18650 Battery Box

Battery nerd-out alert!!

WARNING: Li-ion batteries can be extremely dangerous. Don't try this at home. I have a B.S. in Electrical Engineering and a M.S. in Power Systems and even I let the smoke out of the wires sometimes.
DISCLAIMER:  I am not responsible if you hurt yourself or others while messing around with this kind of stuff.

A coworker of mine is big into tinkering.  He’s got a garage full of scooters and a fleet of 3D printers.  He convinced me to get a 3D printer early last year but more on the 3D printer in another post.  One thing the 3D printer has got him into is making his own drones.  Drones, for obvious reasons, need lots of light weight power.  Some of these motors pull over ten amps of current.  So naturally I was intrigued when he started showing me some of the batteries he has been using.  I’d been getting tired of lugging around the ol’ dependable lead-acid gel cell even though it’s been good to me. 

He showed me an NCR18650B Li-ion cell made by Panasonic.  This same form factor had been used by Tesla in some vehicle battery packs and is also popular in vaping devices.  Rated at 3.7 volts and 3400 mAh per cell they are quite a nice amount of juice for only weighing 46 grams.  The only problem with the Panasonic NCR18650B is they are unprotected cells. Many 18650 cells have a button style protection circuit at the top of the cell to keep them from being over discharged or rapidly discharging when shorted. This protection chip takes up space in the package though at the expense of current capacity.

So I bought a dozen of them and decided to put a pack together.  I had done a lot of picking my coworkers brain about using these things without a protection circuit.  I was somewhat sure that I could use them without a protection circuit since I was dealing with a very low current draw relative to what others use them for.  I fused the whole setup at 1 amp so I felt pretty safe about using if for a while.  My friend printed some caps for me so I could put some packs together and test them out.



I used this configuration a few times but went back to the lead-acid because the thought crept into my head about the ass end of my kayak exploding because of some accidental short malfunction.

I decided to revisit the idea when I did more research and found some Li-ion protection circuits online for $10 each from amazon.com.  These circuits provide protection from over-charge and over-discharge conditions, as well as over-current conditions for each 4-cell pack. They also have a very low operating and stand-by current draw.  I printed up some new four cell cases that would be better to mount the protection circuits to the back of them.  I also printed some plates with stand-offs on them to screw on to the back of the packs to cover the protection circuits after they were mounted on.  Wired and strapped 4 of these packs together and I have a battery rated at 14.8 volts and 13.6 Ah.  I haven’t tested it but I did get great performance out of using only 3 parallel packs of four cells in my first configuration.  I’m thinking I’ll get at least 15 hours of run time, maybe 20 with my Garmin sonar that pulls about 0.5 amps on average.












For the case I’m using a Plano Guide Series 3600 with an Ancor wire seal to run the cord out to my usual two-prong trailer wiring connector.  I used an Ancor “waterproof” fuse holder inside the box too(I don’t see how this item is waterproof - it’s good product, but I wouldn’t call it waterproof).  The bonus of upgrading to this Plano case is not only does it give me room for 4 parallel packs, it gives me enough room to potentially upgrade to 8 parallel packs if I really wanted to. For now though, I just filled the space with a chunk of closed cell foam.





So the older box, which I’ll likely still use from time to time, was a Pelican case with a 12 volt, 10 amp-hour battery and weighed 7 lbs 12 ounces.
The new box weighs 4 lbs 4 ounces and is rated for 13.6 amp-hours.

The protection circuits definitely work.  I inadvertently tested them while putting the pack together.    I’m going to get some testing in as soon as it isn’t so damn cold out in the garage and I’ll add some numbers when I get them.

Costs:
NCR18650B cells(bought in sets of six): ~$6.10 per cell x 18  = ~$110
Protection Circuits(DROK 4-series Li-ion Protection Cirtuits): $12 x 4 = $48
Printed battery cases: Probably less than $1 per case just considering the filament
Plano Guide Series 3600 case: $25
Ancor fuse holder: ~$6.50
Ancor wire seal: ~$5.50
Lots of wire and misc hardware: $0 (Had plenty of extra lying around)
2-pole trailer light plug: ~$2.00

Grand total: ~$200

So not exactly cheap or easy to put together, but it was a really fun project and I'm really happy with it.

That's impressive. Thanks for sharing


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Nice write-up. I've considered doing similar but decided the cheap lead acid battery was probably enough since I'm only putting a tiny sounder.

The weight savings is nice regardless.

I love it. I need to see those printed parts up close to see how the batteries are connected in series in each pack.  they do make conductive printer filament if you really want to go crazy. Now I want to see you put it in your carry on luggage. It would be a real cool X-Ray. 

I love it. I need to see those printed parts up close to see how the batteries are connected in series in each pack.  they do make conductive printer filament if you really want to go crazy. Now I want to see you put it in your carry on luggage. It would be a real cool X-Ray.

Followed by a body slam and a full cavity search... NOT from a dentist either!!!

Better question is how much you charging each and when you taking orders?

Better question is how much you charging each and when you taking orders?

Yeah, but I'm not so much interested in a finished unit as much as I'd like to get my paws on some of your clever sleeves.  It looks like an great way to escape the blue brick madness, but getting a 3D printer puts it a bit outside of my DIY budget.

Really cool idea and darned impressive job of putting it together.

very nice! I am curious though, why go the protection circuit boards, rather than just getting protected 18650 cells? Current capacity loss concerns?  Also, how do you charge the system?

very nice! I am curious though, why go the protection circuit boards, rather than just getting protected 18650 cells? Current capacity loss concerns?  Also, how do you charge the system?

Thanks!  Yes, the cells that have a built in protection circuit are rated for about 2500 mAh instead of about 3400 mAh without.  I use an iMAX B6 charger by SkyRC.  It's very programmable and has settings for all different types of batteries.

Added cost of parts.

Good DIY stuff. Did you print using ABS or PETG? Any other 3D printing projects for kayak fishing?

Good DIY stuff. Did you print using ABS or PETG? Any other 3D printing projects for kayak fishing?

All I print with so far is PLA but I will likely start using other stuff soon.  More on the other stuff I've been printing a little later, but yes.   

Any concern about using an airtight, sealed container to house the batteries? I thought I'd heard that li-ion batteries need to "breathe," and suspect that housing it in my closed pelican is what caused my li-ion weego to burn itself to into a black blob on my kitchen counter a few months back

Wow that is crazy tech.  I was just proud of my self for using a torch to heat up som pvc and jam it in my yaks built in pole holders
 

Any concern about using an airtight, sealed container to house the batteries? I thought I'd heard that li-ion batteries need to "breathe," and suspect that housing it in my closed pelican is what caused my li-ion weego to burn itself to into a black blob on my kitchen counter a few months back

There is a chance of the batteries giving off gasses, mostly while charging but possibly during discharge too.  The Plano box has a vent hole in the front that is covered by a rubber stopper on the front latch when it is latched closed but it seems like the pressure will need to build up at least a little before it can actually vent.  If you unlatch the front latch the hole is open so I'll need to try to remember to unlatch it when I connect the charger.  Many of the Pelican boxes have a vent on the front of them too. Not sure how well it works though.

Any concern about using an airtight, sealed container to house the batteries? I thought I'd heard that li-ion batteries need to "breathe," and suspect that housing it in my closed pelican is what caused my li-ion weego to burn itself to into a black blob on my kitchen counter a few months back

There is a chance of the batteries giving off gasses, mostly while charging but possibly during discharge too.  The Plano box has a vent hole in the front that is covered by a rubber stopper on the front latch when it is latched closed but it seems like the pressure will need to build up at least a little before it can actually vent.  If you unlatch the front latch the hole is open so I'll need to try to remember to unlatch it when I connect the charger.  Many of the Pelican boxes have a vent on the front of them too. Not sure how well it works though.

Obviously my experience is anecdotal and you can't draw sweeping conclusions from one person's, but FWIW the shit hit the fan when it was unplugged. Mine had finished charging when i removed it from the charger, placed it in the plano, closed the lid, went to sleep, and x-hours later the fire alarms went off.