3rd ebike battery. This time, doing it right

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Mar 28, 2017
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Like the title says. I'm starting the design process of my 3rd ebike battery. To go into a little history:
[*] The first ebike battery was a super weird shaped battery that hugged the frame tube on my bike. I created individual cell balancing leads and I hot glued every cell together. I used solder wick wire as my cell connector and that has done me well.
[*] My 2nd battery consisted of mostly new cells between panasonic ncr18650 and LG S3 18650 cells.i still have some older laptop cells in the mix and I'm wanting to finally kick those to the curb. I also have a few cheap Chinese cells I've verified have at least 2000mah capacity. The cells are made into a right angle triangle pack and hot glued together.
[*] Finally to the new battery. I'm hoping to replace almost all if not all of the Chinese cells and any other older cell with the Panasonic cells. I can get them for just under $2 a cell right now and that seems to be a decent price. This time around I'm going to be using cell spacers. The 20mm puzzle piece ones that I can create my own design. This will be a 13s 8p 104 cell pack. Bms of course and I'll be using the same solder wick wire for my soldered cell connections. I'll be doubling up the safety by shrink wrapping the cells a 2nd time along with the cardboard tabs at the positive terminals.

2 questions so far.

1) What glue should I use for the cells in the spacers? I'm definitely gluing each spacer together once I have the final design, however do I need to glue each cell into the spacers or no?
2) so I'm going to use solder wick wire for the connections. This is great since it's braided copper and it's 3.5mm wide. I am going to encase the battery in either a plastic or aluminum triangle case. Which material should I use? I feel like the polypropylene will flex better but not hold up as well. And it's non conductive. My other option is aluminum sheet. That will hold up better, look better, but pose a short potential thst I will mitigate and require more tooling. Which should I go with? And more $$$.

I have a design planned out for the cells and their connections. I'll share that later.
I'll also mention that at a later time I'm planning on doubling the battery as a backup battery / power wall. It'll only be around 1kw but it should be enough to run enough devices if there's an outage.
 
Lexan is too brittle of a material so polypropylene is much better.

I'm looking at at least 2100watt max burst draw. I regularly ride in stop and go so I'm typically need a good 1700-1900w bursts to accelerate. After that I level off around 600-900w. My target is around 5-6amps max draw per cell. For the Panasonics that's no problem. That's a bit of a squeeze for my LG S3 cells though...
 
OK little update I this...

I've ordered my cell holders/spacers. I will have enough for at least a 13s9p battery. I'm really considering adding another parallel group because I want a 1kw battery and I don't think a 8p will cut it. Plus with my burst and acceleration desires, the 9p is going to be better on the cells and max amp draw. I'm planning on getting a 60w load tester so I can crank the loads up to 5a per cell so I can test each one to make sure it can handle the battery.

I haven't decided on the housing yet but I will definitely need one. The plastic is sort of expensive once you add shipping so I'm holding out for scraps for now.


I'm really hoping the bigger battery will really get me some added range then I'll easily be able to commute the entire way to work and back rather than my current commute sharing it with the metro. I can save a ton of money per month by doing that and it'll be a great test on all my bike equipment and battery!
 
Here's the design right now. It'll fit my battery bag perfectly. I'm also planning on using it for a battery backup. For now I can get a 48v to 12v converter and run a 150w inverter....

45353433074_55ca438ac6_b.jpg


I'm hoping to also switch to 10 awg wire and do a really safe battery design with a plastic/aluminum case along with positive end circle insulators. I basically want to build the battery to last me at least a few years.
 
Philaphlous said:
Lexan is too brittle of a material so polypropylene is much better.

???

Lexan is polycarbonate. I've seen it crack from long term static stress or from hot forming without annealing, but I've never seem it crack from load or impact. It's very tough, which is why it's used in bullet resistant windows. In the cycling industry, it's used for pedals. A brittle material wouldn't work in either application.

Maybe you're thinking of acrylic?

I'm curious-- why did you choose a square stacking pattern instead of hex grid?
 
Square is going to be easier to make a box out of it and it'll provide a little gap for air to keep the cells from getting too hot.
 
Philaphlous said:
Square is going to be easier to make a box out of it and it'll provide a little gap for air to keep the cells from getting too hot.

For what it's worth, I think keeping the cells warm is just as important as keeping them cool, unless you're running them so hard that you're beating them up. Anyway, unless you use forced air, the difference in air space probably doesn't matter.

But if you have enough room for all the battery you want, then no problem.
 
Well I'm hoping the panasonic (toshiba) battery packs go on sale sometime soon. I'm hoping to get them for around $1.60/cell, right now they're like $2.25 a cell, still not bad but I got them cheaper a year ago so who knows. I check the ebay listing daily. I've seen it go on sale once and also the seller isn't willing to sell for the price I paid a year ago...


I got the cell holders coming and the positive end insulators. I also ordered a 60w load tester to check my cells and see how they do under reasonable load rather than the 1A that my iMax can discharge.

I'm not worried about the cells getting cold. They're always inside and they're in a battery bag when I'm biking so its not like they're really exposed to the cold, plus I plan on having it encased in plastic once its built. I'm going for maximum safety with this 3rd design. I'm also hoping the design will prove to be maximum performance and capacity so I can do full commutes to and from work.

:bigthumb:
 
Got the cell holders already! That was fast shipping!

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I'm still waiting on a sale or good deals on battery cells. I'm still trying to stick with the Panasonic NCR18650 cell for my entire battery...

The cells are a little loose in the holders so I'm planning on using a 2nd layer of shrink wrap along with the cardboard positive end protectors...doing all I can to keep it safe from shorting out essentially...I just won't have the individually fused cells...
 
After my first time working with bending pvc pipe I realized that this is such a great option for the frame of my battery. I can do a straight cut on the pvc and then just heat it up and lay it down flat so easily! Best of all is its super dirt cheap compared to regular sheets of plastic. So pvc it is once I get it!

I'll probably do whatever is cheapest for the sheet to cover the rest of the battery. I'll be on the lookout for good plastic deals.

I'm selling an old motorcycle helmet to offset the cost of the new battery cells so I hope to have those sometime soon in the new year.

I want this battery to be incredibly robust and last a long time so the case is really important. Along with doubling up on the shrink wrap and double positive cell insulators and a full plastic/pvc case the battery should be great. I'll be using 10awg wire for an anti-spark xt90 connector. I'm thinking deans for the charge port but we'll see....

My plan is to have this battery last a good 3+ years of ebike abuse. I'll regularly be pulling 5amps from the Panasonic cells which is well within their ratings.
 
Alright!!! We're in business! :bigthumb:

I've ordered the rest of the battery cells this am. This should get me all the necessary cells for my battery now. I'll have to do some major tare down work on my old battery to get the new one all set for soldering and wiring.

Stay tuned in the next few weeks for progress!
 
999zip999 said:
Do order the gasket for on the pos. side if extra still put it on the pos. side. .

Yes! I have those and I also got additional shrink wrap to shrink the cells to fit extra snug in the cell spacers and extra safety on the positive side. This battery is basically to address some safety concerns I have with my current battery.
 
So I got the 60w load tester and it's great!! I think some of the ah and wh calculations are slightly off though... My older panasonic ncr cells get around 3aH which they should only be around 2700-2900 at best...

Additionally I'm not sure if the internal resistance is really high or what but under load I go from 4.16V to 3.62v at 4A....

Cell testing has begun! I've got a decent setup. I'll have to post pictures later. I've got the design of the new battery already set out on the cell spacers. I use my imax charger to charge up 6 cells at a time then u use the 60w load tester to apply 4amps down to 3.1v to get my wH capacity and then based on those numbers I'll equalize each series of cells so they balance properly...

I'm probably going to go a good week without my current battery since I'll be using 38 of the cells from that battery so I'll need to tare it down to get those cells out.

I'm actually a bit disappointed in the Panasonic cells. They don't do really well for very high currents and are only able to deliver about 4A per cell consistently...when I get to 5A the voltage sags alot and the actual wattage output isn't very good. Apparently the max continuous rating is 5.8A but with about 8 year old cells it's more like 4.8A... I still shouldn't have any issue pulling 1800w from my battery hopefully... Overall I really need range over speed so I'm hoping for a good 40-50miles of range with this battery at about 20mph average.

Overall I'll be really happy once the battery is finished. The pack design is so much simpler then my hot glued one...and it'll be way safer using these cells over the mix of cells I currently have with old laptop cells and Chinese cells...ugh...I cringe at night thinking about them... :oops:
 
999zip999 said:
How you going to conect the cells.?

3.5mm solder wick wire.
24293905757_217a4de44a_b.jpg

It works great and it's super easy to solder to each cell. I only need a few seconds on the cell to solder it to it. Plus with it being stranded copper, it offers the least amount of resistance so the current flow isn't inhibited.
 
Oh . The only way I would do that if I put a full sheet of that red paper on top of pos. side with holes punch out for the placement of wired copper. Look at the 4th cell of from bottom and see the melted shrink wrap next to the Neg. can ? A tiny amount of flux makes flow.
 
Picture update:
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I use a 6 cell holder to charge a battery pack at a time once I break it down to get each cell. It's a modded imax and it's a Chinese clone. It does the job.


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I love this thing!!! So easy to use and I can load the cells way more than the imax. Gives me a much better idea of how each cell will perform in my battery pack!


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A good start! I still need to grind down the nickel spot welds on the positive and negative ends. I use a grinder wheel on my dremel. Works quite well and it roughs up the surface of the cells for soldering...the solder sticks much better and flows much easier when its a rough surface.
 
999zip999 said:
Where did these cells come from ?

I'll share the link now that I have all the cells I need. Lol last I checked he has about 50 available..
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F263455733158

The batteries are still sealed in the original Toshiba battery. They're super easy to break apart and depending on which cells you get, you'll get either the older nca or slightly newer nca cells with the different wrap. I've seen a few packs down to about 2V per cells and all charge up right away with no issues. They all hold their charge and discharge just fine... I trust these cells over anything else I've ever bought.

To add to my list of mods for this year:
I don't have any connectors from my controller to the hub motor...the wires are soldered directly together... I need to fix that in case I have a flat. Im dreading that day... So I need to get some xt150 connectors. I've been reading up on phase amps and I'm a bit concerned that the amps are soo high they will even compromise these connectors. I plan on using loctite 8008 conductive antiseize for each bullet connector. The copper/graphite in the grease should help conduct the electricity and hold up to the amount of amps I'm pushing through the hub. I also need to upgrade the wires eventually so I'm looking at some 10awg wires right up till the hub motor since I won't be able to thread 10 awg through the shaft.

Quick update: ordered the new xt150 connectors and 20ft of 10awg wire. That should be enough for my new battery and to wire the controller and hub motor with.
 
Progress is happening!

I got all 8 laptop battery packs in the mail this past week. I'm charging them up, 6 at a time. All cells thus far were resting at around 3.2V which tells me they're all great! Will obviously do the IR and wH test once they're all charged up and add them to the rest of my pack.

I'm in the process of getting my old bike tire for the rear and some rewriting before I can take apart my old battery. I need to be able to swap out my rear hub motor with my old standard rear hub for the bike. I'll ride a week or two without the motor as I'm finishing up the battery. I'm still not sure how I want to mount it. I'm thinking of doing some click in type mount on the downtube and frame using the screws for the water bottle....trying to get the battery as low as possible essentially. I'm hoping to make he battery housing completely waterproof so there's no real need to keep it in a frame bag...
 
Cell testing is going well. All cells are within specs and I've tested almost 50 cells. Ill probably test a few from my old battery once I take it apart to check the capacity and resistance of the cells after a year and a half of use.

I've decided to go with hdpe for the frame of the battery. 3/8" thick hdpe is like $7 for 4 feet of the stuff so I'm pretty excited for how cheap the stuff is. I think to keep costs down unless I can find some thin scrap aluminum sheets I'll use vinyl tile to cover the sides. That along with plenty of screw and some sealant should keep the battery waterproof.

I really really really want to ditch the frame bag and have the battery mounted directly to the bike using the m5 screw holes for the water bottle... I just don't know what would make an easy slide on / slide off attachment for the battery to the bike...but I think I have an idea... Drawer slides!!! These are all metal, they're ball bearing and have tight tolerances, can handle heavy weight...and should be easy to slip in and out of the frame... I can have the long side of the battery with the slider screwed into the hdpe and it should just be able to slide right down into the frame. I'll probably need some guides or L brackets on the downtube so the battery can't move side to side when I'm turning... I think it's a great option and I can hopefully make it look really clean and professional.

I have the advantage now of being able to make the battery into whatever shape for the frame so it'll fit the bottom of the frame and keep the center of gravity as low as possible.

I've got plenty of 10awg wire so that'll make up the internal wire of the battery and then I plan on rewiring the controller to the 10awg and phase wires also. I was looking at some 6 or 4 awg wire for the phase wires since Im guessing they'll see 100ish amps at low speed but it's kinda pointless considering Im not planning on rewiring the phase wires in the motor with 10 or 12 awg ptfe coated wire...so 10awg should suffice.


So my very next upgrades will be to rewire the phase wires from the controller and motor with the 10awg silicone wire and add my new xt150 thats in the mail right now. Once that's done I'll need to swap out the motor with my original rear hub so I can ride it like a real bike for a week or two as I'm taking apart my old battery and using the cells for the new battery. That won't happen till I'm all ready to build and finish the battery in a weekend hopefully. I'm hoping by like March/April time I can have the new battery finished and ready to go.
 
I just found some automotive 8 awg wire...I ended up getting that and I'll being that as my phase wires. I might have enough to use that as my battery output wires also. They're thick stranded wires so they aren't flexible at all. Basically bend and stay in place wire similar to building wire or THHN wire. Going from 14 to 8 awg phase wires should be nice! When I get some downtime I'll solder up these wires on the bike! I looked at 6 awg but for what I'm pulling that's basically getting into the overkill range.. 8 awg shouldn't be too difficult to work with.
 
Not much change this week...
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I made a quick cardboard template for my battery box. I'm ordering 3/8" thick hdpe for the edge and then I'll use brass heat-set inserts for 8-32 screws. I'll be heating the hdpe to bend it around each corner of the battery. This design fits very well in my frame and the battery bag.

I also received the 10awg wires and solder wick wires to solder all the cells together. I'm thinking I might want to use an xt60 for my charge port and xt90 for my discharge...
 
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