Solar panels vs battery charger

[sailscubasurf]

I'm having a problem I can't seem to figure out.

I have 400 watts of solar panels and a 660 amp hour battery bank. Just recently my panels won't charge my batteries to 100%, even though it only took about 3 hours before during a sunny day. I'm still showing that the panels are outputting 12 or more amps into the batteries via the MBPT Controller.

If I switch to shorepower with my 20 amp battery charger within a couple of hours my battery bank is showing 100% charge.

Any thoughts?

[GILow]

Originally Posted by sailscubasurf

I'm having a problem I can't seem to figure out.

I have 400 watts of solar panels and a 660 amp hour battery bank. Just recently my panels won't charge my batteries to 100%, even though it only took about 3 hours before during a sunny day. I'm still showing that the panels are outputting 12 or more amps into the batteries via the MBPT Controller.

If I switch to shorepower with my 20 amp battery charger within a couple of hours my battery bank is showing 100% charge.

Any thoughts?

A few things that would help us to help you:

-Solar controller make and model.

-Battery chemistry

-Voltage profile being used by the controller if it is adjustable.

-Some idea of how much sunlight the panels are getting. (For instance, I swapped pens a few months ago and now, because I rotated the boat 180 degrees, my solar panels have just about halved their output.)

Matt

[sailorboy1]

You didn't provide any details really. 12 amps is 1.8% of C20 rate. That could be charged, you would have to see the manufacturer says is charged.

[wingssail]

Originally Posted by sailscubasurf

I'm having a problem I can't seem to figure out.

I have 400 watts of solar panels and a 660 amp hour battery bank. Just recently my panels won't charge my batteries to 100%, even though it only took about 3 hours before during a sunny day. I'm still showing that the panels are outputting 12 or more amps into the batteries via the MBPT Controller.

If I switch to shorepower with my 20 amp battery charger within a couple of hours my battery bank is showing 100% charge.

Any thoughts?

I think that if you could measure the amps and voltage coming out of the controller it would tell you the story. Possibly one or more of the panels is not putting out, and amps will be low. Or the MPPT is reducing the voltage, in which case it is not functioning properly. If a panel is out you can easily tell which one by putting a boat cushion over the panels one by one and watching the amps.

In my case we have had connections which failed reducing the output.

[StuM]

Assuming FLA, iIf you think your batteries have been charging to 100% in 2-3 hours, the odds are that they have been operating in a partial state of charge all along and they are seriously degraded.

[Mirage35]

Stu has a good point. A recent thread has much discussion around it:

https://www.cruisersforum.com/forums...0-a-36977.html

[Bill O]

Originally Posted by wingssail

I think that if you could measure the amps and voltage coming out of the controller it would tell you the story. Possibly one or more of the panels is not putting out, and amps will be low. Or the MPPT is reducing the voltage, in which case it is not functioning properly. If a panel is out you can easily tell which one by putting a boat cushion over the panels one by one and watching the amps.

In my case we have had connections which failed reducing the output.

Yes, agree and would check the panels and/or controller as the output of 12 amps (or more) seems low for 400W of panels. Would expect to see and output >20 amps at times.

Are you getting heavy smoke in your area from the fires?

[OS2Dude]

Also could be a neighbor with a mast blocking a panel during part of the day, bird or other dirt on the panel, the angle to the sun being different, a corroded/loose/chafed wire or connector, etc.

[Robhwa]

Obviously, details on your system and performance numbers would help. I have several systems for research and have monitors for voltage, amps and watts from panels, from controller, and into and out of house and, in the case of boat and camper, starting batteries. Remember, watts = amps * volts, so 12 amps at 18-22 volts (typical voltage output from 12 volt panels) is >200 watts, which is pretty decent for a 400 watt system on average here in fogland. Amps is not power, it is only electron flow. Amps from solar panels to the charge controller usually measure less than amps from the controller to the battery when charging, but watts is always greater. If you have panels in series, which I do (up to 48 volts nominal) to reduce the wiring voltage drop, then that would be 12 amps at 36-44 volts and would be near 100% of the rated output of panels. 20 amps from an alternator at 14 volts, on the other hand is only 280 watts and shouldn't result in a higher charge state, but maybe require less time. Sounds to me like your solar controller's charging profile isn't correct if the batteries are charging fully (and holding the charge) with the alternator. What is the battery chemistry, and what is the final resting voltage (measured with no load after a few hours) after charging with each source? Are you sure your solar charging controller is set with the proper battery chemistry? I've also found that some of my charge controllers don't register fully charged even though my 100 amp Li batteries can discharge their full 100 amp hours. Li needs to go up to >14 volts to show fully charged, but at 13.5 volts it is 99% charged. Of course, don't discharge that much with lead acid systems to test them.

[waterman46]

Originally Posted by StuM

Assuming FLA, iIf you think your batteries have been charging to 100% in 2-3 hours, the odds are that they have been operating in a partial state of charge all along and they are seriously degraded.

Right.

The indication from the shorepower charger that is showing 100% charge, is possibly in error. That should be checked manually, by taking measurements of the battery with an accurate multimeter.

A 660aH FLA or AGM bank fully charged in good condition should be accepting less than 8A charge at 14.3V to 14.5V, and after resting a couple hours with no discharge it should then read about 13.4V to 13.6V with zero load.

Check those numbers but I think they are close.

[kmacdonald]

Originally Posted by StuM

Assuming FLA, iIf you think your batteries have been charging to 100% in 2-3 hours, the odds are that they have been operating in a partial state of charge all along and they are seriously degraded.

Yes, exactly!!!!

[Robhwa]

I'll assume FLA...before replacing batteries, which is an expensive and wasteful operation that many people make prematurely IMHO, please TEST the existing batteries. Voltage is useful, but can be misleading in measuring full state of charge performance.



Obviously, if the batteries are fully charged and voltage drops quickly with little or no load the batteries are probably shot.



Battery banks should be similar so the normal course would be to replace all of them.



Using voltage only is probably the single most common source of replacing batteries that still have useful life.



These little monitoring wonders...


https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1


are only $15 and are easy to install.



Yes you can use a Victron or similar for a lot more $, but any system should measure amps (and accumulated amp-hours), and/or preferably watts and accumulated watt hours, not just voltage.



You can then take your batteries to the indicated full state of charge with your alternator, then shut off charging, and monitor output. I use an inverter attached to a heat gun (like a hair dryer) to draw 100 amps (1200 watts) or so. If you are getting 40-50% of the nominal amps out and can recharge and do this again, the batteries are likely fine. Remember you should never discharge FLA batteries >50% nominal capacity except in emergencies.

[waterman46]

CORRECTION to earlier message, TYPO, open circuit voltage should be 12.6V not 13.6V.

[roland stockham]

First thing I would check is the panel diodes, if one has blown that could cause the problems you describe. I agree with the advice above, you need to do a systematic diagnostic on the system and post the results to get detailed help

[Compass790]

Originally Posted by StuM

Assuming FLA, iIf you think your batteries have been charging to 100% in 2-3 hours, the odds are that they have been operating in a partial state of charge all along and they are seriously degraded.

Not necessarily. It depends on the SOC when he started charging with the solar.
Note he did say it only took 2 hrs on the 20 amp shore charger so not much difference than 3 hrs on solar.
Depends on his overnite power usage.
However we need more info.
Actually I guess he means by fully charged that it has gone to float voltage.