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Understanding LiPo Batteries

October 6, 2016

 

 

  

Why is looking after your LiPo batteries so important?

 

In the modern world Lithium Polymer (commonly known as LiPo or li-po) batteries have exploded onto the scene (no pun intended), none more so than the radio controlled market. If you own just about anything that’s an electric powered radio controlled vehicle, it’s almost guaranteed to be powered by some sort of LiPo battery, from the tiny little polystyrene helicopters all the way through to the big 3D helis and planes.

 

LiPo's have  both advantages and disadvantages though, some of the key advantages are size and weight for the punch they pack they are hard to beat, which makes it hard to understand what the disadvantages are, unfortunately though the disadvantages are real and need to be considered, the primary concern is that they can be volatile if not cared for correctly, they only have a limited life expectancy, and some of the larger versions can be expensive, although the price seems to be continuing to drop slowly as higher capacity batteries are becoming more and more available.

 

In order to care for LiPo's correctly you first need to understand the different markings and ratings on them. LiPo's are split into cells, the number of cells are dictated as 1S for one cell 2s for 2 sell 3s for 3cell etc, in recent years you may have come across a LiPo with the marking 6s2p, since we know the 6s refers to the number of cells, that just leaves the 2p, this would denote the battery is made up of 2 batteries, thankfully in today’s market there is no need to manufacture LiPo’s in 2 pieces.

The next major point is the mah rating, this refers to the capacity in milli ampere hours, so for example a 2000mah LiPo could deliver 2000mah for an hour before its depleted,  or  2amps (to convert from mah to Amps divide by 1000), sounds simple enough? It a little more complicated than that though as we have to look at the C rating, this refers to the rate of discharge, so taking our 2000mah example from earlier we know for 1 hour it can deliver 2 amps, this would be a discharge rate of 1C or  1 times its capacity, now with the LiPo’s available today we see 60C and above, the 60C simply means it can deliver  60 times its capacity, so a 2000mah 60c battery could potentially deliver  120,000 ma  or 120amps, however if we increase the discharge we decrease the time it can sustain that power for, so we would have to divide the hour by 60 so effectively that battery would only last at best  1 minute before its depleted! In summary S denotes the number of cells, mah the capacity and C the discharge rate.

 

Now comes the interesting bit, the voltage (if your still awake and I’ve not bored you yet!), each LiPo cell has a nominal voltage of 3.7v but in reality it can be anywhere from 3v-4.2v, in order to maintain a LiPo correctly any cell should never drop below 3v (normally stated as 3.1v to allow a margin of error) if it does, it’s pretty much toast! It  should also not exceed 4.2v, so when charging they need to be charged on specific chargers designed for LiPo’s that balance charge them, simply put this means it makes sure each cell has the same voltage and capacity in it so that when in use each cell depletes to roughly the same voltage.

 

 

Now I mentioned earlier they can be volatile, which I found out the hard way when I first got into radio controlled flying back in about 2002/3! Usually the first sign there is an issue is the LiPo puffs up, if you ever have this happen, drop it in a bucket of salt water and leave outside for a week or 2, if like me you have no idea what’s going on and leave it plugged in to the charger its almost guaranteed it will explode, and when it does the smoke and flames are hard to explain! Needless to say though it goes with some ferocity and the smoke is phenomenal for the size of the LiPo, I was luckily though as I was in my kitchen and had a sink of full of water right next to me which I threw it in, what’s more I now know that the electrolytic fluid when mixed with water creates hydrochloric acid! Fortunately for me though I sustained no damage to me or my kitchen (other than the smell of acrid smoke).

 

This video on YouTube demonstrates beyond doubt the potential hazards a LiPo poses

 

 

Probably the most common issue where LiPo’s are concerned is overpowering the LiPo, i.e. drawing too much power from it or directly shorting it out, I should point out as well that a lithium polymer fire is self sustaining and as such you can’t actually extinguish one, you can only control what it burns, until it has run its course

 

All things considered though with correct balance charging and care you can get 300+ charges from a LiPo, but it’s important to make sure they are carefully stored in a safe place so that in the event there is an issue the surrounds wont ignite, and make sure they are rated correctly for the application they are to be used for.

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