About to build my first LifePO4 pack

[RV Adventure Couple]

I drew out a diagram of the setup in my head, would appreciate if someone could chime in and tell me if it is correct. Thanks in advance.

 

[Turd Furguson]

the battery protect should be applied to everything touching the battery. However, they don't pair well with inverters... recommended practice is to wire the inverter direct to the cells via fused link and use the remote circuit of the BP to trigger on/off.

Alternatively, a cheap BMS can achieve the same result while also providing HVD protection for charging..

 

[RV Adventure Couple]

I have the epever 150v 40a CC with the MT50 to program the charge profiles. I have been building the system over the course of a year and am trying to use items I have already purchased along with the new things that have come with the lifepo4 battery purchase round.
So you are saying the positive from the charge controller needs to be connected to the battery protect? Even if it is programmed to Will's suggest lifePO4 charge profile?

 

[Turd Furguson]

the BP only passes discharge current - You should add the battery monitor but not the charge controller. Sorry if my last comment wasn't clear - I was referring to any device that draws current from the battery.

the charge controller will have a small self-consumption value, so there's a risk of over-draining the batteries in a situation where the panels aren't charging for a significant timeframe.

A BMS seems better suited than the BP in your scenario.

 

[RV Adventure Couple]

Ah okay, thanks for the input. This setup is going into our RV which we are pretty much full time, and I keep a close watch on the systems. I forgot to put on the diagram I will be putting a cut off switch between the battery and the BP. Also I have a 50A breaker going from the CC to the battery that I disconnect when we aren't traveling. So were those the only discrepancies you saw in the diagram?

 

[MisterSandals]

Also I have a 50A breaker going from the CC to the battery that I disconnect when we aren't traveling.

Is your plan to leave panels connected to SCC?

 

[Turd Furguson]

I did, but they're some major points:

• The inverter can't connect to the BP. you need to determine how to handle LVD.
• You need a solution for pre-charging the capacitors on the inverter.. there are other threads about this.
• The CC could drain power infinitely damaging the batteries.
• You have no protection should the CC fail beyond a 50a surge. (i.e. overvoltage)

Consider a holistic solution where you don't need to intervene and won't risk damaging equipment under any circumstance. You don't want a situation where you've damaged cells because you went to sleep without flicking a switch.

 

[RV Adventure Couple]

I am under the impression to power a 3000 watt inverter I would need at least a 250a BMS. Or build out 2 - 12v batteries and put 150a BMS on each. Since what I have ordered is 8 cells.

 

[RV Adventure Couple]

Is your plan to leave panels connected to SCC?

I have a on/off from the panels to the CC also.

 

[MisterSandals]

I am under the impression to power a 3000 watt inverter I would need at least a 250a BMS. Or build out 2 - 12v batteries and put 150a BMS on each. Since what I have ordered is 8 cells.

Does your inverter have a low voltage cutoff? It should do what you appear to be doing with a BMS.
Most folks only use a BMS on the charge side.

 

[RV Adventure Couple]

Does your inverter have a low voltage cutoff? It should do what you appear to be doing with a BMS.
Most folks only use a BMS on the charge side.

Inverter cuts off at 10.6 volts

 

[MisterSandals]

Inverter cuts off at 10.6 volts

And unless configurable, a BMS would "likely/probably/YMMV" cut off at 2.5v. (10v).

 

[RV Adventure Couple]

And unless configurable, a BMS would "likely/probably/YMMV" cut off at 2.5v. (10v).

If I were to use a BMS, I was under the impression a 3000 watt inverter needed a 250a BMS on the 8 cell pack or 2 - 12v packs with 150a bms in parallel?

 

[MisterSandals]

If I were to use a BMS, I was under the impression a 3000 watt inverter needed a 250a BMS on the 8 cell pack or 2 - 12v packs with 150a bms in parallel?

I dunno. I only use a BMS on the charge side. Maybe some else knows about what you are trying to do... of which, I cannot understand why.

 

[RV Adventure Couple]

I dunno. I only use a BMS on the charge side. Maybe some else knows about what you are trying to do... of which, I cannot understand why.

Well I am still learning so I guess I have my setup all wrong

 

[RV Adventure Couple]

I dunno. I only use a BMS on the charge side. Maybe some else knows about what you are trying to do... of which, I cannot understand why.

Okay I ordered a BMS - https://www.aliexpress.com/item/4000425316662.html?spm=a2g0s.9042311.0.0.6d204c4dI5cMcc
Should I return the battery protect since I will have the bms?

 

[LukeVader]

Looking forward to your video on the cell build. I just watched your solar install you uploaded 3/29

I am under the impression to power a 3000 watt inverter I would need at least a 250a BMS. Or build out 2 - 12v batteries and put 150a BMS on each. Since what I have ordered is 8 cells.

 

[LukeVader]

Okay I ordered a BMS - https://www.aliexpress.com/item/4000425316662.html?spm=a2g0s.9042311.0.0.6d204c4dI5cMcc
Should I return the battery protect since I will have the bms?

I watched this video and it looks like he has 2 battery protects and he's using LiFePo4 batteries. Maybe I'm not seeing it right?

 

[RV Adventure Couple]

Looking forward to your video on the cell build. I just watched your solar install you uploaded 3/29

Thanks, yea the video won't be so much as a how to but rather a what I did.

 

[MisterSandals]

Should I return the battery protect since I will have the bms?

You can still use a battery protect if you have other non-inverter loads that are not going thru the BMS.

I am still a little mystified why you want a BMS to cut power to an inverter that will have already shut down .6v earlier.
I guess if a single cell got below 2.5v and the battery was above 10.6v (way out of balance), the BMS would shut down first.

Like i said earlier, like most folks, i only charge thru the BMS, not discharge.

 

[RV Adventure Couple]

You can still use a battery protect if you have other non-inverter loads that are not going thru the BMS.

I am still a little mystified why you want a BMS to cut power to an inverter that will have already shut down .6v earlier.
I guess if a single cell got below 2.5v and the battery was above 10.6v (way out of balance), the BMS would shut down first.

Like i said earlier, like most folks, i only charge thru the BMS, not discharge.

You can still use a battery protect if you have other non-inverter loads that are not going thru the BMS.

I am still a little mystified why you want a BMS to cut power to an inverter that will have already shut down .6v earlier.
I guess if a single cell got below 2.5v and the battery was above 10.6v (way out of balance), the BMS would shut down first.

Like i said earlier, like most folks, i only charge thru the BMS, not discharge.

I was trying to build the system without a BMS because I already had bought previously a 12v 3000 watt inverter. So I was trying to keep the system 12v. I can program my CC and I figured with a battery protect, I could get away with not having the BMS and just balance the cells a couple times a year. I understand the CC can drain the battery and damage the cells, but it has never even gotten close to draining my 100ah deep cycle lead acid battery and when we are not using the camper I turn the breaker that's between the CC and the battery off as well as the on/ off switch between the solar panels and the CC. From what I have seen in Will's videos if I wanted to put a BMS on my bank to power my 12v 3000 watt inverter, the BMS's would have to be rather large. I am barely learning so I have feed myself a ton of information so maybe I didn't retain something correctly.

 

[RV Adventure Couple]

You can still use a battery protect if you have other non-inverter loads that are not going thru the BMS.

I am still a little mystified why you want a BMS to cut power to an inverter that will have already shut down .6v earlier.
I guess if a single cell got below 2.5v and the battery was above 10.6v (way out of balance), the BMS would shut down first.

Like i said earlier, like most folks, i only charge thru the BMS, not discharge.

Could I see a picture of your setup maybe that will help my ape brain understand. Also I am not understanding why the battery protect cant go between the battery and the inverter.