Panels output full amps on MPV but 1/2 amps omn MPPT

[chrisb]

I have two panels that are giving strange results.
On eac panel the open circuit voltage is about 41v and open circuit amps are about 5a.
The panels output up to around 5 amps each when used with a MPV solar controller connected to a 12V battery bank. However, when connected to a MPPT controller the panel output drops to about 2.5 amps each. I have confirmed this with both the solar controller meter and a clamp ammeter. We even tried a new MPPT solar controller to ensure that the controller was not the issue.
I believe there are no issues with the bypass diodes.
My real problem is the 1/2 output when connected MPPT. I should be getting up to 30 amps on a 12V system but never get above 15 as for some reason the panels seem to fail under load.

Can use some help. Do you need more info.

[Naptown]

yes lots more info
panel brand and specs
controller brand and specs
how is the system wired

and open circuit amps should be 0 not 5

[Sunking]

On eac panel the open circuit voltage is about 41v and open circuit amps are about 5a.

Impossible, no current can flow through an open circuit.

[chrisb]

Impossible, no current can flow through an open circuit.

ok wrong term short circuit amps

also panel spec

Sun Electronics
Model SUN 220 220Wp

Voc 47.8V
Vmp 36.2V

Isc 6.81amp
Imp 6.08amp

[Naptown]

what is the state of charge on the batteries. The controller will cut back on the current as the batteries get near full.

[chrisb]

what is the state of charge on the batteries. The controller will cut back on the current as the batteries get near full.

The batteries are at 12.6v so the controller is not holding back. It works fine with different panels.
The voltage stays up but the amps cut in half. It does not matter whether the panels are in series or parallel the results are the same.
I think the panels are failing under load but don't know how to prove it.

[Beanyboy57]

The batteries are at 12.6v so the controller is not holding back. It works fine with different panels.
The voltage stays up but the amps cut in half. It does not matter whether the panels are in series or parallel the results are the same.
I think the panels are failing under load but don't know how to prove it.

As I understand it, if your PV array (2 panels) is wired in parallel you should maintain the voltage and double the amps.
In your case you should have somewhere near 41v and 12amps giving you around 400 watts allowing for inefficiencies.

If wired in series you should have around 82v and 6amps or about 400 watts allowing for inefficiencies.
I think this is correct but I am sure somebody will correct me if I am not.

Your charge controller should be capable of handling these high volts and protecting your batteries at the same time.
Have you a battery monitor that gives you an accurate read out of the state of charge of your batteries or do you use a good quality MM?

[chrisb]

As I understand it, if your PV array (2 panels) is wired in parallel you should maintain the voltage and double the amps.
In your case you should have somewhere near 41v and 12amps giving you around 400 watts allowing for inefficiencies.

If wired in series you should have around 82v and 6amps or about 400 watts allowing for inefficiencies.
I think this is correct but I am sure somebody will correct me if I am not.

Your charge controller should be capable of handling these high volts and protecting your batteries at the same time.
Have you a battery monitor that gives you an accurate read out of the state of charge of your batteries or do you use a good quality MM?

You are correct in how it should be. What I actuaslly get is
In parallel 5 amps, in series 2.5 amps coming to the controller and 15 amps going to the batteries using the Mppt controller. My problem is where using the Mppt controller. I have aslso tried another new Mppt controller andf got the same results.

In parallel 10 amps, in series 5 amps if using MPV controller.

The MPV is about right but once I use the Mppt the panels seem to fail.

The controllers are Morningstar Mppt 60 and Morningstar MPV 60.

[Sunking]

If your batteries are fully charged are near fully charge currne twill be low as that is the nature of the beast. Put a good size load on the system and see what happens.

[Beanyboy57]

If your batteries are fully charged are near fully charge currne twill be low as that is the nature of the beast. Put a good size load on the system and see what happens.

All the evidence seems to be pointing towards the SOC of your batteries. Those charge controllers you are using are high quality and reliable and your panels seem to be working fine.
I am not sure what parameters the Morningstar is configured to or even how you configure them, but when I set up my Victron CC I had to enter the exact specifications of my battery bank into it so that it charged my battery correctly. Is that a possibility?
I think you need to follow Sunking's advice and drain those batteries to around 50% DOD. Then check how the charge controllers respond.

[Sunking]

I think you need to follow Sunking's advice and drain those batteries to around 50% DOD. Then check how the charge controllers respond.

You do not have to drain the batteries to test, although that will work, just more power than the panels can supply. For example if the panel array is say 200 watts, put a 400 watt load on the batteries. That should force the CC into bulk mode. This assumes a nice bright sunny day around noon.