OK need a little help with my first system

[jfrasier71]

Ok been following solar and your videos, but I think I may have borked it. I am moving into my RV for a while, and I work on my computer alot. So I wanted to set up an independent system just to run my desktop computer, my cellular modem and my monitor (maybe a couple led lights hence the 12v fuse box). I wanted this system separate from my other regular electrical for now.
I have 2 mono 200w 24v panels, which are in series for 400 watts. My battery set up is 8x 3.2v 150ah lithium (got that from one of your videos so thanks) that I have in series to make a 24v 150aH battery. I tested with my multimeter so all good there. The problem I have right now, is I think I got the wrong controller. I got the Epever 40a MPPT. So I am wondering, is that max amps or will it scale down? my panels only put out 5.32a.

Since I was just running my computer, modem and monitor I went with a Pure sign 1500w 3000 surge inverter, but dammit I got a 12v rather than a 24 so I am going to return that and get the 24v inverter that you recommend.

I have done some reading and it seems with a MPPT controller, if I choose to I can run the 24v into the 12v batteries although there is some loss so I would prefer to keep it 24v

I have attached my diagram so far to give you an idea of my setup. I have not hooked anything up yet thank god, I just have the panels installed and the wiring run to where I need it. Any help I would so much appreciate.

 

[MisterSandals]

I got the Epever 40a MPPT. So I am wondering, is that max amps or will it scale down? my panels only put out 5.32a.

EDIT: just picked up on 24V battery

The EPEver 40A charger charges at a max of 40A.
400W solar / 28V charge voltage = 14.25 charging amps max from your panels

 

[MisterSandals]

if I choose to I can run the 24v into the 12v batteries although there is some loss so I would prefer to keep it 24v

No. You have a 25.6V battery. Are you going to have an 8S battery or 2x 4S in series. Your drawing is unclear but it should only matter if you need 1x 8S BMS or 2x 4S BMSs.

Don't worry about the panel voltage, the MPPT takes the input voltage and amps and does the work creating a charging voltage that you set (optionally) at the max amps possible (or lower as you choose in the settings, optionally).

 

[jfrasier71]

The EPEver 40A charger charges at a max of 40A.

Awesome so it will still work with my smaller 24v system than

No. You have a 25.6V battery. Are you going to have an 8S battery or 2x 4S in series. Your drawing is unclear but it should only matter if you need 1x 8S BMS or 2x 4S BMSs.

Don't worry about the panel voltage, the MPPT takes the input voltage and amps and does the work creating a charging voltage that you set (optionally) at the max amps possible (or lower as you choose in the settings, optionally).

Right now I have them all just in series. Would it be better to connect them into 2 4s? I was going to split it into 2 4s if I went 12v so that would double my amp hours connecting the 2 in parallel.
I was looking into a BMS whether I needed it or not, but I read that with a MPPT and lithium you did not need one. Was that incorrect? Or does that just work with say a single battery with MPPT? I am assuming since I built my own battery with multiple ones in series that I will still need a bms?

 

[MisterSandals]

Awesome so it will still work with my smaller 24v system than

Yes, just fine.

Would it be better to connect them into 2 4s?

No, 8S is much simpler.

I was looking into a BMS whether I needed it or not, but I read that with a MPPT and lithium you did not need one.

Wrong. You need a BMS.

Search results for query: do i need a bms

diysolarforum.com

 

[MisterSandals]

but I read that with a MPPT and lithium you did not need one.

Link?

 

[jfrasier71]

Yes, just fine.

No, 8S is much simpler.

Wrong. You need a BMS.

Search results for query: do i need a bms

diysolarforum.com

Is there one you could recommend?

 

[jfrasier71]

Link?

Lithium battery management systems, are they required?

In this blog article you will discover why it is highly recommended to a use a lithium battery management system (BMS) to ensure safety and longevity.

www.lithiumbatterysystems.com.au

I googled it using "do you need a bms for lithium batteries" and that was the answer, the first paragraph saying you don't need it. But actually after seeing the link and reading the article I guess maybe they should edit that google answer that comes up. It is pretty misleading. I am glad you said something so I didn't hook it up without a bms.

"Well, actually, no – lithium batteries don't need a battery management system (BMS) to operate. You can connect a few lithium battery cells in series to make a battery pack without any sort of lithium battery management system, and it will be able to power various loads and be charged just fine"

I did pick up a Victron Battery Protect 12/24v 65a. Thought that would protect the battery without the BMS. I did not even think about the fact that the batteries Will was working with in that video already had the BMS inside of it. I know it was stupid, but this is all new to me. I can figure out a diagram and use the right wires that are recommended, but I am still learning about the controllers, the panels and the batteries. I do GREATLY appreciate the time your taking to help me.

 

[MisterSandals]

It is pretty misleading. I am glad you said something so I didn't hook it up without a bms.

A BMS helps to keep you from destroying your battery (easily).

I ran without a BMS for about 6 months powering a greenhouse. The reality of it was that I was the BMS... i was responsible for monitoring the cell and battery voltages 24/7. Its possible but not without risks. Conservative charging and discharging along with battery monitors that have alarms help quite a bit.

Is there one you could recommend?

I like Overkill. Its the same as the JBD. There are a couple others with similar designs and reputations. Daly is a popular one but i do not like them. I have a couple Overkills, a couple Dalys and a couple Chargerys.
A smart BMS with bluetooth connectivity is a necessity as far as i am concerned.

You will need to size the BMS for your largest expected loads (usually an inverter is the largest consideration).

 

[jfrasier71]

A BMS helps to keep you from destroying your battery (easily).

I ran without a BMS for about 6 months powering a greenhouse. The reality of it was that I was the BMS... i was responsible for monitoring the cell and battery voltages 24/7. Its possible but not without risks. Conservative charging and discharging along with battery monitors that have alarms help quite a bit.


I like Overkill. Its the same as the JBD. There are a couple others with similar designs and reputations. Daly is a popular one but i do not like them. I have a couple Overkills, a couple Dalys and a couple Chargerys.
A smart BMS with bluetooth connectivity is a necessity as far as i am concerned.

You will need to size the BMS for your largest expected loads (usually an inverter is the largest consideration).

TYVM, I will take your recommendation on the Overkill, they have a 8 cell 100a for a really good price. Not to mention, the smartphone monitoring is a plus as well.

 

[jfrasier71]

Ok so got my BMS from Overkill just have one small question. I get the diagram for where the wires go, and the blue wires. But my batteries basically look like the 8 below, they are not in a case or anything that has additional terminals. So my question is, where do I connect the 2 black wires since I have no additional output terminal?

 

[MisterSandals]

But my batteries basically look like the 8 below, they are not in a case or anything that has additional terminals. So my question is, where do I connect the 2 black wires since I have no additional output terminal?

Can you post a pic of what you have? Do you have 8 cells connected in series to make a 25.6V battery?

 

[MisterSandals]

So my question is, where do I connect the 2 black wires since I have no additional output terminal?

Okay i see what you are asking, the 2 black wires from the BMS (right?) go to your negative bus bar or whatever your loads will be.

 

[upnorthandpersonal]

But my batteries basically look like the 8 below, they are not in a case or anything that has additional terminals. So my question is, where do I connect the 2 black wires since I have no additional output terminal?

Doesn't matter that yours aren't in a case. You have a main positive from your total battery (the main positive terminal from your cells) and a main negative one, which is the two black leads from the BMS. Remember that your BMS has to be able to disconnect your battery: it does that by interrupting the current in the negative path of your battery. So you have this:

Main positive ----> (Cell 1) | | | | | | | | | (cell 8) <----> (Blue Wire) |BMS| (Black Wire) <---- Main negative

You should consider the BMS just a part of the battery.

 

[jfrasier71]

Can you post a pic of what you have? Do you have 8 cells connected in series to make a 25.6V battery?

Awesome thanks! I assumed that was the case, but I didn't KNOW. Would rather be sure before doing something wrong and blowing my battery or something lol.

 

[jfrasier71]

Well just wanted to post this. Big thanks to MisterSandals for your help. Everything seems to be working, I have my overkill synced to my phone and controller is working as it should. Now I just have to plug in my panels tomorrow and I am finally done.

 

[upnorthandpersonal]

Now I just have to plug in my panels tomorrow and I am finally done.

DIY batteries and solar are never done

 

[MisterSandals]

One thing about this breaker, its a cheap audio breaker and will likely run hot and/or trip before its rated amps.
Bussman and Blue Sea are the typical recommended quality breakers.

 

[jfrasier71]

One thing about this breaker, its a cheap audio breaker and will likely run hot and/or trip before its rated amps.
Bussman and Blue Sea are the typical recommended quality breakers.
View attachment 82394

Already have a 50amp ready to switch it out. They all arrived yesterday with my 12v fuse box. I assumed it would be ok just to test the panels since they are only putting out 5 amps and there is no loads on it yet. But thanks for the warning 8) I checked and they were not those brands they are Anjoshi 50amps I picked up on amazon though.