Need Electrical Expertise


#1

I need someone who is well versed in electrical tinkering to make the Pillar more efficient. Currently, I have my system running off of a car battery, through an inverter, and then the plugs of the RPi, USB hub, and Tuner plugged into the inverter. However, the inverter has a resting consumption of power and converting from DC to AC and back to DC just because the plugs of the components are designed to be plugged into AC wall sockets is inefficient. What do I need to use to bring the output of the battery in line with what the Pillar components need? Also, factoring in a solar panel to maintain the battery charge, the draw of the components should be less than the input of the solar panel. I used this: http://www.amazon.com/dp/B006Q7C7L6/ref=cm_sw_r_tw_dp_gieoub1VBK820


#2

Once we get the connections settled and we can look into power consumption. If it’s wrong, you can always just build an array, or get a bigger panel.

Can you provide a more detailed schematic?

12V / 5 Watt Panel

Connected to 12V battery? what kind? whats it rated for?

Can RPi draw from USB? ( not totally familiar, looks like 5V source)

What are the specs on the Tuner?

With both devices plugged into the battery can you use a non-powered usb hub?
e.x. http://www.newegg.com/Product/Product.aspx?Item=9SIA1VJ0NN1318&nm_mc=KNC-GoogleMKP-PC&cm_mmc=KNC-GoogleMKP-PC--pla--Misc+Hardware-_-9SIA1VJ0NN1318


#3

Which version of RPi? This one has some USB on it, Can you lose the hub and use on-board ports?


#4

We need to standardize the power.

The Pi runs on 5V and if it is powering other things, often recommended to use 2A power supply.

USB hubs are often wall powered on AC and converts in wall wart to DC power @ 12V. The hubs then downconvert internally to 5V.

Ideally the tuner is USB powered. Meaning more 5V power.

Has anyone done any power consumption / use modeling estimates for this Pillar? If Pillar is to be limited in run time based on limited time use (i.e. school hours for instance) then we can start with ~ 10 hours of run time per day.

10 hours x total average wattage. The Pi itself is 3-5 watts estimated. Hub will add to that and a tuner certainly will ramp that up.

5-10 watts is being optimistic. 7-15 probably more like it.

7 x 10 hours = 70 watts
15 x 10 hours = 150 watts

These are huge numbers when talking about solar, cost and running such many hours per day.

To cover 70 watts you would really need 210 watts of solar combined input per day. At conservative 3 hours of usable sun we are talking about need for a 70 watt panel. These are bulky - certainly not the tiny pillar size. These are expensive even at dumped silicone mass pricing of $1~ per watt = $70.

You need 70 watts in order to bank extra storage for less sunny, rainy, and other days where sub optimal solar.

Easiest and cheapest solar route still is dealing with 12V panels, 12V controllers and 12V batteries. There are tons of 12V accessories on the cheap and down converters from 12V to 5V USB (large collection of cheap @ $1 model intended for automotive use from cigarette lighter / DC power port).

You also have abundant buck converters such as:

Those are adjustable in broad range. Can find set say 12V input side to 5V output side probably bundled with USB jacks right there.

Going to need some sort of DC charge controller for the solar so you get better charge controlling of the battery. Otherwise life of batteries is going to be not so great.

$15 USD for an acceptable charge controller.

Note the charge controller can be fancy and are a source of power drain. Some of them have night time on modes intended for lighting.


#5

Also, I’d do away with ALL AC to DC power conversion. It tends to be lossy and gets you spoiled.

Target market for these devices in many ways are places with lacking infrastructure and likely costly power. Stand alone, off grid is the approach to adhere to.

Thermal based power where a fire is used to power a semi-conductor and thus generates DC power should be considered also perhaps as an addon option. Such is suitable for fires which people world wide live by.

An example of these thermoelectric devices:


#6

Worth thinking about the social context for these deployments too.

To take sub Saharan Africa as an example: Running a phone charging business is a job for many there.

If you build in spare capacity to charge 20 cellphones, then all of a sudden you have created a job for someone, importantly they now have a vested interest in replacing the 12v battery when it dies, keeping an eye on security etc etc.

I’d have thought if you just dump these devices in villages they will only work for a short while.
It’s likely the panel will get nicked for someone’s phone charging business, as no one really has a personal interest/ responsibility for maintaining it.

http://www.appropedia.org/Good_intentions,_disastrous_outcomes#Aid_and_development


#7

All the math aside on watts and amps:
Here’s the power layout for cheap and simple off the shelf:

Power input:
12V solar panel —> solar charge controller —> deep cycle battery
(70W at least @ $1 per watt) —> < $20 for controller —> deep cycle is watts consumer x hours running x 3

So… deep cycle 5 watts at 10 hours = 50 watts x 3 (for days of potential rain) = 150 watts.

150 watts / 12v = 13Ah battery. Round up to 15 or 20Ah ideally.

Solar mounting ideally would be top of the column and have some sun tracking ability movement. The vertical facing on prototype will perform poorly. The solar rotation stuff exists as DIY kits and surely Pi projects for such. Unsure of parts cost. Should be considered.

Power output:
deep cycle battery —> 12V to 5V buck converter capable of pushing 2-3A @ 5V–> Raspberry Pi Model B
Batteries are pricey $40 for 15Ah Sealed Lead Acid (SLA) —> Buck converter < $5 --> Pi at build cost.

Ideally the B has enough USB plugs and everything can run off 2A to the Pi.

Might need USB split out cables as to clear space on all USB ports.


#8

I think you might need to consider several solar options. In Africa you will need smaller panels than in Norway. It simply makes no sense to design a solar system with no context.

http://pveducation.org/pvcdrom/properties-of-sunlight/average-solar-radiation


#9

I agree @sam_uk.

There are clear zones so many degrees from equator. Easy enough to right size things compared to hours of run time.

There is also the issue with air bound particulates that greatly reduce usable sunlight. That can be local phenomenon in areas with lots of industry or where everyone is burning traditional fires to sustain life. Big reduction of sunlight in such places.

Clearly usable sunlight as defined elsewhere in solar world involves properly installed panels set at local near proper angles. Said installs aren’t extremely complicated, but do incur additional costs raising the cost for such a project in offgrid scenario.

Outernet should consider other enhancements promoting other FTA programming on the same satellite. Unsure if the tuner dongles support multiple simultaneous programs and / or easy switching of said channels. Both birds have quite a bit of AV content on them.


#10

Advertised battery life was 12hr passive, 4hr with Wifi.

@sam_uk

I disagree. Make a standard, add an option for extended panels, for extended life. Requires minor complexity addition, but defiantly worth it, especially if it means you can chain them. You could make a hierarchy, that increases storage.

(I can only reply so many times, sorry for the editing)

Solar tracking is not robust enough, for the intent in my opinion.


#11

just to be clear we are talking about the ‘village’ option here not the standard lantern.

I also think the 4hr/ 12hr spec is misleading. as with the size of solar panels proposed 300ma or so. You’d need to charge it for a week or so to be able to run it for that long.