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My 24v 24kw Blueprint

yambine

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Dec 13, 2021
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Hi guys,

I've just received most of the parts to build a 24v 24kw two battery (eventually I will upgrade to a 48kw four battery) solar battery bank. Before I move on with any wirings, I want to post my blueprint below to get your opinions. Just to let you know that this is my first time building any sort of solar generator so feel free to point out any issues. Also on the blueprint, I have marked 2 boxes in red with A and B. For location A, I think I probably need a breaker for this. For 12v I'm thinking maximum I will need 400w, so a 40a breaker? For location B, I want to have a battery monitor so should I install the shunt at this location? Is it safe to connect the positive wire of the shunt to the low terminal of solar controller? Thanks in advance and Happy Holidays!

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I've just received most of the parts to build a 24v 24kw two battery (eventually I will upgrade to a 48kw four battery) solar battery bank.
FYI - Your battery bank is measured in watt-hours, not watts. 2 batteries x 12.8V/battery x 100Ah/battery = 2560Wh or 2.56kWh.

I know Will rarely does this in his diagrams but I would add a positive bus bar to mirror the negative bus bar. This way you are not trying to wire everything to one central fuse. With the positive bus bar in place you can use separate fuses/breakers for each item. You would wire the main battery fuse (Class-T) between the battery and bus bar. You would have a fuse/breaker between the inverter and the bus bar. You would have the breaker between the charge controller and bus bar. You would have a fuse (A) between the 24V-12V DC-DC converter and the bus bar.

For location A, I think I probably need a breaker for this. For 12v I'm thinking maximum I will need 400w, so a 40a breaker?
The 40A 24V-12V DC-DC converter has a max output of 40A on the 12V side. This means the 24V input side would be half of that plus a little so let's call it 25A. So I would use a fuse in the 30A-40A range. Just make sure the wire you use can safely handle more than the chosen fuse.

For location B, I want to have a battery monitor so should I install the shunt at this location? Is it safe to connect the positive wire of the shunt to the low terminal of solar controller?
The shunt goes between the battery and the negative bus bar, just where your B box is located. The small power lead for the shunt should go directly on the other battery positive terminal.

One big mistake I see in your diagram is the wire from the inverter's battery negative is going to the wrong end of the shunt. Only the battery can be connected to that end of the shunt. Everything else must go on the other end.

You should also add a disconnect breaker between the solar panels and the charge controller. When setting everything up, make sure you connect the charge controller to the bus bars before you connect the solar panels to the charge controller (or turn on the breaker I just suggested). Do the opposite when disconnecting things.
 
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What is this system going to be installed in? I'm assuming it's an RV since you are feeding a 12 volt system.

If this is the case, then you may need to include an AC-DC converter for charging the battery bank when connected to shore power or a generator.
 
I know Will rarely does this in his diagrams but I would add a positive bus bar to mirror the negative bus bar. This way you are not trying to wire everything to one central fuse. With the positive bus bar in place you can use separate fuses/breakers for each item. You would wire the main battery fuse (Class-T) between the battery and bus bar. You would have a fuse/breaker between the inverter and the bus bar. You would have the breaker between the charge controller and bus bar. You would have a fuse (A) between the 24V-12V DC-DC converter and the bus bar.
I'm glad you've mentioned that! It was on my mind for a while but I told myself what do I know and I didn't want to ask too many stupid questions haha. I definitely going to get a positive bus bar.

The 40A 24V-12V DC-DC converter has a max output of 40A on the 12V side. This means the 24V input side would be half of that plus a little so let's call it 25A. So I would use a fuse in the 30A-40A range. Just make sure the wire you use can safely handle more than the chosen fuse.
I only have 10AWG wire, by looking at the chart it will only cover up to 30A, should that be enough? And if I use 10AWG, the fuse should be no more than 25A correct?
ne big mistake I see in your diagram is the wire from the inverter's battery negative is going to the wrong end of the shunt. Only the battery can be connected to that end of the shunt. Everything else must go on the other end.
Do you mean the wrong end of the "negative busbar" instead of the shunt, right? Btw why is that? Aren't the ends still all connected on the same piece of conductor any way?
You should also add a disconnect breaker between the solar panels and the charge controller.

How do I calculate the amp for the breaker? As you know I have 8 panels right now but may need to expand to 12 later. Will that require a higher amp breaker?
 
I only have 10AWG wire, by looking at the chart it will only cover up to 30A, should that be enough? And if I use 10AWG, the fuse should be no more than 25A correct?
Since it's a 25A load and 10AWG is good for up to 30A then 10AWG is fine. And using a 30A or even 40A fuse is just fine on 10AWG. You wouldn't want a 25A fuse on a 25A load since you would likely blow fuses under normal working conditions.

Do you mean the wrong end of the "negative busbar" instead of the shunt, right? Btw why is that? Aren't the ends still all connected on the same piece of conductor any way?
Doh!. Ignore what I said there. I was thinking about the shunt when I made that comment so I was thinking the negative bus bar was the shunt. My point about wiring the shunt is still valid but your diagram for the negative bus bar is fine. Sorry for the confusion.

How do I calculate the amp for the breaker? As you know I have 8 panels right now but may need to expand to 12 later. Will that require a higher amp breaker?
As I recall from one of your other threads you may have 8 panels in 4S2P and then later you may have 12 panels in 6S2P. In such a case the PV breaker isn't going to be used at all for current protection. It's just there to act as a disconnect. The main thing is to ensure the voltage rating of the breaker can handle the Voc of 6 panels in series. The amperage rating of the breaker just needs to be 20A or more so it doesn't trip during normal usage. Many people use a dual-pole DC breaker that can handle high voltage.
 
Since it's a 25A load and 10AWG is good for up to 30A then 10AWG is fine. And using a 30A or even 40A fuse is just fine on 10AWG. You wouldn't want a 25A fuse on a 25A load since you would likely blow fuses under normal working conditions.
Why will a 40A fuse be ok with 10AWG? I thought the main point of having a fuse or breaker is to protect the cable. If a 10AWG cable can only handle up to 30A, wouldn't the cable be melting before triggering the 40A fuse or breaker or it can handle 40A for short period of time?
he amperage rating of the breaker just needs to be 20A or more so it doesn't trip during normal usage. Many people use a dual-pole DC breaker that can handle high voltage.

I'm getting these 2 parts below
should I go with this 63A or go down to 32A?

One more question, is there amp requirement for busbars? Some of them on Amazon don't show a Amp stat.

rmaddy, you're a wealth of knowledge! thank you!
 
Why will a 40A fuse be ok with 10AWG? I thought the main point of having a fuse or breaker is to protect the cable. If a 10AWG cable can only handle up to 30A, wouldn't the cable be melting before triggering the 40A fuse or breaker or it can handle 40A for short period of time?
Yes, a fuse must be the weak point so it protects the wire. When you look at various charts/calculators to determine the appropriate wire gauge for a given current, the size you choose is based on many factors including the current and voltage drop (from the wire length) along with a few others. So when I say 10AWG can only handle 30A, that is taking into account lots of factors. But the wire can handle more raw amps which is why you can use a 40A fuse on the wire even if you want to limit the loads to 30A.

is there amp requirement for busbars? Some of them on Amazon don't show a Amp stat.
Absolutely. Treat the bus bar just like any other wire. It must support as many amps as the largest wire you will connect to it.

I'm getting these 2 parts below
Amazon.com Amazon.com should I go with this 63A or go down to 32A?
Since the breaker is only for disconnect and not circuit protection then it doesn't really matter. I've seen lots of people on this site reference the 63A breaker for this use. But the 32A is fine too as long as the parallel arrangement of your panels won't get over about 25A.
 
Yes, a fuse must be the weak point so it protects the wire. When you look at various charts/calculators to determine the appropriate wire gauge for a given current, the size you choose is based on many factors including the current and voltage drop (from the wire length) along with a few others. So when I say 10AWG can only handle 30A, that is taking into account lots of factors. But the wire can handle more raw amps which is why you can use a 40A fuse on the wire even if you want to limit the loads to 30A.


Absolutely. Treat the bus bar just like any other wire. It must support as many amps as the largest wire you will connect to it.


Since the breaker is only for disconnect and not circuit protection then it doesn't really matter. I've seen lots of people on this site reference the 63A breaker for this use. But the 32A is fine too as long as the parallel arrangement of your panels won't get over about 25A.
ok! Can you recommend an economical battery monitor?

For busbar online I saw the amperage number shown below, does it mean 150 AC or DC?

  • RANGE FOR USE---- Max voltage: 48VDC. Max continuous amperage: 150ADC. Max intermittent: 20 A per connection (less than 1 minute).
 
You would have a fuse (A) between the 24V-12V DC-DC converter and the bus bar.
Why did you specifically point out that this DC-DC converter requires a fuse instead of breaker? I normally prefer breakers instead of fuses just to avoid hassles in the future such keeping spare fuses. But if there is a legitimate reason I won't mind at all.
 
The only place in my system where I have a breaker is where I also needed it to act as a disconnect. That's between the charge controller and bus bar and between the solar panels and charge controller. Fuses everywhere else. The only reason you should ever blow a fuse or trip a breaker is because something went wrong. And whatever went wrong needs to be fixed before you replace the fuse or reset the breaker. I have a few replacement fuses and I will likely never need them. I just don't see the benefit of using a breaker where a fuse can be used.

Whichever you choose, do spend the money on high quality fuses or breakers made by known brands like Bussman and Littlefuse. Saving $5 on cheap junk isn't worth the risk.
 
You will like your setup. I am currently running three of those 40 amp controllers, 2-4000 watt Giandel inverters and 12 battle born batteries.
Everything is pretty well bullet proof.
 
The only place in my system where I have a breaker is where I also needed it to act as a disconnect. That's between the charge controller and bus bar and between the solar panels and charge controller. Fuses everywhere else. The only reason you should ever blow a fuse or trip a breaker is because something went wrong. And whatever went wrong needs to be fixed before you replace the fuse or reset the breaker. I have a few replacement fuses and I will likely never need them. I just don't see the benefit of using a breaker where a fuse can be used.

Whichever you choose, do spend the money on high quality fuses or breakers made by known brands like Bussman and Littlefuse. Saving $5 on cheap junk isn't worth the risk.

Hi Rmaddy,
I have completed most of the wirings. Can you take a look at the attached configuration and let me know if I’m missing anything before I start hooking up the batteries and solar panels? Thanks in advance!
 

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You will like your setup. I am currently running three of those 40 amp controllers, 2-4000 watt Giandel inverters and 12 battle born batteries.
Everything is pretty well bullet proof.
Hi GLC,

Can you take a look at my attached final configuration and see if there’s any issues. Thanks in advance!
 

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Seems right after a quick pass.

Remind me about a few things - for the 24V-12V DC-DC converter, what size wire do you have and what size and kind of fuse do you have?
 
Seems right after a quick pass.

Remind me about a few things - for the 24V-12V DC-DC converter, what size wire do you have and what size and kind of fuse do you have?


I use a 40A fuse. The wires from both the positive and negative busbars to the fuse are 10AWG. From the fuse to the converter I used the wires that comes with the device, by looking at the attached photo ( I compared it with 10AWG next to it), it looks like it's about 12AWG. What do think I should do? 12AWG for sure is not gonna able to handle 40A.
 

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10AWG on the output side is fine given how short it is. 12AWG on the input side should be fine since that will be under 25A. I have the same basic DC-DC converter. I cut the supplied leads as short as possible and butt spliced 10AWG to that.

The real trick is to avoid ever actually trying to pull 40A from the converter. If it was a 40A Victron Orion then I would say you could pull 40A all day just fine. But one of these cheap converters may not be able to handle the full 40A very long.
 
Hi GLC,

Can you take a look at my attached final configuration and see if there’s any issues. Thanks in advance!
Wiring schematic looks ok, You are fused and a breaker on the positive side? Redundant but ok. Looks like a #6 from controller to battery? If so, good. What is the size of wire from Inverter to batteries? Is that a 120 amp breaker going from inverter to battery?
 
10AWG on the output side is fine given how short it is. 12AWG on the input side should be fine since that will be under 25A. I have the same basic DC-DC converter. I cut the supplied leads as short as possible and butt spliced 10AWG to that.

The real trick is to avoid ever actually trying to pull 40A from the converter. If it was a 40A Victron Orion then I would say you could pull 40A all day just fine. But one of these cheap converters may not be able to handle the full 40A very long.
got it thanks!
 
Wiring schematic looks ok, You are fused and a breaker on the positive side? Redundant but ok. Looks like a #6 from controller to battery? If so, good. What is the size of wire from Inverter to batteries? Is that a 120 amp breaker going from inverter to battery?
Hi,
Thanks for the feedback! First of all just letting you know I'm very new to this so if I say something silly feel free to correct me. Btw I'm building a 24v system. Below are my answers and questions.

  1. why is it redundant to have fuse and breaker on the positive side? What will be a more efficient setup? The 250v Class T fuse protects the wires to the batteries and the batteries. 40A fuse for the 40A DC24V to DC12V converter. 50A breaker is for the 40A solar controller. 120A breaker is for the 2000w inverter
  2. yes its 6AWG from the controller to the batteries
  3. 2AWG from inverter to batteries
  4. yes, it is a 120a breaker going from inverter to batteries. something wrong?
 
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