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diy solar

mppt charge controller recommendation

John Wolf

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Oct 14, 2020
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I have a new 12v 200ah 2560W ampere time battery that has a built in 200amp BMS 400amp max, building a basic solar charging system. How do I calculate what is the best mppt solar charge controller for this battery, considering the bms amperage? Planning on using 3000/6000 pure sine for dc to ac. I have 600w of panels, 800w down the road. If you have a recommendation for a particular mppt charge controller for these specs, please drop it here! Thanks!
 
The charge controller you choose is mostly dependent on your solar panels, their specs, and their arrangement. Post how many panels you have, their wattage, Voc, Vmpp, Isc, Impp, and the voltage temperature coefficient. Also post how you want to arrange them (series/parallel). And tell us the absolute coldest temperature you are ever going to encounter with the solar panels.
 
Coldest it will get here is in the low teens dF, but that is rare, avg for winter is 43dF. I have 6 x 12v/100w solar panels monocryst, specs...
  • Max Power at STC: 100W
  • Open Circuit Voltage: 21.3V
  • Short Circuit Current: 5.83A
  • Opitmum Operating Voltage: 18V
  • Optimum Operating Current: 5.58A
  • Operating Temperature: -40℃ to 90℃
  • Dimensions: 35.6x25.9x1.2 in
  • Weight:14.3 lbs
 
Coldest it will get here is in the low teens dF, but that is rare, avg for winter is 43dF. I have 6 x 12v/100w solar panels monocryst, specs...
  • Max Power at STC: 100W
  • Open Circuit Voltage: 21.3V
  • Short Circuit Current: 5.83A
  • Opitmum Operating Voltage: 18V
  • Optimum Operating Current: 5.58A
  • Operating Temperature: -40℃ to 90℃
  • Dimensions: 35.6x25.9x1.2 in
  • Weight:14.3 lbs
If you have not purchased your inverter yet, check out the all in ones, as they include rhe MPPT charge controllers. The MPPT needs to support 130VOC for your 6 panels if you are putting them in series.
 
800W panels / 2560 Wh battery = 0.31C charge rate
That's fine over a certain range of temperature.
BMS would disconnect for extreme cold, like 0 degrees C. But charging 0.31C at 5 degrees C would be too much.
Will battery be kept warm?

If you get a hybrid/all-in-one, it should have programmable charge rate. You could set it for a current that is 0.15C, acceptable at lower battery temperature (about 10 degrees C and above). It would let more power through from the panels when needed for inverter loads.
I don't think any of the charge controllers implement a current vs. temperature curve, so I think people should set a current limit and temperature limit (rectangular operating area) that remains within safe limits.
I figure 0.15C is enough to fully recharge the battery during daylight. Other applications might benefit from fast charging, but for PV home/RV power, make it gentle.

The same limiting can be accomplished with some individual charge controllers. Victron plus battery shunt and a controller is the one I've heard of. But a hybrid has all in one box so it has the measurements needed.

 
Given the specs for those panels with a 12V battery you have several options.

You will get about 60A output from a charge controller so you want a controller that can handle 60A output to the battery.

Depending on the layout of the panels, you need to worry about the highest Voc you will see for the lowest temperature you could encounter (not the average but the coldest it could ever get). The following represent the max input voltage required by the controller:

6S - 150Voc
6P - 30Voc
2S3P - 50Voc
3S2P - 75Voc

The last two layouts are best since you get enough voltage and it can handle some partial shading better.

With 8 panels you would get close to 80A output from the charge controller to the battery. If you plan to have 6 panels now and 8 later you should get a controller that can handle the 80A to allow for the growth.

With 8 panels you would probably want to do:

2S4P - 50Voc
4S2P - 100Voc

Or you could use two charge controllers and put half of the panels on one and half on the other. Lots of options.
 
I have a 12v200ah battery but all the systems I can find are either 12v100ah battery, the 200ah battery systems all seem to be 24v. I need a system that will maximize the 200ah for my 12v battery. I'm not trying to live off solar, I'm just trying to keep my kid's insulin cold if shtf, and food, etc. Running freezer, fridge, fan, laptop, cellphones, lamp, etc., simple survival stuff. I'm not an engineer so I don't need the numbers and specs, I just need a system that will stay on and not drop off so we don't lose months of insulin. I thought the 12v200a battery was a good buy and would provide power longer, and is expandable in future. Is there a 12v charging system to maximize this battery performance that is expandable, or did I buy the wrong battery? Do you suggest buying another one to series up to 24v?
 
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Once you get to higher amps or longer-term backups with moderate to higher amps is where the advantages of 24V batteries come into play.

If your load is going to be around, say, 10A/120V your discharge at 12V is 100A. Or ‘static’ like two hours with that battery.

However, a small fridge and basic lighting won’t be anywhere near that 10A/120V. You really need to assess the power required to be accurate but a wild-hat guess is that if you can add a second 200Ah battery you’ll have one to two days of backup. With 500W of charging from solar that can make sustainable ‘forever’ if your backup fridge is <75W. But that’s a guess based on using a low-watt fridge like I have. (I have 400W solar and ~300Ah useable storage right now)

You can get more accurate by doing the assessment of your desired loads
 
Once you get to higher amps or longer-term backups with moderate to higher amps is where the advantages of 24V batteries come into play.

If your load is going to be around, say, 10A/120V your discharge at 12V is 100A. Or ‘static’ like two hours with that battery.

However, a small fridge and basic lighting won’t be anywhere near that 10A/120V. You really need to assess the power required to be accurate but a wild-hat guess is that if you can add a second 200Ah battery you’ll have one to two days of backup. With 500W of charging from solar that can make sustainable ‘forever’ if your backup fridge is <75W. But that’s a guess based on using a low-watt fridge like I have. (I have 400W solar and ~300Ah useable storage right now)

You can get more accurate by doing the assessment of your desired loads
Thank you so much for your insight! I need to run a fridge, 5cf deep freezer, led lamp, a small fan, device chargers, survival stuff...mostly for food and insulin. It's hard to do an energy audit because I'm trying to build something I can expand on in the future as nec, without changing out expensive components. I live in the SE so there is plenty of sun, and as I get my feet wet with solar, I will add batteries down the road for more capacity, so there's that too. Thank you again for replying, most of this makes sense but a few things are a little intimidating.
 
my system is very similar to what you are looking to do.
it is all 12v, 8-100w panels, 1-200ah 2560w LiFePO4 battery, and a Renogy Rover 60a mppt solar charge controller.

I only run a frig and some led lights, it covers that but just barely.
it all works reliably but I think I would change to a 100a mppt and 1200watts of panels.
 
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