RV Solar breaker sizing

Hi everyone, like a lot of you I would like to, and I am in the process of installing solar on my RV, I thought it would be fun and allows for some "boondocking" I have 4 panels 19 v/ 8.9 amps.  I am going to parallel two and two to give me 640 watts, 38 v @ 16.8 amps. Wiring from the panels is whatever came on them and I would like to install a breaker/switch between the panels and charge controller and between the charge controller and batteries.
Charge controller MPPT 30 amps
4 12 V 96 Amp hour batteries

My issue is after hours of searching I cannot get an actual answer, I just get led down the road of 100 more questions. Some say I don't need to install a breaker and will argue the point but I want to be able to isolate the panels from the charge controller and the controller from the batteries for my own reasons. Can anyone here that is really familiar with solar give me the straight up answer to these questions? I would really appreciate it so I can order what I need and get on with it. I have attached an image of the style breaker I thought I would use.

Just something else to get corroded and cause problems.>>>Dan

Some say I don't need to install a breaker and will argue the point but I want to be able to isolate the panels from the charge controller and the controller from the batteries for my own reasons.

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Not sure why you are asking. You say you have your own reasons for it, so other's reasons (or lack there-of) would seem to be irrelevant.  You don't need to install that breaker to make the system work properly, but you can certainly have one to meet whatever your other reasons my be.
If you are doubtful about your own reasons, please state what they are and the rest of us can comment on them, pro or con.

Maybe try a solar forum?  I don't see why solar in an RV would be substantially different than in a small farm type application that is not tied to the grid.

Cholmes100 said:

Hi everyone, like a lot of you I would like to, and I am in the process of installing solar on my RV, I thought it would be fun and allows for some "boondocking" I have 4 panels 19 v/ 8.9 amps.  I am going to parallel two and two to give me 640 watts, 38 v @ 16.8 amps. Wiring from the panels is whatever came on them and I would like to install a breaker/switch between the panels and charge controller and between the charge controller and batteries.
Charge controller MPPT 30 amps
4 12 V 96 Amp hour batteries

My issue is after hours of searching I cannot get an actual answer, I just get led down the road of 100 more questions. Some say I don't need to install a breaker and will argue the point but I want to be able to isolate the panels from the charge controller and the controller from the batteries for my own reasons. Can anyone here that is really familiar with solar give me the straight up answer to these questions? I would really appreciate it so I can order what I need and get on with it. I have attached an image of the style breaker I thought I would use.

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it is good practice to fuse both sides of the charge controller.
I would recommend either BlueSea 285 series or Bussman 25X series breakers.
do yourself a favor and avoid the cheap china breakers found on ebay.

also for 640 Watts of panels you will need a 50 Amp controller ( 640 / 12 = 53 )
using a 30 A with ( 96 * 4 = 384 Ah of capacity ) will not make the C/10 minimum charge rate ( 38.4 A )
unless you are moving to 24 Volts. ?

KandT said:

Maybe try a solar forum?  I don't see why solar in an RV would be substantially different than in a small farm type application that is not tied to the grid.

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as an off grid designer, I can tell you there are many differences in requirements and the implementation
of these systems. their use cases are very different.


and moderator, could you please move this thread to the solar section, thanks

Why I am asking is obvious, not sure what my reasons are factor into the question, but my "reasons" are so I can shut off the panels before and after the charge controller instead of crawling up on the roof and covering them. Again, not sure why I want to do it matters. I also know I don't have to install a breaker to make it work properly but installing one won't make it not work properly. Moderator, I couldn't find a solar section or I missed it so that is why I posted here, sorry for that.

I couldn't find a solar section or I missed it

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It's a "child" of the TECH forum.

"Best practice" would be to install circuit protection between the panels and the controller, and the controller and the batteries, but I think you'll find that very few RVers have fuses or breakers between the panels and controller - and few (if any) have experienced any problems. I would strongly recommend, however, installing a catastrophic fuse or breaker between the controller and batteries - as close to the batteries as possible.

FWIW, I installed DC disconnect switches between my panels and the controller, and the controller and batteries, and the switches are co-located next to the controller. They allow me to remove power to both sides of the controller for any number of reasons. I suppose that if you were dead-set on having breakers, you could install circuit breaker switches instead of simple switches.

The wires attached to panels are usually only short leads, so in all likelihood you will be running additional wire. You didn't mention what kind of RV you have, and long wire runs, or thin gauge wire can cause unnecessary voltage loss. Just food for thought.

Kev

Easy solution that I did was to place fuses before and after the controller.  easy to unscrew and remove the fuse to isolate the controller.

Yes, breaker switches. Question remains: What amperage's?

I would look at the max operating current for the controller and then add a little to prevent blowing the fuse with normal operation.  There is no single answer because the current of the specific controller will determine what to use,

Cholmes100 said:

Yes, breaker switches. Question remains: What amperage's?

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Remember, fuses protect the wires. So if your wiring is rated at 15A, use a 15A fuse or less.

I have a similar setup -- three, 245W panels in parallel.
https://rvseniormoments.com/projects/solar-panels/

I suggest you check out the MidNite Solar Forums:
http://midniteftp.com/forum/

Also, besides charge controllers, MidNite Solar sells breakers, breaker boxes, and combiners.
http://www.midnitesolar.com/products.php?menuItem=products&productCat_ID=16&productCatName=Breakers

http://www.midnitesolar.com/products.php?menuItem=products&productCat_ID=10&productCatName=Small%20Breaker%20Boxes

solarman said:

as an off grid designer, I can tell you there are many differences in requirements and the implementation
of these systems. their use cases are very different.


and moderator, could you please move this thread to the solar section, thanks

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Sorry solarman. 

Solar panels have a maximum current into a short circuit that's only slightly above their operating current.  For example, a Renogy 100 watt solar panel produces 5.3 amps at it's Maximum Power Point and only 5.75 amps into a short circuit.  This makes a solar array inherently safe as long as it's wiring is properly sized.

Nothing catastrophic happens if you short the output of a solar panel, it just produces it's rated short circuit current.  There's no need for a circuit breaker since a circuit fault won't produce enough current to trip it.

Batteries on the other hand are capable of discharging thousands of amps into a short.  They absolutely need a catastrophic fuse that is large enough to pass all of the current the wiring can normally handle but will blow before the wires have a chance to heat up to a dangerous level if there's a short.

Since solar panels are inherently safe, you can use anything you want to disconnect them for service.  Pull apart an Anderson Powerpole connector set or flip a battery disconnect switch.  Or just remove the wire from the input of the controller.  You're not limited to using a circuit breaker.

KandT said:

Sorry solarman.

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no need to apologise, 

Lou Schneider said:

Nothing catastrophic happens if you short the output of a solar panel, it just produces it's rated short circuit current.  There's no need for a circuit breaker since a circuit fault won't produce enough current to trip it.

Since solar panels are inherently safe

You're not limited to using a circuit breaker.

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sadly incorrect, this may be the case for a single panel, but it's a different story when multiple series/parallel strings are
combined, then we have a situation where failures in one string can cause damaging currents
to destroy the other strings, hence the requirement to provide combiner boxes and fuses.

secondly, solar panels are not intrinsically safe, there is a case for reverse polarity bypass diodes to short and cause
sufficient  overheating to cause ignition. this does occur, although not frequently ( i have seen panel interface boxes melted and burnt on large installations )
and is probably of minimal concern for a low wattage RV installation.

although not strictly necessary, there is a valid case for a circuit breaker in the solar string, one particular function is to act as a switch
for disconnecting the array from the controller. some MPPT controllers have issues with an active array connected when the batteries are disconnected.