How much safer is 24v vs 48v ?

[meetyg]

Where did you purchase from, what did it cost you, and how long did it take?

I’m also looking for a 24V hybrid and didn’t know about the offering s from MUST prior to this thread.

Very interested in your impressions of build quality and performance as you get things working…

Because it’s Nur an inverter that was designed for the US market. EU is single-phase 230VAC…

I also have a string preference for 24v because of the fact that a 24V batters can be charged by a 1S string. I have severe shading that moves across my array in the morning, so I get +15% daily output from a parallel 1S array versus what I’d get from a 2S or higher series string,

How did you learn about MUST? What do you think about the build quality?

I got mine from Aliexpress:

https://www.aliexpress.com/item/1005004240998631.html

Price was very tempting, about half of a Growatt 3000.
I got this inverter thinking that it's an MPP/Voltronic, just rebranded, but it's not.

I haven't given it much use yet, just temporarily connected for some testing. But I think that in hindsight I would have gotten an MPP Solar or Growatt. These MUST inverters are less known, and run proprietary firmware, different than MPP Solar.

On paper, it's specs are nice and has many features and modes. But time will tell how it holds up.

 

[kuranaga]

telephone wire nearly shocked me to death, be careful. maybe they were out of spec, idk, but definitively very dangerous

 

[berksrunner]

I have worked with my 16s bank, and only once have I felt a little tingle when resting my arm across a bus bar on accident. It was 110* outside and I was very moist. The only thing I felt was a little tickle, and just enough to remind me to be safer.

I would not worry too much about safety of 24v vs 48v if the only thing you are worried about is getting shocked. Just be safe and wear PPE.

What PPE should we be wearing in this context, in addition to safety glasses?

 

[MisterSandals]

What PPE should we be wearing in this context, in addition to safety glasses?

Have you seen the wedding ring electrical injury threads? They are gruesome. A good example of what not to wear.

 

[meetyg]

I would like to get myself some of those "electrician's gloves". Seems like a good idea when working with any voltage.

 

[Lt.Dan]

What PPE should we be wearing in this context, in addition to safety glasses?

Safety glasses would be my big one. Rubber/insulated tools would be a bonus.

 

[Shimmy]

Proper insulated rubber electrical gloves are a great starting point. Insulated tools are the next step, and a set of arc fault jumpers comes next. Step zero is to take off all metal on your body.

I don't think anybody needs to be using a space suit for 48VDC, but you do need to respect the fact that you should not be touching live parts with your body or tools unless it is absolutely necessary.

 

[12VoltInstalls]

Don't forget even though your 24v inverter is only 3kw, most of the AIO (MPP or Growatt) can be stacked for more output. This way you can keep adding cheaper 24v batteries/inverters as money allows.

This is a seldom mentioned feature but is a big bonus imho.
Disadvantage number one is the idle current doubles when stacking, but this is usually surmountable with a couple ’extra’ panels.

Old thread, I know, but was an interesting read. I have an MPPSolar 1012LV-MK that is stackable. But realistically at only 1000W inverter output it’s not particularly practical to ‘stack’ this model. Great machine- I use it (inverter off) for an SCC for one small array; I run a 2000W 12V inverter separately, and it’s on the wall only for backup or to utilize the 60A (80A?) built-in charger off a generator if it’s ever needed.

With 2500W or maybe 3000W as a working maximum practical limit for 12V (due to high amps), 24V makes some sense- but 48V perhaps makes more sense. Useable DC is basically not available at 24V or 48V is why I have that opinion- just going 48V doesn’t affect anything else.

However, I would like to stay at 12V myself for many reasons including that my lighting is all 12V and - I don’t know why- the idea of 24V or 48VDC stepping down to 12V through a transformer is something I have a big aversion to. For OP @meetyg as well as myself I wish MPPSolar had a non-existing “2512LV-MK” because that would let me have what I need now, and perhaps grow/scale to 5000W should I desire to. That would be practical and efficient to scale up imho.

However, I’m probably just going to go to a 3000W QZRELB/WZRELB pure sine box this fall. Then create a totally separate system next year at 48V for the shop since 2000W is more than I really need “residentially” and I have a ton of panels on hand already. 3000W will acceptably run my bigger table saw, the midsized compressor, and do light 120V welding.

I write all this to say: just as in meetyg’s situation (and recognizing he’s 240V)- I truly am surprised there aren’t 2500W 12VDC AIO’s in the market. (It even appears that the 5048 split phase has gone away?)
So I guess we’ll just keep asking and answering these kind of small-midsize system questions, and coming up with the least offensive compromise to get it done.

 

[meetyg]

Just updating:
I ended up going with double DIY 24v batteries in parallel, with a 24v 3kw AIO.
This gives me some redundancy, as I have two batteries each with its own 200A BMS.
I feel more comfortable with 24v rather than 48v (which goes higher than 50v when fully charged).

It will power some critical loads, so I think 3kw is enough for my current use. Plus, I like the fact that my AIO has a max PV voltage of 145v. I think most 48v AIOs are only higher voltage (250-500vdc). Since my array is fairly small (1.2kwp) it suits the inverter well.
Another advantage with the lower voltage AIOs is presumably that they don't have the AC voltage on PV connections, as some of the higher voltage ones are plagued with.

Although the manual if my inverter says that only 5kw models support paralleling, mine came with the parallel board installed already, so I think it still can be paralleled in the future, if I choose.

 

[googdot]

Just updating:
I ended up going with double DIY 24v batteries in parallel, with a 24v 3kw AIO.
This gives me some redundancy, as I have two batteries each with its own 200A BMS.
I feel more comfortable with 24v rather than 48v (which goes higher than 50v when fully charged).

It will power some critical loads, so I think 3kw is enough for my current use. Plus, I like the fact that my AIO has a max PV voltage of 145v. I think most 48v AIOs are only higher voltage (250-500vdc). Since my array is fairly small (1.2kwp) it suits the inverter well.
Another advantage with the lower voltage AIOs is presumably that they don't have the AC voltage on PV connections, as some of the higher voltage ones are plagued with.

Although the manual if my inverter says that only 5kw models support paralleling, mine came with the parallel board installed already, so I think it still can be paralleled in the future, if I choose.

I have a very similar system size wise to yours, and am about to change over to a DIY 8s2p battery. Any chance you could share a pic of your new battery setup?

 

[fafrd]

Just updating:
I ended up going with double DIY 24v batteries in parallel, with [/b]a 24v 3kw AIO.[/b]

Can you share what 24V 3kW inverter you went with? Is it split-phase?

This gives me some redundancy, as I have two batteries each with its own 200A BMS.
I feel more comfortable with 24v rather than 48v (which goes higher than 50v when fully charged).

It will power some critical loads, so I think 3kw is enough for my current use. Plus, I like the fact that my AIO has a max PV voltage of 145v. I think most 48v AIOs are only higher voltage (250-500vdc). Since my array is fairly small (1.2kwp) it suits the inverter well.
Another advantage with the lower voltage AIOs is presumably that they don't have the AC voltage on PV connections, as some of the higher voltage ones are plagued with.

Although the manual if my inverter says that only 5kw models support paralleling, mine came with the parallel board installed already, so I think it still can be paralleled in the future, if I choose.

Interested to know what inverter you went with and what it cost.

I’m currently at 24V running 2 1kW grid-tied inverters (GTILs) and looking to move to an off-grid-system powered by a new 1.5kW array (6 panels).

I could move to 48V and get a split-phase hybrid charging from a 6S1P string of ~180VDC at cost in the $1500-2000 range but reading through this entire thread again has reminded me why I chose 24V when first building my 16-cell battery (8S2P).

My current 60ACC can charge from a 3S2P array of the new panels so one option I’m coming back to considering is a 24V split-phase solution delivering 3kW per leg which does not need to be AIO (no SCC).

 

[fafrd]

Can you share what 24V 3kW inverter you went with? Is it split-phase?

Interested to know what inverter you went with and what it cost.

I’m currently at 24V running 2 1kW grid-tied inverters (GTILs) and looking to move to an off-grid-system powered by a new 1.5kW array (6 panels).

I could move to 48V and get a split-phase hybrid charging from a 6S1P string of ~180VDC at cost in the $1500-2000 range but reading through this entire thread again has reminded me why I chose 24V when first building my 16-cell battery (8S2P).

My current 60ACC can charge from a 3S2P array of the new panels so one option I’m coming back to considering is a 24V split-phase solution delivering 3kW per leg which does not need to be AIO (no SCC).

Two of these can stack to deliver split-phase power: https://signaturesolar.com/growatt-24v-3kw-150vdc-stackable-off-grid-inverter/

At $660 each that is $1320 for a split-phase 3+3=6kW solution running at 24VDC.

I don’t need the SCC but unless I find a cheaper 24V split-phase alternative costing much less than this, a little redundancy is never a bed thing…

Interested to know how the 24V AIO you opted for compares with this.

 

[meetyg]

My AIO is a MUST 24v 3k PH-18 Plus, for European AC (230v, single phase). I'm not in the U.S. so I don't need split phase.
I haven't put it through a stress test yet, as I need to complete some connections to my AC distribution board / panel. But from various tests I've done, it's working nicely. The fans are pretty loud, and seem to be load controlled, not temperature.
This AIO is basically a clone of MPP/Voltronic original design, but with some tweaks. It has a different firmware too.
Very similar to an MPP LV2424, but with 3k/3kva power. It can also work as grid-tied, if excess solar is available.
Unfortunately, this model isn't available on Aliexpress anymore for some reason. Looks like MUST have a newer model, but isn't grid-tie capable (not at low PV voltage models anyways).

For those of you looking for a split phase, I think you have various options, like the LV2424 and the Growatt 3000.
If I recall correctly, some models of the LV2424 can be paralleled.
Certainly I would get something with local support/warranty, if available.

I was tight on a budget, and wanted to get a decent AIO, so I went with MUST.
Time will tell if that was a good idea or not.
We don't have a large variety of solar equipment available locally (Middle-East), mainly Victron, and some no-name Chinese brands for inverters.

 

[fafrd]

My AIO is a MUST 24v 3k PH-18 Plus, for European AC (230v, single phase). I'm not in the U.S. so I don't need split phase.

Got it - thanks.

I haven't put it through a stress test yet, as I need to complete some connections to my AC distribution board / panel. But from various tests I've done, it's working nicely. The fans are pretty loud, and seem to be load controlled, not temperature.

Increased load generally translates to increased temperatures (after some lag). If it is load-driven then the fans will shut down as soon as the load does (with no lag). That could actually suggest an effective cooling system preventing heat buildup…

This AIO is basically a clone of MPP/Voltronic original design, but with some tweaks. It has a different firmware too.
Very similar to an MPP LV2424, but with 3k/3kva power. It can also work as grid-tied, if excess solar is available.

Meaning it will export? Not a desirable feature for my use-case.

Unfortunately, this model isn't available on Aliexpress anymore for some reason. Looks like MUST have a newer model, but isn't grid-tie capable (not at low PV voltage models anyways).

For those of you looking for a split phase, I think you have various options, like the LV2424 and the Growatt 3000.
If I recall correctly, some models of the LV2424 can be paralleled.

Yes, those are the two stackable 24V split-phase offerings I’m focused on.

Certainly I would get something with local support/warranty, if available.

I was tight on a budget, and wanted to get a decent AIO, so I went with MUST.
Time will tell if that was a good idea or not.
We don't have a large variety of solar equipment available locally (Middle-East), mainly Victron, and some no-name Chinese brands for inverters.

Back to the original topic of the thread, 24V is certainly cheaper for a minimum-capacity system than 48V but eliminating that advantage and just focusing on safety, I’m just having a hard time seeing that 48V LiFePO4-based ESS will be treated very differently in terms of safety than 24V LiFePO4 systems or 48V AGM-based systens, despite the fact that fully-charged voltage can be as high as 57.6VDC…

The question I’d like to ask those with experience in the world of higher-voltage DC systems is:

‘Which would you consider the greater increased risk moving from an all-under 50VDC system (8S LiFePO4 and 1S solar string with 45V Voc):

-sticking with 8S / 24V LiFePO4 but movies to an 8S solar string with 210V Voc

or

-moving to a 16S / 48V LiFePO4 battery but sticking to a 1S solar string with Voc under 50V

I’m basically considering the options of sticking to the under-50VDC voltage levels I’m using now, making one of the changes outlined above, or making both.

If code compliance of high-voltage DC solar strings charging 24V batteries is likely to be greatly relaxed versus code entailed when battery voltage exceed 50VDC, that might’ steer me towards staying with the battery voltage I have currently…

 

[12VoltInstalls]

fans are pretty loud, and seem to be load controlled, not temperature

The convention in design seems to be load and solar input power controlled- plus a temperature switch. Once ‘you’ control the fan(s) it’s just some code and a cheap sensor to do that which is probably why they do that.

I’m basically considering the options of sticking to the under-50VDC voltage levels I’m using now, making one of the changes outlined above, or making both.

I don’t think it’s a concern- use a proper DC rated CB as a disconnect and once you kill both legs you can do whatever safely. You can even make a dummy MC4 filled with epoxy or something nonconducting to plug in to the panels to be more better saferish.

think most 48v AIOs are only higher voltage (250-500vdc)

I never noticed that!

Another advantage with the lower voltage AIOs is presumably that they don't have the AC voltage on PV connections, as some of the higher voltage ones are plagued with

from reading on this BB I gather that this is caused by two things: inductive pickup and the switching of the inverter section.
I don’t believe it is mains level and from past threads probably near zero Amps. And I’m not sure this is exclusive to 48V AIO’s.
I do not believe it to be of concern.

 

[meetyg]

Got it - thanks.

Increased load generally translates to increased temperatures (after some lag). If it is load-driven then the fans will shut down as soon as the load does (with no lag). That could actually suggest an effective cooling system preventing heat buildup…

Meaning it will export? Not a desirable feature for my use-case.



Yes, those are the two stackable 24V split-phase offerings I’m focused on.

Back to the original topic of the thread, 24V is certainly cheaper for a minimum-capacity system than 48V but eliminating that advantage and just focusing on safety, I’m just having a hard time seeing that 48V LiFePO4-based ESS will be treated very differently in terms of safety than 24V LiFePO4 systems or 48V AGM-based systens, despite the fact that fully-charged voltage can be as high as 57.6VDC…

The question I’d like to ask those with experience in the world of higher-voltage DC systems is:

‘Which would you consider the greater increased risk moving from an all-under 50VDC system (8S LiFePO4 and 1S solar string with 45V Voc):

-sticking with 8S / 24V LiFePO4 but movies to an 8S solar string with 210V Voc

or

-moving to a 16S / 48V LiFePO4 battery but sticking to a 1S solar string with Voc under 50V

I’m basically considering the options of sticking to the under-50VDC voltage levels I’m using now, making one of the changes outlined above, or making both.

If code compliance of high-voltage DC solar strings charging 24V batteries is likely to be greatly relaxed versus code entailed when battery voltage exceed 50VDC, that might’ steer me towards staying with the battery voltage I have currently…

I don't think you will be able to charge a 48v battery with only 50v PV. I think that you need a higher PV voltage for that. At least around 80-100v.

 

[12VoltInstalls]

I don't think you will be able to charge a 48v battery with only 50v PV. I think that you need a higher PV voltage for that. At least around 80-100v.

Right. I noticed that but forgot to mention it.

 

[fafrd]

I don't think you will be able to charge a 48v battery with only 50v PV. I think that you need a higher PV voltage for that. At least around 80-100v.

Right. I noticed that but forgot to mention it.

Apologize for not being more clear.

I’ve considering two options for charging 48V LiFePO4 battery with 1S strings:

-AC-coupling: 1S strings into 240VAC Microinverters and 48V battery charged by 240VAC charger

-DCDC booster: 1S string into SCC programmed for maximum voltage output based on Vmp and then boosted to target 48V charge voltage using DCDC booster (you can even purchase Boost SCCs these days: https://www.amazon.com/Renogy-Contr...cphy=9032001&hvtargid=pla-1206462025871&psc=1

But it’s definitely off the beaten path to charge a large 48V battery bank with ~2.5kW of 1S solar power and honestly it might be more forward to stuck to the 24V battery I’m using now.

I have 6 new panels to add and would need to go to 3S in any case, so my new string will either be 6S/1P 210V Voc (for which I’d need a new SCC) or 3S/2P 105V Voc (for which I already have a 150V SCC).

So that’s one decision I’ll need to make regardless of battery voltage (though it appears easier to charge 48V with 210V strings than 24V).

But the more fundamental decision is whether to switch my 8S2P 24V battery to 16S1P 48V. Potential code impact sounds like it should be a more important consideration than increased risk / safety concerns and on the downside, sticking to 24V will mean being capped at a max of 3+3 = 6kW of split-phase power while 48V offers headroom to almost double that at modest incremental cost.

If I do decide to just stick to 24V for another few years while the dust on ESS continues to settle, another option I’m considering is this: https://reliableinverters.com/produ...ine-wave-inverter?_pos=2&_sid=d39febad3&_ss=r

$950 for 2.5+2.5=5kW is not bad and might be enough for my purposes and I read enough in the Growatt manual to get concerned about some AIOs only operating with specific BMS (communication).

The usual conundrums of being an early adopter…

 

[12VoltInstalls]

I have a 2000W 12V Reliable (QZRELB) inverter that impresses me. I would not be opposed to that! I like their hardwired outputs, but the input terminals you should be two-wrench and gentle with; they are delicate and one of them cracked trying to put 35ft-lbs on it with a 3/8 torque wrench.

That’s so good to know about but in a quick look apparently- as usual- no 12V options.

decide to just stick to 24V

I likely wouldn’t normally concur but in your circumstances I say, “do it.” 24V is fine; I’d consider it if I wasn’t married to 12V lighting and such.
If you really need to “go big” 48v would probably be best just building from scratch and either run redundant or sell off the old system.

3S/2P 105V Voc (for which I already have a 150V SCC).

I would do 3S2P myself

 

[fafrd]

I have a 2000W 12V Reliable (QZRELB) inverter that impresses me. I would not be opposed to that! I like their hardwired outputs, but the input terminals you should be two-wrench and gentle with; they are delicate and one of them cracked trying to put 35ft-lbs on it with a 3/8 torque wrench.

I’ve got the 3kW 120VAC single-phase WZRELB as my current backup inverter and I’m also impressed with it. Thanks for the heads-up on torquing the DC input terminals…

That’s so good to know about but in a quick look apparently- as usual- no 12V options.

I’m coming to the conclusion that for my priorities, which are backup power for 5 fridges/freezers averaging 300W @ 120VAC and offsetting those same loads using 1.5kW of DC-coupled solar power, sticking to the 24V I have now is the wisest choice.

In fact, the primary reason for me to get a split-phase off-grid inverter is if I am bringing my existing split-phase subpanel off-grid and want the headroom to increase offgrid loads in the future.

For the fridges/freezers only, I could get by with a 120VAV single-phase critical loads panel, bypassing the inverter for service with a single 25A 120VAC breaker from my MSP.

I may just wire up a new CLP for single-phase 120VAC but design-in a split-phase contactor allowing me an east upgrade to split-phase such as this new 2.5+2.5=5kW model from WZRELB in the future…

I likely wouldn’t normally concur but in your circumstances I say, “do it.” 24V is fine; I’d consider it if I wasn’t married to 12V lighting and such.
If you really need to “go big” 48v would probably be best just building from scratch and either run redundant or sell off the old system.

I don’t need to ‘go big’. During an extended multi-day PSPS power outage for fire safety, it’s really only the fridges we care about powering.

And it’s also those same fridges/freezers running 24/7 that end up consuming over 50% of our energy on an annual basis.

So with all the changes both in terms of rules and regulations, keeping it simple, safe, and cheap for this next phase with wiring designed to provide for an easy upgrade down the road seems like the prudent plan.

I would do 3S2P myself

I’m currently running at 1S due to issues with shifting morning shade and if I’m sticking to 24V, I believe I can also stick to 1S for the new panels. Charging at 28.8V would require 30.8V of incoming solar which is a hair over the 30.2Vmpp of my panels, but Voc is 37.2V so there should be no problem maintaining +2 volts over battery voltage through the day and lost output once the battery is charged up past 37VDC should be modest…

Of course, if I ever decide I need a 48V inverter I’ll either need to rewire the 3 1S2P strings as 2S1P or pick up 3 of these new boost-SCCs, but that’ll be a hairball for another era.