Budsy
New Member
This is my first system and I need to know what fusing is nessisary for a 4 x 100w panels with 4 100 ah agm batteries and 30 amp charge controller and a 1500 watt pure sine wave 24 volt inverter. Thanks
Fusing 24 volt system
- Thread starter Budsy
- Start date
Budsy
New Member
Budsy
New Member
Thanks I will have a look for amps and as it’s a 24 volt system the panels would be wired 2 P strings in series.
Budsy
New Member
Hi the open current voltage is 22.6 and optimum current voltage is 18.3. X 4 100 watt panels
Budsy
New Member
So am I correct in my calculation that with
2 12 volt 100ah batteries wired in series would be 24 volts 100 amps and 1200 watts then another 2 12 volt batteries also in series and then the 2 series banks wired in parallel would be 24 volts 50 amps and 2400 watts?
HarryN
Solar Enthusiast
There really are several power systems running in parallel in a system like this.
Battery pack A ---- breaker ---- main bus bar
Battery pack B ---- breaker - main bus bar
Inverter ---------------------main bus bar ( some like to put a T fuse or breaker on this line )
Fuse block ----- breaker ----main bus bar
If you wanted, you could use an 80 or 90 amp breaker in each location for commonality and do the bulk of the wiring with 2 awg.
________________-
Most fuse blocks can handle 30 amp loads and chargers per fuse position, so you can just run the solar charge controller into the fuse block
For the solar charge controller fuse, ( 400 watts of solar ) / (nominal 28 volts charging conditions ) ~ 14 amps under perfect conditions.
Most likely you will use 10 awg wire for this and it is rated for 30 amps, so you can fuse at 20 or 30 amps and be just fine.
If you do the bulk of your wiring with 10 awg, then many of the fuses can be 20 amp or 30 amp ( you can pick a common size for spares vs having a bunch of sizes )
I have built a number of setups like this - very straightforward and reliable.
_______________
Your 2 Series , 2 parallel setup from 4 each, 100 amp-hr batteries
Battery pack A is ( 100 amps - hrs ) x ( 24 volt ) ~ 2400 watt-hrs
Same for pack B
Battery pack A ---- breaker ---- main bus bar
Battery pack B ---- breaker - main bus bar
Inverter ---------------------main bus bar ( some like to put a T fuse or breaker on this line )
Fuse block ----- breaker ----main bus bar
If you wanted, you could use an 80 or 90 amp breaker in each location for commonality and do the bulk of the wiring with 2 awg.
________________-
Most fuse blocks can handle 30 amp loads and chargers per fuse position, so you can just run the solar charge controller into the fuse block
For the solar charge controller fuse, ( 400 watts of solar ) / (nominal 28 volts charging conditions ) ~ 14 amps under perfect conditions.
Most likely you will use 10 awg wire for this and it is rated for 30 amps, so you can fuse at 20 or 30 amps and be just fine.
If you do the bulk of your wiring with 10 awg, then many of the fuses can be 20 amp or 30 amp ( you can pick a common size for spares vs having a bunch of sizes )
I have built a number of setups like this - very straightforward and reliable.
_______________
Your 2 Series , 2 parallel setup from 4 each, 100 amp-hr batteries
Battery pack A is ( 100 amps - hrs ) x ( 24 volt ) ~ 2400 watt-hrs
Same for pack B
Last edited:
Budsy
New Member
No just 2 batteries in each of the series packs and I won’t be needing any DC fuse block as this system is for my shop
Budsy
New Member
Sorry. I get it now. Do you know where I can find a wiring diagram that allows you to plug in the values of your components and it will give you fusing and wire gauge’s nessisary?
HarryN
Solar Enthusiast
Hi - I was thinking of a mobile system since you had posted in that forum.
There are additional code requirements for a stationary building that you may or may not need to deal with. Mostly on the solar controller and power shut down side. I am more familiar with mobile setups vs stationary - still learning on that end.
HarryN
Solar Enthusiast
In general, wiring and fusing needs to deal with:
- ampacity charts
- voltage drop
- amp interrupt rating
Start with the highest load:
- Your highest load is the inverter = 1500 watts
- There are conversion losses from DC - AC, so just to make it easy, let's use 2000 watts as the amount of DC amps feeding it
( 2000 watts ) / ( 24 volts ) ~ 100 amps going through the wire to the inverter from the bus bar
Now look at an ampacity chart - here is an example but they are the same:
Cerrowire Resources - Ampacity Charts
Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.
www.cerrowire.com
____________
A wire's ampacity is basically an indication of power loss in it that will result in it getting hot. You can buy wires with different insulation quality but in general for DC, you want the wires to be as cool as possible, so use either the 60 or 75 C rating ( far left ).
This sets the absolute minimum size that you should use no matter how long the wire is.
From the chart, you are in the 2 awg / 3 awg size, so don't use anything smaller than that for carrying the power for the wire from the bus bar to the inverter.
___________________-
HarryN
Solar Enthusiast
The next step is to look at voltage drop:
You can do this by hand, but a lot of people use an on line calculator. The blue sea web site has an on line calculator - that is actually for boats and allows for the wires to get hotter than some would choose - but it is commonly used, especially for DC wiring.
Plugging in 24 volts and 100 amps, and I made an assumption that the total round trip wire distance is 10 feet.
It comes back with 6 awg for a 3% power loss in the wires.
For a 1% loss, it comes back with 3 awg, so we are in the right territory wire size wise.
For a 1% loss and 20 foot - round trip, it would require 0 awg, so it is a balancing act.
_________________
Wires in this size range, I buy with the ends terminated with quality, tin plated lugs done for me.
The difference in a wire that is 2 awg vs 3 awg, price wise is negligible and even 6 awg is not that much less.
____________________
So that covers the highest load wire on the DC side.
If you like, you can go in and individually put the info for each wire on to the ampacity chart and the voltage drop calculator. I like to just make all of them the same unless there is a really good reason to not do it.
For instance in theory, since each wire from ( battery pack A ) is only carrying 1/2 of the load, in theory you could reduce the size of those wires. In practice, keeping them all the same size would allow you to run one pack - at least for a short time - if for some reason you had to take pack B off line.
Let;s assume that we are using 2 awg for the next step.
You can do this by hand, but a lot of people use an on line calculator. The blue sea web site has an on line calculator - that is actually for boats and allows for the wires to get hotter than some would choose - but it is commonly used, especially for DC wiring.
Plugging in 24 volts and 100 amps, and I made an assumption that the total round trip wire distance is 10 feet.
It comes back with 6 awg for a 3% power loss in the wires.
For a 1% loss, it comes back with 3 awg, so we are in the right territory wire size wise.
For a 1% loss and 20 foot - round trip, it would require 0 awg, so it is a balancing act.
_________________
Wires in this size range, I buy with the ends terminated with quality, tin plated lugs done for me.
The difference in a wire that is 2 awg vs 3 awg, price wise is negligible and even 6 awg is not that much less.
____________________
So that covers the highest load wire on the DC side.
If you like, you can go in and individually put the info for each wire on to the ampacity chart and the voltage drop calculator. I like to just make all of them the same unless there is a really good reason to not do it.
For instance in theory, since each wire from ( battery pack A ) is only carrying 1/2 of the load, in theory you could reduce the size of those wires. In practice, keeping them all the same size would allow you to run one pack - at least for a short time - if for some reason you had to take pack B off line.
Let;s assume that we are using 2 awg for the next step.
HarryN
Solar Enthusiast
The next step is to select a breaker for the wires that go from battery pack A to the bus bar.
A common breaker for this is this one from bus
www.bluesea.com
It is a thermal breaker, so you can think about it like a fuse that trips when it gets hot from too much current flowing through it, but has a re-set handle so that you don't need to get the tools out to change it.
______________
Since there are two parallel battery packs, then each one would need to carry ~ 50% of the load.
( 50% ) x ( 100 amps ) ~ 50 amps
The wire ampacity from the chart is ~ 100 amps
So now you have the option to choose a breaker really anywhere between 50 and 100 amps to make it all work and to some extent, it does not really matter.
There is a small amount of resistance in the breaker and that is what is determining the amps trip point, so going to the bare minimum can result in the breaker running a bit warm, so I would pick at least 1/2 way in between - so ~ 75 - 80 amps minimum.
If you plan to put a breaker in between the bus bar and the inverter and use 2 awg, then the right size would be to go 100 amps as that is the max load.
I like to buy common sizes and ratings for things, as this provides a way to just buy one size and have things as self spares, so as common as possible.
The breaker and fuse are to protect the wire in case it comes loose and does a dead short basically - that sets the absolute max rating.
The end device might not be capable of handling the current that the wire can, for instance a fan might only use 1 amp and require it to be fused at 5 amps.
_____________-
I am still drinking morning levels of coffee, so hopefully others will check my work and suggest edits.
A common breaker for this is this one from bus
187-Series - Blue Sea Systems
Thermal circuit breakers provide heavy duty circuit protection for 25 to 200 Amp loads when switching and circuit protection are both required.
www.bluesea.com
It is a thermal breaker, so you can think about it like a fuse that trips when it gets hot from too much current flowing through it, but has a re-set handle so that you don't need to get the tools out to change it.
______________
Since there are two parallel battery packs, then each one would need to carry ~ 50% of the load.
( 50% ) x ( 100 amps ) ~ 50 amps
The wire ampacity from the chart is ~ 100 amps
So now you have the option to choose a breaker really anywhere between 50 and 100 amps to make it all work and to some extent, it does not really matter.
There is a small amount of resistance in the breaker and that is what is determining the amps trip point, so going to the bare minimum can result in the breaker running a bit warm, so I would pick at least 1/2 way in between - so ~ 75 - 80 amps minimum.
If you plan to put a breaker in between the bus bar and the inverter and use 2 awg, then the right size would be to go 100 amps as that is the max load.
I like to buy common sizes and ratings for things, as this provides a way to just buy one size and have things as self spares, so as common as possible.
The breaker and fuse are to protect the wire in case it comes loose and does a dead short basically - that sets the absolute max rating.
The end device might not be capable of handling the current that the wire can, for instance a fan might only use 1 amp and require it to be fused at 5 amps.
_____________-
I am still drinking morning levels of coffee, so hopefully others will check my work and suggest edits.
Budsy
New Member
I was thinking of getting a Victron battery protect for between the battery and inverter. Would the 100 amp model work for that? And would it go before or after the positive buss bar? ThanksThe next step is to select a breaker for the wires that go from battery pack A to the bus bar.
A common breaker for this is this one from bus
187-Series - Blue Sea Systems
Thermal circuit breakers provide heavy duty circuit protection for 25 to 200 Amp loads when switching and circuit protection are both required.
It is a thermal breaker, so you can think about it like a fuse that trips when it gets hot from too much current flowing through it, but has a re-set handle so that you don't need to get the tools out to change it.
______________
Since there are two parallel battery packs, then each one would need to carry ~ 50% of the load.
( 50% ) x ( 100 amps ) ~ 50 amps
The wire ampacity from the chart is ~ 100 amps
So now you have the option to choose a breaker really anywhere between 50 and 100 amps to make it all work and to some extent, it does not really matter.
There is a small amount of resistance in the breaker and that is what is determining the amps trip point, so going to the bare minimum can result in the breaker running a bit warm, so I would pick at least 1/2 way in between - so ~ 75 - 80 amps minimum.
If you plan to put a breaker in between the bus bar and the inverter and use 2 awg, then the right size would be to go 100 amps as that is the max load.
I like to buy common sizes and ratings for things, as this provides a way to just buy one size and have things as self spares, so as common as possible.
The breaker and fuse are to protect the wire in case it comes loose and does a dead short basically - that sets the absolute max rating.
The end device might not be capable of handling the current that the wire can, for instance a fan might only use 1 amp and require it to be fused at 5 amps.
_____________-
I am still drinking morning levels of coffee, so hopefully others will check my work and suggest edits.
HarryN
Solar Enthusiast
A low voltage cut off is a good idea.
Some are available that detect the low voltage and trip an on / off relay on the inverter.
Waytek and others sell them - but the trip method needs to match the inverter on / off.
Here is the data sheet on one from inpower. The voltage might be too high for your needs so double check.
https://inpowerelectronics.com/wp-content/uploads/2023/05/VCM-24-Data_Sheet-2.pdf
Littelfuse also offers some options - some are programmable so that you can pick the trip points.
www.littelfuse.com
___________
I have not used the victron version, but if your primary charging method is solar, then you will want the solar to be able to keep charging even if the low voltage cut off has tripped.
So I guess in between the bus bar and the inverter.
I have been looking for some options that I can use with 24 and 48 volt and made in US but am still looking. My current method is to just turn off the inverter if there is not enough power.
It might make sense to go a bit larger on the solar or have some of them facing morning, some facing late in the afternoon. For this area, I can pretty much double up the total solar panel wattage by having them face different directions. It really helps capture more total power over the day vs just relying on one direction of sunlight.
For instance you could easily have 600 watts facing early morning and another 600 watts facing late afternoon if there is the physical space.
Some are available that detect the low voltage and trip an on / off relay on the inverter.
Waytek and others sell them - but the trip method needs to match the inverter on / off.
Here is the data sheet on one from inpower. The voltage might be too high for your needs so double check.
https://inpowerelectronics.com/wp-content/uploads/2023/05/VCM-24-Data_Sheet-2.pdf
Littelfuse also offers some options - some are programmable so that you can pick the trip points.
Low Voltage Disconnect - Littelfuse
___________
I have not used the victron version, but if your primary charging method is solar, then you will want the solar to be able to keep charging even if the low voltage cut off has tripped.
So I guess in between the bus bar and the inverter.
I have been looking for some options that I can use with 24 and 48 volt and made in US but am still looking. My current method is to just turn off the inverter if there is not enough power.
It might make sense to go a bit larger on the solar or have some of them facing morning, some facing late in the afternoon. For this area, I can pretty much double up the total solar panel wattage by having them face different directions. It really helps capture more total power over the day vs just relying on one direction of sunlight.
For instance you could easily have 600 watts facing early morning and another 600 watts facing late afternoon if there is the physical space.
Last edited:
HarryN
Solar Enthusiast
The general topic of low voltage disconnect is a good one for the forum.
I found a thread that is already started and added a few links to it here:
diysolarforum.com
If you find additional info on them topic - putting it there to make it easy for people to find would be great.
I found a thread that is already started and added a few links to it here:
Low voltage disconnect for inverter
The Victron BP65 low voltage disconnect is installed. The Samlex 1500 has a 3 position toggle (on/off/switch), as well as +/- to wire it. In my case, can I wire the + from the load terminal of the LVD, and the - the inverter - post? Will the low voltage disconnect switch the inverter off as...
diysolarforum.com
If you find additional info on them topic - putting it there to make it easy for people to find would be great.
Budsy
New Member
Thank you so much. Very helpful. I’m actually building two systems, one the 4 agm 100ah’s 4x 100w panels and my little trailer build with 2 100ah lithium iron and 1 395 w panel. Both 24 voltThe next step is to select a breaker for the wires that go from battery pack A to the bus bar.
A common breaker for this is this one from bus
187-Series - Blue Sea Systems
Thermal circuit breakers provide heavy duty circuit protection for 25 to 200 Amp loads when switching and circuit protection are both required.
It is a thermal breaker, so you can think about it like a fuse that trips when it gets hot from too much current flowing through it, but has a re-set handle so that you don't need to get the tools out to change it.
______________
Since there are two parallel battery packs, then each one would need to carry ~ 50% of the load.
( 50% ) x ( 100 amps ) ~ 50 amps
The wire ampacity from the chart is ~ 100 amps
So now you have the option to choose a breaker really anywhere between 50 and 100 amps to make it all work and to some extent, it does not really matter.
There is a small amount of resistance in the breaker and that is what is determining the amps trip point, so going to the bare minimum can result in the breaker running a bit warm, so I would pick at least 1/2 way in between - so ~ 75 - 80 amps minimum.
If you plan to put a breaker in between the bus bar and the inverter and use 2 awg, then the right size would be to go 100 amps as that is the max load.
I like to buy common sizes and ratings for things, as this provides a way to just buy one size and have things as self spares, so as common as possible.
The breaker and fuse are to protect the wire in case it comes loose and does a dead short basically - that sets the absolute max rating.
The end device might not be capable of handling the current that the wire can, for instance a fan might only use 1 amp and require it to be fused at 5 amps.
_____________-
I am still drinking morning levels of coffee, so hopefully others will check my work and suggest edits.
