# Must I reduce USB's 1A output to 450mA?

I have a bluetooth headset that charges at direct current 5 Volt and 450 Milliampere. I charge it with its original AC-DC-converter and I want to be able to charge it over USB (e.g. from a portable pre-charged battery/charger or a solar USB charger).

I could easily cut the cable and solder the one end to a charging USB cable, but with this I would almost always give 5 Volt and 1 Ampere since that is the standard, right?

• Are there modified USB "cables" with extra electrical components on the market that use 500mA from 1A?
• Is there a DIY way to take out those 650mA or 500mA?
• The device will only draw 500ma – Ramhound Oct 18 '16 at 2:14
• This logic must be based on Grassman Algebra or something... – Ale..chenski Oct 18 '16 at 3:07
• @DanielB, The simple Ohm or Kirchhoff formulas are applicable to circuit components with constant parameters. The AD-DC adapter is not a linear voltage source, and it will either abruptly reduce the voltage output when connected load exceeds its rated DC current capability (either along some artificially defined cut-off function, or just turn off). The device is also a non-linear load, starting with constant current, which will be reduced when the internal battery enters a constant voltage stage of charging. So these simple formulas do not apply. – Ale..chenski Oct 18 '16 at 6:55
• @DanielB, I believe that the details are necessary because otherwise some curious people get confused with the discrepancy between their expectations and measured results. – Ale..chenski Oct 18 '16 at 7:20
• @fixer1234, certainly the load is defined by Ohm's Law, if you mean that to consume 450mA from 5V it must have about 11 Ohms of effective resistance. However, there is a bunch of active elements that make this "impression", and this "resistor" will change in time as charging mode changes. So, given an unknown state of battery in the device when you plug it in first, you never know what its resistance is. How does the Ohm Law help here? So I am unsure what the objection is. – Ale..chenski Oct 18 '16 at 22:07