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[lunchsack86]

So looking at adding 2 5v .15A fans to my helmet.

Im not electrician and do not understand the math involved.

Looking to run both fans for like 8hrs ( i love in Phoenix and our "comic con" is end of May super nice heat)

Can anyone help point me in the right direction of size of power bank?

Please and thank you

[Fi-8015]

Hi, two fans at 0.15 A will have a total current of 0.3 A or 300 mA. To run them for 8 h you'll need a powerbank with 300 mA x 8 h = 2400 mAh.
The capacity they usually tell you is for the cells in the powerbank and at their rated voltage (3,7 V). Since the powerbank transforms the voltage to 5 V it's usually less than this capacity. To compensate this issue, I would recommend to get a powerbank with 3000 mAh or more (I guess next larger ones should have about 4000-5000 mAh). As another option you could also get two of the smaller ones with 2400 mAh and change them when empty. This way you may spare a bit of room in your helmet.

[lunchsack86]

Hi, two fans at 0.15 A will have a total current of 0.3 A or 300 mA. To run them for 8 h you'll need a powerbank with 300 mA x 8 h = 2400 mAh.
The capacity they usually tell you is for the cells in the powerbank and at their rated voltage (3,7 V). Since the powerbank transforms the voltage to 5 V it's usually less than this capacity. To compensate this issue, I would recommend to get a powerbank with 3000 mAh or more (I guess next larger ones should have about 4000-5000 mAh). As another option you could also get two of the smaller ones with 2400 mAh and change them when empty. This way you may spare a bit of room in your helmet.

Wow thank you very much for this info!