Solar to MPPT Victron 75/15

Alshymer

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Hi
Could someone tell me if the fuse holders in the photo with 15 amp fuses are good enough for the cable from solar panels to the controller and from the controller out to the battery?
Thanks
 

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I would say it depends how much solar power you have and what amperage they can deliver to the MPPT. The cables can handle way more than that assuming you are using at least 4mm2 from the panels to the MPPT (and probably 16mm2 to the batteries?) but I think you maybe should go higher than 15A so as not to have to often replace fuses if you have a lot of solar?

Just my opinion and bear in mind that I am a novice at this - I'm sure that Merlin or David will be along soon enough to correct me!
 
Alshymer said:
Hi
Could someone tell me if the fuse holders in the photo with 15 amp fuses are good enough for the cable from solar panels to the controller and from the controller out to the battery?
Thanks
Click to expand...
From the size of the MPPT I assume you are not using more panels than a victron 75/15 can handle.
But even if you were your output would not be greater than the rating of the MPPT.
As your solar controller will max at 15amps I would use a fuse slightly larger and go for a 20a fuse.

If your panels can give you a larger capacity I would recommend a larger controller.
Obviously this would necessitate a larger fuse. A 120w solar panel will max at between 6 and 7 amps. Therefore if you only have one 120w panel a 10 or 15a fuse would suffice.
 
Thanks. Yes the cables are 4mm to the Victron mppt I think. They were fitted by the dealer so are 2 inners in 1 black outer casing.
From the Victron to the battery looks around the same. One to the shunt and the red to the battery.
 
Fuses shown are fine.
Cablewise, I wouldn't bother with anything bigger than 4mm2. Absolutely no point in bigger unless you happen to have it kicking around and spare, but also note 6mm2 is officially the largest cable that will fit, and even that would be a struggle to get into the terminals.
 
I would have a fuse between panels and control unit but not one after it to battery, because if it blows you may risk damage to control unit, but do use a fuse unit from battery to all outlets, this one is good with leds which light up if you blow a fuse.
fuse block.jpg
 
Personally I don't like blade fuses in circuits carrying over 10A. They're ok when new clean and tight but often they get hot as they age and get tarnished.
There's no need for a fuse between panels and controller, it doesn't serve a purpose and doesn't protect anything. A fuse does however allow you to isolate the panels from the system simply by pulling the fuse which can be handy but a proper switch is a better option for the reasons above.
You should try and keep the cable resistance between the controller and battery to a minimum to get better charging speed and efficiency so short runs, fat cable and large fuse (because resistance drops as rating gets higher).
4mm cable and a 25A fuse or 6mm cable + 40A fuse depending on cable run and ideally something better than a crappy blade fuse. Best do the job once and right IMO.
.
 
Midi or ANL fuse and holder. About £10. Fit the fuse as close to the supply (battery positive) as you reasonably can.
Tip .
Measure the cable run distance (1 way) in metres and multiply by 4, this will give you the minimum cable size to use in square mm. (So for example 1m run use 4mm cable)
Next multiply the cable size by around 6 (so a 4mm cable = 24) and this will give you the fuse size so use 20 or 25A fuse[.
Now, this is what I would do, others may think it's OTT BUT as I mentioned previously low resistance wiring between controller and battery means accurate voltage tracking and faster charging.
Good luck 👍
 
Good morning
Thank you for the information.
Whilst re-jigging things I notice that I have 5 extra cables on the positive battery terminal.
Are these ok or should I use a busbar?
If a busbar, is 6mm cable enough to connect the busbar to the battery?
 

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If they are power feeds to things like lights etc they should be through a fuse block, does not look neat work to me.
 
Alshymer said:
Good morning
Thank you for the information.
Whilst re-jigging things I notice that I have 5 extra cables on the positive battery terminal.
Are these ok or should I use a busbar?
If a busbar, is 6mm cable enough to connect the busbar to the battery?
Click to expand...
What you have there is pretty typical of a system that's grown and adapted over time. All of those cables should really be fused individually close to the battery so if you were starting from scratch or tidying things up then you'd use a fuse block which is essentially a multiple fused bus bar. If the cables are already fused correctly then there's nothing stopping you simply adding another fused cable, it may look a bit of a rats nest but it'll work. I guess it all depends on how you feel about it and how many if those feed cables are not yet fused.
If you do add a fuse block then I suggest the main cable should be the next size up from the largest cable current being used.
 
Thanks, you are probably correct about the system evolving but now I want to put it right.
I have ordered a 20amp ANL fuse and holder as you suggested but am now thinking of adding a fuse block to tidy things up.
I don’t have too much room though so need something relatively small.
 

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So, all the small positive leads from the
+ battery go to the fuse holder positive and all the small negative feeds that currently go to the Victron Shunt go to the fuse holder negative.
Then just one + cable from fuse holder to + battery terminal and one negative from the fuse holder to the out of the shunt?
That would look prettier!!
I so appreciate all your help in this as ever.
Regards
Martin
 
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