Circuit Protection & On/Off Switch

[MarkK]

Question around the use of a DC inline automotive fuses and on/off load switch on panels wired in series.

In my current parallel set up of 2 - 80W panels, I have wired inline fuses on both legs (15A) and installed a simple AC/DC rocker switch on the positive leg after the inline fuse which is off when I am making my connections to the CC and batteries, and then turned once all connections are made. Picture attached.

When I re-wire the panels into series are there any considerations needing to be made with respect to how I use the inline fuses and on/off switch which is rated at 10A @250V? Seems to me I should be able to continue to use what I have.

 

[ChetLazar]

The #12 AWG wire can take 20 amps.  If you put a 20 amp fuse at the battery it will keep the hundreds of cranking amps from igniting the wire.  Since the panels can only produce 5 amps max the panels cannot ignite the long wire and cannot blow the fuse.  Multiple fuses and switches have resistance.  Resistance is futile.  You want less of it.

 

[tx2sturgis]

When wiring two panels in series, normally, no inline fuse is needed, and I would not even install an inline switch.

Fuses and switches both have a very small voltage drop, and as the contacts age, weather, and oxidize, you might have a failure at some point.

If you need to interrupt the output from the panels, simply disconnect them or pull the positive wire from the input of the controller.

K.I.S.S. philosophy.

Of course you DO need fuses in the other lines to the battery and inverter.

 

[Boyntonstu]

#12 wire has 1.5 Ohms of resistance per 1,000 feet!

Very low resistance.

Are you using 100 feet?

10 feet?

Why worry?

http://www.interfacebus.com/AWG-table-of-different-wire-gauge-resistance.html

 

[MarkK]

When wiring two panels in series, normally, no inline fuse is needed, and I would not even install an inline switch.

If you need to interrupt the output from the panels, simply disconnect them or pull the positive wire from the input of the controller.

Of course you DO need fuses in the other lines to the battery and inverter.

So given my portable setup using a 2-pin SAE connector just plug in, or unplug as needed, even with the panels in the sun?

 

[MarkK]

#12 wire has 1.5 Ohms of resistance per 1,000 feet!

Very low resistance.

Are you using 100 feet?

10 feet?

Why worry?

http://www.interfacebus.com/AWG-table-of-different-wire-gauge-resistance.html

I though protecting the panels, and the CC, from an accidental short from the oanles or batteries was what is recommended. I'll keep the inline fuses in the run from CC to batteries close to th enbatteries, but get rid of the other hardware.

 

[MarkK]

The #12 AWG wire can take 20 amps.  If you put a 20 amp fuse at the battery it will keep the hundreds of cranking amps from igniting the wire.  Since the panels can only produce 5 amps max the panels cannot ignite the long wire and cannot blow the fuse.  Multiple fuses and switches have resistance.  Resistance is futile.  You want less of it.

In my setup, unless I'm trying to start the onboard generator, this is going to the coach batteries. Are you saying you would, or would not, have the inline fuses between the CC and batteries? That will be a short 2' run.

 

[tx2sturgis]

So given my portable setup using a 2-pin SAE connector just plug in, or unplug as needed, even with the panels in the sun?

Yep.

Thats what I do.. neither the panels nor the controller care how the power from the panels is cut off.

I assume you plan on disconnecting them a couple of times a day or a week or some variation on this.

 

[MarkK]

Yep.

Thats what I do.. neither the panels nor the controller care how the power from the panels is cut off.

I assume you plan on disconnecting them a couple of times a day or a week or some variation on this.

Yes, have a dry camping trip planned to Great Basin Ntl Park and will likely put up and take down a nandful of times during the 10 day stay.

 

[tx2sturgis]

Yes, have a dry camping trip planned to Great Basin Ntl Park and will likely put up and take down a nandful of times during the 10 day stay.

Ok...this is all pretty normal...one thing to be aware of...your controller may have a day-night counting algorithm and/or a weekly or monthly equalization program. I dont know what you have, but if it does, be aware that part of the charge 'intelligence' may not function correctly due to the on-off cycling. It wont hurt anything though.

If you leave the controller on power all the time it should be able to determine daylight, dark, and morning correctly.

 

[MarkK]

Ok...this is all pretty normal...one thing to be aware of...your controller may have a day-night counting algorithm and/or a weekly or monthly equalization program. I dont know what you have, but if it does, be aware that part of the charge 'intelligence' may not function correctly due to the on-off cycling. It wont hurt anything though.

If you leave the controller on power all the time it should be able to determine daylight, dark, and morning correctly.

I belive it does, Victron mppt 75/15, with equalization turned off.

 

[ChetLazar]

In my setup, unless I'm trying to start the onboard generator, this is going to the coach batteries. Are you saying you would, or would not, have the inline fuses between the CC and batteries? That will be a short 2' run.

The 2 Lifeline batteries can put out a lot of current.  In a catastrophe the charge controller, which is not a fuse, could have internal parts like transistors turn into useless dumb conductors.  that would connect the batteries to your 25 foot cable that is on the ground.  If it is shorted there could be fire.

An example catastrophe is where there is a nearby lightning strike that induces a lot of watts into your 25 foot #12 AWG antenna.  Those watts could roast the controller and the solar panels.

Every battery connection needs protection at the battery, within inches.  The first wire segment may be only 2 feet but that's enough.

 

[MarkK]

The 2 Lifeline batteries can put out a lot of current.  In a catastrophe the charge controller, which is not a fuse, could have internal parts like transistors turn into useless dumb conductors.  that would connect the batteries to your 25 foot cable that is on the ground.  If it is shorted there could be fire.

An example catastrophe is where there is a nearby lightning strike that induces a lot of watts into your 25 foot #12 AWG antenna.  Those watts could roast the controller and the solar panels.

Every battery connection needs protection at the battery, within inches.  The first wire segment may be only 2 feet but that's enough.

2 questions.

Are you saying an inline fuse inline from the panel to just before the CC is a good idea, and

2) does this inline set up at the batteries look acceptable?

 

[tx2sturgis]

An example catastrophe is where there is a nearby lightning strike that induces a lot of watts into your 25 foot #12 AWG antenna.  Those watts could roast the controller and the solar panels.

Every battery connection needs protection at the battery, within inches.  The first wire segment may be only 2 feet but that's enough.

CL, a little fuse that's an inch across is NOT lighting protection. If a direct (or indirect) lightning strike destroys the panels, well...the nearby people and the motorhome or RV are the main concern, not a couple of hundred dollars of silicon. If a lightning bolt just jumped 2500 feet or 2 miles, either way, it wont be stopped by a 50 cent fuse.

But I do agree that fuses should be used on every in and out cable to the batteries.

 

[Weight]

The 12 AWG wire can safely carry 40 amps. You don't need fuses between the series panels and controller. You do need a fuse close to the battery terminal on the controller wire. If you get struck by lightning, it is all over, even with fuses.