Lipo and 18650, I was shocked

[zhili]

Sorry if this is a common sense here and I am repeating posting facts that are well-known.

I was bored at work and just thought of doing a little intuitive comparation of RC lipos and 18650. I know 18650s may be a bit lighter sometimes, but not sure about the size...

I got shocked, been using lipos whenever I needed high power and light weight, and thought these are the best if not considering stability. Never realised these old school type of 18650 are less than 1/2 in volume than RC lipos. So, for any DIY ebike application except high power, high volt, small pack(low in capacity), the power grade 18650 which can do 1c-2c well are always the best chice?

3 battery packs all are all 12S 14.5Ah

the RED ones are power-grade panasonic NCR18650PF(PD) 2900mah. packed together with spacing in between.

the BLUE ones are typical 6s 8000mah RC packs, I used a spec of 155x75x55(turnigy nano is 195x50x60, similiar volume),one piece shortened to make a 14.5AH pack

the ORANGE one is the pure cell volume of the 18650, if they are not in cylindrical form.

 

[zhili]

I really like clean looking ebikes that doesn't look like an "Ebike"

 

[circuit]

Yup, this is what all the buzz is about. The only problem with 18650 is more complex battery assembly.

 

[spinningmagnets]

There has been enough experimentation with high current cordless tool 18650 cells that I started a list of viable options. Also, there has been an interest expressed by many builders I have chatted with about high current options that are not LiPo (for various reasons). Local college students who didn't mind trying LiPo were told they would be kicked out if they had RC LiPo in the rental/dorm-rooms, so...I wrote this.

If you don't want to solder/spot-weld a high current 18650 pack, em3ev.com has them right now (available as a block, or a triangle)

http://www.electricbike.com/high-current-batteries-that-are-not-lipo/

 

[zhili]

There has been enough experimentation with high current cordless tool 18650 cells that I started a list of viable options. Also, there has been an interest expressed by many builders I have chatted with about high current options that are not LiPo (for various reasons). Local college students who didn't mind trying LiPo were told they would be kicked out if they had RC LiPo in the rental/dorm-rooms, so...I wrote this.

If you don't want to solder/spot-weld a high current 18650 pack, em3ev.com has them right now (available as a block, or a triangle)

http://www.electricbike.com/high-current-batteries-that-are-not-lipo/

Thanks for the info! Now my dream battery would be 26650 with the same density as the panasonic NCR18650PF, which should then have 6A per cell, and fit nicely into the bike frame tubes, but couldn't find any 26650 with similiar spec(chemistry?)

 

[Supersleeper]

I've had much success with 18650 batteries. I'm developing a new 12s 2p PCB based off the following:

http://www.aliexpress.com/snapshot/315573261.html

These compression clips are much better than the typical spring clips as the compression clips place more force and has a higher contact area to the battery. My first prototype with spring clips still worked just fine, with no heating concerns, but they tended to bounce out much more. Me new design will prevent the battery from bouncing out by locking them in with either a bar or another pcb layer above it. Here was my first go at it:

http://endless-sphere.com/forums/viewtopic.php?f=14&t=48746

 

[Supersleeper]

Here's a photo of what I've got so far...



I'm looking to build-in a 12s charge socket and Anderson power pole adapter right off the end of the pcb. This will allow me to build a box that I can slider the pcb into, and easily remove for charging or maintenance.

 

[mvly]

Here's a photo of what I've got so far...



I'm looking to build-in a 12s charge socket and Anderson power pole adapter right off the end of the pcb. This will allow me to build a box that I can slider the pcb into, and easily remove for charging or maintenance.

Those spring will melt if you pull too much current. Keep in mind the contacts on those spring type 18650 battery holders are only good for light load. Pull some hard current and you will burn those contacts.

 

[Supersleeper]

Right, that's why I keep all 12s in a single bank, so there will never be enough current draw to cause that issue.

 

[neptronix]

Keep in mind that the lipo can deliver 5-20 times the amps in that same size.

For low power builds, 18650's are very ideal. You got a 250 watt motor? then about 15AH is just fine and will perform well. What if you have a 2000 ( peak ) watt bike? you are going to need around 2000 watt hours to supply it's peak power demand without sagging terribly. That means you would need a 27AH 72v pack, or a 36v 54AH pack if this was done at a low voltage.

Those spring will melt if you pull too much current. Keep in mind the contacts on those spring type 18650 battery holders are only good for light load. Pull some hard current and you will burn those contacts.

With a super low power cell like the ~250whr/kg LG D1's and 3400?AH panasonics, the cells aren't even good for 1C output, so they would perform best at 2 amps or lower. I think that the spring contacts might be OK for something like that. This would be good for building a monster-sized, ultra long range, charge it once a week but use it for 7 days kind of affair, lol.

 

[friendly1uk]

Anyone point me to an 18650 pack that is considerably smaller than Lipo? These drawings are unbelievable. From my own brief calculations, the best of each makes packs of similar size. Did I really buy the wrong stuff? It seems laughable...

 

[dogman dan]

Inevitably, with any kind of pack there is some more space used for connecting hardware, insulated spacers, etc. But it should not take up all that much space. With 18650's the air space in the cell stack is very small. It can get bigger though with larger round cells, depending on how you stack them.

I would be more ready to adopt the 18650 cells, if they came with 5-8 p sections all spot welded to a tab and ready to go, at good prices, from vendors you know and trust. Preferably a more or less square stack glued together rather than a strip. But they would have to be able to do 1c, in the real world use. So not the same cells as some of the reclaimed laptop stuff that I have seen recommended to be used at about .5c.

Then you could home build a pack that could be diagnosed and fixed as easy as 5000mha lico packs. Pop in a new pack/section, and on your way. A battery holder could be designed like a honeycomb, with a slot for each parallel group section of battery.

The big problem I see continuing, is the price pressure causing the use of 8 or 10 ah packs. Then unless the bike is really only 250w, the battery is just always running at close to it's spec rate and failing early. There is also a problem with dod with smaller packs. People run them very low every cycle, then don't charge long enough to fully balance. It would be better if the pack got 80% dod on a long ride than 99%.

But because the cost is so high, it will always be easier to sell the thing with a 10 ah pack, vs a 15 ah.

 

[friendly1uk]

Packaging stops me dead too. I expect cells to be tabbed. I thought briefly about battery holders but faults seemed a bit too likely. Loosing a parallel string would load up what is left, and you wouldn't know. As I only want a small pack, this shifting of the workload would actually cause an overload in the cells left connected. It all seems like a lot of bother. I just want a working bike.

 

[TheBeastie]

Yeah I kind of dreamed a few days ago of a 18650 cell that would have some kind of threaded bolt/nut setup on each end of the battery instead of blank smooth surfaces they have now, and you could just lock them together or in holders by just threading nuts and bolts type connectors on. I hate soldering, I crimp everything I can these days even if its not pretty.

 

[izeman]

but even those sony vtc4 sag a lot more than a cheap lipo. i thought of going the 18650 route as well because of safe operation. but still bought some lipo. if you want 40a+ you need a lot of those cells.

 

[Supersleeper]

Like I said, I've had a lot of luck running my 18650 (recycled laptops) batteries, and at only 2p was very stable and no hot spots anywhere. Checked with infrared thermometer on each and every battery. Now, this is with springs holders too. The new compression clips will carry significantly more current than the springs. But don't take my word for it, do your own controlled tests, and be safe. I went 7 miles unassisted and with only 24 cells on a 50v pack.

 

[ecross]

.

 

[dogman dan]

Yeah, I shudder to think about having to tab 2-300 cells. or just solder individual tabbed cells.

But if you could buy 6p strings or something like that, then it's not going to be that big a deal to assemble them, soldering jumpers from one string to the next.

Likely there are places you can get what you want, tabbed. But maybe not in one guy at a time quantities. Most of the ready to hand sources are series strings.

 

[Spicerack]

Many good points made about these cells. I run 15s24p on my bike and up to 40A. The cells are all from second hand laptop packs and have been going well for a couple of years now. They get bulk charged and I've balanced them once. The biggest issue is weight if you want decent power. My batteries weigh 15kg! Oh and the other is assembling the packs. What a long tedious task- mine are soldered into 3s8p packs so there's alot of wiring as well with all the balance leads.

 

[friendly1uk]

The cells are all from second hand laptop packs and have been going well for a couple of years now. They get bulk charged and I've balanced them once.

So best case scenario is you balance once a year. I hope they're (somewhat rare) protected cells or your next in line for a fire. Presuming you actually use the batteries.

I actually ask for no other reason than safety. Someone could be mislead into thinking this was acceptable behaviour with there battery. When in fact cells this age could easily fall off the cliff in 12 months. If your not using protected cells yourself, I hope there is a lot more to this story such as actively checking most weeks. Checking once a year would most certainly miss them going downhill.

 

[rscamp]

Do any of you guys end-to-end solder these cells? I used to do this with all manner of NiCd and NiMH cells. It is pretty quick and easy with the right tool and some practice...

 

[Spicerack]

The cells are all from second hand laptop packs and have been going well for a couple of years now. They get bulk charged and I've balanced them once.

So best case scenario is you balance once a year. I hope they're (somewhat rare) protected cells or your next in line for a fire. Presuming you actually use the batteries.

I actually ask for no other reason than safety. Someone could be mislead into thinking this was acceptable behaviour with there battery. When in fact cells this age could easily fall off the cliff in 12 months. If your not using protected cells yourself, I hope there is a lot more to this story such as actively checking most weeks. Checking once a year would most certainly miss them going downhill.

Thanks for being concerned for my health and assuming I'm an idiot. I built the packs with balance leads and check them regularly. These are probably some of the safest type of lipo you can use- as long as you keep the amps low, which is why I made the pack 24p. After a year of bulk charging and using regularly,my top cells were at 4.20 and bottom ones at 4.08 after a full charge so about time to balance charge the packs. So yes there is more to the story, I could go on but there are already alot of doom and gloom merchants telling us how we can't build our own battery packs and how dangerous they are etc

I took a long time going through all the cells initially rejecting quite alot and selecting the best ones. I wouldn't recommend that anyone use these cells to assemble a pack unless they have some idea of what they're doing.

As for end soldering- I wouldn't recommend that as you want to minimize the heat getting to the cells. Because mine were all laptop cells they had linking tabs on them and I soldered on those tabs as far away from the cells terminals as possible.

 

[migueralliart]

Switched to high discharge rate 18650 some time ago. NEVER going back to lipo for commuter bikes. Only for Off Road <5 mile range fast bikes.