Is this particular DC Circuit Breaker OK for my 600w series setup?

[jasonhc73]

Hello, I am new here and plan to build a PV system in my van. I start with a stupid question ... What is the job of this DC-Braeker? Some people say it is cut for "backflow" ?! but I'm going to use an MPPT, how can I get a "reverse current"? And if I have a short circuit at the DC input of the MPPT or in connection with the solar cell, the current is not more than 5-6 amps. so the DC Braeker would never trigger.
many thanks for your help

The DC circuit is no different than a fuse if it gets "popped" it can be reset.
It is not a diode.
If it is on the panel side then back feed from the battery to the panel is not possible.
Get a DC Circuit breaker just an amp or so higher than the IMP you expect to setup. (that is, the maximum amps you intend to have)

MidNite Solar 150 VDC MNEPV Din Rail Breakers

MidNite Solar Breakers - rated to break the full rated load at the rated voltage repeatedly, with NO DAMAGE. Always use a properly sized breaker for disconnecting.

mwands.com

 

[JoeHam]

Square D QO series breakers are rated for DC use. Available at Amazon and home improvement stores.

Cost around $10 US

Note, NOT the Homeline series, just QO

 

[JoeHam]

See here:

Are QO load centers suitable for use on a 125V DC application? | Schneider Electric USA

And here:

https://download.schneider-electric.com/files?p_enDocType=Catalog&p_File_Name=0730CT9801.pdf&p_Doc_Ref=0730CT9801

 

[Black-on-Plus]

Thank you for your answers. So if I understand it correctly, should the fuse only protect the panel from a short circuit? but why is the user kenkoh recommended a 12 amp fuse? he has 6 x 100 watt panels connected in series. So there should be no more than 6 amps in the event of a short circuit.

 

[JoeHam]

Thank you for your answers. So if I understand it correctly, should the fuse only protect the panel from a short circuit? but why is the user kenkoh recommended a 12 amp fuse? he has 6 x 100 watt panels connected in series. So there should be no more than 6 amps in the event of a short circuit.

The fuse generally is used to protect the wires from catastrophic failure.

 

[JoeHam]

The fuse generally is used to protect the wires from catastrophic failure.

@FilterGuy posted a whole thread about this subject which is well worth the read time.

 

[Dzl]

Your system is grounded dc input. They all get 'grounded' but your pv line should not have a break in the negative side. Single pole breaker there. Some high voltage pv breakers have 2 poles but they have a bus on one side.

What determines this? I have seen double pole breakers used between PV array and the SCC before (for example in this victron schematic).

 

[Dzl]

@FilterGuy posted a whole thread about this subject which is well worth the read time.

It's a great thread! Well worth the read.

The fuse generally is used to protect the wires from catastrophic failure.

As a general rule I totally agree ("fuses protect the wire, not the device"), but I think the PV Array charge controller connection is at least a partial exception to that rule. My limited understanding is that unlike fuse protection on a battery circuit where current can easily be in the hundreds of amps, PV arrays are naturally self limiting and even in the case of dead shorts won't surpass their Isc (short circuit current) which for an individual 300-400 watt panel will probably be roughly 5-10A. For this reason the purpose, and proper size of a breaker between the PV array and the mppt controller is a little less clear.

I definitely don't want to give the impression i'm knowledgeable about this, because i'm not, this is just my impression based on the little bit of information I've read on the topic (I believe this subject was discussed in the thread you mentioned, and also this article addresses it). I'm not informed enough to have an opinion or offer advice, just sharing what I've learned.

 

[kernel]

For multiple combined strings, the combined current could be shunted through a single or several strings of conductors. Modules are generally going to be 15 or 20 amp rated amd generally wired with #10. #10 rated 30A with a 15 or 20A fuse or breaker.

That string of modules cannot degrade the wiring nor break the overcurrent protection device with its available power. Likely 3x 9.6ish amp strings would be required to approach max ampacity of the wire, but you will have overheated amd degraded the insulation and encapsulation materials of the module and there would be danger of fire.

Its nice to have a switch and safer to provide overcurrent protection on more than 2 strings of panels approching or exceeding 20A continuous (panel rating) and 30A combined on the #10 pv leads. 20A is the maximum current that the circuit can be asked to handle, weakest link sets the rating for overcurrent protection.

In the case of charge controllers battery connection, i suggest overcurrent protection is desired.
In the event of certain control failures the control will short the battery line internally...... the case/enclosure and all wire connected along with overcurrent protection amd even sometimes the materials the device is mounted to needs to be rated to withstand this catastrophic failure as a system in order to provide acceptably safe operation and use.