# USB battery bank supplying a circuit wiTh power

#### Jalius W

Joined Aug 16, 2018
1
I want to give 5v to my ebike (broken 5 volt regulator). I have a usb power bank with an output usb at 5v 1a. When I measure the voltage when nothing is plugged in or just a cord is plugged in, I get .77 volts. When I measure the voltage when my phone is in I get 5 volts and my phone says it’s doing 1 amp. So how do I get the power?

#### 128ITSH

Joined Jul 20, 2017
101
Probably the phone has some way to tell the power bank when to give 5V, so it doesn't waste power when the phone is not connected.
If your power bank is rated for 5V@1A output, then the formula to find the maximum output power is V x I = P (voltage in volts times current in amps equals power in watts).
Therefore the maximum output of the power bank is 5Vx1A=5W (5 watt).
I would guess an electric bike needs much more than 5W so you need higher power than that.

#### OBW0549

Joined Mar 2, 2015
3,566
I want to give 5v to my ebike (broken 5 volt regulator). I have a usb power bank with an output usb at 5v 1a. When I measure the voltage when nothing is plugged in or just a cord is plugged in, I get .77 volts. When I measure the voltage when my phone is in I get 5 volts and my phone says it’s doing 1 amp. So how do I get the power?
Some USB battery power banks have internal load-detection circuitry that keeps the voltage regulator (i.e., a step-up switching regulator that steps up the battery's 3.7 volts to 5.0 volts for the USB) turned off to avoid wasting energy when nothing is connected. This circuit periodically checks the USB connection and if there's a load present, turns on the regulator to give full power.

I have one that works like that, and I suspect that is what's happening with your unit, too.