External Battery pack for Sky

I might have the incorrect terminology , I meant that they bypass the battery pack and connect directly to the circuitry is that correct?

They are in parallel with the battery.

Thanks, now I do get it , Cheers :slight_smile:

There is nothing to protect the Sky circuit board in case of excessive voltage or current.

A whole lot of ideas sound great in theory, but do not make the final cut when the engineers have to figure out how to package components into a housing or the bean counters work out the per-unit cost.

Working from my admittedly crude experimental math with the most power-hungry Sky version, it was able to run for 10 minutes from a 10 farad ultracapacitor (same as allegedly used in a Davis VP2). Napkin-math says that’s 1 farad/minute runtime, or 1,440 farads of capacity to make it through a day. We’ll ignore some surplus power from the solar panels after charging is completed, and size our needs at 3,000 farads to keep a reserve for a snowy day or two with the solar panels covered.

Moving on to the bean counters, these are the wholesale prices in quantity for a few different sizes of ultracapacitor:

10    farad | $ 1.78 each (qty 200) | need 300 | = $534
350   farad | $16.97 each (qty 5)   | need   9 | = $153
3,000 farad | $65.89 each (qty 1)   | need   1 | = $ 66

They wouldn’t even get to the extra costs of having to make PCB’s to link the smaller units and the labor required to assemble them before they threw out the idea of using lots of smaller components instead of one larger one.

Moving onto the engineers, each one of those hundreds of smaller components has its own housings, labels, etc adding to the final product’s mass and size. Add on that trying to package hundreds of little cylinders with wasted air gaps between them into an available space, and you are living the Tesla battery engineer’s nightmare.

10 farad    x 300 units = 93,000 mm^3 volume
350 farad   x   9 units = 16,414 mm^3 volume
3,000 farad x   1 unit  =  8,376 mm^3 volume

The final nail in the coffin is the lack of charge circuitry or power isolation in the current Sky’s hardware. If you want to use the external power connector pads, there can be no batteries inside the Sky because it can’t magically switch over…the pads are connected directly to the battery box terminals. The Davis unit was designed from the beginning for solar/ultracapacitor with battery backup, and getting the same capability out of the Sky will require either a wholesale re-design or else moving the batteries to an external housing which contains the needed circuitry.

Not trying to argue, just explaining what I’ve learned over the years about tradeoffs and engineering decisions…


There was a more technical discussion about remote battery boxes buried in this thread.


One of the big concerns pointed out in that thread is the lack of power conditioning on a long, unshielded power wire when exposed to nearby lightning strikes or the RF power from that pesky ham radio operator in the basement sending out a 1,000+ watt CQ. :slight_smile:

There is also a picture of my butchered-up Sky mounting adapter that taps the external power pads for whatever you want. Just make sure to take the batteries out of the Sky, or bad things may happen due to the lack of charge circuitry or protection…


Thank you. Im hoping for advice on how to protect from energy of nearby lightning strikes.

I honestly don’t see that as an issue. If it’s strong enough to interfere it’s going to destroy more than the Sky unit.

I like this idea. I need to get modify a base to provide power via two pin connectors.

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Thanks Gary. Do you think we can get a pole adapter base to modify?

I have two that I can test with. I just need to find the correct pins to use.

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I picked up a whole bundle of pogo pins, since they were sold in large quantities. Haven’t had a chance to see if the ones that I picked up are long enough to reach through the plastic, but I will gladly share my leftovers if they work.

I noticed yesterday that my Sky Mk2’s batteries are down to 2.69 V on the bunny death spiral, so I will probably be taking the mast down over the Thanksgiving holiday weekend. If the mast is coming down, I’m definitely doing a remote battery box…

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I am trying to find short pins that can press into the top. I’m looking for ones that are about 1/4" tall.

Like this:

Are you guys fabricating a battery pack to hold them to provide 3V or is there one to purchase? I’ve looked at mouser and parts express cannot locate one in this unique config. Simple option appears to combine 4 2 battery serial packs in parallel.

I have a lifetime supply of medical-grade C-cell batteries, paid for by my health insurance company thanks to the hotdogs-versus-buns conundrum in my weekly IV infusion bag shipments. Battery holders for two C-cells in series are readily available on Amazon, and my Acu-Rite 5-in-1 has been running on C-cells with a remote battery box for 5+ years with changes every few months. I would expect to need at least monthly battery swaps running a Sky, but schlep out there every morning to dump the Stratus rain gauge so that’s just a few more seconds.

I’m hoping that my ultracapacitor and solar cells will work well enough as a remote battery box where I can skip the batteries, but that isn’t quite ready for deployment right now…

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I located a project based AA battery holder system that can be assembled in any config.

Let me know how the pogo pin install goes and which size / where you got them.

Thanks for the ideas…
For those of us in warmer climates where Ordinary Alkaline batteries dont suffer from the freezing temperatures which require Lithium then using a column of D cells down the pole is reasonably economical. If I use the current design of 8xAA Energiser Alkaline cells http://data.energizer.com/pdfs/e91.pdf at $0.80aud (Australian) of about 2500mAh each (20Ah total) they last well over 100 days (Non power saving mode) for $6.40. If I line up 8xD Energiser Alkaline cells http://data.energizer.com/pdfs/e95.pdf at $3 aud. (Yes I would require some insulating spacers and wires to arrange them to 3V) of about 16Ah each (128Ah total) Perhaps well over 600 days (Maybe 2 years, Non power saving mode) for $24aud. D cell dimensions are Nominal diameter of 33.2 ± 1 millimeters (1.3 inches). Overall length of 61.5 millimeters (2.42 inches) And in power saving mode I guess several years of life. And I suspect the mass of the batteries might reduce vibration. My current mount includes lead, but a column of D cells would be good so long as they are firmly secured in the pipe with rubber. I might try it…
cheers Ian :slight_smile:


I have been thinking about how to maintain the mass in the Sky where the internal AA cells currently sit. And how to utilise the better economics of D cell Alkaline cells with longer duration between battery changes, and increasing the mass of the pole to reduce high frequency vibrations. I reckon (for the cold climates) still putting the recommended Ultimate lithium AA cells http://data.energizer.com/pdfs/l91.pdf into the current mount AND 8 D cell alkaline cells into the pole. Then a power supply changeover system which only selects the lithium when the sub freezing temperature causes the alkaline cells to drop their voltage below perhaps 2.1V total output. The D cell holder including the power supply changeover circuitry could be built within a mount to match the current SKY design. And if something like my vibration reducing mount Rain sensor and vibrations is still/also required to reduce false rain vibrations then the rubber cone adapter concept could be included around the D cell holder.

So a thought of mine is now considering the concept of combined Lithium and alkaline (or rechargeable) battery types with a changeover circuit…

(comment: I like the portability and reliability and obscurity of the inbuilt cells without long wires or solar panels so that it is less susceptible to lightning damage and if I put a Sky hidden it is less likely to be vandalised)

cheers Ian :slight_smile:

I received the Sky pole mount. Did you do modifications to install pogo pins? If so, what size and where did you purchase them?


I am still searching for the proper pin to install.

Modified a pole mounting base and built battery pack. Ran wiring inside pvc pipe. Running great!

Battery changes will be simple. Wish larger C or D cell were available in lithium so I could build a pack to use them.