Solar blowing fuse problem

[VXman]

I had one 175 watt panel fitted by a pro company. They put in a 25amp fuse between the negative solar and the negative battery terminal.

A few months ago I added an additional 175 watt panel connected in parallel. This last week or so is the first time the panels have been used in earnest. Good sunshine and inverter for hair dryer, toaster and electric bike.

Twice this week the 25 amp fuse has blown. In fact on the first occasion of melted. Should I have increased the ampage of the fuse?

Would it be that when I used something that drew a lot of power then the power drawn from the panels overloaded the fuse?

 

[Lenny HB]

If you are getting a decent output from the panels 25 amps is borderline. I would fit a 35 amp fuse.
If its melted likely to be long term slight overload if its a blade fuse I would change it for a midi fuse.

 

[Guigsy]

175w x 2 / 12v = ~30 amps

 

[Guigsy]

If you are getting a decent output from the panels 25 amps is borderline. I would fit a 35 amp fuse.

Will the wiring and connectors be ok?

 

[Lenny HB]

Will the wiring and connectors be ok?

Without knowing what they are I can't answer that.

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[Guigsy]

Without knowing what they are I can't answer that.

Personally I'd not put in a bigger fuse without at least checking the wiring gauge.

 

[Gromett]

Personally I'd not put in a bigger fuse without at least checking the wiring gauge.

This is the absolute correct answer. The fuse is there to protect the cable. The fuse should be rated at or below what the cable is rated to carry over the distance it is carrying it.

 

[VXman]

This is the absolute correct answer. The fuse is there to protect the cable. The fuse should be rated at or below what the cable is rated to carry over the distance it is carrying it.

Solar panel cables seem to be fairly standard don't they? It's the same width as the ones coming from the panel. Also the victron controller had tiny connection points, you'd struggle to get anything bigger in there.

Another thought though. I have a Victron 100/20. That's 20 amps. It was the one recommended by the calculator on the Victron site. If the controller is only 20 amps????

 

[Lenny HB]

Solar panel cables seem to be fairly standard don't they? It's the same width as the ones coming from the panel. Also the the victron controller had tiny connection points, you'd struggle to get anything bigger in there.

What length are the cable runs? And a photo would help.

Another thought though. I have a Victron 100/20. That's 20 amps. It was the one recommended by the calculator on the Victron site. If the controller is only 20 amps????

Max panel size 290 watts, you will lose any extra and the controller will probably run a bit warm.
But you are unlikely to ever generate a full 350 watts.

 

[Guigsy]

So the controller should top out at 20 amps. So it's odd that it's cooking a 25 amp fuse. It could just be a poor quality fuse box. I had an eBay one that claimed to be safe to 30 amps, but it got very warm when I was bench testing my 20 amp mains charger with my new lithium battery.

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[VXman]

What length are the cable runs? And a photo would help

From controller to battery about 50 cm.

 

[autorouter]

There is no reason to put any kind of fuse in the solar panel wires to the controller, on a small installation of a couple of panels. Solar panels do not behave like batteries. A battery can push out over a thousand amps if it is directly shorted, so you need a fuse to prevent wire overheating and possible fire. The output of the solar panel when shorted is shown on the label (Isc), and is only slightly higher than the 'Maximum Power Point' Amps, (Imp), also shown on the label. A fuse that is happy carrying the MPP Amps will never blow if the panel is shorted, and the wires will never overheat.

Having said that, you need to check that the solar panel wiring is capable of carrying the increased current from adding the extra panel, assuming they are wires in parallel.

If the 350W of panels are installed flat on the roof, not tilted like on a house roof, then that 350W is equivalent to about 290W of tilted panel, which is what the 100/20 is designed for. This 20A figure is not a hard limit, the controller won't put out more than 20A, and any extra power will be just wasted. This is quite normal. If the batteries are full the solar controller will waste all the power from the panels to avoid overcharging the batteries, that's what its job is.

 

[Gromett]

Solar panel cables seem to be fairly standard don't they?

To be a pedantic there is no such thing as solar panel cables with respect to the wires themselves. There is a couple of parameters to a wire but the main ones (presuming stranded copper) we need to be concerned with are cross sectional area and length.
This dictates how much current they can carry and that leads to the fuse size.

You really do need to know the size of your cable and the length and check this against a wire size calculator. If you are exceeding the current rating a blown fuse is likely to be the least of your worries.

 

[VXman]

There is no reason to put any kind of fuse in the solar panel wires to the controller, on a small installation of a couple of panels. Solar panels do not behave like batteries. A battery can push out over a thousand amps if it is directly shorted, so you need a fuse to prevent wire overheating and possible fire. The output of the solar panel when shorted is shown on the label (Isc), and is only slightly higher than the 'Maximum Power Point' Amps, (Imp), also shown on the label. A fuse that is happy carrying the MPP Amps will never blow if the panel is shorted, and the wires will never overheat.

Having said that, you need to check that the solar panel wiring is capable of carrying the increased current from adding the extra panel, assuming they are wires in parallel.

Sorry, not sure if you understood - the fuse is between the controller and battery - negatives.

 

[VXman]

To be a pedantic there is no such thing as solar panel cables with respect to the wires themselves. There is a couple of parameters to a wire but the main ones (presuming stranded copper) we need to be concerned with are cross sectional area and length.
This dictates how much current they can carry and that leads to the fuse size.

You really do need to know the size of your cable and the length and check this against a wire size calculator. If you are exceeding the current rating a blown fuse is likely to be the least of your worries.

OK I would say the the cable is 6mm2 looking at the infor on the website I bought it from. Peak output of each panel is 8.95 amps so really 25 amps should be enough? 6mm2 should take 35 amps? The output put of the controller cannot exceed the output of the panels I presume?

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[Guigsy]

OK I would say the the cable is 6mm2 looking at the infor on the website I bought it from. Peak output of each panel is 8.95 amps so really 25 amps should be enough? 6mm2 should take 35 amps? The output put of the controller cannot exceed the output of the panels I presume?

The controller effectively works like a transformer. It'll take the 18 amps at roughly 19v from the parallel panels and drop it to 12ish volts. It'll max out at 20amps on the output side (this is safe BTW).

 

[Gromett]

OK I would say the the cable is 6mm2 looking at the infor on the website I bought it from. Peak output of each panel is 8.95 amps so really 25 amps should be enough? 6mm2 should take 35 amps? The output put of the controller cannot exceed the output of the panels I presume?

Pop it in the calculator along with the length to check. For the current I use the nominal 12v for my calculation. So total wattage of panels / 12 will give you the total amps. The charge voltage is likely to be higher so the current will be lower than this so it gives you some leeway. That is why I use nominal voltage.

 

[autorouter]

Sorry, not sure if you understood - the fuse is between the controller and battery - negatives.

Oops, yes, as my old French teacher used to say, that is perfectly wrong.

A fuse in the battery negative wire??? Even more strange. You get all kinds of currents flowing along the negative wires unless you are careful to isolate them, and nobody bothers to do that, there's usually no reason to. It needs to be in the positive wire to be sure it's covering the amps coming out of the controller, and nothing else..

 

[Gromett]

Oops, yes, as my old French teacher used to say, that is perfectly wrong.

A fuse in the battery negative wire??? Even more strange. You get all kinds of currents flowing along the negative wires unless you are careful to isolate them, and nobody bothers to do that, there's usually no reason to. It needs to be in the positive wire to be sure it's covering the amps coming out of the controller, and nothing else..

I thought it was odd and not recommended but there is enough going off without worrying about that lol. However, while he is making changes might be worth fusing the live wires instead of the negative.

 

[VXman]

OK this is taking a completely different turn than expected. So to be clear. Solar panel to controller - positive and negative, no fuse. Controller to battery fuse the positive not the negative?

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[Lenny HB]

OK this is taking a completely different turn than expected. So to be clear. Solar panel to controller - positive and negative, no fuse. Controller to battery fuse the positive not the negative?

Yep.

 

[Gromett]

OK this is taking a completely different turn than expected. So to be clear. Solar panel to controller - positive and negative, no fuse. Controller to battery fuse the positive not the negative?

Yes

 

[Tombola]

OK this is taking a completely different turn than expected. So to be clear. Solar panel to controller - positive and negative, no fuse. Controller to battery fuse the positive not the negative?

Yes but to throw another spanner in the works you could put a fuse or switch between the panel and controller on the pos to isolate it when doing any work.

sorry lol

 

[VXman]

OK this is taking a completely different turn than expected. So to be clear. Solar panel to controller - positive and negative, no fuse. Controller to battery fuse the positive not the negative?

Yep.

Yes

Well, you lot need to have a word with https://www.directmotorhomeservices.co.uk/ who fitted the original panel/controller/fuse.

Mine you it doesn't surprise me. They managed to cause water ingress through the gland that they fitted for the cables too.

 

[Lenny HB]

I prefer to do things myself I've seen enough professional bodges to last a lifetime.

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[Gromett]

I prefer to do things myself I've seen enough professional bodges to last a lifetime.

Same here.

 

[paddymcc]

Yes but to throw another spanner in the works you could put a fuse or switch between the panel and controller on the pos to isolate it when doing any work.

sorry lol

I was about to add a similar comment. The other reason for doing that is it makes it easier to connect the battery to the controller before connecting the panel. This ensures the controller knows that you have a 12v rather than 24v system