# Top charge for LiPo 18650's?



## McRat (Jul 10, 2012)

I just charged 144 LiPo 18650 cells individually.
Two went in the trash that were under 2,7v after charging.

After 24hrs, they have a range of 4.18 to 4.12.

So I guess I discharge them to 3.00v and record the time it takes?

I just need to get a good initially balanced battery of 48vdc.

It won't have BMS at all for this application. It's a solar bicycle. Just a toy for the kids. The first version that didn't have batteries was useless.


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## lithiumlogic (Aug 24, 2011)

McRat said:


> 144 18650 cells


LiPO is not a chemistry it's a construction method i believe. One that involves semisolid polymer electrolytes and a mylar pouch enclosure, as opposed to the liquid electrolyte and rigid containers of "lithium ion".

As 18650 cells are packaged in a rigid metal can, i doubt they are LIPO.

I'm assuming you mean you got a batch of lithium-ion 18650s off Ebay, of unkown vintage (possibly harvested from dead laptop battery packs)?

They are almost certainly of lithium-cobalt chemistry then, though it is possible you landed with some lithium manganese cobalt cells out of cordless drills.




McRat said:


> Two went in the trash that were under 2,7v after charging.


They don't sound like geniune Tesla-grade Panasonic NCRs then!



McRat said:


> After 24hrs, they have a range of 4.18 to 4.12.
> 
> So I guess I discharge them to 3.00v and record the time it takes?


With 144 cells, I guess your plan was to group 12 cells together in parallel to make a 2.7volt (empty) to 4.2volt (full) "brick", then connect 12 of these bricks together in series to get your 48 volts.

The paramount thing is to make sure that these 12 "bricks" are as close together in Amp-Hour capacity as possible. If one has lower capacity than the others, then during charge it will experience a faster voltage rise, and could reach the catching fire/exploding stage while the other bricks aren't full. On discharge, your weak brick could go below 1volt while the rest are still strong, damaging it and reducing it's capacity further, increasing the likelihood of a fire next time you recharge.

Now with 12 cells in one brick, the law of averages should mean they're pretty close together in capacity, with strong and weak cells evenly distributed throughout the pack. But as you've chucked two already, maybe get rid of the 12 weakest cells and have a config of 11 cells per "brick".





McRat said:


> It won't have BMS at all for this application. It's a solar bicycle. Just a toy for the kids. The first version that didn't have batteries was useless.


It might be a toy but it shouldn't burn your house down or "vent with flame" while kids are riding it.

Preventing fire means making sure the cells can't go above their max voltage.

In fact i'd set a very conservative max of 3.85v or so. You'll only be charging to 70% capacity but the cells will last forever that way and be at much lower risk of "thermal events".

I'm assuming there's no regenerative braking so there's only two ways it can charge

1 - off the mains
2 - by solar panel

both methods need to have a way of stopping when the pack is full ie. 12 x 3.85 = 46.2V

I'd also probably "top balance" my bricks.

IE.


Once you've weeded out your weaklings and made your "bricks", i'd connect them all in parallel and charge the whole lot to 3.85v or whatever you've decided your fully charged voltage is going to be. Then put 'em in series and start using your bike.

My reasoning is that if "top balanced" they should all reach 3.85V together if you charge the whole pack to 46.2V . When discharging, weaker bricks may drop lower than others, and if you run the pack all the way empty some of the weaker bricks could be damaged. It's still preferable to a fire, you just have to avoid running it empty!


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## McRat (Jul 10, 2012)

lithiumlogic said:


> LiPO is not a chemistry it's a construction method i believe. One that involves semisolid polymer electrolytes and a mylar pouch enclosure, as opposed to the liquid electrolyte and rigid containers of "lithium ion".
> 
> As 18650 cells are packaged in a rigid metal can, i doubt they are LIPO.
> 
> ...


Thanks!

The El Cheapo main charger is 50.4v x 4.5a. I used an individual cell charger to verify DOA's. The batteries were shipped at 3.8 when I checked a handful. I could stop it at 46.2v manually at first, then with a timer. The BLDC controller is supposted to stop 3.0v discharge IF they are correct.

I used an infrared thermometer to check heat during charging. It was a 4°C rise, pretty uniform at 28°C in a 24°C room.

The 2 DOA's had signs of rust at the positive terminal, the rest were shiny.

I'm trying to learn by mistake and advice with very cheap batteries. They are going to be more erratic, and I won't cry if I destroy $200 bucks worth. The factory rating is laughable. They are all identical "GOOD Brand" blue cells with 5000mAh printed on them. Yeah. Right. In their dreams, I guess ink is cheap. I'm guessing 1000mAh or less, but I do not know or do I know the discharge rate. Hence the huge number of batteries for bicycle.

The solar panels are 19.2v x 5.5a dead short on a clear cool day with no clouds. Not sure what voltage they produce under load.


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## lithiumlogic (Aug 24, 2011)

McRat said:


> The El Cheapo main charger is 50.4v x 4.5a. I used an individual cell charger to verify DOA's.
> The BLDC controller is supposted to stop 3.0v discharge IF they are correct.


Sounds like your charger is non adjustable? If you want to go with undercharging, you could go with a 13 bricks in series config. With a charger that stops at 50.4V, each brick will be at 3.88V end of charge.

I must admit i know next to nothing about controllers. Is the BLDC controller also non-adjustable? If it's set up to run off 12 cells in series and to cut off when down to 3v per cell, that means the lower voltage cutoff is 3 x 12 = 36volt. With 13 cells it's going to keep going till you're at 2.77V. In terms of voltage laptop cells give a lot more wiggle room at the bottom than at the top (cell damage not occuring till below 1v, kaboom occuring at 4,5v ) though on the other hand the voltage does fall off a cliff below 3V. If you're top balanced instead of bottom balanced it's possible the weakest "brick" will get damaged further everytime you run it down to cutoff... depends how well capacity matched they were to start with i suppose.



McRat said:


> The solar panels are 19.2v x 5.5a dead short on a clear cool day with no clouds. Not sure what voltage they produce under load.


Don't have much experience with them either. Obviously the no-load voltage of your solar array needs to be above the full charged voltage of the pack. Even if you had 5 panels in series with a "no load" voltage of 100v, i'd assume they'd sag down to whatever the battery pack voltage is when you connect them across it, the current those panels can put out will be no match for what the batteries can swallow.

However, you need to rig some way of stopping the current flow in the unlikely event the solar panels do fully top off the pack, or they'll keep going till they destroy it.

Maybe your children visit a friend's house and disappear indoors to check out his new xbox game, leaving the bike unused in full sunlight for 6 hours. 

To my mind, the simplest way of achieving this might be with a 4 pin linear voltage regulator IC.

They're really simple devices, probably available from places like Radio Shack but they usually come with a data sheet to help you all the same. The 4 pins are input voltage (the solar panel array), output voltage (the battery pack), ground (goes to the negative terminal of the battery pack) and the voltage feedback pin, which tells the regulator whether to let more or less voltage though. The feedback pin is the only techy bit, you basically have a resistor or variable resistor in between the output pin and the feedback pin, the values of the resistor tell the voltage regulator what to limit to. I've used some National Semiconductor ones before and the data sheet was well written, it explained in plain english and schoolboy maths how to calculate the value of the resistors needed to get the output voltage you want.

So, let's say this voltage regulator is set to 50V. 90% of the time, the battery pack voltage will be below that and the solar cells will sag to their level. The voltage regulator will just be a power transistor thats fully "ON" and letting everything through. 

If the pack does get full, the regulator will increasingly throttle the output from the solar cells to make sure the voltage to the battery terminals never exceeds 50. As this will cause the charging current to drop, the load on the solar panels will decrease, they will sag less and the input voltage goes up some more etc. till eventually the regulator is a transistor in the fully "OFF" state.

Mind you, when i used these simple linear regulators it was much less demanding application than you have in mind. You'll need to make sure your regulator can handle the full unloaded input voltage of the solar cell array, and it might need some heatsinking to cope with the power disippation in the worst case scenario.


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## McRat (Jul 10, 2012)

Epic Failure. 

I finally got a way of testing battery performance.

0.8 ohms internal resistance
At 1 amp discharge, it will yield 750mAh before hitting 2.5v.
At 1.5amp discharge, it drops to under 2.5v in less that 2 minutes.
It won't support 2amps at all. Less than 1 second.

12 amps is the most I could expect out of a 12p12s pack. I'd be better off with lead acid.

Completely useless, even for a bicycle.


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## dougingraham (Jul 26, 2011)

McRat said:


> Epic Failure.
> 
> I finally got a way of testing battery performance.
> 
> ...


I am not surprised with those cells. Typically the 18650 cells with 2-3 AH of capacity can do 2C as their max current. I have played with Samsung and Panasonic cells and both can do that. So Between 4 to 6 amps per cell. And they get warm when used this way. You should look into Jehu Garcia's approach as it would work pretty well for you. He has videos on youtube and you can look at his Samba Bus project on this forum. Jehu came up with an approach where the cells cost him about a quarter each but after buying these neat plastic clips I think it was about 50 cents per cell.

What current and voltage do you need for the bike?


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## Karter2 (Nov 17, 2011)

Ha, Ebay lesson learned the expensive way !
Never buy cells with the word "Fire" in the name , or with a claimed capacity of more than 3400mAhr !
Even the "Brand name" cells are often fake, sometimes just old laptop cells that have been "re sleeved" with a "brand" name and a new loose end cap to hide the old tab weld marks.
Buying cells from an unknown source is a huge gamble, best to ask for "samples" first.
Used laptop cells can be very good if selected carefully and used appropriately ..( usually there is just one dud in a pack)
You may want to read this before you invest in any more 18650's..
http://lygte-info.dk/review/batteries2012/Common18650Summary UK.html


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## McRat (Jul 10, 2012)

dougingraham said:


> I am not surprised with those cells. Typically the 18650 cells with 2-3 AH of capacity can do 2C as their max current. I have played with Samsung and Panasonic cells and both can do that. So Between 4 to 6 amps per cell. And they get warm when used this way. You should look into Jehu Garcia's approach as it would work pretty well for you. He has videos on youtube and you can look at his Samba Bus project on this forum. Jehu came up with an approach where the cells cost him about a quarter each but after buying these neat plastic clips I think it was about 50 cents per cell.
> 
> What current and voltage do you need for the bike?


48v x 20amps for short grades. The solar panels are only 400w max. I upped the motor from 500w to 1000w.

Due to the 120lbs of extra weight for the solar trailer, grades were impossible, especially in less than full sunlight.


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## lithiumlogic (Aug 24, 2011)

12 amps x 48 Volts is 576 Watts.

I'm heading off to the gym now and depending on which machine i climb onto, I output 120 Watts (the crosstrainer thingy), maybe nearer 200 on the exercise bike (hopelessly optimistic). That's all i can manage in a sustained way.

To put another way, 576 Watt is three quarters of a HORSE power. How much power does a CHILD output?

If you're trying to make an urban scooter, that can do 30mph uphill downhill and mix it with the car traffic, it's not enough.

For a bicycle, or a kid's toy, especially one which can still be pedalled, it's plenty.

Edit - my meagre power output gives me a cruising speed of 14mph on flat roads on a mountain bike with slick tires and triathlon bars, all 85kg of me plus touring panniers etc. A kid's bike with a kid riding would have less weight and much less frontal area drag and probably go a lot faster on 200 watts. On that discharge rate the batteries would last a lot nearer their rated capacity too. Where are you putting your solar panels btw? You want to be careful they don't shorten the range by adding more drag than they extend it by adding power. I can't think of any good places to put them on a bike without adding to frontal area.... on top of the pannier deck is about all that springs to mind right now.

If i was converting a bike to electric drive , i'd probably make a flat, slim pack that takes up the triangular space in the frame between the top tube, down tube and seat post. If needed there's a bit of additional room behind the rider on a pannier deck. That way i'm not creating extra frontal area drag or having to worry about trailers.

Edit 2 - now i want to build an Ebike. It's a really interesting exercise, especially if you're doing a lot of homebrew. What puts me off is the utility of the finished article, i can't see what such a machine can do over and above an ordinary bicycle

1 - speed. 

bikes have terrible drag coefficient, doubling the input power adds little to your cruising speed.

2 - range

after two hours or so i'm going to be getting very saddle sore, whether i've pedalled or not.

3 - practicality

you still need to carry a puncture kit, waterproofs, lights and a lock with you at all times. You're going to need a shower and change of clothes afterwards if you pedalled, if you didn't , you got no exercise so why not just take the car?

You have little cargo capacity, just like a regular bike. You have to worry about it getting stolen and parts getting stolen from it even more than with a regular bike.

4 - durability

I used to get about 1500-2000 miles out of my bike before the chain, chainset (front gears), derallieur and rear cassette (back gears) would need replacing. Every couple of years the bottom bracket would wear out. Every half dozen rides, i'd need to adjust the rim brakes because they'd be loosing effectiveness or have started binding on. The pads would need replacing after about a dozen. And this is commuting/touring, not downhill/offroad riding! 

These days i have a car and gym membership instead. Less Maintenance!


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## Duncan (Dec 8, 2008)

I used to get about 1500-2000 miles out of my bike before the chain, chainset (front gears), derallieur and rear cassette (back gears) would need replacing. Every couple of years the bottom bracket would wear out. Every half dozen rides, i'd need to adjust the rim brakes because they'd be loosing effectiveness or have started binding on. The pads would need replacing after about a dozen. And this is commuting/touring, not downhill/offroad riding!

What were you doing!
I am a similar weight 85Kg and my stuff lasted a lot longer! - I used to do about 4000 miles a year - with occasional century rides (once a year)

My chain and mechs would last four or five years - pads would last a year
I used one of the sealed bearing bottom brackets

To be cheeky - what sort of cadence were you using? - I used to try and keep above 80 rpm
If you were lugging at a much lower cadence then all of the loads go right up


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## Karter2 (Nov 17, 2011)

> now i want to build an Ebike. It's a really interesting exercise, especially if you're doing a lot of homebrew. What puts me off is the utility of the finished article, i can't see what such a machine can do over and above an ordinary bicycle


 If you are a fit guy who loves nothing more than grinding slowly up a long hill or battling against a 30mph headwind whilst getting hot and sweaty (probably wearing uncomfortable skin tight clothes and shoes you cant walk in...
...then you wont get much from an Ebike.
but if you love the freedom & mobility a bike gives you , especially in the city, and you prfer not to end up needing a shower every time you finish a ride, or just dont enjoy the battle with the wind and gravity as much as you used to... then an Ebike will become an addiction.
Only yesterday, i was recalling how an Ebike makes a daily commute to work a practical reality , and an economic sensible option to a car for me.
Fuel savings are not huge as its only a 10km journey across town, but tolls add up to $10 a day, and parking can be $20+ if i dont find a free space. And of course there is the difference between sitting in city traffic jams , and cruising the cycle lanes and back streets.
It really is a enlightening experience.
And that does not even consider the technical satisfaction of ceating you own transport system, !
..Give it a try !
PS : Check out "Endless Sphere" first, ..if you have not already.


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## lithiumlogic (Aug 24, 2011)

Duncan said:


> What were you doing!
> I am a similar weight 85Kg and my stuff lasted a lot longer! - I used to do about 4000 miles a year - with occasional century rides (once a year)
> 
> My chain and mechs would last four or five years - pads would last a year
> ...


Were you riding a mountain bike or a hybrid/utility/road machine?

I get the impression MTB gearsets are marketed on feature count (number of gears) , weight and price, not longevity. People who hop off rocks probably replace a lot of other stuff so the transmission is not gonna be high in their radar.

The chainwheels were made of a really light, soft aluminium that would wear down like nothing - and going up to the top of the line stuff on the Shimano range just bought less weight not more durability.

I think what may not have helped in my case was that the chain was always filthy. I commuted to work across the city in all weathers. My route took me along this road which was quite wide so the traffic could pass me without taking any evasive action, provided i cycled close to the curb. So most of the time i was riding through salty, muddy water which splashes up from the tyres onto the chain. I'd pour more oil on it every few days but cleaning it was a weekend thing at best. 

I didn't have a garage, and i'm not going to do that in my kitchen. Coming home from work in the dark in the pouring rain, am i really going to lock it up to the drainpipe, go inside, get a bucket of water and cleaning kit, then go back out into the rain and clean the chain off every night? Even if i had, the chain would have been filthy again before i got half a mile.

I certainly did keep the cadence high, though there were some situations in the commute where blazing acceleration was needed from a standing start. I had these spring loaded trigger shifters that had a ridiculously fast upshift, so i used to start in lowest and be in 8th in under 10 seconds. Front wheel would unintentionally come off the ground in the first few gears!


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## lithiumlogic (Aug 24, 2011)

Karter2 said:


> If you are a fit guy who loves nothing more than grinding slowly up a long hill or battling against a 30mph headwind whilst getting hot and sweaty (probably wearing uncomfortable skin tight clothes and shoes you cant walk in...
> ...then you wont get much from an Ebike.
> but if you love the freedom & mobility a bike gives you , especially in the city, and you prfer not to end up needing a shower every time you finish a ride, or just dont enjoy the battle with the wind and gravity as much as you used to... then an Ebike will become an addiction.
> Only yesterday, i was recalling how an Ebike makes a daily commute to work a practical reality , and an economic sensible option to a car for me.
> ...


Yeah i've had a look this morning. 576 watts is enough to push a mountain bike nearly 30mph according the Wiki.

Part of the reason i stopped biking for fitness was that i'd "done" all the routes in my area. I like exercise but only when i've got something to keep me entertained. At the gym, i've got episodes of Breaking Bad downloaded to my tablet. When i cycled, exploring unfamiliar countryside provided the mental stimulation.

However, there was a couple of twisty country lanes that i got to do with a tailwind, which increased my cruising speed to the point that the bends were getting quite "sporty". If a steady 200w from a hub motor means i get to enjoy the sporty feeling more often, my biking could enjoy something of a renaissance.


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