are AW IMR batteries safe to stack??

[scalewiz]

My favorite mod I've built may or may not worry me, as there is a lot of talk about stacking batteries nowadays. Features are:

Metal tube construction. Tube is lined with another plastic tube, making it impossible for a short to occur from the battery to the tube.
Top and bottom caps screw on; bottom cap has 4 vent holes, 3/16 in. diameter.
Mod is regulated; should provide decent overcurrent protection. 10 amps max (I have accidentally shorted output without problem).
batteries are 26500 AW IMR (hopefully genuine). 2 batteries are stacked for higher voltage.
Switching is low current using a turn-on terminal on the regulator.

Does anyone see any problems with protection needed? My major question is the stacking of the batteries. Is it considered a dangerous
practice to stack these two AW IMR batteries?

One more thing: I monitor my batteries very carefully. I check their voltage to be sure of balance before charging, and I measure them
immediately after my charger indicates full charge, again checking not only for proper voltage but for balance between them. If I would
ever see any difference my attitude is to replace both of them as a pair, immediately.

 

[LucentShadow]

Sounds to me like you have a good handle upon the safety concerns.

There is always a risk with putting batteries in series, but if you keep a balanced pair, monitor them regularly, and make sure that one of them does not deplete completely, you're doing about all that you can to make it safe. I'd be comfortable with those batteries in that setup.

I'd also advise swapping the order of the batteries on each change to keep them better balanced. A sharpie or paint marker works well to track that.

 

[Java_Az]

Only way i would stack them is get tabs spot welded on them add a protection circuit and then shrink wrap them together. If you look at all the big commercial companies that make 7.4 volt li ion devices this is what they do. you will never find a product made by Sony or Samsung or any of the big companies that have been sued countless times that will require you to put two separate li ion's in series. They are always 7.4 battery packs you will be putting into their devices. Really that how mods should be , but i guess no one wants to spend the time to make cheap 7.4 volt li ion battery chargers. But yes it can be safe if you take the time to do what you do check voltages before stacking. They don't have to be exactly the same but should be no more then a couple or 3 tenths of a volt apart. So this is not something that a mod built for your girlfriends mother should require the end user to do. well unless you don't like your girlfriends mother. Anyway kinda went off on a tangent there but 7.4 volts done in li ion can be very safe if done in packs.

 

[asdaq]

Only way i would stack them is get tabs spot welded on them add a protection circuit and then shrink wrap them together. If you look at all the big commercial companies that make 7.4 volt li ion devices this is what they do. you will never find a product made by Sony or Samsung or any of the big companies that have been sued countless times that will require you to put two separate li ion's in series. They are always 7.4 battery packs you will be putting into their devices. Really that how mods should be , but i guess no one wants to spend the time to make cheap 7.4 volt li ion battery chargers. But yes it can be safe if you take the time to do what you do check voltages before stacking. They don't have to be exactly the same but should be no more then a couple or 3 tenths of a volt apart. So this is not something that a mod built for your girlfriends mother should require the end user to do. well unless you don't like your girlfriends mother. Anyway kinda went off on a tangent there but 7.4 volts done in li ion can be very safe if done in packs.

This is still an important delicate phase, as there is still a warranty period. After the ring is on the finger, then build any mod you see fit.

 

[scalewiz]

Excellent point, well taken, on the creation of a battery pack. Never have found the correct protection board that could be easily implemented into a tube arrangement. At least not when the batteries get this large. I assume the purpose of the board is like any other protection circuit, only adding a balancing function because of dual batteries. That is the purpose of my homebrew balancing technique. With batteries this large, I definitely don't want any kind of meltdown. Also, sealing them into a pack defeats the purpose of using a standard li-ion charger; the charger then becomes dedicated to just this one mod.

Rather than go that far with this mod, I might just design my next mod to use the flat li-ion packs; in a flat box design, a protection circuit board would be much easier/practical. Anyone know how to connect those little flat tabs properly?? I've seen some of these flat packs with a pretty good C rating to handle the current demands OK.

 

[BJ43]

Excellent point, well taken, on the creation of a battery pack. Never have found the correct protection board that could be easily implemented into a tube arrangement. At least not when the batteries get this large. I assume the purpose of the board is like any other protection circuit, only adding a balancing function because of dual batteries. That is the purpose of my homebrew balancing technique. With batteries this large, I definitely don't want any kind of meltdown. Also, sealing them into a pack defeats the purpose of using a standard li-ion charger; the charger then becomes dedicated to just this one mod.

Rather than go that far with this mod, I might just design my next mod to use the flat li-ion packs; in a flat box design, a protection circuit board would be much easier/practical. Anyone know how to connect those little flat tabs properly?? I've seen some of these flat packs with a pretty good C rating to handle the current demands OK.

I have been using these for over a year with a battery monitor. They are 20c and can be charged rapidly.

HobbyKing R/C Hobby Store : Turnigy 1300mAh 3S 20C Lipo Pack (USA Warehouse)

HobbyKing R/C Hobby Store : Battery Monitor 2-6S

or

HobbyKing R/C Hobby Store : HXT Lipo Monitor 3S. A must have for all lipo users!

I fasten the connecters in the box so the battery charger just plugs in and you don't have to remove the battery.