Lipo Battery info needed

[japudjuha]

I have some turnigy 5000mah 6s lipo batteries.

Is there a minimum recommended voltage per cell that I should
not discharge them below.
If so what is it?

Also what is the max charge voltage per cell to charge them up to?
I have been told 4.2v per cell. Is this correct.

Thanks

 

[jhn.holgate]

Some good info here: http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries I try to re charge before I hit 3.6v per cell or thereabouts. And yes, 4.2v per cell is what you generally charge them up to. Any higher can result in a mini BBQ event. There's a good article at Battery University about prolonging the life of your LiPo's too. I'm pretty sure that Lithium Ion charging/discharging protocols are the same as for LiPo's.

 

[japudjuha]

Awesome, thanks mate.

 

[japudjuha]

A couple more queries.
What does the 22.2v rating mean (for a 6s), is it the storage voltage or the fully charged voltage?
I would have thought the fully charged voltage would be 25.2v (4.2v/6s).
Could someone please clarify this for me.
Finally what is the ideal voltage to not discharge below for a 6s pack?

 

[jhn.holgate]

Yep, 22.2v is 6 cells in series (6s). And they use 3.7v for the cell voltage....which does seem weird as fully charged they're 4.2v. (Dunno.....anyone?) I had a feeling that storage voltage was around 3.85v per cell or thereabouts. Safe discharge is not below 3.5-3.6v per cell (multiply by 6 for your pack). I have a bunch of 11.1v (3s) lipo packs - I have occasionally over-discharged them to around 9v (ooops) but they seemed to charge back up fine and haven't been a problem for me. Don't think I'd like to make a habit of taking them that low though...

 

[SilverFox]

Hello Japudjuha,

Secondary cells and battery packs are rated at a nominal voltage. This is the mid point voltage under load. With Li-Ion you start at 4.2 volts then the voltage drops to around 3.7 volts half way through the discharge and you end up at around 3.5 volts.

Keep in mind that there is a difference between voltage under load and open circuit voltage.

Let's jump to AA sized cells for another example.

Primary cells like alkaline cells are rated at their unloaded initial voltage. This gives you around 1.5 volts for an alkaline cell. Secondary cells like NiMh are rated at their mid point voltage under load. While NiMh cells come "hot off the charger" at close to 1.5 volts their "nominal" voltage is 1.2 volts. If you look at discharge graphs you see that is roughly a mid point voltage under normal loads.

Tom

 

[HKJ]

Primary cells like alkaline cells are rated at their unloaded initial voltage.

How would you explain 1.5 volt marking for 1.5 volt lithium cells, they have 1.8 volt unloaded?

 

[japudjuha]

Thanks heaps for the advice guys.
I think I have my head on straight with LiPo's now:twothumbs

 

[SilverFox]

Hello HKJ,

That is simple... Marketing. :)

I think that battery manufacturers understand that open circuit voltage doesn't have a lot of meaning. With the addition of the Energizer lithium primary cells, they exceeded the 1.5 volts open circuit that has been normal for alkaline cells. Rather than trying to explain the difference they just labeled it as 1.5 volts. They are trying to fit into the alkaline primary market and using similar labeling helps.

If they put 1.8 volts on the cell the average person wouldn't purchase them. They are looking for a 1.5 volt cell.

Tom