Hi Jason, thanks for your comments! That is all very well, but we are not expecting to power the modem by its USB port - in fact the modem does not support powering over USB cable {which adds to my uncertainty whether the result will be stable :-} The concept we are working on is to use a USB cable that simply takes the 5v power from the cable and terminate in a barrel plug to fit the modem power socket ;) Since the 8816 is a really bare-bones basic unit, then I feel mildly optimistic that it will (as you also suspect) much less than the spec of the power supply. So I'm keen to hear whether the concept is worth testing. The other fellow who I've been discussing this with is also on this list, and has indicated that he intends to source a suitable cable and give it a go. But if someone else who has already tried it can say without a doubt that it's doomed to failure, then maybe we can save a bit of heartache! :-D Cheers! Mike.
-----Original Message----- From: Public [mailto:public-bounces@talk.mikrotik.com.au] On Behalf Of Jason Hecker (Up & Running Tech) Sent: Tuesday, 6 October 2015 10:07 AM To: MikroTik Australia Public List <public@talk.mikrotik.com.au> Subject: Re: [MT-AU Public] power routerboard and modem with one supply
Have a look here:
https://en.wikipedia.org/wiki/USB#Power
The USB 1 and 2 specification calls for consumption to be 500mA at down to 4.5V (4.5V allows for some cable loss under load).
A USB1/2 device should draw no more than 500mA.
Typically you will find modems with 5V supplies at 1A or 2A. If it's minimalist modem-only device you might find it never draws more than 500mA at 5V in spite of having a 1A supply. You'll really need to get a multimeter/ammeter in the path to see just how much current is really drawn by the device under full load at 5V to be sure.
On 6 October 2015 at 09:57, Mike Everest <mike@duxtel.com> wrote:
Hi All!
I've been discussing possibility of using USB port on 2011/951 series to power up a modem like TP-link 8816 which uses 5v power supply using a cable like this:
http://miniimg2.rightinthebox.com/images/384x384/201403/ljhnpo139462469 3508.
jpg
I checked with MT engineering team, and received promising response:
"The minimum output current both models can provide is 500mA. RB951Ui-2HnD and RB2011 with wireless should be able to supply even up to 1A of output current. RB2011 without wireless should be able provide up to 2A output current. Only note that we guarantee the minimum output current"
So TP-Link ships with a 5v/1A power supply and so assuming that the device actually consumes 'up to 1A' then perhaps routerBoards able to supply 'up to 1A' might actually work as a pair.
Although I'm thinking that the power consumption will increase as packet throughput increases on both, then perhaps as the transfer load ramps up, power available to the modem may be constrained, and so might cause trouble under load.
So I find myself wondering whether someone else may have already been own this path and so if you have, and are willing to share your observations, I'm most curious as to how it turned out! :-)
Cheers!
Mike.
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