The "BIG ONE", 5.3kWh BMW i3-module battery trailer build

Could integrate brakes in to the toe hitch I think you will needed to as that trailer is going to push hard on down hill braking

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I have the negative terminal exposed now.


Looks like it’s nickel but the backside is copper plated, or it’s tin plated copper

It’s probably possible to solder onto that, or drill a hole into it and use ring terminals.

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How big will the trailer be? It looks tall on the video. I assume it will be used to carry your luggage as well. What wheels will you use on the trailer? Same as on your board or bigger like bicycle trailers have?

Would be cool to have a single motor in the trailer powering a live axle that just runs with the other motors…

Wonder what the dynamics of a trailer that pushed it self would be like :thinking::thinking::thinking:

You could gear it so that it always pushed just a tiny bit less than the board to avoid any fuckery… :man_shrugging:

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And I’m over here considering a 12s9p trailer lol.

I’m not sure if you’ll have any braking issues or not. Mentally, that’s a decent weight behind you. The last time I towed my kid in one of those bike trailers, he was about 40 lbs so decently less but I didn’t notice much of an issue.

/following

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12s9p of these bmw i3 batteries is a lot

thats 144series groups (its a lot of cells)

:laughing:

In the pictures above the board has 8" wheels, but I’m currently printing new rims for 10" tires, which I’m planning on using. I think I’ll be using the 8" wheels on the trailer.

More about those wheels and rims here:

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I’m presuming some thing horrible that could easily throw you off balance. Wonder if settings in the VESC could be altered enough to make some thing ok. Going to be a interesting project to follow. Be safe @SimosMCmuffin were you can

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Throw an inverter on this thing and you have group ride hosting vehicle

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We got cables. I think those are 10AWG.

EDIT: checked and they were 6mm^2, so 10AWG, but considering the DC load is at max 160W, it means a max current of 4 amps at 40V, so I don’t think were cable limited for testing purposes.

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oh my lord, how even are you even going to be able to make it ride comfortably or be comfortable yourself ?

The module is going in the battery trailer, it isn’t gonna be on the board itself.

MTB setup with pneumatics isn’t too bad on even a slightly rough ground and I’m also upsizing the wheels from 8" to 10" just to improve the ride a bit. Just stretch every once in a while just to make sure you keep the blood flowing in your feet and legs, otherwise I get cramps with my toes.

EDIT: also charging atm.

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For all your ring terminal needs, I’ve always found using “One-Hole Lug Compression Connector, Straight Barrel” to be a bit nicer than standard copper marine grade lugs. The yellow 10-16 ton hydraulic crimpers for ~$30 are also great for the crimping part. However, you can always drill a tiny hole in the barrel of a lug, heat w/a blow torch/butane torch, and feed solder in until it peeks thru the entrance of the lug/completely fills in the drilled hole.

A lot of argument to be had on why soldering lugs on 8 awg or lower is bad… But I’ve seen enough real world experience of crimped & soldered and either method is fine if you’re not going to space lol.

EB-Flex by Electronbeam is also amazing wire for 8 awg or lower heavy duty needs. Can tie my 2/0 in pretzels with ease.

Sweet battery.

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Doing a capacity test now.

Running on a Maynuo M9711, which is a cheap chinese clone of a HP electronic load.

I have an arduino in the back that hooks up to the RS232-port of the load and then uses modbus-protocol to control the load settings and measure what the voltage is on the input, which is the battery in this case.

It then echoes back the voltage and a timestamp to a serial terminal on a PC.

Current test cycle is as follows:

  • Constant current load @ 3.2A
  • Load ON for 15 minutes
  • Load OFF for 5 minutes
  • Repeat until battery hits 41.4V (more on that later)

The three values seen on the serial terminal are voltages sampled at different points. The first one is the voltage at the end of the 15 minute ON period, but before the load is turned off (under-load voltage), next voltage is the voltage about a second after the load has turned OFF (immediate release voltage) and the last one is the voltage at the end of the 5 minute rest period (resting voltage).

Okay, the DC load is a max 160W load, so it doesn’t really stress the battery so in this case all the voltage are going to be pretty near each other, but for example in the case of my 10S6P pack there is a bit of a difference between these voltages, as is shown in the graph below. This helps to get a little bit better picture of what the SoC is based on the resting voltage.

Now here’s some data I dug up on the battery pack, because I needed to figure out what the discharge cut-off voltage was before starting the capacity test.

The 12 cells are manufactured by Samsung SDI and are meant for electric vehicle use. They also upgrade their design and chemistry over time, but keep the same cells dimensions so car manufacturers don’t need to completely redesign their battery modules, but can just upgrade the cells to a higher capacity one.

This also explains the little confusion I had as I had looked at the 4,15kWh and 5,3kWh i3-modules, as they had the same dimensions based on their product pages. I even contacted the shop about this and they confirmed that the dimensions were correct, but now knowing this upgrade thing happening to the cells on the manufacturer side it makes sense, especially as I found this little sheet that reported the different cells based on their manufacturing date. This would also mean that the 4,15kWh i3-module uses the 94Ah cells, which then lowers the energy capacity to the 4kWh mark.

But boy oh boy, if they are gonna release those 150Ah and 180Ah cells sometime in the future :drooling_face:

I was still missing the datasheet for the cells, which specify the cut-off for both charging and discharging for the cells and no matter how hard I looked I couldn’t find the datasheet for the 120Ah cells in the module I have, but I did find the datasheet for the 94Ah cells, so I guess I’m gonna go with that info.

So it looks like operating voltage is specified at 2.7-4.15V but looks like effective SoC is 0% at ~3.4V, so I then decided to stop at 3.45V at the cells, so this then lead to the 41.4V termination voltage for the capacity test.


EDIT: it’s gonna take like 2 days to get the full discharge done on the battery

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1st world Esk8 problems. :ok_hand:

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Trailer hitch, should attach with rod end, to the back of truck. Middle.

Level to ground.

Possibly surge brake mech, on hitch, and a foot brake made from a caliper cut or split in two. Shoves a puck into tarmac.

ahem

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:exploding_head: this project is like got my mind blow so hard…its also very inspirational :grin: I thought my 18s12p tesla pack was huge…loooool, its like a drop in the bucket compared to this :rofl:

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@kalebludlow

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