# WRT54G Solar Power Project

Discussion in 'General Electronics Discussion' started by dan091, Jan 26, 2011.

1. ### dan091

9
0
Feb 7, 2010
Hi Guys,

I am looking at building the below

http://www.voltsxamps.com/?p=532

My question if I buy a 7Ah 12v battery which I have read elsewhere should last around 29hrs (over night would be fine) ideally what solar panel wattage would I need. Because I need to keep unit running in the day but the battery still needs to be charged throughout the day ready for night time power use. The guy says on that guy the wrt54g's have a inbuilt voltage regulator. I guess there is a formula for working out current power usage and charging the battery at the same time.

Any help would be greatly appreciated. I can understand most of the other stuff its just being able to charge battery in day and power unit.

2. ### Resqueline

2,848
2
Jul 31, 2009
It depends on where you are in the world, and how much power your router really draws (I've seen figures all over the place).
But let's say you have 6 hours of effective insolation, and that your router draws 240mA at 12V. That drains your battery down to a safe 62% during the 18 sunless hours.
So, 0.24A * 18h = 4.32Ah - that needs to be replenished during the 6 sunny hours.
However you need to put in 11 - 43% more than you took out. Let's say this amounts to roughly 5.4Ah input. Charging current = 5.4Ah / 6h = 0.9A
Add then the 240mA you need to run the router at the same time and you'll need 1.14A from the panel.
Considering most panels have 36 cells - and their wattage is stated at an output of 18V or so, you'll need a 1.14A * 18V = 20.5W panel.
Change any of the figures ever so slightly and you'll get a completely different result though.

3. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,500
2,840
Jan 21, 2010
The WRT54G has a switchmode regulator from memory, so run it directly from the battery (i.e. don't add another regulator) for min current draw.

Also turn down the output power. It may not make much difference, but it may help if you don't need the max power.

4. ### galenwollenberg

2
0
Mar 10, 2013
Last edited: Mar 10, 2013
5. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,500
2,840
Jan 21, 2010
Great! How does it perform?

Will it last a couple of days without sun?

I presume you seal it up when you're not showing it off?

Is that a bottle cap being used as a heatsink?

6. ### galenwollenberg

2
0
Mar 10, 2013
so the two 10 watt panels will certainly power + charge the battery in full sun but it takes all day long for a full charge. In fact it might even come up a little short. I turned it on today at 5pm, battery was trickle charging at 14.0v , so i expect it to go almost all night and some of the morning.
It would certainly benefit from an additional 3rd solar panel. I think it just needs a little more charge power to fully keep the 7.5ah battery at its max use. You could probably go 12 hours easy i think. Otherwise you could just add batteries like 1.4AH till you get your desired run time...