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Can/should a DC breaker be used between a LifePo battery bank and a hybrid charger-inverter?

chewface

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Sep 17, 2021
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Hi Fellow Solar Enthusiasts,
I'm in the late stages of installing a 10Kw solar system on my retirement home. The set-up consists of 24 Trina 450w PV panels, 2 separate (NOT in parallel) 5KW solar charger-inverters (MPP Solar PIP5048MKX) and 3 x 200AH 48V LifePo batteries.

In the MKX user manual, it "strongly recommends" using a current limiting device between the battery bank and the MKX. I assume I could use a 250A in-line fuse but think that a 250 DC breaker would be better since it could be used as a disconnect device as well. However and this is where I could use some expert advice, is a DC breaker bi-directional? Since the MKX both charges the battery as well as draws power from the battery to invert to AC, a DC breaker should provide protection in both directions, no?

My rudimentary understanding is that a DC breaker is designed to extinguish arcs when the circuit is broken, so it's not intuitively obvious to me that DC breaker design is inherently bi-directional. In fact looking at the specs of various DC breakers, one side of the breaker is generally labelled as "Load", which is why I am confused when the MKX is both a battery charger as well as an inverter.

Would appreciate some clarification in this area from more advanced solar practitioners.

Thanks very much for your attention.
 
Yes. Breakers are bidirectional. The designations are for when the breaker is open, so ya know which side is hot.
 
My Outback Skybox has a built in DC breaker on the Negative leg. Also I have a Kilovac contactor on that leg and the only polarity markings on it are the red and black wires for the coil. I do not think it matters which direction the arc is going for those devices to work.
 
Howdy and thanks for your replies. I received some important info on another solar website which wanted to share with you all.

I learned that DC breakers can be 'polarised' or 'non-polarised'. If using polarised breakers (check the specs very carefully cos its not universal nor obvious) then the wiring is VERY specific and it is absolutely critical that the 'load' be wired to the proper +ve and -ve terminals on the breaker. Otherwise the breaker can suffer catastrophic failure (catch fire) if disconnected under load. Best to buy non-polarised breakers to remove uncertainty.
 
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