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diy solar

please take a look at this offgrid 24v 3000w layout

E

ElectricTraction

New Member
Joined
Dec 2, 2024
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42
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USA
Please take a look at this arrangement and let me know if I did anything dumb or could do something smarter.

I have purposely oversized the cabling. It's all the good stuff from BatteryCablesUSA.
The batteries will be on a plywood base with casters for portability.
I have not shown the finer details of the small wires from the Victron SmartShunt.
I have not shown connections to the inverter's AC output.
I'd rather do a more modular fuse arrangement for the PV input but haven't done that yet.
I don't know what I'm going to do about the balancers yet.
Please excuse my Excel-photo-shop skillz.

24v system - rev0.jpg
 
You don't need 4 total bus bars, just 2 (one for each positive and negative side).

I would get rid of the big bus bar on the negative side and connect the shunt directly to the batteries.

I would use a MRBF on the positive post of each battery string, then a battery switch for each battery string to the positive bus bar. Inverter and charge controller also connect to this bus bar.

You don't need a fuse (F3) on a single string of solar panels.

Put F1 fuse between the positive bus bar and the inverter, sized for the inverter.
 
In general it looks good.

I use the same software approach - or by hand.

Consider to wire the batteries slightly differently.

With 1000 watts of solar, that is just 50 amps coming in, so you could either wire it in similar to one of the fuse blocks shown, or via a power hub.

There are some places that require a rapid shut down to bring the panel voltage down during shut down. Just look at some questions that I have asked recently as examples.

Use 600 amp or similar bus bars.

_____________

As far as balancing the batteries, start off by charging them all in parallel and do this for a few days.

If you have a 12 volt load, discharge them down 50% and then recharge. Not always possible.

Recharge again and they will often stay in balance for a long time. ( if they are decent batteries. )
 

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  • Example Electrical Diagram Harry Niedecken 11 July 2024.jpg
    Example Electrical Diagram Harry Niedecken 11 July 2024.jpg
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Thank you Q-Dog! I've read a lot of your posts and I really appreciate your experience.

I've read about fusing each LIF battery on the positive side of the string, but thought that required a T-class fuse. No? That would be great because I'd much rather use a MRBF there if it's OK.

Thank you Harry! I've read so much here on the forum that I've gotten behind about the balancing. I know I'm making it harder on myself with the series strings. But those are the batteries I have on hand to work with, so thanks a ton for that info.
 
Design makes sense. Keep in mind without any breakers or switches that cable ends will be powered during disconnect operations.
 
ElectricTraction said:
Thank you Q-Dog! I've read a lot of your posts and I really appreciate your experience.

I've read about fusing each LIF battery on the positive side of the string, but thought that required a T-class fuse. No? That would be great because I'd much rather use a MRBF there if it's OK.

Thank you Harry! I've read so much here on the forum that I've gotten behind about the balancing. I know I'm making it harder on myself with the series strings. But those are the batteries I have on hand to work with, so thanks a ton for that info.
Click to expand...

Just use your batteries as series strings that you have. I do it all of the time with battle borns and Lifelines.

Instead of one battery as in the drawing, just pretend that it is 2 batteries in series.

Buy a clamp meter so that every 6 month you can check the current flows and voltages at various points and see how it is going. Double check your connections to make sure that they are still tight.

After years of use, those stay pretty well balanced. I have not had to do anything other than look.
 
I'm using 12 volt batteries in series on my 24 volt shed system, even though that can be problematic, and I still think a 24 volt battery for a 24 volt system is better. I installed a Victron Battery Balancer and haven't had any problems with that setup yet. You could use one balancer for 2 pairs of 12 volt batteries.

 
ElectricTraction said:
Harry, are 250A busbars out of the question/dangerous? Or are the 650A just nice to have?
Click to expand...

Great question.

Just as an example, the current flow in your system from batteries to the inverter will be ~ 150 amps during use.

Normally the 250 amp bus bar current rating is just between adjacent studs of the bus bar, not the ones further away.

Unfortunately I don't remember all of the details for how much it varies from stud to stud, but it is less. Usually the result is less even current flow between the different locations on the bus bar, and some heating.

There should be a spec sheet with the details on the bus bar documentation to on how much it will vary.

You are using Li batteries, so it does not matter as much if the current flow is a little higher in one side vs the other.
 
Per Epoch's spec sheet they say max allowed discharge current is 100A, with a 200A surge for no more than 10 seconds. So by "allowed" it sounds like that's a limit imposed by the BMS. But I don't know much more about Epoch's BMS since I haven't found anyone who has cracked the code.

specs.jpg
 
I would lean towards a 125 amp fuse on each battery string. 100 amp continuous load should not blow it. Make sure your wires are sized correctly for that.
 
Got it, thanks Q-Dog. I'm going to use 1/0 throughout the battery strings and into the inverter. I've got it on hand, so I might as well take advantage of it, and it will give me room to grow. And the 175A T-class is in the mix too.
 
Q-Dog said:
I would get rid of the big bus bar on the negative side and connect the shunt directly to the batteries.
Click to expand...

I'm working on building a battery box on a furniture dolly, which has casters for easy mobility. I'm leaving room to add foam insulation for winter and remove it in summer, as the bank will be in an unconditioned space. The photo below is just a mockup for planning, I haven't built the walls of the box yet.

Looking from the top down, is it OK to wire the positive leads directly on the T1 fuseblock, and the negative leads as shown? The fuseblock and switch take up a lot of space. I want to keep the T1 and switch on the battery bank component, so when separated from the rest of the system there's protection.


BatteryBox1.jpg
 
Q-Dog and Rednecktek, I saw your thumbs-up; much appreciated. BTW today I found a basic teardown video of the Epoch 12v 105Ah Essentials battery, in case others are interested. First tear-down I've seen on that unit.
 
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