3 build projects, plus harvesting 16580 cells

[TheBossUT]

Hi All,

I have a few projects lined up that I want to do, trying to figure out if it is cost effective. looking for input and suggestions.
Project 1:  Battery pack for x2 16ft Cool White LED lights running at 12v 2.40 amps = 57.6watts hours, I am looking to run the lights for 3 hours for SUP.
Project 2:  Same as above but for a kayak.
Project 3: Cpap battery backup for 16 hours for camping. its 24v @ 3.75amp hour or 90w, I am figuring the amp hour will at least be half since this is for a heated humidifier and heated hose I won't be using these while camping. so maybe 1.875 amp hour ?

Tools for the job = Limited.
*  I will need to get a new 60w solder iron
*  different gauge wires, I most likely have this.
* 16850 salvaged unprotected cells,  recharging and discharging to calculate mah from salvaged laptop batteries. Was looking at this for the charging system and maybe discharge test as well http://goo.gl/AqEX3s  paired with this http://goo.gl/q49ITR to calculate the discharge rate using a 1amp load.  to build the charging system is cheap as I have spare  PC PSU I can use,  the discharge test a bit more expensive looking to do a few batteries at a time.
* Pretty sure I am going to need to get a  SKYRC iMAX B6 and watch out for the knock off clones as well.
* better solder
* pretty much unlimited supply of used laptop batteries, talked to a E waste recycling center, they collect a few 100 pounds a month, I have 40 packs now to dismantle.
* some way to balance the batteries, BMS, individual charging
* buck or boost converter,  I will need to either step up / down to 12v 2.4 amp for the LED project and step up or down 24v  roughly 2amp for the CPAP project.
* lipo firebag, I know the risks of lipos even more so with unprotected cells.  most of the work is done outside, or next to the front door for a quick toss.
* could I salvage a BMS from one of the dismantled laptop batteries ?

I am going to be spending about $40 as it is just to get the charger and most likely another $20 - 30 for remaining supplies.   Is it even worth it ? do I just by RC packs and be done with it ? I know I will still need a charger.    Once I invest in the initial setup building my own packs might be worth it. figuring I can get at least 1500mah out of used cells taking them down to the 2.7v area.

I know soldering the batteries is a risk as well since I won't be tack welding. 60w iron is recommended ? when pulling packs out of laptops maybe it is best to try and keep the tabs on the cells.

salvaging the cells from laptops packs,  I have sparked a few nothing happened other then the spark, the pack was tossed outside after, is there a major risk from a quick spark ? I know shorts are a issue.  I am guessing if anything is going to happen the battery is going to get hot before thermal runaway happens.

on to the project specs. 

Project 1 & 2 are pretty much the same, just one is a SUP the other a Kayak.  I know there are already pre done kits for  $200+

*building the battery or buying it ?  if building I was thinking of just a simple 16850 battery holder and load them in like you do the do AA batteries, depending on mah I can get from the cells I will need between 10-14, then when I am done I individually charge each cell, I am hoping this eliminates the need for balancing.
Step up or step down ? to keep things simple it would be nice if I can just do  3.7 high mah pack and step it up to 12v using a protected boost converter, really looking for input here,
I know I could just run the LED strip off a straight pack, but now I am pushing 16.8 volts to the strip, and they really did not like it when I was pushing 20v wires and strip started to get to hot.  then everything will have to go into a waterproof box with a waterproof DC barrel connector.


Project 3 CPAP battery backup, ResMed S10 elite 24v @ 90w or 3.75amp max, looking for 16 hours run time 2 8hr nights.  I am figuring it will run at 1.8ap to 2amp, have not tested yet, this would be with the heated hose and humidifier off . 
 
build or buy a pack ? if can salvage cells that are at 1500mah I will need about 22, or 32 if at 1000mah, again I would like to do the style of a battery holder, but this might add to the weight and build and may not be feasible, so   if I build a pack it would need a balance system or BMS.  again is it best to Step up or step down, I will need to have some sort of discharge protection, think of taking the cells down to 2.7v


looking for suggestions, thanks for the comments and help.

[sokoloff]

I've tried many times to solder to batteries and finally gave up and bought a tack welder. That makes things wildly easier. You could do the battery holder design or a tack weld pack design, but I'd plan around not being able to solder them.

[TheBossUT]

I've tried many times to solder to batteries and finally gave up and bought a tack welder. That makes things wildly easier. You could do the battery holder design or a tack weld pack design, but I'd plan around not being able to solder them.

Yes that could be an issue as well, along with shorts, Tack welder is not worth the investment to build my own pack, if I was always building pack it would be, but I see this as maybe being a 1 or 2 time. if the pack goes bad then I would have to rebuild.  I have seen a few youtube videos of them soldering to the batteries, sandpapering might be best before hand.

If I could find battery holders in the configs I need and not singles it might work better.  maybe 5 or 10 cell holders then stacked on each other.    The more I think about it, the more I think it might be worth just buying even if packs are not cheap....  i have already has some cells short that I was trying to salvage.... Tossed outside they went,  nothing happened other then they got a bit warm.

[sokoloff]

I suspect you might be able to find an RC club nearby and someone is bound to have a battery spot welder. A well equipped hackerspace also might.

Lastly, if you by chance happen to be in/near Cambridge MA, I can do it for you for just a handful of spare, used cells. It's not worth the hassle of mailing the batteries back and forth, of course.

[TheBossUT]

I suspect you might be able to find an RC club nearby and someone is bound to have a battery spot welder. A well equipped hackerspace also might.

Lastly, if you by chance happen to be in/near Cambridge MA, I can do it for you for just a handful of spare, used cells. It's not worth the hassle of mailing the batteries back and forth, of course.

Never thought to look for RC groups. Thanks.  And I live in Tampa FL. 

[TheBossUT]

wow at a181 views and only 2 replies ? do I have this post in the wrong section ?

[CJay]

I suspect you might be able to find an RC club nearby and someone is bound to have a battery spot welder. A well equipped hackerspace also might.

Lastly, if you by chance happen to be in/near Cambridge MA, I can do it for you for just a handful of spare, used cells. It's not worth the hassle of mailing the batteries back and forth, of course.

Never thought to look for RC groups. Thanks.  And I live in Tampa FL.

If you're harvesting cells from laptop batteries you'll find the interconnects are spot welded onto them and can be soldered to very easily.

Cut them carefully and you have a tagged cell.

[TheBossUT]

Yea, currently I have been ripping them off carefully while trying not to short the cell, the tack marks are left behind and i am sure they can still be solder to, the other thing I have been thinking about is I most likely don't need a driver buck /boost converter for the LED strip lights. or under voltage for that matter, since I am shooting for a total run time of about 3 hours for the LEDs I think once the voltage starts getting low, I will be able to tell by the dimming of the Led, tho a boost buck converter would keep the Leds bright all the time,  but I need to get the BMS system worked out.  unfortunately I am not getting alot of help on forums or crawling the web.

[CJay]

Yea, currently I have been ripping them off carefully while trying not to short the cell, the tack marks are left behind and i am sure they can still be solder to, the other thing I have been thinking about is I most likely don't need a driver buck /boost converter for the LED strip lights. or under voltage for that matter, since I am shooting for a total run time of about 3 hours for the LEDs I think once the voltage starts getting low, I will be able to tell by the dimming of the Led, tho a boost buck converter would keep the Leds bright all the time,  but I need to get the BMS system worked out.  unfortunately I am not getting alot of help on forums or crawling the web.

Well you may be able to solder to the tack marks but what  I meant was cut the thin sheet material that's used to interconnect them so you have a length of that still spotwelded to the cells. Then you can solder to that.

I'd not rely on an LED getting dim as a reliable indicator of state of charge, depending what current you want to draw from the LiIon cell I would definitely consider adding a protection bord that will safely disconnect the cell when it's discharged.

As for charging, I recycle cells from 'dead' laptop battery packs and use the cheap TP4056 boards to charge them.

[TheBossUT]

looks like I might be soldering the 16850's I cant seem to find anyone one with a spot welder near me, there is a local shop that does batteries but they wont touch them, I understand why.