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Noob Here Needs Recommendations on where to put a fuse

craigbuchjr

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I have 2 100w Renogy solar panels running in parallel down to a Renogy Wanderer Li 30a PWM Charge controller. I have a 12v 100AH gel battery Finally connected to a 700w Renogy Pure sine wave inverter. So my question is I know there is a fuse that goes in between the battery and the charge controller on the posotive line.. but isnt there a fuse that goes between solar panels and charge controller? 2nd question between the charge controller and the battery can you guys give me some recommendations on best fuses?
 
Yes, you should have a fuse or circuit breaker between battery and solar charge controller (SCC) as well as battery and inverter. From solar panels to SCC you could put a breaker in that can also act as a disconnect switch. Have a look at Will's classic 400W solar blueprint or any of his others to see that they always include circuit protection devices. Location of the protection devices and sizing is covered in the resources I've included below. There are lot of different fuse and circuit breaker options and people have different opinions depending on what their use cases are. I'm partial to the Blue Sea Systems MRBF fuses and blocks as they fit my needs well. I'm sure you'll hear from others here soon...

Some resources:
General guidance on wire sizes and fuse sizing can be found in my post in this thread:

Very detailed info on fuse/circuit breakers in PV systems courtesy of @FilterGuy:

A thread where Blue Sea MRBF fuse options are discussed:
 
thanks for ur reply any idea of what fuses i should have? drop links?
Need to know wire sizes between components in order to properly size the fuses. Once you figure out fuse size (see my first reference post for how to do that based on wire size, it’s a quick read) my opinion is the easiest thing to do is buy one of the dual fuse holders in the third reference link and bolt it to your battery post. Connect your SCC battery wires to one fuse and the inverter battery wires to the other fuse. See the nice diagram by @kenkoh in the third reference link for an example.
 
So this is what I understood from your discription:
1582839227240.png
Assuming your inverter is the only load, the fuse at the battery should match the max current the inverter manual says. This fuse should be as close to the battery as possible. The wire size between the battery and the inverter must be at least large enough to handle the current the fuse allows (preferably a bit larger). If the run is greater than a few feet (round trip from the battery to inverter and back), the wire size will be larger so you will need to look up the wire size for your current and distance. (This site has a nice chart you can use to look up wire size for various round trip lengths. You should use the critical voltage - 3% drop values from the chart)

The fuse for the charge controller should be slightly larger than the max current expected from the controller. This fuse should be placed as close to where it branches from the other circuit as possible. The wires from the charge controller to the battery must be at least large enough to handle the current the fuse will allow. If the run is greater than a few feet (round trip from the battery to controller and back), you will need to look up the larger wire size for your current and distance.

With just two panels in parallel, I am not sure a fuse is needed (or even feasable) on the panel circuit. However, the wires must be large enough to handle the full current from both panels. Even though you may not need a fuse, a lot of people like to put in a disconnect.
 
Last edited:
So this is what I understood from your discription:
View attachment 8172
Assuming your inverter is the only load, the fuse at the battery should match the max current the inverter manual says. This fuse should be as close to the battery as possible. The wire size between the battery and the inverter must be at least large enough to handle the current the fuse allows (preferably a bit larger). If the run is greater than a few feet (round trip from the battery to inverter and back), the wire size will be larger so you will need to look up the wire size for your current and distance. (This site has a nice chart you can use to look up wire size for various round trip lengths. You should use the critical voltage - 3% drop values from the chart)

The fuse for the charge controller should be slightly larger than the max current expected from the controller. This fuse should be placed as close to where it branches from the other circuit as possible. The wires from the charge controller to the battery must be at least large enough to handle the current the fuse will allow. If the run is greater than a few feet (round trip from the battery to controller and back), you will need to look up the larger wire size for your current and distance.

With just two panels in parallel, I am not sure a fuse is needed (or even feasable) on the panel circuit. However, the wires must be large enough to handle the full current from both panels. Even though you may not need a fues a lot of people like to put in a disconnect.
I knew you’d show up here eventually. :)
 
So this is what I understood from your discription:
View attachment 8172
Assuming your inverter is the only load, the fuse at the battery should match the max current the inverter manual says. This fuse should be as close to the battery as possible. The wire size between the battery and the inverter must be at least large enough to handle the current the fuse allows (preferably a bit larger). If the run is greater than a few feet (round trip from the battery to inverter and back), the wire size will be larger so you will need to look up the wire size for your current and distance. (This site has a nice chart you can use to look up wire size for various round trip lengths. You should use the critical voltage - 3% drop values from the chart)

The fuse for the charge controller should be slightly larger than the max current expected from the controller. This fuse should be placed as close to where it branches from the other circuit as possible. The wires from the charge controller to the battery must be at least large enough to handle the current the fuse will allow. If the run is greater than a few feet (round trip from the battery to controller and back), you will need to look up the larger wire size for your current and distance.

With just two panels in parallel, I am not sure a fuse is needed (or even feasable) on the panel circuit. However, the wires must be large enough to handle the full current from both panels. Even though you may not need a fuse, a lot of people like to put in a disconnect.
I'm no expert but shouldn't your fuses be in parallel rather than series?
 
Do you mean like this?
1582845949916.png
That works too. They are both safe. This may be even better from a functionality point of view. (The charger can still work if the inverter fuse is blown.- good catch.) In either circuit, the important thing is the fuse is on the battery end of the line going to the controller.
 
Sometimes in Vans and boats, you just don't have the option of running everything back to one spot and you end up 'taping off' like I showed in the first circuit. This is fine as long as the 'main' line is sized and fused to handle the combined current and the 'secondary' smaller line is fused appropriately at the point it branches off.

Having said that, it is generally cleanest to bring everything to one central point if possible. If nothing more, it will be easier for the next guy to understand the circuits if it all goes back to a central distribution point.

I should probably update my posts about fusing to include this.
 
10awg from panels to CC 10 awg from CC to Battery 4awg from inverter to battery I appreciate everyone responding! thanks
 
I have 2 100w Renogy solar panels running in parallel down to a Renogy Wanderer Li 30a PWM Charge controller. I have a 12v 100AH gel battery Finally connected to a 700w Renogy Pure sine wave inverter. So my question is I know there is a fuse that goes in between the battery and the charge controller on the posotive line.. but isnt there a fuse that goes between solar panels and charge controller? 2nd question between the charge controller and the battery can you guys give me some recommendations on best fuses?
Fixed link to my chart
 
Fixed link to my chart

I may be missing it but I don't see any indication on the chart that the calcs are for a 12v system.

It would be cool to see it replicated for a 48v system so when people ask about the difference with higher voltage they can see it easily.

Either way, thanks for a good reference nicely done.
 
I may be missing it but I don't see any indication on the chart that the calcs are for a 12v system.

It would be cool to see it replicated for a 48v system so when people ask about the difference with higher voltage they can see it easily.

Either way, thanks for a good reference nicely done.
This helps, I will update it with clear 12v. I'm just learning 24v not even going to tackle 48v yet. I'm more noob than you keep that in mind.
 

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