Any inherent reason cells need to be aligned the same way?

[thebootfitter]

Some element of this question may have been discussed in the past. I've done a bit of searching and couldn't quite find the answer I was looking for, but if you're aware of a previous thread, please feel free to point me in that direction.

I have an Ohm bike that now has a BBSHD after the original Bionx hub motor died. The frame doesn't have a top tube. Rather the down tube and seat tube join with twin cross bars joining those two just a few inches above where they meet to make a little "pocket" near the intersection. (See photo here: https://electricbikereview.com/wp-co...e-review-1.jpg.) I currently have a simple rectangular battery that I keep in that little pocket near the intersection of the down tube and seat tube. I'm looking to build a battery that fits securely into that pocket (and extends above it like the stock Bionx/Ohm battery does in the photo).

I'm going to attempt to explain below what I'm considering, though I can appreciate that a drawn diagram may be an easier way to communicate this. If the description below doesn't do it, I'll try to draw something up and post it here.

In order to meet my desired specs, I'm looking at building a 14s7p or 14s8p pack. The challenge is that the "pocket" in the frame is only 2.75" wide. I think any DIY pack is likely to be closer to 3" wide with padding and exterior, etc, assuming the cells are oriented horizontally such that + is to the right and - to the left and vice versa, for example. I could try to arrange the cells horizontally such that +/- are oriented front to back instead so they could fit inside the pocket, but then I would have to arrange them so that one parallel set is "on top" of another as it is lying down front to back inside that pocket of frame. Alternatively, I could probably fit one or two parallel sets inside the pocket with the cells arranged vertically, then for the remaining sets of 7 or 8, I could arrange them horizontally Right/Left for the part of the pack that would sit on top of the cross bars.

Pretty much all of the battery packs I've ever seen photos of or diagrams of have all of the cells aligned in the same direction -- probably for ease of construction and to maximize the cells within a regular shape. But to fit the unique shape of this frame, a combination of orientations may fit most efficiently.

Soo... from the perspective of technical difficulty or safety or any other reason... is it NOT advisable to change the orientation of some sets of cells within a battery pack? Or would it be just fine and only require a little extra wiring to make sure the various sets are connected properly?

Hope this made sense. If not, please let me know and I'll try again in pictures.

[AZguy]

Just make sure everything is welded (don't rely on pressure between two cells like a household device with AA's) and orientation is unimportant. BTW - in most packs I have the + side and - side aren't on the same sides of the pack all the way through...

[thebootfitter]

Thanks, AZguy.

Yeah, based on diagrams I've seen, I've noticed that you won't have all + on one side and all - on the other, but I meant that they are all arranged so they are side by side rather than crossing or some lying on their side horizontally while others are arranged vertically.

I'm sure it will make more sense once I start to diagram out my specific design, but my primary concern is whether there is some risk of shorting a connection somewhere if the cells are arranged in different directions rather than all going the same way. It sounds like from your response, that this isn't really a particular issue. (As long as I apply common sense and don't have part of an active circuit touching or close to another one where they shouldn't be touching. I would assume if my cell arrangement within the case requires this, if I keep a plastic or rubber sheet in between, that should be sufficient?

[AZguy]

The other big thing is to keep the distance on the nickel sheets between cells as short as practical.. this is muy important..

[Tommycat]

Perhaps this may help, or confuse. :-) Thread on batteries and vibration

HERE.


Sounds like to me vertical may be a less desirable position...needing better support?

T.C.

[max_volt]

Why not just slap a shark pack on the water bottle bolts.

[thebootfitter]

I've thought about a shark pack, for sure. I haven't ever seen a 52V 24-28ah shark pack. And if there were one, I'm afraid at 11-12+ lbs it would probably be too heavy for the bolts. I also like the idea of keeping the weight as low to the ground as possible, so nestling something into the space at that intersection would be ideal.

[thebootfitter]

I just picked up one of the OEM Ohm battery cases as shown in the link photo from my first post above. I'm going to cut it open and see if I can just configure new cells inside the same case in a 14s7p or 14s8p arrangement. Not exactly what I was hoping for (which is perhaps something more like one of the sleek Luna Fusion cases to fit the bike perfectly), but it may end up being workable with some modifications.

[thebootfitter]

Here's a photo of the inside of the battery case. I think this will accommodate a 14s7p pack -- just not all in a rectangular brick. I'll need to play around a bit with the placement, but I could easily fit 98 cells in here all horizontally, along with a BMS and have a little room for cables to ports. Kind of excited to make it happen now.

I have seen a few recommendations posted elsewhere for purchasing a BMS, but if anyone paying attention here has any recommendations, I am all ears. I'm willing to pay more for something that will last a long time.

[calfee20]

Here's a photo of the inside of the battery case. I think this will accommodate a 14s7p pack -- just not all in a rectangular brick. I'll need to play around a bit with the placement, but I could easily fit 98 cells in here all horizontally, along with a BMS and have a little room for cables to ports. Kind of excited to make it happen now.

I have seen a few recommendations posted elsewhere for purchasing a BMS, but if anyone paying attention here has any recommendations, I am all ears. I'm willing to pay more for something that will last a long time.

That case seems to be set up for the batteries all laid out and stacked like normal or all laying in one direction. There is a web page that might help you lay out the batteries. http://e4bike.ru/page/battery-shape-...urator?lang=en

I am interested in a good BMS also. Maybe commuter ebikes could let us know where he got his.

[thebootfitter]

Thanks for the link, Calfee. I'll need to play around with it. I recognize that if I use this case that I can arrange them all in the same direction. I was just drawing configurations on paper last night

Because this would sit higher I may still opt for a design that uses the space closest to the intersection of the frame. We'll see.

[calfee20]

Thanks for the link, Calfee. I'll need to play around with it. I recognize that if I use this case that I can arrange them all in the same direction. I was just drawing configurations on paper last night

Because this would sit higher I may still opt for a design that uses the space closest to the intersection of the frame. We'll see.

I was talking to commuterebikes about BMS's and he was just plugging in the parameters into a browser. Like "72 volt 100 amp BMS" and getting results that way. Almost everything seems to be out of china of course.

I have gone through the trouble to get an account with Aliexpress so I will probably get one from them. However first I will spend a day doing searches and reading on endless sphere.

That battery shape configurator has 5 settings at the top, 3 - 7 which corresponds to the number of movable point you can play with. So 3 points is only Triangles, 4 rectangles and so on. The more points the more complex the shape you can make.

[Scoonie]

Ann Power aliexpress, just google those three words. Signing up fo4 Aliexpress is easy, no problem, just never acknowledge delivery until you confirm product wrks. Over 50 orders with few problems. Huge savings!

[Scoonie]

Get ebikeschool on youtube and Micah Toll book diy battery building. On Amazon. Will dispell much of the poor infortion, even found here.

[Scoonie]

Almost forgot...soon, second week of February th3 Chinses spring festival and New Year begins. Very little moves, essentially the entire country shuts down. Expect even longer delays and order problems if orders made during this period. Banggod is an OK alternative, except during holiday.