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Oct 07, 2004, 11:03 AM
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Assembly of Lithium Ion cells (18650)


I have several of these cells ranging from 1200mAh to 1680mAh. Unfortunately, when I broke them apart from my used cell phone and laptop packs, I pulled the welded connectors as well. Now, I have just the plain cells.

I have gotten proficient at soldering NiCad cells end to end (using Keith Shaw's method) with an 80 watt soldering iron. It seems that the higher wattage allows for quick soldering (slower heat transfer) without any heat damage to the cells.

I am assuming that the second I touch that iron to the tip of my Li-Ion cell that I will at least damage the temperature sensor and at most blow myself up.

Can anyone tell me if they have experimented successfully here or does anyone have an alternative method to making a pack with these loose cells?
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Oct 07, 2004, 12:02 PM
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R101's Avatar
I can only comment on the Konion cells which I think are similar.

Soldering these presented no problem - I just treated them as NiCds and used a very hot bolt for a very short contact time.
Oct 07, 2004, 12:53 PM
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According to all the published data, raw cells should only be assembled with spot welding.....

Below is what I DO,OTHERS MUST BE WARNED!!! IF YOU ATTEMPT THIS, KNOW THE DANGERS AND ASSUME THE RISK!!! OVERHEATING BATTERIES CAN BE DANGEROUS!!!!

Personally, I have made many (over 30) packs Nimh and Li-ion (18650 and prismatic) soldering the shorting straps and connector wires with a good >100w pistol style gun... I believe a lot of heat applied for a short time is best... Tin all leads and strapping FIRST before soldering to batteries, shortens heating time... for battery strapping I use copper Solder Wick makes great connections....

Put good insulation between the cells, and under the strap at the edge of the + terminals (18650) or the - on prismatics.. The image below is a bit exurated but chould give you the idea....

Carl
Last edited by crvogt; Oct 07, 2004 at 01:16 PM.
Oct 07, 2004, 01:47 PM
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Yah, I've soldered I dunno how many 18650 cells. Dozens and dozens. I haven't noticed that I've hurt any yet. Lots of heat and speed ARE the way, you get quick heating of the area that needs heating, and in the end less heat bleeds into parts of the cell that will suffer. I do try to preserve the spotwelded tabs when I can. They take the solder much quicker, needing much less heat.
Oct 07, 2004, 01:58 PM
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From my experience, I agree with the suggestions above. I soldered my 18650s exactly the same as I've done NiCd and NiMH in the past. There are people who recommend against soldering directly to any type of cell, even NiCd and NiMH, as any type of cell has the potential to be damaged by soldering. Experience has shown that if you use the best soldering practices, odds are that you will not have a problem. But there are no guarantees.
Oct 08, 2004, 08:35 AM
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Good Advice Guys, Thanks!!! How about your current draw results?


I think I will give it a whirl. I have a 10 cell pack (NiMH) that I need to solder anyway. So, that will be a good warm up before touching the soldering iron to these (18650) cells.

I really appreciate you guys sharing your results. Due to the bad press that working with these cells has brought about, almost all manufacturers want to steer you away from messing with these. Usaually, you have to get with a curious hobbiest to get the real scoop.

I have heard from Duralite that the rule of thumb with Lithium Ion packs is that you should plan on 2C (Continuous) and 5C (Burst).

Have any of you pushed the limits and if so, what happened?
Oct 09, 2004, 04:11 PM
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You might want to try a search in Batteries and Chargers for 18650 or Li-ion. There have been many reports over the past few years. Different people have gotten different C ratings out of different brands of cells. My experience with the newer Sony Energytecs (1500mAh and higher) is that they can handle ~3C continuous (~4.5A on 1500mAh cells).

Someone reported getting as much as 5C continuous out of the newest Panasonic 18650 cells (2150mAh), or a little more than 10A. It's really hard to say, in my opinion, because I don't believe that everyone really knows exactly what the maximum continuous current is that they are drawing in flight. In fact, it's difficult to get a completely steady current drain in flight, because every time you move the controls, the prop tends to load up or unload with the different aerodynamic loading on the aircraft. So you would be getting continuously variable current draw during most flights.


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