# Getting Current from USB Power bank to breadboard

#### NathanielZhu

Joined Dec 5, 2011
50
I'm trying to make a life logging camera because the products sold for life logging is rediculously overpriced.
Basically, a lifelogging camera is just a normal camera with a rediculously long battery life and storage.

So I bought a Keychain "Spycamera" from China and I'm considering removing the 3.7V lipo battery and replacing it with a USB Power Bank(5V, 2A, 10Ah) so the camera would last a VERY long time. I'd put in a 16gb microsd and I calculated for the low resolution, I'd be 4GB/day or ~1.5TB/Year or ~100TB-150TB/Lifetime.....pretty good to be able to have a record of an entire life.

But I'm having an issue with the USB Power bank. It charges my phone just fine which means it is producing current, however when I try measuring the Power and GND pins of the Power Bank, it shows 5V, and basically 0A of current....No current at all!!!

I assume it has some sort of short protection but I've tried putting a 1K Ohm resistor in series and it's still 0A.
I took a microusb cable, plugged it in, and cut off the end to expose the Red and Black wire, measured the voltage, 5V and the current... 0.
I NEED the 2A or at least 1A...

I'm not sure what to do.

***btw. My power bank is http://www.ebay.com/itm/10000mAh-Dual-USB-Power-Bank-External-Battery-Portable-Charger-For-Cell-Phone-/251853815890?hash=item3aa3a84052:g:vc0AAOSwEetV76E4

I noticed that it has a list of compatible hardware....which is odd cus it's just a 5V usb power bank, it should seem so obviously that it should charge any device that having a compatability list is making me question whether it has some detector in there that only lets compatible hardware get current?...,

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#### NathanielZhu

Joined Dec 5, 2011
50
hi NZ,
Have you considered a module like this.?
https://www.amazon.co.uk/MITSUGAWA-1-Port-2000mA-TRAVEL-Charger/dp/B00FEA12RG/ref=sr_1_14?ie=UTF8&qid=1482398182&sr=8-14&keywords=mains+to+usb+charger

If you have a life time of recorded data, how and when are you going to review the data.??

E
Yeah I got a lot of those...but the chinese built in battery only last less than an hour and it's a huge hassle to be charging it all the time.
I don't like messing with lipo batteries cus of their...reputation. So I wanna use something like a usb power bank.

Since high school, I've been recording videos daily. Basically, I just organize them day by day, year by year, and super categories of "High school", "College", "work", etc.

My motivation is personal. My memory has always been terrible. Time passes, you forget. Sometimes I wonder if I have ever lived at all.

#### ericgibbs

Joined Jan 29, 2010
10,001
So I wanna use something like a usb power bank
I was suggesting you recharge the 'power bank' using the module I posted, it will output 5V at 2Amp charging current.
E

#### blocco a spirale

Joined Jun 18, 2008
1,546
The obvious solution is to simply replace the original lithium cell in the camera with one (or more in parallel) of larger capacity; Why make it more complicated than that?

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#### NathanielZhu

Joined Dec 5, 2011
50
The obvious solution is to simply replace the original lithium cell in the camera with one (or more in parallel) of larger capacity; Why make it more complicated than that?
The camera uses 200mah Lipo. I Want to replace it with Li-ion (power bank)....which should have been easy.
I don't like lipo. Bad experience with catching the bed on fire as a kid. Not messing with it

And cost: 4X1200mah lipo = 4800mah lipo is ~$21 and 10Kmah Li-ion is$10.

I was suggesting you recharge the 'power bank' using the module I posted, it will output 5V at 2Amp charging current.
E
My power bank recharges just fine. No issues there. It's at max capacity right now.
It recharges my phone, and everything else just fine. And since my phone battery is more or less around 2aH, the fact that it fully charges my phone quickly means that it's 2A when it's charging my phone.

But for some reason, it just doesn't output 2A when I'm using the GND/VCC directly from the USB pins...

I've also getting tempted to use an Arduino micro as the power source and connect the Arduino to the Power bank. But I tried the 3.3v from arduino, 1A and it wasn't enough to power it. I'll try the 5V and step it down to ~4V.

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#### blocco a spirale

Joined Jun 18, 2008
1,546
The camera uses 200mah Lipo. I Want to replace it with Li-ion (power bank)....which should have been easy.
I don't like lipo. Bad experience with catching the bed on fire as a kid. Not messing with it.

And cost: 4X1200mah lipo = 4800mah lipo is ~$21 and 10Kmah Li-ion is$10.
Then use Li-ion cells.

How did you measure the current from the power bank?

#### OBW0549

Joined Mar 2, 2015
3,368
So I bought a Keychain "Spycamera" from China and I'm considering removing the 3.7V lipo battery and replacing it with a USB Power Bank(5V, 2A, 10Ah)...

...But I'm having an issue with the USB Power bank. It charges my phone just fine which means it is producing current, however when I try measuring the Power and GND pins of the Power Bank, it shows 5V, and basically 0A of current....No current at all!!!
What load did you have the power bank connected to when you measured zero amps?

#### NathanielZhu

Joined Dec 5, 2011
50
Then use Li-ion cells.

How did you measure the current from the power bank?
Yeah true.... If the power bank doesn't work, I'll likely do that.

I tried measure it two ways. I tried sticking my multimeter's probes onto the usb pin (since there's 4, 1 is GND, 1 VCC, and 2 for communication). I touched the GND/VCC pins
When I switch the meter to voltage it gives me 5V. Then when I switch it to Amps, it give me 0A/nothing,
I've also stripped the head of a micro usb cable revealing the 4 wires corresponding to the 4 pins and when I measure the voltage current from the stripped wires (red/black) I get 5V, 0A.

#### OBW0549

Joined Mar 2, 2015
3,368
I tried measure it two ways. I tried sticking my multimeter's probes onto the usb pin (since there's 4, 1 is GND, 1 VCC, and 2 for communication). I touched the GND/VCC pins
When I switch the meter to voltage it gives me 5V. Then when I switch it to Amps, it give me 0A/nothing,
I've also stripped the head of a micro usb cable revealing the 4 wires corresponding to the 4 pins and when I measure the voltage current from the stripped wires (red/black) I get 5V, 0A.
You CANNOT simply connect an ammeter across a voltage source; in effect, that shorts out the source. Instead, you connect the ammeter in series with the voltage source and a proper load; for instance, with a 5 volt source a 5Ω load resistor will result in 1 ampere of current flow, and that's what your ammeter will show.

The reason you measured zero amps is probably because the power bank sensed the short circuit (through its internal overload protection circuit) and shut down. Once it shuts down, no current (or only a very small current) will flow until the short is removed and it resumes normal operation.

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#### dannyf

Joined Sep 13, 2015
2,197
rediculously long battery life
the solution depends on how ridiculously long life you want this "ridiculously long life" to be.

many power banks have auto-shutoff function: it turns itself off if the current load is less than a certain amount. Because of their low efficiency at low load, they aren't that suitable for anything application longer than a couple days.

Joined Jan 15, 2015
5,421
Per OBW0549, when measuring a voltage we measure across the load. When measuring current we place our current meter in series with the load.

Placing a current meter across the USB Power Pins is not a good idea and on some systems is about like placing a short across the USB power pins.

Ron

#### NathanielZhu

Joined Dec 5, 2011
50
You CANNOT simply connect an ammeter across a voltage source; in effect, that shorts out the source. Instead, you connect the ammeter in series with the voltage source and a proper load; for instance, with a 5 volt source a 5Ω load resistor will result in 1 ampere of current flow, and that's what your ammeter will show.

The reason you measured zero amps is probably because the power bank sensed the short circuit (through its internal overload protection circuit) and shut down. Once it shuts down, no current (or only a very small current) will flow until the short is removed and it resumes normal operation.
Makes sense. However I did try using a 1kohm resister(used it cus it was just sitting next to me) in series yesterday, but now that I think about 1kohm is too big which would have blocked current anyways. So at ~3.7V the camera runs out of charge in about an hour or less and It's battery capacity is .2ah. So the current draw 200ma. As a reference, the power bank doesn't autoshut off when powering my idle arduino nano which draws much less power so that means this device shouldn't autopower off from it's load.

yeah so it's likely the short
I'll test it again with the 5ohm resistor when I get home.

the solution depends on how ridiculously long life you want this "ridiculously long life" to be.

many power banks have auto-shutoff function: it turns itself off if the current load is less than a certain amount. Because of their low efficiency at low load, they aren't that suitable for anything application longer than a couple days.
1 full day is good enough. I was gonna copy the files each day, recharge, go to bed, and then resume recording. Yeah I've left my arduino nano on for long periods of time without powering off and it draws a lot less power.

#### drc_567

Joined Dec 29, 2008
842

... image from Ron's post above.
Just for the record, if you are able to obtain the two measured quantities here, amps and volts, you can multiply them together and get the power that the load is using, in watts.

#### dannyf

Joined Sep 13, 2015
2,197
I was gonna copy the files each day, recharge, go to bed, and then resume recording.
sounds like a regular camera would do it just fine.

#### MrSoftware

Joined Oct 29, 2013
1,775
Check the USB specification. I vaguely remember reading somewhere that USB negotiates for power, so I don't know if you can pull much from the bus without your device negotiating. Maybe you can get a little by default, but have to negotiate for more. This might be a good starting place:

"Powering electronics from the USB port" - http://www.ti.com/lit/an/slyt118/slyt118.pdf

#### RichardO

Joined May 4, 2013
2,271
The reason you measured zero amps is probably because the power bank sensed the short circuit (through its internal overload protection circuit) and shut down. Once it shuts down, no current (or only a very small current) will flow until the short is removed and it resumes normal operation.
Hopefully the battery pack protected itself. If it didn't then you probably blew the fuse in your meter.

#### OBW0549

Joined Mar 2, 2015
3,368
Hopefully the battery pack protected itself. If it didn't then you probably blew the fuse in your meter.
Dangit, I wish I'd thought of that. That sure would explain the zero reading, wouldn't it?

#### RichardO

Joined May 4, 2013
2,271
Dangit, I wish I'd thought of that. That sure would explain the zero reading, wouldn't it?
That's what makes this forum so great. I wouldn't have thought about the battery pack shutting itself down.