Lipo Cell/Pack Info

Here’s some good info on Lipo cells/packs that can be helpful in determining what pack to purchase for your application.


First thing to note is not every Lipo cell/pack is the same.  This means you can’t think that all Lipos are the same.  There are many different materials that can be used to make up a Lipo cell.  The differences in materials will impact the power/performance and milliamp hour of the cell.  There will be a tradeoff using certain materials as typically when you try and improve power/performance you can hinder reliability and cycle life.   It’s very complicated to balance things out to get a gain without too much of a drop off.  SMC has been known to produce some of the best cells for power/performance as our goal is to try and offer packs that make a difference.   We work closely with factories to offer models that have a good balance between performance and reliability.  We do allot of in house testing on equipment to make sure the cells/packs are as reliable as possible.   That being said with any Lipo cell/pack there is always a risk of a cell having an issue due to manufacturing defects or the nature of how Lipo cells react over use.  Factories that make RC style cells are not the biggest factories with the latest and greatest equipment so there is more chances of manufacturing defects from these factories.  This is due to them not having the very beat clean room or humidity control. None of the best equipped factories like those who make cell phone cells or real car cells are interested in making RC style cells as the volume is simply too low and we have to many different formulations/models of packs needed.  We do have a good warranty against manufacturing defects or other issues we know are not due to mishandling.


The way the Lipo pack is handled and treated will have a direct impact on how well it will hold up and how many useful cycles you can get it out of it.  A few common mistakes are discharging the cells down to low under load due to an improper voltage cut off setting.  Ideally you don’t want the cells to be under 3.6V right after the cutoff has kicked in.   You must not leave the packs stored fully charged or with too much charge.  You should store them around 3.8 to 3.85V per cell.  If you follow these guidelines you will have less chances of cell damage and you will get better cycle life out of your Lipo packs.


Lipo pouch cells will have natural expansion under charge and discharge.  This can be referred as swelling/puffing but this doesn’t mean the cells/pack is no longer good.   There is a difference between cells that have natural expansion and cells that balloon up like air bags.  Natural expansion means the cells are still good and safe to use.  Ideally when the packs are put into plastic cases/hard case we should leave clearance inside the case to allow the cells to have natural expansion.  Unfortunately we don’t leave enough or any clearance at all as we try and maximize cell performance so the packs have the best possible specs.  Bigger cells means higher mAh or lower internal resistance or a combination of both.  The materials the cells are built with have an impact on expansion as well.  Some materials make the cells expand more than others and also make them expand more if used outside the recommended guidelines.   For example our True Spec Premium V2 series, Extreme Graphene series packs use oil in the cells formulation to help lower the internal resistance which increases the power of the cell.  Cells that have oil tend to have more natural expansion then cells that don’t.  There can also be batches of cells that are more prone to expand then others due to small fluctuations in the raw materials.   Recently we released our True Spec DV series.  These cells use water and no oil in the formulation so they tend to expand less naturally and can withstand certain conditions better without expanding.   The down side is the internal resistance of the cells is a bit higher so the performance is down.  These are still more powerful than the low priced packs found on Amazon or Ebay as they are done using quality Lithium Cobalt Oxide in the cathode which keeps the power/performance level good.  The very cheap packs are built with a Lithium Cobalt Oxide substitute that is much cheaper to purchase but also offers lower performance.


Check out this YouTube link at 16 minutes and 45 seconds for few minutes and the man in the video will mention that cells expand under charging and discharging and when designing equipment that uses Lithium cells you need to understand this to allow clearance.


Hope this info is helpful to better understand Lipo cells/packs.  If you have questions you can email us at orders@smc-racing.com


 

 


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