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= Low power equipment = | |||
This section is about very low power equipment. The rest of this page is more focused on running stuff like TP-Link dual band routers and Ubiquiti AirMax gear on solar which is a different scale of cost/difficulty. | |||
== Low power nodes == | |||
The [[Mesh/Hardware experiments|hardware experiments]] page lists some nodes that can be used with low power. | |||
We can probably assume power usage of about 1 watt for most of the lower power stuff but probably not a lot less. | |||
== Solar == | |||
A small 4 watt panel that outputs 5v directly is available [http://www.ebay.com/itm/201493671665 for $14 on ebay]. It comes with a female USB A plug but the plug is of visible crappy quality and it failed after a few uses, however it's trivial to just solder on e.g. a male micro-usb end instead. We haven't yet tested what the actual power output is for these panels over a day of california sun but will do so soon. | |||
== Battery == | |||
If we have the solar hooked up straight to the node then any passing cloud might take it offline. Better to have a small battery acting as a UPS. Since we can use a 5v solar panel why not use a cheap Lithium Ion portable USB battery packs. We've been lead to believe that it will wear out Li-Ion batteries faster if they're kept at 100% charge all the time. We're just going to try anyway and see how long the last. | |||
Some USB battery packs don't allow charging and discharging at the same time. We ordered a selection of the cheaper units and tested them. Here are the results: | |||
* [http://www.ebay.com/itm/321850110492 2600 mAh CoolGo pack] - $6.79 - Works and verified at 2600 mAh! | |||
* [http://www.ebay.com/itm/301573240761 2600 mAh No-name "extruded aluminum square" with button] - $6 - Works but only ~1300 mAh capacity :( | |||
* [http://www.ebay.com/itm/181725452512 2600 mAh PowerBank "extruded plastic square" without button] - $3.75 - Works but max charge rate 500 mA :( | |||
* [http://www.ebay.com/itm/252224862952 2000 mAh Motorola flat pack with integrated micro-usb cable] - $6 - No discharge while charging :( | |||
* [http://www.ebay.com/itm/221974269792 Cylindrical unit without included 18650 battery] - $1.25 - Waiting for it to arrive. | |||
Most of these are rated to charge and discharge at 1 A, except the cheaper "PowerBank" which is rated at 1 A discharge but only 500 mA for charging which would limit charging to 2.5 W. | |||
Assuming that these batteries actually have a capacity of 2600 mAh at 5v that's 13 Wh which is enough to power a 1 watt router like the NEXX WT2030F for 13 hours. That means that 2600 mAh is not enough to carry such a device through the night during winter in Oakland since the longest night is just under 14.5 hours long. It's probably a good idea to double the capacity since the capacity will drop over the lifetime of the battery. | |||
Then the question remains if a 4 watt panel is enough to charge 14.5 hours worth of power in the ~9.5 hours of "sun" on the shortest day. We need 14.5 Wh generated in 9.5 hours. So we need a bit more than 1.5 watts of charge. Let's say 2 watts given conversion losses (how big are losses?). So if we have a solar panel that's theoretically generating 4 watts in full noon sun that's definitely not going to cut it on a cloudy winter day. We need some numbers on the efficiency degradation of standard solar panels on a cloudy day. | |||
= Power usage = | = Power usage = | ||
Ubiquiti routers all use 8 watts (actually maybe only 6.5 watts for current gen gear). That comes to 5856 watt-hours per month. As of May 2013, the average price for electricity in the bay area was 22.8 cents per kilowatt-hours. $0.228 * 5.856 kilowatt-hours ~= $1.335. So less than $1.5 per month. | Ubiquiti routers all use 8 watts (actually maybe only 6.5 watts for current gen gear, and we should test that). That comes to 5856 watt-hours per month. As of May 2013, the average price for electricity in the bay area was 22.8 cents per kilowatt-hours. $0.228 * 5.856 kilowatt-hours ~= $1.335. So less than $1.5 per month. | ||
== Voltage == | == Voltage == | ||
The Ubiquiti gear takes between 10.5 volts and 25 volts. I believe most of their official numbers state something like 12 to 24 volts, but one of their engineers posted a spreadsheet on their forum which listed the actual limits. | The Ubiquiti gear takes between 10.5 volts and 25 volts. I believe most of their official numbers state something like 12 to 24 volts, but one of their engineers posted a spreadsheet on their forum which listed the actual limits. | ||
TP-Link N750 routers use a [http://www.monolithicpower.com/desktopmodules/documentmanage/api/document/getdocument?id=428 MP1482] voltage regulator which takes between 4.75v and 18v input. | |||
Western Digital N600 routers use a [http://www.richtek.com/assets/product_file/RT8293B/DS8293B-03.pdf RT8293B] voltage regulator which takes 4.5v to 23v input. | |||
= Solar = | = Solar = | ||
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On top of that some electronics are needed for battery charge control. I'm not sure what the price for that is, but probably around $20. And then there's the battery. | On top of that some electronics are needed for battery charge control. I'm not sure what the price for that is, but probably around $20. And then there's the battery. | ||
== Battery == | == Battery == | ||
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Either way we shouldn't discharge car batteries below 11 volts. How do we prevent that? What is the simples/cheapest low voltage cut-off circuit? | Either way we shouldn't discharge car batteries below 11 volts. How do we prevent that? What is the simples/cheapest low voltage cut-off circuit? | ||
Twisted_Haywire has some ideas for super simple circuits. Another option is to use a voltage comparator + divider + mosfet. You can get cheap comparators for $1 or less on ebay/aliexpress. | |||
== PCB == | |||
If we end up wanting low voltage cut-off then if makes sense to put it on a PCB. [http://dirtypcbs.com/ Dirty PCBs] charge $14 for ten 5x5 cm PCBs, so $1.4 extra per unit, and it drops to $75 for 100 units. | |||
== Higher voltage extended version == | == Higher voltage extended version == | ||