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lemon avatar image
lemon asked

SmartSolar 75/15: fuse to battery blown twice

Hi everybody,


I have a 280W peak panel on my camper, worked with the SmartSolar 75/15 flawlessly for 3 years now. A few weeks ago the SmartSolar suddenly did not charge the battery anymore and gave strange battery voltages (p.e. 7V when the battery was at 13.4V).

Last week I had time to check and noticed that the 15A-fuse in the 20cm long 10AWG cable to the plus pole of the battery was blown. So I changed cable and fuse and the SmartSolar charged the battery again. Good.

Two days later the fuse was blown again. Strange. we have winter here in Italy, a 280W panel can't produce as much current as needed to blow the fuse away, and then the SmartSolar is limited and should not send more than 15A to the battery.

My reseller told me to use a 20A fuse on the cable to the battery, but I can't understand why it happens now and not in summer when we have much more current coming from the panel.

What do you say?


Thank you very much!

MPPT SmartSolar
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7 Answers
Paul B avatar image
Paul B answered ·

I would do as you have been requested. you may find its just surge that causing it, anyway a 20 amp fuse will tell the story

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klim8skeptic avatar image
klim8skeptic answered ·

@lemon What do you say?

You sure can blow a fuse if it gets hot due to a poor holder or cabling.

Check your mppt's history to see what the P max has been.

Check your wiring and fuse holder are ok for a 20a fuse, and fit one.

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lemon avatar image
lemon answered ·

Hi,

here you can see the values just before the second fuse has died, maybe this can help to understand. But for me these values are ok, they look quite typical.2024-01-16-15-13-44-t5solar-vrm-portal.png

2024-01-16-15-17-27-t5solar-vrm-portal.png


2024-01-16-15-13-44-t5solar-vrm-portal.png (24.3 KiB)
2024-01-16-15-17-27-t5solar-vrm-portal.png (23.9 KiB)
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klim8skeptic avatar image klim8skeptic ♦ commented ·
@lemon Looks like you setup can get to 15a even in winter.

Do you have any loads on the load output?

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ejrossouw avatar image ejrossouw klim8skeptic ♦ commented ·

Current is very low around 2A so are you confusing V with A in graph?

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klim8skeptic avatar image klim8skeptic ♦ ejrossouw commented ·

@ejrossouw Battery current is above 14.25a @ noon.

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ejrossouw avatar image ejrossouw klim8skeptic ♦ commented ·

@klim8skeptic 14.25V not A. Current scale is depicted in orange on the right and shows just over 4A ;)

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klim8skeptic avatar image klim8skeptic ♦ ejrossouw commented ·

@ejrossouw your right :)

Wonder what the history looks like.solar-history.png


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solar-history.png (161.1 KiB)
lemon avatar image lemon klim8skeptic ♦ commented ·

This was from the day the fuse was blown:

2024-01-18-10-36-08-t5solar-vrm-portal.png

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2024-01-18-10-36-08-t5solar-vrm-portal.png (16.5 KiB)
klim8skeptic avatar image klim8skeptic ♦ lemon commented ·
@lemon Cool, doesn't look like that would pop a fuse. Unless the wire has been pinched / rubbed through.


Do you have any thing connected to the load output terminals? An overload there will pop the batt fuse.
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lemon avatar image lemon klim8skeptic ♦ commented ·
No, loads are connected directly to the battery (through another fuse box obviously).
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pim57 avatar image
pim57 answered ·

Maybe one of the cables (pv or battery) wore out in these three years and touches the frame somewhere?

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kevgermany avatar image
kevgermany answered ·

The automotive inline fuses are usually rated at a continuous current of half the max. You may need to go even higher than 20A. But as said, check the cabling.

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ejrossouw avatar image
ejrossouw answered ·

@lemon My money is on a bad connection or cable in light of it having worked for 3 years without problem. Vehicles and movement, normal oxidation heat etc all impact connections and even cables over this time. Based on my own experience with numerous customers who experienced erratic voltages, it has always been the place to start.

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k-k avatar image
k-k answered ·

What type of batterie do you have, lead acid or LiFePO4?

What temperatures do you have (had on a windy hill -15°C)?

Enough water in LA batterie or heating on/off for LFP?

What is switched shortly before 14:00 first picture shows heavy load (low voltage but 0A to see*), second picture shows no load (0A but high voltage) a that time -> 'polar batterie' with rotten heat mat?

*maybe frozen elco inside MPPT

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lemon avatar image lemon commented ·
Hi,


battery is LiFePo4 without heating mat, temperatures in the last weeks were never < 5°C in the car.

The only load I have in the car (besides the Raspberry with Venus OS) is my freezer which switches on a few times a day consuming about 5A for some minutes only).

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