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Old 02-25-2017, 02:53 PM   #11 (permalink)
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My daily commute is 14.5 miles (we'll call it 15 miles) one way. 30 miles round trip.

I agree completely about having enough batteries to complete my trip, and not lugging around a bunch of extra weight. Part of my thought behind having the setup i'm proposing (75-80 cells, 15-16 in series x 5 parallel), I can get longer life out of the batteries if I only drain them down to 80% or 70% between charges. Where as if I drained the batteries completely (or nearly completely) they might not last as long?

An average speed of 18mph-20mph is just a figure I am going to throw around until I get the bike built. Who knows, I may actually ride it closer to 30mph once built, (that will depend on real world testing).

3D:

I am very proficient in the 3D modeling/rendering software Autodesk 3DS Max. I will start posting renderings of the proposed battery setup and various other components until the bike is built.

Here's two ideas for the battery:

16 series x 5 parallel (oops, I accidentally only made 4 parallel in the renders, but you get the idea)





Once cut into two pieces, the blue "D" cell battery holders will require something on the back side that I can glue them to (not pictured above). I was thinking maybe thin (3mm) plexi-glass or balsa wood?


Last edited by TexasElectric; 02-25-2017 at 03:01 PM..
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Old 02-25-2017, 03:58 PM   #12 (permalink)
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Nice project!
I'd face the cell opening all the same direction, and make a template. Then I'd use fiberglass cloth and epoxy to make up the modules. They would be strong and light.
Put a piece of tape across the battery side of the holder to back up the glassing operation.
2 layers of 4 Oz cloth and epoxy would be plenty.
Then I'd make some sort of system that clamps each module into the pack. You could do a quick health check of each module with a meter, and pull out that module to see what was up.
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Old 02-25-2017, 05:02 PM   #13 (permalink)
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You're correct about the batteries. Their nominal state is at 3.2 volts per cell. Full charge level is 3.6 volts per cell which means you would need about a 56 volt charger for full charge on 15 cells. Probably 60 volts to charge 16 cells. I like the battery holders. In most states the maximum legal speed for an ebike is 20 mph on a level surface with no help from the rider. You can go faster with rider input but I would check Texas laws. Apparently California changed the max speed of ebikes to 28 mph a few years ago before they call it a moped which needs to be licensed. Anyway it's good to know your local laws. Your two horse motor should easily go 30 mph if you want it to. My one horse would do 30 with room to spare and that was with 75 pounds of bike, motor and battery plus my 200 pounds. My bike might be in the archives on this site. Can't remember if I posted it here or not. I'll look.
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Old 02-25-2017, 05:23 PM   #14 (permalink)
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Not on this site, but found it on Endless sphere.
https://endless-sphere.com/forums/viewtopic.php?t=2339

Mine is near the bottom of the first page.
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Old 02-25-2017, 09:08 PM   #15 (permalink)
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I don't think LiFePO4 really benefits from shallow discharges. I think it's better to only go down to 20% instead of completely discharging it, but most batteries are that way. The new thing with Lithium batteries is only charging to 80%, which gives a pretty good increase in cycles, but I don't think LiFePO4 benefits from that as much. There's some that are of the mindset that extreme babying of batteries to increase the cycles you get out of them isn't really worth it, because the cycles most batteries will give are enough for years of use for most people. By then, the batteries will have also degraded due to time and new batteries will be better/cheaper.

I would probably only do 3 in parallel to save weight, provided the batteries can supply enough power with that many.

A reason I've read that people don't do plastic holders for the batteries is durability. They're fine for a stationary setup, but an ebike is a lot harder on materials.
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Old 02-27-2017, 12:40 AM   #16 (permalink)
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That's a neat idea. A few years ago (in 2009) I bought a few sheets of carbon fiber and resin to play around with. Irregardless of what material is used with resin (ie. carbon fiber or fiberglass), the resin will get crazy hard, which is good. It's an idea.

jjackstone
I agree, always a good idea to know the local state laws. I just checked out your bike on Endless Sphere. 72v, wow! I love the idea of high voltage low amperage. I also like your DIY setup of the wooden holder for the batteries.

vskid3
I plan on being careful with the batteries (and the bike as a whole) from the stand point that I'm not going to ride it like a bat out of hell everywhere I go, constantly slamming on the gas and brakes, etc... However, once built I do want to test the upper limits of the bike (see what it's capable of).


Plastic holders
Bad news... The plastic holder idea is dead. The problem with the plastic holders (as I found out this afternoon), is that when connected it creates a short. To illustrate what I'm talking about, Imagine you had 4 batteries connected in parallel. You then take two of those batteries and flip them around (ie. swapping positive for negative). It would create a short. Which is how those plastic holders are designed. Oh well... The plastic holders was an expensive option anyway.


Today's update
Going against my previous post where I cursed the idea of using Nickel strips to connect the cells. I purchased the following items on eBay.



I am going to use solder to attach the Nickel strips. Later this week I'll purchase a good soldering iron (any suggestions?).

Lastly, I found this video on YouTube for excellent (step-by-step) instructions for making the battery.

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Old 02-28-2017, 09:15 AM   #17 (permalink)
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The more cells in parallel the more amperage is available for torque. Motors draw maximum current at start up and some are designed with capacitors to give that initial boost. My garden shredder is that way as it has a heavy flywheel.

For gearing look at triple chain rings such as 28/38/48T and a rear cluster 28-11T. Check to see that the thumb shifter clears the throttle.

Since you are adept with Autodesk you may be able to use the fluid flow software to determine wind drag. The HPV shell software is designed to do upright bikes as well and the file will transfer. Wayne is very helpful if you have questions. There are a range of options to reduce drag once you get the bike set to where you are most comfortable.
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Old 02-28-2017, 12:29 PM   #18 (permalink)
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Thanks for the heads up. According to the YouTube video i posed in my previous post (as well as the information on the BMS i ordered), I will be connecting 5 cells in parallel and then connect each parallel stack in series (16 total).

I'll look deeper into HPV shell software. As you say, i'm sure there is some compatibility between Autodesk products.

Update:
My next purchase is going to be a bicycle. In the next 2-3 weeks I plan to make a purchase. I am going to check out used bikes before making a new bike purchase. I've been lucky to find a lot of used 26" full suspension bikes on craigslist (some are local, some are not).

I am going to wait to construct the battery pack until I purchase a bike, because I don't know how the frame will be configured (full suspension geometry is different than hard tail geometry). In the mean time I will make sure I have all the appropriate gear/equipment to assemble the battery.
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Old 03-08-2017, 03:28 PM   #19 (permalink)
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You could find a pvc tube or carbon fibre tube and stuff the batteries in there to get one series chain.
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Old 03-09-2017, 02:46 PM   #20 (permalink)
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From what I understand, soldering LiFePO4 batteries will make you sad. Spot welding your nickel tabs is what you really want to do. My batteries (which are totally wrong for ebike use, but I got them cheap... $7/cell and I'm just doing 1P) are screw terminaled with solid bus bars and heavy duty interlocking plastic holders.

They look just like this:

https://www.copybook.com/companies/goodwolfe-energy

What motor are you looking at? I recently got a Bafang BBS02 mid drive. The kit is very complete and the only thing you really need to supply yourself is the battery+bms.

As for BMS, the best one for LiFePO4 is the SignalLab (now Ping Battery). That's what I've bought. I did my initial chargeup and everything is going well. I just need to wrap/mount my battery now: What's new on V5 LiFePO4 BMS (Battery Management System)? - PingBattery

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