solar chargers

[Bill 112]

I bought a Epever 12v 40 amp solar charger. I have 3, 12v 200 watt mono solar panels. I was told those panels may be pushing my charge controller limits. I heard you can wire two charge controllers together to handle more input power. So would I be doing better to buy another 40amp 12v epever controller and wiring them together. Would that give me the ability to handle my 3 solar panels or even 4 ....12v 200 amp panels. tks Bill

[Mike90250]

It is normal to connect more than one charging source to batteries.

Is your Epever 12v 40A a PWM or MPPT controller ?
MPPT controllers have a Minimum and Maximum voltage input range.
What is the output of the 200w panels. 30Vmp 40Voc ??

My thought is if you had one more identical panel, you could wire 2 in series, and then the 2 pairs in parallel. Aim one pair partly east, other pair partly west, and neither pair would simultaneously produce full power, allowing you to use your existing controller - IF your panels fall within the acceptable voltage ranges.

[Bill 112]

yes it is an Mppt.... will have have to go look at the output of the panels...all i know is they are 12v ...200 amp ...ok...Vmp is 20.4....Voc is 24.3

[Mike90250]

Hopefully, your Epever 12v 40A can manage 60 or 70V open circuit ( Voc ) that's the voltage 2 panels in series, produce on a cold frosty morning. The colder it is, the higher the voltage rises above the room temp of 24.3Voc


Vmp of 20V, 2 panels in series should be enough to activate the MPPT circuit and charge your battery.

[Bill 112]

Here are the stats on the epevers...

• Nominal system voltage:12/24VDC auto work
• Rated charge current :40A
• Rated discharge current: 40A
• Battery input voltage range: 8-32V
• Max. PV open circuit voltage:100V(at minimum operating environment temperature) 92V(at 25℃ environment temperature)
• MPP voltage range:V(BAT)+2V～72V
• Max. PV input power:520W(12V Battery) & 1040W(24V battery)

[Mike90250]

You are good with 2 panels in series for charging a 12V battery.. Now if you can get a 4th panel and set up a E-W virtual tracker ( 400w easterly, 400w westerly) you should be able to charge the batteries and run some significant daytime loads too.

[chrisski]

Those three 200 watt panels will max your controller out in ideal conditions. You are fine the way you are. After you're setup and have taken some measurements of actual power consumption to your power audit, and you can tweak the input. If you set up three in parallel, you'll need thicker than 10 AWG wire once combined. Not a huge deal. If you get a fourth, you can set them up two in series and two in parallel like described.

What you do need to look at is if your batteries can handle that much amperage. I currently have Flooded Lead Acid Solar Golf Cart Sized Batteries. Two of them at 12 volts can be charged at 30 amps max, which you'd need to limit the Epever, and Four of them would be 60 amps, which would be fine with the EPEVER. I'm upgrading to Lithiums and going to a 24 volt system, so there'll likely be no amperage limits, at least none that my 1700 watts of panels would reach.

I have three SCCs with my RV build. One is six hundred watts of panels similar to yours. Because they are not ideally oriented, I have seen them push only 30 out of 36 possible amps.

I have a second SCC that runs 400 watts of portable panels, because with angle of the sun, I wanted to start charging earlier, and be able to charge later than my flat roof panels allow.

I got sick of setting up the portable panels, so I put two more panels, 350 watts total on my roof. Those push up to 20 amps to the charger. Now unless its an extreme usage day, the portable panels need not come out.

[Bill 112]

Good info Mike and Chris. I will be charging 2, 12v 206ah lithium batteries. I will not be mounting my panels on the roof. I'm going to do a lot of boondocking, so I want to be able to put the panels out into the best sunlight wherever I am. I will be able to move, tilt or turn them anytime I need to. I am wondering if it is possible to wire 2 panels in parallel...giving me 400 watts at 12v...then wire those to the 3rd panel in series which would give me 400 watts at 24v. lol if I figured that correctly. So i would be feeding the controller 400 watts at 24v....it is a 40 amp 12/24v controller. Would it be able to charge my 2 lithium batteries which i was planning on wiring in parallel to give me 12v at 412ah. All these calcs. are driving me nuts, but it is fun...lol. Let me know if this will work. I have been mainly concerned if the controller will let me take in 24v from the panels an charge the two 12v lithium batteries without harming anything. Tks Bill

[Mike90250]

Groups of panels HAVE to be identical. 2 parallel & 1 Series will not work,

20V of PV generally is NOT enough to activate the 12V MPPT charging circuit, and the controller will fall back to PWM charging.

[chrisski]

This is a good article on mixing and matching solar panels in series and parallel with math that explains why although you can hook those three panels like you ask, the third panel adds no power to the system with math:

https://solarpanelsvenue.com/mixing-solar-panels/

For my VIctron MPPTs, they require 5 volts over battery to charge, and I am able to charge at 18 volts with four 100 watt panels and in good sun, charging amps can come out really close to the max output of 30 amps. 24 amps in at this higher voltage, and 30 amps out. Not sure if its MPPT mode or PWM, but the charging gets done.

[Bill 112]

Wow so much to learn and understand. Tks much guys. So if I have this right....I can take 2 of my 200w 12v panels and wire them in series...connect them to my 12/24v 40amp mppt controller...then connect that to my 2 12v 206ah lithium batteries and everything is good. Should I wire the batteries in series or parallel. I'm thinking parallel since all DC equip in my RV is 12v.

[chrisski]

As Mike told me when I was learning, the Magic of MPPT is you can choose what's best whether series or parallel. PWM is picky and requires certain voltages in parallel.

In general, Parallel is better until amperage for wires becomes an issue. 10 AWG is good for about 30 amps, and the MC4 connectors are rated for 30 amps.If you have 3 panels, would be good to do calculations for three parallel combined somehow like with fuses and Y connectors and then feed to the SCC. If one panel gets shaded, the other 2 work good. In series, voltage is higher and amps are lower so it helps with amperage issues, but when one panel gets shaded it seriously reduces output. I have a series of 3 panels, and when I put my hand over one panel, the entire series drops by 25%, but when I shade one entire panel in series, output drops by as much as 3/4.

[Bill 112]

ok tks.....so the batteries...right now I have 2 12v 100ah wired in parallel....I'm thinking I should do the lithiums the same way...I have 2 lithiums coming next week. They are 12v 206ah each.

[Mike90250]

Your system voltage is set by the loads the inverter sees:
<1000w = 12V battery
1000w - 2000w = 24V
> 2000w = 48V This keeps the battery wire within safe amperage expectations.

If you have small loads for long times, it's better to build capacity by going to higher voltages and using batteries in series, than batteries in parallel