Cell phone backup battery - useful gadget

Jeff Haas

Senior Member
I was at a trade show recently, and one of the booths was giving away cell phone backup battery packs with the company name on them. These are a useful gadget for use with a microcontroller!

They have one or more 18650 batteries in a case; you charge them up via USB and then they put out a steady 5V via a USB cable. The free one I got is about the size of two packs of gum, and uses the same cable for both charging and powering a device, you just flip it around after charging.

These are currently a popular gadget on ebay. They would make a good power source for a robot or other project that needs a battery. Just need to work out a cable.
 

hippy

Technical Support
Staff member
These do look quite convenient and I have picked up a few myself but haven't got round to trying them. The big advantage is that they are high capacity so once charged should last for a good while. My only real concern was that they can deliver high currents which might be a problem in a fault condition. It's probably advisable to use normal alkalines or current limited PSU during development.

I would probably add a USB-A female socket to the PICAXE project, connect +5V and 0V from there, so a standard USB cable can be used for connection without having to hack things about too much, and no need for a special cable. Pound and dollar stores often sell products like USB hubs with sockets which can be easily unsoldered and reused which can be an easy and cheap supply.
 

premelec

Senior Member
ON current requirement?

An oddity of these units to consider is that they usually require a minimum current to stay ON - when Spark Fun introduced one a year or two ago I asked them what that current was and got no reply - only their warning that it wouldn't keep a bare ardweeny going without extra load... I wonder if a brief current draw pulse every 10 seconds or something would keep them putting out -
 

beb101

Senior Member
Hackaday had a hack for the low current draw problem,

http://hackaday.com/2013/11/08/tricking-a-usb-power-supply/

A commenter had a simpler solution. I tried it and it worked; battery charging
port to 1A output, 2.1A output to device.

Quote Jonn: "Bought one with an integrated micro USB cable to charge
devices and a free USB port for other cable types. Wanted to
use it to run a bluetooth audio receiver in my car. Same thing,
wouldn’t continually power, only charge a battery. I just plugged
the integrated micro cable into the battery charging port
and , viola, tricked it into doing the same thing as this hack."
 

premelec

Senior Member
Thanks for that reference! Clarifies what must be tried [I presume different for each pack mfr]- good to know.
 

premelec

Senior Member
Thanks for that ref! also don't forget the unit itself probably drops about .2v and draws up to 20ma [which would keep the battery on...]
 

john2051

New Member
Hi, I dont know if this helps, but radiospares were selling 5AH lithium battery packs with two usb sockets
an on/off switch and three charge remaining leds.
They werent that expensive, and with rs you can have them next day.
You also get a fair warranty. I'm not on my home pc at the moment, so I dont know their code.
I bought two, and early tests look promising.
john
 

jims

Senior Member
Is the Picaxe AXE091 development board susceptible to the concerns that have been noted here in the FORUM? Jims
 

hippy

Technical Support
Staff member
Is the Picaxe AXE091 development board susceptible to the concerns that have been noted here in the FORUM? Jims
Not sure which concerns you mean exactly but it should be possible to power the AXE091 from a battery pack, but there would be the same risks of adverse consequences should there be a wiring fault on the AXE091. As to keeping such a battery pack delivering with low current draw, then yes that would be same case.
 

john2051

New Member
Hi as an update to the radiospares battery packs I mentioned earlier. I apparently bought them in an introductory sale at eight pounds each.
I looked again last night and they are now over thirty pounds..not quite the bargain.
sorry
john
 

Jeff Haas

Senior Member
I just measured one of these USB charger packs on my multimeter - the volts shown bounced around but went as high at 5.7V. Is this a problem for use with a Picaxe?

Another one of these units (bigger, seems to have more of a circuit inside) maxes out at 5.13V and stays steady at that level on the multimeter.
 

geoff07

Senior Member
I think the Microchip spec for a PIC (on which a Picaxe is based) is 5.5 volts (operating). The max Vss-Vdd stress is 6.5v (non-operating). So 5.7v shouldn't damage it but it might not work correctly, though it probably will.
 
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