DIY battery build + matching solar array

[nowwegrow]

Aloha From Hawaii!
Brand new here and have scanned through looking for info and answered some of my questions. I just want to lay it out here and see what kind of advice I get, and where I need to educate myself and do a bit more research. I am intending to build a 24v set up to go in a chevy express extended van.

Using 8 cells to make a 24v 400 ah battery, Are these BMS's quality enough?
Bms 400A 24v - https://bit.ly/33HyUEQ

400 AH DIY Lifepo4 cells - https://bit.ly/2FKiZh1
800Watts Total Solar 4 x 200 Watt Rich Solar Panels https://amzn.to/32KFnzE
3000Watt Inverter https://amzn.to/35NmfCX
80A Mppt solar charge controller - https://amzn.to/3kuFsxb

I am not well versed with How big of an MPPt solar charge controller I need, is this overkill?

I have tried to research the difference between "24v" and "12v" panels. from my understanding, as long as the combined panel voltage is high enough, the panels can be configured for 24v charging? Guessing its still a better idea to get 24v panels for this setup if they are available?

24v https://amzn.to/32KFnzE VS 12v https://amzn.to/35OuoHd


Has anyone Installed an additional 24v Alternator to charge while driving?

Also links to preferred wiring, Fuse Boxes, ETC.
Am I missing anything?

THanks!!!

 

[snoobler]

800W/24V = 33.3A charge current. 80A MPPT SCC will allow for 80A*28V = about 2200W of total solar.

With MPPT, you can use whatever panels you want as long as their combined Voc is below the SCC voltage limit (best to have a 20% margin as well for cold weather voltage spikes) and above battery voltage (this varies, Victron is +5V). Most have an MPPT voltage range specified. Try to hit this. A good guideline for optimal efficiency is Panel Vmp = 1.5X battery voltage, i.e., 24V battery with panel Vmp at 36V. Note that higher voltages only lose a very small amount of efficiency, and the higher voltage also results in lower wiring losses, so they often wash each other out.

There are chargers designed to work with alternators to keep from overloading them (LFP batteries can take everything the alternator has to give and burn them up). Renogy and Victron make them.

Items in link #2 in my signature help with fusing and wiring.

Please consult Will's website, https://www.mobile-solarpower.com/, for system blue prints and recommended components.

 

[NCblueridge]

Using 8 cells to make a 24v 400 ah battery, Are these BMS's quality enough?
Bms 400A 24v - https://bit.ly/33HyUEQ

400 AH DIY Lifepo4 cells - https://bit.ly/2FKiZh1
800Watts Total Solar 4 x 200 Watt Rich Solar Panels https://amzn.to/32KFnzE
3000Watt Inverter https://amzn.to/35NmfCX
80A Mppt solar charge controller - https://amzn.to/3kuFsxb

If you use (8) of those 200 ah 12V batteries in series to create a 24v pack, you will have a 200 ah 24v system, not a 400 ah 24v system, if you are converting output to 12v though, you would get @400AH at 12v.

 

[nowwegrow]

If you use (8) of those 200 ah 12V batteries in series to create a 24v pack, you will have a 200 ah 24v system, not a 400 ah 24v system, if you are converting output to 12v though, you would get @400AH at 12v.

would I only then need a 200A 24v BMS?

 

[NCblueridge]

would I only then need a 200A 24v BMS?

Keep in mind that I am a newbie to much of this also and just going by what I've learned (or think I have) so far. I'm sure some of the more experienced folks will chime in on all this as well.

As I understand it, the BMS amp specs are based on how many amps you plan to draw, not your amp hour capacity. If I have my math right then a 3000 watt inverter at 24v would pull @125 Amps (plus a little more for the inverter itself). So, at 24v with a 3K inverter, I think you would be fine with a 150a 24v unit with a little extra to spare. Look at snooblers energy audit link, you really should do that before you get into sizing all this regardless.

I could be wrong though (and often am) so wait for others to chime in before hitting any "buy button" ?

 

[nowwegrow]

If you use (8) of those 200 ah 12V batteries in series to create a 24v pack, you will have a 200 ah 24v system, not a 400 ah 24v system, if you are converting output to 12v though, you would get @400AH at 12v.

As for the BMS that I would need, I havent been able to get a for sure answer but it looks like I would need no more than 150A or 200A BMS max?

48.6US $ |Lifepo4 24v 8s 80a 100a 120a 150a 200a 18650 Battery Pack Management System Balanced For Solar Inverter - Battery Accessories & Charger Accessories - AliExpress

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[ianganderton]

As for the BMS that I would need, I havent been able to get a for sure answer but it looks like I would need no more than 150A or 200A BMS max?

48.6US $ |Lifepo4 24v 8s 80a 100a 120a 150a 200a 18650 Battery Pack Management System Balanced For Solar Inverter - Battery Accessories & Charger Accessories - AliExpress

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As mentioned it does depend on your loads. Most things do to be honest. What you intend to run and for how long is a very important part of the picture.

A 200Ah 24V battery will store approx 4800W. Because you don’t want to damage the battery by fully discharging it you can only really use a maximum of 80% of that so 3800W

Your 3000W inverter will draw 125A at 24V When fully loaded. What are you planning to run off he inverter and for how long?. Do you have any other loads like a DC fridge, DC heater or lighting? You need to calculate how many amps total you might need to size your BMS correctly. A 200A BMS should give you plenty of wiggle room and prevent catastrophic damage in the event of a problem (if your wiring and fused are both sized and installed correctly). Apart from cell balancing your BMS should only ‘activate’ if something is wrong elsewhere in the system.

You are unlikely to but if you used your 3000W inverter continuously you would use all your available power (3800W) in 1.25 hours

 

[nowwegrow]

thanks so much for the info and input! I think 200A is the way to go just to be safe. I dont imagine my intended usage to be too demanding or full-on. based on all the videos and reading I have done, It seems that running a regular mini fridge fridge on a 24v system is about equal to a RV 12v efficiency fridge?
with that in mind, I thought to start with a regular mini fridge freezer and potentially upgrade to an efficiency camper style.

so far my lose an estimate of items and usage times
consumer mini fridge freezer 3.2 cubic ft and vent fan(s) would be running pretty much constant
medium led light setup approx. 2-6 hours a day
laptop usage 2 - 8 hours a day
instant pot approx. 40 minutes a day
vitamix blend approx. 10 minutes a day