diy solar

diy solar

Fuses/breakers & Safety

I meant about the circuit fuse not protecting the appliance.
I think its common for intuition to get in the way of understanding on this one.
I liked how you consider some devices like the BMS, shunt, busbar to be like wires - "wire like devices". Protecting the wire you protect those as well.
A proper inverter or mppt won't need protection since it has this in-built.
 
Fuse protect wires.
Example; LFP battery -> fuse#1 -> cable#1 -> BusBar -> fuse#2 -> cable#2 -> device -> internal fuse -> internal wires.
Drop a gold watch on the BusBar, waamm! fuse#1 opens. Or instead, Drop your gold watch on the connection at the device, waamm! fuse #2 opens.
No fuse#1 or fuse#2? Drop the watch and a cable gets hot enough to melt the insulation, glow red hot, and incinerate your bed. All before the device even shuts down.
Complements to Joey. Much more patient than me.

That is if it is a Class-T or MRBF with enough interrupt. If it is a MEGA or ANL fuse, there could be fireworks and a melted wire.
 
Thank you all. Everyone's patient and I'm grateful...
The example above does explain the matter even better.
 
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Hello Everyone! Hope someone from this thread will still be able to patiently have a look at my updated schematics, wire sizes, fuse sizes and dc breakers please.

I have re-read @smoothJoey 's initial post many times with wire and fuse sizes, then have read again the manuals for the Multiplus II and SmartSolars.
Here is an updated version of my schematics. I have oversized some of the wires but kept to the fuses as per Joey's recommendation and the manuals. Following the schematics you can find the screenshots from the manuals regarding fuses and wires.

1651350156896.jpeg


The following is from the Multiplus II manual (shorturl.at/ayIT0), page 13.:
1651349253905.png















The following was taken from the MPPT 150\45 manual (shorturl.at/uCD17), page 9.
1651349438278.png
For the DC breakers between the solar panels and MPPTs, which of the two would you recommend? I suspect the thermal one has an extra layer of protection.
For that Class-T 300 A fuse, between the battery and the inverter, could I not use a DC breaker instead?
Similarly, would it not be better to have a DC breaker between the inverter and the busbar, rather than the 250A megafuse?

I know DC breakers are more expensive, but looking at doing the best option in the end even if it is going to cost more.

Thank you.
 
Hello Everyone! Hope someone from this thread will still be able to patiently have a look at my updated schematics, wire sizes, fuse sizes and dc breakers please.

I have re-read @smoothJoey 's initial post many times with wire and fuse sizes, then have read again the manuals for the Multiplus II and SmartSolars.
Here is an updated version of my schematics. I have oversized some of the wires but kept to the fuses as per Joey's recommendation and the manuals. Following the schematics you can find the screenshots from the manuals regarding fuses and wires.

View attachment 93133


The following is from the Multiplus II manual (shorturl.at/ayIT0), page 13.:
View attachment 93131















The following was taken from the MPPT 150\45 manual (shorturl.at/uCD17), page 9.
View attachment 93132
For the DC breakers between the solar panels and MPPTs, which of the two would you recommend? I suspect the thermal one has an extra layer of protection.
For that Class-T 300 A fuse, between the battery and the inverter, could I not use a DC breaker instead?
Similarly, would it not be better to have a DC breaker between the inverter and the busbar, rather than the 250A megafuse?

I know DC breakers are more expensive, but looking at doing the best option in the end even if it is going to cost more.

Thank you.
That table is silly.
The solar charge controller has built in protection circuits so you fuse for the wire.
The manual says the solar charge controller has output short circuit protection.
The solar charge controller protects the branch circuit not the other way round.
The branch circuit fuse protects the wire not the solar charge controller.
But if you ever need Victron support doing it there way means one less thing to argue about.

The multiplus 2 manual includes some silliness as well.
They spec 2x 50mm2 with a single 300 amp fuse.
Double wires should get double fuses.
I suggest you do 2x 250 amp fuses one for each parallel circuit.
Its just safer.

Alternatively use the same 1x 120mm2 cable that you used for the battery circuit with this fuse.
MEGA fuse 300A/58V80 mV0, 17 mΩ
Which is the highest ampacity fuse that Victron makes.
Just because the device has double lugs does not mean you have to use them.
Most of the good installs I've seen use a thicker single wire.
 
Using double cables on the MultiPlus is not good. Use the appropriate size single cable for negative and positive.
Glad to see the Class-T at the battery. Glad to see the device fuses at the power source end of circuit.
Parallel panels need specific fuse protection, but I can't think today.
 
I thought they want two wires because maybe one thick one would be too big to fit in there, but I agree with you both, I'd rather have one thick wire.

Thank you both, glad you both replied.
 
That table is silly.
The solar charge controller has built in protection circuits so you fuse for the wire.
The manual says the solar charge controller has output short circuit protection.
The solar charge controller protects the branch circuit not the other way round.
The branch circuit fuse protects the wire not the solar charge controller.
But if you ever need Victron support doing it there way means one less thing to argue about.

The multiplus 2 manual includes some silliness as well.
They spec 2x 50mm2 with a single 300 amp fuse.
Double wires should get double fuses.
I suggest you do 2x 250 amp fuses one for each parallel circuit.
Its just safer.

Alternatively use the same 1x 120mm2 cable that you used for the battery circuit with this fuse.
MEGA fuse 300A/58V80 mV0, 17 mΩ
Which is the highest ampacity fuse that Victron makes.
Just because the device has double lugs does not mean you have to use them.
Most of the good installs I've seen use a thicker single wire.
I suppose it's fine to use the mega fuse 300a on the wire to the inverter, same size as the T class fuse at the battery, right?
I see no reason why not, but I'm no expert.
 
I suppose it's fine to use the mega fuse 300a on the wire to the inverter, same size as the T class fuse at the battery, right?
I see no reason why not, but I'm no expert.
Its the best you can do.
Since the wire on the battery circuit and the wire on the main circuit are the same size you could land the inverter on an un-fused port.
A class-t will very likely blow before a mega fuse of the same amp rating so the mega fuse is kinda pointless.
 
Using double cables on the MultiPlus is not good. Use the appropriate size single cable for negative and positive.
Glad to see the Class-T at the battery. Glad to see the device fuses at the power source end of circuit.
Parallel panels need specific fuse protection, but I can't think today.

Why is using double cables not good?
 
Because if one fails the other will either fail if fused separately or melt down and perhaps ignite something.

If both cables are fused separately, and one fails, then you're out two fuses instead of one. That makes sense. With a Victron product that has two positive lugs, the flip side is you can double the copper with two cables and lower the resistance and make it less likely either cable fails as a result, right?

Any other reason two cables fused separately might be bad?
 
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