Single Cell LiPO Testing

Hardware
#1

I am currently upgrading my existing Electron-based counters with newer Boron-based ones. As I do, I will rework / recycle as much as I can from the older units to reduce waste. These units have been operating on solar power for anywhere from 1 to 4 years.

How can I tell if it is time to replace a Single Cell LiPo Battery? I use this one:

I don’t want to replace and have to dispose of a battery if it still has ~70% of its capacity as Parks are very cost conscious (as they should be).

Any advice on a piece of test kit that I could use to make this determination. Field or desktop use is fine. Ideally, I would like to know - this 2000mAH battery is now a 15000mAH battery. With solar, I don’t think that charge / recharge cycles is the right metric. Here is what I have looked at so far:

Could do this job and much more - but expensive ($500):

I also tried these little testers but they are more about RC sports and don’t support single cell LiPO ($15):

I even looked at this one but the “no case” look caused me to be a bit suspicious ($50):

Any recommendations?

Thanks, Chip

#2

@chipmc, I am using this coulomb counter that I connected to a Photon to publish current use of a device under test during normal operation (mostly sleeping). The reason for not using a load simulator is that the DUT uses less than 400uAh when sleeping which most electronic loads can’t simulate. At that rate, LiPo self leakage starts playing a role.

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#3

@peekay123 ,

Interesting and, thank you for sharing as this is where I need to go next.

What I am looking for here, and I am sorry if I was not clear, is some way to remove a battery from a device I am refurbishing / recycling and determine if the LiPO battery is still fit for use. I am assuming, that after 2-3 years outdoors some of my batteries need to be retired / disposed of. I would assume that the right piece of test equipment might be able to exercise the battery at sufficient load to give an idea of battery “health”.

Thanks, Chip

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#4

@chipmc , the quick way is to measure the Internal Resistance (IR) of the cell. Be sure to take the measurements at/near the same temperature and SOC for comparison.

I believe (from memory) you’re Park Counters are pretty low power, so typical load testing for the LiPo might not be a fair test for the used cell. Thus, it would take a week or two to simulate the load the cell actually sees.

Is your charge termination voltage 4.1 or 4.2V ?
I wouldn’t be scared of a Li-Po that spent most of it’s 3-4 year life at 3.8 - 4.1V w/ such a small load.
It would be neat to compare the change in Self-Discharge, but your Solar Application negates that as being a major concern.

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#5

@Rftop,

Thank you for the great advice.

So, if I took a new cell, charged it to 75% and measured the internal resistance at room temperature, this would be a benchmark to compare to my “veteran” cells? Sounds easy.

My cutoff voltage is 4.208V, here is my Solar Power configuration:

conf.powerSourceMaxCurrent(900) // Set maximum current the power source can provide (applies only when powered through VIN)
        .powerSourceMinVoltage(5080) // Set minimum voltage the power source can provide (applies only when powered through VIN)
        .batteryChargeCurrent(1024) // Set battery charge current
        .batteryChargeVoltage(4208) // Set battery termination voltage
        .feature(SystemPowerFeature::USE_VIN_SETTINGS_WITH_USB_HOST); // For the cases where the device is powered through VIN
                                                                     // but the USB cable is connected to a USB host, this feature flag
                                                                     // enforces the voltage/current limits specified in the configuration
                                                                     // (where by default the device would be thinking that it's powered by the USB Host)

My devices do draw a small amount of power and are most often fully - or near fully - charged. Ofcourse, this last week stressed some of them with little sun and cold weather that can prevent charging.

Thank you,

Chip

#6

@Rftop,

OK, I have been trying to make progress on this and hopefully you can help me along.

First, I was disappointed to learn that the data sheet for the batteries I am using does not specify an internal resistance:

Do you know what a reasonable value should be?

Also, I underestimated the challenge of measuring the internal resistance of a single cell LiPO battery. I purchased (and returned) a couple battery charger / testers with no luck. Any advice here?

Thanks, Chip

#7

Well, you have a good point.
I don’t track the IR for single cell Li-Po’s… as we generally aren’t pushing/requiring much from them.

But for reference:
I’ll write the IR for each cell of each new Li-Po pack for UAV’s with a sharpie on the battery.
Then monitor the IR change over time during the “storage” charge cycle.

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