Two Alfa USB Wifi Adapters on Raspberry Pi?

I have two Alfa AWUS036ACM USB Wifi Adapters (MT7612U chipset) that work fine if I have one plugged into a powered hub but fail to function properly with both plugged directly into my Raspberry Pi 3B. It will boot fine and act as if it's functioning then one of the adapters will throw a bunch of erroneous errors during load. Supposedly the Pi is capable of outputting 1200mA total for all USB ports and the Alfa wifi adapters only draw ~380mA max per adapter (verified with voltmeter/ampmeter). Why isn't this working if the only two devices I have plugged in only draw ~760mA total? The math doesn't check out.

Are there other components on the USB bus drawing ~400mA+ such as onboard ethernet/wifi/BT? I have been able to recreate these same conditions no matter the power supply (Canakit 2.5A & Canakit 3.5A & Battery 4.5A of available power.

Have you checked adding ?

max_usb_current=1

to

/boot/config.txt

or

/boot/distroconfig.txt

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Thanks, sure have. It doesn't have an impact. Which does make sense given the linked article (mine is a Raspberry Pi 3B, not a B+). But I've read conflicting information regarding this.

The B + model also introduced a parameter that controls how much power USB devices are allowed to pull out of the USB port. By default, the total current from the USB ports is limited to 600 mA...

If I'm limited to 600mA that makes sense why I'm getting errors, but, am I really just finding out that the Raspberry Pi 3B only outputs 50% of what the Raspberry Pi 3B+ is capable of?

I will have a Raspberry Pi 4 to test it with next week although in the interim I wanted to reach out and see what the community has experienced. Thanks for your input.

Yes, it seems lots of conflicting information the more i look also

however , here is some discussion on how to check the maxpower when device are plugged into USB port

https://forums.raspberrypi.com/viewtopic.php?t=105502

install usbutils

opkg update; opkg install usbutils

On my Raspberry Pi 4 Model B Rev 1.4 a SanDisk Ultra Flash drive

plugged into black USB 2.0 port (224mA)

root@raspberrypi:/home/pi# lsusb -v | grep -e 'MaxPower' -e 'Bus [0-9]'
can't get debug descriptor: Resource temporarily unavailable
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
    MaxPower                0mA
Bus 001 Device 003: ID 0781:5581 SanDisk Corp. Ultra
    MaxPower              224mA
can't get debug descriptor: Resource temporarily unavailable
Bus 001 Device 002: ID 2109:3431 VIA Labs, Inc. Hub
    MaxPower              100mA
can't get debug descriptor: Resource temporarily unavailable
can't get device qualifier: Resource temporarily unavailable
can't get debug descriptor: Resource temporarily unavailable
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
    MaxPower                0mA

VS

plugged into a blue USB 3.0 port (896mA)

root@raspberrypi:/home/pi# lsusb -v | grep -e 'MaxPower' -e 'Bus [0-9]'
can't get debug descriptor: Resource temporarily unavailable
Bus 002 Device 002: ID 0781:5581 SanDisk Corp. Ultra
    MaxPower              896mA
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
    MaxPower                0mA
can't get debug descriptor: Resource temporarily unavailable
Bus 001 Device 002: ID 2109:3431 VIA Labs, Inc. Hub
    MaxPower              100mA
can't get debug descriptor: Resource temporarily unavailable
can't get device qualifier: Resource temporarily unavailable
can't get debug descriptor: Resource temporarily unavailable
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
    MaxPower                0mA

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It's my fault, I retraced my steps. I was under the impression that running the command max_usb_current=1 manually and adding it to /etc/rc.local through Luci (System-->Startup-->Local Startup) would have the same affect as adding it to /boot/config.txt. It does not.

After adding max_usb_current=1 and safe_mode_gpio=4 (for good measure?) to /boot/config.txt the issue seems to be resolved, I've been running two adapters all day without a hiccup.

Thanks for your input and being so clear (and the links), I apologize for wasting your time.

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