Topic: VP2 ISS questions about solar and UV

[kobuki]

Though they're not perfectly related, I thought I just put both questions into one post, since both are about the VP2 ISS.

First, I'm using an old UV sensor for the VP2, which IIRC was made for the VP1 but is compatible and works perfectly, but one weird thing is that when there's no detectable UV light, the ISS presents it as "no sensor", which is quite baffling. For the more technically inclined and in the know with the radio packet format, here are 2 samples:

No sensor or no light (C1 vs. C3 is random, unrelated to sensor presence): 49-00-E9-FF-C3-00-D9-0B-FF-FF or 49-00-E8-FF-C1-00-C9-DD-FF-FF (late night, probably 0.0 UVI)
Broad daylight, single sample: 41-02-00-4C-C3-00-40-F8-FF-FF (6.1 UVI)

Is that normal? Could anyone confirm the same with a VP2 sensor and a way to look at the raw radio packets? It'd be important to represent de difference between "no sensor" and "no UV light" for maintenance, proper status, etc.

Second, I want to add a solar panel to my extra SIM (used with my anemometer) which came with none - it's a "temperature transmitter" which is incidentally a fully fledged SIM board in a shelter box with hinged door but no panel - would higher voltage ones suffice? The original is a 4-cell, 2V 0.5W one IIRC. Would something like a common 5V panel cause damage? I'd think the electronics can bear more voltage though I can be mistaken. I definitely don't want to kill my SIM.

[johnd]

Re the solar panel: Since you can run the ISS SIM board from a standard Davis 5v mains adapter, the board can take this voltage in principle (perhaps provided the voltage is applied in the right place).

But I would have thought that the simplest (but certainly not the cheapest) solution was to buy a solar door, which is available as a spare part.

[kobuki]

Re the solar panel: Since you can run the ISS SIM board from a standard Davis 5v mains adapter, the board can take this voltage in principle (perhaps provided the voltage is applied in the right place).

But I would have thought that the simplest (but certainly not the cheapest) solution was to buy a solar door, which is available as a spare part.

Yeah, but they might follow a different current path. I could imagine the adapter path is traversing a DC-DC step-down converter, possibly. The 2V panel doesn't need this step-down. But since the electronics itself is 3V, they might have prepared it for accepting higher voltages for the panel... And since both can be connected at the same time (panel and adapter), the 2-path theory looks more feasible for me at the moment, but I have no idea.

I could buy a door but I placed my transmitter in the attic, while the anemometer itself is out on the roof. So I want to put a solar panel on the mast of the anemometer. I made cabling for that, I only need a suitable panel now.

[johnd]

I could buy a door but I placed my transmitter in the attic, while the anemometer itself is out on the roof. So I want to put a solar panel on the mast of the anemometer. I made cabling for that, I only need a suitable panel now.

Connect the lead to a 5v mains adapter with the correct plug on the transmitter end???

[kobuki]

Yeah, that's a possibility if I drill a hole from one of the rooms up to the attic, run about 20m of cable for mains, properly insulated and tubed for the attic wooden structure, etc So I'd like to avoid that. Of course it occurred to me too, but I'm not looking for alternatives, but a possibility to attach a suitable solar panel. Maybe someone else has done it before.

[dalecoy]

I could buy a door but I placed my transmitter in the attic, while the anemometer itself is out on the roof. So I want to put a solar panel on the mast of the anemometer. I made cabling for that, I only need a suitable panel now.

So, the door comes with a correct solar panel, as well as the correct connector to hook to the transmitter.  Put the panel on the mast (you will have to make a suitable bracket for any panel you buy), splice the cabling, .....

I'm obviously missing some important problem.

[SLOweather]

The solar door is hideouosly expensive if you only need the panel. At Scaled Instruments, the ISS door is $45, the hinged station door is $58.50.

OTOH, this from Jameco should work:

http://www.jameco.com/z/SP3-37-Powerfilm-Flexible-Thin-Film-Solar-Module-3-0-Volt-22-mA_227985.html for $3.95...

[dalecoy]

The solar door is hideouosly expensive if you only need the panel. At Scaled Instruments, the ISS door is $45, the hinged station door is $58.50.

OTOH, this from Jameco should work:

Agreed.  In fact, almost any solar panel with approx 3 volt output should work.

The Davis parts will work.  So, it depends on kobuki's philosophy.

[kobuki]

I'm obviously missing some important problem.

Yeah, you are As I mentioned in my first post, this extra board didn't come with a solar panel. It's sold as a T or T/H transmitter that probably runs from a battery for years. It was at a convenient place first so I could use a mains adapter or could replace batteries easily. Now it had to be relocated and the board is on the attic which is a little quirkier to get to. So I'm looking at the possibilities.

[kobuki]

The Davis parts will work.  So, it depends on kobuki's philosophy.

I have panels with different voltages. If I can't use them I might buy something factory-made for the Davis units. Though a common ~2-3V panel shouldn't cost as much as they're selling it for.

But it appears no one has ever tried something similar? Not saying being the first is bad though

[dalecoy]

As I mentioned in my first post, this extra board didn't come with a solar panel. It's sold as a T or T/H transmitter that probably runs from a battery for years. It was at a convenient place first so I could use a mains adapter or could replace batteries easily. Now it had to be relocated and the board is on the attic which is a little quirkier to get to. So I'm looking at the possibilities.

I actually did understand that.  You're hunting a solar panel to be mounted on the roof mast, connected by wiring that you have already installed, to a SIM board in the attic.

The fact that the Davis part has a name that includes the word "door" - isn't significant. 

I didn't know that you already have panels.  Yes, other people have done that with good results, using panels in the 2 to 5 volt range, connected in various ways. 

[kobuki]

OTOH, this from Jameco should work:

http://www.jameco.com/z/SP3-37-Powerfilm-Flexible-Thin-Film-Solar-Module-3-0-Volt-22-mA_227985.html for $3.95...

Thanks for the hint. The thin-film panels have notoriously low efficiency. But for a similar price one can buy a suitable one that meets or overperforms the Davis one. I agree though, 3V would probably alright as alternative.

[kobuki]

I actually did understand that.  You're hunting a solar panel to be mounted on the roof mast, connected by wiring that you have already installed, to a SIM board in the attic.

OK, sorry, I misunderstood you. I don't want to buy an original door with a panel if possible.

The fact that the Davis part has a name that includes the word "door" - isn't significant.

... what? OK, I see what you mean. Of course the exact shape or form doesn't matter, but I have to be able to attach it to the mast somehow. The Davis doors for their shelters would be fine should my choice fell on one.

[kobuki]

I didn't know that you already have panels.  Yes, other people have done that with good results, using panels in the 2 to 5 volt range, connected in various ways.

Now, that's very good to know, thanks. This IS the answer I was waiting for. I didn't think that I have one is significant, probably because I can get 5-6V panels for the cheap locally any time (besides having one).

...

After checking it I have a 6V panel for phone chargers. Would that work, I wonder?

[dalecoy]

After checking it I have a 6V panel for phone chargers. Would that work, I wonder?

If you also put a 6V rechargeable battery in the attic, and hook the assembly to where you were plugging in the AC adapter - yes.

But not hooked to where the solar panel normally is wired.  Voltage is too high.

[kobuki]

Thanks, I had the feeling it wouldn't be a good idea. The additional battery is an interesting idea.

[dalecoy]

Thanks, I had the feeling it wouldn't be a good idea. The additional battery is an interesting idea.

The solar panel charges the supercap through the "normal" connection.  The supercap has a much lower voltage specification.  So, if you used a 2 or 3 volt solar panel, hooking it to the solar panel connection point would be OK.

[kobuki]

Yes, I had that suspicion, though at one point it occurred to me that path might cross the voltage step-down converter too. You mentioned earlier that several people used higher voltage panels with success - I guess they used the same way you just suggested? BTW, doesn't the mains adapter connection charge the supercap, too? It would make sense since the transmitter could countinue to work on power from the cap in case of a blackout (assuming no 3V battery is installed).

[dalecoy]

...BTW, doesn't the mains adapter connection charge the supercap, too? It would make sense since the transmitter could countinue to work on power from the cap in case of a blackout (assuming no 3V battery is installed).

I don't know (perhaps someone else can give an authoritative answer).  We do know that the 3V battery does not charge the supercap.  But the exact circuitry seems to be a mystery.  Note also that the mains adapter is not a "usual" method, so Davis may only have considered the other 3 power sources in their design.

[kobuki]

We do know that the 3V battery does not charge the supercap.

That's interesting, because I remember reading the opposite. And when I replaced the battery yesterday in the anemometer transmitter without the solar panel, it didn't skip a single packet. It steadily transmitted them in the correct sequence when the battery was out for 10 secs or so. I know because I run my own receiver for tests and it clearly shows there were no missing packets at that exact period. I still have the logs.

[dalecoy]

We do know that the 3V battery does not charge the supercap.

That's interesting, because I remember reading the opposite. And when I replaced the battery yesterday in the anemometer transmitter without the solar panel, it didn't skip a single packet. It steadily transmitted them in the correct sequence when the battery was out for 10 secs or so. I know because I run my own receiver for tests and it clearly shows there were no missing packets at that exact period. I still have the logs.

Well, perhaps I'm incorrect about the battery charging the supercap.  I'm quite willing to hear an authoritative correction (or an experiment in a system like yours, that has no solar panel, removes the battery after some charging time, and then demonstrates that the system continues to operate for several hours)

However, it is usual in this most types of circuit to have a "supply voltage filter" that contains a regular capacitor, and has the side-effect of handling short-term power outages (like changing a battery).

Of course, then there's another investigation about the mains supply and the supercap.....

[kobuki]

Actually, charging the cap all the time from any available source has the benefit of bridging maintenance periods and power outages plus makes the design simpler somewhat.

Next time I need to replace the battery I'll leave it without one for an hour and report back. Well, assuming that I still won't have a solar panel installed by that time.

[kobuki]

And to answer the first question in my opening post, the UVI values are correctly transmitted as 0.0 now, in darkness. It seems the ISS needs to sense something above zero UVI before it decides to have a UV sensor.

[dalecoy]

Actually, charging the cap all the time from any available source ..... plus makes the design simpler somewhat.

I'm not certain about that, when there are 3 potential sources with widely differing voltages ~~(5, 3, 2) charging a supercap with an even-smaller maximum voltage (2.7), and all four have to be capable of running the system.

[kobuki]

I'm not certain about that, when there are 3 potential sources with widely differing voltages ~~(5, 3, 2) charging a supercap with an even-smaller maximum voltage (2.7), and all four have to be capable of running the system.

Well, I'm not an EE but I've seen "smart" buck/boost converters that no matter the input voltage (within specific bounds, of course), produce a desired output voltage. Using something like that as the final power stage before all electronics is powered doesn't sound a bad idea. Of course some sources must be mutually exclusive, flowing current to the battery must be avoided (protection diodes?), etc. But as you said, the complete schematics is a mistery so treat this as thinking out loud. I agree, even if such solutions are used here, they're simple at the block level but might be more difficult in their concrete implementation. Who knows, someone might RE the SIM sometime