AP Battery Powerpack
From Bob's Basement
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Project Inception: Sunday 13th May 2007
Status: In progress
Project Leader: Bob Plonker
Project Members: None
Contents |
Laptops are portable, their network infrastructure isn't.
If you want a network available while you and your friends/colleagues are working on laptops and regulary moving from site to site this is a problem. Wireless accesspoints or hubs/switches require power. The solution is to make the networking equipment as portable as the laptops. Of course, what you actually do here is to get everyone to network in "Ad-hoc" mode, then you don't need an AP but hey, where's the fun in that?
The simplest piece of network equipment to battery power is the wireless accesspoint as they typically have an external transformer. This negates making a 240V battery pack out of a large number of individual cells, just for the voltage to be stepped back down within the networking device. Or manually modifying every piece of networking equipment to be used, bypassing their internal transformers.
When using a wireless AP with an external transformer you only need 3 pieces of information:
- The transformer output voltage which is usually printed on the transformer label
- The type of AP power transformer connector, pop down Maplins and try each one!
- The polarity of the connector, for the Linksys WRT54G this is on the socket
Next assembly your components shopping list, buy your components and build it. We successfully prototyped this at the Bobs Basement meet on [Sunday_13-05-07] Sunday 13th May 2007, To follow.
Connectors
The great thing about standards is that there are so many to choose from. Connectors come in an infuriating range of shapes and sizes meaning you can never find the one that fits. They are measured by length and width and also polarity (of course, the latter just depends on how you wire it up but be aware before you toast an expensive CISCO AP). Most generic power bricks come with a selection of connectors: Maplins though that's an expensive way to get hold of just the connector. Try searching the web and add to our short list of common connectors:
Alternatively you can cheat and use PoE if your AP supports it
Different cell technology
NiMH
Cell voltage: 1.2V
Typical battery voltages: 1.2V
Typical Size: Standard sizes: AAA, AA, C, D, PP3
NiMH batteries are available is standard sizes, are recharable, cheap and offer good capacity. Due to their standard size, there are a range of off the shelf holders available for them. Although they do not offer the capacity of an SLA or the light weight of Lion, they are a good all around compromise of features.
Pros: Off the shelf battery in standard sizes, easy to use multple batteries with off the shelf holders
Cons: Don't have the capacity of SLA or the light weight of Lion
Lion
Cell voltage: 3.6V
Typical size: Lions don't tend to come off the shelf but are generally custom made for appliances
Lions are expensive but give the best power to weight ratio. They are generally custom built for devices, although you can buy cells and wire together your own battery. Although they are easy to make explode if you wire them incorrectly!
Pros: Light weight, high capacity, you can buy cells and wire up your own battery
Cons: Expensive, prone to exploding, you can really hurt yourself if you're an idiot
SLA
Cell voltage: 2.105V
Typical battery voltage: 6V, 12V, 24V
SLA batteries are extremely versatile and come in all sorts of sizes, they can be anywhere between a few Ah and upto 200Ah! However, they don't give fantasic capacity to size or weight ratio. Use when maximum capacity is an issue and price is a concern.
Pros: High capacity, cheapish
Cons: Capacity to size/weight is not fantastic, heavy and due to their almost none existant internal resistance, they can put out an almost unlimited amount of current until they burn. Dangerous in the hands of an idiot
Common APs
Linksys WRT54G
Connector: 5.5mm O.D. and 2.5mm I.D. Radio Shock type "N" plug, centre positive
Power requirement: Linksys power block is 12V, 1A = 12W. However, there are reports it will work with 4-18V (We accept no liability if the smoke escapes)
How can I help?
If you can add details of AP power requirements (voltage, current, power draw, connector types, etc) that would be good.
Also, any more technical information that can be added to this page would be helpful.
