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Question ? RC Batteries: Status   [
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 The Status in RC Batteries gives a very fast overview on the actual real health of the LiPo pack. To make understanding easier, the explanation will be based on a real example - as shown below.

Battery: 1300mAh 3S1P 45C HobbyKing Nano-Tech
Status: FOM1.15, MP0.72, IR ~7mΩ σ2mΩ 

We have here 4 values, FOM, MP, IR ~ and IR σ.
FOM tells us that from the expected 30C, we have more than expected. Good. 30C is a fictive value from experience. It is not linked to what the manufacturer promised us.
MP tells us that from the "promised" 45C we get only 72%. Bad
IR ~ average shows us 7mΩ per cell. There are way better cells out there. OK, but not excellent either.
IR σ is the Variance, telling us how many mΩ apart the individual cells are. Remember that the worst cell defines the overall state of the pack. In general, the smaller the σ value the better.

Warning

FOM0.02, MP0.06, IR ~111mΩ σ253

In case the IR ~/ IR σ are displayed in red color - it means the variance between the cells is higher than the cell average. This is an indication that one cell of the pack is way worse than all others and that this pack can explode if not charged using a Balancer-capable charger. Best would be to retire this pack ASAP!

More detailed explanation on each information type:

  • FOM: Figure of Merit is a calculation that uses measured cell internal resistance and normalizes it to cell capacity. It is very useful when comparing packs of different sizes and from different manufacturers
    The meaning is as below, taking into account that a FOM=1 means a 30C Cell able to deliver 30C based on the cell with the highest IR.

    • FOM < 1: below average < 30C capable
    • FOM == 1: average - 30C capable
    • FOM > 1: good - More than 30C capable
    • FOM >> 1: outstanding - much more than 30C capable

  • MP: Manufacturer's Promise is there to tell us if the C-Rating of the LiPo pack is actually accurate.
    Based on what the Manufacturer claims the pack is capable to deliver, we calculate the actual C-Rate based on the worst cell's Internal resistance.
    The relative number out of there tells us how good the C-Rating statement of the Manufacturer is.

    • MP == 1: Very good. The proclaimed rating matches the mesured one
    • MP < 0 : No good. The LiPo pack delivers less than claimed
    • MP > 1 : Excellent - The LiPo pack delivers more than claimed

  • IR ~: This is the Average Internal Resistance of all cells. Average value is taking into account how the cells are arranged (Serial or Parallel) and computes an overall average. In the battery details view, the color will change accordingly depending on the overall IR of the pack.

    • Green: IR < = 6mOhm : Excellent
    • Yellow: 6mOhm < IR < = 12mOhm: Good/Reasonable
    • Orange: 12mOhm < IR < = 20mOhm: Aging signs
    • Red: 20mOhm < IR : Read for retirement

  • IR σ: The variance of the Internal Resistance tells us how similar the cells internal resistance actually is. The smaller the IR σ, the better. The bigger the difference, and the older the cells probably are. Remember that the overall LiPo pack capability is defined by the worst cell in that same pack!
    The danger of the IR difference is that cells will be discharged differently. The worst cell will generate most heat that needs dissipation in the pack, and reach lower voltage levels first. Also - if charged without balancer control the worst cell can very fast be overcharged which can cause an explosion of that cell.

 

Entered by smurphy on Wednesday, 08 June 2016 @ 10:33:44  
Electronics - RC Models, # Hits: 17502

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