Charging too fast, how much is too much?

wayneworkman2012wayneworkman2012 Registered Users Posts: 15 ✭✭

At home I have 600AH worth of 12 volt battery storage, it consists of 6 UB121000 batteries. Here's a link to the battery:

I have 2 Epever charge controllers, they are 40A each. I have 4 solar panels connected to each of those charge controllers, they are around 165W each. Link to the charge controller:

The batteries are all in parallel (with terminal fuse blocks too). I have the 2 charge controllers connected to the common positive (also fused).

On a sunny day, both charge controllers max out at 40A. They seem to do a curtailment so that no more than 40 amps goes to the batteries. So with both of these combined, I have 80A of charging going on.

I'm considering adding another of these 40A charge controllers and also another 4 solar panels connected to it. I'd attach this charge controller the same way I did the others, through a fused connection to the common positive, and the negative going to one of the negative poles.

My question: How much charging is too much? When is it more damaging than helpful? Also to consider is how very, very little sunlight I get in the winter time too. The low light in the winter time is most of my motivation for adding a third set of panels and charge controller.

If 120A is too much, I can add the extra 4 panels onto the existing charge controllers, they should curtail it back to 40A each as they do now so I'd get the benefits of those only in the winter, but all that electric would be wasted in the summer days.

Opinions? Thoughts? Suggestions?


  • Raj174Raj174 Solar Expert Posts: 650 ✭✭✭✭
    edited April 2018 #2
    According to the data sheet the AGM batteries you have can handle 30 amps. So 6 in parallel is 180 amps max current. I also think it's a good idea to check battery balance occasionally. The battery data sheet is attached.

    3600W PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 54.4V 207AH LiFePO4 no BMS, 4500W genset.
  • EstragonEstragon Registered Users Posts: 3,120 ✭✭✭✭✭
    My 350ah 48v (flooded) bank has nominal 94a arrays over two ~90a mppt controllers, plus a winter backup for another ~13a on a pwm. Combined 350ah/107a = ~C/3 potential charge rate. I've never seen anywhere near that, and I don't think the bank would draw that much unless severely discharged.

    Having the extra pv definitely helps in winter - even in summer it helps get a better charge on cloudy days.

    600ah/120a proposed potential charge rate would be C/5. As Rick notes, well within spec.
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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