Solar + MPPT + Battery Setup Check

[Fluqz]

Hey guys, I would really appreciate a bit of help here with my setup for my car. Im kinda new to this, got some knowledge here and there, but Im unsure about a few things.

Setup:
So I wanna use 2 Solarpanels which have 100Watts, 36V and 2.5A. I have a MPPT device which can handle 100V and 15A and says its for 12v or 24 systems. I wanna load a 12v Lithium LiFePo4 100Ah Battery.

So my questions are:
1. How does the MPPT loader decides if its for 12v or 24v system? Is there a switch? Or does it recognize the battery's voltage?
2. I was reading that the Battery should be charged with 5-50Amps. If I use a series connection with my two solarpanels I would only have 2.5A. Is that a problem? Should I go with a parallel connection?
3. Is there anything I could do better? I used higher voltage Solarpanels, because I heard this would help with loading, because if its in shadow and voltage drops below ~13v the MPPT device wont work anymore, which makes sense.
Im open for any recommendations

Really appreaciate your help!
Thanks

 

[Rednecktek]

Hey guys, I would really appreciate a bit of help here with my setup for my car. Im kinda new to this, got some knowledge here and there, but Im unsure about a few things.

Setup:
So I wanna use 2 Solarpanels which have 100Watts, 36V and 2.5A. I have a MPPT device which can handle 100V and 15A and says its for 12v or 24 systems. I wanna load a 12v Lithium LiFePo4 100Ah Battery.

That controller is just barely adequate. Those panels are capable of ~200w which would be 200w / 12v = 17a. Realistically you should be fine but you'll never be able to add more panels to that.

So my questions are:
1. How does the MPPT loader decides if its for 12v or 24v system? Is there a switch? Or does it recognize the battery's voltage?

When you connect it to your battery (first step always) it's going to auto-detect your voltage and start its charging program for whatever profile it defaults to at whatever voltage it detects. The only thing you should have to do is connect with the app and make sure it's set to the FLA charging profile since that's what the battery in your truck is.

2. I was reading that the Battery should be charged with 5-50Amps. If I use a series connection with my two solarpanels I would only have 2.5A. Is that a problem? Should I go with a parallel connection?

You'll have up to 15a coming out of the controller since that's what it's designed to max out at. The wonderful thing about MPPT is that it's trying to max out the watts available. Series will be fine since it gives the controller more voltage to start working its magic with, but if you have shading concerns (like parking next to a tree or something) then parallel will be more forgiving. Either way will work, there are pro's and con's both ways.

3. Is there anything I could do better? I used higher voltage Solarpanels, because I heard this would help with loading, because if its in shadow and voltage drops below ~13v the MPPT device wont work anymore, which makes sense.

The higher voltage will help with lower light conditions as it'll hit the 15v it needs to start charging in less light. As for the shadows issue, there's really no panel that can make effective power in the shade.

Im open for any recommendations

Really appreaciate your help!
Thanks

Any time. Welcome to the forum!

 

[Fluqz]

@Rednecktek Thanks alot for your explanations!

Those panels are capable of ~200w which would be 200w / 12v = 17a.

That means if I have more watts from the panels, I will need more Amps, because its going to convert it to 12v to feed the battery, right?. Solar Watts / MPPT Output voltage.

What does the voltage value on the MPPT device mean? Is it how much voltage it can handle comming in from the Panels? If I connect the panels in series, I would have a voltage of 36v + 36v = 72v right? That works with two, but will already be a problem if I have 3 panels in series, because it would be over the MPPT's 3 * 36v > 100v? Is that correct?

What about parallel connection? I could use as many solarpanels as I want, the voltage would stay 36v. Would I need even more Amps?

I was just looking for a MPPT Device with 100V 30A and saw that there the "Load" +- is missing. Only +- for Battery and PV. Why is that?

 

[Rednecktek]

@Rednecktek Thanks alot for your explanations!


That means if I have more watts from the panels, I will need more Amps, because its going to convert it to 12v to feed the battery, right?. Solar Watts / MPPT Output voltage.

Yup, exactly. The amp rating on a SCC is what it can output to the batteries at $Nominal Voltage, so in your case that guy can pump out a maximum of 15a. It doesn't matter if it's 12v or 24v, it's still 15a.

What does the voltage value on the MPPT device mean? Is it how much voltage it can handle coming in from the Panels? If I connect the panels in series, I would have a voltage of 36v + 36v = 72v right? That works with two, but will already be a problem if I have 3 panels in series, because it would be over the MPPT's 3 * 36v > 100v? Is that correct?

Right again. Solar panels will also produce more voltage as they get colder so you really want to stay 20% under the maximum voltage limit so if it gets cold out you don't fry the controller. Your math is also correct in that if you did 3 in series you'd have 108v and the SCC would possibly be damaged.

What about parallel connection? I could use as many solarpanels as I want, the voltage would stay 36v. Would I need even more Amps?

Right again and you got the hat trick! The only way to use more panels would be to do them in parallel which would keep you at 36v, or a 2s$p which would keep it at 72v, which would be pointless since you're already maxing out the amperage your SCC can put out anyways.

What you really CAN'T do is mix & match an oddball pile of panels, I.E you can't do 2 in series (72v) and then parallel in a single panel from there (36v) as they'd drop to the lowest common voltage and you'd nerf the hell out of your panels.

 

[Rednecktek]

Stupid slow internet and double posting...

 

[Fluqz]

Awesome I think I got it with your help! Thanks alot! Nice Profle pic btw! :D

Just one last thing. I was just looking at a MPPT Device with 100V 30A and saw that there the "Load" +- is missing. Only +- for Battery and PV. Why is that? Do you know what it does? Couldnt find a good explanation for it.. A friend told me its to have a direct 12v output that could be used for LED lights or USB adapters, but now I was reading its "to enable the user to control a load either manually or automatically using certain algorithms." and "can also be used as a safeguard to disconnect the load under low battery or overload conditions."

 

[Rednecktek]

Yeah, the LOAD ports are low amperage ports for devices that need power all the time short of the low voltage cutoff setting in the SCC. As an example, I use mine at my camp to power some 12v LED lights in the utility room so when I get there at night I have some light to see by while I'm turning the system on. Most of the time they're limited to 5 or 10 amps at whatever the battery bank voltage is so no inverters or motors or pumps or the like. They can often be programmed to run for X-hours, or only work when the panels are getting light (day/night) or vice versa, things like that.

Also, is there a reason you're stuck on Victron? There are a LOT of other options that will turn PV volts into Battery volts for significantly less money. Unless you want all the Bluetooth wizzies & gizzys and dog grooming and window washing features they're supposed to have. EPEver is a very well regarded brand and about 1/3 to 1/4 the price per amp. Just a thought.

 

[Fluqz]

the LOAD ports are low amperage ports for devices that need power all the time

Ah okay good, so thats unfortunate that the 100/30 controller doesnt have load ports.

is there a reason you're stuck on Victron?

No I actually was just thinking Im not gonna pay the extra money for the bluethooth shizzle. Victron was just having the best ratings, but Im gonna checkout EPEver, thanks!

The only way to use more panels would be to do them in parallel which would keep you at 36v

Whats the calculation here? Im thinking of putting my panels in parallels because I got some shading concerns after all..
Having the 2,5A and 36V per 100W, I still get 200 / 12 = 17A out of the MPPT controller, right? But I have to stay below the max. PV short circuit current. 2,5A * 2 = 5A would be below. So I could still use max. 350Watts / 12V = 29A of my panels in parallel with a 100V/30A controller with 35A max. PV short circuit current.

Really appreciate your help on this

 

[Rednecktek]

Whats the calculation here? Im thinking of putting my panels in parallels because I got some shading concerns after all..

In parallel the voltage stays the same and the amperage increases yes. In series it's the voltage that increases and amperage stays the same.

Having the 2,5A and 36V per 100W, I still get 200 / 12 = 17A out of the MPPT controller, right? But I have to stay below the max. PV short circuit current. 2,5A * 2 = 5A

If it lists a maximum PV current limit then you'll need to pay attention to that also. My internet connection is timing out trying to load anything on the manual for that guy but it's the first I've heard of a documented max current limit. Most of the time it'll just let you draw whatever the controller's limit is (in your case 15a) and just clip the rest.

 

[Fluqz]

Homage of the Photon Sorcerer ?