Solar Power = Battery

[Leonard Payne]

Hi Guys

I've read the existing threads on power/solar but I'm afraid its clear as mud. (My fault)

I understand that 5v or smaller than 12v which is smaller than 240v
but when it comes to amps and watts, I go all blond.

Consider

1 x AR150 which requires 5v at around .75 of an amp.

My lithium battery can keep this little thing running for around 3-1/2 days.
Any ideas on a small solar panel that would put out 5v to keep it charges?

Alternative i've got this solar thingy

http://www.ebay.co.uk/itm/262802929588?_trksid=p2057872.m2749.l2649&var=561798385276&ssPageName=STRK%3AMEBIDX%3AIT

that was cheap and nasty and suggests inital charge from mains
and sunlight would probably take 50 hours to fully charge 12000mah

So consider an emergency grid down situation.

Any recommendations for powering. 

Cheers
Leonard

[smtsali20]

Try www.insele-solar.co.za

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[Paul Gardner-Stephen]

What matters is 5v x 0.75A = 3.75VA ~= 3.75W.

This means you need a panel that can in the number of day light hours available to it, provide 3.75W * 24 hours = 90Wh per day.

So if you want to be able to have it full recharge in 1 hour, you need a panel that can provide 90W.  If you expect 4 hours of good light per day, then you only need 22.5W.

But also remember that you won't likely get 100% of the panel's rated output.  

If you live in a sunny area, about 50% is probably reasonable to expect, but remember that days on end of overcast weather will still be a problem. The solution there is to have your battery big enough to hold multiple days of power, i.e., n*90Wh, where n is the number of days you want.

In short, I'd recommend a 40W panel as a bare minimum for running 3.75W load, and ideally 180Wh or more of battery.  I'd recommend LiFePO4 batteries as they last longer than either sealed lead-acid or LiPo, and unlike LiPo, aren't prone to bursting into flames and melting through concrete.

You then need a nice MPPT solar panel controller, and a good battery charge controller.  Many cheap solar panels have low-efficiency panel controllers, that mean you get much less than the rated power in real life. This is why the new Mesh Extenders have built-in MPPT panel controller and multi-chemistry battery charger, so that you can just add a bare panel and bare batteries.  The flip side is that the Mesh Extenders are (currently quite a lot) more expensive than a little GL-AR150.

BTW - Are you sure that the GL-AR150 uses that much power? Do you have a USB device connected to it? We have GL-AR150s in the lab, and they use a lot less than that, even with wifi running in ad-hoc. We see current consumption (without a USB device, but with one ethernet plugged in) of only around 160mA - 250mA, i.e., 0.8W - 1.25W.  This means that you could get away with about 1/3 to 1/4 of the recommended values below.  In fact, I just tested a Mesh Extender prototype PCB, and it consumes only about 200mA = 1W (without an RFD900 packet radio, to make it comparable with the GL-AR150).  Thus I'd be surprised if the GL-AR150 was really using 0.75A. In fact, you have said your 12000mAh battery can run it for 3.5 days = 84 hours.  Thus it is drawing an average of only 143mA from your battery, which backs up my measurements here.  

So the good news is, you only need something quite a bit smaller that I calculated above.  I'd recommend a 20W panel + 40Wh of battery as a starting point, provided you have efficient panel regulator and battery charger elements.

Paul.

[Anish Mangal]

In my experience the AR150 draws about 0.75W power, or less.

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Anish

[T Gillett]

My experience is the same.

That's 5Volts at 0.15 Amps making 0.75Watts.

The battery pack shown in the eBay link is nominally 12,000 mAHrs.

The AR150 draws 150mA, so you would theoretically expect the battery pack would run the AR150 for

12,000mAHrs / 150mA  =  80Hrs

In practice you will likely get something (perhaps considerably) less than this period, but it is indicative.

These battery packs look like a simple solution to solar powering a small device, but most of them will not charge and discharge at the same time. If you can find a better one then it may be possible to use it in conjunction with a solar panel designed to charge/run a USB powered device.

Other than that, as Paul has described, you need to assemble a system from scratch with a solar panel, battery and regulator.

You may find it easier to set up a 12Volt system because the solar panels, batteries and regulators are more readily obtained. You will need a 12V to USB converter of course, but these are also readily available as car chargers, albeit you lose a bit of power due to their conversion efficiency.

I have used commonly available 20Watt solar panels and 12V 9AH  sealed lead acid (SLA/VRLA) batteries and a suitable regulator to power small routers like the AR150 on a continuous basis.

(Full disclosure: Both Paul and I live in very sunny Australian locations :-)

A 12V 9AH battery is nominally 84WattHrs capacity, of which you can effectively use about a half, so ~40WattHrs.  The AR150 draws just under 1 Watt, so you can expect the battery will run the AR150 for a couple of days without sunlight to recharge the battery.

Of course you do have to consider the climate conditions in your area. If you experience a low percentage of "sunny days" then you are going to have to increase the solar panel and battery capacity to compensate.

Consider also that you can combine both solar and intermittent mains power to keep the router running and the battery charged. This way you don't have to completely rely on solar power - only when the mains is down.

A discarded laptop power supply makes a nice source of 19V power which you can feed in to the regulator along with the solar panel, just using isolation diodes in each supply just as you would if you were using two solar panels.

Regards

Terry

On Thu, Mar 16, 2017 at 1:27 PM, Anish Mangal <ani...@umich.edu> wrote:

In my experience the AR150 draws about 0.75W power, or less.

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