MPP Solar backflow to Solar Panels?

[wangzen]

I have a 24v MPP Solar unit. I have 4 Battleborn 24v 50amp batteries connected in parallel. I have eight 160watt solar panels split into 2 sections: 4 panels in series that are connected in parallel to another 4 connected in series.

Overnight, my batteries would drain to near zero unless I turned the MPP Solar off at night. I thought it might be an energy backflow from the batteries to the panels. So I added a disconnect from the panels to the Charge Controller. At night I would disconnect the panels from the MPP Solar unit. The result was no more power loss.

What confuses me is that I thought that Charge Controllers were supposed to prevent energy backflows from the batteries to the panels, especially overnight. Is there something I might be missing?

 

[Craig]

You are correct there should be no backflow. Your SCC could be damaged

 

[April]

The solar panels usually have built in diodes to stop any reverse current flowing at night . have they been removed or shorted out somehow? Put a large 10 to 20 amp diode (used in car alternators) in the line from cells to controller. I don't think its the controllers job to prevent backflow at all but probably some have diodes built in anyway. (Diodes only allow current to flow in one direction so get them in the right way.)

 

[thedodgersonline]

Hi Wangzen.
I have a very similiar setup (except 48V with similiar solar panels and definitely do not get any back flow out of the batteries. Have you checked there is no load? Also check the state of the batteries because these MPPs do use a bit of power when in idle. If you have a clamp see if you can see teh current flowing back into the solar panels. But as April stated - could be the diodes are cactus or have been removed.
Regards

 

[Thor]

I had the same issue with some old solar panels i used that didn’t have any blocking diodes in them. Added these Mc4 diodes and the problem was solved.

 

[wangzen]

I had the same issue with some old solar panels i used that didn’t have any blocking diodes in them. Added these Mc4 diodes and the problem was solved.

The panels I have are new, so I’m assuming they would have the diodes, but maybe they were damaged as some of the replyers state. The inline diodes you suggest seem like an easy plug and play solution I can try - thanks!

 

[wangzen]

Hi Wangzen.
I have a very similiar setup (except 48V with similiar solar panels and definitely do not get any back flow out of the batteries. Have you checked there is no load? Also check the state of the batteries because these MPPs do use a bit of power when in idle. If you have a clamp see if you can see teh current flowing back into the solar panels. But as April stated - could be the diodes are cactus or have been removed.
Regards

I thought I checked the overnight load as being around 5watts. Maybe there’s something else pulling a load I’m not aware of - thx. The Lithium Battleborns are new, and seem to charge up fine, just get discharged overnight.

 

[wangzen]

You are correct there should be no backflow. Your SCC could be damaged

Hmm, that’s what I thought. Thanks for the confirmation.

 

[wangzen]

The panels I have are new, so I’m assuming they would have the diodes, but maybe they were damaged as some of the replyers state. The inline diodes you suggest seem like an easy plug and play solution I can try - thanks!

I’m trying to figure out if these MC4 diodes would have sufficient amps based on my panel config of 2 sets of 4, 160w, 12v panels grouped in series, then the 2 sets connected in parallel?

A single panel would be 160w/12v=13.33amps right? And since series configs don’t increase amps I would just double the 2 sets amps to 26.66amps correct? So I would need a beefier diode, right?

 

[thedodgersonline]

I’m trying to figure out if these MC4 diodes would have sufficient amps based on my panel config of 2 sets of 4, 160w, 12v panels grouped in series, then the 2 sets connected in parallel?

A single panel would be 160w/12v=13.33amps right? And since series configs don’t increase amps I would just double the 2 sets amps to 26.66amps correct? So I would need a beefier diode, right?

Hi

These diodes are generally 50A I recall.
Regards

 

[gnubie]

MC4 diodes have various ratings, usually 10 / 15 / 20 amps. The MC4 connectors themselves are nominally rated at 20 amps but it is possible to buy higher rated connectors.