I need help building a Lithium battery for my E-Bike

[Kingcodez]

Sorry if this isn't the correct forum, I didn't exactly know where to post this.

I think it may be called an E-Scooter, I call it an electric bike, but it dosen't have pedals.

Anyways, this is the info I know about the bike:
It uses 4 12v car batteries I think, Each batt must be 2.5v.
The batteries are 3" deep, maby 7" wide, and 5" tall roughly. it would take three of these to equal the size of my Toyota Corolla's battery in America.

The Motor, right now, is 800w, needs 48v of power.

The battery controller is set to only handle 48v.

What I want to do, is either double, or extend my battery life 1.5x it's current life. My bike can go 40km/h, for 20KM, or 20km/h for 30-40km depending on speed and occupants.

My goals are to get the bike to go probably 50KM/H or at least have it get better acceleration. Goal distance is double of what it is now, so 40Km @ max speed.

I have no clue how to do this, the guy here in Beijing said it will cost me 1,000 USD, and he will get me a battery, but the cells are semi/half 'used' from the US. He says he uses A123 cells.

I know enough about batteries from airsoft, I know all about LiFePO4, and building batterys but only up until 11.8v. I kind of know a little about Parallel and serial wiring, I simply need to know a price.

I plan to throw in a 1500w 60v motor, but most likely a bigger one. If it is super detrimental to speed.longevity, then I will stay @ 48v.

What really sucks now, Is that on a fresh charge, my volt meter on the bike says the battery is @ 56v, once I drive it up the ramp out of the garage, 10 meters, it's down to 54. lower and lower it goes, until the cutoff point at 43v where I have to walk it, or sit and wait a few mins for 'the cells to equalize' or something. Then I have a short burst of power until I do it again.

I'm sick of lugging my four big batteries up and down 4 flights of stairs every day. Their too damn heavy, and my girlfriend can't carry them either, so I have to go out and do that whenever she uses the bike for the day.

I go back and fourth to school maby 3 times a day, plus other short trips, but the constant starting and stopping kills the battery so much. And when I ride with my and my girlfriend on the bike it dies even more.

How many cells do I need, and where in the US can I buy them?
Can I buy from a good dealer in China/asia? I'm not sure if it's cool if I stash 300 batteries in my suitcase and fly to china.

Here are some pics of the bike if you are interested:
http://img05.taobao.com/bao/uploaded/i5/T1sIJdXnFEIIDZlnEW_024720.jpg
http://img04.taobao.com/bao/uploaded/i4/T1NZJdXj76otM0QmZW_024631.jpg

Also another quick question, I bought an alarm for the bike, but it sounds like a bird chirping, and it's not loud at all, it's really embarrassing lol. Can I: Wire a car horn, or something not bird like, to the alarm box (which has the shake sensor inside), to the bike, and also wire the headlights, and taillights, to a 'blinker box' and set it on a 1 min or so timer?

I'm really paranoid about it getting stolen, I park it in a garage, but I've had one stolen from right outside my apartment before. I have a good lock, it has a little nub that slots right into my front disc brake. I dunno if it can be picked, but if I had the right tools, and time, I might be able to pry it off, but I know it'd probably damage the front disc (bend it) and mess the brakes up badly.

 

[myzter]

resistance and route are key
try the A123 for a weight savings, they also have voltage drop under load

Carry another spare small pack, A123 booster pack in a hip-sack for additional range
If you can find 3.3V cells for under $6-7 shipped

other than that, get a pedal bike with a hub motor

I have gone thru your situation, and it takes too much from the ride

Year later Im testing 4" wheels on a mini ebike weighing under 50 lbs using supercapacitors

 

[MrKang]

Hi Kingcodez

I think i have the same build of your scooter i'm working on. It drove on 4 x 12V SlA which have no power compared to Lipo.
If you want the power and speed you have to upgrade it with some lipo packs !
First read some important basic here on this forum when you deal with lipo for your own safety.

 

[Kingcodez]

Yeah I saw a pic of your scooter that thing is sick, if I could find one over here I'd probably buy it.
I'm already well read on charging, and maintaining the life of a LiPO pack, but I just cannot understand something as basic as the formulas to get one. I don't know how to get the aH rating, or how to build something with my current aH x 2.
I just really need to know what cells to buy (a123) and how much (ballpark) it will cost so I know what to budget for. I'm going to have a friend build it for me, and probably replace the wires in the bike with higher guage wiring. I know enough about pack building from my airsoft days, but that was just simple "wire 5-6 cells together and pick how much MaH you want them to have).

Right now like you my bike has 48v and a 800w motor, but I plan on putting in a 1500w motor, or bigger if I can find it. Those run 60v also.
But I might just keep it at 48v, since at peak preformance, my bike is just as fast as traffic (40KMH) so I don't really want it to go faster, just accelerate faster, and not be so sluggish when I ride with my girlfriend. ( what does increasing the voltage in the motor do? Better power/speed, less range?)

That's why I don't buy a bicycle, because It's usually ME, and my Girlfriend, along with a backpack, and other stuff.

 

[dogman dan]

You are in China now? That's where all the batteries sold in the USA have come from. Many of us have bought from pingbattery.com or there are some others on Ebay. Most of those battery sellers are in Hong Kong, or some other port in China.

Your problems are all typical of sealed lead acid batteries. They are heavy, and the voltage begins to drop soon. Changing to a 48v lithium battery of some kind will really help. The voltage will drop a bit under load, but it won't get lower and lower as fast as lead acid batteries. You won't have more speed, but you can carry a lot bigger battery for less weight, and get more distance.

A bigger motor with more power will send you into a need for even bigger and more powerfull, and more expensive batteries. Increasing voltage should increase speed, but more speed will decrease the distance you can go.

I would advise to stay with 48v for now, and then keep adding to the size of your battery as you can afford it. Start with a 48v 20 amp hour lithium, and keep adding more 48v lithium batteries , paralell connecting them, as you can afford them. A 48v 20 ah lithium battery should get you double the distance you ride now. Adding more later will keep increasing the distance you can go. If 48v 20 ah is too expensive at first, you could get a 48v 10 ah and paralell connect that with your lead batteries. But as soon as you can afford it, get rid of the lead batteries, and then the bike will get a lot lighter and be easier to carry up the stairs. For a bike carrying two people, 48v 20 ah is the smallest lithium battery you should use. A 10 ah battery may be too small and ruin the battery too soon, or if good cells like A123's are used, it still will not provide that much distance. For what you need, you need as big a battery as you can afford.

Don't forget, when making paralell connections, have all the batteries fully charged. Better still, diodes can be used to keep one battery from overcharging the other. Good Luck, once you change to lithium, you will like your bike a lot more.

 

[MrKang]

You can try A123 cells which you can buy from hobbyking. http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=6444

Thinking of your budget , mayb it's a wise plan to upgrade only your batteries to 66V.
Because if you want to upgrade the motor to 1.5KW 60V you also have to buy a new controller.

Your controller now for the 48V 800W motor is capable to have a maximum of 66volts with no problem.

depending of your average distances with or without your girlfriend is the capacity too choose from.
best is to measure your amps when you and your girlfriend are driving it.... but like you say that you are not that kind of person who hobbied with this kind of stuff would be a litlle problem.

Let's say you want to make a configuration of 66V with 9.6Ah . then you have to buy 20 x 4 = 80 cells.
80 x 15 = 1200 dollar. (you also can make a deal with them cause you're buying in large quantities)

to charge these cells you can buy a meanwell psu and modify it o the desired voltage for your setup.
also more info availabe on this forum.

 

[dogman dan]

Oughta be able to get a 48v 20 ah pingbattery a lot cheaper than that. A less expensive cell will not provide the amps of a123's, but he will need 20 ah of whatever he gets to have any large increase in range anyway. Cost will depend on where he lives, exchange rates taxes etc. In the USA a large pingbattery is well under $1000 USD. And he doesn't have to wire it, find a bms, rig up a charger, etc. The 48v pingbattery should be about 60v hot off the charger, and even under load, should be in the mid fifties voltage. About all a 48v controller should have anyway.

 

[Kingcodez]

AH Would basically be the total capacity of the battery?
How would I go about finding the total AH of my current setup?
Right now, a random taobao listing says a 48v 20AH batt is a tad under $280. (chinese ebay, also it's probably a bunk battery) VPower, says it has BMS and Charger.

I'll probably stick with 48v.
If lets say I bought a 48v 10AH battery, can I connect two of those to make a 20AH battery? (Simply to spread the cost of the battery rather than spend it all now).

What exactly do I need to make a 20ah 48V battery?
80 A123 cells?

In the morning, on a fresh charge, my Bike's WOT goes from 55-53v, and when it's at 53v the thing screams, accelleration is almost perfect, and I can usually hit 40KM/H. I want my bike to be like that all the time.
What is the line for 48/60v motors? Right Now I'm @ 800w, and I know 1.5kW is 60v, is there a motor that is maby 1200w, but still is 48v? Would a motor like this increase the speed, or the acceleration? (I think it'd be accel since more V= more Speed.)

 

[Lock]

other than that, get a pedal bike with a hub motor

What he said. Yer starting off w/a vehicle loaded down with many pounds of ugly plastic... Lightening the vehicle is the cheapest and simplest "mod" to add range and better acceleration and faster braking... Most of the folks on EV are riding on vehicles that weigh less than 100lbs. How heavy is that bike of yours?
G'Luck
Lock

 

[MrKang]

i noticed now that you're not located in the US. so it's easier to buy a lifepo4 48V20Ah from vpower directly

prices are cheaper cause of the taxes and shipping costs.

you could buy a 36V/20Ah and a 24V/20AH ..put them in series and you have a good powerfull scooter.

 

[Kingcodez]

I was looking on the VPower site, and they have (http://vpower.hk/B_LiFePO4/48V_20AH.html), another problem I have is that My battery box is 18cm Tall, 18CM Wide, and 30CM long, and the OPENING, for that, is 18x18x15, since I have two batteries, it's no problem, drop the first in, slide it forward, drop the second, and everything is snug.

Do the companies build custom sized packs? That pack above seems good for what I need, it just needs to be sliced in two.

On taobao.com it says "ICR 18650 VPower" I'm assuming these are the type of cells, are these any good? **Nevermind I went on kayobattery.com and it says these are 12-1400 mah cells, I know that means they are small, is mah the total capacity, and ah is the amount of power it can put out???
http://item.taobao.com/auction/item_detail-0db1-497acbcc9430d38c8a94689aae9ed8e4.htm?cm_cat=0&pm1=3
2000 Kuai = 292 USD, for a 48v 20ah battery.
This looks like the regular duct tape battery reviewed in another thread here.
How many cells are needed for this type of battery?
It seems like it'd be better just to buy the cells individually, and work my way upto a 20AH pack.. In the future, if I decided to add another 'module' could I just buy X amount of cells, and keep adding 10AH to my existing battery as I had the money?

Under my seat, has a ton of space, just the battery box is smaller.

 

[MrKang]

You can unscrew your budy sit and then have full acces to your battery box.
the 48V/20Ah can be delivered in different sizes. 18 x 18 x 30 is your maxiumum size ?

then you buy two 24V packs ..one in the battery compartment and one in under the buddyseat were your helmet goes in.
but i would go for the 24V and one 36V to get more power..

 

[scoot]

The following suggestion is based primarily on the 5x7x3" dimensions of the SLAs you described. My build has a predefined battery compartment as well, so stacking/fitting the cells effeciently became a primary concern for me. I ended up using the 10ah Headway cells as a result (they are made in China). They are 5" long by 1.5" diameter. From my rough calculation, you should be able to stack 8 of these cells to roughly achieve the dimensions of one of your SLAs you described. That should give you 20ah at 48v. They may not have quite the performance repuation as the American made A123s, but they are well respected LiFePO4 cells from what I have read, and it is a whole lot fewer individual cells to deal with. Of course battery management would be the next issue to address.

If you look at the prebuilt Headway packs (with BMSs), they appear to be "splittable" because of the way they are assembled with cell holding "Lego" style blocks.

Just a something else to consider

 

[Kingcodez]

The following suggestion is based primarily on the 5x7x3" dimensions of the SLAs you described. My build has a predefined battery compartment as well, so stacking/fitting the cells effeciently became a primary concern for me. I ended up using the 10ah Headway cells as a result (they are made in China). They are 5" long by 1.5" diameter. From my rough calculation, you should be able to stack 8 of these cells to roughly achieve the dimensions of one of your SLAs you described. That should give you 20ah at 48v. They may not have quite the performance repuation as the American made A123s, but they are well respected LiFePO4 cells from what I have read, and it is a whole lot fewer individual cells to deal with. Of course battery management would be the next issue to address.

If you look at the prebuilt Headway packs (with BMSs), they appear to be "splittable" because of the way they are assembled with cell holding "Lego" style blocks.

Just a something else to consider

Wow their literally half the size of my current setup?
You are saying that it's be harder for this setup because of the management issue? is that because there are a lot less cells to deal with?

 

[julesa]

mah = ah/1000

Every connection is a possible failure point, and you can't necessarily buy two packs and just hook them together with no consideration for preventing one pack from overcharging the other, etc. I think you would be better off saving your money until you can buy one good quality pack that meets all your needs from the first day.

I think this is Headway's web site:
http://www.xhnykj.com/index_en.asp

 

[scoot]

You are saying that it's be harder for this setup because of the management issue? is that because there are a lot less cells to deal with?

All LiFePO4 cells (Headway or A123) should have cell mangement incorporated which certainly makes it more complex than just replacing SLAs.

Cell mangement, including balancing, LVC (low voltage cutoff for discharge), HVC (high voltage cutoff for charging) is higly recomended for LiFePO4 cell connected in series... in your case for 48v it would be 16s. If you paralled two complete 48v Headway packs of 16s each, they would each need their own battery management system (BMS).

With bigger/fewer cells, it would be easier identify when and where a bad/weak cell gives out or shows up... if it ever happens. Example:

If you put pairs of individual Headway cells (parallel connected) in a series string of 16s (16 pairs for 32 cells total) then a single BMS could be used. That way if you detect a weak pair, then you know the weak cell is narrowed down to one or the other cell of the pair. If you were to attempt the same approach with smaller A123s, only instead of pairs, you have say 6 of them paralleled in a group, then it gets a little harder to narrow down the weak cell(s). Plus i think the odds of having a weak cell somewhere goes up statistically speaking when you have to deal with more cell count. Plus like julesa said, and I'll interpret his remarks as... the fewer connections the better.

It gets even more complicated if you try to parallel say 6 or so A123 packs that are 16s each.

If you want to avoid cell mangement, You could do a search on the Konion cells (e.g., Bosh Fatpacks, LiMn) in this forum. They have been reported as being very rugged and are less dependent on "cell mangement" than other Li cells. I have read recently however that they are getting hard to find at reasonable pricing. Maybe they'll show up after the holidays :?

If you end going with some premade LiFePO4 48v (or whatever voltage) packs w/BMS (any brand) and choose to parallel the packs for more capacity/range/amp dischgarge, you can protect them from each other with schotkee diodes (even the "ideal diodes" offered by forum member Tiberius).

Hope I haven't overcomplicated things... it has taken me many months to get the point where I can spout this stuff off, and thought I would give it a shot today :lol: , but I feel like my knowledge is progressing and I know how confusing it can be when starting off on this road It's great fun though

BTW, I concluded a long time ago that Lipoly was just too dangerous (road flare) for charging/storing in my cubicle, puplic transportation (train) or garage... especially for a DIY... JMHO though.

 

[Kingcodez]

Well put julesa and scoot, I wasn't quite planning on hooking two packs together, that's definately way too expensive for me. If anything if I got more cells in the future, I'd have the packs rebuilt or something.

But I'm still confused on a few things, how many cells are in a 48v 20ah pack? And what type SPECIFICALLY.

Someone earlier said 80 or so for maby a 60v pack.
Can someone link me to some cells that are good for capacity/price? Not necessarily the best, but not the cheapest either.
So there are 16 pairs of cells, for 32 cells total, and that makes a 48v/20ah pack? If every pair of cells had only 1ah, 16 pairs would make the battery 16ah? Is that how you get that number? a 20ah pack uses 16 1.25 ah cells?

 

[scoot]

These concepts will be crucial to you:

Cell amphours are additive when parallel connected, and, Cell voltage is additive when serial connected (all LiFePO4 cells are 3.2 v nominal-- that's defined by the cell chemistry.

So for example, if 20 1ah cells are parallel connected, you end up with 20 ah at 3.2 volts.

Conversely, if 20 1ah cells are connected serially, you end up with 1h at 64v volts.

Hope that helps unravel the mess I made of my previous post and answers most of your techincal questions about cell configuration.

About, cost effective choices there are probably many choices and preferences folks will attest to here. I personally selected Headway 10ah cells... we can finally get them here in America for $20 a cell shipped. It would be cool if you could find them in China even cheaper. But that still leaves the cell management issue which can be further elaborated on as we go 8)

 

[Kingcodez]

Ok I understand it better now.
I need 15 strings to get 48v and 20 1AH cells to get 20AH??
Is it better to use 1ah cells, or 2 ah cells? Does the AH matter much, as long as I get to 20ah?

Does anyone know what my SLA's AH is now, just a ballpark guess?

 

[julesa]

No idea about your SLAs. Usually a nominal 48V 20Ah pack made from LiFePO4 cells is 16 cell groups in series.
If it's made from Headway 10Ah cells it's 16 sets of 2, 32 cells total.

You might also look into Thundersky cells for a scooter. If you can find a local vendor, ask them for spec sheets, which should list the sizes of the different cells.

 

[Kingcodez]

How much mah should the cells I use have?

If I took the Headway batteries for ex, I'd need 16 sets of 4 cells?

 

[morph999]

Kingcodez, it's suggested that you get a BMS with your lithium but there are several people on here who use lithium without BMS. I'm about to be one of them. I plan on only using about 80 % of capacity though to make sure I don't mess up my battery.

Vanilla Ice bought some Lipos and he's charging them all individually.

You could buy like 12 of these for a 44v 15ah

http://hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=8579

then buy about 6 of these
http://hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7637

charge 6 of them at a time

I'm buying Thundersky Lifepo4...a 36v20ah pack for $400.

 

[morph999]

yes, finding about Lithium is kind of difficult because the information is spread out all over the place. It takes about 48hrs of constant reading to understand everything. It's more of a do-it-yourself kind of thing right now. It's not really packaged for the average consumer yet.

Here is what I'm buying

http://elitepowersolutions.com/products/product_info.php?cPath=1_8&products_id=82

I'm not buying the charger...instead I'm buying 2 of these to charge them...and make sure each cell is balanced.

http://www.batteryspace.com/smartcharger60afor32vli-fepo4batterypack1cellalligatorclipplug38vcut-off.aspx

then use anderson connectors to connect the individual cells so they can be easily unplugged and charged and also maintain balance. That's what I'm doing.

Hope that helps.

 

[Kingcodez]

Yeah thanks for the input, I'm going to buy single cells, and make a 20ah pack, all in one go, I don't wanna risk anything going wrong.
I'm going to investigate this guy (http://item.taobao.com/auction/item_detail-0db2-863ced6543043cc214ee17c9037073f2.htm?cm_cat=0) He's selling A123 cells (he says) for $5USD a cell.

I'm not sure if their real or re brands.
I know about the BMS, and I'll look into that when the time comes.
But I still have a few basic unanswered questions.
16s how many p to make 48v 20ah? If for ex I used a123 cells. Some cells I see out there are 1200 mah, others 2400 mah.
How much AH is one P string? It would be the amount of the battery I'm using right?
2.4AH x like 5 P strings or so, is only 12AH. So to make 20AH I'd need 8.333 strings?

 

[morph999]

This company says to be wary of chinese copies. He sells his A123 for $14/cell. He says they are genuine A123.

This cell below..the 26650A is 2300mAH...so 2.3AH.

so you'd need about 84 of them to do a 48v 14ah...that's about $1200. With A123, you might not need as many though to get same distance as other chemistries.

http://hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=6444