Mixing Solar and Grid charging

OS2Dude

I have a bank of 2 Group 27 AGM batteries.  Initially I just had a ProMariner Sport 20 battery charger plugged into shore power.  A few times a breaker tripped (Dock or Boat) and charging stopped.  Once this killed the batteries because I forgot to turn off the 12v fridge....  So I bought a Renogy 100 W mono panel with Renogy Wander PWM controller to be a 'backup' in case it happened again.  

I connected the solar panel to the bank as well as the charger.  Came back after a few weeks and could barely crank the engine.  I never had that issue before.  The time on the 110v devices was still accurate, so no loss of power while I was away.

QUESTION:  Is it OK to have both solar and a charger connected to the bank at the same time?  ProMariner said to ask Renogy about it, Renogy has not yet responded.  

Estragon

Yes, it's generally ok to have multiple charging sources connected to a bank. 

Depending on how far the bank was discharged, how long it sat that way, and ambient temps, it may have suffered some permanent loss of capacity.  Adding solar may help prevent further damage, but may not reverse any that's already happened.

I'm wondering how/why a breaker is flipping though.  Assuming just a 20a@12vdc (~2a@120vac) charger is on the circuit, this may indicate an issue with charger or related wiring?

OS2Dude

After killing the two AGMs with the cooler, we replaced them with new.  I did not have an issue trying to start the engine until after I added the solar to the setup.  The only draw on the batteries when we're gone is the bilge pump and the ghost voltage for the power indicator light on the TV.  (I just leave the 12v switch for the dual-voltage cooler off all the time now.)

If both the charger and controller are trying to push 14+ volts into the battery, how does the one source differentiate the battery's true voltage from the 14+ volts coming from the other source since they are all connected to the same terminal? 

Figured out what was tripping the breaker(s).  I was at the boat when a storm came through.  The power went out for a few hours and when it came back on everything in the boat was trying to start.  Boat has 30A service.  We had added marine A/C to the boat a few years back, and recently I got the hot water heater working again.  It seems now when it all (A/C, Water Heater, Cooler Conversion, Mini-Fridge, Charger and Anything else plugged into the 110 outlets) tries to come on at the same time it draws over the breakers trip voltage.  I recently added a separate 30A service dedicated to the A/C to rectify this issue.  

Estragon

That makes sense.  

BB.

AGM batteries generally charge at ~14.4 volts (at 75F)... And you probably want to float them at ~13.4 to 13.6 volts. If you push 14.4 volts 24x7 at them, they will over charge and wear out the catalysts sooner (with AGM, you cannot add distilled water back to them). Once charged, holding them at 13.6 volts (or whatever the manual from the Battery Mfg. says) is "float service" and they should do fine.

100 Watts of solar is fine for float charging the batteries... But if your loads (sump pump, indicator lights) are significant, and you do not have an AC float charger, then you simply may be drawing more energy than the 100 Watt panel can restore... For example, a 100 Watt panel mounted flat near Atlanta Georgia:
http://solarelectricityhandbook.com/solar-irradiance.html

Atlanta
Average Solar Insolation figures

Measured in kWh/m2/day onto a horizontal surface:

Jan	Feb	Mar	Apr	May	Jun
2.50	3.12	4.28	5.19	5.80	5.59
Jul	Aug	Sep	Oct	Nov	Dec
5.72	5.17	4.46	3.91	2.82	2.36

December at 2.36 hours of sun per day:

• 100 Watt * 0.61 DC system eff * 2.36 hours of sun (Dec) = 144 WH per day
• 144 WH per day / 12 volt = 12 AH

If you have a 4 amp sump pump:

• 12 AH / 4 amp load = 3 hours average maximum runtime per day for December

And I would suggest that if your pump runs more than 1/2 that amount (1.5 hours per day), you are expecting too much from the 100 Watt solar array in December.

Or if you have other phantom loads that were 24 hours per day...

• 12 AH per day / 24 hours per day = 0.5 amps maximum

Or 1/2 that would be 0.25 amps 24x7 would be pushing it if you are not there every few days to check up on battery charge (and/or if you have 4 days of heavy clouds).

Anyway--Some math to start the discussion and set expectations.

If you have a 120 VAC float charger, then you may have other issues (problems with charger/wiring. Problems with solar charger and/or other loads you did not expect, etc.).

Do you have a DC Current Clamp DMM (digital multimeter) that you can measure the current in the various parts of your system?

https://www.amazon.com/gp/product/B019CY4FB4 (mid-quality AC/DC clamp meter)
https://www.amazon.com/gp/product/B07546L9RT ("good enough" for our needs)

-Bill