Southern California Wireless Users Group

Battery-Powered Wireless Repeater - Electronics for Dogs
by Mike Outmesguine

A lot of talk came up on the SOCALWUG Discussion List recently regarding running a wireless access point off of a battery. Why would you run an AP from a battery? First, the AP can be totally mobile. Secondly, and the reason I looked into this, you can put a repeater on a hilltop where regular AC power is not an option. Ultimately I would like to run an access point and a bridge from a single battery and a solar panel for daylight recharging of the battery.

A group in San Diego has been running remote access points in this fashion. This project aims at using off-the-shelf products and a lower budget.

Let’s do this project in stages…

1. Determine power consumption of access point hardware
2. Determine run-time from low-cost battery - can it run overnight?
3. Determine recharge-rate using solar panel
4. Increase power efficiency by eliminating wasted power
5. Configure access point & bridge
6. Deploy and test!

On to the first stage.

Question: How do we know how much electricity an access point uses?

The only good answer is to see for yourself! Since I didn’t want to make any commitments at this point, I decided to use all of the cables intact. Therefore, I set up the test as shown below. The power inverter converts DC power into AC that the Access Point uses. This is very inefficient, but a good first step.

Of course, it’s nice to see what’s going on in this system, so we will need to monitor the voltage and current. I’m especially interested in seeing at what point the AP shuts down.

Here’s what I found:

The AP pulls about 900 mA or 0.9 Amps. With a 7.0 Amp-Hour battery, this system should run for a little over 7 hours at 12 volts. The bonus turned out to be that the Inverter can convert successfully down to about 11 volts. Which gave us extra runtime.

Note on batteries: A 7.0 Amp-Hour battery will run for an HOUR on 7 Amps, or 7 hours on 1 amp. Simple!

Stage two is easy. Turn it on and let it run down. In this simple test, the AP ran totally on battery for over 9 hours!

If we can remove waste from the system (i.e. inverter/transformer), or use a bigger battery, we can increase runtime substantially.

Next time: Stage 3, Determine recharge rate using a solar panel - I will post this part when the project is ready!

Battery-Powered Wireless Repeater - Electronics for Dogs
by Mike Outmesguine

A lot of talk came up on the SOCALWUG Discussion List recently regarding running a wireless access point off of a battery. Why would you run an AP from a battery? First, the AP can be totally mobile. Secondly, and the reason I looked into this, you can put a repeater on a hilltop where regular AC power is not an option. Ultimately I would like to run an access point and a bridge from a single battery and a solar panel for daylight recharging of the battery.

A group in San Diego has been running remote access points in this fashion. This project aims at using off-the-shelf products and a lower budget.

Let’s do this project in stages…

1. Determine power consumption of access point hardware
2. Determine run-time from low-cost battery - can it run overnight?
3. Determine recharge-rate using solar panel
4. Increase power efficiency by eliminating wasted power
5. Configure access point & bridge
6. Deploy and test!

On to the first stage.

Question: How do we know how much electricity an access point uses?

The only good answer is to see for yourself! Since I didn’t want to make any commitments at this point, I decided to use all of the cables intact. Therefore, I set up the test as shown below. The power inverter converts DC power into AC that the Access Point uses. This is very inefficient, but a good first step.

Of course, it’s nice to see what’s going on in this system, so we will need to monitor the voltage and current. I’m especially interested in seeing at what point the AP shuts down.

Here’s what I found:

The AP pulls about 900 mA or 0.9 Amps. With a 7.0 Amp-Hour battery, this system should run for a little over 7 hours at 12 volts. The bonus turned out to be that the Inverter can convert successfully down to about 11 volts. Which gave us extra runtime.

Note on batteries: A 7.0 Amp-Hour battery will run for an HOUR on 7 Amps, or 7 hours on 1 amp. Simple!

Stage two is easy. Turn it on and let it run down. In this simple test, the AP ran totally on battery for over 9 hours!

If we can remove waste from the system (i.e. inverter/transformer), or use a bigger battery, we can increase runtime substantially.

Next time: Stage 3, Determine recharge rate using a solar panel - I will post this part when the project is ready!