Friday, March 1, 2013

Solyndra Art Project Part 2

Proof of Concept-Engineering Prototype

Check out my super hi-tec experimenters set-up below.

Yep, that's a shipping pallet and saw horses.

If you like that you'll love how I made the electrical connections.

Yep zip ties and a mish-mash of wiring.
For now I've decided that I will use 8 tubes. Four pairs in parallel of two tubes in series.

Open circuit that gives me.

Volts

milli-Amps
So with P=IV that's a whopping....25.86Watts...hmmmmm

I've recently learned that switching power supplies can take DC input? Who knew?
Ordered a 15V output unit from Jameco.
Here it is hooked up to the array and generating a useful voltage.

When the array is loaded down with just the power supply the voltage drops to.
221V
The power supply is connected to a nifty solar charge controller, also from Jameco.
Besides the manual being written in some fierce Chinglish its pretty awesome.
It monitors the battery so it won't overcharge, or undercharge. When the battery is fully charged
it converts to a float charger. You can also power something off the controller while the battery is charging. It has a built-in timer which is going to be really handy for this crazy idea.
Once the sun goes down you can set it to power the output for a set amount of time!
The only problem with this output is that it appears to be 'on' all day also...I don't want the lights
on the art piece to be on all day only for several hours after it gets dark.

Here's a closer up shot of all the widgets.
That grey thing next to the SCC is my solution to the always on problem.
Its a photocell switch powered by 12V. It turns on when it gets dark and allows current to flow
to the load.

The load
Just for now I have the set up powering an old bit of El-wire. It glows very brightly during the night.

One thing I have to say about these Solyndra tubes...they are SUPER ITALIAN! As in VERY FRAGILE!
I've already broken two....
So know I'm just going to let this thing run for a couple of days and see what happens. I don't have a lot of confidence that I have the controls set correctly on the SCC....stupid Chinglish.

Questions:
What kind of electrical connectors are those and where can I get some?

I'm not sure how many pairs of tubes I'll need to pull this off. I'm not sure how a switching power supply works. I believe that some DC-DC converters take a higher voltage at a certain current and can down convert it into a lower voltage with a higher current. Is that's whats happening here? If not, I don't see how I'm going to get any useful power from 111mA...

When I hook up the SCC to the PS the array voltage swings all over the place...could be a sign of not enough current? Would it be possible to connect some 'boost caps' to the PS input?

And finally, what in the heck am I going to do with these things after I solve the electrical engineering problems???


 

3 comments:

Ragnar said...

The fluctuating voltage is perfectly normal for solar setups AFAIK - solar panels are current sources, not voltage sources, i.e. they should output a rather constant current rather than a stable voltage. That's why you need nifty electronics to convert the output into anything useful.

And yes, the power supply should give you a stable voltage with more current than the tubes put out at 230 V.

The MadScientist said...

Thanks Ragnar,
One thing that I'm worried about is the PS shuts off if the input voltage drops below 127VDC, then the SCC shuts off then the PS kicks back on...
I'm worried about the system getting stuck in a kind of negative feedback loop, which was why I was wondering if boost caps on the input to the PS might make sense to prevent the voltage from dropping below the PS cutoff.
What do you think?
Or, is the answer just add more tubes so the voltage never drops below 127V?

Ragnar said...

Good question... I think that's actually an issue of the power supply. A good solar charger/power supply should only shut off when the array voltage drops below the battery voltage. It's been more than 5 years that I've learned anything about photovoltaics though and I never put that knowledge to any practical use, so I might be way off.

I think the usual setup would be a power supply/charger combo that converts any useful output from the array into around 14V DC and charges the battery with that. The battery then acts as a buffer if the current demand of any load exceeds the power supplied by the array.