Lithiums in parallel?

[Bunk3r]

Is it ok to put rechargeable protected lithiums in parallel? I am planning a 3D mag hotwire conversion and putting in parallel will give me some better power options.

 

[FlashCrazy]

Yep, you can run them in parallel. One thing to be careful of though is keeping the voltages fairly well matched. Charging the cells individually would be best. But then again, I guess the over/under voltage protection should kick in if it needs to.

 

[mudman cj]

They should be matched to within about 0.5 Voc from a post by Silverfox. He is considered the authority on such matters and this thread even goes into details of tests he did to verify the safety of this practice.

 

[Bunk3r]

Great thats what i wanted to here.

 

[Avatar28]

Personally, it would still make me a bit nervous to do that, though possibly some sort of protection circuit might not be a bad idea.

 

[VidPro]

with hotwire, be sure that the parellel connections are very low resistance. if you use long wire, springs, alloy wire, small guage wire, AND then put a high load on it, then the batteries can depleat offset.
use fat copper connections or something and the battereis will work in unison even if the load is high.

----------------------------------------------------------------------

also, you can do a little trick when making your parellel pack
have all the wires or connections be the exact same length.
so instead of CHAINING the batteries
__________ (+)
[] [] [] [] [] . BAD
------------ (-)
where the LAST cell is furthest from the load

every cell is the exact same connection to the load.
what i call center tapping the parellel pack
all the connections go to the center, and are the exact same length, the load is connected to these small lenght connections, thereby the resistance to & from each cell is EXACTALLY the same.

or at least like this

____(+)___
[] [] [] [] [] . BETTER
-----(-)----

that becomes more nessisary when things aint TABBED or you dont have copper bar going to the cells, or you are running wire distances from them, or are running very high loads.

 

[Bunk3r]

I am (probably) only having 2 cells in parallel at a time (3 parallel pairs in series). my plan for a holder at the moment uses magnets on the contacts, it will then (probably) have compression from the mags original tail-spring to hold it all together tight. -will magnets be OK for low resistance high current contacts? (with sheet stainless steel used to pair them up) i presumed so as many people use magnets as spacers that you they will take the current without adding too much resistance?

 

[mudman cj]

Definitely don't use the dark-colored magnets that lack nickel plating.

Nickel plated magnets work OK at a few amps, but I have not tried to use them at high currents. You should be OK if you reduce contact resistances using Pro Gold or the like.

 

[LuxLuthor]

Also make sure you use the magnets in a way that they will not move and short to a side.

 

[VidPro]

Also make sure you use the magnets in a way that they will not move and short to a side.

yes ,if you DROP a light that a magnet can move around in, it will move, no mater how powerfull the magnet is, and if it gets in the right place it can cause a short between the nipple and the can

i cant see using magnets (loose) in a flashlight, in a charger mabey, but especially not in a hotwire, its making contact, but it can have resistance, and lesser metal to metal contact point.

 

[Curious_character]

Also make sure you use the magnets in a way that they will not move and short to a side.

I just stick them to the top of the battery with a tiny dab of super glue.

c_c

 

[LuxLuthor]

I just stick them to the top of the battery with a tiny dab of super glue.

c_c

That's a good idea. Someone else came up with a nylon washer that it fits in the middle of, and keeping it from being able to move to side.

 

[DM51]

Leef was making these, which would be super-safe, but Lighthound is out of stock.

In practice, strong neodymium magnets are extremely unlikely to slip off a flat-top anode (because of its smaller diameter) and cause short on the sides of the light, but it is possible.

 

[VidPro]

Leef was making these, which would be super-safe, but Lighthound is out of stock.

In practice, strong neodymium magnets are extremely unlikely to slip off a flat-top anode (because of its smaller diameter) and cause short on the sides of the light, but it is possible.

i dont think of them shorting on the sides of the light, but on things like those driver boards, where it only has to move a bit, or on the outer can of the cell itself, where the insulation is often very thin and useless. both poles to the battery exist right there on the top, which would make a great full scale li-ion short. or on a protected cell it can punch the flat protection wire through its insulation.
it seems MOST of the nippleless issues can be solved with a solderblob better than another loose piece of metal.
but mabey they dont so that, because it then cant be used With or In other things?
you just quickly put a blob of solder on the top of the battery or the driver board, then there is nothing else to ever have to do? sand the blob lightly to remove the flux.
on other things you can solder a spring in, anyway you do it, its one less un-permanent connected item, which is a better connection.

 

[DM51]

I agree, those Leef safety magnets are for Ns0p (ie flat-top cells in series with no parallels), maybe not ideal for use with boards or battery packs, so another solution is needed there.

I personally would not want to mess around with soldering direct onto batts unless they are tabbed ones, but that is because instead of 10 fingers I have nine thumbs and a big toe lol. I'd be bound to make a mess of it. Some people have done it with no problems, but you have to be pretty careful.