My First System - For My RV - 24v - 9kW LiFePO4 - 2500w Inverter

[SolarAntics]

Hi y'all,

Getting closer to finishing my designs and could use some guidance. I am building a system for my RV and I unfortunately have not the most ideal components to work with and want to build with what I have. Batteries are miss matched a little, but the ones in series are the exact same. This should be a 24v system. Inverter and chargers are rated at 24v. Please see the diagram

I really don't want to add more bus bars than I need to, but unfortunately the charge controllers will need to be in a separate compartment, so bus bars there. Also, I can't connect the three negative cables from the banks to the shunt, so I figure I need a bar before that. Can confirm?

As far as fuses and breakers go I think I got all that I need. The 120v charger is for emergency generator charging only and is going to be disconnected unless in use (will cut off the MPPT when that is in use manually at breaker). The 120v charger has its own fuses.

Also am wondering about grounding. My understanding is to ground the batteries and the inverter for the AC side. As well as the panels would need grounding, but I think they are all set considering that they are the 400w Renogy solar suitcases (that's why I didn't add a ground there). I need to dig into documentation on that, and possibly a ground is needed at the solar charge controller. Thoughts?

Grounding Plan UPDATE: The manuals are giving me jack squat for answers or no answers at all - - at best they say ground if necessary. I think I should ground the MPPT and AC Charger with 8awg to their own negative bus bar; which goes to the main - and use 4awg to ground the inverter to the main - bus bar and then 4awg from the bus bar to the RV chassis. Logical?

@Supervstech
@Horsefly
@ScrotpusGobbleBottom
@wpns
\_ Would love to hear what y'all think of my progress and design since you all set me straight on my mix match battery bank dilemma thread a little while ago please and thanks!

Thank you for all y'alls help!

v5 - Decided to add a kill switch to terminate the batteries since these breakers at each bank likely will not be good enough to act as a cut off (worried about repeated use will eventually wear them to failure - they're cheap with 1/4" posts, so I imagine the rest of internal materials / components are skimpy too. I expect them to not break at 200a, likely more like 100a, which is fine because the BMS are rated at 100, and in this set up the most I should be pulling from each bank is like 50amps tops)

(Previous designs in attachments)

v4 - put grounds to bus bars
v3 - added balancers
v2 - made some silly corrections and added data
v1 - lost in the aether

 

[time2roll]

The 200 amp breakers on the battery seem redundant. 300A class T seems rather large. I would be closer to 150 amp. Keep in mind a class-T will pass 2x rating for close to a minute before it opens. No need for allowing for surge performance. And there is very little to no start surges with an RV, really only the A/C.

 

[B-ManFX4]

I would replace the battery breakers with battery switches. Being able to quickly and easily disconnect battery power when working or troubleshooting is handy.

 

[SolarAntics]

I would replace the battery breakers with battery switches. Being able to quickly and easily disconnect battery power when working or troubleshooting is handy.

Can't a breaker be used as a switch?

 

[SolarAntics]

The 200 amp breakers on the battery seem redundant. 300A class T seems rather large. I would be closer to 150 amp. Keep in mind a class-T will pass 2x rating for close to a minute before it opens. No need for allowing for surge performance. And there is very little to no start surges with an RV, really only the A/C.

I oversized them because the purpose was to prevent an extreme current causing arcing past a regular fuse or breaker. They are so expensive, I can't really afford for it to blow, only when it absolutely needs to prevent catastrophe.

 

[chrisski]

May need a battery balancer to avoid 12 volts from getting out of balance.

For the grounding batteries and AC of the inverter, just wire it as the inverter says. Easiest way for me was to plug the three wire AC from the inverter onto shore power with a plug I made from hard wired port to a shore power adapter. The case gets grounded to chasis. I did not tie any of the three AC wires to bus bars. That seems dangerous.

With 800 watts of power, I’d plan on 3 kWh of production on the shortest day of the year around the AZ latitudes if you move them twice to face the sun on a clear shortest day of the year. Could be 1.6 kWh if not moved and less if they can’t be out all day. That should be enough if you don’t use electric heat or electric refrigeration, or electric water heater.

With AC to DC conversion losses and the inverter maxed out like the propane heater on with the microwave on and a couple other things, could push more than 100 amps and trip the breaker.

 

[SolarAntics]

May need a battery balancer to avoid 12 volts from getting out of balance.

For the grounding batteries and AC of the inverter, just wire it as the inverter says. Easiest way for me was to plug the three wire AC from the inverter onto shore power with a plug I made from hard wired port to a shore power adapter. The case gets grounded to chasis. I did not tie any of the three AC wires to bus bars. That seems dangerous.

With 800 watts of power, I’d plan on 3 kWh of production on the shortest day of the year around the AZ latitudes if you move them twice to face the sun on a clear shortest day of the year. Could be 1.6 kWh if not moved and less if they can’t be out all day. That should be enough if you don’t use electric heat or electric refrigeration, or electric water heater.

With AC to DC conversion losses and the inverter maxed out like the propane heater on with the microwave on and a couple other things, could push more than 100 amps and trip the breaker.

Thank you, I forgot about the balancers. Am planning on using them for the series banks. My plan is to plug my shore power cable into the inverter. My system is not connected in anyway to the RV system aside when I do that. Will that provide the grounding? Do I still need to ground the inverter case (Is the case grounded already by the negative terminal to DC side? I suppose I should check manual..)?

 

[chrisski]

Thank you, I forgot about the balancers. Am planning on using them for the series banks. My plan is to plug my shore power cable into the inverter. My system is not connected in anyway to the RV system aside when I do that. Will that provide the grounding? Do I still need to ground the inverter case (Is the case grounded already by the negative terminal to DC side? I suppose I should check manual..)?

Check the manual.

All my RV type inverter have the case grounded to chasis. I forget the exact size, but I connected the chassis ground on the inverter to metal on the RV that I drilled and put a star washer between the ground lug and RV chassis to maintain a tight fit.

 

[B-ManFX4]

Can't a breaker be used as a switch?

If you are going to keep the Class T fuses why would you have a breaker too ? A switch is made to do just that - and a switch is going to be less expensive than a quality breaker.

 

[SouthernSolar]

I would parallel a 100ah battery with a 180ah battery, then run those in series 2p2s.

This would eliminate one battery balancer, and give you one common point to run your mid point voltage reading, assuming you use a victron smart shunt. Or you could just run a cable between the mid points of the two 12v series strings if they are close enough together and run you battery balancer and mid point voltage wire there.

Class T fuses are nice, but I would just have a breaker like this on each battey string. I use it as a switch, it's not like your going to be switching it on and off everyday. I don't know if it's considered a quality breaker, but it works. It's mainly to protect the battery if a positive cable gets grounded.

https://www.amazon.com/FELTECHELECTR-Circuit-Breaker-Switchable-Protector/dp/B0CMPHBJG8?th=1

 

[chrisski]

I would parallel a 100ah battery with a 180ah battery, then run those in series 2p2s.

This would eliminate one battery balancer, and give you one common point to run your mid point voltage reading, assuming you use a victron smart shunt. Or you could just run a cable between the mid points of the two 12v series strings if they are close enough together and run you battery balancer and mid point voltage wire there.

If you do put the 12 volts across one battery and not the other, the batteries get unbalanced.

A typical 12 volt load on a cold winter day for me is 200 watts from lights and propane heater blower motor. That is a lot to pull off one battery in a 24 volt system.

Class T fuses are nice, but I would just have a breaker like this on each battey string. I use it as a switch, it's not like you’re going to be switching it on and off everyday. I don't know if it's considered a quality breaker, but it works. It's mainly to protect the battery if a positive cable gets grounded.

https://www.amazon.com/FELTECHELECTR-Circuit-Breaker-Switchable-Protector/dp/B0CMPHBJG8?th=1

That most definitely is not a quality breaker and does anything from pop early, to late, to getting extremely hot.

May be fine for audio, but not for a electric power install.

 

[SouthernSolar]

If you do put the 12 volts across one battery and not the other, the batteries get unbalanced.

It must be a misunderstanding in the way I explained it. Their no puttling 12 volts from just one battery. I was trying to discribe this

 

[chrisski]

It must be a misunderstanding in the way I explained it. Their no putting 12 volts from just one battery. I was trying to describe this

You explained it just perfectly and were correct. I thought it was a 24 volt battery, not 12 volts :embarrass:

 

[SolarAntics]

I would parallel a 100ah battery with a 180ah battery, then run those in series 2p2s.

This would eliminate one battery balancer, and give you one common point to run your mid point voltage reading, assuming you use a victron smart shunt. Or you could just run a cable between the mid points of the two 12v series strings if they are close enough together and run you battery balancer and mid point voltage wire there.

Class T fuses are nice, but I would just have a breaker like this on each battey string. I use it as a switch, it's not like your going to be switching it on and off everyday. I don't know if it's considered a quality breaker, but it works. It's mainly to protect the battery if a positive cable gets grounded.

https://www.amazon.com/FELTECHELECTR-Circuit-Breaker-Switchable-Protector/dp/B0CMPHBJG8?th=1

Like this?


Isn't there a concern that the 100ah on the left won't balance properly? Also, the 100ah and the 180ah batteries are different manufacturers. Wouldn't this be problematic? @chrisski your thoughts too?

 

[chrisski]

Like this?
View attachment 260929

Isn't there a concern that the 100ah on the left won't balance properly? Also, the 100ah and the 180ah batteries are different manufacturers. Wouldn't this be problematic? @chrisski your thoughts too?

This would limit capacity of each pack to 100 amp hours each. The balancer would probably work a lot harder.

 

[SolarAntics]

This would limit capacity of each pack to 100 amp hours each. The balancer would probably work a lot harder.

Yeah, my eyes went cross for a second there. I'm sticking to the original plan in my original post and diagram. Good, point two different capacities wired in series will limit the series to the capacity of the smallest battery. Thanks for getting back to me so soon!


Technically what I have diagramed originally is 2s2p with the additional 24v battery added to the parallel. I don't think you can use a balancer across a parallel connection properly.


What I think @SouthernSolar is suggesting?



Or is it?



But again, I don't think battery balancing 4 batteries across a parallel works. I think you can only balance batteries with a single balancer per series - no matter which way you slice it 2s2p is still 2s. Also to note, batteries in parallel naturally balance / equalize.

 

[SolarAntics]

It must be a misunderstanding in the way I explained it. Their no puttling 12 volts from just one battery. I was trying to discribe this

View attachment 260565

Actually, I think I see what you are talking about. The shunt instead is a balancer. So string together the midpoints and use a single balancer connected to the parallel bus bars, and the midpoint string. I suppose its similar logic to this diagram, but 2s2p not 4...

Ok yeah, I think I get it. I'd have to either add additional bus bars, or route the 24v to the main bars and add its own killswitch.

 

[SouthernSolar]

This would limit capacity of each pack to 100 amp hours each. The balancer would probably work a lot harder.

no. you are creating two 280 amp batteries and then putting them in series.