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Old 13-08-2022, 21:11   #1
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Solar panel fuse question.

I just bought my first solar panel, a 50 watt Sunpower panel. Eventually i will add more panels as the boat restoration reaches that stage. For now I just to get some experience and real world practice, i figured i'd put the small 50 watt panel on the main sliding hatch cover. I have no real experience and am beginning my research and study, but just want to confirm some things im learning.

So my question i want to confirm for now is, since its a single panel, the short circuit current is 3.1A and the max series fuse rating is 15A. Since im not going to wire it with other panels in series or parallel, as i understand it, i dont need to fuse the wires on the panel. Im going to use 10AWG wires with a total round trip run of about 30 feet so the panel current as i understand it will never exceed the ampacity rating of the 10AWG wires. Am i understanding this correctly?
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Old 13-08-2022, 21:44   #2
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Re: Solar panel fuse question.

Essentially you are correct in your understanding.
But... this is assuming the solar panel is being wired to a controller.

If you are planning to connect the panel directly to a battery, then a fuse is required in the wiring at the battery end as the battery could deliver many more amps than the 10AWG can carry. Note, wiring directly to the battery is very poor practice, you should always use a solar controller.
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Old 13-08-2022, 21:54   #3
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Re: Solar panel fuse question.

Quote:
Originally Posted by Wotname View Post
Essentially you are correct in your understanding.
But... this is assuming the solar panel is being wired to a controller.

If you are planning to connect the panel directly to a battery, then a fuse is required in the wiring at the battery end as the battery could deliver many more amps than the 10AWG can carry. Note, wiring directly to the battery is very poor practice, you should always use a solar controller.
Yes, thank you. I should have added that bit of information. I have a Victron 75|10 MPPT charge controller that will handle the power from the panel. This will be fed to a positive charge bus that feeds the house bank. Also, between the panel and the controller i was thinking of adding a Blue Seas mini on/off selector switch as well.
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Old 13-08-2022, 22:06   #4
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Re: Solar panel fuse question.

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Originally Posted by BAD ORCA View Post
Yes, thank you. I should have added that bit of information. I have a Victron 75|10 MPPT charge controller that will handle the power from the panel. This will be fed to a positive charge bus that feeds the house bank. Also, between the panel and the controller i was thinking of adding a Blue Seas mini on/off selector switch as well.
Hi, I would suggest that you wire it with a gauge that will accommodate future additional panels, should you go that way. Should you choose not to then the larger wire will not cause any problems. Unfortunately the reverse is not true.
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Old 13-08-2022, 22:11   #5
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Re: Solar panel fuse question.

Presumably you are fusing the wire between the positive charge bus and the MPPT charge controller at the charge bus end.

Personally I don't see any advantage with adding a switch between the panel and controller. You can turn the panel 'off' easily enough by shading it, especially as it is situated on the main hatch cover.

Is the panel connected by MC4 connectors or similar?
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Old 13-08-2022, 22:33   #6
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Re: Solar panel fuse question.

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Originally Posted by Uncle Bob View Post
Hi, I would suggest that you wire it with a gauge that will accommodate future additional panels, should you go that way. Should you choose not to then the larger wire will not cause any problems. Unfortunately the reverse is not true.
Much thanks, good point. I thought of running 8AWG but im pretty convinced that this single panel will never be connected to any others. I know...famous last words right?

If everything works out as i expect though, i think my future additions would be two more panels on a dodger/bimini type arrangement, and possibly two more on an arch. In this scenario i would think i would wire each set of two in parallel which should put me in the 8AWG range.
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Old 13-08-2022, 22:43   #7
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Re: Solar panel fuse question.

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Originally Posted by Wotname View Post
Presumably you are fusing the wire between the positive charge bus and the MPPT charge controller at the charge bus end.

Personally I don't see any advantage with adding a switch between the panel and controller. You can turn the panel 'off' easily enough by shading it, especially as it is situated on the main hatch cover.

Is the panel connected by MC4 connectors or similar?
That was going to be my next question. I was assuming that i would have to even though it will only be about a 24" wire run between the busbar and the controller. I have a couple extra 30amp MIDI fuses. I was thinking of using one coming off the busbar to the controller. I would use the same 10 AWG wire between the controller and the busbar.

Yup, the panel has MC4 connectors installed.
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Old 14-08-2022, 05:37   #8
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Re: Solar panel fuse question.

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Originally Posted by BAD ORCA View Post
That was going to be my next question. I was assuming that i would have to even though it will only be about a 24" wire run between the busbar and the controller. I have a couple extra 30amp MIDI fuses. I was thinking of using one coming off the busbar to the controller. I would use the same 10 AWG wire between the controller and the busbar.

Yup, the panel has MC4 connectors installed.

For the time being, with 50w solar, wouldn't the fuse between battery and controller be 4 or 5 amps?


Bad Orca, what were you thinking for a mounting system for your panel to the hatch? I have 50w solar on my 21', like it a lot, still working good after 3 years in a tough climate...but I have never permanently mounted the panel. I like your idea for location.
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Old 14-08-2022, 06:41   #9
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Re: Solar panel fuse question.

if your wiring ampacity exceeds the maximum output current of the panel ( which in all cases it most definitely should) , then I see no point in fusing the run between the MPPT panel input and the panel .

The MPPT to the battery run should be ideally fused at both ends , at the MPPT controller but most definitely alway at the battery termination point , The MPPT controller should never be able to exceed the wiring , but the battery almost certainly will
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Old 14-08-2022, 07:36   #10
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Re: Solar panel fuse question.

Quote:
Originally Posted by Spot View Post
For the time being, with 50w solar, wouldn't the fuse between battery and controller be 4 or 5 amps?


Bad Orca, what were you thinking for a mounting system for your panel to the hatch? I have 50w solar on my 21', like it a lot, still working good after 3 years in a tough climate...but I have never permanently mounted the panel. I like your idea for location.
I believe ideally 10A. Id have to figure the max cold weather output but i cant imagine it would be over 10A. It may push near 5A though so may be subject to nuisance trips with a fuse that small. Still learning about cold weather output though so not 100% sure yet. I think i may have an extra inline ATC fuse holder so this may be a more appropriate option than the MIDI fuse between the busbar and controller.

For the mounting, I was thinking of getting a piece of 1/8" thick aluminum from McMaster-Carr and mounting the panel to that, then mounting that to the hatch cover with 1/4 or 3/8" aluminum standoffs. My thinking that it might help cool the panel a bit but thats debatable. Iv'e seen pictures of solar panels cooking the gelcoat underneath them when mounted directly to the boat so at the least, hopefully it will protect the gelcoat if nothing else.

THe panel has grommets so a few washers and aluminum machine screws would allow me to easily remove it from the aluminum backing plate if i had to, but it would essentially be permanently mounted to it. The aluminum backer would get through bolted to the hatch cover with all aluminum bolts to minimize corrosion. The wiring would come in through cabin roof under the hatch cover so would be protected from sun and water. Unfortunately that means cutting off the MC4 connectors on the panel and replacing them, but it doesn't look that difficult to do. I think it will be a lot cleaner install this way.
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Old 14-08-2022, 07:43   #11
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Re: Solar panel fuse question.

Quote:
Originally Posted by goboatingnow View Post
if your wiring ampacity exceeds the maximum output current of the panel ( which in all cases it most definitely should) , then I see no point in fusing the run between the MPPT panel input and the panel .

The MPPT to the battery run should be ideally fused at both ends , at the MPPT controller but most definitely alway at the battery termination point , The MPPT controller should never be able to exceed the wiring , but the battery almost certainly will
Much thanks. I noticed that the controller does have a 10A ATC fuse on it at the bottom. I'm not sure though what it specifically protects the controller from? I'm guessing an internal fault , but maybe from overcurrent? Trying to find out in the Victron documentation.
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Old 14-08-2022, 08:09   #12
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Re: Solar panel fuse question.

Quote:
Originally Posted by Spot View Post
For the time being, with 50w solar, wouldn't the fuse between battery and controller be 4 or 5 amps?
Actually, reading the Victron manual now and it specifies a 15 or 20A fuse at the battery for this particular controller.
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Old 14-08-2022, 19:33   #13
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Re: Solar panel fuse question.

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Originally Posted by goboatingnow View Post
if your wiring ampacity exceeds the maximum output current of the panel ( which in all cases it most definitely should) , then I see no point in fusing the run between the MPPT panel input and the panel .

The MPPT to the battery run should be ideally fused at both ends , at the MPPT controller but most definitely alway at the battery termination point , The MPPT controller should never be able to exceed the wiring , but the battery almost certainly will

I'm curious. Why would you need to fuse a wire at both ends?
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