Noob 280ah 12V battery build (solar ready) - please advise before I buy? Charger questions too....

[Justins311]

So I'm pretty mechanically inclined (engineer) and have built several LiFePO4 ebikes @52V, but am learning electrical and I've never built my own battery pack. Starting with a 12V solar/lithium build for my motorhome and have been learning from here and Will's great youtube channel. Here is my build and LOTS of associated questions, I appreciate input on any of them!

Build
1) 12V LiFePO4 battery. Planning to order:
a) (4) EVE LF280 280Ah 3.2V LiFePO4 at $580 + tax = $625 shipped
b) (1) 4S 12V BMS w 24" leads and crimped ring terminals = $165 shipped
c) Foam, allthread inside a plastic battery box

2) Distribution/charging:
a) Victron Multiplus 12V/2000w/80a charger/converter/inverter [already purchased]

b) WFCO 8955PEC for 12 & 120V power distribution [came installed in the coach - REMOVING CHARGER/CONVERTER PORTION]

c) AiLi 500A Battery Monitor w/ shunt installed at negative battery [already purchased]

3) Solar/MPPT: Rich Solar 400W 12V kit w/ 40a MPPT solar charge controller

Questions
1) BATTERY: I find wildly varying prices on EVE cells, Docan power seems to have the best price and was recommended. I was planning to get a server battery but 400ah is all thats currently available @$1500 which is way more than I need/can afford right now. Are there any other options or is the 280ah build @ about $800 all built my best options? Anything inbetween? I'd prefer a pre built solution w case but haven't found anything in the 300ah/$1000 range which is my max budget

If I do end up building it, I'd prefer a prebuilt case like SOK offers. @$1029+ shipping for 206ah it seems like I get way more for my money DIY. I'd spend a little more for a decent case but can't seem to find any offered. The Ampere time 200ah @ $710 seems interesting and affordable but I dont want to cheap out and have read mixed reviews.



2) Converting/Battery CHARGING:

a) From research it appears I need to disconnect the charger/converter from the WFCO. The WFCO has a built in/add on T30a transfer switch to transfer between my Onan generator and shore power inputs. I originally assumed I could remove this transfer switch and use the Multiplus, but it appears the only transfer the Multiplus compact can do is between 12V DC and a single 120V input (from my T30). So I need to feed keep the T30 and feed into the Multiplus input, correct?

b) Random question - I have a 52V/24ah ebike battery I'll be carrying with me on most trips. Rather than use the 52V satiator charger I own, is there any way to integrate it into my Multiplus system as extra capacity? It would be 104ah extra @12V if I could find an economical way...but the Multiplus external battery charger is 12V so I think I'm SOL. Will the Multiplus at least use the small 12V vehicle starter battery as extra capacity, or is it just charging it? Thoughts welcome.

c) Do I NEED any other monitors to be safe? I'd love the Victron Smart Shunt but its seems like an extravagent 200 bucks I dont need to spend when I'm already topped out on my budget. If it'll be unsafe and adds safety switches to the charging I'm open to it, but will the AiLi and an alarm be adequate?

3) MPPT Charger: I would love the Victron 30a MPPT w bluetooth which I could make work for my budget @$220, but it leaves no room for growth and is probably undersized for 400W panels @33a. Victron doesn't seem to offer a 40a so I'd have to jump all the way to a 50 amp version @$323 which means I'm spending twice as much as the Rich Solar. A 3rd option is the Renogy 40a also at $160 - is this a better option than the $160 Rich Solar 40a MPPT?

If you read thru all this and can offer any input this NOOB appreciates you!

 

[ncsolarelectric]

Check out Power Queen 12V, 300ah on Amazon. It is $1039. I bought the 12V, 50ah and after I received it they offered me a 4% discount if I buy more. So maybe buy the 100ah, then wait and get a discount on 2 more. IMO, the time I would spend assembling and testing the BMS is worth more than the cost difference between a DIY and OTS battery. I got a plastic case for mine, snap-cover lid with handles. Works great! Looks like plastic, but nothing will fall on my battery terminals.
Your two charge controllers are 80A each, they are going through 1 BMS? Did you check the current rating of the BMS?
2 b) A step-down DC to DC converter to step down from 52 to 12V. That's a whole other electronics project! The best I have is 24V to 12V. Anything more than 2:1 is a stretch. So yeah, SOL, sorry.
3) You could get an all-in-one /solar/battery-inverter/charger like the EG4 or the MPP and skip putting all the pieces together. One of these will be a better match for 400W solar panels. The engineers who put those units together did a much better job than anything I've seen DIY. Will's EG4 setup is sweet!

 

[Justins311]

Thanks ncsolarelectric! I looked at Powerqueen but its great to get real world feedback. I'm going to highly consider it now.

An all in one would be great, wish I would have found this forum earlier. I snagged a new MultiPlus Compact on ebay for $660 (half price) so I'm going to have to get a separate MPPT unfortunately. The EG4 would have saved me some $ but in the long run I'm happy with the Victron quality.

 

[ncsolarelectric]

Are you tied to the power grid? You could just plug the Victron inverter into the grid, let it run on the battery and charge the battery from the grid. Then you offset that usage with grid-tied solar. It's AC coupled, not a direct solar PV to DC to Battery, and you need an Interconnection Agreement with your local utility.
I prefer this because I would not need to worry about if there was enough sun today to charge the battery, and I don't need to oversize the solar system to support the load 100% from solar. I just need enough to offset a percentage of what I use over the course of a year.

 

[Justins311]

Are you tied to the power grid? You could just plug the Victron inverter into the grid, let it run on the battery and charge the battery from the grid. Then you offset that usage with grid-tied solar. It's AC coupled, not a direct solar PV to DC to Battery, and you need an Interconnection Agreement with your local utility.
I prefer this because I would not need to worry about if there was enough sun today to charge the battery, and I don't need to oversize the solar system to support the load 100% from solar. I just need enough to offset a percentage of what I use over the course of a year.

Its for my motorhome so the 3 inputs to charge the battery bank will be 400w PV, gas generator and shore power when available.

 

[chrisski]

One single 12 volt battery won’t deliver a lot of power. At the max discharge rate of 1C it may, but probably shouldn’t power a 3000 watt inverter. Check the spec sheet for a max discharge rate.

As unlikely is the battery to power the 3000 watt inverter, the BMS is less likely to do that. A 100 amp BMS WILL not, and a 200 amp BMS IS HIGHLY doubtful and only fully charged at wattages under 3000 watts.

If there’s some reasonable safeguards put in to prevent approaching 3000 watts, than that may be OK. I have found many safeguards that are good for me, but have failed to find one that is “family and friend proof.” I end up designing to component capacity, because someone will do that.

 

[Justins311]

My inverter is the Multiplus compact at 2000W. I don't plan to use more than 1500W in normal use.

I'll check discharge rate on the Powerqueen but for small RV solar systems the average user is stuck with a single 12V battery source.

edit: here is what Powerqueen is advertising on Amazon: 200A BMS WITH 2560W MAX. LOAD POWER Power Queen 300Ah LiFePO4 battery has built-in 200A BMS (Battery Management System) to protect it from overcharge, over-discharge, over-current, and short circuit. Our battery has 12 cells inside, the auto motive grade cells are high-density and stable, it’s safe when used in our daily life and friendly for the environment. And 2.56kW Max. Load Power would allow us to connect more common applications simultaneously to enjoy a more convenient life.

 

[Justins311]

As far as the MPPT, can anybody tell me if I can wire the MPPT output directly to the Multiplus DC input? Similar to below, this isn't my system but a quick drawing I found. I dont see any difference electrically, but all the instructions show the MPPT directly connected to the battery.

 

[chrisski]

I’d really recommend joining battery, inverter and SCC at a busbar with spare studs. I have 8 different connections at a busbar. Other than that, I’d look in the tech data. One of my busbars allows 4 connections per stud. The most I’ve doubled up on is two wires carrying 10 amps for 20 amps total on a 125 amp rated switch.

If you have a windmill, I think it would be converted to DC power and not coupled into the multiplus AC side. Another reason for a busbar.

 

[Justins311]

Thats a great point, I do have a busbar with spare capacity.

I dont have a windmill, this is on an RV, just a quick picture I grabbed to illustrate

 

[chrisski]

My RV grew from one SCC to 3 as I found the best way to get the power I needed. Mines a 24 volt build. I did create a few 24 volt items throughout the RV. 3 charging stations and three sets of lights.

 

[Justins311]

That's valid, I could get one Victron 30a and then add another later. Just hate spending money twice and its cheaper to get a larger SCC now.

I also haven't broached the alternator charging. Maybe I could get a larger 50a unit with DC-DC charging like this: https://renogy.com/dcc50s-12v-50a-dc-dc-on-board-battery-charger-with-mppt/

 

[chrisski]

I think the DC to DC charger is a valid charge method and could be easier than setting up a generator for the AC to DC converter like I do.

For my SCCs, each has a different panel type and orientation. I have one SCC for the portables, and two for the roof. I would be difficult to do one, but possible, unfortunately, I did not do the planning. If you can, that is great.

 

[Justins311]

Any feedback on Docan Power's OTS batteries? The pricing they emailed me on the 300ah @ $740 is very intriguing but I dont have clarification on if these are prices in CHINA or the US and what shipping and leadtime will be. Looking at these vs Powerqueen vs Ampere on amazon.