DIY light battery packs - TSA concerns

[ScubaBunga]

Thought I would post this - I built some battery packs and was not sure what TSA or others in line will think, so updated my plans.

I have a dive rite canister light and last time I traveled - following all TSA docs, I labeled my AGM battery as sealed, packed it in my carry-on... and got stopped and questioned at every gate check - but passed with no issues other than the search. Well my light leaked just a bit at the switch and basically the switch is now dead - so I started a path to replace the switch. In the process I decided to use some 18650 batteries to give me a longer life battery pack. The switch is now a reed magnetic switch with a mosfet (used as relay) to turn light on and off (still working on the slide holder for the external magnet - maybe a followup later, this post is about the batteries). The AGM battery is a 12v 2.9ah battery - which for usability sake is only about 1.45ah. In building my 18650 batteries ( pack of 6 batteries, 2p/3s) I end up with basically a 3.6ah (assuming my cells are about 1800ma) where most of it is usable per li-on use. I am also able to fit two of these (in parallel) in my canister. I tested this and the light (an older 20w halogen) ran for over 8 hours with plenty of battery life left when I shut it down. The AGM battery runs for about an hour and that's it.

The problem: when I stepped back and looked at packing this, I realized that a diy battery pack soldered together, electrical tape wrapped, and with wires (power cable and balancer cable) sticking out didn't seem TSA friendly. I did talk to them and after they did some research said it was ok, just get their early, put them in their own tray and give TSA time to look at them. The thought of dropping these in a container while in line did not give me confidence!

The solution, I built an assembleable (is that a word) battery pack that I can store the components in my checked bag and then just carry on a box of 18650 batteries in a much more approved and non-dangerous looking way. I made these holders out of wood with the terminals bought off amazon. I hope to eventually have these 3d printed, but for now the custom wood ones work, look good, and fit right into the canister. The bonus is before I could fit 2 6 battery packs, now I can fit 2 9 battery pack (like a 5.4ah or combined over 10ah). Once assembled I can even charge the pack as a whole as I built in the balance cable as well. I'm thinking I may be able to night dive all week and never have to recharge these packs.

 

[guruboy]

Did you add a protection circuit board?
How is your balancing cable wired?

Personally, I would just take the batteries out and charge individually and avoid the extra cable.

 

[ScubaBunga]

Pack is a simple setup. No protection board but balance cable is wired for checking/balancing each parallel set, per the balance charger I have. The charger handles the balance instead of a balance board on the pack. I plan to bring my individual charger too which can hold 4 batteries. But I can charge the entire 9 battery pack at once. I’ve measured each cell to ensure I start with equally rated cells. For the time they will be used in the light (a few recharge cycles), I’m not concerned if they get off a little. When I get home they go back to other uses - individual cell flashlights and other things. I may rewire a bit before the trip to provide a fuse between cells, Just in case of a short.

 

[tbone1004]

not legal to fly if the cells are in a pack that isn't UN38.3 certified. Please make sure it is fully disassembled before you take it on the plane. They can be deadly without proper protection

 

[JohnnyC]

Disassemble your ghetto pack and put the cells in a proper container for air travel and you're fine.

Those look like a bunch of random different cells. Are they matched in any way? I don't think a simple balance cable is going to cut it as far as protection. And you really want protection on something like that. It's not just charging, it's discharging as well that you want to have some smarty pants stuff going on in there. 18650's are a lot more energy dense than most people realize, and in a sealed container, the potential for a serious issue can't be overstated.

If I were you I'd just bite the bullet and buy a real pack from batteryspace.com. Get a NiMH so you can fly with it and drive on. Battery projects are fun, but a sealed pressure vessel attached to my hip isn't somewhere I would want a thrown together project without a little more engineering built into it.

 

[ScubaBunga]

hmmm, "ghetto pack" is a bit harsh for a DIY forum, but ok. As was mentioned TSA is actually ok with the original pack, the new one is just more visually friendly which was the point of the post. TSA has no issues with li-on/18650 batteries - they just need to be in carry-on and show that contacts are protected. But to answer the other questions (statements?)..

The main difference between my DIY pack and the $65 pack found on batteryspace.com (LiFePO4 18650 Battery: 12.8V 4500 mAh ( 57.6Wh, 7A rate ) w. PCB) (besides the large cost difference) is their pack has a built in balance and over under voltage protection and a much nicer shrink wrap. I don't need the over voltage or balancer as the pack is built to use a specific charger that has the balance and over voltage protection in it. The under voltage is up to me to turn my light off. It does have one thing I don't today which is the over amperage protection via a resetable fuse. I can accomplish this by adding fuse wire or getting this $2-3 part and that I probably will add.

Yes they are random different cells in the picture - they are however all at the same rating for capacities. I charge and discharge each cell to determine their power curve so all cells are matched. They may come from many different laptop battery packs, but are matched. It's part of the DIY thing.

 

[kelemvor]

Nice work!

You could add a TI balance and protection chip for $2.59. Super cheap, it will make the pack much more safe and may make your cells last longer. I like to get stuff like that from mouser, here's a link: https://www.mouser.com/ProductDetail/Texas-Instruments/BQ7791500PWR?qs=sGAEpiMZZMve4/bfQkoj%2bGkkI53dxmb51AruYFlLGbI=

You would probably want some kind of board as the chip looks like surface mount to me. You COULD get away with soldering wires to the chip leads, but it would probably be a mess.

The chip only draws 8μA and you have more than enough juice to run that light for a few dives...

 

[tbone1004]

@ScubaBunga
doesn't matter if TSA was OK with it, it's still illegal. This in reference to your original plan of having one assembled and what it sounds like you are looking to do in the long term.
If you travel with a battery pack, or cells for that matter, that is not UN38.3 tested, it is against federal law. If you burn down an airplane, you will be held liable. I have no problem with people DIYing battery packs, but have big issues with you endangering the lives of everyone on board that aircraft with an untested battery pack.

https://www.batteryspace.com/prod-specs/UN_Test_Manual_Lithium_Battery_Requirements 6.pdf

If you want to fly with that thing, then please make sure the cells are all taken out so it is legal and less unsafe. The way you are transporting is not terrible, though I would be VERY careful with charging and assembling that thing. Like would never do it indoors or near anything flammable or expensive....

That said for less than $100, I'd buy one of the Battery space packs that have already passed UN38.3 tests and then you never have to worry about it

 

[ScubaBunga]

Nice work!

You could add a TI balance and protection chip for $2.59. Super cheap, it will make the pack much more safe and may make your cells last longer. I like to get stuff like that from mouser, here's a link: https://www.mouser.com/ProductDetail/Texas-Instruments/BQ7791500PWR?qs=sGAEpiMZZMve4/bfQkoj%2bGkkI53dxmb51AruYFlLGbI=

well as I mentioned, this is built into the charger so the battery pack only has the balance wire connected just like the chipboard would be connected. The charger has two plugs, one for the correct voltage for this type and series of cells and one for the balance cable. It's made to charge these types of packs. I do have plans for some packs that will use a dc-dc regulator fed by solar panels which will have an onboard BMS, but that's an entirely different DIY project that seems will generate more "you're gonna die" responses.

@tbone1004: it's interesting that TSA would not know it was illegal. But anyway as I don't want to fly with something the may look like a bomb (and it seems many here have concerns it actually is, even though it has the same components, once I add the fuse, as a purchased pack), I had already planned on carrying the batteries in a nice cardboard box with all terminals covered in my carry on just like a pack of AA's and assembling at my destination, so legal or not, it doesn't apply here. For cost, it's not just the $100 for ONE pack, I have 3 with extra parts for around $20 and I have several other packs (not round, but more standard) for several other uses - i.e. the only thing "new" to me for my dive light is the fact I can take it apart. Most of my packs are soldered.

Sorry, I thought this would be more humorous about something TSA would get upset over (which they say they wouldn't). I've done MANY DIY projects from rewiring my home, to air powered and chemical rockets, to turning raw lumber into picnic tables. I also service my own gear and am VCI certified to visual my own tanks. I know you shouldn't just cobble things together and I've done a lot of research to ensure the result does not explode. So I do appreciate the words of caution, a bit surprised at the strength of some of them, but better safe than sorry I guess.

 

[tbone1004]

@ScubaBunga too many of us have seen what happens when packs go bad. Messing with LiPo cells is no joke so there isn't a lot of levity that you'll get on it. Even from those of us that DIY just about everything.