48v vs 2x24v

[JJJJ]

I have read the discussions on 24v vs 48 v. Smaller wires for higher voltage, availability of components (is improving for 48v) etc.

The reason I ask is redundancy. While requiring larger wires, a 2x24 volt system has in essence a backup supply should one need to go down for repair. In parallel the amps double which help make up for additional consumption due to doubling every time one steps down (48-24-12).

Another consideration is battery storage. From reports, these cells are not light. A 24v system would improve the chances of finding a battery case that does not require a team to lift or move it (albeit it may still be quite an effort since one 100 AH system weighs 100 lbs and I am considering a larger battery).

One other consideration would be top balancing preparation. My guess is it would take less time to top balance a 24v system than a 48v system.

Granted there would be 2 BMS. That is a given.

Your thoughts?

 

[JaVid]

Well, I had the same questions and thoughts when I was designing my system.

In the end I went with the 24V system for all the reasons you state - more redundancy in the battery/BMS and better choice of 24V equipment.

It might come down to how many watts your peak use is - mine is only around 2000 max and usually <1000. If you want to pull more than 3000 watts, maybe best to go 48V.

 

[Diysolar123]

It will take time to prep and build your system, so I would not worry about top balance time. Battery prep (initial balance and capacity testing) is going to take what it takes depending on capacity. Paralleling inverter/chargers requires specific devices that support that, you should not just hook two together as if they are batteries. Do you really need that level of redundancy? A properly made all-in-one inverter/charger can run many years without any issues at all (do not go cheap chinese clone for this), so ponder if you really need redundancy? Do not forget that in some scenarios whatever has caused one device to fail may take out both anyway (lightning strikes, dropping a wrench onto things, whatever)...

It may make more sense and be simpler to just "buy a spare" and put it on the shelf. What you may just need is minimum downtime which is wayyyyy easier, and cheaper, than guaranteed uptime.

energy density per kg of weight is a very different issue. Propane is something like 12kwh/kg, while lithium batteries (which are great) is like 0.1kwh/kg!

You want to write down the scenarios that you really think you may find yourself in where weight matters. Batteries are heavy, even lithium based batteries.
Like so many things (even tho folks do not like it) the right way to start is with ..."math"...
Use online calculators, a spreadsheet, whatever, and right down how much power you will need. You may quickly find out that what you are thinking of will never fit in a backpack hehe
If you need a LOT of power and be mobile, the answer may be a small generator and propane or other fuel!

 

[MichaelK]

I could mention two issues that are important in your design. First, you need inverters that are designed to be paralleled. That means they will sync their AC outputs so their two waveforms are in phase. That's not a big deal, as most quality inverters these days are designed for parallel operation.
Here's one of my inverters that is parallel capable.

Schneider Electric Conext SW4024-120/240 Inverter/Charger - RES Supply

Free Shipping! Schneider Electric Conext SW4024-120/240 Inverter/Charger, 4000W, 120/240VAC, 50/60Hz, 30A Transfer, 24VDC, 90A Charger, RNW8654024

ressupply.com

Secondly, for two inverters that are sharing the same load, they should be powered by the same battery bank. That is so the two inverters will not become imbalanced because of battery bank state of charge.

With one of the main points being redundancy, I can see how having a single battery bank will be problematic. What you might want to try is a wiring scheme that allows you two parallel 24V battery strings where you can switch to either bank one, inverter one; or bank two, inverter two for regular loads, but switch to parallel operation for big loads? An extra hassle, but doable. With dual banks, one important issue would be the state of charge for each string when switching from individual to parallel. You will NOT want to suddenly switch to parallel banks when there's a significant state of charge difference. The best practice might be to leave the batteries in parallel when using either one or both inverters.

 

[Alphacarina]

It might come down to how many watts your peak use is - mine is only around 2000 max and usually <1000. If you want to pull more than 3000 watts, maybe best to go 48V.

I agree - Much depends on how large your load is - If your inverter is 3Kw or less, I think 24 volts is fine. If you don't have big loads, you don't need big wires, and if you don't need big wires at 24 volts, what's the advantage of 48 volts?

Don

 

[time2roll]

I like the idea of 2x 24v for a bit of redundancy and easy of service.

 

[farmhand]

Been searching for an hour... any updates on balancing 2x24 (48v LifePO4)? I can't find anything out there....

 

[Ampster]

any updates on balancing 2x24 (48v LifePO4)?

There are lots of 16S BMSs from JBD, JK, Orion, REC and others. Overkill sells a variation of the JBD BMS with real person support.
I assumed you are referring to a 48 volt pack and not two 24 volt packs in parallel. If two 24 volt packs is the case then you would need two 8S BMSs.

 

[sunsurfer]

I think you are on the right track. I'm off-grid. I'm building multiple systems too! Imagine if one gets a lightning strike, you would have a back up system assuming it is isolated enough.

I also avoid the AIO units for better redundancy. Its more work and cost but way more redundant. I run multiple SCCs, multiple batts(parallel), and multiple inverts(when needed) or at least keep spare inverters on the shelf.

When you are the power company and no one is coming to the rescue, it changes your build designs.

 

[sunsurfer]

For batts (lifepo4), I like the idea of using the matching voltage and just running multiple in parallel. 2 in series might be a negative compromise for redundancy vs reliable(simpler).

You get your batt backup by having many in parallel. Yes, you can't go down in volts but you should make it so you don't need to (have spares)

 

[time2roll]

Been searching for an hour... any updates on balancing 2x24 (48v LifePO4)? I can't find anything out there....

2x24 in parallel will self balance. 2x24 in series I recommend a battery balancer. Single 48v battery will be self balanced by the BMS.

 

[JaVid]

I run 4x24v in parallel with no balancing issues at all.

 

[sunsurfer]

I run 4x24v in parallel with no balancing issues at all.

Thats the nice thing about parallel. They can be out of balance and its no big deal. Now in series its an issue. You can trigger a BMS to go into protection mode at one point if you don't have a balancer between each BMS. Projects in paradise had a youtube video up for a few hours with some Battleborns that had a melt down. His friend had a 48v with 2P4S setup. They went out of balance and the BMS DID NOT SHUT DOWN. A couple of the batts where seeing like 18v or something real bad. Big holes burned in the side of the batteries. Battle born made them take the video down in exchange for a warranty. Don't want the public to know your over priced batteries have crappy BMS I guess.

 

[farmhand]

Right, but does anyone know of a 2x24 (series) ballancer?

 

[time2roll]

https://www.ebay.com/itm/125455406168

Shop around

 

[farmhand]

https://www.ebay.com/itm/125455406168

Shop around

Oh I have done so. The one you linked (and ALL others) are for 12v batteries

 

[farmhand]

Adding this here as a maybe:
https://www.amazon.com/gp/product/B09MCXJ7XD/ref=ask_ql_qh_dp_hza