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Smart Pie Vector

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Thuktun:
Isn't 40Ah at 2A .5C? If 10Ah at 1A is 1C it should be.

I don't have a long ride, about 6kms, and I work at least 11 hours every day, so both. :)

Bikemad:

--- Quote from: Thuktun on June 12, 2015, 02:59:22 PM ---Isn't 40Ah at 2A .5C? If 10Ah at 1A is 1C it should be.
--- End quote ---

If 10Ah at 1A was 1C then it would be, but 10Ah at 1A is only 0.1C (1A/10Ah = 0.1C, 10Ah at 10A would be 1C)

The "C" is used to represent the battery's charging and discharging capability, so if a 10Ah battery has a charge rating of 0.5C , it can safely be charged at up to 5 Amps (0.5 x 10A). My 5Ah LiPo packs have a maximum continuous discharge of 20C and a peak discharge of 30C, which means they can output up to 100 Amps continuously (20C x 5Ah) and a peak current of 150 Amps (30C x 5 Ah) but only for 20 seconds bursts. The maximum recommended charge current for these packs is 5C (25 Amps).


--- Quote from: batteryuniversity.com/ ---Smaller batteries are rated at a 1C discharge rate. Due to sluggish behavior, lead acid is rated at 0.2C (5h) and 0.05C (20h).
--- End quote ---

The Ah rating of most lead acid batteries is based on a 20 hour discharge (0.05C) so a fully charged 10Ah lead acid battery should theoretically discharge at the rate of 0.5 Amp (0.05C) continuously for 20 hours.

Unlike a 10Ah lithium battery (which will typically deliver 10 Amps continuously for ~1 hour) most 10Ah lead acid batteries will not deliver their stated capacity of 10 Amps for anywhere near an hour, in reality you'd be lucky to get ~35 minutes from a lead acid battery when discharging it continuously at a rate of 1C, which only allows around 5.8Ah capacity to be realised instead of the expected 10Ah.

The size and weight is not the only reason why people prefer Lithium over lead acid.

Once you have become used to the power, size and weight advantages of lithium, it would be very difficult to go back to lead acid again. A bit like swapping from a young thoroughbred race horse back to an old retired shire horse.
 
Alan
 

Thuktun:
Hey they get me from a to B with minimum hassle and cost. Good enough for me. :)

Thuktun:
The data sheet for these batteries says they can be charged at up to 3C. So you are saying I can charge them at 30A of current safely? My understanding of C rating is it's 1/10 of capacity. That's how I've seen it explained everywhere else. Guess they are wrong or I'm reading it incorrectly.

Bikemad:
3C sounds much too high for the charging rate of a lead acid battery. Are you sure it isn't ".3C" or "C/3" or perhaps a discharge rate of 3C?


--- Quote from: http://web.mit.edu/evt/summary_battery_specifications.pdf --- A C-rate is a measure of the rate at which a battery is discharged relative to its maximum capacity. A 1C rate means that the discharge current will discharge the entire battery in 1 hour. For a battery with a capacity of 100 Amp-hrs, this equates to a discharge current of 100 Amps. A 5C rate for this battery would be 500 Amps, and a C/2 rate would be 50 Amps.
--- End quote ---

If you look closely at the attached picture of a typical 12V 10Ah lead acid battery, you will see that the maximum charge rate is 3 Amps (0.3C).
You should also notice the 10Ah/20hr rating of this battery which means the 10Ah rating is actually derived from a 20 hour discharge test at C/20 or 0.05C.

The “C” rating refers to the total capacity of the battery in terms of Ampere-hour (Ah) and is a rating of how quickly energy can be discharged from a battery, and is often used to indicate the rate at which the battery can be recharged as well.
Typically, the discharge "C" rating (the one commonly shown on the battery) will be much higher than the recharge "C" rating.

I hope that after reading this that some of it will make more sense to you.



Alan
 

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