My Cell Testing

[longwolf]

So I received my order for 108 6x6 cells from eBay.
It may be a couple more weeks before I can put a panel together, so I figured I'd better inspect and test the cells while I have a little time.
I'd also rather find any bad ones before I add them to a string.

These cells are suppose to be 0.5 volts at 8 amps.

First I made a sort of wire cradle for the cells to sit on. The idea was to have spots for each of the tab soldering points, on the back of the cells, to sit on.
I made a wire bending jig by drawing two parallel lines an inch apart on a board.
The solder points on these cells are 2.3 centimeters apart, so I put in 6 nails, at that spacing, on the top row and 7 on the bottom row. Then I cut the heads off the nails.

Next I cut a piece of wire about 3 and a half feet long and stripped off all but about 8 inches of the insulation in the center of the wire.
Then used the jig on each end of the wire.

Sorry about the quality of the images.
I started with an cheap camera, then the forum only allows very small file uploads so I had to reduce them

[longwolf]

I wanted to have a consistent light source so the cells could be compared to each other and any weak ones weeded out.
So next came the light box. I cut one side of the box off leaving about a 1-1/2 inch 'frame', to keep the box strong. Then cut a 3-1/4 by 3-1/4 hole in the top for the 1000 watt work light.
I covered the top of the box with some aluminum foil to help protect it from the heat.

Note: you can also see more details of the wire cradle.

[longwolf]

Next I bent the back/insulated section of wire so that when a cell is placed against it, the tabbing points should be above the points on the cradle.
Then I drew two parallel lines, 3-1/16 of an inch apart, inside the bottom of the box. That's the distance between the two tabbing areas on the bottom of the cells.
Tape was used to position the wire points at the correct distance and to hold the whole rig in place.

An alligator clip was used to hold one of the multi-meters leads to the wire cradle.
I found that I could place the point of the other lead on one of the top side soldering strips and lay the butt of the probe on the 'frame' area I'd left while cutting the side off the box.
Then I could take hands free readings of the meter.

[longwolf]

As far as the testing went, most of the cells ranged between 0.510 and 0.527 volts.
One came out at less than half a volt and won't be used.
The amp readings ranged from 1.63 to 1.847 amps.
I didn't expect high amp reads from the light box, just wanted to be able to find the weakest cells.

About 50 of the cells look perfect, the rest had chips and or blemishes.
Four of the cells have cracks from 1/2 to 2-1/2 inches long.
Luckily, the seller sent an bakers dozen worth of extra cells.
The chips and blems didn't seem to have an effect on how well a cell read.

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.

[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.

[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.

[Mike90250]

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

Lucky you. Most aren't so lucky.

[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?

[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]

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]

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.

[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.

[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]

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]

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.