Planning first LifePo4 battery build - am I on the right track?

[mateo]

Hello, I'm converting a short bus and am planning on building my own battery bank out of prismatic cells. I'm new to this, and I believe I have thoroughly done my research... But I still have a few uncertainties and wanted to get some advice/verification before I start ordering things, as I'm not 100% sure if I'm spot on.

My plan is:
I already have two 230w panels.
Looking to purchase 8 176Ah 3.2v cells from Xuba on alibaba (only $583 shipped!)
I then want to wire them into one 352Ah 12v battery, so I only have to use one BMS and one case, etc.
I'm terrible with vocabulary, but I'd put two cells together to make one, then treat it as if I have 4 and wire as normal (2 parallel 4 series??)
As for the BMS I was originally looking at the Chargery BMS8T-300A 4.0, but I'm not set on this.
I will have a 1500-2000w inverter, and won't have any appliances that draw more than 1000w.
Haven't decided on a charge controller yet, but I'm guessing I should get a 35-40 amp one. Are the Victrons worth the price tag? Renogy?

This seems like the cheapest way to get 350ah, but I haven't seen anyone else do 2p4s with 176Ah cells so I'm hesitant for no good reason (or for good reason)

The thing I'm least sure about is the BMS.
If my battery capacity is above 300ah, is the 300a bms too small? If I understand correctly, the bms is less relevant to how much capacity the batteries have, and more to do with how much draw is needed at once?
And since I'm just having a 1500-2000w inverter that won't often go above 1000w, is that overkill? I believe a 1500w pull through the inverter would equate to about a 150a pull from the batteries. Is that correct? And therefore the 300a bms would more than handle that? Could I get away with a smaller one or is that ill-advised?

I've also heard some mixed reviews about the Chargery and it being very hard to program/set up and finicky to work with. Is there a better (still affordable) BMS that would work for my application?
I just came across this: Heltec BMS with a 330a option and it seems like it could work?
Looks like Daly also makes a high amp bms

Also, is the one battery method a smart move? Something about putting everything in one battery and if it fails I have zero power seems a bit risky.. but also I'd love to save the money on building two separate 176Ah batteries. So leaning towards the one large battery.

Am I missing anything important? I think the bms comes with temp sensor so that's covered. I've heard of some people putting a fuse somewhere in their battery, but haven't been able to find too much info on it. I know fuses go elsewhere in the electrical system. Is the battery one necessary/advised, and if so, where does it go?

Thanks for reading! Any advice is greatly appreciated!

 

[wmills_92105]

Victron gear is very well regarded.

The BMS rating is based on your load not on the pack size. You need to handle the max of charging and discharge.

1500w / 12v = 125amps.

 

[wmills_92105]

Is the bus originally 12v or 24? 8 calls can be a 12v or a 24v pack.

 

[Marinepower]

Your use case might be a good candidate for the BMS made by Electrodacus (the "SBMS0"). Will P. reviewed it at some point last year.

It comes with optional solar charge controllers for around USD 30 for up to 20Amps - and you can add as many of these as you like. However, your panel voltage will have to roughly match your battery voltage, so that may mean a 24v battery set up for your 230w panels. If you have no 12v loads, then 24volts may be preferred for your inverter efficiency.

Anyway, check out the Electrodacus website for details.

If you go this route, you will want to choose an inverter with a remote on-off switch.

 

[HRTKD]

I already have two 230w panels.
Looking to purchase 8 176Ah 3.2v cells from Xuba on alibaba (only $583 shipped!)
I then want to wire them into one 352Ah 12v battery, so I only have to use one BMS and one case, etc.
I'm terrible with vocabulary, but I'd put two cells together to make one, then treat it as if I have 4 and wire as normal (2 parallel 4 series??)
As for the BMS I was originally looking at the Chargery BMS8T-300A 4.0, but I'm not set on this.
I will have a 1500-2000w inverter, and won't have any appliances that draw more than 1000w.
Haven't decided on a charge controller yet, but I'm guessing I should get a 35-40 amp one. Are the Victrons worth the price tag? Renogy?

This seems like the cheapest way to get 350ah, but I haven't seen anyone else do 2p4s with 176Ah cells so I'm hesitant for no good reason (or for good reason)

2p4s sounds good initially, but there are some good arguments for switching that around to 4s2p. I started down the 2p4s route but was convinced (eventually) to go 4s2p.
1. Better monitoring of individual cells with 4s2p. A cell could be completely fried in a 2p4s configuration and you would never know it.
2. More amps. With two BMS you get double the amp rating.
3. Redundancy. You can take on 4s battery offline while the other carries the load (within its rating of course).
4. It's easier to move a single 4s battery than a single 2p4s battery. 45 lbs vs 90 lbs in my case.

Downsides of 4s2p
1. More expense. A second BMS and more cable.
2. There is a concern that if one battery unknowingly goes offline, you could stress the remaining battery.

I'm using the Overkill Solar 4s 120 amp BMS and they are working well for my needs. The vendor support is excellent and based in Florida.

 

[mateo]

Thanks for the responses everyone!

Is the bus originally 12v or 24? 8 calls can be a 12v or a 24v pack.

I was originally planning on going for a 12v system with 352Ah as opposed to a 24v with 176Ah.

Your use case might be a good candidate for the BMS made by Electrodacus (the "SBMS0"). Will P. reviewed it at some point last year.

It comes with optional solar charge controllers for around USD 30 for up to 20Amps - and you can add as many of these as you like. However, your panel voltage will have to roughly match your battery voltage, so that may mean a 24v battery set up for your 230w panels. If you have no 12v loads, then 24volts may be preferred for your inverter efficiency.

Anyway, check out the Electrodacus website for details.

If you go this route, you will want to choose an inverter with a remote on-off switch.

Is there a reason that I shouldn't go with a 12v setup with my panels? I was planning on doing as much wiring is 12V as possible (lights, chargers, I'll be taking a full set of m18 power tools and there's a DC charger I was planning on using instead of charging those off AC which seems like a big waste) and only using the inverter for the light appliance use, namely a mini fridge, small electric water kettle, and occasionally an 800w instant pot or a 600w nutribullet.

But I also hadn't yet considered the fact that my panels are a much higher voltage than the battery system. But my thinking was that shouldn't be an issue because of a charge controller. These are the panels I have, they're rated at 41v

Thanks!

 

[HRTKD]

The general rule of thumb that has been suggested here on the forum is that if your inverter is rated for 3000+ watts then a 24v system is appropriate. Your inverter is only 2000 watts so you're fine.

Going with 24v presents added cost for step down converters so you can power the 12v loads. A bus conversion shouldn't have high amperage loads like a fifth wheel does (landing/leveling jacks, generator starter, etc), so a 24v system would be easier to implement in your case. The step down converters wouldn't have to be heavy duty.

 

[mateo]

2p4s sounds good initially, but there are some good arguments for switching that around to 4s2p. I started down the 2p4s route but was convinced (eventually) to go 4s2p.
1. Better monitoring of individual cells with 4s2p. A cell could be completely fried in a 2p4s configuration and you would never know it.
2. More amps. With two BMS you get double the amp rating.
3. Redundancy. You can take on 4s battery offline while the other carries the load (within its rating of course).
4. It's easier to move a single 4s battery than a single 2p4s battery. 45 lbs vs 90 lbs in my case.

Downsides of 4s2p
1. More expense. A second BMS and more cable.
2. There is a concern that if one battery unknowingly goes offline, you could stress the remaining battery.

I'm using the Overkill Solar 4s 120 amp BMS and they are working well for my needs. The vendor support is excellent and based in Florida.

I honestly hadn't thought much of a 4s2p setup, mostly due to cost factor.. but this would slightly solve the high amp bms needed and I could use two smaller ones instead.
I've heard good things about the Overkill but had chosen against it due to the 120a max.

 

[mateo]

The general rule of thumb that has been suggested here on the forum is that if your inverter is rated for 3000+ watts then a 24v system is appropriate. Your inverter is only 2000 watts so you're fine.

Going with 24v presents added cost for step down converters so you can power the 12v loads. A bus conversion shouldn't have high amperage loads like a fifth wheel does (landing/leveling jacks, generator starter, etc), so a 24v system would be easier to implement in your case. The step down converters wouldn't have to be heavy duty.

Yes I will only have a 1500w to 2000w inverter. I should be well over my regular use with a 1500w, but was planning on sizing up just incase.
I also don't have much understanding of 24v systems/step down converters etc.
So 12v system should be fine?

 

[HRTKD]

Yes I will only have a 1500w to 2000w inverter. I should be well over my regular use with a 1500w, but was planning on sizing up just incase.
I also don't have much understanding of 24v systems/step down converters etc.
So 12v system should be fine?

Yes, 12v will work just fine. I'm running 12v in my RV trailer. It was easier to keep it all 12v than to add more equipment to go 24v.

If you want to read up on a 24v to 12v converter, here is a link to the Victron Orion model. Scroll to the bottom of the page for links to brochures and the datasheets. I mostly look at the datasheets to quickly get the specifications.

Orion DC-DC Converters Non-isolated, High power - Victron Energy

Eliminate the need for a high current switch in the input wiring with the remote on/off connector on the Orion DC-DC Converter. Find a dealer near you.

www.victronenergy.com

 

[mateo]

Yes, 12v will work just fine. I'm running 12v in my RV trailer. It was easier to keep it all 12v than to add more equipment to go 24v.

If you want to read up on a 24v to 12v converter, here is a link to the Victron Orion model. Scroll to the bottom of the page for links to brochures and the datasheets. I mostly look at the datasheets to quickly get the specifications.

Orion DC-DC Converters Non-isolated, High power - Victron Energy

Eliminate the need for a high current switch in the input wiring with the remote on/off connector on the Orion DC-DC Converter. Find a dealer near you.

www.victronenergy.com

That is money I don't want to spend! 12V it is.

Now to decide between 2p4s or 4s2p....

 

[Marinepower]

Thanks for the responses everyone!

I was originally planning on going for a 12v system with 352Ah as opposed to a 24v with 176Ah.



Is there a reason that I shouldn't go with a 12v setup with my panels? I was planning on doing as much wiring is 12V as possible (lights, chargers, I'll be taking a full set of m18 power tools and there's a DC charger I was planning on using instead of charging those off AC which seems like a big waste) and only using the inverter for the light appliance use, namely a mini fridge, small electric water kettle, and occasionally an 800w instant pot or a 600w nutribullet.

But I also hadn't yet considered the fact that my panels are a much higher voltage than the battery system. But my thinking was that shouldn't be an issue because of a charge controller. These are the panels I have, they're rated at 41v

Thanks!

Mateo,

there is no reason you need to go with 24v over 12v. However, if you want to go the route of the Electrodacus DSSR20 to save money on a solar charge controller, then you may be restricted by your existing solar panel voltage as to what voltage battery you run.

If you do not use the DSSR20, then there is no issue.

See: https://electrodacus.com/SBMS0/SBMS0.pdf

 

[mateo]

Mateo,

there is no reason you need to go with 24v over 12v. However, if you want to go the route of the Electrodacus DSSR20 to save money on a solar charge controller, then you may be restricted by your existing solar panel voltage as to what voltage battery you run.

If you do not use the DSSR20, then there is no issue.

See: https://electrodacus.com/SBMS0/SBMS0.pdf

The electrodacus looks really cool, but also seems pretty open source-diy-complicated? Maybe I'm wrong about that tho, so correct me if I am. But thinking about leaning into going about as simple as I can with the bms for my first time building batteries

And I did finally decide on going with a 4s2p setup instead of a 2p4s setup.
I talked to the legendary Amy and getting 8 202Ah cells for ~$630 including shipping and transaction fees and all that.
And since I'm now up to 202Ah cells, seems appropriate to make two instead of having one 404Ah behemoth..

Does this mean I can make each battery with the classic overkill 120a BMS and I'd be good to run a 1500-2000w inverter?

 

[HRTKD]

Does this mean I can make each battery with the classic overkill 120a BMS and I'd be good to run a 1500-2000w inverter?

I would have no qualms about running that inverter on my 4s2p LiFePO4 battery bank.

 

[Marinepower]

The electrodacus looks really cool, but also seems pretty open source-diy-complicated? Maybe I'm wrong about that tho, so correct me if I am. But thinking about leaning into going about as simple as I can with the bms for my first time building batteries

And I did finally decide on going with a 4s2p setup instead of a 2p4s setup.
I talked to the legendary Amy and getting 8 202Ah cells for ~$630 including shipping and transaction fees and all that.
And since I'm now up to 202Ah cells, seems appropriate to make two instead of having one 404Ah behemoth..

Does this mean I can make each battery with the classic overkill 120a BMS and I'd be good to run a 1500-2000w inverter?

Agreed Mateo, it is more complicated.

Sounds like you are on the right track.

I hear good things about Amy.

 

[michael d]

I use the Electrodacus SBMS0. it will work with 12 volt or 24 volt battery builds. I have mine wired in 2P8S for 24-volt battery using Lishen 272Ah cells. you could easily do a 2P4S with one BMS. the 2 cells connected in Parallel act as one cell. the Electrodacus SBMS0 monitors each cell individually. the Electrodacus DSSR20 is the solar charge controller that matches well with 60 or 72 cell PV panels in parallel pairs. you should definitely go with a 24-volt battery right off the bat and use 24 to 12 volt converter for 12 volt items. I bought 24-48 volt LED lights which can be direct-wired to the battery without the inverter being troubled. just use a dc breaker for a switch.

Victron are way overpriced. 2 DSSR20's will handle 48 amps for about 80 dollars. but you will only need one to start for about 40 dollars.

Electrodacus SBMS0 requires 2 shunts to get all the monitoring in 3 decimals - it is the BMS. and will shut off the Electrodacus dssr20's so no overcharging.
the dssr20's digital solar charge controllers are solid-state relays and likely outlive the MPPT. no electrolytic capacitors. the victron is /was designed for lead-acid and adapts to LiFePO4. lots of people like Victron but it is expensive.
good luck! ?

 

[michael d]

also a 24-volt inverter will need less amps and smaller wires. 12 volts are definitely heat-producing inverters due to the high amperage to get the same power. the amperage draw is a function of the inverter and is not even an issue with the sbms0 and dssr20 route. 1000 watts divide by 24 volt = 41.66 amp draw.
1000 watts divided by 12 volt = a 83.33 amp draw----- more heat bigger wires needed. bigger fuses needed.

the bms type that have all the amperage go through the bms are just asking for heat build-up on use.

only sense wires 24 to 28 gauge attach to the electrodacus sbms0. >>>>no high amperage there.

the dssr20 will handle 20 amps from your solar panels without the heat problems others produce.