R2D2 Battery Safety
Thank you for purchasing cells for the “Build your own R2D2 kit” from Deagostini. We hope you’re very happy with them and excited for the final issues of the build if you’re not quite there yet!
Get to know your product
Before we get into the nitty gritty of battery safety, lets take a look at what you’ve bought because for the majority of users, this is their first time owning/using Li-ion cells! For 99% of people purchasing through 18650 UK, this is the Samsung INR18650-30Q Button Top pictured below;
Here are the specs from our product page
- Size: 18650
- Chemistry: INR
- Nominal Capacity: 3000mAh
- Nominal Voltage: 3.6V
- Discharge: 15A Max Continuous
- Positive: Button Top
- Protected: No
- Rechargeable: Yes
- Dimensions: 18.33mm x 64.85mm
- Weight: 46.1g
Deagostini were quite vague in their suggestion, advising only an unprotected button top 18650 cell with a capacity of 2800mAh or higher. The button top 30Q fulfills all of this criteria.
Button tops on 18650 cells should always be welded on. Not glued or stuck in any other kind of way. Ensure that if you have purchased your cells elsewhere (regardless of which cell you have chosen), that the button top is firmly fixed on. The reason for this will become apparent later on.
You’ll see on your cells that there are some markings you wont see on any other button top cells. These are compliance markings to satisfy UK/EU regulations. If you cell doesn’t have these, your supplier is providing a non-compliant product. This doesn’t mean that the cell is automatically counterfeit or dangerous, but it does mean that the seller isn’t complying with UK battery law. To be brief on this part, the top line is information about the cell, the second line is our unique cell serial code (we hold a database of every cell sold), chemistry type and nominal voltage. The third line will have “Sold by 18650.UK” to designate it was sold through our retail website. There are also polarity markers, and the WEEE bin symbol. (If you wish to read more about UK battery legislation or our work with the Government and in the industry, you can find further information here ).
The chemistry type for this cell is INR – Lithium Manganese Nickel. It blends nickel and manganese to form the positive cathode, providing low resistance and the ability for high current output. A lot of effort is put into this chemistry by manufacturers and it considered one of the most stable Li-Ion chemistries.
Protected vs Unprotected – Its a common misconception that “protection” is for the user. The protection circuits built into some cells is there to protect the cell from over-discharge in devices without internal power management like torches. It is a small PCB attached to either the top or bottom of the cell (with a link wire between the two) which cuts power from the cell when its voltage drops to the “discharge cut off voltage”. Your R2D2 has this technology built into the circuit board on the back of the battery sled. Not only are protected cells several millimeters longer than unprotected cells therefore unlikely to fit in applications that dont call for them, they can also confuse on-board charging systems that already have it built in leading to charging faults or premature cutting of power to the unit.
The 30Q cell has a discharge cut off voltage of 2.5V, and a maximum charged voltage of 4.2v (+/- 0.05v). This is standard across almost all 18650 Li-ion cells.
Removal and refitting of the cells in the R2D2 sled
The sled in R2D2 is sprung. This is great for keeping cells stable while he is moving around, but no so great for battery wraps. When removing or refitting the cells, take care to release by pulling gently (in a backward and then up direction) on the positive (button) end of the cell. Refitting should be done in reverse, seating the negative end of the cell onto the spring, compressing the spring and then pushing downward on the positive end.
ATTENTION – Take care not to damage the wraps on your cells. If you notice any tears in the wrap of the cell (through which you can see the bare metal of the cell can), STOP USE IMMEDIATELY. Li-ion cells are very energy dense and short circuiting them can have severe consequences not limited to fire and/or explosion causing severe damage to property or persons. All is not lost however. Should you notice any damage to the cell wraps, you can still save the cell. Re-wrapping lithium cells is far from uncommon in the vaping industry and as such, there is an almost limitless range of both very cheap plain wraps and premium branded/designed wraps. You can find our selection in the online store or you can hit the common online auction sites (where you can find star wars themed ones! ). If you want to learn about re-wrapping cells there are lots of How-To videos on YouTube and its very simple. You’ll only need a sharp knife and a hairdryer.
If you are removing the cells for storage, always keep them in the cases we provided in your order and do not let them come into contact with other metallic objects (keys, change etc). Do not simply place them in drawers etc.
Charging your 18650 Button Top cells.
You have two primary options for charging your new cells. You can either charge them inside R2D2 with the Deagostini supplied plug from Issue 100, or you can use an optional external charger. We have a fantastic range of external chargers right here. We have three options that will charge all cells at the same time/rate. They are the Xtar MC6 II Queen Ant, the Nitecore Q6 and the Nitecore Q8.
I’ve not been able to get information out of Deagostini on the charging rate that the supplied plug/BMS (Battery Management System) is capable of (if anyone would like to send me photos of the writing on the plug to firstname.lastname@example.org, that would be great!) but could conservatively estimate it at around 500mAh per cell (a total of 3 amps supplied to the on-board BMS to be distributed to each cell). If my assumption is correct, it means that it should take around 6 hours to fully charge all 6 cells. The advantage to this method is that you are unlikely to ever experience issues with damaging wraps etc through repeated removal, and you will only ever need to remove them for long term storage (remember to put them in the cases provided!)
If you are charging them in an external charger, options range from 370mAh right up to 3000mAh per cell. The manufacturer “standard” charging rate for the Samsung 30Q is 1500mAh (1.5A). The maximum charging rate is 4000mAh (4A). There are a lot more advantages to using an external charger for your cells. If using a charger of 1000mAh (1A) per cell or more, you will more than half the charging speed, giving you more time to use R2D2 and less time waiting! External chargers also have lots more features built in to them. Fully independent cell charging, temperature monitoring and on some chargers, a screen with a readout for voltage, capacity being put in (great for keeping an eye on cell health), etc. The other major advantage is being able to physically keep an eye on them. While no cell (or R2D2 unit) should ever be left unattended while charging, this is far more important with lithium cells. Equally, if the worst ever happens you’re more likely to only lose cells, not your whole R2D2!
If you plan to store your R2D2 for periods of over a few days, remove the cells and place them in the cases provided. If your R2D2 is likely to not see use for weeks or months at a time, discharge/charge the cells to around 40% and keep them somewhere cool and dry. (Room temperature is absolutely fine. Samsung’s specified long term storage temperature while guaranteeing a retention of more than 90% of capacity for 18 months storage is between -30’C and +25’C.)
Wraps and insulators – As mentioned above, take time to inspect your cells each time you remove and refit them. Check there are no tears in the wrap, that the insulator is present and not distorted (this is the white ring at the positive end. It separates where the outer cell can [negative/ -]) meets the positive [+] part of the cell). Also be sure to make sure the contact areas (top and bottom) are clean and clear of any dirt/debris.
Button top – I briefly touched on this earlier in this post. Our button tops are welded on but this doesn’t make them infallible to daily use. Check that they are securely attached. A button top that becomes detached through mishandling/drops etc can easily slip under the insulator ring and short the cell. There should be no movement in the button top and it shouldn’t “lift” on any side. If you notice your button top appears to be lose, cease use immediately. Welded button tops are designed to turn what is an industrial cell into a consumer usable product and its for this reason that welding is the industry recognised attachment method for anything on a Li-ion cylindrical cell. Button tops which are glued or otherwise “stuck” on are unlikely to stand up to long term repeated removal and insertion.
Other maintenance – Li-ion cells have a “cycle-life”. For the Samsung 30Q, Samsung specify that it should retain 60% (>1800mAh) of its rated capacity (3000mAh) after 250 cycles (a complete “standard” at 1.5A and discharge at its maximum discharge rate of 15amps). Given that the R2D2 unit will not be pulling the full discharge rating of the cells, you should see well in excess of a couple of hundred cycles before you notice any drop of in run time between charges. We recommend replacing the cells after 250 uses or 1 year, whichever comes first.
I hope this is in some way useful for everyone building their R2D2, that it highlights some of the most important parts of 18650 cell use and dispels some of the mis-information circulating social media. While Li-ion cells can be dangerous if mistreated (and from a personal aspect i still think an integral Li-Po pack would have been a better option from the manufacturer!), they’re not as troublesome as they are sometimes made out to be and there’s a reason they are second most highly used cylindrical cell behind the AA batteries in your TV remote!
As always, if this has left you with questions, if you need more information, or if you have something you want to share with other builders, dont hesitate to drop it in the comments section below.
Ben – Sales Director