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Fusing a 48v system with small MPPTs (Victron 100/20s)

micander

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Joined
Jan 28, 2023
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6
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Nevada, US
Hi, just joined as I'm beginning my first "real" system, a small off-grid setup with mostly Victron components. This will be the 3rd solar setup I've done, first one powers a remote LTE router and camera, second is our travel trailer.

With this new system, I'm going straight to 48v so I can expand without having to replace components too much. I'm starting off with one SOK 48v/100AH battery, a Victron Multiplus 48/3000, and two 600w arrays. The two arrays will have drastically different shading so I want each on its own MPPT, thus the 100/20s. Next phase will be to add a much larger array, but this is what I have for now. Won't be powering a ton to start with, just some "always on" loads like a freezer, and some networking gear.

Here's the difficulty - fusing between the MPPTs and the battery (connected via a Lynx Power In), what in the world do I use for a fuse that is rated for 48v but only 25 or 30 amp? All the fuses I'm seeing rated for 48v (58v fuse rating) start at 100amp and go up. I have 25a DC breakers between the panels and the MPPTs, but from what I read around here I should be using fuses and not breakers between the MPPTs and the battery.

I'll try to create a proper diagram soon to help show the whole system, what I have now is just on paper and not digital. Thanks in advance!
 
The fuse is meant to protect the wires. Depending on what wires you are using between the battery and the mppts, you should fuse them accordingly. So, if your cables are rated to 100A I would fuse them with either with an 100A or 125A fuse. It does not matter that you are charging with less amps. The problem appears when you exceed the cable rating, that's when fuses come into play.
Use a fuse anyway, even if in practice under normal circumstances there will not be any current close to that cabling rating.
 
Hi, just joined as I'm beginning my first "real" system, a small off-grid setup with mostly Victron components. This will be the 3rd solar setup I've done, first one powers a remote LTE router and camera, second is our travel trailer.

With this new system, I'm going straight to 48v so I can expand without having to replace components too much. I'm starting off with one SOK 48v/100AH battery, a Victron Multiplus 48/3000, and two 600w arrays. The two arrays will have drastically different shading so I want each on its own MPPT, thus the 100/20s. Next phase will be to add a much larger array, but this is what I have for now. Won't be powering a ton to start with, just some "always on" loads like a freezer, and some networking gear.

Here's the difficulty - fusing between the MPPTs and the battery (connected via a Lynx Power In), what in the world do I use for a fuse that is rated for 48v but only 25 or 30 amp? All the fuses I'm seeing rated for 48v (58v fuse rating) start at 100amp and go up. I have 25a DC breakers between the panels and the MPPTs, but from what I read around here I should be using fuses and not breakers between the MPPTs and the battery.

I'll try to create a proper diagram soon to help show the whole system, what I have now is just on paper and not digital. Thanks in advance!

Working on something similar as well, although still at the theoretical level, working out the bits and pieces as I go.

So, I hope you don't mind me asking, but what panels will you use with the MPPT? Voc and Isc? Thanks


..The fusing of the MPPTs.
I see you've mentioned the Lynx distro, are you looking for fuses that fit into the Lynx, or external fuses would do too?

Best,
D.
 
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Hi, just joined as I'm beginning my first "real" system, a small off-grid setup with mostly Victron components. This will be the 3rd solar setup I've done, first one powers a remote LTE router and camera, second is our travel trailer.

With this new system, I'm going straight to 48v so I can expand without having to replace components too much. I'm starting off with one SOK 48v/100AH battery, a Victron Multiplus 48/3000, and two 600w arrays. The two arrays will have drastically different shading so I want each on its own MPPT, thus the 100/20s. Next phase will be to add a much larger array, but this is what I have for now. Won't be powering a ton to start with, just some "always on" loads like a freezer, and some networking gear.

Here's the difficulty - fusing between the MPPTs and the battery (connected via a Lynx Power In), what in the world do I use for a fuse that is rated for 48v but only 25 or 30 amp? All the fuses I'm seeing rated for 48v (58v fuse rating) start at 100amp and go up. I have 25a DC breakers between the panels and the MPPTs, but from what I read around here I should be using fuses and not breakers between the MPPTs and the battery.

I'll try to create a proper diagram soon to help show the whole system, what I have now is just on paper and not digital. Thanks in advance!
Little fuse makes class T fuses from 1amp up in JllS and JllN types, class T are the recommendation on 48 volt system
but there are Anl fuses that are rated up to 72 volts in renolgy brand available at inverter supply but I would use class T personally, victron also uses Anl fuses in some of there equipment but I don’t know the amp selection they have available
 
The fuse is meant to protect the wires. Depending on what wires you are using between the battery and the mppts, you should fuse them accordingly. So, if your cables are rated to 100A I would fuse them with either with an 100A or 125A fuse. It does not matter that you are charging with less amps. The problem appears when you exceed the cable rating, that's when fuses come into play.
Use a fuse anyway, even if in practice under normal circumstances there will not be any current close to that cabling rating.
I get what you're saying, but Victron still calls for a max of 35 or 30a fuse between the MPPT and the battery, so ideally I will follow that spec.
 
Working on something similar as well, although still at the theoretical level, working out the bits and pieces as I go.

So, I hope you don't mind me asking, but what panels will you use with the MPPT? Voc and Isc? Thanks


..The fusing of the MPPTs.
I see you've mentioned the Lynx distro, are you looking for fuses that fit into the Lynx, or external fuses would do too?

Best,
D.
Right now I have some Renogy 100w panels that I will be using in a 3x2 series/parallel setup, should be around 70v/10a. Panels are 23.4 Voc, 5.21a Isc.
I was thinking I'd keep it clean by using MEGA fuses in the Lynx, and I will for the inverter (125a), but looks like I'll be doing something else for the MPPTs.
 
Little fuse makes class T fuses from 1amp up in JllS and JllN types, class T are the recommendation on 48 volt system
but there are Anl fuses that are rated up to 72 volts in renolgy brand available at inverter supply but I would use class T personally, victron also uses Anl fuses in some of there equipment but I don’t know the amp selection they have available
Ah ha, thanks! Class T is the one I didn't dig into, looked at all the MIDI/MEGA/ANL options but anything thats rated for 48v is 100a and up. Smaller amp ratings are only 32v. Any recommendations on where to look for the Class Ts and associated holders/blocks? Amazon seems to not have much in the smaller sizes.
 
Right now I have some Renogy 100w panels that I will be using in a 3x2 series/parallel setup, should be around 70v/10a. Panels are 23.4 Voc, 5.21a Isc.
I was thinking I'd keep it clean by using MEGA fuses in the Lynx, and I will for the inverter (125a), but looks like I'll be doing something else for the MPPTs.
I can tell you've spent some time thinking this design out. It's crazy how similar our two designs are in many ways, with a big difference that you are way ahead of me with actually getting to start building it. Very intrigued! :)

Anyhow... I'll share what I've found thus far in facing similar design challenges, hope it's helpful.

Likewise, somehow along the line between shading challenges, the bigger panels, and the other things that need to be taken into account in the long run, The 100W came into the picture as well. Again, just crazy. :)

My only concern, if you could call it that, is if the 3x100W in series will have a high enough voltage to charge the 48V storage throughout the year. Would love to hear your thoughts on this.


As for the SCCs fuse, here's what I was thinking about how to address the two SCCs fuse protection for my 48V build.

Everything considered, this is really not that expensive, yet very reliable and practical.

BlueSeaSystem double terminal block and 30A fuses with 10AWG cables.
BlueSeaFuseBlock.jpgspecs.png


Anyhow, hope it helps. Definitely subbed, hope you'll share the final build. :)

Best,
D.
 
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You may have to find a local distributor that sells little fuse or check website and see if they sell directly or dealer/retailer
 
I can tell you've spent some time thinking this design out. It's crazy how similar our two designs are in many ways, with a big difference that you are way ahead of me with actually getting to start building it. Very intrigued! :)

Anyhow... I'll share what I've found thus far in facing similar design challenges, hope it's helpful.

Likewise, somehow along the line between shading challenges, the bigger panels, and the other things that need to be taken into account in the long run, availability, design flexibility, practicality, and so forth, Renogy 100W came into the picture as well and is in my humble opinion the winner. Again, just crazy. :)

My only concern, if you could call it that, is if the 3x100W in series will have a high enough voltage to charge the 48V storage throughout the year. Would love to hear your thoughts on this.


As for the SCC fusing, here's what I was thinking about how to address the two SCCs fusing for my 48V build.

Everything considered, this is really not that expensive, yet very reliable and practical.

BlueSeaSystem double terminal block and 30A fuses with 10AWG cables.
View attachment 132030View attachment 132031


Anyhow, hope it helps. Definitely subbed, hope you'll share the final build. :)

Best,
D.
They only have 10% of the interruption ability compared to a class T
 
Yes, I wasn't recommending this for the main fuse for the battery storage. Only for the SCC's fusing.
For that application they would be ok it would take a big pv system to hit 2000amps I don’t think that’s what’s he planning for future expansion ?
 
Ohh, the MRBF Terminal fuses are actually a great idea. I have some from the camp trailer build and they fit perfectly on the end of the Lynx. I might go this route.

PXL_20230129_203840057.jpg

As far as the 100w panels, with 3 in series the voltage should be in the 60-70v range. So shouldn't have a problem being enough above 48 to charge. I've done 6 in series and seen it around 140v pretty consistently. I will test the 3x2 setup here in the next couple days and let you know how it looks.

Honestly if I didn't already have the renogy panels I might look for something that gave me more wattage in the same space I have.


I can tell you've spent some time thinking this design out. It's crazy how similar our two designs are in many ways, with a big difference that you are way ahead of me with actually getting to start building it. Very intrigued! :)

Anyhow... I'll share what I've found thus far in facing similar design challenges, hope it's helpful.

Likewise, somehow along the line between shading challenges, the bigger panels, and the other things that need to be taken into account in the long run, availability, design flexibility, practicality, and so forth, Renogy 100W came into the picture as well and is in my humble opinion the winner. Again, just crazy. :)

My only concern, if you could call it that, is if the 3x100W in series will have a high enough voltage to charge the 48V storage throughout the year. Would love to hear your thoughts on this.


As for the SCCs fuse, here's what I was thinking about how to address the two SCCs fuse protection for my 48V build.

Everything considered, this is really not that expensive, yet very reliable and practical.

BlueSeaSystem double terminal block and 30A fuses with 10AWG cables.
View attachment 132030View attachment 132031


Anyhow, hope it helps. Definitely subbed, hope you'll share the final build. :)

Best,
D.
 

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  • PXL_20230129_203840057.jpg
    PXL_20230129_203840057.jpg
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Ohh, the MRBF Terminal fuses are actually a great idea. I have some from the camp trailer build and they fit perfectly on the end of the Lynx. I might go this route.

View attachment 132085

As far as the 100w panels, with 3 in series the voltage should be in the 60-70v range. So shouldn't have a problem being enough above 48 to charge. I've done 6 in series and seen it around 140v pretty consistently. I will test the 3x2 setup here in the next couple days and let you know how it looks.

Honestly if I didn't already have the renogy panels I might look for something that gave me more wattage in the same space I have.
Heh, that really looks as if it was made that way. Very nice fit! :)

As far as the 100w panels, with 3 in series the voltage should be in the 60-70v range. So shouldn't have a problem being enough above 48 to charge. I've done 6 in series and seen it around 140v pretty consistently.
Voltage-wise, it does sound like it shouldn't be a problem at all.

I will test the 3x2 setup here in the next couple days and let you know how it looks.
That would be fantastic. Thanks.

Honestly if I didn't already have the renogy panels I might look for something that gave me more wattage in the same space I have.
True, it's very possible to get a 400W within almost the same footprint as a 3x100W panel.

Best,
D.
 
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This is mainly for @Daxo - a small update on the panels now that I'm starting to get some plugged in. I'll start a new thread with the overall build of the system.

I hooked up three of the 100W Renogy panels in series yesterday, in complete shade, and they put out 62.8 volts (and .4 A). This morning in some intermittent sun, voltage is around 72-74. So should be no problem staying high enough to keep a 48v battery fully charged :)
 
I'll start a new thread with the overall build of the system.
Can't wait :)

I hooked up three of the 100W Renogy panels in series yesterday, in complete shade, and they put out 62.8 volts (and .4 A). This morning in some intermittent sun, voltage is around 72-74. So should be no problem staying high enough to keep a 48v battery fully charged :)
That's fantastic! Thanks for taking the time, much obliged.

Best,
D.
 
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