoff at 3.0V

For my 450, i've used a device called HRPolyX, that gives an alarm sound and blink at a preset voltage. The intensity of the sound increases as you go lower.
I know i have it set to 3.4V, but i dont know if this is when it starts beeping, or if this is when the sound is "solid".

For my own sensor and FrSky telemetry system, i guess I will go for 3.4-3.5 for initial alarm, then second alarm at 3.3 or so..
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Re: LiPo Safe cell voltage?

Postby RCModelReviews » Wed Aug 04, 2010 6:25 am

It would be under a modest (1C) load. Even a fully-charged battery will drop below 3.2V per cell if you apply enough load to it.
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Re: LiPo Safe cell voltage?

Postby takilara » Wed Aug 04, 2010 6:57 am

Well at least that is easy to verify using discharge program on my charger then. Kinda hard to use as a guideline for onboard sensors though :)
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