“C” is a 1000:1 ratio of the capacity of a cell or pack in mAh to a given current in Amps.
(Taken from RCMP)
I think Nightshade is correct.
If a 6000Mah pack can only be charged at 1 C then you divide 6000 by 1000 then multiply it by the C rating which is one in this case which gives you 6 amps. If it where a 2 C value then you could charge it a 12 amps for example
So you can charge the big mutha at 6 amps it seems. _________________ Bots that do not destroy you, only make you stronger.
Sun Feb 06, 2005 7:06 pm
Philip Experienced Roboteer
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That is correct. I have seen LiPol chargers up to 8A. _________________ So even the rain that falls isn't actually going to fill our dams and our river systems
Sun Feb 06, 2005 7:08 pm
Valen Experienced Roboteer
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it isnt 1000 to one
its just one is generally measured in mili amp hours and the chargers in amps.
the SLA's are a notablle exception, they seem to have less marketspeak in their naming, a 2.2 AH SLA not a 2200mah SLA.
they really should be 6AH Li-Poly and 3.6Ah Ni-Cd
you dont buy a 2000 mililiter bottle of coke.
C is the capacity of the battery in amp hours.
so with a 100% efficent battery if you charged it at C you would put the batteries capacity in in one hour and then it would be charged
so a 6 Ah Li-Poly would be charged in one hour at 6 amps ( or 6 hours at 1 amp)
generally though charging is only 50-80% efficent. so a 1C charge will usually last for 1.5 hours.
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Sun Feb 06, 2005 10:54 pm
Nexus Experienced Roboteer
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Dont know if I agree with C being just the capacity in amp hours.
If you apply that to a sub c battery then what you are saying is that C is 2.4AH but C would be more like 40 - 50 amps sustained current.
When I have been looking at various cells I look at the C rating to tell me what current it can sustain and what its peak current is.
The same capacity cell can have different C ratings actually depending on who made it.
Thats how I saw it anyway
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Sun Feb 06, 2005 11:32 pm
Philip Experienced Roboteer
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Some batteries have a number in front of the C rating. They can be greater or less than 1C.
when you see something like 10C they are refering to the rate of discharge (or charge) in reference to the cells capacity
so a 10C discharge on a 2.4Ah cell is 24 amps (for 1/10th of an hour theoretically, generally about half to 80% that) _________________ Mechanical engineers build weapons, civil engineers build targets
Mon Feb 07, 2005 7:23 am
DumHed Experienced Roboteer
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yes, C is always the capacity in Ah, and a multiplier can be used to show peak discharge rates, or charge current.
It really just lets them use the same numbers on different battery capacities.
eg, several batteries of different capacties might all be able to discharge at 10C, so marking them all as 10C discharge is easier than putting the actual discharge current on each one,
It also will account for capacity drop off over time. _________________ The Engine Whisperer
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Mon Feb 07, 2005 8:52 am
Nexus Experienced Roboteer
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quote:Originally posted by Valen:
when you see something like 10C they are refering to the rate of discharge (or charge) in reference to the cells capacity
so a 10C discharge on a 2.4Ah cell is 24 amps (for 1/10th of an hour theoretically, generally about half to 80% that)
Yeah pretty much.
The whole things sems like a simple formula where 1000:1 is to convert Milliamps to AH. The AH is not a variable but. When u buy a 2.4AH battery thats not going to change.
The only variable is how much current you can get from the battery. (ignoring resistance) THere is a relationship between AH and C but it seems similar to what we are doing with our Nicads.
Many of us using Sub C need more current so the way to do that is change the capacity to change the equation. We have to go up to 3.6 AH to give us more current C. BUt we dont really need more Capacit its just that bigger batteries generally give you more Current and if you want to change C you go bigger batteries or go super high discharge CElls which have a High C rating.
Another example using nicads is changing to Sub C batteries that have a discharge of 80 amps. In this case the Capacity doesnt change but the C rating will almost double.
Personally speaking talking in AH is not useful at all as it doesnt change, it seems the discharge current is the only variable and if u want more then you go back to change the AH at the start of the equation to give you a higher C rating or you go Parralelpacks which is simulating a bigger battery anyway.
I suppose its all maths in the end and can be looked at in many ways depending on what you need.
I need high discharge and a capacity of at least 2AH myself.
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Mon Feb 07, 2005 10:34 am
DumHed Experienced Roboteer
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quote:Originally posted by Nexus:
Another example using nicads is changing to Sub C batteries that have a discharge of 80 amps. In this case the Capacity doesnt change but the C rating will almost double.
It's not the C rating that doubles though, it's the multiplier of C to give the discharge rate.
A 1Ah cell that can discharge at 20A will have a discharge of 20C. If you had a 1Ah cell that can discharge at 40A then it'd be a 40C rate. If that cell was 2Ah though the 40A discharge rate would be 20C. _________________ The Engine Whisperer
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Mon Feb 07, 2005 11:26 am
Valen Experienced Roboteer
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C is capacity, not current
I is current _________________ Mechanical engineers build weapons, civil engineers build targets
Mon Feb 07, 2005 2:38 pm
Nexus Experienced Roboteer
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quote:Originally posted by Valen:
C is capacity, not current
I is current
That might be the case but when I am looking at these batteries I am making desicions based on Current.
Capacity doesnt really mean that much and RCMP seem to express the current in C as they have the current in brackets when referring to C.
Its like a theory versus practise exercise, in practise all you need to supply is enough current to your motors even if the theory is confusing. _________________ Bots that do not destroy you, only make you stronger.
Mon Feb 07, 2005 3:03 pm
DumHed Experienced Roboteer
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I would have thought capacity would be more important...
No use supplying a peak of 100A when you only have 100mAh of capacity! _________________ The Engine Whisperer
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Mon Feb 07, 2005 3:29 pm
Nexus Experienced Roboteer
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Thats fairly obvious, after having tried 2.3 SLAs, 2.4AH nicads, drill batteries, 4/5A NiHh and others you dont need to consider that too much.
You get a feeling how much you need depending on your voltage.
And having literally melted the glue out of my packs it seems obvious that current is more important to me when I get 6 minutes out of the batteries in a lightweight.
Thats just my priority atm, if I had a spinner then Capacity would be more important but I end up with time to spare and would rather turn that to current somehow.
The other big factor is if running at 12 volts and your batteries cant supply the current then you get voltage drops, your failsafe kicks in and you become a sitting duck. Not cool at all _________________ Bots that do not destroy you, only make you stronger.
Mon Feb 07, 2005 4:12 pm
Nick Experienced Roboteer
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OK, so you need two of those 6AH Lipoly packs in parallel so you can get 180 amps and still only recharge once per event Only $504 US and a mere 1.36Kg _________________ Australian 2015 Featherweight champion
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Mon Feb 07, 2005 4:29 pm
Nexus Experienced Roboteer
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Imagine the fire that would make……… Coool _________________ Bots that do not destroy you, only make you stronger.
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