My DIY Portable PSU - Repurposed Li-ion Ebike cells

meetyg

Solar Addict
Joined
Jun 4, 2021
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424
Well, it all started out when I saw an Ebike battery pack by the trash can one day while walking home.

There were some wires ripped apart, but I though it would be nice to take it home, and repurpose the 18650 cells in it.

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To my surprise, this was actually a 36v 10ah Li-ion 10s pack using pouch cells, with a small BMS !
While the external casing looked pretty beaten up, and wires were ripped, the internal pack looked like new!
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The pack itself had these plug connections, so only the external wires were ripped. It was pretty easy to dismantle from the casing.

So to check if this battery was OK, I first check voltage, and it was around 36.5v.
Then I charged the pack a little, to see if it will hold its charge, and yes it did!

I understood this was a good pack, but I started wondering what to do with this pack... And then it came to me: why not build a portable power supply?

We use desktop PSUs alot at work (in the lab), but sometimes we need to go out on the field for some testing. A portable PSU would be great.

I found a really cool PSU step down module on Aliexpress, which fit the plastic casing I bought at a local hardware store.
I also added a voltage and temperature meter (configurable, with low voltage and high temperature alerts/beeps).

Then I decided it would also be nice to have a QC USB port (for charging our phones when out if the lab) and a 12v barrel jack socket, for small 12v appliances (like a wifi router) which could be used in parallel with the PSU module (even if the PSU is set at a different voltage).

I added a 10A DC breaker (up to 250vdc) for safety and as a main switch. Also installed a 3-pin XLR socket for charging (which also goes through the DC breaker, as the BMS has a common positive, but separate negative port for charging/discharging).
For the 12v I added a separate compact step down converter with 6A current limit, a fuse holder, and a LED lit switch just for the 12v and USB socket (which also takes 12v input).

After assembly and successfully testing all connections, I put alot of hot glue on all connections to make sure that they won't move much (just as added safety) because this will be portable. So it may look like a mess, but safety first!
I put some strong VHB tape to hold the battery in place, and then surrounded it with some flame resistant spray foam, for added stability.

It was fun making, although somewhat scary working with 36v (I had built some DIY 12v and 24v Lifepo4 packs, but never 36v).

I also order a 42v 4A Li-ion charger from Aliexpress (MATE brand if I recall correctly), which I had experience with a similar 24v model for Lifepo4. What I like about these chargers is that they have a potentiometer on the output side (you need to open the case) which you can adjust output voltage with.

So I adjusted it to 40v, in order to increase the battery's longevity.

The guys at work were stunned and really like the idea and the implementation. We recently took it out on the field and it worked great!

Here are some pictures of the build:
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Hope you liked it!
 

meetyg

Solar Addict
Joined
Jun 4, 2021
Messages
424
And here it is charging:
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The white foam next to the module is attached with some tape (to act like a hinge) so it can be closed and protects the PSU module when being halled around / transported.
 

meetyg

Solar Addict
Joined
Jun 4, 2021
Messages
424
Some specs summary, if anyone wants to know:

- Battery: 10s Li-ion Pouch cell pack, 36v, 10Ah 360Wh

- PSU: WEGE WZ6012, Step down (up to 60v input), 12A max

- 12v DC step down (from 40v), 6A max

- 2 port QC USB socket (12v input)

- 250v (max) 10A DC breaker

- Total weight: 3.5kg

- Main charging/discharging cables are 12AWG silicone insulated wire.

I will be adding links to most of the parts soon.
 
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