Thursday 30 August 2018

Recycling Lithium Cells

The other night, i found myself repairing a Dyson V8 vacuum cleaner.

It's taken me some time to decide if these Dyson hoovers are a good thing. They are really expensive, the suction up until the new V10 (as it claims to be) hasn't been comparable to a regular vacuum, they are frequently breaking down, charger leads breaking, overheating, and the batteries are commonly failing.

After calling Dyson customer care and being told some exorbitant amount for repair which like Sony repairs, can often cost you more than a replacement, stripping the Dyson all down and examining each part myself, I finally found out that the battery was problematic.

Now, the genuine Dyson battery has inside a protection circuit which is pretty much over-zealous in it's protection. I'm guessing Dyson wished to ensure it's reputation and avoid lawsuits for injury by making their smart battery more safe or more likely to shutdown than other batteries. I bought a replacement battery for the unit and sure enough it works again.

As a maker and someone who likes to try to use things instead of throwing them away, I decided to strip the old battery unit to see what is inside.

The stripped Dyson battery pack

It took quite some effort to strip the battery unit down to the bare cells. It's just as tricky trying to open up and repair power supply units because obviously, companies don't want you doing that in case you electrocute anybody so they usually use strong adhesives inside.

What I learned is that the circuit board inside the battery pack is usually the thing to fail and the cells are usually always intact and good. Looking at the extracted cell pack, I had to snip the nickel strips of each cell to allow me to slide out the 18650 cells as they're spot welded in series to make a 24v pack.

Looking closely at the cells, Dyson used high amp draw 18650 cells which makes sense considering the vacuum cleaner is a high amp draw device. So no using low amp 18650 cells here. In the genuine Dyson pack that I got there are LG 18650 cells, taking a closer look and you find that they are of the LG HD2C type, meaning they have a rated capacity of 2100mah (or 2500mah), and an amp draw of 20a/35a peak. That's quite an impressive cell if you want to achieve rocket speed.

These cells usually come in at about 6 pounds each on ebay, and after checking each cell to be good, I have 6 of them to play with. So, I figured I could make two 3s packs for my quadcopters and planes. The cells should be pretty useful for quadcopters, maybe a little overkill for a plane, but they're free so no harm.

To make a 3s Li-ion flight pack I need:
3x 18650 cells (matching)
1x JST lead (under $1)
1x 3s balance lead (under $1)

Other things used will include: Soldering equipment, Sticky Tape.
The correct way to solder the cells together, solder the JST wire, and solder the balance lead

I used JST connector because it is more light weight than XT60. I am fairly sure the wires can handle the amp draw as i have been using them on a 250 quad pulling 20amps for a while.

Soldering all together in my shed

As i'm not so fussed about a professional pack, i'm just happy to use any tape I have around, but using something to cover the exposed ends of the packs to prevent short circuit happening somehow. I check that it is all wired up correctly, first using a multimeter to check nominal voltage (was around 11.8v), and then test the balance lead with a voltage buzzer. If the cell readings on the led buzzer are off then you likely have your balance lead wired incorrectly. Go over the wiring and rewire if required.

My two free completed lithium ion packs next to my regular 1000mah 3s lipo
The packs weigh around 150g, compared to my lipo which is around 90g. it is heavier yes, but also it is more than double capacity so it will be interesting to see how flight times are different.

I can balance charge these packs using my Turnigy Reaktor 300w charger. It is recommended to charge 18650 cells at 0.5c, so if the cell capacity is 2100mah then we will charge at just over 1amp. 

These cells can be run down to 2.5v per cell safely, but I figure the voltage drop off from below 3v will not be sufficient to keep the quadcopter in the air. Usually the quadcopter will gently float to the ground as the power diminishes.

I'm hoping to use these in my quad drone, in parallel with my hexacopter, and in my future UAV plane. Yes, that's right, i'm now learning how to fly planes.

Cheap as chips practice plane, will become an fpv plane with maybe a stabilised flight controller, then will upgrade to a larger UAV Plane when I can confidently land a UAV Plane :)

I also plan to use 18650 cells to power my fpv screens and goggles. For these as the power draw is much less, I can use low amp draw 18650 cells such as the few Panasonic 3400mah cells I have powering torches. Using a 2s 18650 sled, soldering a balance lead to it I can have a power solution where I can remove the 18650 cells for other purposes similar to the fatshark 18650 holder that is available. 
I'm just waiting for the sled to arrive :)
I also wonder if it is viable to use a 18650 sled as the foundations to a 3s flight pack. There are some high amp draw sleds available due to the vaping community requirements, so I think it is quite reasonable to believe some will be strong enough.

1 comment:

Julia Harrow said...

This is interesting. I have a Dyson and hate it-its way more high maintenance than a hoover should be. I also hate cleaning. Any chance IoT technology and something like the LTE-M will make for more efficient, hoovers that can clean for me?