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



Venus OSfuses
scan-28-jan-2021-2-2.jpg (279.8 KiB)
circuitschematics.jpg (82.1 KiB)
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

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.

3 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

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

0 Likes 0 ·
wkirby avatar image wkirby ♦♦ next-day-solar commented ·

Current can only flow in one direction, out of the MPPT. Current cannot flow in to the MPPT at its output.
Imagine it as if there is a diode blocking reverse flow.
If the 100A charge was switched off and the MPPT was charging, you would not expect energy from the MPPT to go in to the 100A charger either.

Think of it another way, what would happen at night when the MPPT is not charging, the battery is capable of delivering more than 1000A. You would not expect 1000A to go in to the MPPT.
Likewise, if you switch your 100A charger off, you would not expect 1000A to go from the battery into the 100A charger either.

The 40A fuse is there in case of a fault with the MPPT causing current to flow in to it.

0 Likes 0 ·
next-day-solar avatar image next-day-solar commented ·

Thank you very much, super helpful.

0 Likes 0 ·

Related Resources

Victron Venus OS Open Source intro page

Venus OS GitHub (please do not post to this)

Additional resources still need to be added for this topic