Recs for Solar Cut Off Switch?

[Powertour]

Looking for help finding some sort of cut off switch that I can mount on the wall inside my coach next to where the charge controller is currently mounted.

Side note: I'm pretty much hemmed into putting the cut off switch next to the charge controller due to the way the previous owner wired the array into the coach.

Trying to find anything that isn't big &/or big & ugly has proven to be an exercise in futility.

Thanks in advance!

[RLS7201]

pianotuna wrote:
Hi,

On AC power the direction of the voltage changes 30 times a second. On DC it is one way, so an arc requires a larger gap.

Here is a high voltage example:

https://www.youtube.com/watch?v=d3U1yrBI3xc

That is what is happening inside the switch. The arcing causes pitting of the contacts.

RLS7201 wrote:

pianotuna wrote:
BFL13,

With respect, using a switch rated for AC in a DC circuit may lead to arcing.

Don, what are the design characteristics of AC and DC switches that differentiates the two? What inhibits the arching in one design and not the other. Inquiring minds want to know.

Richard

I would suggest that 60 cycle AC service changed direction 120 time a second NOT 30.

Richard

[Powertour]

Thanks for all the info & the ideas. i ended up going with this little switch purchase off Amazon.

https://imgur.com/a/qi0CCw2



As seen Installed next to my inverter controller.



https://imgur.com/a/PDYSFJn

[BFL13]

TechWriter wrote:

BFL13 wrote:

Ok, so which is the higher potential????

Follow the PV array-to-Controller circuit and the Controller-to-Batteries circuit through the 4 breakers.

Thanks! OK, so the MNEPV-15s have their double pos such that the panels are higher than the controller, and the controller is higher than the batteries.

This would support the panels as a current source to charge the batteries, with the panels having a higher voltage than the batteries.

I don't understand the arrows on the controller drawing, where pos and neg are pointing the same way. What are the circuits here?

EDIT--the battery cell while being charged, has electrons flowing through an external circuit to the battery's negative plate from the positive plate. (Reversed for when being discharged)

So you put the pos to pos and the neg to neg with the charger (panel)and battery, and you have the charger being discharged (neg to pos) and the battery being charged (pos to neg)

[TechWriter]

BFL13 wrote:

Ok, so which is the higher potential????

Follow the PV array-to-Controller circuit and the Controller-to-Batteries circuit through the 4 breakers.

[pianotuna]

Hi BFL13,

The higher potential is a dead short across the battery bank.

[BFL13]

Here is something about being 80v or over on the solar and no auto-reset breakers allowed,

https://www.technicalsafetybc.ca/sites/default/files/csa-fia36443694-polarityidpvdc.pdf

[BFL13]

TechWriter wrote:

BFL13 wrote:

On polarity "direction" I don't see the way that is marked on a switch, so how to get it right way around if on the battery neg wire or pos wire?

The higher potential terminal on this DC breaker is marked with a ++ on this switch:

Ok, so which is the higher potential????

I remember around 1981, some of our electronic techs took a course in the States on a particular equipment. After, they said it was a good course, except they had to get used to "how they taught diodes". (Backwards)

Off topic, but anyway, one of them was French from Quebec, and he said the trouble was the instructor kept calling everything (like a diode) a "critter". After some of that he had to ask, "Please, Sir, what's a "critter?" 🙂

[TechWriter]

BFL13 wrote:

On polarity "direction" I don't see the way that is marked on a switch, so how to get it right way around if on the battery neg wire or pos wire?

The higher potential terminal on this DC breaker is marked with a ++ on this switch:

[BFL13]

The ads don't mention bi-directional (at least not at this store)

Here is one that is "negative" polarity and it says to mount it on the battery's negative post. Does that change the idea of what "polarity" means?

https://www.princessauto.com/en/detail/300a-rotary-dial-battery-disconnect-switch/A-p8618415e

[pianotuna]

BFL13,

I'd use a bi directional switch with arc protection both ways.

BFL13 wrote:
On polarity "direction" I don't see the way that is marked on a switch, so how to get it right way around if on the battery neg wire or pos wire? Would want an arrow toward the battery (or solar panel) positive post in the States (or negative post in Canada?)

With the solar controller in the middle and the array as the "current source", which way is "positive"? You have the battery circuit direction and the array circuit direction, but the PWM controller passes the battery voltage to the array. How can it do that if they are in opposite directions?

[twodownzero]

crcr wrote:

BFL13 wrote:
Don't know what counts as big and ugly, but you can use an ordinary 120v household light switch in the wall next to the controller. IMO not ugly, but might be too big, no idea. Doesn't matter if the wire being switched is 120v or 12v.

You can switch either the pos or neg "ARRAY" wire to the controller and it will cut off the array.

There might be a trick as to which wire to switch depending on whether the controller is positive or negative grounded and if it is grounded--in an RV no need to ground the array or controller, but who knows what an installer will do?

Or it might not make any difference no matter what. Somebody else who knows more can jump in on that as required.

I am not an expert on solar systems, but from my study, I believe that the positive leg should be switched, as opposed to the negative side. This is the same as wiring in 110V, where the positive side of a load should be switched, as opposed to the negative side.

You might be surprised to learn that AC doesn't have a positive or negative "side."

[BFL13]

So if it is all about the voltage for the amps rating within the watts limit, then:

2700w/12 = 225 amps rating, but in the RV at 14.8v, it is 2700/14.8 = 182 amps?

On polarity "direction" I don't see the way that is marked on a switch, so how to get it right way around if on the battery neg wire or pos wire? Would want an arrow toward the battery (or solar panel) positive post in the States (or negative post in Canada?)

With the solar controller in the middle and the array as the "current source", which way is "positive"? You have the battery circuit direction and the array circuit direction, but the PWM controller passes the battery voltage to the array. How can it do that if they are in opposite directions?

[pianotuna]

BFL13,

DC switches often do exhibit "polarity". This came up in a solar installation thread, a few weeks ago. There is arc inhibiting built into the switch. If it is installed "backwards" then there is little arc fault protection.

Some switches have the technology for arc protection on both "sides" of the switch--then the polarity no longer matters.

[pianotuna]

Hi BFL13,

What matters most, in my opinion, is the contacting amperage. Mine are rated at 1000 amps, contacting, but only 100 amps continuous. As I use two in parallel that gets me to 200 amps continuous.

AC switches can be used but they have to be de-rated by about 90% on the voltage side. That means a switch with a rating of 125 volts is "right on the edge" for 12 volt use--because we often see 13.4 or higher. It would not matter when the circuit is closed--but it would matter when turning it "off" or "on"