Ready to order entire system - looking for last minute feedback on wiring diagram and components

Wildman13

New Member
Joined
Aug 30, 2021
Messages
42
My wife and I live on the road full time and are going to pick up our new RV in California and then drive to pick up the MPP and panels and install them. I need to order all the small stuff to a friends house to make sure it's there and ready to go when we arrive.

MPP HYBRID LV2424 2.4kw

370 Watt or 390 Watt panels x 2

*Wired in parallel. I'm open to hear specific examples of why these should be put in series. I have my current RV in parallel do to shading as we move around being full timers. The MPP will take up to 145V so series or parallel is fine.

SoK 12v 206ah Lithium batteries wired in Series for 24v

Ampper battery cut off switch

24V to 12V Buck Converter - uxcell New BIG-Size Converter DC 24V 12V 40A 480W

PV Breaker - ANJOSHI 30 Amp Circuit Breaker

Red/Black 250amp Bussbars

***on a 24v system pretty sure I only need half of this but this is what I could find, any reason not to go this high?

Battery Fuse - Windy Nation 150amp ANL Fuse

Battery Monitor - LNEX with Shunt, 500A

10awg PV wire (Panels will be 15' max from MPP)

1/0 Battery cable (batteries will be 1'-2' from MPP)

Raised solar brackets

*** Looks like I might have to build something out of L brackets and flat aluminum as I won't know if the panels will actually fit until I pick up the RV. The people we are buying it from are to old to get on the roof and the factory says I have 39"-40" width in the place I am looking at putting them and the panels are 39" wide. Any insight, thoughts, or ideas here would be great.

Did I miss anything?

Any of the components a no go? I got most of them of @Will Prowse site.

Thanks in advance to anyone who takes a look.
 

Attachments

  • Solar Schematic Image.png
    Solar Schematic Image.png
    182.7 KB · Views: 36

rmaddy

Full-time Solar-powered Trailer Life
Joined
Nov 16, 2019
Messages
1,189
What 12VDC loads do you have? Make sure you aren't trying to power slide outs with the 40A buck converter.

Consider a Class T fuse instead of the ANL fuse for the LiFePO4 batteries.

Make sure your chosen PV breaker can handle the Voc of your panels, especially if they are in series. Take into account cold temps since Voc increases in the cold.

You have proper fuses between the bus bar and the inverter and between the bus bar and buck converter.

The 250A bus bars are fine. Being larger than needed is not an issue. Wire the bus bars close to the batteries.

Your diagram doesn't show your battery monitor/shunt.

The 1/0 wire should go between the two batteries, between the batteries and bus bars, and between the bus bars and the inverter. You don't mention what wiring you will use to/from the buck converter. And you don't mention what AC wiring you will use to/from the AC in/out on the MPP.

Don't forget all of the various sized cable lugs and wire connectors.

Series vs parallel for the two panels. Parallel is of course better if there are shading issues. Just arrange the panels so only one is ever shaded. You don't want both partially shaded. Better if one is fully in the sun while the other is partially or fully shaded. Serial tends to give more charging early/late/clouds as long as neither is shaded.
 

Wildman13

New Member
Joined
Aug 30, 2021
Messages
42
THANK YOU so much for replying. I have tried to address each of your comments below. Please let me know if you have anything to add.

What 12VDC loads do you have? Make sure you aren't trying to power slide outs with the 40A buck converter.

No slide outs on the new rig. 12VDC loads are going to just be LED lights, water pump. propane fridge, stereo, maybe TV. Do you have a better recommendation?

Consider a Class T fuse instead of the ANL fuse for the LiFePO4 batteries.

I have a ANL on my current set up and saw that was what Will recommended on his site. I'll look at the T Fuse. I assume it needs to be the same rating

Make sure your chosen PV breaker can handle the Voc of your panels, especially if they are in series. Take into account cold temps since Voc increases in the

Yup, the Voc is 47-53 Voc per panel and the MPP can handle up to 145. I put that under the solar panel item above as I figured that would be a question people asked. I assume I did that correctly

cold.

You have proper fuses between the bus bar and the inverter and between the bus bar and buck converter.

The 250A bus bars are fine. Being larger than needed is not an issue. Wire the bus bars close to the batteries.

Your diagram doesn't show your battery monitor/shunt.

I forgot to add that, I was waiting to hear back from MPP to see if the unit had that feature built in. It doesn't lol. it will be off the Negative busbar and end of run. added new image with it in

The 1/0 wire should go between the two batteries, between the batteries and bus bars, and between the bus bars and the inverter. You don't mention what wiring you will use to/from the buck converter. And you don't mention what AC wiring you will use to/from the AC in/out on the MPP.

On the wiring details:

I was going to pick up the wire where I pick up the solar panels and MPP (Either Watts247 or Santan solar) to make sure I bought the correct length & size. I don't have the RV or either of those units in front of me and I wanted to make sure I got what worked with them; components and correct wire for length of run.

Buck converter:
The fuse box will be probably 12' away but not sure on wiring path until I get the unit. The buck converter has wires on it. Once I put all the components next to each other and see "exactly" where they will go in the passthrough I can use the wire attached or add to it. Image of converter and wires attached for visual

I need to have all of the other items shipped due to I don't know local availability and of course to save a few $$$. The cash I will save on shipping the panels will be way more than the extra spent on wire locally.

Don't forget all of the various sized cable lugs and wire connectors.

Same thing as the wire here. I can get a pack that will work on the 1/0 between busbars / battery etc.


Series vs parallel for the two panels. Parallel is of course better if there are shading issues. Just arrange the panels so only one is ever shaded. You don't want both partially shaded. Better if one is fully in the sun while the other is partially or fully shaded. Serial tends to give more charging early/late/clouds as long as neither is shaded.

One thing I forgot was a battery balancer.

Ian at Watts 247 said he had those as well. I'm going to go do some research on those unless you have a suggestion


Once again thank you for your input.

Lee
 

Attachments

  • Solar Schematic Image.png
    Solar Schematic Image.png
    189 KB · Views: 10
  • Buck converter image.png
    Buck converter image.png
    696.8 KB · Views: 10

rmaddy

Full-time Solar-powered Trailer Life
Joined
Nov 16, 2019
Messages
1,189
No slide outs on the new rig. 12VDC loads are going to just be LED lights, water pump. propane fridge, stereo, maybe TV. Do you have a better recommendation?
Those loads might be fine. Make sure that you will never need more than 40A (or 24V * 40A = 960W) at any given time since your buck converter can only handle 40A. If you run some water while the fridge is on while watching TV in a brightly lit room, you might need more than 40A, especially since it's all at 12V.

I have a ANL on my current set up and saw that was what Will recommended on his site. I'll look at the T Fuse. I assume it needs to be the same rating
It's a "Class T" fuse, not just "T" fuse. Yes, it would still be the same amperage.

Yup, the Voc is 47-53 Voc per panel and the MPP can handle up to 145. I put that under the solar panel item above as I figured that would be a question people asked. I assume I did that correctly
I was referring to the breaker between the panels and the MPP, not the MPP itself. You need to make sure the breaker can properly handle the 53V (or 106V if in series) of the panels. Many DC breakers can only handle 32V or 48V. Given your panels you need a breaker that can properly handle 60V/120V (parallel/series). MidNite solar has PV breakers rated at 150V.

it will be off the Negative busbar and end of run. added new image with it in
The shunt goes between the battery negative and the negative bus bar. Treat it like part of the battery wiring, not just another load hanging off of the bus bar. The whole idea of the shunt is that every electron being used goes through it.

Buck converter:
The fuse box will be probably 12' away but not sure on wiring path until I get the unit. The buck converter has wires on it.
I have the same buck converter. The wires it has are too small, at least for the 12V 40A output wires. When you get the correct wire for your runs, cut the buck converter leads a little shorter to minimize the amount of undersized wire that's in use.

One thing I forgot was a battery balancer.

Ian at Watts 247 said he had those as well. I'm going to go do some research on those unless you have a suggestion
I have two 206Ah SOK batteries in series just like you are planning. I am using the Victron BMV-712 battery monitor/shunt which, among it's primary features, allow me to monitor the mid-point voltage of my batteries. This basically lets me verify whether the two batteries are staying at the same voltage or not. Based on what I have seen over the last few months, the use of a battery balancer has not been needed. It can be useful if you have one. Just make sure the balancer you get is meant for LiFePO4 batteries and make sure it is meant to balance two drop-in batteries and not meant to balance individual cells.

When you get your two batteries, wire them in parallel (yes, I mean parallel) and use a good LiFePO4 charger (be sure you connect the charger so one lead is on one battery and the other lead is on the other battery) and get the two batteries fully charged to 100% SOC. Leave them in parallel for a day so they are both at exactly the same SOC (state of charge). With both batteries now at the same SOC you can connect them in series and they should stay balanced for quite some time.
 

Wildman13

New Member
Joined
Aug 30, 2021
Messages
42
Thanks again for the answers.

Those loads might be fine. Make sure that you will never need more than 40A (or 24V * 40A = 960W) at any given time since your buck converter can only handle 40A. If you run some water while the fridge is on while watching TV in a brightly lit room, you might need more than 40A, especially since it's all at 12V.

Have you had issues with yours? That would be a lot of draw from those items


It's a "Class T" fuse, not just "T" fuse. Yes, it would still be the same amperage.

Found a Blue seas one

I was referring to the breaker between the panels and the MPP, not the MPP itself. You need to make sure the breaker can properly handle the 53V (or 106V if in series) of the panels. Many DC breakers can only handle 32V or 48V. Given your panels you need a breaker that can properly handle 60V/120V (parallel/series). MidNite solar has PV breakers rated at 150V.

Interesting, I was told if I went Parallel that the amps was what mattered and volts if series. Maybe I am misunderstanding what they were referring to. Yeah it's hard to find a breaker above 48v that I can mount easily. I don't really want one that looks like it will mount in a circuit box as I don't have a box for it. I'll have to see what I can find. The 47.7 Voc Panels is really close to 48v lol

The shunt goes between the battery negative and the negative bus bar. Treat it like part of the battery wiring, not just another load hanging off of the bus bar. The whole idea of the shunt is that every electron being used goes through it.

I have the battery shunt as just a dead end on my current system and been told by other people and posts about this build that it goes in the same place. You are the first person to say otherwise. I have attached a picture of current system

I have the same buck converter. The wires it has are too small, at least for the 12V 40A output wires. When you get the correct wire for your runs, cut the buck converter leads a little shorter to minimize the amount of undersized wire that's in use.

Good to know, I thought those wires looked a little small but then it is 24v and 12v

I have two 206Ah SOK batteries in series just like you are planning. I am using the Victron BMV-712 battery monitor/shunt which, among it's primary features, allow me to monitor the mid-point voltage of my batteries. This basically lets me verify whether the two batteries are staying at the same voltage or not. Based on what I have seen over the last few months, the use of a battery balancer has not been needed. It can be useful if you have one. Just make sure the balancer you get is meant for LiFePO4 batteries and make sure it is meant to balance two drop-in batteries and not meant to balance individual cells.

When you get your two batteries, wire them in parallel (yes, I mean parallel) and use a good LiFePO4 charger (be sure you connect the charger so one lead is on one battery and the other lead is on the other battery) and get the two batteries fully charged to 100% SOC. Leave them in parallel for a day so they are both at exactly the same SOC (state of charge). With both batteries now at the same SOC you can connect them in series and they should stay balanced for quite some time.
I Just looked at Battery chargers and they aren't cheap. I literally only need to use them 1 time. uggh. Then I really have no where to store it. Is there an inexpensive one you recommend?
 

Attachments

  • Solar Board Layout.jpg
    Solar Board Layout.jpg
    848.6 KB · Views: 12

rmaddy

Full-time Solar-powered Trailer Life
Joined
Nov 16, 2019
Messages
1,189
Have you had issues with yours? That would be a lot of draw from those items
No but most of my stuff is running at 24V. My buck converter is only running a few small items and if it ever reaches 20A I'd be surprised.

Your water pump will be at least 15A when running. I don't know what load the fridge needs. Probably not much if it's propane. I have no idea what the stereo and TV would use. Do a quick power audit for your DC loads and be sure. I bet the stock DC panel in your RV is rated for over 120A. Doesn't mean you need that much but you want to really know.

Interesting, I was told if I went Parallel that the amps was what mattered and volts if series. Maybe I am misunderstanding what they were referring to. Yeah it's hard to find a breaker above 48v that I can mount easily. I don't really want one that looks like it will mount in a circuit box as I don't have a box for it. I'll have to see what I can find. The 47.7 Voc Panels is really close to 48v lol
Amps and volts matter. With wire you normally only worry about amps because most quality wire (insulation) can handle 600V. With most fuses and breakers in a 12/24V system you only worry about amps because most fuses/breakers can handle 36 or maybe 48V. But your PV breaker will be exposed to higher volts. The 47.7Voc is at STC (25ºC). It will get over 50V in cold temps.

And remember that this breaker is only needed as a PV disconnect so the breaker should be somewhere near the MPP so you can disconnect the solar panels when needed. The MidNite Solar breakers typically have DIN rail mounts. You can buy their "little" Baby Box breaker box and install it next to the MPP.

I have the battery shunt as just a dead end on my current system and been told by other people and posts about this build that it goes in the same place. You are the first person to say otherwise.
In the picture you posted are you connecting the battery negative cable to the end of the shunt where the "-" is labeled on the board and are you connecting the battery positive cable to the end of the fuse where the "+" is labeled on the board? If so then that is what I described. And that picture is not what you show in the 2nd diagram you posted when you added the shunt to the diagram.

I Just looked at Battery chargers and they aren't cheap. I literally only need to use them 1 time. uggh. Then I really have no where to store it. Is there an inexpensive one you recommend?
You might need it once a year to rebalance. I ended up buying the Victron Energy Blue Smart IP67 12V/17A charger. It's $133 but I know it's high quality and it works with LiFePO4. You can probably find cheaper ones. Try searching on this forum a bit. Plenty of people have asked about battery chargers.
 

Wildman13

New Member
Joined
Aug 30, 2021
Messages
42
Amps and volts matter. With wire you normally only worry about amps because most quality wire (insulation) can handle 600V. With most fuses and breakers in a 12/24V system you only worry about amps because most fuses/breakers can handle 36 or maybe 48V. But your PV breaker will be exposed to higher volts. The 47.7Voc is at STC (25ºC). It will get over 50V in cold temps.

I found this:
2P 250V Low-voltage DC Miniature Circuit Breaker For Solar Panels Grid System din rail mount(32A)
uxcell IP65 ABS Transparent Cover Power Distribution Protection Box for Circuit Breaker

This combo is only $42 and takes up less room than the midnight solar combo. However it's 250v not 150v, not sure if that makes a difference though. 145VDC is the max the MPP all in one will except. Meaning I'm not sure if this just a "power on/off switch" or if we're trying to get something below that 145VDC to protect the unit, if thats the case I don't see anything between the 48 and 145 in my searches.


In the picture you posted are you connecting the battery negative cable to the end of the shunt where the "-" is labeled on the board and are you connecting the battery positive cable to the end of the fuse where the "+" is labeled on the board? If so then that is what I described. And that picture is not what you show in the 2nd diagram you posted when you added the shunt to the diagram.

Ahh you are correct that is how I did do it. I found another picture with "ALL" the wires attached. I'm at information overload lol.
 

Attachments

  • Full Wiring.jpg
    Full Wiring.jpg
    61 KB · Views: 7

rmaddy

Full-time Solar-powered Trailer Life
Joined
Nov 16, 2019
Messages
1,189
However it's 250v not 150v, not sure if that makes a difference though. 145VDC is the max the MPP all in one will except. Meaning I'm not sure if this just a "power on/off switch" or if we're trying to get something below that 145VDC to protect the unit, if thats the case I don't see anything between the 48 and 145 in my searches.
The idea is to buy a breaker that won’t burst into flames due to too much voltage going through it. The voltage rating of the breaker is not there to protect the MPP.

The 250V breaker may be ok. But I wouldn’t cheap out on an important component. Fuses and breakers are not the place to save a few bucks. Why burn down a $100,000 RV by saving $20 on a breaker?
 

Just John

Photon Sorcerer
Joined
Aug 15, 2020
Messages
2,380
I suggest ordering more lugs and "consumables" than you need. Add a few extra feet of wire, order a spare fuse etc. Especially crimp on connectors, you will need extra.
 

Wildman13

New Member
Joined
Aug 30, 2021
Messages
42
I suggest ordering more lugs and "consumables" than you need. Add a few extra feet of wire, order a spare fuse etc. Especially crimp on connectors, you will need extra.
Yup learned that on the last go round. Getting the wire where I pick up the panels and MPP so I can buy that after I have everything laid out.
 
Top