Topic: DIY 24 Hour FARS

[Phil23]

So I installed my DFARS a couple of day back...

24 hour conversion was always in my mind; Maybe a garden solar light.

But the original single panel SIM cover is sitting on the table looking at me....

Has me thinking maybe I could go back to the original cover, just for the ISS,
Get another housing; put the DFARS cover on that;
Parallel the solar cells;
Add some electronics & batteries;
Have it mounted at a more appropriate angle to the ISS Cover;
Connect the fan.

2 things that appeal are the more flexible orientation option & the ease of battery maintenance.

Could start with one or both of these items:-

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And obviously have this already.

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What have others done regards converting DFARS to 24 hour?

Thanks

Phil.

[CW2274]

By far the cheaper route is if you're able/want to go a/c. Other benefits abound.

[Phil23]

By far the cheaper route is if you're able/want to go a/c. Other benefits abound.

AC is doable, but not very desirable for various reasons.

A good solar garden light is $30 here.
Lithium battery,
100 Lumens, 10 hours runtime.

Just not sure of the voltage & current draw of the LED,
but if they become known, it will give me a good idea of how it would go running the fan.

Phil.

PS. Anyone know the voltage & current draw of the fan?

[johnd]

PS. Anyone know the voltage & current draw of the fan?

People running on mains supply usually supply the fan at 2-3v DC. (More volts - within reason - gives faster fan speed, but also shorter fan life. I've had comments that 2v is a good compromise - a reasonable fan speed that's fast enough to move air through the shield, but still giving a decent fan life.)

I don't know the current draw but would guess at 100mA @3v. And at a very rough guess also this could be something like 100x the current draw of the garden light.

[Phil23]

I don't know the current draw but would guess at 100mA @3v. And at a very rough guess also this could be something like 100x the current draw of the garden light.

I'm Guessing as well,

These particular Li-Ion spots are extremely bright, 100 Lumens,
they may have either  1/2 or 1 watt LEDs.
I'm assuming they also have 2 18650 (3.6V) batteries, typically 1800mAh.

So that would be a total capacity of 12.96 Watt hours.
That fits pretty well with the 6 & 10 hour run times they have (switch selectable),
and assuming they not designed to be fully discharging completely charged cells each night.

Had a quick look at some LED specs & I tended to see ratings around 400 Lumens for about 1000mA current draw,
so roughly 250mA @ 2.95V would be 738mW.
If the fan was drawing 100mA @ 3V it would use 300mW.

So these particular solar lights should have heaps of capacity.

As far as the voltage is concerned, an LM2596 regulator module could look after that & allow the fan to be set as desired.
Assuming the batteries are in parallel, their output would be above 3.6V, & these regs could efficiently deliver the 2V that you mention.

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Cheers

Phil.

[Phil23]

These are the lights I had in mind, I've got two of them in the yard.

The panel is about 4 inches wide. All Diecast alloy.
Pretty good value at $35.00.

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[Bashy]

If you are able to, I would go the PSU route, i have for both my sheilds, running a PC fan in them at 4k rpm on a shared 12v psu

[Gomer]

the AC-fan mod is probably the best option for 24hFARS.
Here is a nice list of parts:

Power Supply--https://www.amazon.com/gp/product/B00BXAM694/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
Fan Disconnect--https://www.amazon.com/gp/product/B00TLEKXA8/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
Extra Motors--https://www.amazon.com/gp/product/B00E4WQENM/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

If you do go with this option, you might as well run 2-pair and have a Rain Gauge Heater for a WIN-WIN

[ct]

If considering a 3V DC motor, you could also go with the 6V motor which spins about 25% more RPMs in my FARS than the 3V one does.

http://www.jameco.com/z/RF-500TB-14415-R-J-32-Nichibo-Taiwan-MOTOR-DC-6V-1-6V-RANGE-2755-RPM-164A-077-SOLDER_2230037.html

I power this motor from a solar panel during the day and a 26650 5200mAh battery at night.  The battery can last about 30 hours powering the fan at 3.3V, 1400RPM, which is around the same RPMs as the stock Davis product at maximum sunlight.

[Phil23]

Someone broke one of my solar lights mentioned above...

So out with the screwdriver.

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2000mAh 18650.

So comparing this with a Davis 24 hour FARs.

1.2V x 2300mAh = 2.76Watt Hours Capacity with one Cell.
1.2V x 4600mAh = 5.52Watt Hours Capacity with two Cells.

The capacity of the Cell in the solar light.

3.7V x 2000mAh = 7.40 Watt Hours.

So with an adjustable Reg to set the output voltage as required, the Solar light would have more capacity available than the standard Davis.

There is also another solar light in that range that contains 2 of the same 18650's so double the capacity again.

You can make the assumption that the solar panel has sufficient capacity to maintain the battery as it's runtime for the 100 Lumen LED is about 10 hours.


Phil.

[Bashy]

Just a thought, would increasing the mAh to say 3500 give you extra during the darker months?
or would they be too powerful to be charged on that panel, if so, can always break another
They would certainly last longer, i use them in my ecig

[ct]

I recently disconnected my solar panel to allow the battery which powers my fan to discharge completely, as a test to determine how many hours the battery would last on a single charge.  It is a KEEPPOWER 26650 Li-ion 3.7v 5200 mAh 19.24Wh.  The Davis motor is replaced with a Jameco 6V motor.  During the night I power it at 3.2V 1400 RPM through a step up/down voltage regular, so output voltage is constant throughout the battery discharge curve.

The battery lasted over 49 hours, as shown in this graph.

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[Phil23]

This is currently work in progress.

Have 2 x 3400mAh Lithium batteries.
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Fully Charged they will have a total capacity of 24,480mW hours.
The fan running at 2.0V consumes 200mW.
Push it up to 2.4V and it consumes 290mW.

At 2 Volts the batteries would have enough capacity to run the fan for a total of 122 hours; a bit over 5 days.

Battery is charged & protected by a $3.00 module that uses a TP4056 for charging & a DW01 for battery protection.
Maximum charge rate is 1 amp; accepts 4.5 to 6.5 Volt input.

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Output to fan is regulated by a LM2596  module. Accepts a 3.5V minimum input voltage & adjustable down to 1.35V.
I've got a stack of these in a drawer & it's worth noting that some have a series diode on the input for reverse polarity protection.

They are worth avoiding if working with a single or two parallel Li-Ion's, as I'd lose about 0.6V on the input.
Easily identifiable, some modules have 2 diodes, others have just one; on the output for protection.

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It's currently wired up just to test charge currents, which are generally above 120mA @ 3.9V for 7 hours, including a 3 hour period of around 200mA.
Only unanswered question is whether the Davis Panel can provide enough power to recover the overnight usage.

Guessing that could be a battery dependant period of 18 hours, or 3600mAh.
That is a bit touch & go, but if it fails, I'll just change to a bigger solar panel.

Got a few on order. Some will fit the Davis cover, some won't.

The Largest one coming is 6V 4.5W, 165x165mm & $10.00US.
It will be able to provide sufficient current to recover overnight usage in roughly 1 hour.

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I know there's a lot of support for AC, but for many that's impractical.
So for under $20.00US plus batteries (open to choice), this seems like a good wire free solution.

Cheers

Phil.

[Phil23]

The cobbled up mess is working, but need to improve the efficiency, on principle...
The TP4056 module charges the batteries at around 450mA, starting with 200mA in by 7:30am.

ATM a "Juice Bank" module boost's it to 5V, before an LM2596 buck module drops it to 2.0.
In-efficient, I know, but will try a single LDO Regulator to drop the 18650's directly to 2.0V.
(LM1117T-Adj LDO regulator, with a 1.2V dropout).

Guessing at present I have about 50 hours run time on a full charge.

Few Pic of the cobbled up Test Mess...

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