diy solar

diy solar

How big can you go?

Deveak

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Mar 19, 2021
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Trying to figure out the max size for a 48 volt system. What do you consider the practical limit?
Parallel charge controllers and inverters are a must. Largest CC I have seen is 120 amps.

I would say 200 amps is the practical easy limit but 400 amps is pushing it. Depends on the battery as well. Those terminals can only handle so much current.
Any ideas? What's the largest off grid system you have seen that's DIY?
 
Many. Many. Many thousands of kwh.

There are people here who buy 280ah cells by the pallet.

You just use more batteries and more controllers as needed.
 
Though I would say the practical limit is when grid scale power storage becomes cost effective for you lmao
 
Many. Many. Many thousands of kwh.

There are people here who buy 280ah cells by the pallet.

You just use more batteries and more controllers as needed.
I'm speaking of off grid DIY systems. Most of the limitations I see are based off battery terminal amp limits, max parallels for charge controllers etc.
400 amps is a lot, even for 4/0 cable. Massive busbars would help if you can get them all lined up at the terminals.
 
You can put those things in parallel. And I'm also speaking of diy.

There are people with over a hundred or more large cells in a single bank.

I haven't seen it myself but 4/0 isn't the limit either. You don't need to limit yourself to one single 4/0 cable either, and can attach multiple large inverters to a single battery bank.

But keep in mind also that high current isn't the only "kind" of large. You might have a max of 200a draw on your system but have an insane amount of storage.

You can feed a huge bank with several chargers too. Not sure that there is actually a limit to how many chargers you can utilize in parallel either, aside from current handling of course.
 
As an example, BlueSea makes a 1000 amp bus bar (e.g. to connect multiple 48v batteries together). With the right amount of copper and the right amount of parallel, anything is possible (albeit you start to need to understand electrical engineering when you get really large).
 
I'd limit my self to 200a through a single wire conductor. Parallel setups all connected to a LARGE buss bar (3"x.25" flat bar....) just keep stacking parallel inverters. Currently Growatt will support up to 30kw of 6x 5kw inverters in parallel. Each unit running wire size for 100a from the main busbar. 280ah LFP pack for each inverter (so 6x of those) puts each one at the same 100a
 
I would start looking at 96 volts at > 300 fault amps.
But if you want to stay at 48 volts, you will need big fuses.
Here are some big fuses.
Bit of an exaggeration.

300a fuses are easy to come by and inexpensive. You can buy a 5 pack for $6 on Amazon with "free" prime shipping and there's no reason you can't have multiple 300a fuses from a bank (using previously linked 1000a bar) to multiple inverters.

1000a 48v is rather on the absurd size for a home. That's the equivalent of a 200 amp residential 240 volt service (which gives you 2x 120v 200a legs in the US). From there it's a matter of stacking batteries in parallel.

So for the purposes of this thread I'd say that's probably the largest "practical" system for the "typical" home but it's still far beyond what's necessary for the average family. My house has 100a 240 service and it's *way* more than enough for our multiple gaming PCs and constant central air usage.


But it's still possible to go way beyond that by just adding additional banks which are not connected to each other.

At some point you're more likely to run into not having enough breakers and wiring in the house to support it even at 120vac then you are to run into any physical limitations on storage and inverters.

You're also far more likely to go to a 120v dc storage system long before you ever hit that point but typically anything over 48v is frowned upon by local regulatory agents.


So again, the question is far too open ended and you're better served trying to figure out what you need rather than the "practical" limits.

Your "practical limit" is likely very different from mine for example.
 
Its not an exaggeration, its my policy.
No. It is very much an exaggeration. You don't and never will need a 5000a fuse lmao.

You should fuse everything but the fuses needed for this kind of thing are small and literally cheaper than condoms lol
 
looking to move up in system voltage when fault current exceeds 300 amps is my policy.
There is no exaggeration in that statement.
Fault current will never need exceed 300a unless you are dropping something onto your battery bars because everything drawing off it should have its own fuse directly at the bar.

Even if you have a 500a load you can use two runs of cable with a fuse on each. If one blows the other one will follow almost instantly.

Do you fuse each cell terminal to prevent short circuits on your bus bars also?

I doubt it. So far I've never seen anyone do so. But it's certainly possible.


What situation would you have a need to exceed 250-300a without multiple runs of cable?

Furthermore, I'd love to see the >1000mcm cable you're using to do it.

THAT SAID.

I definitely agree with moving up in voltage at that point, but OP is talking about 48v circuits specifically, and anything higher voltage usually requires permits and licensed electricians.
 
Maybe I'm just too used to the car stereo world where several runs of 4/0 with a 250a fuse on each isn't uncommon.

I'll reiterate that you're right that op should go higher voltage if at all feasible.


But I suspect he's just having a thought experiment since that amount of power is far beyond what any typical household needs.
 
No. It is very much an exaggeration. You don't and never will need a 5000a fuse lmao.

You should fuse everything but the fuses needed for this kind of thing are small and literally cheaper than condoms lol
I don't know if I would trust those cheap high amp fuses on ebay etc.
Maybe I'm just too used to the car stereo world where several runs of 4/0 with a 250a fuse on each isn't uncommon.

I'll reiterate that you're right that op should go higher voltage if at all feasible.


But I suspect he's just having a thought experiment since that amount of power is far beyond what any typical household needs.
I would like to go big for a few reasons.
1. I own a small farm with plans for a lot of greenhouses. Grow lights, pumps, fans and HVAC add up.
2. Large over sized arrays help the batteries last longer.
3. E peen, the biggest.
 
Well I can understand that but "name brand" ones are only a few bucks each.

And if you have all that you need to do a proper energy audit long before considering the practicality of any given solar installation and the hardware involved in it.

At some point you're essentially talking about a commercial application and 48v isn't really viable.

In the mean time multiple smaller 48v systems are equally viable but less cost effective long term.
 
Well I can understand that but "name brand" ones are only a few bucks each.

And if you have all that you need to do a proper energy audit long before considering the practicality of any given solar installation and the hardware involved in it.

At some point you're essentially talking about a commercial application and 48v isn't really viable.

In the mean time multiple smaller 48v systems are equally viable but less cost effective long term.
Yeah I guess in this case the "practical" limit is 300 amps and just building multiple systems. Although a few thick busbars could make 500 possible.
That or use some grid tie stuff with a hybrid inverter so you can add more PV and allow the charge controllers to top off the battery unimpeded.
 
3,000+ amps total is possible with enough cables, fuses, and a massive enough bus bar because no single cable and fuse will exceed the fuse rating if properly designed.

Hell. I've got a 5000 amp sub panel behind my desk at work. Granted it's 240 volt AC, but it's still the same current involved. The bus bars in it aren't really all that big.

But of course that's insanely stupid to bother with. You're definitely not limited to 500 amps when a 1000 amp bus bar is available right off the shelf.

The hardest part will be getting multiple cables installed and fused to cover that.

The largest "12v" system I ever had my hands on was actually running 16v (I think) continuously and had 3x 375 amp alternators and a high idle controller installed. It had 5x 4/0 "oversize" cables ran to the back.
In the car stereo world some companies sell underrated/oversized cables, so these were the rough equivalent of 5/0 in wire size. I had no idea 5/0 was even a thing at the time but turns out it technically is.


So yeah. You're definitely not "limited" to 500a either.
 
If I were to build a 48 volt system, I would want to limit max continuous power to 5 kw, which comes out to 100 amps on the wires. If I were to trust 200 amps continuous, that would get it close to 10kw. If a residential hookup is at least 100 amps at 120 VAC, so 12 kw.

My comfort limit with wiring would be no more than 100 amps, with a surge to 200 amps, so I’d stick to 5 kw. That would still limit me on the number of high amperage devices I run at once. I’d not be at the residential hookup level where I can run as many high amperage devices at once as I want without breakers tripping.

I’d be interested to see what those who’ve built 48 volt systems use for max inverters.
 
If I were to build a 48 volt system, I would want to limit max continuous power to 5 kw, which comes out to 100 amps on the wires. If I were to trust 200 amps continuous, that would get it close to 10kw. If a residential hookup is at least 100 amps at 120 VAC, so 12 kw.

My comfort limit with wiring would be no more than 100 amps, with a surge to 200 amps, so I’d stick to 5 kw. That would still limit me on the number of high amperage devices I run at once. I’d not be at the residential hookup level where I can run as many high amperage devices at once as I want without breakers tripping.

I’d be interested to see what those who’ve built 48 volt systems use for max inverters.
Knowing your limits is good, but you often learn along the way and grow in confidence.

200+ amps isn't any more scary or different than 100, or even 20 however. At least up to 300 anyways in my opinion.

Once you get much past 350a though that's when I would need/want to take even more precautions but it's easy enough to stay under that on any one circuit.

And short circuiting a battery is always going to be way more fault current than that even if it's only a 100 amp "system" in terms of load devices, so that part of the safety requirements is always the same: very important.

The basics are all the same. Minimum voltage drop, good crimps, clean contacts and fuse everything, wear some PPE (ESPECIALLY safety glasses).

I'm sitting in my truck right now running right about 90 amps under my seat lol
But I will say I am rather uptight about inspecting the connections from time to time for corrosion.
 
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