running a 5V gadget of a 4.2V battery

Thread Starter

mikewax

Joined Apr 11, 2016
184
Hi folks i got this cheap chinese electric heating vest, 5V, with no wattage rating, intended for use with a typical usb power bank, 3 power settings. It works pretty good for $20.
I'd rather power it off a regular lipo with just a PCM, but i dunno if the control circuitry will get an attitude. I assume it has some kinda logic level hexfet and a preset PWM chopper with one of those... whadyacall, bootstrap gate driver output.
 

ElectricSpidey

Joined Dec 2, 2017
2,783
4.2 might be a little low, but the only way to find out without a schematic is to try.

Can't say how long your battery will last, or if the current draw will be too high.

That battery is only 3.7 volts...wont be 4.2 under load, maybe not even 3.7.
 

MisterBill2

Joined Jan 23, 2018
18,582
Probably it will work with two of those 3.7 volt cells in series, but it will make a lot more heat. With 3.7 volts, if the PWM still works, you will get about a third of the heat, since cutting the voltage also cuts the current.
 

BobTPH

Joined Jun 5, 2013
8,998
You can get a higher capacity power bank fo less money, and it boosts the voltage to 5V. They come pretty small too.

Bob
 

Audioguru again

Joined Oct 21, 2019
6,705
That battery is only 3.7 volts...wont be 4.2 under load, maybe not even 3.7.
A cheap battery that is mostly full of rice (no kidding, there are videos of it) will drop its voltage when loaded but the voltage on a good battery slowly drops as it discharges. The heating will get less and less since the voltage is not regulated.
A Lithium-Ion rechargeable battery is destroyed if it discharges below about 3V so a voltage sensor is needed to shut off the discharge.
 

Thread Starter

mikewax

Joined Apr 11, 2016
184
You can get a higher capacity power bank for less money, and it boosts the voltage to 5V.
well yeah that's what i'm using now, but it's big n heavy n the reason for wanting lower voltage is that the lowest heat setting is a bit too high for my taste. That's why i figured a 1s lipo is the solution. The device doesn't have temperature settings, it just has 3 different PWM settings. So i can just lower the power output that way. The same battery capacity will last longer.
 

Thread Starter

mikewax

Joined Apr 11, 2016
184
A cheap battery that is mostly full of rice
yeah the 650s are notorious for fraudulant vendors. i've seen ebayers claim a rating of 8 or more amp-hours which is about 3 X thier theoretical capacity.
battery is destroyed if it discharges below about 3V so a voltage sensor is needed to shut off the discharge.
yeah that's what this is for. Do this kinda stuff without knowin how to do it, you'll just waste ur money.
 
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