testing solar cells

[elhifnawyplast]

schematic

Thank you for the schematic you sent to me,i am trying to understand it as much as i can as i am a mechanical Engineer and my electrical knowledge is limited

[bcroe]

without a schematic it is not perfectly clear for me,if please attach a schematic for testing or sorting a 4.5w solar

Try this. The load is chosen to put the voltage around 80% of Vmp on a good cell. Letting
the voltage rise a lot higher won't draw enough current for the best test. A couple 0.1 ohm
resistors (in parallel) are generally easier to find than a single 0.05 ohm 3 watt resistor.
Voltmeter wires are attached directly to resistor wires to avoid wiring drop error (Kelvin
connection). For reading cell overall, I use 100 ohm resistors to average the lead voltages.
Bruce Roe

[elhifnawyplast]

schematic please

without a schematic it is not perfectly clear for me,if please attach a schematic for testing or sorting a 4.5w solar

[SunEagle]

My bad guys, should have looked at the testing rig. My only question left is what can you tell from an artificial light, rather than a reference source of known w/m^2 or noon sun?

I think bruce is looking for consistency from one cell to another as opposed to V & I mp of the cell. At least if all the cell "test" have similar results then you can "assume" (I hate that word) they will work if properly connected together.

[Sunking]

My bad guys, should have looked at the testing rig. My only question left is what can you tell from an artificial light, rather than a reference source of known w/m^2 or noon sun?

[bcroe]

It is hard to tell for sure without a schematic but from Bruce's verbal description it sounds like he is separately testing for current in both metalized tabs of a two tab panel. To do this properly he has to have approximately the same repeatable resistance in each of the two (or three?) circuits. That cannot easily be done with a single DMM in ammeter mode.
Instead it requires one load resistor (or one shunt) per circuit, and a switch to move the DMM, on a voltage range, from one place to another in the circuit.
Whether the information obtained this way is worth the added complexity depends on just how much you want to know about each cell that you are testing, beyond just the single Voc and Isc with all tabs of the same polarity on the cell connected in parallel.

The above pretty much describes it. I wanted to test a lot of cells, and quickly. Connecting and
disconnecting leads is time consuming; meanwhile the light is heating up the cell & changing
the reading. Turning the bulb on and off burns it out faster.

Even just switching an ammeter around is a problem, because the high currents
and low voltage means standard switch resistance isn't negligible anymore. Bruce Roe

[inetdog]

It is hard to tell for sure without a schematic but from Bruce's verbal description it sounds like he is separately testing for current in both metalized tabs of a two tab panel. To do this properly he has to have approximately the same repeatable resistance in each of the two (or three?) circuits. That cannot easily be done with a single DMM in ammeter mode.
Instead it requires one load resistor (or one shunt) per circuit, and a switch to move the DMM, on a voltage range, from one place to another in the circuit.
Whether the information obtained this way is worth the added complexity depends on just how much you want to know about each cell that you are testing, beyond just the single Voc and Isc with all tabs of the same polarity on the cell connected in parallel.

[Sunking]

The picture is earlier in this same thread. Those who would rather see (almost) short circuit
current instead of some power delivery, can replace my load resistors with shunts in the
20-50 mv at 5A range, along with a more sensitive voltmeter. Bruce Roe

Bruce you do not need a shunt to measure current, just a DVM. The meter provides the shunt. Depending on what type of meter you may not even need to switch leads to test Voc and Isc, just toggle via selector switch.

[bcroe]

Bruce can you please attach the design or photos of your jig i will be very grateful

The picture is earlier in this same thread. Those who would rather see (almost) short circuit
current instead of some power delivery, can replace my load resistors with shunts in the
20-50 mv at 5A range, along with a more sensitive voltmeter. Bruce Roe

[elhifnawyplast]

design or photos

Bruce can you please attach the design or photos of your jig i will be very grateful

[Sunking]

Right, it doesn't produce lab standard results. INSTEAD, it locates a fault feeding one of
the leads, and allows matching a bunch of cells, or determining the best ones, to make
up a DIY panel. It does so under conditions much closer to actual operation, than the
Voc or Isc points. That IS where we are ultimately going. A useful DIY function, not
suitable for commercial use as defined. Bruce Roe

Yeah Bruce I understand, but you do not need a resistor load to do that.

[bcroe]

Bruce DIY cannot measure Imp, that can only be done in a Lab. Best one can do is find out which cells are stronger by shorting out the cell. Adding a resistor just reduces the current to some unknown value and does not gain you anything.

Right, it doesn't produce lab standard results. INSTEAD, it locates a fault feeding one of
the leads, and allows matching a bunch of cells, or determining the best ones, to make
up a DIY panel. It does so under conditions much closer to actual operation, than the
Voc or Isc points. That IS where we are ultimately going. A useful DIY function, not
suitable for commercial use as defined. Bruce Roe

[Sunking]

Bruce DIY cannot measure Imp, that can only be done in a Lab. Best one can do is find out which cells are stronger by shorting out the cell. Adding a resistor just reduces the current to some unknown value and does not gain you anything.

[bcroe]

Power test

Dummy Load on a ISC test? Huh?

You cannot and do not want to use any load resistance doing Isc test. Isc is Current Short Circuit test where the output leads of the panel are connected to each other or Shorted Out. To test it all you do is short the panel or cell out with a DVM and read the current.

That is all true, if you are running your most basic Voc and Isc tests. I chose to run
a POWER test, which can be difficult to set up on a panel & varying sun. But not so
difficult here with one cell and controlled (if somewhat reduced) light.

My cells had 2 leads on EACH face, any one of which could have problems if there is a
crack. In addition there is the issue of overall total cell performance. I connected one
end of a a 0.05 ohm 5 watt resistor to each of 4 leads. The other end of all 4 resistors
were all shorted together with a heavy (dual 12 gauge) wire. This presents a 0.05 ohm
load overall to the cell. So if it put out 10 amps, the voltage would reach 0.5V. The 8A
cell will never put out that much, so I would see voltages around 0.4 volts. This would
vary so I could weed out poor performers.

IN ADDITION, I have a 5 position switch which connects the voltmeter to the whole cell
(averaged through some 100 ohm resistors), or to ONE of the 4 resistors at a time. The
voltmeter wires were connected by a dedicated pair directly to one of the resistors at a
time, to avoid any loop shifts (Kelvin connection). IF ONE of the cell output lead's current
was reduced significantly from the other 3, it could indicate a flaw in the cell current
paths there. It was necessary to switch thru the 5 positions pretty quickly, before the
lamp heated the cell and numbers started drifting. Bruce Roe

[Sunking]

The dummy load was chosen

Dummy Load on a ISC test? Huh?

You cannot and do not want to use any load resistance doing Isc test. Isc is Current Short Circuit test where the output leads of the panel are connected to each other or Shorted Out. To test it all you do is short the panel or cell out with a DVM and read the current.