What inline fuse rating?

[NorthernSands]

Hi all,

I'm planning on adding 3 x 80 watt solar panels (short circuit at 24.3 V and 3.98 A) in parallel to a Votronic MPP 250 Duo. The connection point will be a three MC4 into one adaptor, with 6mm cables running from the junction, through the roof, to the controller. I'd like to put an MC4 inline fuse just before the controller.

Two questions, actually:

1. What fuse rating would you recommend?
2. Do I actually need one, as the controller has one built in (I don't know where this fuse sits in the circuit)?

Many thanks.

Peter

 

[tonyidle]

3 x 3.98 = 12. I'd use a 15A fuse.

 

[Misterg]

Do I actually need one, as the controller has one built in (I don't know where this fuse sits in the circuit)?

As long as there's a fuse between the battery and the controller, then "no".

Solar panels are incapable of generating enough current to blow any fuse which is rated to pass their working current continuously. That said, fitting one in the feed from the panels provides a means of disconnecting the panels from the controller (for maintenance, etc.) if you so wished. 6mm^2 solar cable is good for >50 amps, so any fuse rating over 12A and under 50A would be OK for that. Otherwise it's just something else to go wrong.

 

[Stealaway]

I have one of these in the live wire from the panels - Fuse and isolating switch.

15 Amp In-Line Circuit Breaker Stereo/Audio/Car/RV 15AMP Fuse 12V/24V/32V UKstoc | eBay

1 X 15A Circuit Breaker. No fuse change trouble. its up to a 4 Gauge Wire (8mm2 max). Ideal for car, marine, bost, bike, etc. Mount on Panel or Firewall. Works with 12v-24v DC battery. Unique Push Button Reset can also be used as a Kill Switch.

rover.ebay.com

 

[Richard n Ann]

Ordered a 60a breaker for mine just so I'm able to disconnect the solar panel from the controller. If you fit a fuse, make it a big one so it doesn't get warm. If it gets warm there is a voltage drop across it and that wastes power.
The fuse in the Votronic is in the battery circuit.

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[NorthernSands]

Thanks for all your help; it's been useful. I like that 15amp breaker. I can see it would be useful to isolate the panels for whatever reason.

All the kit arrived today, but as we're going on holiday tomorrow evening, I have no time to mount the panels. I'll take at least one and stick it outside the van when we're around and staying put for any length of time. I would build a frame for all three, but the garage door has just broken and I can't get in to use my wood and tools.