hi,
just brought a few battery's (18650's Li-ion) for a project brought them from china im pretty sure they are not counterfeit as they seem to be heavy, another one i brought seemed very light i guess that one has a much lower capacity.
anyway just wondering how to work out the capacity of it, im wondering if i could work out the capacity of it by the charging rate?
im charging it at 500ma, so if it takes 6 hours to charge can i assume its roughly 3000mah battery? or can it only be worked out on the known current discharge rate?
thanks
For all you know there could be a lump of lead inside your battery (for feel-good weight) and a low capacity battery to give an output. One way to determine capacity is to fully charge it then conduct a controlled discharge, measuring current and voltage at specific periods of time. From that data you draw a curve of watts versus time then totalise your readings to get watt-hours, divide the results by average voltage to establish a rough idea of AH capacity. It would be even better if you could discharge at constant current but that is a little more complicated to do.
Charge of a battery is measured during discharge under specified conditions (often
the 10-hour rate) and after a specified full-charge cycle. The amount of charge it
takes to recharge is usually 20+% more than the capacity.
Actual practical capacities are less because you don't always start using a battery
immediately after a full charge cycle, and don't discharge uniformly at the recommended
temperature.
Measuring a discharge curve requires either a specialist battery discharge monitor
or a suitable load-resistor and regular measurements by hand - divide the voltage
values by R and integrate to get the charge.
Most battery types do not tolerate over-discharge (lithium batteries actually become
dangerous), so never discharge a battery into a dummy load unsupervised, or you'll
just trash the battery. Observe the minimum voltage and stop the discharge, immediately
recharge.
jonwhite:
hi,
just brought a few battery's (18650's Li-ion) for a project brought them from china im pretty sure they are not counterfeit as they seem to be heavy, another one i brought seemed very light i guess that one has a much lower capacity.
I've seen videos on youtube where there's a chunk of metal in a "battery" and a couple of tiny coin cells in the top to make you think it's working when you buy it.
I'm guessing they feel heavy.
jonwhite:
im charging it at 500ma, so if it takes 6 hours to charge can i assume its roughly 3000mah battery?
I could put in a resistor to shunt 495ma of that around the teeny battery I put inside.
jonwhite:
or can it only be worked out on the known current discharge rate?
thanks