Choosing the right Charger -> how to?

[Bikemad]

The voltage drop during discharge is not linear:



I'm guessing that the software will contain a look up table containing a series of 100 measured cell voltages (and their corresponding remaining capacities as a percentage) compiled from cell testing, which the lowest cell voltage of the battery being monitored is then compared against in order to roughly estimate the remaining capacity of the battery pack.

Alan
 

[Just]

Okay, thank you!

[Just]

Is there a way to achieve/get such Look-Up-Table  for LiFePo4 cells?

[Bikemad]

If you can't find anything on the web, you would need to carry out your own discharge test at 0.1C discharge rate over a 10 hour period, using a suitable charger equipped with a discharge function and PC interface to monitor and record the entire discharge process, and then study the recorded data either during or after the complete test.
For example, a 5Ah cell would need to be discharged at a constant 500mA and the voltage readings noted at 50mAh or 6 minute intervals throughout the test.

Here is a typical graph to give you an idea of what the test results should look like:



On the graph above, the voltage difference between 20% and 80% consumed capacity is only 0.1V, but the difference between the no load state and loaded state could possibly be greater than this, so maybe it's not worth all the hassle.

Alan
 

[Just]

yap... as for the Battery Checker http://media.hyperion.hk/dn/sentry/, which I mentioned in the post, it's very interesting how does it calculate the remain battery capacity - based on the load or unload battery conditions...
Should battery discharge curves would be different for different discharge currents (from remaining capacity point of view)?

[Bikemad]

Yes Dmitryl, the discharge curve does vary according to the current load:



This is why Hyperion's EOS SENTRY Battery Checker is designed to be used on a disconnected pack, which would obviously be in a no load condition. With radio control electric models, the first thing you are supposed to do when retrieving your model is disconnect the battery (or turn off the power switch) for safety reasons. Therefore testing the remaining capacity at the end of each flight or race should automatically be done with the power turned off, so theoretically, the battery is always being checked under "no load" conditions.

Take a look at the EOS Sentry in action on YouTube.

Even if safety guidelines were not being followed, with most of the typical R/C models, failing to turn the power off would only result in minimal standby current being drawn by the receiver and speed controller. So, the estimated remaining capacity should still be reasonably close if the throttle and servos were not being operated during the test.

Alan
 

[Just]

This EOS SENTRY Battery Checker indicates only the remaining capacity of the battery without saying the actual capacity, right?
So, what's good for? 10Ah battery with edging loose a maximum capacity it's able to hold. So, as for the EOS SENTRY Battery Checker, what capacity does it refer when calculate the remaining capacity?
Thank you!

[Cornelius]

The iCharger can tell you the capacity of the pack by discharging it at a set current.

I don't have a snapshot of that, but here's a logview of a charging cycle of a tired 36V, 16Ah LiMnPo4 battery from GM, which tells you much the same...:

[Just]

WattUp Meter could also do this job, but a full battery charge/discharge should be involved... Not always practically.... Probably having such Battery Checker could help solving some doubts regarding the battery ...

[Cornelius]

The only way to get an absolute precise Ah capacity reading of a battery, are to charge it up and Discharge it with a 'normalized' current (the current the battery are discharged at on normal use) while timing the discharge process.

All other methods would be approximate.

[Bikemad]

This EOS SENTRY Battery Checker indicates only the remaining capacity of the battery without saying the actual capacity, right?
So, what's good for? 10Ah battery with edging loose a maximum capacity it's able to hold. So, as for the EOS SENTRY Battery Checker, what capacity does it refer when calculate the remaining capacity?

If you have a well used 10Ah battery that is only able to deliver 5Ah before it is exhausted, I would expect the estimated remaining capacity to be a percentage of the battery's actual capacity rather than its rated capacity.
So if the battery checker estimates 40% remaining, I would expect to have approximately 2Ah remaining (40 / 100 x 5) for that particular battery.

Alan