Thursday, August 30, 2018

CWNP Conference in San Diego, CA

At this year's CWNP Wi-Fi Trek Conference we will be having many great topics covered from some of the best Wi-Fi experts in the business.
I consider it an honor to be selected among this group to speak at the conference this year.
The Topic I will cover is
"Alternative Power Sources".
Many access points have the option to be powered from various inputs and these can be leveraged for renewable energy sources such as solar power.
For Example: The Cisco 1552e access point operates on UPoE and requires a different power injector than many of the other Cisco APs. But... The 1552e also has a 12VDC input to where variations of power sources can be used.
One note to be aware of:
If your access point requires .625 amps of current from a 48VDC power source to achieve a required 30Watts of power,
Then...
It will require 1.25 amps of current from a 24VDC power source to achieve the same 30Watts.
One more step to 12VDC and you now require 2.5 amps to get the 30Watts you are looking for.
Here is a link to a helpful calculator for these numbers:
https://www.rapidtables.com/calc/electric/ohms-law-calculator.html
Electric power calculation
P =  IP is the electric power in watt (W).
V is the voltage in volts (V).
I is the current in amps (A).
These are important factors when determining the voltage input for your wireless AP. The Power (Watts) is a given factor as you should know the required watts it takes to power the AP. If not, the technical papers on your AP will provide this information.
Once you have one of the values in the formula, i.e. P or (watts), then you can determine the rest based on the inputs made available to you. 
In the case above, we need 30W from a 12VDC power source:
P = 30W, V = 12VDC, I = ?
12 x n = 30   We solve for n
30 / 12 = 2.5
so our current needed is 2.5A
From the standpoint of a 12VDC battery, we look at "Amp Hours" to see the supplied current from the battery. In other words, a 100 Amp Hour Battery would supply 2.5 amps to our AP for approximately 40 hours (factors like battery type and chemistry, battery age, weather and temperature all factor into this number being accurate). 
Note: Deep Cycle batteries are typically rates at a 20 hour discharge rate. Lead Acid batteries are rated at a 10 hour discharge rate. What this means is the ability of the battery to sustain the load changes significantly past this time rating so if you want to run your AP 24/7 deep cycle batteries are highly recommended.Now let's look at the UPoE requirements: UPoE delivers up to 60 watts so our numbers change.
P = V x I
60W = 12VDC x n . We solve for n
60 / 12 = 5
so our current needed is 5A
The above mentioned 100 Amp Hour Battery would only supply current for approximately 20 hours.
This is important to know due to the discharge of the battery in a 24 hour time period VS the amount of time you have to recharge the battery.
If you are discharging the battery every 20 hours, then there is a 4 hour period that must be supported by the charging source itself while recharging the battery. This is where the math begins to really come into play.We will be discussing the details of the charging rate at the Wi-Fi Trek Conference.
See details of the conference at www.CWNP.com

Brett Hill CWNE #147