abadcaffeinetrip said:
I can't speak to the RPL specifically, but there are two things you want to look for:
-capacity
-protected circuit
I think you can get 18650s up to 2400mAh. You want the protected cell to prevent fires from over and under charging.
Hi abacaffeinetrip,
Actually for the RPL, you should use unprotected cells.
The reason for this is that the RPL already has a built in Li-ion battery protection circuit.
If the battery is also protected, that in effect puts two protection circuits in series with the battery.
So, you would think that would make it extra safe or even more protected, but each protection circuit adds series impedance and that added series impedance will have a voltage drop across it. More impedance/resistance means more heat which is dissipated in the battery itself. Also each protection circuit has it's own set current and voltage trigger levels that kick the protection circuit active (they are available in a range of current and voltage trigger levels) and if the wrong combination of the two happen, not only will there be less output power due to having two circuits in series, but it will also cause the circuit with the lower thresholds to kick in 1st and shutdown the laser. In my experinece it nearly always reduces the "run time" before the battery protection kicks on and shuts off diode current.
Time and time again I've helped customers troubleshoot problems of lower than normal output power or that their RPL is shutting off faster than it use to, only to find out that they are using a protected 18650 cell rather than the unprotected cell that their RPL is shipped with. They had either bought extras online or often they are using using the 18650 cell that came with their WL spyder.
Protected cells are easy to find, it's the unprotected ones that are more difficult to find as they don't want people to harm themselves by using an unprotected without the proper battery protection circuit.
You can usually use a protected cell in a pinch, but there is a good chance of having a shorter run time and will nearly always reduce the maximum output power due to the added series impedence; it's a very small added impedance, maybe 0.1ohms, but it's internal to the cell and for high current/low impedance RPL system, 0.1 ohms can make a marked difference performance.
oh and yes, of course you will always want the maximum capacity in mAhrs as well as look for a high maximum discharge rate (usually is higher for high mAhr capacity, but not always), go for 2400mAhr minimum and try for 2600mAhr.
Jack
