There are light pole taps and many other ways to provide power to your access points but I want to help you out here with designing your own reliable power source at a very affordable price.
Many companies offer solar solutions for powering 802.11 devices but they are usually very pricy (Up to $12,000) and most customers do not want to pay such a price to power one device.
If you understand the principle of power consumed over time, then you can calculate the power supply needed in order to sustain consistent, stable power to your device.
Lets start with time -
Amp Hours are better explained as how long a power source can provide power.
For example: If a battery is rated for 10 Amp Hours then you could power a device requiring
1 Amp for 10 hours, 2 Amps for 5 hours or 5 Amps for 2 hours.
So if your device requires 2 Amps to operate and you want it have a 48 hour power reserve, then you
need to multiple TIME by POWER USED
2 Amps x 48 Hours = 96 Amp Hours
Disclaimer: These values are always assumed calculations and climate and temperature conditions can effect the totals so you should always provide a buffer as a reserve.
If you need 96 Amp hours you should provide 120 Amp Hours to be on the safe side.
Now that we know our discharge rate (2 Amps per Hour), we know we need to provide a charging rate to keep our power source (battery bank) charged.
Discharging faster than we are charging will eventually result in a power failure.
To figure out a dependable figure to work with, we need some values and a formula to work with:
DC watts to amps calculation
The current I in amps (A) is equal to the power P in watts (W), divided by the voltage V in volts (V):
I(A) = P(W) / V(V)
The current is Amps and since solar panels are measured in Watts, we need to convert based on the voltage we are using.
If you are using a 12VDC power source, we use 12 as our V.
If we are requiring 2 Amps, we use 2 as our I.
Since we are solving for P or watts, we multiply 12V x 2A and we get 24 Watts.
Now we know how many watts we are burning per hour so we can start looking for a way to provide battery recharging to prevent our batteries from a complete discharge.
The Sun is not always in an optimum position for a solar panel to produce power at 100% all the time so we MUST plan for this.
First plan for a maximum of 50% utilization of your solar panels to be on the safe side of engineering. With the above calculations, a 50Watt solar panel would fit the bill, except...
- THE SUN INSN'T ALWAYS UP -
Your solar panels may get 6 or 7 hours per day of peak solar power but it could be as little as 3 or 4
or cloudy or winter days. With this information, you should plan on providing enough power in a 4 hour period to recharge your battery bank.
If you discharge at a rate of 2 Amps per hour then you will discharge 48 Amps in one 24 hour day. you need to replace those 48 Amps during the daylight hours, preferably you will calculate your recharge rate based on the worst conditions, so we will use 4 hours.
In 4 hours time, we need 48 Amp Hours recharged so we need to replace 12 Amp Hours per Hour. This will quickly recharge the batteries from the power consumption of the night before.
12V x 12A = 144W
I(A) = P(W) / V(V)
In 4 hours time, we need (at Minimum) a 144 Watt charging source provided to keep our system running.
Using these Factors, you now know your MUST HAVE recharge rate based on your device's discharge rate.
NOTE* use an overcharge circuit protector to keep from damaging batteries and other equipment.
I personally have used Harbor Freight's 100W solar panel kit ($145.00) and their solar charging protection circuits to do this very thing and it works great.
For less than $600.00, I have successfully built a dependable solar power source for an 802.11
wireless access point.
Enjoy and I hope this helps!
Brett Hill, CWNE #147
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