Circuit Breaker on output side of MPPT 100/50

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smartin asked May 20, '19

Circuit Breaker on output side of MPPT 100/50

I have the MPPT 100/50 charge controller fed by 2 (280W) panels in parallel. I have a 20A DC circuit breaker between the panels and the charge controller. I have a 60A DC circuit breaker between the Charge controllers battery connection and the batteries. During the best sun of the day, the 60A breaker keeps opening. Even though while I have been watching I never see the amperage go nearly that high. I believe the charge controller should limit current to the battery to 50A since that is its maximum. What am I missing?

MPPT Controllers battery

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klim8skeptic ♦ commented · May 20, 2019 at 12:27 PM

Hi,

Not all breakers are created equal.

Post a photo, or a link to your breaker.

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Pat Davitt answered · May 20, 2019 at 12:44 PM

The previous comment is correct. "Not all breakers are created equal."

A quality 60A DC breaker with the proper trip curve will cost around $40.00 USD. Link to one is below:

https://www.bluesea.com/products/7246/C-Series_White_Toggle_Circuit_Breaker_-_Single_Pole_60_Amp

I suspect your breaker does not have a proper trip curve.

Pat

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nebulight commented · May 21, 2019 at 03:59 PM

This. There are certain things it's okay to go "cheap" on, breakers and fuses are not those items.

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Modifications Space

Node Red Space

Answer 1 · 2019-05-20T13:09:34Z

Elimac answered · May 20, 2019 at 01:09 PM

Check the ambient temperature near the breaker. Some MCBs are magnetic AND thermal, so they can trip on short pulses of high currents (short-circuit condition) and slowly rising currents (overload condition). If the MCB is of this type and the environment temperature is high, you can have it tripped on lower currents. There is a de-rate even when you place MCBs side-by-syde. Heat sources can come from copper conductor with insufficient cross-section (for 50A I would use 25mm2 as minimum), improper crimping (check crimping/ connections) and the MCB itself.

So, try keep it cool and see if helps. If is only magnetic type, shouldn't be affected as much.

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Answer 2 · 2019-05-21T12:07:22Z

smartin answered · May 21, 2019 at 12:07 PM

Thanks for the tips: below is the breaker currently installed.

1558440412715.png (517.0 KiB)

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wkirby ♦♦ commented · May 21, 2019 at 12:35 PM

Oh no, those are awful devices. You'd be much better off with a good quality fuse or the best is to use a proper DC circuit breaked like the ones that Pat Davitt has lined to.

Good circuit breakers are even available on Amazon: https://www.amazon.com/MidNite-Solar-Breaker-150VDC-MNEPV60/dp/B00BSYSLXU/ref=sr_1_3?keywords=dc+circuit+breaker+din+60A&qid=1558442040&s=gateway&sr=8-3

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Answer 3 · 2021-10-17T07:27:01Z

mobile-rv30 answered · Oct 17, 2021 at 07:27 AM

I was going to use the same type of circuit breaker as above ?

Is there unanimous opinion on avoiding them ?

Can people also give some guidance how to calculate the Circuit Breaker ratings on this proposed schematic below please ?

4 x 350 Watt Panels , 2P x 2S
Victron 100 / 50 mppt
4 x 6 V / 440 AH AGM batteries in series.
Victron Multi 24/3000 inverter.

Should i have a CB on each Solar String , and what is the correct size per 2 panels in series ?

Are my ratings correct for the other parts of the circuit ?

My cables are 6 mm sq for the 9 metre run from panels to mppt , 65 mm sq cable for batteries to Multi 24/3000.

Yes i will have an electrician doing the connections but i already have lots of CB's in stock and want to pull the cables and mount the breakers before he arrives.

solar-circuit-breaker-sizing.png (82.1 KiB)

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JohnC ♦ commented · Oct 18, 2021 at 11:32 AM

Hi @Mobile - RV30

Unanimous opinion might be found amongst those who've used them. And there are better ones than the real nasties. But all are thermal devices, and they get hot, dissipating their heat the only way they can.. down the wire.

Spurious trips they're great at, and to avoid that they need oversizing by 50% or so. I wouldn't use them in any of the spots you have in your diagram.

I use double pole din breakers for the solar>mppt wiring and fuses/isolators elsewhere.

I still have a couple of those thermal cb's I use essentially as isolators, and only because I already had them.. a 100A on a 5A 48V load, and a 150A on a 20A 12V max load.

They don't belong in serious systems.

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