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Sizing solar charge controller for 1.65kw solar panel array wired in parallel

Offgridder8888

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Jul 5, 2022
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Hi guys, I am building an off grid solar system with 3x 550 (Voc=49.9 A=13.3) watt solar panels (total of 1.65 kw) wired in parallel. They will be feeding 2x Lifepo4 batteries (2x24V100AH wired in parallel). Do you guys recommend I get three solar charge controllers for each solar panel? Or can I just use one solar charge controller for all three panels?

If I get a solar charge controller for each panel, they should be at least 30amp (550watts/24V=22.9 x1.25=28.65amps) charge controllers with Vmax of 50V correct? If I get a solar charge controller for all three panels, it should be around 100amps (1650watts/24=68.75A x 1.25=86amps) with Vmax= 50V. I am leaning towards having 3 solar charge controllers for increased redundancy. What are the advantages/disadvantages of having 3 solar charge controllers vs just 1 solar charge controller? Thanks for all the help guys I really appreciate it!!!
 
Whatever charge controllers you get must have a max PV input voltage of at least 55V or even 60V. Voc goes up as the temperature goes down. If you get an SCC with a limit of 50V then your 49.9V panel will exceed the 50V at about 76ºF. Not good.

1650W / 24V = 69A. So if you went with one charge controller you probably want one with an output current of 60A, maybe 65A. You will rarely get the full 1650W from the panels and your batteries will spend time closer to 27V.

If you go with 3 separate charge controllers then 3 20A controllers would work. In either case make sure it supports 60V or more.

What is the 1.25 for in your calculation that results in 28.65A or 86A?

One controller is much simpler but the higher amps requires much thicker wire, fuses, and probably a combiner box. Three smaller ones give some redundancy but it's 3 times the wires (but smaller wires) and you don't need fuses or a combiner box.

I'd price each setup and see what the total cost is for each. If the difference is enough that might be your deciding factor.
 
The 68.75A is too high. Most of your charging is going to occur at higher voltage, so 1650/27.6 = 59.8A, round up to 60A. You'll need MPPT charging totaling 60A.

Entirely your preference.

1 EA on 3 MPPT
2 on one MPPT, 1 on another MPPT
3 on a single MPPT

Advantages are redundancy.
Disadvantages are increased cost. 3 smaller will likely cost more than a single MPPT. You'll have triple the wiring and a fuse/breaker for each MPPT to battery connection.

Note that with 3 panels and with typical MPPT voltage limits, if you put 3 panels on one MPPT, they will need to be in parallel.
 
Thanks for all the fantastic replies guys! How important is it that I get a charge controller with Vmax of 60V? The reason is that I live in the tropics where it rarely gets below 76 degrees. Most of the charge controllers that I can find have Vmax of 50V. If I wanted Vmax of 60V, I will have to source from China which will be alot more expensive. Would it be dangerous or a fire risk to use solar charge controllers where Vmax is 50v on the few days that temperature drops below 76? Or would it just be less efficient? I can live with less efficiency but if it's a fire risk then I am willing to pay more. Thanks again guys!!
 
If the panel Voc exceeds the max PV input voltage of the charge controller you run the risk of damaging the charge controller. It won't likely be a fire risk but your solar will stop working and you may need to buy a new charge controller. If you can only get a 50V charge controller, get solar panels with a Voc at 48.0V. A panel with a Voc of 48.0V won't exceed 50V until you get down to 53ºF/12ºC. Even 48.5V is good for 59ºF/15ºC.
 
Thank you Rmaddy!! According to this guide, I'm suppose to include a safety factor of 1.25 when sizing the solar charge controller:

Example: A solar array is producing 1 kw and charging a battery bank of 24V. The controller size is then 1000/24 = 41.67 amps. Introduce a safety factor by multiplying the value you have found by 1.25 to account for variable power outputs: 41.67 x 1.25
Link: https://solartown.com/learning/sola...ke the power produced by,1000/24 = 41.67 amps.



What do you guys think? Would 60amp be enough? I found a 60amp solar charge controller with maximum pv voltage of 190v so it would work (if I don't include the 1.25 safety factor). I want to pull the trigger soon I'm buying it but I'm worried about the safety factor issue? Am I worrying about nothing?

Thanks again for all your help I really appreciate it!!!
 
You definitely do not need a 125% safety factor when calculating the needed output amps for the charge controller. Many people deliberately go over the value. This is known as over paneling. It allows you to get more power in less sunny conditions. The controller's max output amps is simply the most amps you will get out of the controller. For example, with a 60A controller it can make use of up to 1632W if your battery is charging at 27.2V. Even if you had 2000W of solar panels, it would be perfectly fine. It's just that if current solar conditions allowed the panels to produce more than 1632W at the moment, the charge controller would still only pull 1632W from the panels. The extra potential simply goes unused. And that's if it even needed the full 60A. If your battery was full and you had no loads running, the charge controller won't pull any watts from the panels no matter how much sun there was.

A 60A controller that has a max PV input voltage of 190V will easily handle your 3 panels in series or parallel.

One last thing to consider is your battery bank's recommended charge current. Make sure the two batteries in parallel can handle 60A of charge current (most likely they will).
 
Ok I can probably swap out the battery with another one in their store, I found this one that has:

Charge currentStandard charge: 10 Approx 15 Hour
Rapid charge: 20 Approx 7.5 Hour
Max. charge current50A

It comes with a 20 amp charger, but since it allows a max charge current of 50A, can I swap out the 20 amp charger with a 50 amp charger? I can't find any batteries in their store with more than 50A max charge current. Would I be ok with a max charge current of 50 amps with a 60 amp charge controller? I won't be able to put all 60amps in, but it should charge the battery pretty quickly still, and there's no inherent dangers with this setup, correct?

Battery link: https://www.aliexpress.com/item/400...1e16582659960532729e8132!10000002522051510!sh

Thanks again everyone for helping this newbie!
 
If you will have two batteries in parallel then with a 60A charge controller you just need each of the two batteries to support 30A or more. Then combined in parallel they will accept 60A or more. If each battery supports 50A then you can charge at up to 100A with two in parallel.

Also note that some charge controllers can be set to limit their charge current. So your proposed 60A charge controller might allow you to tell it to limit its charge current to 40A, for example. It would be a waste to do so long term but let's say you get two batteries that each support 20A of charging then you can tell the charge controller to limit itself to 40A. Then you can later add a 3rd battery and now your bank of 3 supports 60A of charge current. Then you can tell the charge controller to use the full 60A. That's just an example for planning purposes if needed.
 
I have bad news, they said they can't change the order for the battery. If the battery is only 10amp charge, what can I do to make this work? Can I use 3 x20amp chargers and wire the batteries in parallel? Would the batteries just charge slowly? Would I be wasting excess solar energy? Thanks for all your help guys!
 
As I said, if the batteries can be charged at 20A each then 3 in parallel can be charged at 60A which means you can use the 60A charge controller with 3 of those batteries.
 
The implication is if you apply > 10A to the battery, you will trigger over-current protection of the BMS or damage the cells.

100Ah battery that can only be charged at 10A is very irregular. It's possible they say 10A because that's the limit on the provided charger. You might find that the cells and BMS can actually handle more.

Unfortunately, ordering things from Ali often results in disappointment.
 
Thanks for your reply Rmaddy! Unfortunately the charge current is only 10amps for these batteries, so I would need 6 of these in parallel to handle the 60amp solar charge controller. If I had 2 of these batteries wired in parallel, can I charge it with 3 x20amp solar charge controllers instead of 1x60amp solar charge controllers?

Thanks to both of you for all your help I truly appreciate it!!!
 
The implication is if you apply > 10A to the battery, you will trigger over-current protection of the BMS or damage the cells.

100Ah battery that can only be charged at 10A is very irregular. It's possible they say 10A because that's the limit on the provided charger. You might find that the cells and BMS can actually handle more.

Unfortunately, ordering things from Ali often results in disappointment.
I agree that it's irregular and you might be right. Here are the exact specs of the batteries that I bought :

Deep Cycle 24v 100Ah with waterproof case LiFepo4 lithium battery pack with 100A BMS for golf trolley golf cart camper caravan motorhome solar energy RV+29.2V 10A charger​


Description

  • Voltage : 24V
  • Capacity : 100Ah
  • Chemistry : lifepo4
  • Size:415*335*180mm / 166*272*355mm
  • Charge voltage : 29.2V
  • Discharge Cut-off Voltage:20V
  • Charge Current:10A
  • Continuous discharing current:100A can be customized
  • Battery pack weight: about 12kg
  • Recharge cycle : More than 2000 times

Intelligent BMS protections:

Temperature protection

Over-current protection

Over-charge protection

Over-discharge protection

Short-circuit protection


Features

A. Long Cycle life
B. Stable Performance
C. High Safety
D. Customized Batteries
E. Non-Toxic, environmentally-friendly product.


Application​

Wind-Solar Energy Storage system
Solar street lights
Off-grid energy storage
Household energy storage
Telecom backup system
Emergency backup energy sources
Uninterruptible power system
Mobile base stations
Grid load shifters
and more...


Packing List:
1.1pcs 24V 100Ah Lifepo4 Battery pack

2.1pcs 29.2V 10Amps LiFepo4 battery charger with EU US AU or GB plug.
 
If I had 2 of these batteries wired in parallel, can I charge it with 3 x20amp solar charge controllers instead of 1x60amp solar charge controllers?
If the batteries really can only take 10A each then with 2 in parallel you could only use 1 20A solar charge controller. You really need better batteries.
 
Ok good news, after a lot of pleading, they are going to let me change the order to this 24V200AH lifepo4 battery. They also said I can swap out the 20amp charger to a 50 amp charger. Would I have a problem with a 60amp solar charge controller feeding into the 50amp charger of the battery (even though the battery can handle up to 80 amps).

Thanks for all your help guys I really appreciate it!!!

********

Parts Included:

1.24v 200ah lifepo4 lithium battery, 150a bms board build inside.
2.29.2V 20A Charger (with EU/US/UK/AU AC charger plug you can choose)



At the.ItemSpecification
1load cut-off voltageDC 29.2 V
twoRated voltage24 V
3Nominal capacity200 Ah
4direct current unloader150A (Can be customize)
5load currentStandard charge: 10 approximately 20 hours
Quick charge: 20 approximately 10 hours
6Default Loading Method0.2cc (constant current) load at 73v, then cv (constant voltage 58.4v) load until the load current decline to less than 0.02c
7Max. load current80A (Can be customize)
8Max. discharge current2150A (Can be customize)
9Max. Current Pulse200A (2s) (Can be customize)
10Discharge cut-off voltage17.5 V
11Cell3.2v lithium
12Operating TemperatureCharging: 0°C-45°C
Discharging: -10°C-60°C
13storage temperature-10°c + 45°c
14battery weightapprox. 28 kg
15battery size521*238*218mm
16battery output voltageFrom 17.5v-29.4v
17BMS built inYea
 
If you have a battery that can be charged at 50A and you put 2 of them in parallel then you can charge at 100A.
 
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