48V vs 24V why/why not?

[kwest364]

I have:
-skoolie build
-24V system
-batteries: 4 x 12V 100Ah Amperetime lifepo4 batteries (5000Wh battery capacity)
-panels: 1100W --- 6 x 185W 36V 5A panels ~1100W (either 3s2p @ 108V 10A or 2s3p @ 72V 15A)
-gifted 30A 48V to 12V buck converter (with inline fuse)
-also have 40A 24V-12V, but can buy higher 48-12 capacity converter
-now broken 24V Edecoa 3000W inverter. Came with bus (Edecoa brand), cheap, and temp fan (or something) stopped working recently, so I'm going to upgrade and get a new all in one, which was the plan for some time now.
-lynx distributor


Why not 48V? What are cons of 48V vs 24V besides 24V needing bigger wires and more inefficient? My system is smaller (1100W panels + 5000Wh battery capacity), but if 24V vs 48V all in one unit price is the same, why not save $ on wiring and go 48V? Could expand system later on, but will still have plenty as is.

I've decided on a growatt all in one system. Was gonna get 24V but now I'm thinking why not 48V? The only specific thing I had that was 24V specific was inverter and charge controller. I'm replacing both those, so why not 48V? Seems like at 24V, I'm just paying more for wire and I'm replacing all equipment with 48V or 24V all in one, anyways.

4 batteries in series charging issues? Other potential issues?

Buck converter at 30A: I'll never come close to that.
12v loads: 26.5Amps if all on at once
6 gal water heater 12Amps
Water pump 8Amps
Furnace 6.5Amps
Maybe some max air fans I'll install way down road.

Yes, 40A+ buck would be good for extra ceiling and I have a 24V one, but I was given a 48V 30A. I can buy a new one with higher Amp capacity.

Other reason to do 24V vs 48V?

 

[hwy17]

One thing to check is if your batteries are rated to run in 48v series.

You will have balance problems over time either way, from putting 12v in series.

Otherwise 48v is great.

 

[Supervstech]

If system is small, getting 48v same range will be difficult

 

[kwest364]

One thing to check is if your batteries are rated to run in 48v series.

You will have balance problems over time either way, from putting 12v in series.

Otherwise 48v is great.

manual says can run up to 4 in series or 4 in parallel (16 total), but who knows.

Thought parallel batteries don't balance well? Series doesn't balance well either?

How to mitigate balance issues?

At 24v 2s2p, would I run into balancing problems? Better to stick with 24V to eliminate balancing problems? Or will I still have balancing issue anyways and need to buy or make a doohickey for that problem? It has BMS

 

[kwest364]

If system is small, getting 48v same range will be difficult

What do you mean by 48v same range will be difficult?

 

[Supervstech]

What do you mean by 48v same range will be difficult?

If you only need a 1200W inverter, getting an all in one 48V inverter likely you would need to use a 6000W inverter.

 

[Supervstech]

In parallel, batteries are fairly easy to wire to keep in balance.

In series, you have to either periodicly set the batterys in parallel to balance, or install a battery balance device that does it automaticlly

 

[kwest364]

If you only need a 1200W inverter, getting an all in one 48V inverter likely you would need to use a 6000W inverter.

I have a 24V 3000W inverter. All in ones I'm gonna get are both 3000W, just 48v vs 24v.

I have 1100W of panels on roof.

The all in ones are:
3000W 24V $675
3000W 48V $675

If the 48V was more expensive, I'd go with 24V, but same price. So I thought why not save on wiring anyways, and go 48v? Since I'm replacing all 24v specific stuff anyways.

I'm confused where 1200W inverter is coming from?

 

[rustyrotors]

i think only down side to 48v is chargers and inverters tend to be more expensive and your battery will have more cells to keep in balance, but 48v is easier on equipment, may have better reliability. i would not worry about cell balance in parallel, they will self balance, even if mismatched. in series it can be a problem, i recommend an external balancer.

 

[hwy17]

Thought parallel batteries don't balance well? Series doesn't balance well either?

Parallel can have balance problems, but parallel can stay in balance, it is possible for it to do so.

Series can never stay in balance no matter how perfectly configured. You will always have to either periodically charge each battery individually to restore balance, or use a 12v balancer.

 

[Rocketman]

In an RV (Schoolie), one of your biggest factors is your idle draw of the inverter. Because of limited solar you want as low of idle draw as possible - and best efficiency. One of the reasons I like Victron inverters.

Good Luck

 

[time2roll]

Any chance the skoolie has a 24v alternator? That would be my reason to stay with 24v.
Also if I had started with 24 I would tend to stick with it. I dislike redoing everything if it is working fine.

 

[timm]

From everything I've read, I see two minor drawbacks to 48v.
1) It can be harder to get components rated up to 55 or 60v. People are often asking about fuse blocks and disconnects rated for the higher voltage.
2) You want to make sure you can get your solar panel voltage high enough for the MPPT. Usually at least 5v above your battery voltage.

As long as you can work with both of these, I'd go 48v for all of the wiring benefits. It's really nice to be able to use smaller cheaper wires in tight spaces.

 

[12VoltInstalls]

decided on a growatt

Did you look at the MPPSolar stuff?
I think the MPP 3048 is pretty low idle consumption.

 

[Pi Curio]

If your heaviest load exceeds 3000W-ish DC, or you are working with a very tight space where temperatures are one of the bigger factors, 48V might be the winner.

Just my 2 cents.

 

[kwest364]

How often would I have to balance the batteries? Is there a way to wire so that I don't have to remove all batteries, physically, and charge each one up till balanced? It's just me and my skoolie, no other power sources around so I can't just pull batteries and take to my garage/house and charge to perfect thru garage/house 120V lithium charger. I have no house. How can I use my current bank of 4 x 12V @ 100Ah in series at 48V to periodically and easily charge batteries individually at 12V? Able to charge from other batteries somehow? Guess that's a double feeding system: charging itself, off itself. Possible?

 

[kwest364]

How often would I have to balance the batteries? Is there a way to wire so that I don't have to remove all batteries, physically, and charge each one up till balanced? It's just me and my skoolie, no other power sources around so I can't just pull batteries and take to my garage/house and charge to perfect thru garage/house 120V lithium charger. I have no house. How can I use my current bank of 4 x 12V @ 100Ah in series at 48V to periodically and easily charge batteries individually at 12V? Able to charge from other batteries somehow? Guess that's a double feeding system: charging itself, off itself. Possible?

What's good brand balancer to use? Preferably 1 unit that does all 4 @ 48V simultaneously vs 4 units 4 x 12V.

 

[CaliSunHarvester]

My 24V inverter draws just below 30W when there is no load.

My 48V All-in-one draws just below 100W idle.
That's 2.4kWh daily of your 4.8kWh battery bank.

The 30W comes to 0.7kWh daily, if I leave it on. I don't typically.

 

[time2roll]

What's good brand balancer to use? Preferably 1 unit that does all 4 @ 48V simultaneously vs 4 units 4 x 12V.

I think you want something like this:

https://www.aliexpress.us/item/3256805704027252.html

Shop around

 

[Rocketman]

You will not have to rebalance often. If you go with a Victron shunt, the Smartshunt &BMV712 have a mid-point monitor- so you can see how far out of balance (in percentage) the two halves are. (You get mid-point OR temp sensor OR second battery monitor- the Multiplus inverter does have a temperature sensor for the battery).

Then once in a while - when visiting a RV park with power you could re-top balance each battery.

I would think this would be the process…

Get the batteries through the absorbing mode and just after they go to float connected as a 48v pack. Shut everything down - for the few minutes.

Get a 12v lithium charger and plug it into the park’s power or a generator or a friends rig. Set the charger to a slightly higher(but safe) voltage than you regularly charge to. Connect to battery 1 - charge, when done, move to battery 2 , repeat until done.
If you create access in building you could do it without disconnecting the 48v battery. Because each battery is already at the top - it should not take long to rebalance. You probably want a low amp charger so you give time for the bms to rebalance the cells inside the battery. If you have Bluetooth access to the bms’s that could guide your process.

Good Luck