Amps not adding up

[Gdwats]

This is weird, and might be an issue with the Renogy Rover mppt, but today I was testing out differences in 2 x 2 arrays vs 4 all in series 100W panels with confounding results. Constant haze today,but still a valid test. Mainly what i am measuring is the amps going to the battery.

With 4 panels in series I got from the panels 65v, and am assuming around 5A. Going to the batteries was around 8A at 24V. Battery again was pretty full though(25V).

When making 2 series arrays, then joining the 2 arrays in parallel by taking both neg together and both pos together from the 2 arrays using a 2-1 parallel mc4 connector.
I saw about 33V coming in, and 4.5A at 24v going to the battery.

I expected to see about 33V and thought the amps should now add up to 10 via the parallel connection. Instead they are actually less.

repeated and got same result. Befuddled.

Could this be because I'm barely over 24V to start with here? And the 3x3 array will not act this way at around 45V?

[bcroe]

What adds up, is POWER. Your MPPT controller converts 65V at around 3A to 24V @ 8A, both near 190W.
Changing the panel arrangement WILL NOT change the available power, or output current. HOWEVER,
a parallel arrangement may not supply enough voltage for the MPPT to function, or your batteries could
be finished charging: reduced power and current. Bruce Roe

[Gdwats]

Hmm, kinda what I thought about low voltage in small array. Why don't CCs display input amps as well as amps out. Too much fluctuation?

[AzRoute66]

Hmm, kinda what I thought about low voltage in small array. Why don't CCs display input amps as well as amps out. Too much fluctuation?

Two main reasons:
1. Nobody cares. The wire is already rated for the max amps, and if the value need be known it can be calculated from the battery amps.
2. It is 'too much information' for the average consumer. It would only add to spurious calls/complaints of input power not in line with output power, even though it is within anticipated tolerances. The customer with only one clock will never complain that it is a few seconds off..

[Gdwats]

Two main reasons:
1. Nobody cares. The wire is already rated for the max amps, and if the value need be known it can be calculated from the battery amps.
2. It is 'too much information' for the average consumer. It would only add to spurious calls/complaints of input power not in line with output power, even though it is within anticipated tolerances. The customer with only one clock will never complain that it is a few seconds off..

1) Really? Id like to know how many amps my panels are producing, not trying to draw any more. Not concerned about wires, just amps (which would tell you how many Watts actually reach the controller). Which I assume is different than what reaches the battery.

2) ok
cheers!

[Raj]

-- Could this be because I'm barely over 24V to start with here? And the 3x3 array will not act this way at around 45V? --

You are correct, more voltage is required of PV to down convert to charging voltage than two panels can deliver. Three in series wold be optimal.

[Gdwats]

Great, thanks Raj!

[sensij]

Great, thanks Raj!

Except that it isn't great advice. You are using 12 V panels, which as you've seen, have a maximum power point voltage of around 16 V. As long as you put at least two in series, you'll have enough voltage to properly charge the 24 V battery, and will be benefiting from the mppt function. Increasing the number of panels in series will increase the voltage on the PV side of the charge controller, and reduce losses in the wiring from the array to the CC, but will reduce charge controller efficiency, since it needs to go from a higher voltage to the battery voltage.

In your example, under identical conditions, and ignoring the difference in transmission losses, the charge controller efficiency, and the battery's internal resistance, you might expect to see the following:

4S wiring - CC INPUT: PV voltage = 65 V, PV amps = 3 A, PV power = 195 W
4S wiring - CC OUTPUT: Battery voltage = 25 V, Charge amps = 7.8 A, Charge power = 195 W

2S2P wiring - CC INPUT: PV voltage = 32.5 V, PV amps = 6 A, PV power = 195 W
2S2P wiring - CC OUTPUT: Battery voltage = 25 V, Charge amps = 7.8 A, Charge power = 195 W

3S3P wiring - CC INPUT: PV voltage =49 V, PV amps = 9 A, PV power = 439 W
3S3P wiring - CC OUTPUT: Battery voltage = 25 V, Charge amps = 17.5 A, Charge power = 439 W

The fact that you didn't see this when you switched between 4S and 2S2P suggests that something in the conditions changed. The most common differences that can occur in this kind of testing are that the amount of irradiance might have changed (that "constant haze" would be a likely culprit), affecting the current generated, or the battery may have hit your controller's "bulk" voltage setpoint, and started limiting current flow. I'd encourage you to do more testing to prove this to yourself.

[Gdwats]

Thanks for the data sensij, yes something was fishy. What I am planing is 3s x 2 arrays. Arrays hooked in parallel to controller. I was not aware that one could mix like 3s3p, and that all connections had to be identically symmetric. Both S or both P, and only way to join 2 arrays is in parallel, where the amps are additive through the parallel connection of equal voltages. Too many options to consider, argh. If i could mix s&p, that would solve some limiting factors.

3s would be at around 48V, 5A and 3p around 16v and 15A. Confusing still.

[Gdwats]

Today's experiment:
1pm, overcast. 4 panels in parallel. Changed to 12V battery. Seeing 16.5V at panels with 21A going to 12v battery, which is at 13V. Favorable result, in line with 4s power.

[Mike90250]

Hmm, kinda what I thought about low voltage in small array. Why don't CCs display input amps as well as amps out. Too much fluctuation?

depends on the controller, as to what display is available.