Which solar fuse to purchase?

[sailboatliving]

I am reading 13.40 V at victron mppt but only 12.9 V at the battery.

The fuse holder is 50 amp (too big) and the cable is 10 AWG. Both the cable and the fuse holder is hot too touch. I just upgraded this from the previous owners 8 AWG and a 30 amp fuse holder (very hot to touch). The rest of the cable is 10.AWG anchor marine and it is not hot at all.

This is the fuse holder:
https://www.amazon.com/gp/aw/d/B08BWRSPY1?psc=1&ref=ppx_pop_mob_b_asin_title

What a good fuse holder to use on a sailboat between battery and the MPPT? Any good brands?

I have 4 100 watts solar in parallel, and im using the same type fuse between MPPT and the solar panels. Do i need this fuse?
I had an inline fuse switch but it kept switching of even though amp was not close to 30 amps, so I installed a fuse holder instead.

 

[Daverw]

Those fuse holders are awful, very easy to get the fuse blade in the side of the fitting rather than fully in. Look up Bluesea fuse holders and mega fuse

Victron Energy Mega Fuse Holder

 

[Sea Change]

I am reading 13.40 V at victron mppt but only 12.9 V at the battery.

The fuse holder is 50 amp (too big) and the cable is 10 AWG. Both the cable and the fuse holder is hot too touch. I just upgraded this from the previous owners 8 AWG and a 30 amp fuse holder (very hot to touch). The rest of the cable is 10.AWG anchor marine and it is not hot at all.

This is the fuse holder:
Amazon.com

What a good fuse holder to use on a sailboat between battery and the MPPT? Any good brands?

I have 4 100 watts solar in parallel, and im using the same type fuse between MPPT and the solar panels. Do i need this fuse?
I had an inline fuse switch but it kept switching of even though amp was not close to 30 amps, so I installed a fuse holder instead.

You have 400w in to a single MPPT? So that's over 33A at 12v.
If you switched from 8AWG to 10AWG you actually reduced the size of the cable. 10AWG is only rated to about 30A so you're sailing very close to the wind there, and you shouldn't be using a 50A fuse with it.
The previously installed 8AWG is slightly better at 40A but even so, the undersized cable is the likely cause of the voltage drop you're observing.
What's the length of the run from MPPT to battery? This run absolutely needs a fuse, because if a fault develops inside the MPPT and a short circuit occurs, it's directly connected to your battery which can deliver hundreds if not thousands of amps.
The run from MPPT to panels will likely carry a higher voltage, smaller current, so it can get away with lighter cable. Fusing this is optional.

 

[sailboatliving]

Im not getting more than 330 watt from the solar and it is 12.8+V.


According to AI:
"Ancor 10 AWG marine-grade wire is typically rated for a maximum of 60 amps outside of engine spaces and 51 amps inside engine spaces"

Length MPPT to battery is probably a meter.

 

[Daverw]

The tables I’ve looked at state 30amp at 12v

 

[Sea Change]

Ok that's a higher rating than the generic numbers I was working with.
First thing to check would be that all the connections are good and clean. Look for specific hot spots where you might have a bad crimp etc.
Personally, I would increase the size of the cable on that run. It's only a metre so it's hardly going to cost anything. I tend to just use the biggest cable that will fit the terminals on the MPPT, to minimise voltage drop.

 

[PaulRainbow]

I am reading 13.40 V at victron mppt but only 12.9 V at the battery.

Is that measuring at the PV terminals of the controller or the battery terminals ?
What controller do you have ?

The fuse holder is 50 amp (too big) and the cable is 10 AWG.

The fuse holder is 40A and should have been supplied with 40A fuses.

Both the cable and the fuse holder is hot too touch. I just upgraded this from the previous owners 8 AWG and a 30 amp fuse holder (very hot to touch).

No, you downgraded to smaller cable with a lower current rating, but the cable and fuse should not be hot in either case.

The rest of the cable is 10.AWG anchor marine and it is not hot at all.

This is the fuse holder:
Amazon.com

What a good fuse holder to use on a sailboat between battery and the MPPT? Any good brands?

Refit thicker cable and fit a decent 40A midi fuse. Littlefuse is a good brand.

I have 4 100 watts solar in parallel, and im using the same type fuse between MPPT and the solar panels. Do i need this fuse?
I had an inline fuse switch but it kept switching of even though amp was not close to 30 amps, so I installed a fuse holder instead.

With 3 or more panels in parallel you must fuse each panel. You need to use fuses with the same rating as the panels “Maximum Series Fuse Rating.” You can find this rating on the panel’s spec sheet, usually on a sticker on the back of the panel.

 

[sailboatliving]

Is that measuring at the PV terminals of the controller or the battery terminals ?
What controller do you have ?

The fuse holder is 40A and should have been supplied with 40A fuses.

I used the fuse that came with the fuse holder, it was 50A, i believe. I have been looking for 40A, but no luck so far.

Not sure what PV terminal is. I read the MPPT value (13.4V) at the app on my phone and measured the battery voltage at the battery terminal for the other value (12.9V).

Oh, the old fuse holder and cable was a thinner and one. It was 12 awg,.not 8 AWG. My bad.

.

.

 

[PaulRainbow]

I used the fuse that came with the fuse holder, it was 50A, i believe. I have been looking for 40A, but no luck so far.

The link you gave in post #1 states 40A fuses and holder.

Not sure what PV terminal is. I read the MPPT value (13.4V) at the app on my phone and measured the battery voltage at the battery terminal for the other value (12.9V).

The app gives panel voltage and battery voltage, which are you quoting ?

"Measuring" voltage using different devices/methods isn't reliable. Measure the voltage at the battery terminals on the controller and at the battery, with the same meter, they should be virtually the same with a 1M cable run.

Still not said what controller you have, exactly, not just MPPT.

The PV terminals on the controller are those that the panels are connected to. How are you connecting 4 negatives and 4 x positives to the controller ?

 

[sailboatliving]

Thanks for the reply Paul. The controller is victron MPPT 100/30.

You are right, the fuses are 40A.

Im reading battery voltage at MPPT, the panel voltage is much higher.

I measured the voltage at MPPT and battery now, both with multimeter
13.20 vs 12.85

From the panels i use this, 4 to 1 and then it is an awg 10 cable to the controller with a 40A fuse before the the MPPT:
https://www.amazon.com/gp/aw/d/B07QGTGWX4?psc=1&ref=ppx_pop_mob_b_asin_title

 

[PaulRainbow]

Thanks for the reply Paul. The controller is victron MPPT 100/30.

You are right, the fuses are 40A.

Im reading battery voltage at MPPT, the panel voltage is much higher.

I measured the voltage at MPPT and battery now, both with multimeter
13.20 vs 12.85

Unless the batteries are low, that's lower than i'd expect.

From the panels i use this, 4 to 1 and then it is an awg 10 cable to the controller with a 40A fuse before the the MPPT:
https://www.amazon.com/gp/aw/d/B07QGTGWX4?psc=1&ref=ppx_pop_mob_b_asin_title

OK, each of those cables from the panels must have a fuse in them, rated as i described above. Then a fuse in the final cable to the controller.

 

[William_H]

Why do you fit a fuse in the line PV to controller? It seems to me that the only and maximum current a short circuit can provide is that of the max current of the PV. Like 5 amps for 100w PV. As I see it PV current is self limiting so provided it is less than max current rating for the wire no concerns.
Sea Change above seems to agree.
The run from MPPT to panels will likely carry a higher voltage, smaller current, so it can get away with lighter cable. Fusing this is optional.

ol'will

 

[PaulRainbow]

Why do you fit a fuse in the line PV to controller? It seems to me that the only and maximum current a short circuit can provide is that of the max current of the PV. Like 5 amps for 100w PV. As I see it PV current is self limiting so provided it is less than max current rating for the wire no concerns.
Sea Change above seems to agree.
The run from MPPT to panels will likely carry a higher voltage, smaller current, so it can get away with lighter cable. Fusing this is optional.

ol'will

Sorry, but this is incorrect. When more than two panels are wired in parallel, as the OPs are, each panel must be fused as i have described. Failure to fuse correctly can, if one panel short circuits, cause a fire.

 

[Sea Change]

Sorry, but this is incorrect. When more than two panels are wired in parallel, as the OPs are, each panel must be fused as i have described. Failure to fuse correctly can, if one panel short circuits, cause a fire.

My bad then. So if it's one panel per MPPT, no fuse required, but when you have them in parallel, you should fuse them?

 

[PaulRainbow]

My bad then. So if it's one panel per MPPT, no fuse required, but when you have them in parallel, you should fuse them?

One or two panels in parallel is OK, any more and each has to be fused.