Re: [Cerowrt-devel] solar wifi ap designs?

[Richard Smith <smithbone@gmail.com>]

On 06/06/2017 08:04 AM, Richard Smith wrote:
> On 06/05/2017 04:20 PM, David Lang wrote:
>> On Mon, 5 Jun 2017, Richard Smith wrote:
>>
>>> My WNDR 3700v2 power supply is rated at 12V 2.5A which is a peak of 30W.
>>
>> don't forget that this includes providing power out to the USB port as 
>> well.
>>
>> yet another reason to measure things :-)
> 
> 
> Ah. Yeah good point.  Thats .5A.
> 

I wired up my WNDR3700v2 running a fairly newish version of LEDE to my 
power supply.

Idle with 5G and 2.4G active, upstream link (GibE) connected and 1 sta 
attached to 5G:
	5.2 - 5.3 W.

Running some upload/download tests:
	5.2 - 8 W.

On boot however there are brief spikes that required the current limit 
of my supply to be set up in the 1A zone.

Given the info I saw in the buck regulators datasheet I suspected that 
the only reason it needs 12V is to run the +5V USB supply.  12V wall 
warts are super cheap so 12V is a reasonable choice from a BOM cost 
perspective.

If that is true you don't care about USB then it should run fine at 5V 
Vin, and indeed it runs just fine at 5V Vin.  I needed to up the current 
limit above 1A to allow it to boot.  I set it to 2A and didn't try to 
find the exact spike threshold.

5V gives you a slight savings. Idle at 4.8W.  That's about what I would 
expect. It's pretty easy to get close to 90% on a DC-DC converter these 
days without too much extra effort.

-- 
Richard A. Smith