Would this be a proper statement?

The current in a DC circuit depends on the load and not the source?

I have a headset that uses two AA for powering some ANR.

It says 50 hours of use but it’s never that. Im presuming that has to do with the type of AA used (it’s mA rating)—assuming the device is running properly?

I’d really like to know the load the headset uses without damaging any wires and such.


I’ve got a 5V USB charging port I’d love to use instead of AA’s but even if you were to regulate it to 3V I have questions

things designed to use USB ports go through enumeration to handshake on what power to deliver. This port here can go from SDP (around 100mA?) to giving 2.4 amps to an iPad.

the device isn’t designed for enumeration (it’s expecting 2 AA) would the SDP mA be enough—or too much?

In other words, this device has a specific load, and a dc source will provide only what’s asked of it (if capable) but not more than asked (if capable of far more)?

I cannot find any mA markings on my Costco AA.

 

Most USB port chargers simply provide 5V and have a current limit, usually 1-2A. The actual current depends on the load, up to that limit.

A real USB port on a computer will listen for negotiation, and it is undefined what they do if there is none. I believe most allow 100mA.

Bob

 

The current in a DC circuit depends on the load and not the source?

This is true for different sources with the same voltage. If the voltage changes then all bets are off.

It says 50 hours of use but it’s never that. Im presuming that has to do with the type of AA used

Most likely the discrepancy is down to marketing, though the particular battery and things like volume will also have effects.

the device isn’t designed for enumeration (it’s expecting 2 AA) would the SDP mA be enough—or too much?

The device would not be connected to the USB it would be connected to the 3V regulator.

 

The current in a DC circuit depends on the load and not the source?

It depends upon both.
For a resistive load the current equals the source voltage divided by the resistance.
Electronic loads tend to take a more constant current with change in voltage, but it usually will have some change.
But the current does not depend upon how much current the source can deliver (as long as it can provide at least the maximum current the load requires).

I have a headset that uses two AA for powering some ANR.
It says 50 hours of use but it’s never that. Im presuming that has to do with the type of AA used (it’s mA rating)

It's the mAh (millamps times time) rating that is the capacity of the battery.
Most AA alkalines are around 2000 mAh.
Thus if they last 50 hours, the device current draw would be 2000/50 = 40mA

things designed to use USB ports go through enumeration to handshake on what power to deliver.

That's only at the load (electronics) end so they don't overload the USB port.
If you add a 3V regulator to the USB port 5V, it should be able to deliver the current your device requires.

 

thank you all. Good explanations all around.

I need to go explore a small project to regulate that down to 3v. any suggestions? the projects and circuits I see online (quick search) seem to focus on 5V to 3.3V and not 3. I know nearly every healthy AA I've tested is around 1.56.

I have an iPad that uses that same port, so when I'm done I need to explore the port with a tester to see if it can handle two things at once. I know the port can easily do 5v @ 2.4 amps.

 

You could use a 3V regulator, such as this.
There are more types available from a Google search for 3V LDO regulators.

 

You said you have Costco AA batteries. i think they are called "Kirkland" Alkaline but I have never tried them. No alkaline battery says the max amount of mA current and only rechargeables show the mAh capacity.

I bought Duracell AA and AAA Ni-MH rechargeable batteries with a charger at a very low price at Costco and I was surprised to see that the batteries are made in China with a very low mAh rating. Their charge does not last long.

 

Kirkland. Yes that’s the in-house brand. I haven’t recorded which types are running out faster. I’ll also test their health out of the box next time.

Truth be told I was hoping to find a ready to go converter that didn’t require much board work. I’m kinda bogged down on a side software project and the day job.

but that linked product does look nice!

 

I was hoping to find a ready to go converter that didn’t require much board work

Something like this or this or this?

 

hehe, yeah those might do.

1. This one has it all contained within the USB plug? That's nice.

2. Why 3.3V and not 3? Each product and discussion (outside DIY projects) use 3.3V.

 

3.3V is a common voltage used by modern chips, it has replaced 5V for that.

Bob