Batteries won't charge!!

[bgosper]

I have a 12 volt system with 6 panels and 7 batteries. the batteries are 5, 100 Ah and 2, 55 Ah. I have a 40 amp MPPT controller. The issue I am having is that the batteries will not charge beyond about 11.8 volts. If I only connect a couple of them to the system they do seem to charge beyond 12 volts, though slowly. But with all of them connected, they won't charge past about 11.8 volts. All the batteries are relatively new and test out fine and the controller is also new and functioning properly and I have good solid cable connections between them.
Could I have not enough power from the panels to charge that many batteries or is there something else I should check? HELP!!

 

[gnubie]

What is your total panel wattage? Can you monitor the current from the SCC to the battery? Most SCCs that have a front panel display will show you the current flowing out of the SCC. Does the current out stay as high as expected while your battery is still at 11.8v?

 

[bgosper]

What is your total panel wattage? Can you monitor the current from the SCC to the battery? Most SCCs that have a front panel display will show you the current flowing out of the SCC. Does the current out stay as high as expected while your battery is still at 11.8v?

Right now there is about 16 volts coming in from the system (shade in afternoon), 2.6 amps, and the batteries are at about 12.6 V (the 2 that are connected)

 

[gnubie]

You have 610 Ah of battery. Let's say you are lifting that from 50% charged. At 2.6 amps it is going to take 117 hours just to get that much energy from the panels and your battery will need more than that to actually reach full charge for various reasons. You are going to have to make observations when your panels do not have any shading issues and work out how many hours of direct sun to see how many amp hours you can push at the battery.

How are your panels arranged? Series, parallel etc, and what is the total wattage?

 

[bgosper]

All ki

You have 610 Ah of battery. Let's say you are lifting that from 50% charged. At 2.6 amps it is going to take 117 hours just to get that much energy from the panels and your battery will need more than that to actually reach full charge for various reasons. You are going to have to make observations when your panels do not have any shading issues and work out how many hours of direct sun to see how many amp hours you can push at the battery.

How are your panels arranged? Series, parallel etc, and what is the total wattage?

All kind of confusing to me right now! Panels are 75 watts each I believe, so about 450 watts total?. Not sure how to classify series or parallel for them. They run into a circuit breaker box (6 breakers) and then there is one output (positive and negative) to the controller.

 

[gnubie]

You have a maximum output of 450 watts. If we pitch that against a notional 12v battery we get charging current of around 37 amps. We'd need 8 hours of good sunlight just to generate the energy of half that battery bank. More energy is needed to fully charge the battery from half charged. Your panels probably never actually produce 450 watts so that will further increase that time but now you should be starting to see how many days it will take to charge your battery, and that's without taking any energy out of the system to run your loads.

Your charge controller has a maximum current limit of 40 amps. No matter how many watts are on the solar input it will not produce more than 40 amps on the output. More panels on the solar input will let the controller stay at that peak amp rate for more of the day.

At 75 watts I'm guessing you are using '12v' panels. Your MPPT controller likes to have voltage to play with. If shading issues permit you to, hooking two panels in series may help things. Can you post the spec sheet on the back of the panels?

At this point IMO you will be struggling to bring the battery bank to full charge and lead acid doesn't appreciate being left in a not-fully-charged state.

 

[bgosper]

You have a maximum output of 450 watts. If we pitch that against a notional 12v battery we get charging current of around 37 amps. We'd need 8 hours of good sunlight just to generate the energy of half that battery bank. More energy is needed to fully charge the battery from half charged. Your panels probably never actually produce 450 watts so that will further increase that time but now you should be starting to see how many days it will take to charge your battery, and that's without taking any energy out of the system to run your loads.

Your charge controller has a maximum current limit of 40 amps. No matter how many watts are on the solar input it will not produce more than 40 amps on the output. More panels on the solar input will let the controller stay at that peak amp rate for more of the day.

At 75 watts I'm guessing you are using '12v' panels. Your MPPT controller likes to have voltage to play with. If shading issues permit you to, hooking two panels in series may help things. Can you post the spec sheet on the back of the panels?

At this point IMO you will be struggling to bring the battery bank to full charge and lead acid doesn't appreciate being left in a not-fully-charged state.

Hi, thanks for the info. The panels are homemade so there are no spec sheets LOL. They are typical 36 cell panels, I believe 2 watts each? How do I connect the panels in series? Only 2? So with the limitation of the controller is it even worth adding more panels then?

 

[gnubie]

Hmm, getting worse at every step We aren't even sure of the panel's power now. Are the cells all in series, that'd give Voc somewhere under 22v. We probably can hook two panels in series, and then hook those series sets in parallel. What is the make and model of your MPPT controller?

 

[bgosper]

Hmm, getting worse at every step We aren't even sure of the panel's power now. Are the cells all in series, that'd give Voc somewhere under 22v. We probably can hook two panels in series, and then hook those series sets in parallel. What is the make and model of your MPPT controller?

I believe they are series. I will get about 20 volts each out of them with good sun.

 

[bgosper]

Hmm, getting worse at every step We aren't even sure of the panel's power now. Are the cells all in series, that'd give Voc somewhere under 22v. We probably can hook two panels in series, and then hook those series sets in parallel. What is the make and model of your MPPT controller?

It is a Renogy Rover PG (RNG-CTRL-RVRPG40)

 

[bgosper]

I believe they are series. I will get about 20 volts each out of them with good sun.

I believe they are series. I will get about 20 volts each out of them with good sun.

How do I make those panel connections ?

 

[gnubie]

Something like this, but if you have them in series already at Voc around 20v you are exceeding your controllers maximum input voltage. Your controller can disconnect the panels if the voltage limit is exceeded so you won't blow it up if the batteries ever float up to fully charged voltages but under light loading where the battery is still charging the controller might end up disconnecting the panels and stop charging before the battery is full.

If you have them in series already your MPPT controller will have a good voltage range to work with so we can discount that as being a problem.

Since they are homebrew panels, do you have bypass diodes? Shading without diodes will severely lower your systems power production.

 

[bgosper]

Something like this

View attachment 4131

Ok I will try this. How much will this give me?. Should I still consider adding any more panels to the system or will the controller not be able to handle it? If so, can you recommend where I can get the panel? If not I guess I will have to take a few batteries out of the series.

 

[gnubie]

Re-read my post, I made some changes while posting, check the link below so you understand series wiring.

What is series and what is parallel wiring of solar panels?

 

[bgosper]

Something like this, but if you have them in series already at Voc around 20v you are exceeding your controllers maximum input voltage. Your controller can disconnect the panels if the voltage limit is exceeded so you won't blow it up if the batteries ever float up to fully charged voltages but under light loading where the battery is still charging the controller might end up disconnecting the panels and stop charging before the battery is full.

If you have them in series already your MPPT controller will have a good voltage range to work with so we can discount that as being a problem.

Since they are homebrew panels, do you have bypass diodes? Shading without diodes will severely lower your systems power production.

View attachment 4131

Yes, I do have diodes on each panel to prevent "backflow" after dark. So I should not rearrange the panels as pictured? I think it is just that the panels are not producing enough to charge?

 

[gnubie]

Since you have a MPPT controller with panels in series you don't need a backflow (blocking) diode. The diodes would go across the panel to allow current to flow past a shaded panel.



If your panels are in series there is no need to reconfigure them to be like the picture I posted since the MPPT controller will be getting higher voltage that lets it work better.

Yes, I think your problem is just going to come down to your panels not being able to produce enough power in a reasonable time due to their capacity and shading.

 

[bgosper]

Since you have a MPPT controller with panels in series you don't need a backflow (blocking) diode. The diodes would go across the panel to allow current to flow past a shaded panel.

View attachment 4134

If your panels are in series there is no need to reconfigure them to be like the picture I posted since the MPPT controller will be getting higher voltage that lets it work better.

Yes, I think your problem is just going to come down to your panels not being able to produce enough power in a reasonable time due to their capacity and shading.

Where would I get those diodes? I have a positive and negative cable coming off each panel individually. so a total of 12, coming into the breaker box. 6 going into the breakers and the other 6 onto the ground bar. Then one each out to the inputs of the controller.

 

[Ped]

Just to compound on gnubies point although disagreeing with charge amperage. Which id put at best a touch over 20A

To charge 610ah at say 25% discharged
(25/100) x (610/22a) + 3hrs in absorption = 10hrs to fill up from 75%. Which is impossible even in peak summer.

Youre batteries are now ruined from sulfation. You need about 10:1 watts per amps used to fill lead batteries accounting for winter months and clouds. So your system is good for about 100ah bank taken down to 60% dod. Or you can look at it like a 40AH usable capacity in winter (80ah summer) with any bank size. Anymore and you cant refill by sunset.

And of course you could double that with lifepo4. 80-90a/160-180a winter/summer.

 

[gnubie]

Where would I get those diodes? I have a positive and negative cable coming off each panel individually. so a total of 12, coming into the breaker box. 6 going into the breakers and the other 6 onto the ground bar. Then one each out to the inputs of the controller.

The diodes you are using as blocking (backflow) prevention should be good enough if they are correctly rated so where ever you got them. Can you post the part number for your existing diodes? 1N4007 (not recommended you use this one) etc.

I think you may not understand series and parallel connection based on what you have said here with 6 wires going onto a ground bar. That says parallel connection. Take a look at the link I posted earlier about series and parallel connection of panels.

 

[bgosper]

Just to compound on gnubies point although disagreeing with charge amperage. Which id put at best a touch over 20A

To charge 610ah at say 25% discharged
(25/100) x (610/22a) + 3hrs in absorption = 10hrs to fill up from 75%. Which is impossible even in peak summer.

Youre batteries are now ruined from sulfation. You need about 10:1 watts per amps used to fill lead batteries accounting for winter months and clouds. So your system is good for about 100ah bank taken down to 60% dod. Or you can look at it like a 40AH usable capacity in winter (80ah summer) with any bank size. Anymore and you cant refill by sunset.

And of course you could double that with lifepo4. 80-90a/160-180a winter/summer.

Well so sounds pretty hopeless. I'll just take the system down or take a few of the batteries out of the system and go with just a limited bank.