Laptop Powered E-Bike

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RebelRider.Mike
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Laptop Powered E-Bike

Post by RebelRider.Mike » Oct 14, 2017 6:42 am

Hi folks,
I'm planning an eBike and thought I'd share my progress here. I guess I'll start with some specifics.

Me:
I'm around 230lbs. Could stand to lose around 40. I'd like to ride my bike more, but the hills are killer for me. And they seem to be everywhere. I'm looking to add a motor to help get up the hills. I don't want the bike to do all the work. I need the exercise. But I could really use some assistance.

The Bike:
I have a Raleigh of some kind that I received as a gift a while back, and I've recently put my own seat and handlebar on it. A friend of mine installed new cables that he made to custom length to fit the new bars. He even found me some new brake pads.
Image
The bike weighs about 36lbs. There's an ill fitting rack on the back which I will be replacing. It has 26" wheels and ordinary brakes that clamp down on the rims.

The Battery:
As the title suggests, I will be building a battery from reclaimed laptop cells. It will have a range of 42-58.8V. 51V nominal. I'm hoping to keep the current draw to 9.5A. This should allow a power range between 400-500 Watts, and I think it will be able to operate at that output for 3-4 hours. I'm not sure though. I haven't actually built it yet.

The E-kit:
I'm still researching this, so I'm not sure what I'll be using. I do have some characteristics in mind though.
The wheel should spin freely when there is no power to it.
I want to monitor the battery Volts and Amps directly. I can rig something up if I need to.
I'd like the system to be able to operate on the voltage that the battery can provide (42-58.8V)
I need to be able to limit the current draw from the battery to 9.5A so as not to overtax the cells.
I'd like the motor to have enough torque to assist me up hills. I don't need speed. Just a bit of extra power.
To help distribute weight, I'm thinking of using a front hub motor.

I suppose I'll need to be looking for a motor, controller, throttle, and some kind of display. The Golden Motors Smart Pie caught my attention, but I think it is going to be outside my price range. Also, I don't think that one would spin freely when I don't need it.

Its the geared motors that spin freely without power right? Or have I got it backwards?
Also, I'm seeing 72V controllers out there, but not 72V motors. Are these controllers limiting voltage to the motors?

Well, I've got more research to do. I'll post more as I make progress.
Mike

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Re: Laptop Powered E-Bike

Post by Bobw » Oct 14, 2017 9:11 am

Hi Mike.
Nice to see that you are taking on a DIY project, much like I did this past Spring. I am the same weight as you and did a conversion to my old Raleigh which included building my own battery with 18650 cells.
Doing the research is the best approach to take, I would suggest you first figure out how to build your battery pack and mount it to the frame. I don’t think you can get away with 9.5 amp limit on a hub motor like mine, I can easily draw 20 to 30 amps on inclines. I started out intending to use old cells but ended up buying new ones. Others might have different opinions on this subject.
In case you are interested, I shot a few videos of my project as it progressed along. https://youtu.be/MCGCYa3CFGc?list=PLpXt ... j1K0Q-Hip4
I would encourage you to proceed with a conversion, I am very pleased with my bike and continue to add refinements to it.
Here’s a before and after pics...
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RebelRider.Mike
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Re: Laptop Powered E-Bike

Post by RebelRider.Mike » Oct 15, 2017 8:22 am

Thanks for sharing Bob! That's a nice setup.
Glad to hear that your acrylic is holding up. I have an acrylic windshield on my motorcycle, and its getting pretty cracked. I plan to replace it with polycarbonate. Polycarb is more flexible, and will bend rather than crack. Although it also would probably sag more under weight, and is harder to polish than acrylic.

I've done some more math as far as battery and amps. If I can run the motor at roughly 9.5A most of the time, I could get away with the occasional 20-30A and still be ok. I recently built a starter battery for my lawn mower out of the same old laptop cells, and Its held up fine this whole mowing season. The cells in that battery are giving 3-4A each and I've not had any issues with it. At 30A on the eBike, I'll be drawing about 1.7A. I think that will be ok as long as I'm not doing it constantly.

Right now, I have planned to mount the batteries in panniers on the rear rack, and leave the top space open for cargo. I'd like to put the controller and an onboard charger and maybe some tools in a box in the middle triangle space. I also think a center stand is an excellent idea.
Mike

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Re: Laptop Powered E-Bike

Post by Bobw » Oct 15, 2017 12:05 pm

Solving the battery problem is a big piece of the overall conversion. Two issues with pannier placement might be possible vibration/shock transference (being a hardtail) and managing the power wires from battery to controller. I suggest you get a regen capable controller as the rim brakes are a weak point, given the vehicle weight involved. I do 90% of my braking with regen. Kool stop brake pads would help too.
I’m currently working on a rack mounted cargo solution for my bike. I’m setting it up so the bin is easily removable yet mounted firmly and I’m making it with a locking top so I can securely store my helmet, gloves, glasses, etc. when parked at the store or coffee shop. I also carry tools, spare tubes and a tire pump as a contingency to deal with breakdowns. Couple of weeks ago, the rear tire went flat half way thru my route. I was able to pump it up well enough to get home and fix it in the garage.
Just to finish off... I am very pleased with the quality of conversion parts and supplier support received from ebikes.ca. You might be able to get things cheaper from other vendors but I felt their conversion kits offered a combination of quality, inter connectivity and value that a rookie converter should be looking for.

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Re: Laptop Powered E-Bike

Post by d8veh » Oct 16, 2017 5:32 am

My advice is not to use reclaimed laptop cells. You have to do loads of testing and measuring before you start and you end up with a battery that needs to be four times the size and weight to get the same power and range as a battery with modern new cells.

Nothing spoils a bike more than weight.

You need to buy equipment to test the laptop cells. That money would be better spent on decent cells.

Myself and others guys I know had a go at buiding DIY batteries from laptop cells. We all found the same that it's just not worth the effort to end up with a sub-standard battery.

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Re: Laptop Powered E-Bike

Post by RebelRider.Mike » Oct 16, 2017 5:46 am

Well, I've been reading and searching all day. Still closing in on choosing a motor and controller.
But I did read up on the latest Cycle Analyst device. I definitely need one of those! Its got all the features I'm looking for in a programmable control/display. I won't have to add any other gadgets to the handlebars. It even has features I didn't know I wanted until I found out the CA has them, LOL.

So I'm able to refine my motor/controller requirements a little.
Still looking at a front hub motor, 48V 500W. I guess to optimize it for hills, I'm looking for high torque, low RPM.
Regen would be great, but I do need it to spin freely so I can pedal on my own.
Still don't know if I should be looking for a direct drive or geared motor.
I definitely want a controller that will plug into the CA3-DP, and give me most or all the features that the CA has to offer.
The controller should also be 500W, and able to handle voltage between 58.8-42V. I've been reading that most 48V controllers can do this.
Mike

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Re: Laptop Powered E-Bike

Post by amberwolf » Oct 16, 2017 11:15 pm

The easy way to get that is just get the controller from Grin Tech along with the CA. If the CA is doing the "smarts" of controlling the bike, then the "dumber" the controller itself is, the better, as it's easier to be sure the CA is doing what you want without interference from the controller trying to do something else.

Though you can get a "smart" controller and turn all that stuff "off" that the CA would be doing, if it's programmable to do so, it's more complicated when setting things up.


A DD hub won't stop you from pedalling without motor power, but it does have some resistance a geared hub with internal freewheel/clutch wouldn't, which can get worse the faster you go depending on the controller design and the battery voltage.

However, you can also just use a good plug on the phase wires, and unplug them whenever you aren't going to be using the power. Then the motor can't act as a generator, and so it won't have the worse drag problem (it will still have some). In this mode, it won't work as a brake, either, though, so you have no regen braking unless you plug it back in.

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Re: Laptop Powered E-Bike

Post by RebelRider.Mike » Oct 17, 2017 6:14 am

d8veh wrote:My advice is not to use reclaimed laptop cells...
Totally understable. Unless a person has the time and interest for cell harvesting and battery building, its probably going to be a tedious task. Luckily, I happen to be an 18650 nerd, and have been been working on reclaimed cell projects for a while. I've got about 500 cells ready to go, as well as all the stuff I need to test more. Fortunately, I won't need 500 for the eBike.
Image

The biggest disadvantage to laptop cells is the current they can safely produce. I'll have to use a lot of cells in parallel to get the Amps I need, but the capacity should more than make up for it. If I've done the math right, I should get around 3-4 hours of continuous use if I use it at the full 500W. I hope to be pedalling most of the time though, so that might increase a little. Especially if I can set up some regenerative braking. Also, at $0.30 per cell, I'm willing to give it a try. :)

Amberwolf,
I think I'll be getting the CA ready controller from ebikes.ca. One of their C4825 models. Not sure what the difference is in them, other than one is out of stock, but they look to be a pretty exact match for what I think I need. And the price seems reasonable too.

I do like the direct drive motor as it has fewer moving parts. And I would like to have some regen to help with braking. So if the resistance to pedaling isn't too bad, that would be a good compromise I think.
Mike

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Re: Laptop Powered E-Bike

Post by ddk » Oct 17, 2017 10:49 pm

Too clear up some misconceptions:
The motor's power rating is for how much it can absorb without heating up (too much). It's voltage rating is concerned about it's absolute RPM, as you can apply just about any voltage up to the limits of the motor's winding insulation (usually about 300-600V)

The controller limits the power to the motor and the controller's power rating is the one you're interested in for doing your math.

BTW I'm too lazy to look up the regulations for bikes in Washington, but if you have steep hills to climb like I do, even a 1000W system will struggle up 15% grades without appreciable pedaling power ...and I think Washington uses the same regs as Oregon, where you're legally limited to 1000W applied to the wheel.

what I just wrote is clear as mud as normal.
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Re: Laptop Powered E-Bike

Post by 999zip999 » Oct 18, 2017 12:20 am

I prefer a rear wheel drive and a 11t freewheel to peddle at speed. DrAngle has lots of threads on battery builds. A C.A. is a must. Yes more parallel cells. 10p or ? How cheap is cheap ?

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Re: Laptop Powered E-Bike

Post by RebelRider.Mike » Oct 18, 2017 9:00 am

ddk,
I think you're right, and Washington's limit is 1000W. I've also read that the controller is the unit to base power requirement calcs on, and also, don't believe the Watt rating. Read the specs and multiply the max Voltage with the max Amps (continuous, that is) to get the real Watt rating. So with my battery being 58.8V fully charged, the controller I'm looking at has a max of 60V, so It should be ok. Its also rated for 25A, so it should be able to output up to 1470W. Plenty, assuming my battery can keep up! :)

999zip999,
How cheap is an excellent question. I haven't actually done a cost comparison until now. It occurs to me that a single new cell could replace enough recovered cells to make it cost effective. I used the cheapest brand-name cells I could find in a group of 4 on Amazon for new cell characteristics. I may be a crazy cell harvester, but I will not buy off-brand cells. Even I have limits, LOL.

Anyway, did some mathing, and this is what I came up with:
Image

So the to real considerations are Ah, and maximum current. Volts of course will remain the same, so its 14s regardless. (At least it is for me.) In order to get 36Ah I'd still need 15p. Not enough to make up for the cost increase.

Now, if I were to decide that 10Ah would be enough, that would make a big difference!
Image

Only 56 cells would be needed for that, and the price would be way less, but still more than twice what the used cells have cost. Also consider the basic tools you'd need to harvest and test the recovered cells. (I've spent maybe $70 so far.) If this were a one-off project and I had no other need to test old cells, and I was happy with 10Ah, then building my own battery from new cells would be the way to go. Also, there's a rather large time factor in testing and processing old cells too. As well as the fact that 1A is asking a lot from a laptop cell, whereas You'll probably never come close to the 20A that the new cells are rated to deliver. Unless maybe you're doing some kind of ultralight bike with a 14s1p battery. Which would work great for about 15min.

One last thing I can think of to compare would be weight, as d8veh mentioned earlier. I won't be building a single 14s18p battery. I'm not sure I could even safely lift that sucker. I think it would break under its own weight! What I've done is build six 7s6p batteries which I will wire up in a 2s3p configuration. Like so:

One 7s6p battery at nominal voltage.
Image

Six of the above batteries in 2s3p.
Image

Each one of these batteries will have 42 cells, and weigh in at about 4lbs. That's 24lbs total. A 52 cell battery on the other hand, would weigh only a little more than 4 lbs. But if you're going for a high capacity battery like 36Ah, its going to weigh almost as much anyway. I wonder how much a comparable SLA would weigh?

Well, to switch gears a little (no pun intended), I've also been thinking of how I will fit all this stuff onto the bike. I think I've come up with a vague idea that I think will work. Not to scale or anything, but here it is:
Image
I'm hoping the triangle box won't have to take up the whole space but I won't know until I have all the parts together. Oh- gotta leave some room for a 12V battery too. Or a buck converter. I was thinking of using the space above the panniers for cargo, but I'm wondering if a front rack would be better for weight distribution. Pretty sure the back is going to be heavier than the front.

Anyone know if there is a specific weight ratio for bicycles? Like 40% front, 60% rear? or 50-50? I imagine the rear should be heavier to prevent "stoppies" while braking down hill.
Mike

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Re: Laptop Powered E-Bike

Post by RebelRider.Mike » Oct 21, 2017 8:27 am

Well, I dumped a lot of info in my last post, but didn't really draw any conclusions. As far as new cells vs. old ones, I still think the harvested cells are the way I want to go. This is mainly because I'm harvesting cells anyway for multiple projects, and I'v got the time to process and build the cells and batteries. If your purpose is singularly to build an eBike, then building one from new cells, or saving up for an off-the-shelf unit makes more sense.

Anyway, I thought in this post I'd share my battery calculations. I figure if they are correct, someone might benefit from them in the future. If they're flawed, maybe someone will correct me. I know almost nothing of calculating range or miles/Wh or torque vs. speed or uphill power. I've read the wiki, and played with the simulator on ebike.ca. I'm afraid its all still over my head. But I do know cells and batteries, so I'll share that.

To determine my battery requirements, I have to know my power requirements. That is, I need to know what the motor and controller need in order to function. Some of these things I know, and some I've had to guess at due to lack of experience, but Google and YouTube have helped a little.

Here's my eBike's power requirements:
Voltage: 48V. I figure the higher Volts means fewer Amps per Watt.
Watts: 500W. Another guess. I think this will be sufficient for what I need.
Hours of operation: I'm hoping for at least 1 hour of bike riding time.
Amps, Ah, Wh: These will be calculated values based on Volts, Watts, and Hours.

Another assumption I've had to make is how fast I want to go. I figure 5mph uphill, 10mph on flats, and 15mph down hill. Yep; just call me Captain Slow. Also, I intend to pedal through the ups and flats. The motor is only there to assist, not to drive. This is why I'm thinking 500W will be sufficient.

Knowing the Voltage "category" is great, but I need to know the actual range of Voltage I have to work with. For that, I'll need the first few characteristics of my battery and cells. I'll be using 18650 Lithium Ion cells which have a voltage range of 2.8-4.2V, 3.7V nominal.
Image

For a 48V system, I can choose 13s or 14s for how many cells will be in series. I chose 14s. My battery voltage range will be 42-58.8V, 51.8V nominal. Just multiply everything by 14. For safety margin, I'm choosing to limit the battery discharge to 3V per cell rather than 2.8V. This will reduce the useful capacity somewhat, but you'll see later, this really doesn't matter much.

Now for Amps. I can go about this a couple ways. First is to see what the Amps will be assuming constant 500W through the range of volts from the battery, full to empty. So with W / V = A, I can calculate the range of Amps needed as 8.5A (full) to 11.9A (empty). This averages out to roughly 10A.
Image

Another way to look at it is to limit the Amps and see what the Watt range will be. In this case, at 9.5A I'll have 558.6W (full) to 399W (empty). Roughly an average of 480W.
Image

For now, lets say 500W, and with a nominal voltage of 51.8V the Amps will be 9.65A.
Ah, and Wh is easy. Just multiply by hours of operation (1). Or Wh can be found by V * Ah. Same result either way. Now I have the full list of requirements for the eBike:
Image

Next I need to know how many cells to put in parallel. This is a little tricky, as there are two variables which have to be within a certain value range. The first is Amps. Each cell is going to have a maximum safe Amp draw. In the case of old laptop cells, this is usually somewhere between 0.5-1A. The more cells in parallel, the less current is drawn from each cell under a given load. In this case, I'm going to go for a current limit per cell of 0.55A In the past, I've pushed these cells as far as 3.8A each, but only for a few seconds at a time. With the eBike the draw will be constant, so I want to be pretty strict about the Amp limit if I can.

With the battery current being around 9.65A (assuming full-throttle and nominal voltage) I'll need 9.65A / 0.55A/Cell = 17.55 cells. Of course, you can't have part of a cell, so round up to 18 cells in parallel. The actual current draw per cell can be calculated with 18 cells (parallel) * 9.65A = 0.536A/cell. So that's nice.

The other requirement for determining cells in parallel is the overall Watt-hours. This is important because it will determine how long the battery will actually last between charges. Each cell Wh can be calculated: 2Ah * 3.7V (nominal) = 7.4Wh. The Wh of each cell will add up to the total Wh of the battery. So the required 500Wh (battery) / 7.4Wh (cell) = 68 cells, minimum. But these need to be arranged in a 14s configuration, so this will need to be taken into account. 68 cells / 14s = 4.86p. Again, you can't have part of a cell so this is rounded to 5p.

Only 5 cells are needed in parallel to meet the power requirement of 500Wh, but 18 are needed in parallel to meet the current requirement without overdrawing each cell. So the larger of the two numbers is chosen, and the result is that a 14s18p battery (252 cells) is needed to run the eBike. Clear as mud? Here's the whole thing laid out on my spreadsheet:
Image

But wait, there's more!

Now that the battery configuration is know, we can move from estimated values to actual ones. Some of these were known already, but some are new properties that can be found as well.

The Voltage was already figured: 14s = 42V to 58.8V, 51.8V nominal.
The battery can be safely operated at roughly 10A. This was also already known.
Capacity though is now able to be calculated: 18p * 2Ah/cell = 36Ah. (And I was hoping for just 10!)
Watt-hours can also be calculated: 51.8V (nominal) * 36Ah = 1864.8Wh.
Hours between charges can be calculated too: 1864.8Wh / 500w = 3.73h (assuming full throttle the whole time)

A single 14s18p battery is going to be big, heavy, and unwieldy, so I've elected to break it up into 6 smaller batteries, 7s6p. So these will be the properties of the whole battery bank. I've already built 2 of them, and the other 4 are assembled, but still need to be soldered.

Another fun bit of info that can be found is the battery's overall internal resistance. I can't do the whole thing yet, but I can do the IR of each smaller battery as I complete it. For now particular reason, I soldered batteries 3, and 4 first. So I'll start with battery 3. IR can be calculated as IR=ΔV/ΔA when it is put under load. Batt3 has a resting voltage of 26.4 at the moment, and the largest resistor I have is a 50W which measures in at 10.4 Ohms. Putting the resistor across the battery, the Volts drop to 25.4V. Change in Voltage is therefore, 1V exactly. The current running through the circuit can be calculated: 25.4V (load) / 10.4 Ohms = 2.44A. Then, 1V / 2.44A = 0.409 Ohms. This will likely be typical of all the batteries.

Here's where I'm not sure about my math...
I figure if each battery has about the same internal resistance, I can estimate the total IR of all six put together. Basically, 6 resistors, 2 in series x 3 in parallel. Series is easy: add each value. I'll change 0.409 Ohms to 409 mOhms to make it easier. Each series will be 818 mOhms. For parallel, 1/R1 + 1/R2 + 1/R3 = 1/Rt. Then, 1/818 + 1/818 + 1/818 = 0.00367. Then 1/0.00367 = 273 mOhms.

I'll have to come up with a 10 Ohm resistor that can handle 260W or more to check that in real life.

Speaking of real life, what do all these values mean for my eBike? No idea! LOL
I hope it means that the wheel will turn when I twist the throttle...
Mike

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Re: Laptop Powered E-Bike

Post by Matador » Oct 21, 2017 10:12 am

Been there, Done that. Even calculated my internal resistance of my completed packs...
https://endless-sphere.com/forums/viewt ... 5#p1299110

I was a believer of old laptop cells.
I`m a thorough guy who likes excel calculation. DoctorBass, a very well known member and pionner here was even very impressed by my work, caracterizing all these cells and doiung a solderless pack...

This was extremly tedious experiments I conduced and took more than one whole year.
My results : https://endless-sphere.com/forums/viewt ... 0#p1297562

I've even built my own battery case and system for connections in a solderless manner, looked cool, but wasn`t that great :
https://endless-sphere.com/forums/viewt ... 0#p1213147

Then adopted the Vruzend solderless kit and boiled my cheap old scavendged laptop cells :
https://endless-sphere.com/forums/viewt ... 5#p1299063


Been there, done that.... Spent waaaaaaaaaaayyy more money on all these tools for caracterizing cells and building packs than what a brand new top of the line, high-current rated battery pack woul have cost me initially. I learnt an great amount.... This is not for everyone.

I now use Doctor Bass cells.
Cheap and just rock solid high power cells peridod.
See how consistent they are in capacity and internal resistance !!! (check my rigourous excel file datas collection...)
https://endless-sphere.com/forums/viewt ... 5#p1299346

So if you go down that route and do the same kinda work I did,
please also share your results like I did so we can all benefit and see what to expect from these laptop cells.
In my view, the answer I already very obsious.
But adding your results to mine (I believe I analysed around laptop cells 250 cells, and around 280 DoctorBass Sony VTC4 cells) will make the statistical power of our combined analyse having even more impact.

I`m not even shure I would bother building a laptopo pack anymore unless it is for a 10A or less eBike system, and unless I would want a pack of 100Ah capacity or more (which could make sense since laptop cells are soo cheap).... But then 100Ah would probably be around 32kg (70 pounds) for my 14S system... :shock:

What do you think ?
Anymays... I think I have almost 600 post on the ES, which I pretty sure at leat 400 are about batteries. You can tell that I`m battery obcessed. I wanted to be more cleaver than anybody else and save cost on cells.... My final thoughts on old laptop cells is : "garbage in, garbage out" :lol:

Matador :idea:

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Re: Laptop Powered E-Bike

Post by markz » Oct 21, 2017 11:04 pm

Using used laptop batteries is a pain in the neck.
I am fortunate to have a tab welder, so I can buy new cans easy enough for $3cdn rated at 4.2V and 3Ah and 10A. All in, for a 42V system aka 36V, would be 10 series by 3 Parallel or 30 cans 9Ah for a grand total of $90cdn, which will allow you to ride about 30km, which is plenty. Then I bring along a charger, and do what I do at the strip club, I mean grocery store and allow it to charge for 40 minutes and its topped up, I charge at 16A. Lets say I hit up the high stroll, and I need a quickie 20 minuter, no problem. ;) :oops:

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Re: Laptop Powered E-Bike

Post by RebelRider.Mike » Nov 04, 2017 1:26 am

Slow progress on the eBike, but its still going.

The bicycle got a proper fitting rear rack installed. And a third battery got soldered together yesterday:
Image

Check out those solders. I'm getting better!
Image

I've also been considering the other components I'll need. Here's my list as of today:
- Controller: C4825-GR_STOKE http://www.ebikes.ca/c4825-gr-stoke.html
- Computer: CA3-DP http://www.ebikes.ca/ca3-dp.html
- eBrake levers: EBRAKEWUXD_SILVER http://www.ebikes.ca/ebrakewuxd-silver.html
- Throttle: T-TWIST http://www.ebikes.ca/t-twist.html
- Hub motor: MXUS XF39 XF40 https://www.aliexpress.com/item/Ebike-K ... 0.0.8qACao

Still need to find (or invent) a 14s balance charger. And I still need to figure out how to house it all. I'm thinking of reshaping the plastic shells that the cells originally came in. That's still a ways off though. Gotta get components first.
Mike

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Re: Laptop Powered E-Bike

Post by Matador » Nov 27, 2017 12:57 am

Any progress on that laptop cell powered eBike ?
Tedious job right to test all these cells one by one....

You know, I you want to buy some sriously good cell for less than a dollar fifty (I mean cells that are meant for 10A or more per cell),
there is Doctorbass if your in canada.... He can hook you up with some serious 30A capable VTC4 cells.

Otherwise, there is alarmhookup on ebay, who sells 10S2P(20 cells) battery pack for segways.
There made of Samsung MF1 cells (max 10 amps per cell, 2200 mAh).
I bought one pack of 20 cells.... 35 US dollars... My cells are from september 2015. Pretty damn good deal.
You even get a BMS with it !

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Re: Laptop Powered E-Bike

Post by Synon » Nov 27, 2017 3:13 pm

Nice build! My ebike is similar, large pack of used laptop cells. 14s20p total made up of two bricks of 7s20p, one for each pannier. This solved the 14s problem as well as my charger could support 7s, I would just put the two bricks in parallel and then charge both at the same time. I did not use a BMS, I just monitor the cell voltages which I prefer anyway (how does one know if a BMS has failed?!?). I commuted 800 miles on the bike over the summer, cells stayed in balance remarkably well (only had to bring 1 parallel string up to balance 1 time). I charge to 4.0v, I think this pack will last me a very long time with these cells. It's not light, but the weight does not bother me.

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RebelRider.Mike
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Re: Laptop Powered E-Bike

Post by RebelRider.Mike » Nov 30, 2017 2:46 am

Glad your bike is working well!
The BMSs I've seen all seem to be made for xs1p configurations. Their little resistors are just insufficient to balance multiple cells in parallel. Maybe I'm looking in the wrong place though. At least over/under Voltage, and over-Amp protections is nice, but I plan to accomplish that with fuses and a Cycle Analyst. So I'm not planning to get a BMS either.

I haven't made any progress on my bike in a while. I can't afford any motors! Too many other expenses lately. I should probably be building my panniers, but there seems to be no hurry without a motor, LOL.
Mike

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Re: Laptop Powered E-Bike

Post by DrkAngel » Dec 03, 2017 9:55 am

In reference to your discharging to 2.8-3.0V.
Laptop cells are typically "empty" at near 3.7V.
Consider empty at a static 3.7V rather than any much lower voltage during discharge ... which varies drastically, dependent on battery size, controller amps, throttle position etc.
See - Capacity Mapping

DOD is becoming more universally accepted as a major factor in cell lifespan!
The voltage sag and thermal rise at deep discharge mirror excessive discharge rate conditions and battery "damage".
Lower charged voltage and higher discharged voltage are both being increasingly promoted as major battery condition and lifespan protectors.
See - DOD is major factor in cycle life!
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Re: Laptop Powered E-Bike

Post by miro13car » Dec 03, 2017 10:27 am

completely agree with d8veh,
if you want to carry WHours of energy on your bike
you want to carry as little as possible weight per Whour in your cells.
also agree with d8veh,
time and equipment to test those laptop cells ....even the best ones from given used laptop pack have hundreds of cycles in them.

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Re: Laptop Powered E-Bike

Post by RebelRider.Mike » Dec 03, 2017 6:38 pm

Thanks guys. 2.8v to 3v would be with a load. I already have the cells tested and built into batteries. My only roadblock right now is money for parts. Just like all my other projects, LOL.
Mike

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Re: Laptop Powered E-Bike

Post by amberwolf » Dec 03, 2017 7:12 pm

Just keep in mind that running them down that far (load or not) means they will not last as long, so you will have to build a new pack sooner.

They will also not stay balanced as well, so you'll spend more time balancing them every time you charge them.

They also cannot output as much current once they are dropping that far, without sagging even farther, so unless you also reduce the load on them as they get further down, they'll sag below LVC easier down that far, vs a higher LVC.

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