Low Current and LiPo Low Voltage Cutoff? - RC Groups
May 07, 2005, 01:41 PM
Registered User

Low Current and LiPo Low Voltage Cutoff?

I've searched but not found a great answer...

So, I've been playing with my first 2S 1200ma lipo on a Hyperion E-Meter and a cdrom motor. Haven't put it in a plane yet...

There is a heckuva difference in voltage at say 4C (wide open) discharge as opposed to 1C (1/3 throttle). The voltage doesn't drop as much at low throttle.

With a Lipo, typical LVC is 3.0V/cell, however, I have heard that you should not charge a Lipo that is reading less than 3.3V/cell. I therefore assume that the 3.0V cutoff is dependant on voltage drop due to load, and the resting voltage needs to be somewhat higher.

So, my question is this: If I'm just tooling around the yard at part throttle, is it possible to over-discharge my LiPo?
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May 07, 2005, 02:16 PM
Southern Pride
Quote:
 Originally Posted by cserwin I've searched but not found a great answer... So, I've been playing with my first 2S 1200ma lipo on a Hyperion E-Meter and a cdrom motor. Haven't put it in a plane yet... There is a heckuva difference in voltage at say 4C (wide open) discharge as opposed to 1C (1/3 throttle). The voltage doesn't drop as much at low throttle. With a Lipo, typical LVC is 3.0V/cell, however, I have heard that you should not charge a Lipo that is reading less than 3.3V/cell. I therefore assume that the 3.0V cutoff is dependant on voltage drop due to load, and the resting voltage needs to be somewhat higher. So, my question is this: If I'm just tooling around the yard at part throttle, is it possible to over-discharge my LiPo?
ESCs LiPolys and LVC explained here.
To see how volts under load varies visit there.
 May 07, 2005, 05:11 PM Registered User Yes but that doesnt answer the original question (and I had been wondering the same thing) So what is the safe cut off voltage at say 2C 3c 4c etc Terry
 May 07, 2005, 06:02 PM Registered User 3.7v per cell is very safe at all those discharge rates, the only problem is flight times could be very short! Try “soft cutoff” at around 3.4v per cell. Look for an after flight no-load voltage of 3.7v per cell. Adjust the voltage higher or lower depending on your results.
May 07, 2005, 07:04 PM
Southern Pride
Quote:
 Originally Posted by terry.rigden Yes but that doesnt answer the original question (and I had been wondering the same thing) So what is the safe cut off voltage at say 2C 3c 4c etc Terry
THe safest LVC to use with LiPolys is one which results in an open cell voltage of atleast 3.5 volts per cell with 3.7 volts per cell being much easier on the cells / batteries. THe voltage under load does not rally mater that much as long as the battery spring / bounches back above these levels as soon as the load is reduced / removed. A high drain / load when removed wiil cause the battery to spring back more than if a light load was removed.
There is no magic numbers other than open cell / resting voltage.
As LiPolys are improved and are able to discharge a greater percentage of their capacity above 3 volts per cell under load it become easier to over dischage them to the point that they will not recover to 3.5-3.7 volts when the laod is removed. Not deep discharging LiPoly cells in general add greatly to their life expendency.
Example: Last summer I used E Tec 1200 Classic LiPolys rated at 6C and flew to a LVC of 7.2 volts or 2.4 volts per cell ,soft cutoff. This did not unduely harm the batteiries and was a common recommended practice at that time.
Apogeee ,Tanic and Thunder Power all now clearly state not to use a LVC of less than 3 volts per cell with any of their current LI Poly batteries.

LiPolys ,ESCs and LVC.

Charles
Last edited by everydayflyer; May 07, 2005 at 07:18 PM.
 May 08, 2005, 12:22 PM Registered User Thanks guys that clarifies thing a lot. regards Terry

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