Powering Project Through Portable Charging Bank Not Working.

Hi, everyone! I am making a simple little speaker amplifier using a PAM8403 (https://www.amazon.com/gp/product/B00LODGV64/ref=ppx_yo_dt_b_asin_image_o04_s00?ie=UTF8&psc=1) and two 3-Watt, 8-Ohm speakers. This works great, and it amplifies the audio signal for the speakers perfectly fine.

My problem is that I want to run it off of a USB power bank. I tried with two power banks, but it always goes off after 30 seconds. My guess is that my project doesn't draw enough current to be recognized by the power bank. I tried adding a 100 Ohm resistor across the output of the powerbank to draw more current, but that didn't work. Does anyone have any suggestions on what to do? I am also very big on efficiency, so I would prefer a solution in which I wouldn't have to waste power, but if that is what it takes, i'll do it. Here is the brand new powerbank that I bought: https://www.amazon.com/gp/product/B081SPFH53/ref=ppx_yo_dt_b_asin_image_o00_s00?ie=UTF8&psc=1

I read that most power banks have an always-on feature so you can have it always on, but I have no clue about how I could active that. Thanks for your help.

My problem is that I want to run it off of a USB power bank.

I think you are absolutely correct, that is the problem. You are using a product designed for a purpose and you are trying to use it for a different purpose for which it was not designed.

I read that most power banks have an always-on feature

Did you check the description of the item you purchased for that feature before you purchased it?

100 Ohm will contribute to empty the powerbank But strange it didn't work
I faced the same problem. The solution was a 270 Ohm resistor from D9, I think, to GND and a timer switching D9 at 10% dutycycle. I had a Arduino Uno consuming some current but I don't have the data sheet in front of me.
If switching a load tricks the powerbank better then a constant load.... I can't tell.

Rapid80:
I read that most power banks have an always-on feature so you can have it always on

Very few USB power banks have this feature.

Which Arduino are you using for this project ?

Ya I understand that I am not using it for its intended purpose, but I have seen people use power-banks dozens of times, so I figured it shouldn't be too hard. Also I did check for it saying that, but out of the ten that I checked, none of them have it, because if you are using it for a phone, you shouldn't have to always keep it on. Also, I am not using an Arduino with it, I am only powering the PAM 8403 to amplify the audio signal from my phone. My project is basically just making loud speakers. Thanks for your replies.

Sorry for referencing an Ardiono that You did not indicate. Try and decrease that resistor step by step and hopefully make it work. Different powerbanks have slightly "different needs" as I've found out.

Ok I will go down and let you all know what happens. Thanks for your help.

Awaiting.....

I just put three 200 Ohm resistors in parallel and it worked! The resistors were getting somewhat hot, though. And because I want to maximize efficiency, I will continue to work my way up over 66 Ohms and see if it still works. I will come back and tell you my final solution. Thanks, guys!

Great You're on to it.!

Rapid80:
I just put three 200 Ohm resistors in parallel and it worked! The resistors were getting somewhat hot, though. And because I want to maximize efficiency, I will continue to work my way up over 66 Ohms and see if it still works. I will come back and tell you my final solution. Thanks, guys!

The trick is to switch those resistors in-circuit with a mosfet for a few milliseconds every 15 seconds or so.
Leo..

Ok I have my final solution. At ~83 Ohms (220 Ohms, 220 Ohms, and 270 Ohms in parallel) it did not work. At ~81 Ohms (270, 330, 330, and 390 Ohm resistors in parallel) it did not work. At 80 Ohms (270, 270, 390, and 390 Ohm resistors in parallel) it did not work. However, at ~77 Ohms (200 Ohms, 220 Ohms, and 270 Ohms in parallel) it did work.

On my final attempt I tried to get between ~77 Ohms and 80 Ohms. I got 78.7 Ohms (220, 390, 390, and 330 Ohm resistors in parallel) and it did not work. That left me to use the 77 Ohm solution. I care about efficiency so much that I did several tests that were varying in single Ohms to find the most efficient solution. From doing those test, I improved the efficiency quite a bit, by going up ~11 Ohms. Thank you guys for your help.

As I was typing this, Leo posted. How would I do that? How can I time it to go off after a certain amount of time for a short duration? I think I would need some kind of oscillator. I have not worked with oscillators before, but am ready to try. Maybe a 555 timer could do it?

Yes, the 40, 50? year old NE555 could be a solution.

I decided to change the ratio to about 75 Ohms because I realized that if you turned the volume to low, it wouldn’t draw as much current, and it would turn off again so now it will stay on no matter the volume. Also, I am not exactly sure what “40,50” means. Do you know any schematics for how I could wire up the 555?

Continously drawing that current will lower the life time from one battory charge.
Using a NE555 pulsing a lot less energy from the battory is the way to go. There must be millions of application notes for this veteran, the NE555. I'm sure somebode will tell soon.

Well we also have to make sure the 555 circuit doesn't consume a lot of current, or else that would defeat the point of the resistor. I calculated, and I wonder if just running four leds at about 16 Ma would work, because that is about the same current that would be getting used.

Then use a CMOS 555.

I just tested it, and the leds worked, too, so I will go with them. Thanks for all of your suggestions and help!

Almost everything you try to do has been done before by others.
Time to ask Google.
"555 to keep powerbank alive" returns several such projects.

Pulsing a load with a common 555 shouldn't consume more than 5mA.
You can reduce that with a Cmos555 and ideal current/timing to much less than 0.5mA.
I don't see if that's needed though.
Leo..

I found some "power banks" (TechGeek) that do not have the drop-out current "feature", but a lot more that do.

I bought one because it has an LED flashlight feature, figuring that if it runs that way indefinitely why wouldn't the outputs be the same - but it's a bummer too.

Trying to come up with a "keep alive" circuit involves finding the minimum draw requirement and the interval that satisfies the power bank's requirement (x mA, for y milliseconds, every z seconds).