VERY small off grid solar system do I need to use a breaker/fuse?

[John117]

Hello, I did my very own off grid tiny system in my home (thanks to this forum that helped, by the way) everything works fine, but lately I wonder if I needed to add a fuse/breaker to this system. My system is solely with the intention to power path lights outside my home and I think the charge controller has a fuse right?

Solar Panel is 50w - 12v.
Cable is 10 AWG pure copper low voltage landscape wire.
Charge controller is a Victron Smart Solar 75-10
Battery is a 12v LifePo4 20ah.
Load is 8 lights, each one takes 3w.

I might upgrade to a 30ah and 100w panel in the future if I add more lights. My question is, do I need a breaker/fuse for this? And if so, where and how big? Thank you in advance. I am still learning, so it is hard to understand this.

 

[Alice2021]

Your 8 lights is dc 12V input ?or ac 110V input,I have not seen an inverter in your system

 

[Rednecktek]

At the least a fuse between the battery and the lights, just in case something gets too wet underground. Definitely go with a bigger panel, a 30Ah battery would need 5 hours of perfect sun every day on a 100w panel to recharge from empty and you've only got about (24w lights * 14hrs darkness = 336Wh of battery / 14v =) 24Ah of battery used - BMS overhead. You're rrriiiggghhhttt on that line of making it in a good summer day, but in winter you'll be hosed.

 

[constantspeed]

Should use a breaker or more realistically a fuse in-line with the battery positive terminal. You add a fuse/breaker to protect the wire from over-current, so they don't melt down and start a fire. Maybe just a 3amp, or 5amp at most. The fuse in the Victron will only possibly protect the Victron, maybe. But it won't protect the load from the battery to the lights.

 

[John117]

Your 8 lights is dc 12V input ?or ac 110V input,I have not seen an inverter in your system

Oh yes sorry, lights are 12v DC, 3w each, so I don't have an inverter

 

[John117]

At the least a fuse between the battery and the lights, just in case something gets too wet underground. Definitely go with a bigger panel, a 30Ah battery would need 5 hours of perfect sun every day on a 100w panel to recharge from empty and you've only got about (24w lights * 14hrs darkness = 336Wh of battery / 14v =) 24Ah of battery used - BMS overhead. You're rrriiiggghhhttt on that line of making it in a good summer day, but in winter you'll be hosed.

Thank you, the lights are actually plugged on the load side of the victron charge controller, so they are not connected to the battery directly. I did this because the victron has a “timer” function to turn the lights on/off.

 

[John117]

Should use a breaker or more realistically a fuse in-line with the battery positive terminal. You add a fuse/breaker to protect the wire from over-current, so they don't melt down and start a fire. Maybe just a 3amp, or 5amp at most. The fuse in the Victron will only possibly protect the Victron, maybe. But it won't protect the load from the battery to the lights.

Thank you

 

[John117]

Just for context this are the pictures from the system in question.

 

[soylentgreen]

Check out your negative battery cable, it looks like it is upside down and possibly sitting on top of a washer? Generally you want to have the battery cable directly connected to the battery, not with a washer in between. Otherwise, looks like a nice system.

also, do you have a link for the white box that everything is sitting in? That looks like a handy part to have.

 

[John117]

Check out your negative battery cable, it looks like it is upside down and possibly sitting on top of a washer? Generally you want to have the battery cable directly connected to the battery, not with a washer in between. Otherwise, looks like a nice system.

also, do you have a link for the white box that everything is sitting in? That looks like a handy part to have.

Wow! Thanks, it is upside down! I purchased the box on ebay, https://www.ebay.com/itm/155468666137 it could be cheaper in Ali-express, but I didn't want to wait.

 

[stienman]

You only have three points where you could adda fuse:
1. Panels to MPPT
2. Battery to MPPT
3. MPPT to load

The manual for the MPPT indicates that the load is protected from short circuits, so it already has some protection.

It also has a fuse built in - probably for the battery, though it doesn't clearly state - so the battery is protected.

The solar panel can only generate a maximum of 5 amps into a short circuit. The wire between the solar and the MPPT can handle 5 amps indefinitely without causing a fire, and the MPPT controller is UL listed which means that even if an external overvoltage or overcurrent condition occurred, it's not allowed to start a fire. The manual indicates it can handle panel miswiring, and overpaneling.

You installation is safe. It might not be code compliant depending on your local code authority, and adding external fuses will provide additional safety, but it doesn't pose a significant fire hazard even in the worst case scenario.

 

[soylentgreen]

for fusing the wire off the battery, MRBF fuses are hard to beat:

MRBF Terminal Fuse Block - 30 to 300A - Blue Sea Systems

Easily and economically satisfies ABYC 7 circuit protection rule by mounting on a 3/8 battery post, battery switch or bus bar.

www.bluesea.com

They sit right on the battery terminal (so the entire wire is protected) and don't require any cutting, crimping or soldering. They don't go below 30 Amps however, so may not be what you need?

 

[soylentgreen]

It also has a fuse built in - probably for the battery, though it doesn't clearly state - so the battery is protected.

I have a Victron SmartSolar 100/20 and recently blew the 25A fuse by doing something stupid (pushing 12V through the load + output and shorting the battery+ connector to ground.)

In any case, it suggests both the battery and the load output are protected by this fuse.

You probably don't need the MRBF, but it would protect against some other failure modes

Additional adivce: go back and re-tighten all the MPPT connectors after a day or two, I find mine don't seem to always get tight on the first go.

 

[John117]

I have a Victron SmartSolar 100/20 and recently blew the 25A fuse by doing something stupid (pushing 12V through the load + output and shorting the battery+ connector to ground.)

In any case, it suggests both the battery and the load output are protected by this fuse.

You probably don't need the MRBF, but it would protect against some other failure modes

Additional adivce: go back and re-tighten all the MPPT connectors after a day or two, I find mine don't seem to always get tight on the first go.

Will do, thank you!