thanks for that, i like technical explanations, but are you telling me that for more 3A runtime we should replace the 18650s used in lights with 14500s? I would have thought the other way around
No, what heās saying is 14500 may generally be able to be discharged at higher C, but if you have 800mAh 14500 and a 3400mAh 18650, even if you could discharge the first at 5C, and the second at 2C, thats 4A out of the 14500 and 6.8A out of the 18650ā¦and you are further complicating it with runtime here. It could be said approximate runtime on that 14500 is less than 1/4th the 18650 in the above example (because mAh is miliamps per hour, and you want 3,000 miliamps for the longest time)ā¦but for further info, look up HJKās charts for runtime on a battery at a specific current
i have looked at many of HKJs graphs and thats why i posted that reply, you will get more 3A above 3.6V on an 18650 then you will on a 14500 hence my request for clarification
B42 explained it correctly. While cells usually have a similar C rating (thats the amount of current you can pull in relation to capacity), the amps you can get vary. 2C on a 2600mAh cell is 5.2A while 2C on a 800mAh cell is 1.6A. But thats not the whole story, its "just" the manufacturers rating. The 3400mAh Panasonic cell will reach 60Ā°C when discharged at 2C (6.8A). Thats still safe, but worth noting. Smaller cells (or flat LiPos) will stay cooler when discharged at higher rates but most people dont care much about temperature. RC world is something else..
But of course you can use LiPo cells for flashlights. Maybe some manufacturers are doing so, there are lights from Lupine and the Olight X6 with external power packs.
/edit: Lupine uses Panasonic 18650. No LiPo there. Didnt find info about Olight, but here is a flashlight using LiPos:
They are more succeptable to catching fire. RC vehicles are hard on cells (I have an old electric truck that has a max current draw of 300A, ) and LiIon cemistry can NOT power RC vehicles. LiFePO4 chemistry can but are much safe than LiPO chemistry so the fireproof bags are simply named after the cells that are more likely to burn down your house. Cells can be a fire hazard when over-discharged (can catch fire over discharged and or while recharging,) over charged , charged by a too high current, and if the membranes are punctred or damaged internally (short). The first set of LiPOs were less safe than the current ones and had no physical protection. These days, many are available in a hard plastic case or are protected by a thin sheet of aluminium on the outside.
LiIon (Lithium Cobalt cells in particular) are unsafe as well, hence all the cell phone and laptop fires reported in the past. This is why there are so many warnings and ādangersā associated with unprotected lithium ion cells. Iām pretty sure though that cell phones do not use pure LiCo chemistry alone these days.
I used to have an issue with the cord or cable linking the device to a battery pack. But after I made the pack for my camera I realized the item youāre powering is in hand, and the pack is at your core, any movement of the item coincides with your own movement so in most cases the cord is not an issue. I know there will always be situations where nothing standard works well, but Iāve found the belt mounted pack to be a non-issue.
so i have a new RC car with a 2S 1700mah lipo pack.
the speed controller on the car is rated at 25A and has a 20mm diameter brushless motor.
i have a voltage monitor for the cells that plugs into the balance plug and monitors each cell individually and has a setpoint for an alarm when any cell drops below a certain voltage.
i was running my car around and decided to see how much voltage was dropping under load as bort was asking for. now i couldnt hook a meter up to the setup as i was running it around but i did do a test with the voltage monitor. the pack was down to 3.5V per cell.
i set the alarm to 3.4V and hammered the car. after 5 sec, the alarm started beeping as it dropped below 3.4V. i let off and a few seconds later the alarm stopped beeping.
the car pulls more than 3A im sure and less than 25A steady state and the voltage dropped less than .2v under heavy load (full power up a hill).
I came to the same conclusion back in ā98. I had a Kodak DC120 digicam (less than one megapixel, interpolated) which would consume a set of four AA primaries in about four dozen captures. That got old pretty quickly, so I bought a 7.2v 1700mAh NiCd RC pack at Radioshack and put the appropriate plug with a coiled cord on it. Problem solved.
