*BLF LT1 Lantern Project) (updated Nov,17,2020)

Like I said, the discharged cell will only accept the charge at it’s own rate.

Basically all that is going on is that a cell is being connected to a low impedance voltage source of max. 4.2V.

Which, I don’t think is any danger at-all. Though it may not be good for the cells, long term.

It could be pushed in a lot harder.

These are not the fragile delicate dangerous scary things that some seem to think.

Otherwise you’d never dare to connect your EV to a supercharger and put in 80% energy in 15 minutes.

I have a damaged Skyray King here which suggests the issue is more than an urban legend. The “balance out, quite quickly” thing can happen fast enough to melt springs.

That’s probably a problem with the springs, not the cells. Or overall safety. Or maybe something was put in backwards ?

Still a real issue though. And not ideal. But no obvious alternative, unless we only have cells in series, which is hardly a practical way forward for many devices, and introduces a load of other concerns.

I wouldn’t mix cells of varying voltages if you paid me. I’m from the RC drone world, a lot of us use balance boards to charge several 3-6s lipo packs at a time in parallel. These boards connect the main discharge leads in parallel, and the balance leads in parallel.

Rule of thumb is never connect packs with cells that are larger than 0.1v difference to each other, or balance current can melt wires/damage cells. I push that rule to 0.2v sometimes, but I make sure to connect the higher voltage pack to a bank of lower voltage packs, never the other way around. Why? Discharge current. These batteries don’t like being charge rapidly. They’ll take it, sure. But they don’t like it.

The packs I use are rated for 5c charging current. That’s basically mAh capacity converted to Ah capacity, and then charge at an amperage equal to the Ah rate. Have a 3,000mah pack? That’s 3Ah, so a 1c charge rate is 3 amps. 2c is 6amps, 3c is 9amps, etc.

Discharge current between two packs at 0.2v difference per cell can be 5 or 10 amps, sometimes more, at least briefly.

To connect two batteries, one full and one dead, together, is to essentially cause a dead short. You’re gonna pull a crap ton of current out of the full battery, and dump it into the low one.

This would be bad enough with my lipo’s, with their high charge rate capacity of 5c. But the cells we use usually have a max charge rate of 0.5 or maybe 1c. The 30q has a max charge rate of 1.3c, or about 4amps. But in my experience they get warm charging at 0.3c, or 1amp.

So to mix cells of large voltage difference, and generate that massive balance current? Melting springs? Yeah, no thanks. Maybe it won’t blow up in your face, in fact it probably won’t. But dang it if it isn’t really bad for the battery, and potentially your face. No thanks, I’ll pass.

Sorry for the rant, of course you’re welcome to do as you please. But I agree with TK, it’s not an urban legend. Even if it’s not as bad as I’ve made it out to be, it’s still not good. Please don’t do it.

No, that was the springs doing their job correctly. They’re supposed to act as fuses in case anything like this happens. I’m lucky it was only the springs which got damaged.

… and that was with weak old NCR18650A cells. I’d hate to see what happens with a set of mismatched high-amp cells with bypassed or low-resistance springs.

This was something we worried about when designing the Q8, and looked into fusible links etc. on the tail PCB.

I did some tests and found it was not too bad. In that implementation.

We decided not to bother with that and rely on people being grown-up and responsible for their own actions.

But of course a 4P arrangement like a Q8 or SRK has a multitude of opportunities for putting in the cells incorrectly.

I’m interested. When will it be up for sale.

Interested

Cant help but think of the sign in my local bar ……“Free Beer Tomorrow”

Any idea if this will need high drain batteries like the 30Q? Or will NCR18650GA work fine?

This is a low power regulated light, using NCR18650Bs, Samsung 26Fs, etc, are perfectly fine within the power constraints of the light.

Ok. After months and months of following this thread, you’ve lured me in. Please add me to the list of interested light enthusiast that hide they’re hobby from their wives. :wink:

This is one of my least worrisome justifications to my wife. We haven’t lately, butt we have had many outings that would have benefited from this project.

UPDATE Lexel is getting the parts & working on the driver prototype to test atm.

Ditto, I feel the wife approval rating will be very high for this light

Great news! :+1:

Thanks for the update, Den. I hope you’re doing well!

Once Lexel gets the driver prototypes built & sent to Toykeeper to tesat with the firmware, then to send one to Barry at Sofirn to test and finishing working on the first lantern prototype to get it rolling. ( i hope.

I’ve, unfortunately, discovered BLF. This is not good…not good at all.
Please add me to the list of those likely to buy the ULF…(I haven’t even told my wife about the Taser Strikelight (hey, it was 25% off!) and I’m already modifying it…

It’s a pretty terrible affliction. My sympathies.

What are the runtimes on a 1 x 18650?