Battery Powered 5V Fans - Is this safe?

[talhos137]

Hi,

I have some electronics inside a helmet I'm using for various purposes (I can describe there but I'm not sure that's relevant).

This electronics is composed of:
- 3 Noctua Fans : https://www.amazon.fr/gp/product/B00NEMGCIA/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 => 5V, 0.05A
- 1 Power Bank : https://www.amazon.fr/gp/product/B08ZYPQQF9/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1 => 5V, 2A

I wanted to connect all the 3 Fans to the Battery with nothing else than an On/Off in between.

Is there any danger to that kind of system?

[Konkedout]

When you say "helmet" I think about "bike helmet", so what is going to happen in the event of a physical crash?  Maybe you need to explain more about the environment to which the person wearing the helmet will be subjected.

Other than that;
Fan blades getting into someone's eyes?
The battery going "exothermic".  (Some LiIon batteries have started really bad fires.)

Maybe run all of this with a V-8 turbodiesel engine instead?  (kidding.)

[sleemanj]

There is no electrical danger.  The "powerbank" will protect itself from overdischarge.  The fans don't draw much current.

[talhos137]

When you say "helmet" I think about "bike helmet", so what is going to happen in the event of a physical crash?  Maybe you need to explain more about the environment to which the person wearing the helmet will be subjected.

Sure. It's like a bike helmet with a custom cooling system inside. It's used for cosplaying.
The helmet is in some kind of fiberglass and covers the head entirely. There are two fans on top and one fan below the head of the wearer, inside the helmet.

That's needed because there are no circulation of air. The lenses get foggy and it's getting hot very quickly inside.

The only danger I was thinking about were:
- Explosion or fire of the battery
- A wire melting

[Doctorandus_P]

With Li-Ion batteries there is always a risk of fire. There are billions of those things in use, and the risk is small. bit shit does happen. The risk probably increases with cheap power banks and crappy chargers and BMS systems. And also with mechanical damage. Especially the "plastic bag" type of batteries are (relatively) easily damaged.
Some easy counter measures to reduce the remaining risk are to put such a battery in a place it is not worn directly on the body, and can be easily disposed of when it does catches fire. There is a big difference between a 3rd degree burn on a body part and a blackened spot on the carpet, and to keep it away from other flammable materials. There is a huge range in the flammability of textiles. From easily ignitable to flame retardant. You can easily move a finger though a candle flame, but don't hold it still in the flame.

If you want to reduce any risk even further. Battery capacity of LiFePo is a bit lower, but they are also safer.

[BrokenYugo]

The powerbank will have over current shutdown protection, use reasonably heavy wire (18 or 20 awg) and it will not be capable of heating the wire much should a fan fail or whatever. You could fit a 1 amp fuse right near the USB plug out of a abundance of caution, low voltage automotive types you can find with inline holders at any auto parts store will be fine.

Use a quality powerbank and odds of violent failure may as well be zero.  Anker is decent, or at least something from a physical store that normally sells such things, avoid Amazon/eBay/Chinese marketplace mystery brands.

[talhos137]

All right. I understand that the risk is still very low, even though there's always a chance. Also, I don't have Li-Ion. Mine is a Li-Po.
I think I'll buy a "Battery Box" to have NiMH batteries inside. So then I can choose which battery I want.

To have 5V, I'll need 4 batteries like those : https://www.amazon.fr/dp/B0831957BT?psc=1&ref=ppx_yo2ov_dt_b_product_details

Would that be better?