Lord Gruntfuttock

LG's ebike prob-never-happen project

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My Vruzend kit arrived so had a play with it. I bought used batteries so had to clean up the old spot welds on the terminal ends with a dremel grinder. Then just systematically assembled the kit. I just used body weight and bits of wood to seat them in the holders...
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And when all clicked together and locking screws installed you add the parallel strips...
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Then a figure 8 pattern to series them up...
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And the other side similarly, but offset. Had to take care not to short anything out cos there's a bit of potential there when series'd up...
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And still got the BMS to hook up... 
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Looks straight forward enough but still have some connectors to arrive before I start soldering things up. Also pretty keen to cover exposed bus, but not bad effort for the day after crate day...

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are you going full weirdo and capacity test each cell, then check the self discharge rate before building a pack? or just assuming they are all similar enough and give zero fucks?

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I built that e-bike you say is dorky....

But a quick hint, the BMS that came with the Vurzend kit didnt last for long, I ended up buying another one.  Still  have a bunch of Vurzend connectors.

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Ha, sorry, genuinely no offence intended. :)
LIke I said I was all keen to do my R20, but when I saw it the proportions didn't look like I imagined, plus I had the sweet old BSA just hanging in the shed looking for some wheels...

Oh and I got an Ali BMS, whether better or worse quaility we'll have to see.

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14 minutes ago, Lord Gruntfuttock said:

Ha, sorry, genuinely no offence intended. :)
LIke I said I was all keen to do my R20, but when I saw it the proportions didn't look like I imagined, plus I had the sweet old BSA just hanging in the shed looking for some wheels...

Oh and I got an Ali BMS, whether better or worse quaility we'll have to see.

Yea none taken..... :)

I've since sold it and in fairness didnt enjoy the end product as much as I thought I would.... R20 arent the lightest things in the world and with all the 3-bike stuff it was just incredibly heavy....

I've since gotten over my 'building bikes' phase but there are still bits there for another project...

Still probably have alot of Raleigh specific stuff so let me know if you need any hardware.

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More bits had arrived over xmas and I had a little time over the weekend so hooked up the BMS. Cut a bit of leftover foam from my tool trays as a mounting point, routed out a recess, and stuck it on with hot glue...
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And hooked up the power wires...
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Then ran the balance wiring, beauty of this kit is I can just remove the links to solder on the balance wires, so no heat issues...
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And tied it up. Paused at ths point as I wanted to check all was ok before taping up and heat sleeving the whole thing. And put it on charge... 
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Aaaand I don't think it works...? Charger ran for 40 mins or so and switched off, overall voltage 38V, but checking shows a big variation between the parallel groups of cells (from 3.61 to 4.12V) I thought the BMS was supposed to balance these things out by levelling cell voltages via electronic switching/shunt resistors? 

Google tells me that "with a BMS, balancing is handled by the BMS, not the charger. So when the first cell group reaches full, the BMS cuts off the charger and drains the highest cell group(s) slowly using its onboard resistors. Once its lower, it allows the charger to turn back on. It repeats until all cell groups are full."

Maybe I didn't leave it on charge long enough? I'll leave it on for some time when I'm home again, but if that doesn't work I'm unsure where to go from here. BMS definitely wired correctly, it was only a $7 job though so might invest in another one and try again. 
Any experience/suggestions?

 

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so a BMS like that will only have a shunt of 55mA or something teeny like that. So to discharge a cell thats over volt will take a long ass time, and you need it on charge for hours. Especially first time to balance them all. Make sure its kinda working though by making sure you have power on the output, and the BMS is actually working, or else it will not protect the cells when charging and you might kill a few. Though if any of the cells measure too low it wont turn on, so it could be working without the output being on.

When you say it switched off, was that the charger saying it was done? or did the BMS cut it off? or you turned it off? What is the charger? Just a current limited power supply? or something more fancy?

other option is just using a smaller single cell charger to charge each set of cells of 4.2V and when charged do the next and so forth to 'top balance' all the cells in the pack, and then hope for the best after that.

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Was just going by the LED on the charger, went from red to green, indicating fully charged. It's just an Ali 36V 2A Li ion charger, suitable for 10S 10-15Ah Ebike batteries (output of 42V not connected). I did think it'd take a long time for cells to balance with those teeny wires, will leave it on overnight tonight to see how things go. Cheers...

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Sweet, that will just be a current limited power supply, so when the BMS disconnects the charger, the current stops flowing so the light will go green. Wait a bit for the BMS to pull one of the cells down, and it will (should) turn the charge back on and the light will go red again. If it does that, then you're in business.

 

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So had charger on for days and it is VERY slowly raising the voltages, but I'm still not convinced the BMS is actually doing any balancing? Trend shows very gradual increase overall, but no obvious evening out across the 10 parallel banks...
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So I soldered a few 21W 12V lamps to connectors so I could drain some cells. Started with 2 lamps in parallel on each of the two cell blocks that were over 4V (parallel banks 5 and 7). This drew just over an amp and I ran it till the cells were around 3.8V...
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Then connected 3 lamps in series across the whole battery to drop all cells down, and mowed the lawns...
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Started with 37.8V and 90-odd minutes later had dropped to 35.4V. Chucked it back on charge overnight, and things looked much more even, and overall voltage had increased from 38.6V to 40.2V...
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Different scale shows the improvement overall... 
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Think I'll repeat the exercise, but still confused as to operation of BMS. Is it just because the imbalance was so large? Or does each cycle even things up.
Just want to know if it's worth ordering/connecting another BMS before wrapping the battery up. I did buy a cheap one, and it doesn't actually mention balancing in the description...

[Edit] just ordered a flasher looking one anyway. Reviews, specs seem ok...

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It could be working, it could not be. Best way to check is to monitor the charge light and see if it goes on and off etc, or if it stays off. Though, you have a BMS with a separate port for charging right? and it charges when you first plug it in right? In which case the BMS should be working fine. Thje charge port isnt connected to the battery pack unless the BMS connects it, so if it charges, the BMS should be working...

What BMS did you get? Because the one i found that looks like the one you have doesnt actually have a balance feature, so might be worth checking if your has it or not.

Initial charge is a cunt, especially with mismatched cells, as i assume you didnt check capacity or internal resistance of each cell before building a pack right? If you have access to a lab power supply, just charge each bank individually by setting the power supply to 4.2V with a 1A current limit or something like that, and let them all charge individually and 'top balance' the pack that way. Once they are all charged and balanced, they should be fine.
Or If you're worried, get a Daly BMS. They have fantastic reviews and have a balance feature.

You can also get one of these: active balancers which will start transferring charge between neighbouring cells if the difference is more than 0.1V, which might be nice to have. Plenty of reviews online that say they dont work, but plenty that say they do. I have 2 at home, and both work flawlessly.

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Hey man, nice work. I'm following with interest and learning lots from this thread. Been searching for a way to avoid shitty Auckland traffic without selling my car. I'm keen to build one of these!

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