Can anyone explain the 'C' ratings of batteries

[Andrew]

How important is the C rating?  Does it basically mean how much juice a battery can discharge in one go??

[Cornelius]

Yes, approximately.

'1 C' means the whole capacity of the battery. If you have a battery that have a capacity of 20Ah, and it have a 'Max Continous Discharge rate' of 2C, it means you can suck max 40A out of it continously. (That would also means that you'll empty it in 30 minutes. )
If the same 20Ah battery have an 'Max Charge Rate' of 0.5C, it means that you should use max 10A charging current.

[DirtyGinge]

Also important is the charge C rate, how many amps you can charge at safely...

exceeding the C rate on BMS protected batteries usually shuts them down, but on lipo for instance, it just generates heat ( then a whoosh, then ur a$% goes on fire)

My lipo is 24AH, with a Continuous rating of 20 C, meaning I can output normally 480 amps, but I have 30C burst so for 30 seconds at a time I can output 720 amps

Now here is an important bit....cycle length

Basically, if you exceed the C rating, generally with most lithium chemistries you shorten the life of the battery, in some cases quite dramatically...

So for instance with lipo, cycle length is usually 500-600 cycles, but abuse it ( and if you have a house left) the cycle length can be as low as 50-100 cycles ( as in your battery will only output about 75% within a months time and so on)

What is perfect is if you keep the battery below its C rating, so its never really stressed, then you should have a happy battery for a long time

[Andrew]

Cool!  that answers that one.  I've been reading up on the li-poly batteries, pretty good prices for what you can get out of them, but that's before you account for the power supply, charger and a bomb proof Andersons shelter

So for instance a x2 5ah packs parallel'd(10ah) with a 20C rating can give out 200 amps for how long?   what's the equation?

[Bikemad]

So for instance a x2 5ah packs parallel'd(10ah) with a 20C rating can give out 200 amps for how long?

If you were to consume the battery's power at a continuous 20C rate, you would theoretically discharge it 20 times faster, but as they are less efficient at higher loads, they would not produce their full stated capacity when discharged at high "C" rates, so you could realistically expect less than 3 minutes (60mins ÷ 20) of use from a LiPo pack, and a whole lot less from lead acid batteries.

Alan
 

[Andrew]

Thanks   I now understand why they are designed for RC cars, planes etc

[e-lmer]

The equation, btw, is (2x)5A•hours / 200A=1/20 hours » 60/20 minutes = 3min

[DirtyGinge]

I bulk charge mine with a normal charger, checking balancing once a month

I have 50V 24AH battery, made up of 3ah 20C cells ( 32 in total)

I can run 15 ah continuous power for abou 1.5 hours
the key to safety with these is not to fully charge, not to fully discharge
So even though the floor is 2.7V, I never go below 3,7V

As for their suitability for an ebike, the most voltage drop I get going up a hill, outputting 40A is 0.5 Volt

So bottom line, if you use 12AH, you need at least 18ah of capacity to get the best out of them
But the best is truly amazing
most of the other batteries I have used have just not been able to output massive amps for any length of time without heat or voltage drop, or reduced capacity
Hey andrew, when I come up, ill bring maccie with the lipo pack, and you can catch flies with the smile 

[Andrew]

I seem to have spent most of the weekend reading up on batteries- especially lipos whilst sitting here nursing a nasty head cold.

Mac +lipos sounds likes the mutz nutz.  I've just found myself a steel frame with slotted dropouts which I will be using for my pie and (hopefully) a mean Ginge battery pack to suit.  Any luck with the battery?

[Bikemad]

I seem to have spent most of the weekend reading up on batteries- especially lipos whilst sitting here nursing a nasty head cold.

I know exactly how you feel Andrew, I've be dosing myself up with medication this weekend and have achieved nothing.
A lazy weekend for me too.

I have 50V 24AH battery, made up of 3ah 20C cells ( 32 in total)

Ginge, you seem to have something wrong with those figures, as you would need at least 96 cells to achieve 50V 24Ah.
8 x 3Ah cells in parallel would give you the 24Ah, and 12 cell in series would give you 50V (12 x 4.2V = 50.4V)

To achieve 24Ah @ 50V with those cells, you would need a 12S8P pack containing 96 cells (12s x 8p).

How can you achieve this with only 32 cells?

Alan
 

[Andrew]

the lipos come in so many different configurations he must mean 32 packs?  although that does not sound correct either    cough,sneeze, splutter  eeerrrrrrr!  ......  i'm such a big girl.  I bet Ginge is doing his usual 40 mile round trip today with a cocktail of illnesses caught from the little ones

[DirtyGinge]

yup I rin 32 x 3 packs, nice n warm witht the heated clothing

luckily no ebola today

which pack to buy really depends on which charging solution you are going with ... I had chargers that could do charging 4 packs at once with the balance leads

Now I just charge through the main socket with a 50V charger and check balancing every few weeks

[Bikemad]

Ginge, Do you have them configured as two separate 22.2V 24Ah 6S8P packs which are then connected in series to provide a total nominal voltage of 44.4V (50.4V fully charged)?

Just out of interest, what is the maximum charging current that your 50V charger can output, and is it adjustable for smaller capacity packs?

Alan
 

[DirtyGinge]

got them done as 8 seperate packs configured for 12 SEries

The reason for wiring like that is if I decide to get some excercise, I can take a few packs out to reduce weight

This is the great thing about lipo, you can buy it in installments, and install/remove the capacity you need for a specific journey

The charger can output 10A, 49.8V ( set not to fully charge the battery, 4.15Vish0 per cell)

Teh charger is highly adjustable, as it used to be my 54.6 charger, you can reduce voltage and ampage by turning pots on the board

[MonkeyMagic]

C is for COOKIE



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