Critique this 3D Printed Battery - 14S10P 29E

[Boobyjohn]

Hi all

Long time lurker; been reading on here for more than 4 years now. As such, I find that it is reasonable now to start on the battery building adventure.

I plan on doing a 14S10P build for my ebike commuter. I recently (10 months ago) switched jobs, which extended my commute a fair bit: 28 km in each direction. This battery is designed to have enough capacity to last the round-trip commute, which takes 2 hours. I will be using Samsung 29E cells. I plan to source these cells from user tumich on this site.

To hold the 18650 cells, I plan to 3D print the following casing/holder:

Seen from side:


Seen from end:


Each parallel group is designed in a triangle pattern to minimize space consumption. Two adjacent triangles will be connected in series. The batteries will be spot welded using a spot welder from user pguk on this site. Connections will be made with pure nickel strips from nkon.eu.

Note that each the battery pack is cut into three separate pieces, which is visible from the side. This is to keep each object within the maximum dimensions of most printers. An earlier prototype that I had printed, was solid enough that it could support my weight, 80 kg, so I think the design will be plenty stable.

The three holes seen on the side view, is designed to fit an Ø8 mm threaded rod. These rods will be used to mount the side plates. The side plates are to be made of 5 mm acrylic sheet.

The 2 holes on top and on bottom (see the end-view), are designed to fit an 8mm threaded rod. The four rods will be used to provide rigidity for the pack, and for fixing to the downtube/seat post tube. The the missing spots on the two lower rods will be used to fits heavy-duty nylon strips through to fix the battery pack onto the down tube. The two upper rods will extend a bit out from the pack such that the seat post tube will be in-between the two rods, which hopefully will prevent any sideways motion of the pack.

What do you guys/girls think of this idea? Sound? Or problematic?

The bike has a BBS02 mid-drive, programmed for a max current of 18A. 29E cells in 10P configuration should give close to 29 Ah capacity. Continuous current will be somewhat lower than 18A, probably closer to 10-12A. In winter, it gets cold here (-10 is the lowest where is plan to keep riding the bike), and I plan to keep riding throughout the year, so some extra capacity is required for those cold days. The bike is parked outside while I am at work, and the battery will be left on the bike for that time. The bike is parked in a shed, but wind and rain can still get to it, but much less than was it parked in the open. When at home, the bike is parked in an insulated garage.
A full round trip commute require some 1000 Wh. This pack will hold approx 1.5 kWh, so there should be some in reserve.


Now for the hard parts:
1. Charger: I will bulk charge the pack. I do not have a 14S charger, so I will probably get a satiator and call it a day.
2. BMS. I "plan" to run without BMS and manually monitor the pack. The reason it is just a "plan" is that I change opinion every second day. A normal ebike BMS probably wont be able to keep it in balance anyway, but could be useful for monitoring cell voltages, and prevent over charge/discharge. Any recommended BMS'es out there?
3. Waterproofing: I plan to use type II silicon glue along the outer rim. In addition, I will use an outer cover made of tarp.
4. Connectors: XT 90 connectors with spark resistor.
5. Cell voltages: Min should be 3.3V, max 4.1V.
6. Balancing monitoring: RC lipo alarms 8s. 2x http://www.ebay.com/itm/NEW-RC-Lipo-Battery-Low-Voltage-Alarm-1S-8S-Buzzer-Indicator-Checker-Tester-LED-/271746517929
7. Balance leads: TBD
8. Spot welder: The 6pence welder from pguk on here.

Ideally, I want something plug'n'play, that I can just plug in when I get home, and the battery is charged and balanced in the morning. The only charger for this, that I was able to find, is the hyperion 1420, which appears to not be produced any more. Are there any alternatives for 14S?

Thank you all in advance

[moderator edit to correct title]

 

[spinningmagnets]

What city are you in?

 

[Boobyjohn]

Aalborg, Denmark.

 

[whereswally606]

I used to own a 1420i hyperion, now I have a TP1430c thunderpower charger.

Graupner Polaron Pro Touch Screen Charger 14S 500W 20A from googling (I've no experience with these)

There isn't much out there for 14s, I think its a bit of an odd ball voltage for the RC crowd so mostly they suffice with 6s, 8s and 10s chargers.

What I have used and quite like BC168s (8amps down 6s balance taps), not isolated so blew two of these up being stupid and not detaching my pack in the middle when charging (expensive mistake) was a 12s pack which I charged both the 6s subpacks simultaneously.

and I have now a CB86 radiolink one. which can do 6amp 6s and has 8 ports. What this can do is cycle round all 8 pack you attach and charge them one after the other. The good thing is you can set them all up, leave them in a lipo bunker, (safe place which can contain fire) and come back after a predeterminable amount of time.

Its great if you can build 6s subpacks and have a series parallel harness. Or just a deSerialising plug that you have to pull to get access to the balance taps (thereby making my mistake above impossible). This way you can charge all your subpacks independently and know their internal resistance. Cheaper than a 14s charger too.

 

[Boobyjohn]

@whereswally606: The Graupner Polaron Pro looks like it fits the bill. However, buying a high-quality BMS (e.g. TinyBMS from circuit on here) + cycle satiator is cheaper, and will be less of a hassle in day-to-day operations. Hmm. I guess TinyBMS + satiator will be my way...

 

[Skrzypas]

I'd use 2-3 RC chargers like imaxb6. You can do each time a balance charge if you split the pack into 3 and you can skip bms. You're right, bms for new 29e cells is not so much a need if you monitor voltages.

Make a thick (a few A capable) balance wires on each level and get them to a place, where you can easily reach, so you can charge any level of the battery if it starts self discharging in 2-3 years of ebike abuse. You will finish the season instead of a big battery renovation in summer.

 

[Boobyjohn]

@Skrzypas thank you for your suggestions. I finally decided that I really value a no-nonsense battery in day-to-day operations. Hence I decided to go with a BMS and satiator.

BMS will be the tinyBMS from circuit, the 30A cont' version. (My max controller max current is currently 18A, so plenty of margin).

The BMS is 65x95x9 mm. To make room, I extended the outer shell on the case, and made the extension hollow so that I can mount the BMS in there. The idea is to have an acrylic sheet between the BMS and the 18650 cells to avoid short circuits.

I also designed the side plates, to be laser cut out of acrylic sheet. Surprisingly, this is very cost effective, even though I don't own a laser cutter. For that reason I also included a laser cut BMS holder that most likely will be totally overkill. But better safe than sorry, I guess.

The total width of the assembled battery is going to be: 65 (batteries) + 3 * 2 (side covers) + 3 (sheet between cells ans BMS) + 9 (BMS) = 83 mm. Plus a mm or two for gluing it all together.

I have also Open Sourced the entire setup so others can copy and improve on my ideas: https://github.com/boobyjohn/hexabat
The files are licensed under the "beer license", which means that you will have to buy me a beer if you used my work and you meet me in person

 

[ScooterMan101]

Be Very Careful using a 3D printer inside a small building , small space.

Just last week a young , professional couple in their 30's and their cats were found , Dead in their apartment in Berkeley , California.

For Several Days the Police tried to figure out what killed them,

They found that the 3d Printer / Materials being printed gave off Toxic Vapors , and Killed them, Probably while they were sleeping.

Take note , especially since you live in a Cold Climate Country. Perhaps you have a room that is closed off from all your other living spaces, that you can also vent the fumes to the outside.

 

[Boobyjohn]

@ScooterMan101

I don't disagree with that, but I'm not really at risk since I don't own a 3D printer. I just use online services such as 3dhubs. Usually, there is local provider who is not that expensive. Similarly for laser cutting.

 

[Boobyjohn]

Just had the middle section printed.

Images (cells are 18650): https://goo.gl/photos/ArRC8UpAtrmSJg8g8

On the last picture, notice the threaded nut that fits (very tightly) into the center hole. Bolts with countersunk heads will go through the side plates into this nut from either side, which will (hopefully) result in a nice finish.

Now, I am just waiting for the spot welder and cells to arrive.