D.I.Y. Powerwalls - Building Tesla inspired 18650 Powerwalls.

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Finally: The whole reason I got into harvesting 18650s was to build an eBike without having to spend $500 on a lithium battery. I think I've got enough cells to get started. I'm learning as I go, so bare with me, LOL.

I have a regular bicycle I'll be converting. I'll get a picture and some specs at some point.

I'm considering a SmartPie5 from GoldenMotor.com. Here's the specs:
 - Max phase current: 50A (not sure what this means)
 - Continuous Current: 18A
 - Open Voltage: 20V - 60V
 - Rated power: 200W - 400W

Still learning to calculate what kind of battery to build. Especially since I'm using old laptop cells instead of new cells. But here's what I have so far.

The rated power, being between 200-400W means using a "48V" battery, with a voltage range between 42-58.8V means I'll come nowhere near the 18A limit, right? 18A would be for if I were using a battery as low as 20V to get the 400W power. So more Volts means less Amps, and that's good for these old cells. If I'm right about all that, then assuming a lower limit of 3V per cell, the most Amps I should ever demand from the system is about 9.5A when the battery is at its lowest of 42V.

A 14s battery will give me 58.8V maximum. If I want to keep the current at 0.5A per cell, I'll need 18p. So that would work out to 252 cells, which should be plenty for the Watt-Hours needed for power and range.

14s18p would be a pretty big battery, so I'm thinking of breaking it up into 6 7s6p batteries. Also, I'm thinking I'll make the batteries longer and thinner by clustering parallel cells in groups of 2x6. I made a mock-up out of dead cells just to see how each battery would look:
[Image: bc96eeec4e456ff45912d7fdc0c6e8dd.jpg]

So 6 of these, 2s3p, would look like this:
[Image: ceee0f8d74aef9c096c9ff2151a2de17.jpg]

Seems like a lot of battery though. I wonder if I could get away with only 4 of these. That would require 0.8A per cell. That would save me 84 cells and 1/3 of the weight and space. And it would make charging much easier.

I'm thinking if I want to add lights, I'll put together a little 12V battery. Most things run on 12V nowadays.

Not sure what to do about charging. Chargers don't seem to balance, and all the BMSs out there seem to have very poor reviews.
Charge it with a proper RC charger. Many of them do up to 7s and if you going to run 7s packs thats fine. For instance iCharger Duo and you got 2 ports and can do both of them. 308 or 4010 and you have ones that do 30-40A per port Smile

Aff linked Ebay:
https://rover.ebay.com/rover/1/711-53200...SwrddY7PLY


This is the one I use personally and it works like a charm for chargin larger packs like the one you plan for! And it does balancing very good.
Running a 14S8P from recycled Cells on a BBS02. they get quite warm along with the motor with 40-50km/h riding for 1/2 hour.
When cruising I was probably in the range of 7-10 amps and the batteries wouldn't get warm.
No BMS. At first I cared, now I'm pushing the pack harder. 1500km's and probably have 3-5% loss in charge from when I first built it. If I can get 4500km's I'll be happy out of this pack. I'm charging to 57.4v and usually draining it to 48v under load. it recovers to about 50v. charging twice a day.

I think you should be good with a 14S12P for average riding.
I have a 24v lawnmower and my 7s8p gets to about 38 degrees Celsius after a full dump from 4.1 to 3.6v per cell (resting) so far each string is staying balanced but I use a external Ballance during charge that constantly keeps them in check (50ma drain)
Power tool cells are SO much better than laptop cells for this, however I do understand sometimes you have to use what you have
Totally. I have room to double the cells in parallel so that will decrease the amps per cells which will make the battery cooler.
Here's the bike I have to convert:
[Image: ee8d3c9c7840934822cf26967ec3f236.jpg]
Its an old Raleigh of some kind. I put my own seat and handlebar on it. A friend of mine got me set up with custom cables since the originals were too short for the new bar. I've also got a replacement rear rack that will fit much better than this current one.

Still looking at the same motor/controller even after quite a bit of shopping around. I've also had a look at the cell database and most of the cells I'm using have a recommended discharge of 400-500mA. Now, I can get away with more for a short time I'm sure. Like going up a hill or needing to accelerate quickly, but I think I'll stick with my 6 7s6p battery design for now. I have the room and the cells, and I'm curious how much range I will get.

As far as charging... I'm disappointed so far with what seems to be out there for 48V charging. And I do want to charge the whole thing at once rather than one battery at a time. Six balance chargers is just too much money for me. So in keeping with the DIY spirit of this forum, I'm gonna build my own. I do appreciate all your comments and suggestions though. I've looked into all of them. Smile

So I'm fascinated (or maybe obsessed) with TP4056 boards and how they behave while charging our beloved 18650s. And I'm planning to build a charger with them. I first had to solve the series shorting issue. Thanks to the great suggestions from this thread, and a bit of research, I think I've got a way to make them work together in series without shorting.

The two options I'm looking at are basically the same, but the chargers could be either wall chargers or bare boards. Now, there's a killer deal on eBay at the moment where I could get 42 wall chargers for about $32. Its a 4 for 2 sale. That route though will require power strips and USB ends. Here's a design for one of the 7s6p batteries (I'd need six.)
[Image: b0720e0ab3a8a3b10cda555b4fa188d2.jpg]

The other option is to use bare boards to convert from 110VAC to 5VDC. There's a nice deal on Banggood.com if you buy in groups of 10. This would eliminate the power strips and USB ends, and could all be fit into a project box. So the whole thing would be less bulky and would contain a lot more of the wiring.
[Image: 067767f7d772b84267a671b935866a39.jpg]

The cost comparison of all the parts makes this route about $50 cheaper. And with so many little advantages, I think I'll do it this way. Now I just have to scale up to all 6 batteries. Gotta decide whether to use 6 project boxes, or one big one. And there's still some parallel issues to work out yet.
I've done a proof of concept on this thread, using separate AC to DC power supplies for each TP4056 charge controller. So now I know it will work, I'm looking at how I'll actually build a charger/balancer.
Here is a simplified version of how I plan to wire things up:
[Image: b74b34279b33eafdc4ed88d2dd195a0e.jpg]
This will allow me to use 7s balance cables to charge each battery.

Since I'll have six of these batteries in a 2s 3p configuration, I have to solve the issue of the TP4056s being in parallel. They really don't get along with each other, LOL. To fix this, I'll wire up the batteries so that when disconnected from the motor controller, they'll no longer be in parallel. I'll do this by having a positive and negative lead from each series go through a 6 pin connector, and they won't meat up until after they're past that connector. So when its unplugged, only the balance cables will keep the batteries in parallel. And those will be disconnected in order to hook up the charger. Clear as mud? Here's a diagram of the charger disconnected, and the battery pack in use:
[Image: 1dedd14b332ad7accfd49c1aa6f7d4e8.jpg]

And here is the battery pack being charged:
[Image: 33c92d7a6dc76a8b25b5c5829e666aff.jpg]

So with this design, all the parallel cells should stay balanced during use, and the series will be balanced with every charge, since each TP4056 will stop at (approximately) 4.2V. As for power consumption, each individual cell will be getting about 166mA. Kind of low, but each TP4056 will be charging 6 cells at a time. To add all that up, the charger will be providing 42A at 5V, which works out to about 1.7A at 118V (my actual voltage at home). Maybe a little more, since things are never 100% efficient. But that seems pretty close to the rated current of the store-bought bulk chargers. And they don't do balancing.

Well, does anyone see anything here that will melt, smoke, catch fire, or otherwise ruin my day?

Also, I wonder if I could find some kind of 12 pin on/off switch that would make unplugging the battery from the motor unnecessary?
It would have to handle 10A, though. Or maybe 4A through each lead? I think each lead would be providing 1/3 of the total current.
Incredibly detailed work Mike. Loving it!

Browsing that Golden Motor site and many hopes and dreams are forming.
Ok, got some goodies in the mail, including the isolated power supplies I was waiting for!
[Image: d1ef039c40baf6a2da37e959f0fc1c30.jpg]

Also got a few other things, but those are for other projects. I did some soldering, and of course, I had to do a brief household power test with my fingers (yep, still works). Anyway, I got my little test rig put together.
[Image: a9e046ca4f99e486b90d9d2f78a6c827.jpg]
So 120VAC from a boring old plug to two 120VAC to 5VDC isolated supplies, then to two TP4056 charge control boards to two cells hooked up in series. So far, no melting or burning or smoking. I still need to charge them up and make sure the TPs behave properly, but so far so good!

Also, I was removing some old, unused conduit from my house the other day, and found some old Type TW wire inside. No good to reuse as household wiring, but at 12 gauge (about 2mm) it will make good battery wire. I did the razor blade in the vice thing to get the insulation off. Then I had to clean of this oily stuff coating the wire itself, but I got several meters, which should last me for a few small projects.
[Image: b795ed0d305afdd137ee87d0258e4cc8.jpg]

Very slow progress, but still progress. Smile
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