My Cell Testing

[longwolf]

I should make it clear that in my last post, I did not tie the two cells together.
Each was tested singly.

So I called the folks who sold me the cells and was told that you must tab 3 to 4 cells together before you'll get a good amp reading.

It doesn't make sense to me, all amps should be the same in a series circuit, but I didn't want to start trouble with out being sure.

I managed to complete my first 4 cell string just before noon here.
It tested out at 7.6 amps.
Not 8 but a whole lot better than 4.33
Hopefully it will get even better when the rest of the stings are all tied in.

[longwolf]

Well, some good news and some bad news.

I got to check my meter against a 'known good' tester and got expert instructions on how to read amps (the same way I was doing it).
And tabbing the cells did raise the amperage, but not nearly enough.

I made a bad crack in the 1st cell I tabbed, about halfway across it.
It's best reading was 4.2 amps.
I tabbed a second cell and it turned out very well, but it still only got 4.33 amps.
According to the eBay ad, they should be getting 8 amps.

With both cells I took short pieces of 14 awg wire and alligator clips and tied the two negatives together and the two positives together to make sure and get the highest reading I could.

I'm not happy.
Before I call this guy, I though I'd better ask if there are any other things I should check or know.
Might save me from making a fool of myself

[longwolf]

"Skin Effect" is only applied to AC circuits.

Thx, I learned something new. Nix the braided then.

You can do nothing with .5V, except light a lightbulb. To power a dc-dc step up converter, you need at least 3V. Generally, 12V is the lowest useful voltage.
But, feel free to build as you see best, learning by doing is a good way.

This has nothing to do with how the panel is assembled.
From what I've seen, all solar cells have about the same voltage, around 0.5 volts.
Something like the way each cell of a dry cell battery always gives 1.5 volt, or a wet cell battery gives 2 volts per cell.
In all three cell types increasing the the cell size boosts the amperage, but does nothing for the voltage.

So if you're making a 36 cell panel, you're going to get more power out of higher amperage cells no matter how you put them together (excluding making dead shorts, etc).

[Mike90250]

..
And yes, I'm aware of the electron 'skinning' effect, so maybe a braided conductor.

"Skin Effect" is only applied to AC circuits.

You can do nothing with .5V, except light a lightbulb. To power a dc-dc step up converter, you need at least 3V. Generally, 12V is the lowest useful voltage.
But, feel free to build as you see best, learning by doing is a good way.

[longwolf]

NO. You want watts, and with as high as voltage as practical.

Considering that I'm only testing single 0.5 volts cells, wouldn't I want more amps from each one?
Naturally, you wouldn't want so many amps that you had to shade the cell.
But even then, the tabbing wire could be made thicker and not wider.
And yes, I'm aware of the electron 'skinning' effect, so maybe a braided conductor.

[Mike90250]

You're scaring me
But when you're producing power, you want to make as many amps as you can.

NO. You want watts, and with as high as voltage as practical.

It takes copper to carry amps, and fat copper traces shade PV surface area.

double the voltage = 4x less power loss - I think Sunking had that phrase nailed.

[longwolf]

I think I recognize those cells and I have heard others remark in feedback about getting only 1.25 amp output at .5vdc at 1 mile altitude, with a clear sky.

You're scaring me

Newbie here, but I thought the lower current the better. So long as you are getting the voltage, and the current is low, isn't that a good thing?

A low current is good when you're talking about things that use power or when you're trying to use the smallest wire you can.
But when you're producing power, you want to make as many amps as you can.

[Mike90250]

..... but why is there seemingly a limit of around 200 watts for store bought solar panels?

At 45 pounds and as wide as your arms can reach, that's the limit. It's fragile glass, not a $20 sheet of plywood that doesn't matter if you drop it.

[Sunking]

Volts and amps are usable range but why is there seemingly a limit of around 200 watts for store bought solar panels?

The physical size or area of the panel and a human being able to deal with it. At 100% efficiency a 1 meter square panel is rated at 1000 watts. Or about 10.2 square feet, or 2 feet x 5 feet. The highest efficiency panel you can buy is 20% which is 1 square meter, 10.2 square feet, or 2 feet x 5 feet. Numbers do not lie, only humans can lie.

[crxvfr]

Yes and no.

Grrrrr. Ok. This will soak in at some point and maybe someday the things I think I know will makes sense all the time.

I will be following this thread cuz I think I just bought a KW of these cells.

The roof to my bathroom is 6x12. 5x12 of usable space because of an overhang.

Right now I am thinking 3 big 4x5 feet panels with 80 cells per but that comes to 320 watts per 40 v 8amp panel.

Volts and amps are usable range but why is there seemingly a limit of around 200 watts for store bought solar panels?

[Sunking]

Newbie here, but I thought the lower current the better. So long as you are getting the voltage, and the current is low, isn't that a good thing?

Yes and no. Power (watts) = Voltage x Current. If the power and voltage are fixed values; what is the current suppose to be? So lets say the power is suppose to be 100 watts, voltage 33 volts. What does the current have to be? Hint: I = P/E

Power is the product of Voltage and Current.

You need to know Ohm's Law and understand the relationship of the Power, Voltage, Current, and Resistance. For example 100 watts equal how many amps at the voltages of 12, 24, and 48?

100 W = 12 volts x 8.33 amps
100 W = 24 volts x 4.167 amps
100 W = 48 volts x 2.082 amps

All the above are true accurate statements.

[crxvfr]

I am a bit worried.
Today I used the cradle and tested one of the cells in the full noon time sun.
It only read about 3.65 amps. I'm hoping that either the 'cradle' isn't making full contact or maybe I was using the wrong setting on the tester I got from harbor freight. Or maybe it's just cheap and doesn't read correctly.
We'll see after I get a panel together.

I think I recognize those cells and I have heard others remark in feedback about getting only 1.25 amp output at .5vdc at 1 mile altitude, with a clear sky.

Newbie here, but I thought the lower current the better. So long as you are getting the voltage, and the current is low, isn't that a good thing?

[Mike90250]

.....almost half the things I've gotten from Harbor Freight have been junk.

Lucky you. Most aren't so lucky.

[longwolf]

Well what I can tell you a series string is just like a chain, it is only as strong as the weakest link. So if the lowest cell current in the string is 3.2 amps, that is all it will ever deliver.

True, but if the problem is a highly resistive, bad connection, it should get better once they've been tabbed.

And I don't discount user error or a bad amp probe, almost half the things I've gotten from Harbor Freight have been junk.

[Sunking]

Well what I can tell you a series string is just like a chain, it is only as strong as the weakest link. So if the lowest cell current in the string is 3.2 amps, that is all it will ever deliver.