SKY solar battery charge conversion?

Rooftop is my preferable SKY mount location but not so easy to access in my elder age! While i appreciate the engineering allowing 1 year battery life, replacement every year (set for 1s reporting) will be a hassle even if there ARE no moving parts! My old Davis wind unit with solar panel had this advantage.

I was thinking about running 2 wires out the bottom of SKY in lieu of AA batteries and powering with an easily constructed 18650 Li-on battery(s), TP4056 solar charge module, and perhaps 3.7-to-3.0v buck converter.

I’d appreciate thoughts from folks with more electronics background than I!

its not as difficult as you might imagine just do your homework do some trial and error and reap the benefit of the two contacts …

my project last year i never did anymore the winter kicked in and the thought of going up and down the roof in the high winds deterred me , but. i may resurrect it next week .ps check the polarity prior to doing anything and mark it + or - easy to get confused and the wrong way round if you don’t observe.

@vreihen @dan.gealt @weather-display may have ideas about home diy solutions they have proven to show a very knowledgeable background when implementing DiY ideas…

i should add there is something on the horizon from weatherflow…
image

5 Likes

I was planning to do the same thing. Energizer shows in the specs for their lithium batteries a capacity of 3600mah when calculated with a 0.9v cut off. Since the sky uses 4 parallel pairs of these batteries for a total capacity of 14,400mah at 3v. If you use a couple of Panasonic 3600 mAh 18650s in parallel you should in theory be able to go 6 months with no sun. I have ordered the parts to do this conversion. I’ll let you know how it works out.

Knowing that rechargable batteries have a finite number of recharge cycles before they fail, I’d be looking at an ultracapacitor so that I will never have to take the unit down again in what’s left of my lifetime…

3 Likes

Good point about the ultra-capacitor! The only thing that is missing is a way to disconnect power from the SKY unit remotely. I was thinking that I would run a pair of wires (or maybe a piece of outdoor-rated Ethernet cable or other UV-resistant cable) down from the solar charger to a more easily reachable location so that the inevitable repowering was more convenient.

1 Like

Lipos have a 300-500 charge typical life cycle when charged to 4.2v, this can be roughly doubled by limiting the max charge to 4.1v. Since a couple of 18650s should be able to get 6 months per cycle, we are at the low end looking at a theoretical 150 years.

1 Like

Hope you will consider sharing your solar power design with the group when it is completed.

1 Like

Thanks for posting this

Below is the plan I’m collecting parts for – is it similar to your approach? (aside from me using just one cell)

I’m seeing SKY operate well on 2.7v but not sure what the max allowable is. Do you plan to run the 18056’s max 4.2v straight into the SKY or regulate it down?

Thanks…John

2 Likes

My crazy idea is to just use a 3v solar cell, some spare diodes to get it down to ~2.7v, and then a 2.7v ultracapacitor. (The Sky can tolerate voltages down to 2.1v before I’d start to worry, if the battery card can be believed.) Ultracapacitors allegedly tolerate over-charging by design, if the Internet is to be believed.

Of course, I need to add a disclaimer that I’m a graduate of the “Madman” Muntz school of engineering, so proper electronics practices like buck converters and charge controllers are just inflated component counts to me… :smiley:

2 Likes

My plan is just about identical to yours. I’m pretty sure one cell should work just fine and I will likely start off with just one. The Energizer specs for those batteries is 3600 mAh, but to get that you have to discharge them all the way down to 0.9v. So I think the actual usable capacity will be much lower. So one cell will likely work fine. I was also planning to use 3v regulator, just like your drawing showed.

Make sure to remove AA batteries before hooking up external power solution.

4 Likes

Super/ultra capacitor setup seems pretty straightforward. Curious though, how many farad are you looking at? Will 300F get the job done?

Be careful adding long lengths of wire to the 3v power supply terminals on the SKY. It’s unlikely that WF designed any voltage clamping / surge protection into that power circuit, so by adding a large antenna to the leads you may be creating risk of damage from nearby lightning strikes. There also may be EMI issues depending on what kind of filtering is in the power supply front-end.

2 Likes

Agree completely! I was considering some sort of surge protection such as an MOV or some other device suited to that voltage range. But it was certainly a good reminder. Thanks!

2 Likes

Hi all,
Did you guys get the solar setup running well?

Keen to hear your experience.

I tried a 10F ultracapacitor that I had in my parts bin, and saw a 1 minute per farad drain rate with a power-hungry Sky as soon as the sun went down. I went insane and ordered a 3000F beast of a replacement a few weeks ago ($65 USD!), that has 12mm diameter threaded terminal posts and is larger than a soft drink can. In two days of solid sun with the solar panel that I was hoping to use, it has only charged to 0.42 volts! (Did I mention that it is a beast?) :astonished: I could chain a few more panels onto it from my parts bin, which might put enough voltage into it to actually power the Sky by early next week…sun willing.

Here’s a picture of the mounting base that I butchered as a template. I was planning to put pogo pins through the holes where the wires are, but for testing it has worked fine with just the bare wires as shown:

i

In the grand scheme of things, I received a 50-foot spool of two-conductor wire in yesterday’s package deliveries. I may just go with a remote battery box at ground level, using the above mounting plate modification…

6 Likes

cute !
I will although have (as soon as Europe gets stations) the issue with mounting the Sky to a place with free air blowing and having the access to the repower the device.
Thank you in advance for figuring out one way to solve the situation. :sunglasses: I’ll stay tuned to your experience.

Note: WF is currently testing an optional solar accessory – including PV panel, recharging battery, and control circuitry. It will be designed to snap onto the bottom of the SKY, between the sensor device and the pole mount. Release date and final details are TBD as we are still testing.

11 Likes

I will be very interested in that upgrade, Perhaps early adopters might get a price break?

2 Likes

As you need additional conditions (geographical, weather,…) to test this addon in, please don’t hesitate to contract me :wink: :sunny: