question

next-day-solar avatar image
next-day-solar asked

Help a budding solar enthusiast please ! MPPT/Charger Related

circuitschematics.jpgscan-28-jan-2021-2-2.jpg

Thank you for your time in advance, Setup is for an Electric van with a fridge unit, with PV power to top up batteries.


- 2 x 115W PV panels in series (40A inline fuse) after MPPT before DC BUS

- 1 x MPPT 100/30

(both those elements wired to bus bar) 150A


Connected to Bus bar is

1 x Fridge unit, which draws 50/70amps when under load, with built in 100A / 12V charger system, to charge batteries. Fused at 125A as shown.

1 x Smart Shunt (all negative loads pass through)

2 x212AH 12V Lithium batteries in parallel


Question

- When the 12V charger (rated to 100A) charges the batteries, the charging current is flowing through the whole circuit. What stops the 40A fuse on the + line of the MPPT not blowing, or will it blow ? as current passes through the MPPT as it will happily give voltage of the battery etc.

What can I do, is there a risk of 'back current' or similar, as I am worried, that when I will blow the fuse before the MPPT when I turn the charger on.

I have done a similar setup before where I have not fused the MPPT, but I understand its best practise to do so.

Thank you



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1 Answer
wkirby avatar image
wkirby answered ·

Charge power form another charger will not backfeed the MPPT. Multiple chargers can exist in the system.
The 40A fuse is a good idea to protect the wiring.

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next-day-solar avatar image next-day-solar commented ·

Thank you for helping, what is the 'rationale' or reason' behind the 40A fuse not blowing when I am charging the battery at 100A and that current is flowing around the circuit ?

Current flows to the lowest point of resistance, but surely when the battery is full, it may then flow around the MPPT circuit ?

Thank you in advance

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next-day-solar avatar image next-day-solar commented ·

Thank you very much, super helpful.

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