Battery Bank won't replace a plain old battery

[jimandy]

I have several of the popular smart phone type “Battery Banks” with a USB for plugging in to power up or recharge the phone I wanted to see to see if the bank would simply power a 5V LED (properly wired with resistor) as I would use it later to power a very low current project. With the bank fully charged I plugged in the LED, it lights fully for about 30 seconds then starts to cycle on and off rapidly. My guess is that the charging circuit in the bank, after firing in a bit of inital power, realizes the LED is drawing almost no power and then cycles instead of feeding a continous 5V.
My project fails to run after the first 30 seconds of plug in. when the source voltage starts pulsing.
So, am I stuck with using just a plain old battery?

[Janitor Tzap]

jimandy,
A battery bank won't work for the circuit you want to power.
Here's a wiring diagram of a simple Power Bank.

As you can see, the battery is only 3.7Vdc.
I'm surprised the LED with dropping resister works at all.
You'd be better off using a rechargeable 9V battery with a 5Vdc voltage regulator circuit for the 5Vdc that you need to run your circuit.

Depending on the current draw.
The amount of time you get out of the 9V battery will very.


Signed: Janitor Tzap

[dyarker]

5V LED??
Blues and whites are 3.8V Other colors lower forward voltage. ("raw" LEDS)
Maybe an LED bulb with LED and regulator in one package.

USB power is not just voltage on two wires. The host and device negotiate the current needed. The blinking is the power IC in the "bank" checking to see if a smarter device has been plugged in.

Cheers,

[Janitor Tzap]

USB power is not just voltage on two wires. The host and device negotiate the current needed. The blinking is the power IC in the "bank" checking to see if a smarter device has been plugged in.

Hmmm.........

I used that circuit of a Battery Bank as an example, because it is common and easy to make.
The TL431 Shunt Regulator is most likely why he is getting the flashing effect.
The Regulator will shut down at around 2.5Vdc.
But by changing the resistance on the control lead, you can raise or lower the shut down point about 1%.

Also, even though he is using a LED, to test with.
Not all LED's have the same current rating draw.
I'd try finding an LED that has the same current draw as the project he wants to power.
Then do the test.


Signed: Janitor Tzap

[CeaSaR]

You can also do this:
https://www.youtube.com/watch?v=lOL3ic8msas&t=512s
I may be doing this in the near future.

[jimandy]

As there has been some discussion about the LED, FYI I used a Uxcell 10mm Pre Wired LED, Red DC3-6V.
To make sure the LED worked from "pure" 5V I powered it from one of the jillion Apple iphone chargers accumulated over the years. Bright red.

Then I tried the "battery bank" on a 5V motor. Ran like a champ for way past 30 seconds. No cut off after more than a minute
I was using the LED as a sub for a eMylo Wireless 5V Remote Control Switch that dropped out after the 30 second initial on period before the bank started pulsing.

The bank is the problem. Think I'll go with a 4.8V battery. Whats 2 tenths of a volt among friends.

[dyarker]

Yeap. Checked Uxcell, they call them "lamps". Their LED lamps have built in current limiting.

A red LED itself has a forward voltage of around 1.8V The voltage is set by the chemistry used to make a particular color LED. Higher power LEDs will have a larger max current, but same voltage. Generally, as frequency of emitted light (color) increases, the voltage increases. All well designed LED circuits have current limiting. (Due to shape of voltage/current curve.)

So when saying you have an "X" volt LED, please include the word "lamp" or "bulb".

Cheers,

P.S. AC LED bulbs also have built in rectifier (probably full wave) because LEDs have a low PIV; and many LEDs in series.

[dacflyer]

dyarker >> there are actually Blue and white leds that will work well with 3v. I actually have some..
and a few of them chinese led garden lights, the leds will operate from a 1.2v Nicad battery. Don't ask me how,, but they do.

[dyarker]

there are actually Blue and white leds that will work well with 3v.

could be some newer chemistry.

chinese led garden lights, the leds will operate from a 1.2v Nicad battery.

I'd bet built in boost regulator.

Higher voltages would still mean lamp/bulb with built in current regulation.

Cheers,

[CeaSaR]

Most of those cheap LED garden lights have a tiny boost board built into the main compartment somewhere.

[dacflyer]

The ones i've fiddled with, didn't hardly have anything in them,, a 4 legged transistor looking chip, and a resistor,,could possibly be a resistor looking coil.
The last one i played with just had the solar panel, a battery, the small board and the led.. The led comes on once the solar panel is too low to produce power. no fotocell at all..

[dyarker]

"The ones i've fiddled with, didn't hardly have anything in them,, a 4 legged transistor looking chip, and a resistor,,could possibly be a resistor looking coil." Exactly! Boost circuit.