Testing used panels, 58v, 5.8amp, Voltage and Amps double when connecting 2 in series.

[DanielForrest]

I hope this is just a silly question! I bought a bunch of used panels and I don't have my controller/inverter or batteries yet, I'm just testing out the panels. When I take 2 panels and connect them in series, both the Volts and Amps double? Is this just because its not under load?

- Each 320w panel right now is giving me 58v, 4.2 amps (rated at 54.7Vmp and current 5.86Imp). When I hook them in series, my new reading is 116v, 8.4 amps. Wha?

- Also, my Klein clamp meter gives me different amp readings on the 40A vs 400A settings. 400A setting shows me 8.4A, whereas the 40A setting says something like 1.2A ? Ive just been going with the 400A numbers.

Thank you for any ideas!

 

[DanielForrest]

I'm thinking it mighta been a silly question..

 

[MisterSandals]

both the Volts and Amps double? Is this just because its not under load?

In series, the volts are added. The amps are the lower of the 2 panels.
Without load, you are measuring the Voc (open circuit voltage).

 

[DanielForrest]

Thank you for the reply MisterSandals. So that is normal that both amps and volts will double when 2 panels are connected in series, and tested, while not under load? Just trying to figure out the best way to started an expandable system (charger/inverter wise) with just a few of my panels to start with, so I was checking how the current charged with series vs parallel, and I did not expect both figures to increase with just a single series connection.

 

[MisterSandals]

So that is normal that both amps and volts will double when 2 panels are connected in series, and tested, while not under load?

If the panels are the same, then one could say the voltage doubles when 2 are put in series.
The amps are not "doubled" in series, it is clipped to the lower amperage of the 2 panels.
If both your panels have an Imp of 5.86A, the 2 in series will produce 5.86A under ideal conditions.

Measuring current is measuring a flow from a load. How are you measuring current?

 

[DanielForrest]

If the panels are the same, then one could say the voltage doubles when 2 are put in series.
The amps are not "doubled" in series, it is clipped to the lower amperage of the 2 panels.
If both your panels have an Imp of 5.86A, the 2 in series will produce 5.86A under ideal conditions.

Measuring current is measuring a flow from a load. How are you measuring current?

I'm just measuring the V and Amps with a voltage tester. Each panel was putting out around 3.7amps, then when I hook 2 in series, they amps then showed over 8, and the voltage doubled from roughly 58 per panel, to 116 when in series. This was expected, but 8.2 amps was not expected.

 

[MisterSandals]

I need help understanding the amperage of my PV arrays

You are correct. I need 15a breakers. I can swap out the fuses for 15a for now. I am adding a combiner box once I get my new battery built. At that point all my breakers will be the correct 15a per string. I see an issue with polarized breakers. Unless you can get non-polarized breakers, I...

diysolarforum.com

 

[justgary]

Just to be clear, you are measuring Amps on the Amps setting with the test leads plugged into the correct jack on the meter? Then you touch one probe to each output wire of the panel (a short through the meter)?

 

[DanielForrest]

Just to be clear, you are measuring Amps on the Amps setting with the test leads plugged into the correct jack on the meter? Then you touch one probe to each output wire of the panel (a short through the meter)?

Yes. Its a Klein CL390. There are only 2 places to connect the probes. Not using the clamp probe at all. DC Amps setting. However, I get completely different readings on the 40A vs 400A DC settings. I have no idea why. So Im just using the 400A setting. But yes, 2 panels in series, Pos/Neg connection between panels, and measuring the remaining pos/neg leads, one from each panel, my volts and amps exactly double.

 

[Bkord]

Yes. Its a Klein CL390. There are only 2 places to connect the probes. Not using the clamp probe at all. DC Amps setting. However, I get completely different readings on the 40A vs 400A DC settings. I have no idea why. So Im just using the 400A setting. But yes, 2 panels in series, Pos/Neg connection between panels, and measuring the remaining pos/neg leads, one from each panel, my volts and amps exactly double.

You need to use the clamp for amps

 

[Hedges]

AC/DC Digital Clamp Meter, Auto-Ranging 400 Amp - CL390 | Klein Tools

Klein Tools CL390 is an automatically ranging true root mean squared (TRMS) digital clamp meter. It measures AC/DC current and NCVT via the clamp, AC/DC voltage, DC microamps, resistance, continuity, frequency, capacitance, and diodes via test leads, and temperature via a thermocouple probe. It...

www.kleintools.com

Only reads amps with clamp. Disconnect test leads (at least from circuit under test) when reading current.

There will only be current flowing if you short the panels.

 

[DanielForrest]

es, 2 panels in serie

AC/DC Digital Clamp Meter, Auto-Ranging 400 Amp - CL390 | Klein Tools

Klein Tools CL390 is an automatically ranging true root mean squared (TRMS) digital clamp meter. It measures AC/DC current and NCVT via the clamp, AC/DC voltage, DC microamps, resistance, continuity, frequency, capacitance, and diodes via test leads, and temperature via a thermocouple probe. It...

www.kleintools.com

Only reads amps with clamp. Disconnect test leads (at least from circuit under test) when reading current.

There will only be current flowing if you short the panels.

Ahh ok. Thank you Hedges!

So my testing amps with the leads, without being underload, is pointless? So I should only test the amps with clamp probe when under load? Just the probes for the Voltage. Makes sense.

Which amps do I consider when adding my panels in series amps for sizing my charge controller? The Current Imp (5.86) or the Short Circuit Isc (6.24).

 

[Hedges]

Charge controllers are specified for battery voltage, current delivered to battery, and open-circuit PV voltage.
Neither Imp nor Isc is particularly significant.

PV_watts / battery_volts = charge_controller_current
That's what you would size it for.

But it is usually OK to have charge controller undersized ("over panel") which will clip on good days but maintain power with a bit less sunshine.

You can also parallel two PV string of different orientation, reducing peak current and extending hours.