I have noticed when I look to buy Li-ion batteries they say "3c discharge". What exactly does this mean. Also how do I use this when making flashlights ie does it matter for choosing bulbs? Thaks in advace for all your help.
Li-ion discharge? How do I apply this?
- Thread starter Lumencraft (Matt)
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mdocod
Flashaholic
Hi vestureofblood,
you should point me to a link of a li-ion being sold that is rated 3C, as their aren't many
most are 2C!
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The only way to explain is through examples:
A cell can be discharged at various rates. Different rates will generate different times required to discharge the cell. A 1C discharge rate takes 1 hour to complete. Going from full to dead in 1 hour is 1C. A 2C discharge means going from full to dead in 30 minutes, a 3C would be 20 minutes, a 4C 15 minutes. etc etc. A 0.25C would take 4 hours.
For a 600mAH cell, a 1C discharge would happen somewhere around 600mA discharge rate and take about 1 hour to be dead.
For a 2200mAH cell, a 2C discharge would be somewhere around 4.4 amps, and take 30 minutes to discharge.
when dealing with "C" ratings for cells, it's more about the time, the minimum time the cell can be completely charged or discharged in is what the maximum "C" rating means. When you discharge a cell faster, more energy is wasted as heat, so it's not always going to be direct multiples of the capacity of the cell. Usually it's less.
Does this make any sense or am I making things worse? lol
Eric
you should point me to a link of a li-ion being sold that is rated 3C, as their aren't many
most are 2C!---------------
The only way to explain is through examples:
A cell can be discharged at various rates. Different rates will generate different times required to discharge the cell. A 1C discharge rate takes 1 hour to complete. Going from full to dead in 1 hour is 1C. A 2C discharge means going from full to dead in 30 minutes, a 3C would be 20 minutes, a 4C 15 minutes. etc etc. A 0.25C would take 4 hours.
For a 600mAH cell, a 1C discharge would happen somewhere around 600mA discharge rate and take about 1 hour to be dead.
For a 2200mAH cell, a 2C discharge would be somewhere around 4.4 amps, and take 30 minutes to discharge.
when dealing with "C" ratings for cells, it's more about the time, the minimum time the cell can be completely charged or discharged in is what the maximum "C" rating means. When you discharge a cell faster, more energy is wasted as heat, so it's not always going to be direct multiples of the capacity of the cell. Usually it's less.
Does this make any sense or am I making things worse? lol
Eric
No thats, thats not confusing its EXACLTY what I needed to Know, also I read some info at the link good stuff. If I understand correctly now, it means dont run a 3c battery down faster than 20 min or 2c faster than 30 min Ie my bulb is 3a my batteris are 3000mah hrs so thats fine for a 1c battery, If my bulb was 9amp with the same batteris I would need a 3c battery. Correct?
mdocod
Flashaholic
Just keep in mind that capacity of batteries is almost always tested at a LOW rate of discharge (like 0.1C). As you increase the rate of discharge, some of the capacity is not available.
For example, a 2200mAH cell might deliver it's rated label capacity when discharged over the course of 10 hours, but when discharged in 1 hour, it might only be 2100mAH, and in 30 minutes, might only be 1850 mAH. So a 2C discharge for this 2200mAH cell would actually be 3.7A, not 4.4A.
So whenever you are buying cells with a particular load in mind, always take into consideration some loss from high drain rates when applicable. Also consider that as cells age, their useful capacity will decline. The best thing to do is look at some discharge graphs of the cell provided by the manufacture (assuming a reputable manufacture), or to get some rough estimates, you might have a gander at CPF member SilverFox's test results for many different cells. They can be found in the "threads of interest" section of "batteries/electronics."
Remember, C ratings are dealing with time, not current.
For li-ion with 2C discharge ratings, a good rule of thumb is to try to put together configurations that would have an estimated 45 minute runtime based on the label capacity (or more, if possible), this will usually result in 35-40 minute realistic runtimes on new cells, with steadily declining available runtime with age. When the runtime drops to 80% of original new runtime with age, (around 30 minutes), the cells should be recycled. (this would ordinarily be after a few hundred cycles) Ideally, configurations with longer runtime estimates will be easier on cells and have more useful cycle life, the same 80% rule applies.
For example, a 2200mAH cell might deliver it's rated label capacity when discharged over the course of 10 hours, but when discharged in 1 hour, it might only be 2100mAH, and in 30 minutes, might only be 1850 mAH. So a 2C discharge for this 2200mAH cell would actually be 3.7A, not 4.4A.
So whenever you are buying cells with a particular load in mind, always take into consideration some loss from high drain rates when applicable. Also consider that as cells age, their useful capacity will decline. The best thing to do is look at some discharge graphs of the cell provided by the manufacture (assuming a reputable manufacture), or to get some rough estimates, you might have a gander at CPF member SilverFox's test results for many different cells. They can be found in the "threads of interest" section of "batteries/electronics."
Remember, C ratings are dealing with time, not current.
For li-ion with 2C discharge ratings, a good rule of thumb is to try to put together configurations that would have an estimated 45 minute runtime based on the label capacity (or more, if possible), this will usually result in 35-40 minute realistic runtimes on new cells, with steadily declining available runtime with age. When the runtime drops to 80% of original new runtime with age, (around 30 minutes), the cells should be recycled. (this would ordinarily be after a few hundred cycles) Ideally, configurations with longer runtime estimates will be easier on cells and have more useful cycle life, the same 80% rule applies.
I just noticed Saft's "Li-ion cells for torpedoes" are rated at 4-12C... now to find somebody who sells them.you should point me to a link of a li-ion being sold that is rated 3C, as their aren't many
One more battery question, I have one of mdocod's 6aa>2d adapters I recieved today (awesome by the way) can I charge the nimh batteries in it useing a charger I have from another light? The charger says 7v 250ma (when the charger is not under a load it test more like 8.2 or so) the light it is from is a 6v4a lead acid battery. If not why? Or what about an old nicad 7.2 charger from an rc car? Thanks in advance.
mdocod
Flashaholic
the 7v 250mA wall wart will not properly charge the pack, don't bother, the old NiCD charger would be a closer match, but it depends on how it terminates, or if it terminates at all. Best thing would be to just get a modern NIMH pack charger, they are available anywhere from $20-600 online. share some more information about that old NiCD charger, it may be semi-suitable.
"Wall Wart" LOL mdo! As for the nicad charger Ill have to scare it up before I give anymore specs. thanks for the info.
I know this is a little off subject, but I also need to know If LEDs can be overpowerd at all, I have an unbranded light that has runs on 3 AAA batteris, I want to go to li-ion but at full charge of course they are 4.2v. Can I do this whithout a
? Also I need to know if LEDs can be overpowered like incad. bulbs can I add 1v 2v or 3? If so will the light get any brigter? Thank you for your support
I know this is a little off subject, but I also need to know If LEDs can be overpowerd at all, I have an unbranded light that has runs on 3 AAA batteris, I want to go to li-ion but at full charge of course they are 4.2v. Can I do this whithout a
? Also I need to know if LEDs can be overpowered like incad. bulbs can I add 1v 2v or 3? If so will the light get any brigter? Thank you for your support
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Smile
Newly Enlightened
still confused.
Mr Happy
Flashlight Enthusiast
Maybe not. The unbranded lights that run on 3AAA cells usually have a very simple design that is matched closely to the characteristics of alkaline cells. If you power them from a different source like Li-ion you could supply too much current to the LEDs and shorten their life. However, I have used AAA NiMH cells in one of those unbranded lights without apparent problems.I know this is a little off subject, but I also need to know If LEDs can be overpowerd at all, I have an unbranded light that has runs on 3 AAA batteris, I want to go to li-ion but at full charge of course they are 4.2v. Can I do this whithout a
Unlike incan bulbs, LEDs are specified by their current rating, not supply voltage. The manufacturer will quote a recommended drive current, or range of currents. The supply current should be regulated or restricted in some way so as not to exceed the rating. For large bright LEDs the permissible current may depend on the efficiency of the installed heat sinking. Provide a better heat sink to keep the LED cool and you can use higher currents.
mdocod
Flashaholic
If the little 3AAA light ordinarily runs ~1W (~350mA) across the LED, then you can sometimes get away with driving it on a single li-ion cell instead as these designs usually have a resistor, (an 18500 usually fits in place of the adapter, and will double the available energy storage). It will generally overdrive it slightly, but it can often handle it (and will be a bit brighter, potentially). If it's already setup to run like ~3W on the 3xAAA, then it is likely direct-drive or has a very low value resistor, in which case the li-ion may push it over the edge.
Also, more modern LEDs, like the crees, seem to have more sensitive reactions to voltage change, the older luxeons had a wider tolerance to voltage change. So your milage may vary depending on the LED in question.
There is a way to "test" the idea without risking any real damage to the light:
Use an amp-meter (the 10A or 20A setting on a DMM), and put the DMM leads in place of tail-cap completing the circuit between the base of the cell and the body. Charge the Li-Ion to ~3.8V for the first test and see how much current runs across the LED, then try 3.9V, then 4.0V, etc etc, as long as the current stays reasonable, it should be fine. Continue testing up to 4.20V charge in small increments to se how it responds. In theory most modern LEDs could handle up to around 1A or more. The limitation may be how LONG the light can be run without overheating the LED, so when you start overdriving a stock design, you may change your usage habits to offset the heat issue. If the current gets well over an amp, adding more resistance by soldering in an additional resistor in series, or replacing the existing resistor with a higher value one would be worth a try.
Also, more modern LEDs, like the crees, seem to have more sensitive reactions to voltage change, the older luxeons had a wider tolerance to voltage change. So your milage may vary depending on the LED in question.
There is a way to "test" the idea without risking any real damage to the light:
Use an amp-meter (the 10A or 20A setting on a DMM), and put the DMM leads in place of tail-cap completing the circuit between the base of the cell and the body. Charge the Li-Ion to ~3.8V for the first test and see how much current runs across the LED, then try 3.9V, then 4.0V, etc etc, as long as the current stays reasonable, it should be fine. Continue testing up to 4.20V charge in small increments to se how it responds. In theory most modern LEDs could handle up to around 1A or more. The limitation may be how LONG the light can be run without overheating the LED, so when you start overdriving a stock design, you may change your usage habits to offset the heat issue. If the current gets well over an amp, adding more resistance by soldering in an additional resistor in series, or replacing the existing resistor with a higher value one would be worth a try.
