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MicroBlocks
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Posted: 09 January 2018 at 10:29pm | IP Logged Quote MicroBlocks

For solar panel it is best to measure 'Short Circuit Current'.
Just put your multimeter to measuring current (use the right range) and connect the probes directly to the + and - of the solar panel.
All current will then flow through the meter and this should be higher then 23ma even with just ambient light.

If not then there is probably something wrong with the panel. It said 'module' on your picture, is it only a solar panel or are there integrated electronics?


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lew247
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Posted: 09 January 2018 at 10:43pm | IP Logged Quote lew247

Just tried that and the result is the same







sorry about the reflection of the lights on the panel, it's inside now

Edited by lew247 on 09 January 2018 at 10:44pm
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redrok
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Posted: 10 January 2018 at 4:39am | IP Logged Quote redrok

Hi Lew;

A 36 cell, nominally called a silicon 12V PV panel.
Open circuit voltage should be in the 21V - 22V range.

Ok, we have a couple of problems to solve.

1. The measured OCV is about 14V.
This is an odd number.
It's not 1/2 Of 21V, or 10.5-11V, which would have indicated there was a shorted shunt protection diode inside the panel. But yours reads 14V.
If there are 3 shunt protection diodes and one was shorted you would get about 14V.

2. Broken, or open, connection in the panel would, usually, read about 0V.
But yours reads 14V.

3. A high resistance connection can cause the voltage reading to be low.
The value of this reading depends on the resistance of the meter.

4. Your short circuit current is 23mA. Whether the panel is outputting 14V or 0V.
That is odd. I would have expected the current would be higher at 0V.

My guess is the panel has a high resistance connection inside the panel. (#3 above).
However this doesn't explain what is happening very well.

Get a new panel!!!!!

redrok
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Posted: 10 January 2018 at 7:00am | IP Logged Quote TassyJim

A long time ago, when solar panels were expensive, I repaired a faulty panel.
I probed each cell using sharp pins through the protective surface until I found the open circuit cell. I then stripped away enough of the surface to solder a shorting link across the faulty cell.
A bit of silicon sealer and the panel was good enough to go back into service (but not up on the mountain top it came from).

That was when panels were expensive and I was curious about the working of solar panels.

If the panel surface is dirty, clean it, if not, get a new panel.

Jim




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Posted: 14 January 2018 at 1:29pm | IP Logged Quote Andrew_G

Hi there.
In addition to solving Lewis' specific problem I am interested in the general question he raised - "how do sheders power their remote devices?"
(I do like the idea of wet-cell 12V batteries but they are bulky and hard to house in the weather for a small project.)
Are members able to post more details of their solutions for smaller projects such as weather stations, water tank monitors, irrigation systems etc. Details of their solar cells, regulators, batteries possible suppliers etc would really help a newbie like me to make some progress.
Thanks,

Andrew
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Posted: 14 January 2018 at 2:12pm | IP Logged Quote palcal

I am planning to update a hand held gps I built some years ago, back before TFT screens.
I have ordered a 2.4" screen and am planning to run it on 2 18650 li-ion cells in parallel with a 3.3 volt LDO regulator. I don't know yet what battery life I will get and it is a bit hard to even guess as the li-ion cells are usually over rated.
I only need it to last 5 hours at most.
Paul.

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Posted: 14 January 2018 at 2:35pm | IP Logged Quote TassyJim

Andrew,
There are a few questions that need to be answered first.
How low can you get the power drain?
How long do you need it to last?
If solar, how long between sunny days?
If portable, how small and light?

Most of my monitoring is done via long cat5 cables which supply the power at 5V then regulated down to 3.3 at the 'mite.
The source of that power is a 12V solar powered system which powers a radio transmitter and a couple of Raspberry Pi. It has a 105Ah battery and 200W solar panel with AC mains backup.

My electric fence had 15W solar and 18Ah gelcell. It's going to have a 'mite monitoring it eventually.

The electric gates are 25W solar with a 12Ah gelcell. It's going to have a 'mite as well.
For both the 'gunna do' systems, I will concentrate on low standby power. LM2936 regulators and sleep mode on the 'mite
Only turning on the heavy drain gear when needed.

Jim

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Posted: 14 January 2018 at 3:01pm | IP Logged Quote redrok

Hi Andrew;
Andrew_G wrote:
Hi there.
In addition to solving Lewis' specific problem I am interested in the general question he raised - "how do sheders power their remote devices?"
(I do like the idea of wet-cell 12V batteries but they are bulky and hard to house in the weather for a small project.)
Are members able to post more details of their solutions for smaller projects such as weather stations, water tank monitors, irrigation systems etc. Details of their solar cells, regulators, batteries possible suppliers etc would really help a newbie like me to make some progress.
Thanks,

Andrew
I have some experience with powering amateur radio repeaters, weather stations, and other relatively low power consumption remote applications. That is why I suggested the use of lead acid car batteries and PV panels to charge them.
Of course every application is different:
1. Weather stations and other data collection tend to consume the least power.
2. Private telephone radio relays are kind of in the middle.
3. Electric fences are also in the mid range of power consumption.
4. Radio repeaters consume the most and may need deep cycle batteries.
5. Remote electric water pumping is not in this category.

Car batteries running with small PV Panels providing trickle charge, i.e. no charge controller, have been the most reliable. Provided the battery is periodically watered. I generally use a trickle charge current of 1% to 2% of the Amp-hour rating of the battery. No gel-cell nor AGM types, though, as they can't be watered.

Battery manufactures generally say that 1% to 2% causes no damage even when over charging continuously. However, some water is consumed due to electrolysis so watering is needed every 3 to 6 months or so.

If you need to water every 3 months the panel is probably more than needed. A series power resister can be added to reduce the current.

Lead acid batteries have no problem with cold weather, even down to -40F or -40C. They won't freeze when near full charge and they can deliver the small loads.

Over the last 30 years I've had several hundred customers do this with excellent results.

Of course, a car battery is anything but portable. They are reliable though and often cost less than high tech small battery systems.

Andrew, what do you have in mind doing?

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Posted: 15 January 2018 at 10:15am | IP Logged Quote Andrew_G

Jim and Redrok,
Many thanks for your replies - well considered and spot on!
I suppose that for me, and my level of expertise, the hardware design side of any MM project is the most challenging (I am "OK" at soldering and fabrication and by no means more than "competent" with s/w but that is relatively easy and very logical to resolve - it is also well documented - thanks to many).
All my "boards" are hand soldered on vero- board as I have not mastered the PCB design tools (confused by the choices - I have tried several). That is why I use LCD backpacks and any pre-made PCBs available from sheders.
I have a good "finished" project that measures temperatures at four stations (currently chewing up batteries but I have options to fix) plots Barro Pressure over time and shows an analogue or digital clock (based on Geoff G's). Data transmitted via HC-12s.
I have a project that gives a digital readout of GPS speed in a car, including point to point average between two button presses (a speed enforcement "tool" in Victoria and SA).

My current challenge is a weather station (based on MikeO's code). All was going well except that I have put too much demand on to the remote batteries 2x 18650's in parallel (solar charged from an ex garden light, but powering a MM-28pin, GPS, BMP180, DHT22 and HC-12. It all dies at about 06:00 in summer). I'm now moving the GPS and BMP180 to the base station. I can also drop the HC-12 speed to 2400, sleep it and the MM etc (in another thread). Given I live in suburban Melbourne with a great sunlight I had hoped that I could find a source of "abundant power" - hence my post.

I am using these projects to prepare for our new house which will be environmentally friendly including temperature control, electric blinds, water tank monitoring, irrigation system (20k litre tank) etc.
I think you have helped tip my thinking towards putting in conduit and cat 5 cables to a central battery (we may have Tesla etc for the house - certainly lots of PV panels). I also have several used marine-grade AGM 100+ Ah batteries too.

I'm still interested in other sheder approaches (maybe "someone" might consolidate options for future consideration??) . . .

Cheers,

Andrew

Edited by Andrew_G on 15 January 2018 at 10:56am
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Posted: 15 January 2018 at 11:38am | IP Logged Quote TassyJim

Andrew,
While I do use long cable runs to save on multiple power sources, 2 years ago I lost every device (except one) connected to my home network due to lightning. Also lost lots of other devices but the main point is - I now have my Ethernet broken into two segments with a WiFi link to minimise the losses next time the gods are angry.
That's also one reason for going solar with my electric fence.

If I was starting again, I would run fibre from the house to the shed.

Jim
There's nothing wrong with vero-board.


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Posted: 15 January 2018 at 12:37pm | IP Logged Quote Andrew_G

Hi Jim, that's a good point and certainly one I'll include in my house/system design. One wouldn't want a strike to a $20 remote sensor to take out a Tesla either (it would be protected but you see what I mean).
Cheers,

Andrew
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lew247
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Posted: 19 January 2018 at 3:26am | IP Logged Quote lew247

I just bought a 2nd new solar panel
Same thing as the first
only 8 mAh out of this one
Seems like the sun just isn't strong enough on cloudy days in the UK
(most days in winter are cloudy)
Brand new 10W panel this time connected the meter directly across the terminals it should have give around 800mAh - I guess it will in the summer on a good day!

Edited by lew247 on 19 January 2018 at 3:27am
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