Connecting MPPT directly to battery

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zbj asked Jan 5, '24

Connecting MPPT directly to battery

I have a 75 | 15 MPPT controller and want to know if it's safe to connect directly to the battery. I have a tiny stretch of 14 AWG aluminium wire to connect the controller to the battery and the controller to my solar array.
If this is relevant my solar array is currently 300W of panels in series @ around 25VOC but going to add another 100W and maybe do 50VOC at less amperage.

EDIT:

I have some larger gauge wire however it won't fit inside the charge controller ports.
Currently using some wire from aliexpress which is fine stranded but the insulation is not double. Claims to be tinned copper but I think it's aluminium.

Waiting on some better wire from amazon.
The battery is 12V 120Ah. I'm loosely following mobile-solarpower.com where Will uses a 50Amp circuit breaker for a 40Amp charge controller. Can you use any size circuit breaker above what the charge controller is? Could you use a 180A circuit breaker with the Victron 75 | 15 for example? Is it meant to protect the battery or the controller?

MPPT SmartSolar Lithium Battery safety

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Answer 1 · 2024-01-05T12:16:09Z

Alexandra answered · Jan 05 at 12:16 PM

@zbj

Will be more interested to know if it is fine strand and double insulated wire?

Is it a stationary install?

In theory (according to Google aluminium) 14AWG can do 15A. But I am not a minimalist in wiring size and would put larger cable there with the correct insulation and strand size.

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zbj commented · Jan 05 at 10:27 PM

I have some larger gauge wire however it won't fit inside the charge controller ports.
Currently using some wire from aliexpress which is fine stranded but the insulation is not double. Claims to be tinned copper but I think it's aluminium.

Waiting on some better wire from amazon.
The battery is 12V 120Ah. I'm loosely following mobile-solarpower.com where Will uses a 50Amp circuit breaker for a 40Amp charge controller. Can you use any size circuit breaker above what the charge controller is? Could you use a 180A circuit breaker with the Victron 75 | 15 for example? Is it meant to protect the battery or the controller?

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Alexandra ♦ zbj commented · Jan 06 at 05:32 AM

The protection is meant to stop current/ blow in case of a wire short or other problem.

So the size depends on the current source and the gauge wire. If the gauge wire can't carry the amps for the disconnect then the protection won't work and was a waste of time and money.

The 75/15 has a blase fuse in it as well. Can fit a 6mm² cable in it.

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