Davis VP2 WX running on battery

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1

I hope that someone can point me in the right direction over this one… I have had my VP2 for almost four years and recently it started using only the battery in the ISS to transmit the data indoors. My brother has changed the supercap twice (brand new ones) and it is still not storing solar energy in the supercap. The last supercap was changed on the 12th of this month and a brand new Duracell battery was put in place. Thankfully we have had loads of sunshine, so that probably explains why the battery lasted nineteen days instead of the usual twelve days.

Where do I need to look for a solution?.. Could the supercap have been put in with the contacts the wrong way round?.. is the solar panel kaput? (although under a sun lamp it indicated it had about a 1.5V output if my memory serves me right)… is the PCB defunct?.. although if it was it wouldn’t transmit data with a new battery, would it?

Can someone please suggest a way to cure this problem… I’m running out of batteries! :smiley:

John P

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Check the solar panel again because it needs to generate more potential than the battery voltage (3volts) otherwise the ISS will consume the battery power. Use a voltmeter and check the solar panel output when it is isolated (open) from the ISS and also recheck it when it is connected. Not sure what the solar panel open voltage should be off hand but I would expect 6volts or more.

3

Thank you for that suggestion, Basstudio… I have no idea what the output from the solar panel should be, but under a sun lamp it only recorded about 1.5V, so chances are the solar panel needs replacing.

If, by any chance anyone knows where to get a VP2 solar panel that isn’t a rip-off price, Europe or USA, please tell me because I reckon I am going to need one.

Thanks again for replying, Basstudio.

John P

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Archer Trading, in the U.S., do them for $27 or you could try McMurdo in Portsmouth to see what price they are charging.

Failing that, I have one here that I took off when I fitted the daytime FARS. It’s here as a spare but I’m sure we could come to some agreement via PM. :wink:

5

Thanks for the offer, Martin, I’ll probably take you up on it.

Firstly though, my brother has put a new battery in and he brought the complete cover down and we tested the output with a voltmeter, and it showed a tad over 2V… he cleaned it with toothpaste, although it wasn’t very dirty, and retested it… still the same. I found this on the WX Forum:

"So, today, I took the panel off my existing VP2, and one off a new one, and did some measurements. I repeated them several times and averaged the results, and each time aimed the panel at the sun for maximum reading.

The old, crazed milky panel had an average open-circuit voltage of 2.365 volts, the new one 2.43 volts, a difference of 6.5 millvolts, or 2.67%

More importantly, the old panel had an average short-circuit current of 254 milliamps, and the new one 317 ma, a difference of 63 milliamps, or about 20%.

So, there is a significant reduction in the power output of an older panel with a crazed, milky overlay."

Bearing in mind that the time my brother did both readings there was only 27% solar showing on the station, so whether that makes a significant difference in what its output is, I don’t know, but I would guess so. However, a tad over 2V is nowhere near the figures quoted above.

Anyone’s input will be appreciated… especially if they understand these figures above… because I don’t! :smiley:

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I don’t believe there is anything wrong with John’s solar panel. If the supercap is good then unfortunately I suspect the power circuitry on the ISS board has died - which is a much more expensive proposition.

Back to the solar panel. The Davis ones I have are four cell panels, the theoretical maximum, open circuit (disconnected) voltage from each cell is 0.7 volts, or 2.8 volts for the panel. Per that other posting they saw 2.43 volts which is what I would expect with a lot of sun. If you only had 27% of expected at the time you measured, then > 2 volts is very reasonable. If you take it down again and put it an inch or so from a 60 watt incandescent then you should see 2.4 to 2.5.

The Davis power circuitry is more sophisticated than that, like those cheap Chinese solar yard lights it has a switching voltage converter to make the most of the solar/supercap power.

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Anybody know what cost I am up for if it is the power circuitry on the ISS board, and where to get one?

JP

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I don’t know how it would work in the UK, but here in the US, you can get a swap out
deal from Davis for $82. They send you a new ISS board, then you send back the old
one. This keeps you from having any weather station down time.

-Keith

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Thanks, Keith… I’ll give them a call on Monday and see what they can do for me.

I can get it shipped to a US addressee who will forward it onto me.

John P

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One thing to keep in mind with you being outside the usa, Davis requires the old unit to be returned within 30 days are your credit card will be billed the full replacement amount. They say if you need more time to make arrangements with them. As far as the power problem i had the same thing, the battery would die in a couple of days after replacing the bad super cap. The iss board has isolation circuits built in to keep one power source from draining the other, in my case i had 2 volts showing on the battery holder with no battery installed, that is not good, i had something fail in the circuitry and with the coating they put on the board it is very hard to get a connection with a volt meter to check anything.

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Unless you have an unofficially imported US spec unit you’ll need a UK spec replacement board because the wireless is not the same.

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Hi niko,

I’ll check it out before I speak to them, but they offer two different part numbers… one for US and one for overseas… same price for both, $150… plus sales tax, no doubt! :frowning:

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Before you go ordering or sending anything away, I would speak to the Davis importer & service agent for the UK, McMurdo in Portsmouth.
Explain the problem to them and see what they have to say.
I’ve always had good service when I’ve spoken to them and they may have an exchange service as well, saves sending it across the pond. :wink:

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John,
I’m having a similar problem, but no one has responded to my thread:
http://discourse.weather-watch.com/t/54857
Let me know what you end up doing. I may have to do the same thing.
Thanks.
Steve

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John,

I think I’m going with Niko.
I tested my spare solar cover this morning with cloudy skies and the solar reading at 165 W/m2 (32%) and it was giving me 1.98 - 2 volts which about matches you own readings. So it would seem that your solar panel is working correctly, either that or both yours & mine are broken. :wink:

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Thanks for that info, Martin… I’ll be calling McMurdo tomorrow to see if they can help with a replacement board.

JP

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If your ISS is near enough to a power source you can mains power it using the same psu as the console uses. I have had problem with my VP1 ISS and decided to mains power it as I have a source close enough. I used my console psu to power the ISS and bought a replacement for the console from Maplin.

Stuart

18

Unfortunately not, Stuart… my ISS is at the top of the garden, some 25’ from the house, and the only way to get power to it would mean laying and armoured cable underground.

In the meantime I will continue replacing the battery every 10 days or so. Thankfully I can get two Duracell ones off eBay for

19

I don’t move questions much these days, since a certain incident :roll: but I did move this/John’s thread because it was a discussion that was worthwhile to have available in the correct forum. Reading your question it appears your solar panel is OK too (you can’t expect much solar power from a fluorescent lamp).

Unless there is a voltage doubler or booster on the circuit board, then there is obviously no way that the solar cell can sufficiently charge the cap while supplying just 2.9V. Is it likely that one of the banks of the solar cell is 'out', causing the low voltage. Also, can the battery 'back-charge' the capacitor?

My understanding of the operation is that the supercap is charged by either the solar panel, or the battery - if there is no output from the panel. The supercap powers the rest of the circuitry via a voltage converter that outputs 3 volts. The converter can generate 3 volts from quite a low supercap voltage, I don’t know the lower limit but the one I tested was still operating at supercap = 0.5 volts. On the one I tested, with no solar panel, the battery kept the supercap charged to just below 1 volt.

If it’s feasible for your setup then Stuart’s power suply suggestion is an inexpensive option.

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it is possible that the circuit board is not working right. Any of the components could be wrong, which bring me to this… I think it happens more than we know. The Davis folks have a video on how to replace one, and that alone makes me feel that it probably happens more.

Contact your people about how to go about replacing the board, see if they will send you the replacement and you will return in the return post, the one in question.