I am looking for a 5v USB power source that has a built-in protection against over draining. This would be mostly used to power a few LED lights and a USB fan. I would like to be able to run the fan for 7-8 hours without damaging the battery pack. I've gotten about 5 hours out of cheaper recharge packs before the fan slows down, but the power packs don't seem to work so well afterwards.



Is there such a device?

Well...my two cents:

Get a USB power bank that allows you to replace the cells inside.  Get one that uses 4x18650 and throw some hi-cap Sanyo/Panasonic NCR18650GAs inside, which are 3500mAh cells.  Most USB power banks will have a cutoff of 3.3v, or sometimes 3.0v, which is safe for quality li-ion cells from the Big 5 (Sony, Sanyo, Panasonic, LG and Samsung.)

Whether you get 7-8 hours out of it, with the fan, depends on the draw of the device you're using.

At 500mA, you'll have a total 28 hours, theoretically, with 4x3500mAh cells, but you're not running them down to 0v, so let's say 3.6v is 50% and 3.3v is probably 30-40% of the total.  Add in conversion inefficiencies and you're down even more.  For instance, my fixed cell, 3x18650 Xiaomi Mi (genuine) is a 10,000mAh unit, but it's listed/tested/useable capacity is about 6250mAh, so about 63% of rated capacity and that's a quality unit with LG cells.

My Xiaomi Mi 10,000mAh pack should run a 500mA USB fan for 12 hours.

With some of the cheaper dreck and SHIT-FIRE cells, you're on your own.

I have a Ruinovo 4x18650 pack that lets me change the batteries, but it came with 2600mAh Sanyo FMs, so that might still do about the same, even though there are four cells and not three.

Chris

Great, thanks for the info.

Anker usb battery. They come in many sizes. The 16000mah is a very good size for a edc bag. Good blend on size and capacity. And anker has they best warranty around. 18mo no BS replacement

I killed one of the anker usb devices on three discharges.   It was a 6000mah 3.7 volt.  Input was 5 volt.

I have 8 high capacity anker banks and use them all daily. Ive only had to send one back cause the lights were staying on. Used anker for years and never a issue.

Love this one. I've only killed it once after several days of constant use to intentionally kill it https://www.amazon.com/gp/product/B00X5RV14Y/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

ETA - They make a bigger one but this above one is so ridiculous I don't know what the point would be for the larger size since I have never killed the above one

I have 2 of those 20k mahs and 6 of the 13/16k mahs.

Thanks, I ordered one.



 

I am a big fan of goal zero.  check out their offerings.

I just ordered this Tomo V8, 4x18650, replaceable power bank.  $16.90 from the manufacturer, shipped.

Tomo V8 power bank...

Tomo V8 review/teardown...

I'll probably pick up four cheaper Panasonic 3400mAh NCR-B 18650s cells for it, for $20 shipped and then I'm done for power banks, lol.

Chris