Want to keep it simple and cheap...which is probably dangerous.

So like our drill instructor used to tell us, I’m like a Marine with a tan belt. I know just enough to get my ass kicked.

My first little project was waterproofing and hard wiring this Trustfire 3xT6 to run as a flounder light off a car battery.

Then I do some more reading and I find out you can get a bunch of 18650s out of old laptop batteries. There is a Goodwill across the street so I walk over and they have hundreds of laptop batteries for $5 a piece.

So I’m thinking to myself, why lug around a car battery when I could just use a bunch of 18650s. Do a little more “research” and find out the 18650s that come out of laptop batteries are unprotected which potentially = BOOM.

What I want to do is this. Using small pvc pipe can I stack 3 18650s, then wire three of those stacks in parallel to get a pack that would run around 11V and be about 9AH. Other than the battery connectors on the ends I wouldn’t be soldering anything to the batteries. They would all remain single batteries so I could charge them in just a regular single or double 18650 charger. Also I go on long trips, so if I took out 27 batteries, I’d have enough to do 3 full change outs to the pack.

I’m sure there is PLENTY wrong with my idea. Am I just building a bomb? Is this doable? Would it be more realistic with protected batteries? If I want to use the reclaimed laptop 18650 do I have to wire in some type of protection into the pack?

I want to keep it simple for two reasons.

1. I obviously don’t know all that much about this, and my soldering skills are limited.
2. Less is cheaper, and since I’m running it in salt water the more I have running, the more likely something will get shorted or ruined.

If there is too much wrong here to correct just tell me to quit.

Let the flaming begin!

No flame here.
At $5 each (which sounds like too much for a questionable used battery IMHO) x 27 you are at $135.

For that money you probably could get a Gel-Cell deep cycle battery which will charge up to roughly 13.4-14.2 depending on your battery charger, then apply some resistors or diodes to bring it back down to the 11-12 volts you want.
Heck of a lot safer and should run for a real long time.

Does not have to be a huge battery for the amperage we are taking about here, research Marine or Gel-Cell batteries and see what the price difference is.
Thanks and keep us posted and above all, Fuse the heck out of whatever you chose and be safe.
Keith

Sorry, the used laptop batteries are $5 each, which can yield anywhere from 9-12, 18650s each. Accounting for dead cells, I’m assuming I could get my (27), probably more, 18650 batteries for around $20 worth of laptop batteries.

Thats a 3S3P setup. No problems with that, if you have a hobby charger to check the cells capacity. Only use very similar cells in series.

>>>>>>and find out the 18650s that come out of laptop batteries are unprotected which potentially = BOOM.

I actually think that *fire Chinese junk batteries are FAR more dangerous than reputable brand-name batteries (Sanyo, Panasonic, Samsung, LG) from a pack. But that’s my opinion and many think just the opposite. But even dissassembling a pack can be extremely dangerous. You’re wrong if you think the pack will come apart in an orderly manner and without busting off pieces of plastic and perhaps causing a short circuit that could make the boom you’re talking about. So I would read everything you can find about disassembling packs before trying it. And definitely have somewhere to chuck it FAR AWAY if you get a short and it starts to heat up. It happens VERY quickly. Literally one second it’s cool and three seconds later, it’s too hot to touch.

And then once the cells are out, they need to be tested and dubious cells chucked. So a good DMM is a must. And since there is no protection circuit, I have to do that for the cells and insure that they don’t discharge too deeply.

The cell wrappers inevitably get nicked up during removal, so it’s best (I think) to apply a second layer of shrink tube to prevent shorts. Then they have to be CAREFULLY charged and monitored and tested. Unless, you are willing to go through all this, don’t play with packs. Heck, don’t play with li-ion cells at all, unless you read all about them and have a good idea of the dos and donts.

And the commenting poster is absolutely right, you do not know the history of these cells — but then again no one knows the history of ebay or DX cells or even if they’re rewrapped fakes. At least with a laptop pack, I know that a top company spent some time choosing the batteries and wiring them correctly to keep them safe and to insure long battery life. Unless some idiot rewired the pack and was plugging it directly into the wall or some such foolishness, the hardware in the pack SHOULD keep the batteries in good condition, with proper charge times and proper charging current and proper voltage draining protocols.

The way I think about it, no one ever thinks twice about buying a used laptop and used battery pack, and I certainly hear next to nothing about used battery packs blowing up when used as a laptop pack. So as long as I observe the same charging guidelines with the salvaged cells, I think I am as safe with single cells as with a li-ion in a power pack. Certainly safer (IMHO) than any *fire Chinese battery. Because — again — the pack (if working properly) was maintaining the cells as they should be maintained. Bad cells should be easily recognized by low voltage, inability to hold a charge, overheating while charging, low initial voltage, leaking, discoloration, etc.

BUT I will NOT use unprotected cells in a multi-battery flashlight or in any type of multi-cell arrangement without protection circuits of some kind. Look at the pictures of injured law-enforcement personnel in the infamous FBI li-ion battery warning to see just how real the danger is of improperly using multi-cell lights with dicey li-ion batteries.

I only have scratched the surface here about salvaging packs and li-ion safety. And — yes — li-ion cells do blow up. I had one go (thread somewhere on BLF about it), so I am now extremely careful about all facets of li-ion cell use.

I won’t comment on the pvc pipe thing because I don’t understand what you’re trying to do.

Above all, be careful. When one of these 18650 li-ion cells “vents with flames,” the resultant explosion can be big enough to maim or kill you or a bystander. That is no exaggeration. However, it is a fairly rare event. And as has been mentioned before, nicd cells can also blow up if shorted or charged improperly, so the dangers of batteries seem to come with all batteries, although li-ion cells seem far more volatile.

Hope this helps.

Lots of good info there Ubehebe, thanks.

Here is a quick sketch of what I’m trying to accomplish. This is a rig that would be about 4 feet long and I’d carry and hold the flashlight under water as I walked around in 1-2 feet of water. I would use the PVC tubes themselves as the battery compartment since they aren’t conductive.

+ million for the DMM - even better if you can find one sealed up well enough to be splash resistant and carried in the tackle box. Radio Shack used to sell a small folding meter like that.

Why not just run good single battery lights with a reasonable draw (say 1A - 2A) and a single efficient LED like an XML? Heck, you could easily use cheap bike clamps to clamp 3 cheap lights onto your pole and even point them in different directions if you want. My 2100 XML runs 3 hours on high (not turbo) on laptop pulls.

I prefer springs at both ends of the unprotected battery since they don’t have button tops. And use lights with a driver that will cut off at about 3.0 volt so that the cell isn’t run down any further than that.

Keep your spares in a watertight container and always load your empties so that you keep charged from discharged clear.

That is extemely dangerous for 2 seperate reasons.

1. All of the batteries will be at different voltages and as they discharge they are going to be supplying high currents to the weaker cells so the parallel pairs are at an equal voltage.

2. The series groups will most likely be different capacities (even if all marked as 2600) and this can easily lead to reverse charging. I have dealt with a similar 3S pack of 18650s and I had 1 at 0 volts and the rest around 3.7.

>>>>>>All of the batteries will be at different voltages and as they discharge they are going to be supplying high currents to the weaker cells so the parallel pairs are at an equal voltage.

I think — if I’m reading the suggestion right — that Scaru is correct. The setup would end up with fully charged cells next to not-fully-charged cells, which is a cause of ye olde li-ion multiple-cell “el boomo” in theory and in reality, in both the NASA report on torture-testing 18650s and in the FBI treatise on being careful wit yur li-ions.

We all want to save money, so this might be a little more pricey. And I have absolutely NO idea if they really are, but I am constantly reading how many of these lights are supposed to be waterproof. Would be a chance to find out if they really are. Just attach one waterproof flashlight (batteries and all) to your PVC probe stick dealy. One light with (1 or 2) 26650 batteries would give you a pretty long run time I would think. Then there’s always the “real” diving lights, reviews of which I have skimmed many, but for the life of me I can’t remember what kind of marks they got.

I know they even make tail-caps with remote on/off switches so it would be a semi-cinch to rig up an above-water on/off switch for some lights, although I think maybe the on-off deal is a low priority here.

If you’re asking these questions, it’s probably not safe to do. Notice the packs themselves use fairly sophisticated circuits inside to monitor the state of these cells in xSxP setup.

Unless you know what you’re doing, used cells are best used for 1 cell lights.

>>>>>used cells are best used for 1 cell lights.

Kay-rect!

To be honest, you're better off buying new batteries.

There's no way you can get 9pcs battery that's similar in capacity, discharge rate, rest voltage etc from recycled laptop batteries. You can get few that are close enough, but probably will need to buy many, many packs and will involve a lot of work testing each individual battery with a hobby charger.

Or, you can just get 10 Samsungs 2Ah for around $35, which is probably not far off from buying 6-7 packs needed to find matching batteries. Not to mention all the works.

Here's a link for the $35 200mAh Samsung. Probably could get cheaper if you browse Aliexpress. I plan to buy the 10pc 2600 version ($45) when I have some extra cash myself.

http://www.aliexpress.com/store/product/10pcs-lot-Original-18650-ICR18650-2000mAh-Li-ion-3-6v-Battery-For-zhuo-neng-laptop-Free/112467_606705563.html

Thanks for all the replies. I think I’ll pass on attempting this project for now due to the potential hazards.

Maybe in the future when I have more skills and equipment I can attempt it.

Thanks again for all the help.