Class A RV System

[AES]

Hi Folks from a newbe. I will be setting up a system on a 38' 2000 Newmar Dutch Star. Here is what I am planning on using.

Renogy DCC50S 12V 50A DC-DC On-Board Battery Charger with MPPT (Will suggested)
AiLi Battery Monitor Voltmeter Ammeter Voltage Current Meter 8-80V 0-100A (Will suggested)
10S ~ 24S Smart ANT BMS Bluetooth Lifepo4 Li-ion LTO Battery Protection Board
4 70A 100A 200A 300A Lipo LFP LTO Battery Android IOS
or 7-16S 100A Lipo LiFePO4 Lithium Battery Protection Board Smart Bluetooth BMS 12S (Will suggested)
2 sets of NEW 3.2V 190Ah lifepo4 battery LFP lithium solar 4S $644.00
(https://www.aliexpress.com/item/33035453389.html?spm=2114.12010610.8148356.2.1cef5c64tTrOfk)
Or
4 sets of 2019 NEW 4PCS 3.2V 105Ah lifepo4 battery $452.00.

My question, is the BMS just for 1, 12VDC battery set or for more the 1 set of 12VDC batteries?

 

[Geriakt]

It all depends how you set up your battery. If you are going 12 volt Lifepo i assume 4s BMS. If you build a 24 volt you need a 8s BMS. Then how big will your battery be? 4P4S and so on. For a 38ft rv you may have some longer cable runs where a 24 volt or even a 48 volt battery and inverter system would be more efficient.
With the size of your rig you will need a larger battery bank and larger inverter 3000 watts for to 5000 watts for 30-50 amp service. Larger battery pack means larger solar array means larger MPPT.
Do your homework and size your system appropriately.

Watch some youtube of other build of RVs of your size and learn from their short comings.

 

[AES]

Currently I have a 12VDC system so I am planning to stay with 12VDC. At this time not adding solar but when I do I will only add a suitcase solar array (most of the time I seem to be able to park in the shade). The battery compartment and electrial compartment are strieght across from each (5' apart approx) other.
I have a propane generator and will not feel bad if I need to run it to charge the batteries once in a while.
All Lights are LCD.
I have watched as many videos as possible of others switching to Lithium batteries and all I have seen are using Battleborn type of batteries. I am using 3.2VDC cells. Leaning towards 2 maybe 3 190ah batteries.
I currently have a small inverter that powers the TV/sound system and a plug for charging a laptop. I may not add another inverter.

I think I understand you are saying I need a BMS for each 12V battery as I am staying with a 12VDC system.
I am using 3.2VDC cells. Leaning towards 2 maybe 3 190ah batteries.

Thank you for your input! Hoping to get this project complete and on the road.

 

[Dzl]

I have watched as many videos as possible of others switching to Lithium batteries and all I have seen are using Battleborn type of batteries. I am using 3.2VDC cells. Leaning towards 2 maybe 3 190ah batteries.

I think I understand you are saying I need a BMS for each 12V battery as I am staying with a 12VDC system.
I am using 3.2VDC cells. Leaning towards 2 maybe 3 190ah batteries.

If you go with a 4s BMS (which you will if you want 12vdc) you need a BMS for each set of 4 cells connected in series (for 12v). This is not exactly the same as "a BMS for each 12v battery."

I think thinking of your system in terms of discrete "batteries" is more applicable to drop in batteries. If you are using individual cells it may be more constructive to think in terms of individual cells connected in series or parallel.

For example if you have 8 190ah cells and you want a 12v system, you could:
1. First make 4 pairs of parallel connected cells and then series connect those 4 pairs to create 1 12v "battery" out of 8 cells. This is called 2p4S and would allow you to use a single BMS and give you 380ah @ 12v.
2. First series connect sets of 4 cells then parallel connect the 2 sets of 4. This is called 4s2p and would require you to use two BMS's. This would also give you 380ah @ 12v.

Option 1 seems to be the more common configuration around here. Option 2 is what you were describing when you mentioned '2 or 3 12v batteries'.

My standard disclaimer applies, I'm passing on the knowledge I have accumulated, but I'm still new to this and far from an expert, you should not take my word for anything and do your own research! Best of luck with the build.

 

[Geriakt]

Yes to the above. I myself would use on 4s or 8s BMS and place more cells in parallel for a larger Amp Hour battery. Unfortunately many to most of the cheap Chinese BMSs cant handle the large amps and you will now need external controls to stop charging or discharging. So with this in mind you may be better off with an external BMS. Will just posted how to use an internal BMS connected to a 500 amp contactor and this would be the way to go. One thing to consider is the larger amp hour battery you go with will require a larger inverter and thus a larger compositor pre charge, so you will need to engineer in a pre charge resistor circuit.

 

[Dzl]

For a 38ft rv you may have some longer cable runs where a 24 volt or even a 48 volt battery and inverter system would be more efficient.

I second Geriakt's opinion to at least consider 24v. You won't have to switch everything over to 24v, you can leave all your RV wiring as is and use a 24v to 12v dc converter and use 24v for all your major connects (mppt to battery, battery to inverter, battery to 12v converter). It does add more complexity to the system, especially if you want to charge off the alternator, so I'm not saying its definitely the way to go, but its worth thinking hard about.

Yes to the above. I myself would use on 4s or 8s BMS and place more cells in parallel for a larger Amp Hour battery. Unfortunately many to most of the cheap Chinese BMSs cant handle the large amps and you will now need external controls to stop charging or discharging.

I agree with what I think you are saying here, but I just want to clarify for anyone else reading this (because the wording above is a bit confusing), A BMS could care less about your battery banks Capacity (Amp Hours), what BMS amperage ratings are concerned with is Current (Amps). If your loads and charge rate never exceed BMS specs it doesn't matter how large your capacity is.

One thing to consider is the larger amp hour battery you go with will require a larger inverter

Maybe I'm misunderstanding your point, but I think what you say here is inaccurate. An inverter is sized based on your 120v/240v AC needs (loads), not on the size of your battery bank.

 

[Geriakt]

I second Geriakt's opinion to at least consider 24v. You won't have to switch everything over to 24v, you can leave all your RV wiring as is and use a 24v to 12v dc converter and use 24v for all your major connects (mppt to battery, battery to inverter, battery to 12v converter). It does add more complexity to the system, especially if you want to charge off the alternator, so I'm not saying its definitely the way to go, but its worth thinking hard about.



I agree with what I think you are saying here, but I just want to clarify for anyone else reading this (because the wording above is a bit confusing), A BMS could care less about your battery banks Capacity (Amp Hours), what BMS amperage ratings are concerned with is Current (Amps). If your loads and charge rate never exceed BMS specs it doesn't matter how large your capacity is.




Maybe I'm misunderstanding your point, but I think what you say here is inaccurate. An inverter is sized based on your 120v/240v AC needs (loads), not on the size of your battery bank.

yes true but you cant use too small of battery and a larger inverter. They need to be sized appropriately. I read many posts where people hook one 100 ah battle born to a victron 3000 watt inverter and wonder why they get an amperage overload and the inverter shuts down.

My point is you must do your homework and size your system correctly or you will be wasting your money.

 

[Dzl]

My point is you must do your homework and size your system correctly or you will be wasting your money.

Definitely good advice!

 

[kernel]

Nothing wrong with dc to dc converters. They actually make everything run nice and happy. Imagine the mile of spagheti thin wire rv are wired with.

Having 13.8Vdc feeding all dc loads with low voltage protection is much better most days than having 11Vdc trying to make the trip.