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Old 24-09-2015, 11:53   #1
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Solar Panel Blowing Fuses?

We recently installed a second 140W monocrystalline solar panel on our 1980 Cal 39 which is docked in Merritt Island, Florida.

Each 140W panel is rated for a max of 8 Amps; for a total expected max output of 16 Amps.

We ran 20' of #8 wire (Recommended by Don Casey for that amperage and distance.), to a 21 Amp charge controller which was already installed on the boat and which worked fine with a single 8 Amp panel.

The controller has permanently installed output wires that look like #10 or # 12 although I can't find any size indications on them. Those wires run about 2' to the master switch of the boat with an in-line 10 Amp AGC fuse in the positive lead. Don't know how we would replace these wires as the controller is a sealed unit.

The wires running from the master switch to the batteries are heavy grade battery cables which I believe are # 6.

We replaced the 10 Amp fuse with a 20 Amp one.

Although the panels have worked fine for the most part, that 20 Amp fuse has blown twice right around noon, and the second time it melted the fuse holder.

Does anyone have any ideas why this might be happening?

Should we install a 20 Amp inline fuse or a breaker in the positive incoming lead from the panels?

We are going to try replacing the burned out fuse holder in the outgoing positive lead with a heavy-duty one and a 20 Amp MDL slow-blow fuse; and we are thinking of maybe installing a 20 Amp breaker in place of the fuse. Can't put anything larger in there because the controller is only rated for a max of 21 Amps.

Does anyone have any better ideas?

Any suggestions will be greatly appreciated.

Thanks!
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Old 24-09-2015, 12:09   #2
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Re: Solar Panel Blowing Fuses?

Hey Maple, folks will wish to know your controller brand and model.

Many here will offer good advice, it's a popular topic.

Obviously you are exceeding 20 amps. Apparently the fuse holder is best for the original rating as it started melting below 20 amps.

Stand by for good advice..
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Old 24-09-2015, 14:03   #3
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Re: Solar Panel Blowing Fuses?

Quote:
Originally Posted by MapleSugarMan View Post
.....
Each 140W panel is rated for a max of 8 Amps; for a total expected max output of 16 Amps.
....
140w / 8a = 17.5v, the nominal voltage of your panels. The output of the controller is closer to 13v. 140w/13 = 10.8amps. So two 140 panels can exceed 20amps.
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Old 24-09-2015, 14:29   #4
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Re: Solar Panel Blowing Fuses?

Quote:
Originally Posted by MapleSugarMan View Post
We recently installed a second 140W monocrystalline solar panel on our 1980 Cal 39 which is docked in Merritt Island, Florida.

Each 140W panel is rated for a max of 8 Amps; for a total expected max output of 16 Amps.
You are missing a big factor. The power (W; watts) is roughly the same before and after the controller, but the same does not apply to voltage and current. The controller reduces the voltage and increases the current to compensate. Assuming the battery is taking lots inf current in the early stage of charging (hence the controller is not cutting back power) and the sun is up in the tropics you may have a bit more than 140 watts power and about 13 volts voltage, which will give more than 140VA per panel /13V x 2 panels = 21.5 amps between the controller and the battery. That will fry the fuse around noon.

If you give us the details of your controller and panels we can help you work out if you can solve your problem by connecting the panels in series.

Also donīt forget to install a fuse very close (inches) to the battery so save you from fire if the #6 wires chafe and touch each other or positive touches engine block ,etc).
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Old 24-09-2015, 15:05   #5
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Re: Solar Panel Blowing Fuses?

Your controller is putting out more than 20 amps. Replace it with a 30 amp fuse. I personally prefer circuit breakers, but some people don't.
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Old 24-09-2015, 15:10   #6
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Re: Solar Panel Blowing Fuses?

I haven't run the calculations so won't try and comment on that. But most installations will use 10 gauge wire from the panels to the controller. Higher voltage will send fewer amps of current for the same amount of watts. You can get by with smaller gauge wire for higher voltage.

But be that as it may, you should also carefully inspect the wire itself and all connections. It should be high quality marine grade wire with properly crimped and tinned crimp connectors. Loose or poor connections will generate heat. Also, you do not mention what kind of fuse it is but barrel type fuses often will develop corrosion where the fuse meets the little "clamps" inside. I do not like barrel fuse holders because of that, and because you have to take them apart to inspect the fuse.

If it is exposed to the outside then it has to be a completely watertight fuse holder. I like the automotive syle push in pull out fuses. You can get a variety of different styles. But get one rated for at least 30A. If it is the kind with wire pigtails, the wire should be 10 gauge. If you melted the holder the wire close to the fuse holder will be done for and you should replace it. That much heat destroys wire.

And do put a fuse near where the wire connects to your battery system (as recommended above).

I think your fuse size was too small to start with. If your wire was 12 gauge it was too small too. Too small of wire will heat up the whole circuit. Fuses will get hot too. Absolutely use tinned wire up to the panels.

You''ll enjoy your new panels once you get the fuse/wires sorted out.
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Old 24-09-2015, 15:15   #7
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Re: Solar Panel Blowing Fuses?

While we're on the topic of fusing power sources and cables and chafing, etc...

it would be a good idea to go over all of your cabling and securely ziptie it all together and to a solid bracket or something to eliminate any contact with sharp edges or any potential to breach the insulation. An ounce of prevention is worth an entire cabinet full of fuses.
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Old 24-09-2015, 15:23   #8
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Re: Solar Panel Blowing Fuses?

Some panels will output more than they're rated.

MPPT vs PWM controller can change (significantly) the amount of current going to the batteries. We'd need to know what controller.

As a barely informed guess, I'd want 10g from the controller to the batts, with a 30A breaker as close to the end of the run as possible.
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Old 24-09-2015, 15:48   #9
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Re: Solar Panel Blowing Fuses?

In case I missed anyone's mentioning it.. I wouldn't use a slow blow fuse anywhere on board. If there's something tripping it now, the last thing I would want is it to NOT blow at the weakest link right away, and instead risk heating up another section that would potentially cause quite a hazard.
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Old 24-09-2015, 16:11   #10
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Re: Solar Panel Blowing Fuses?

How did you wire the panels? Parallel or Serial? Depending on your charge controller, you could wire them in Serial. This will increase the output voltage, but current should not increase. Wiring in parallel will keep the viltage the same but increase current. Maybe just reconfiguring the panels is a possibility?

I ran mine in series so I could run smaller gauge wire to the charge controller. Made installation a lot easy. But my Mppt controller can handle the input voltage with a large safety margin.


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Old 24-09-2015, 17:26   #11
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Re: Solar Panel Blowing Fuses?

Have you tried measuring the output at the panels around mid-day? Both amps & voltage. That'll give you one key piece of the puzzle, in terms of what you're working with.

Also, 20A x 14v = 280W. So if the panels are putting out at, or above their rating, then that answers some questions as well.

One other question. Per chance, are any of the key sections of wiring, out where they're subject to direct heating from the Sun? Or bundled tightly together with other wires so that the heat in them can't properly dissipate?
That, & any of the other questions already asked, which might cause their resistance to go up.
Plus, it would also make sense to trace things all of the way from the panels to the batteries, & make sure that all of the connections are free of corrosion, & properly fastened. Such as, for example, that there aren't any stainless washers bolted in between a couple of wire end terminals.

In the end, you could likely save yourself some headaches, & possibly a fire, by just going to either a larger, or 2 seperate charge controllers. But again, at a minimum, measure the true output of the panels @ around noon. Measured right @ or near their output wiring.
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Old 24-09-2015, 18:36   #12
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Re: Solar Panel Blowing Fuses?

Hi Everyone,

Thanks so much for taking the time to write your responses.

A few other details that folks have asked for:
The controller is a Solar Pro Plug 'n Play rated for 21 amps max.
The panels are 140 watt Nature Power brand by RDK.
Wire from the panels to the controller is 20 feet @ #8 (Recommended by the manufacturer of the controller.)
Wire from the controller to the master switch is 2 feet @ # 10 or 12 (permanently installed by the manufacturer.)
Wire from the switch to the batteries is (I think) # 4 or 6 battery cable. Never had a problem with it in 3 years.
All wire is tinned marine grade.
All connections are new, insulated and shrink wrapped.

One person suggested that we not use a slow-blow fuse because of the risk of fire. A very good point.

I think we'll have to go with the circuit breaker and when it pops, it pops and we'll wait a while before we turn it on again. Most of the time the panels don't put out all that amperage.

Thanks once again for all your answers.
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Old 24-09-2015, 19:01   #13
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Re: Solar Panel Blowing Fuses?

Is that cointroller rated for 280 watts of input power? If not, the 21 watt maximum output may not matter, the controller may be trying to pass through all the power it can--and eventually be damaged as well.


Fast blow, slow blow, either should blow well before your wiring when everything is properly sized. "Fast blow" usually means a fuse will blow before the electronics that it is attached to (diodes, transistors) will blow out from an accidental over-power or a static discharge. In comparison, this situation certainly would be safe with a circuit breaker--and that's going to blow slower than most any fuse in any case.


Bottom line, the whole system has to be designed and matched as a SYSTEM.
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Old 24-09-2015, 20:41   #14
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Re: Solar Panel Blowing Fuses?

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Originally Posted by neptunesjester View Post
How did you wire the panels? Parallel or Serial? Depending on your charge controller, you could wire them in Serial. This will increase the output voltage, but current should not increase. Wiring in parallel will keep the viltage the same but increase current. Maybe just reconfiguring the panels is a possibility?

I ran mine in series so I could run smaller gauge wire to the charge controller. Made installation a lot easy. But my Mppt controller can handle the input voltage with a large safety margin.


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That isn't going to work.


Yes, connecting the panels in series will cut the input current in half and double the voltage. Then the MPPT controller will convert that higher voltage down to the charging voltage set by the controller and will put out just over 20 amps to the batteries, once again blowing the undersized 20 amp fuse.

Doing the calculations (and assuming no or very low losses) 280w of input =

280/12v = 23.33 amps
280/13v = 21.54 amps
280/14v = 20.00 amps
280/14.5v = 19.31 amps

So under midday conditions, at anything under 14v, he could be getting 20 amps or more.
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Old 24-09-2015, 21:57   #15
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Re: Solar Panel Blowing Fuses?

I don't think that controller (Solar Pro Plug 'n Play) is MPPT, therefore it won't put out any more current than the solar panels deliver. But panels can put out more than their rated output current, and that's probably what's happening. A bigger fuse, or better yet a circuit breaker is probably the answer.
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