Circuit Breaker necessary between MPPT and Battery?

[Mike & Rebecca]

Every diagram or picture I've seen of solar to MPPT to battery connections have all included a circuit breaker in between the MPPT and the battery. I provided my RV tech with a Tocas 40 Amp Circuit Breaker to install in between the Victron 100/30 MPPT Controller and the SOK Lithium battery.

The tech just called and said he didn't want to install the Circuit Breaker because "it's not needed." He said there is an OEM circuit breaker on the bus bar which already serves the same purpose. He doesn't want to spend my money installing the Tocas.

What is he missing? Why are you all installing the extra Circuit Breaker instead of relying upon the OEM? Just looking for the reason I'm going to tell him to install it anyway.

Thanks!

[Country Campers]

It does not have to be a circuit breaker it can be a battery disconnect switch. There just should be some way to isolate the battery from the solar controller. The breaker at the buss bar location is a self resetting breaker, you can not remove battery power from the solar controller with that type of breaker. Have him either install the circuit breaker or a disconnect, it is needed in my opinion.

Brian

[Mike & Rebecca]

Country Campers thanks for the quick reply!! I had him install a battery switch in-between the solar panel and the MPPT (also based upon others' diagrams) but it seems, to your point, there was still the necessity for a disconnect (switch or circuit breaker) in between the MPPT and the battery. Correct?

[Country Campers]

Yes that is correct.

Brian

[howson]

Mike & Rebecca -- Brian is correct, of course, that it is an important consideration to have a method to disconnect the battery from the MPPT (for maintenance or other purposes). A circuit breaker can act as both a switch and a safety measure (protect the wiring) as the battery is considered an "unconstrained power source". In other words, if the MPPT should catastrophically fail (dead short from MPPT to battery bank) the resulting amperage would melt the wiring which could lead to a fire. With that understanding, a circuit breaker is a better choice (IMHO) over just a switch.

Some may wonder why I would not advocate for a circuit breaker between the solar panels and MPPT. The reason is the panels are a constrained power source--they can only put out a maximum of X amps. If the wiring can handle the worst case scenario, there's no potential for the wires melting or fire.

Note that this input is based on my setup that does NOT use the OEM 30A self-resetting circuit breaker between the MPPT and battery bank. Hope that makes sense...

Howard

[Mike & Rebecca]

Thanks howson !! That makes perfect sense, and easy to understand for those of us who aren't "literate" in electrical matters. I've got the battery switch installed between the solar and MPPT and the circuit breaker installed between the MPPT and the battery. I've already used the new Lithium battery and BMV 712 but had the solar shut off since the tech neglected to install the circuit breaker before today. Looking forward to seeing how much recovery to the battery I get from the sole panel up top. I'm not expecting much and carry a Honda 2200i to recharge when/if we're off grid. My goal for this initial set up is to simply make it through the night without having to run the generator. We dry camp so little I'm not too concerned.

[kadenatcr]

Hey there! This is Kaden at Continuous Resources. Hopefully I can help answer your question.

In all of our designs, we break the wire between MPPT and battery bank with distributor bars and a shunt. Additionally, we install battery switches between the battery bank and distributor/shunt. Moreover, the battery bank is fused inside the distributor.

I am happy to answer any question you have!

Kaden at CR

[Hicks3456]

I read this with much interest in that I am currently installing solar on my GD Rv. One Warning that I have read very clearly on the MPPT is do not hook up panels up without batteries hooked up. If I have a cutoff to the battery every time I use it the panels are on without a battery connection?

[howson]

I read this with much interest in that I am currently installing solar on my GD Rv. One Warning that I have read very clearly on the MPPT is do not hook up panels up without batteries hooked up. If I have a cutoff to the battery every time I use it the panels are on without a battery connection?

If a solar panel is exposed to sunlight it will generate power (PV). That PV is then "live" on the MC4 connectors or wires (as applicable). If those wires are connected to a controller's inputs it will indeed have voltage on the PV input (with or without battery power on the BATT inputs).

Every manual I've read states the same thing: apply battery power first, then input PV, when turning on the controller. To turn off the controller, remove PV, then remove battery power. Easiest way to do this is to install a cutoff switch between the panels and controller.

What type of disconnect to use between the panels and MPPT depends on the maximum open voltage of your array. Good discussion on the topic here: https://gdrvowners.com/forum/solar/9...connect-switch

Howard

P.S. Welcome to the forum--please check out the letter written to new members: https://gdrvowners.com/forum/main-fo...to-new-members

Howard