Protected batteries vs IMR - safety

[rolygate]

The main risk is with stacked batteries, and using cheap batteries, and with no multimeter. Unless you are doing 6v on the SB then you are probably not in the danger zone.

It can't hurt to drill vents, of course.

To be honest, once a battery starts to go, it will need need slots not holes to vent all the gas. The main use of vent holes is to tell you what is happening, because in every report of an incident I know of, where there were vents, gas was ejected strongly for a couple of seconds before the whole thing went up. You get two seconds to sling it. Otherwise the only thing that will work is a bottom section that blows off first.

We're probably talking about a cubic metre or more of gas being produced in a few seconds. It just can't get out of a couple of small holes fast enough. The vent holes will jet hot gas onto your hand and you'll sling it. Natural reaction. It's what has happened in several of the reports. Then it blows.

woooosh......BANG

[Switched]

I like the idea of a press fit bottom vice vent holes, makes sense to me, thanks for the tip folks.

[Retriever]

After reading all of this, my KR808's are looking pretty good!

[markfm]

Actually, an 808 is the only battery I've had that went really flaky, stuck on, let it do its thing outside in a can.

[Retriever]

Actually, an 808 is the only battery I've had that went really flaky, stuck on, let it do its thing outside in a can.

Interesting. I would think that they are safer because of their size. Is that correct?

[D4rk50ul]

Interesting. I would think that they are safer because of their size. Is that correct?

The amount of stored energy in a battery is also how much is released in a failure so smaller is safer in that aspect. I wouldn't count on e-cig companies using high end batteries in $5 pieces though.

Sent from my HD2 using Tapatalk

[Retriever]

The amount of stored energy in a battery is also how much is released in a failure so smaller is safer in that aspect. I wouldn't count on e-cig companies using high end batteries in $5 pieces though.

I agree, but I still shudder to think what the profit margin is on an 18650.

[rolygate]

The small batts in mini ecigs are 'safer' for a number of reasons, such as their tiny size, and the built-in electronics.

The problem is if you want a batt that lasts for a few hours, or that can power LR fittings properly, a mini can't do that. Even a mid-size e-cig can have issues there.

So people go to big-batt mods. That gets them the power they need, plus you can buy replacement cells easily. But the trade-off is the risk factor increases. There's no way of avoiding the fact that you need a higher standard of care. This implies some background knowledge and the will to apply safe working measures.

I think it's hard to argue against a statement that mods aren't really for people with zero electrical knowledge and who don't want to be bothered with safe user practices. Even a single battery mod needs more care in some areas than a mini. When you go to two-cell mods the risk jumps by about 100 times because there are so many more things that could go wrong - or so many more things to check, depending on your point of view.

Inevitably there will be people who buy 2 cheap batteries, maybe mix 2 batts that aren't a match, don't have a multimeter so they have no idea what is going on, have a mod with no gas vents, a mod with no weak point at the bottom meaning the top blows off first, keep batteries in their pocket with their keys and change, have no master switch on their mod or don't take the atty off before it goes in the pocket or purse, buy the cheapest charger they can, never check any voltages, etc etc. What can you do? Mods are going to blow up under those conditions.

The only part-solution to this problem is to make mods idiot-proof, so that whatever happens they can't explode. Easy to do with a boxmod, very hard to fix with a tube mod.

My ideal tube mod would have milled slots for gas venting; be turned on a lathe to cut a V-notch near the bottom of the tube that doesn't quite break through the wall so it's a natural weak point; and so on. So did I do that? No. It's too much trouble just now as I don't have access to a machine shop at this time. But when I get back to the tools I sure will fix that...

[Retriever]

Just curious about 1 thing: Does a "hot spring" that collapses when the battery heats up (breaking the connection) suffice as a safety precaution, along with a vent hole, or is more needed?

Thanks!

[rolygate]

It's a very useful safety feature.

Any single safety feature is just that: a single feature. Safety features are best when layered, that is, if one doesn't work then another will. So one is useful but two or three are better. So for example on a tube mod you could have gas vents, a collapsible spring, and a lockable on/off switch. Even better would be milled gas slots, a collapsible spring, and a separate master switch.

The issue of the top blowing off first is very difficult to address on a metal tube mod. The fact is, that's going to happen on almost all of them if the other features are not present or don't work. So it's sure worth looking at how you can stop things getting to that stage, because if everything else fails (or there are no other safety features in the first place), if the battery/s blow then you're going to get a bullet in the face and no way to avoid it.

When I said this would happen sooner or later a lot of people told me it was impossible or extremely unlikely. In fact there was an almost hysterical reaction from one or two mod makers. OK - now tell that to the guy in hospital.

I'm not going to crow about this because it's an extremely unfortunate event for the poor victim; and because after a lifetime in engineering I know the optimism has been beaten out of me but youngsters just can't appreciate the way things can go badly wrong. The fact is, things will fail, and one day there will be a chain of failures. Planes fall out of the sky even though someone spent $200m trying to make that impossible.

It's Murphy's Law, the most basic law in engineering. If you don't understand that, then maybe making potentially explosive devices that people hold in front of their faces is not for you.


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I'm closing this thread, because we've said everything that needs saying. And because I want to have the last word :-)