Fuse between Solar Charge Controller and Batteries (1 Viewer)

[namwaldog]

I am in the throes of fitting a 150 w solar panel through a 20 amp dual charge controller so that I can charge both my leisure & starter batteries using supplied 4mm cables.

I want to put a 15amp(?) fuse close to the batteries but am struggling to understand what type of fuse & holder to use. My first thought was one of these

but the wires on this are only 20 swg which converts to about 0.8 mm. Surely it doesn't make sense to use 4mm and then join to a length of the wire pictured above??
Anybody able to give me guidance as to which fuseholder and fuse to use?

 

[Reallyretired]

You could use a maxi blade fuse holder, though I think the lowest rated maxiblade fuse is 20A. Don't forget the fuse between the solar panels and the controller, as this makes a convenient way of disconnecting the panels (which must always be disconnected before disconnecting the batteries.)

 

[Kool Kroozer]

Well this was my concern when i fit my 2 panels and 30a controller, having read many threads on Fun about the safety aspect of fitting fuses between controller and battery and controller and panels..So when i purchased my system i made a note of asking the techies at the company about fitting fuses and i was assured i did not need to fit any fuses either side of the controller, so i just took their advice..not had any problems up to now but i know most do fit fuses

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[Stealaway]

Have a look for 20/30amp car stereo breakers on eBay. I fitted one and pressing the test button also isolates the panels just like a switch

 

[Allanm]

We have fitted these on the battery terminals, ours are 30 amp.
Very neat and easy to see if one has blown.

 

[scotjimland]

Maxi Blade Fuse Holder Splash-Proof 80A 8 AWG. Fit whatever size fuse you require..

http://www.ebay.co.uk/itm/Maxi-Blad...124439?hash=item19febf2e17:g:~58AAOSwzhVWtkcB

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[hchris]

Have a look at
eBay item number:
351635982764
It's the same as you looking at but with 14 swg cable.

Chris

 

[namwaldog]

Thanks for all your replies and Welcome back Jim

 

[Stealaway]

See --

http://www.ebay.co.uk/itm/CAR-BOAT-...202878?hash=item419183b7fe:g:HiMAAOSwpDdU8fPM

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[Reallyretired]

Thanks for posting that. I have ordered one myself

 

[RFS]

Hi @Stealaway, did you fit the 30amp fuse? How many watts of solar do you have? I have 2 x 100W panels so hope that's ok for my installation.

Thanks

Rob

 

[Stealaway]

Yep perfect
I have 250w of solar panels and the most I have ever seen on the amp meter is 24A on a very sunny day and very flat batteries.

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[Tedmund]

can I hop in on this please guys. I also was having the same thoughts about the wire size changing to an ordinary blade fuse holder and have been a bit stuck. However the item that Stealaway has shown is just what I need. My question is, I only have a 10amp solar controller, 2x50watt solar panels in series going to a 110amp battery which we plan to use just for lighting, charging phones etc and maybe when I get to it a water pump. can I use the 20amp circuit breakers between my panels and controller or do I need lower amps? although not new to camping I am new to solar power and any advice would be most welcome.

 

[Gromett]

Well this was my concern when i fit my 2 panels and 30a controller, having read many threads on Fun about the safety aspect of fitting fuses between controller and battery and controller and panels..So when i purchased my system i made a note of asking the techies at the company about fitting fuses and i was assured i did not need to fit any fuses either side of the controller, so i just took their advice..not had any problems up to now but i know most do fit fuses

I have a simple rule when it comes to electric. If it can be the source of voltage it has a fuse fitted. In the case of solar controller to battery I have a fuse at each end.

If your wires were to develop a fault, the battery could start putting unrestricted current into that cable causing it to melt/catch fire.

I also fit one at the controller end although it is less important. I can imagine a case where the cable gets damaged so that there is only a few strands of copper left. putting 15Amps from a solar panel charge controller through these few strands could cause fire/overheating again.

I am perhaps over cautious due to my training?

 

[Gromett]

but the wires on this are only 20 swg which converts to about 0.8 mm. Surely it doesn't make sense to use 4mm and then join to a length of the wire pictured above??
Anybody able to give me guidance as to which fuseholder and fuse to use?

If you cut the thin wires as close as you can to the actual fuse it is actually ok to use thinner wires (although not ideal). The losses in a cable are I²R So for an extremely short run of thin cable the R will be very low. The longer the cable the more important R becomes. The losses in say a 1" cable @ 0.8mm will be minimal and therefore generate next to no heat.

The resistance of copper in a 20swg cable is approx 0.025Ω per meter so say you cut the wire to 25mm that would be 0.000625Ω multiplied by 20Amps² = 20 x 20 x 0.000625 = 0.25Watts

Second thoughts, get a better fuse holder....

I was going to delete this and not post, however I thought it may be of interest as to why I proved myself wrong...

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[Richard n Ann]

can I hop in on this please guys. I also was having the same thoughts about the wire size changing to an ordinary blade fuse holder and have been a bit stuck. However the item that Stealaway has shown is just what I need. My question is, I only have a 10amp solar controller, 2x50watt solar panels in series going to a 110amp battery which we plan to use just for lighting, charging phones etc and maybe when I get to it a water pump. can I use the 20amp circuit breakers between my panels and controller or do I need lower amps? although not new to camping I am new to solar power and any advice would be most welcome.

How thick are your cables? The fuse is to protect the cables.
You mentioned 2 x 50w panels in series so that's only about 4.1amps.

 

[Tedmund]

Hi Richard, 2.5mm cable coming from the panels to the controller so I used the same from controller to my battery. Thanks

 

[chaser]

Probably get shot down here, but I have two 100 w panels , running through a 20 amp controller , I have twenty a fuse on the solar input , but on the supply side I have one of those holders at each end with five amp fuses in and not blown one yet.

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[two]

You only need one fuse in a circuit*. Any more will only confuse when it's not working (which one blew?).
*Some cheapskates may use a bank of small fuses in parallel, rather than a single large one, but that's different.

 

[Gromett]

You only need one fuse in a circuit*.

I disagree, you need one at the start of any cable connected to a device capable of supplying an electric current.

For example, if you had a battery at the front of your van and one at the back. If you only put a fuse at one end. If the cable shorts the single fuse will blow disconnecting that battery but leaving the other one pumping out current into the short.

 

[two]

Put the fuse near the battery, then.

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[Richard n Ann]

I disagree, you need one at the start of any cable connected to a device capable of supplying an electric current.

For example, if you had a battery at the front of your van and one at the back. If you only put a fuse at one end. If the cable shorts the single fuse will blow disconnecting that battery but leaving the other one pumping out current into the short.

Your basically saying the same thing. "You only need one fuse in a circuit"

 

[Gromett]

Your basically saying the same thing. "You only need one fuse in a circuit"

No I am not, I am saying you need one fuse per source of electricity.

I have for example 2 fuses in one run of cable that runs between my solar regulator and my battery as both are capable of being a current source.

 

[chaser]

Your basically saying the same thing. "You only need one fuse in a circuit"

No I am not, I am saying you need one fuse per source of electricity.

I have for example 2 fuses in one run of cable that runs between my solar regulator and my battery as both are capable of being a current source.

Obviously if your wire breaks and it connects with the chassis and earth you then have two potential new circuits, one from each source.

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[Richard n Ann]

Explain to me why a solar panel needs a fuse (other than to act as an isolator)
This is how I see it:
Say your panels are capable of delivering a maximum of 10amps and you have 2.5mm cables. What fuse would you use? 15amps?... would never blow even at short circuit. 9amps then?... would blow when the sun comes out. So you see its pointless, the 2.5mm cable will take at least 25 amps safely (using the x10 rule of thumb) so there cannot be a safety issue. The safety fuse is at the battery because THAT can deliver 100s of amps.

 

[Gromett]

Explain to me why a solar panel needs a fuse (other than to act as an isolator)
This is how I see it:
Say your panels are capable of delivering a maximum of 10amps and you have 2.5mm cables. What fuse would you use? 15amps?... would never blow even at short circuit. 9amps then?... would blow when the sun comes out. So you see its pointless, the 2.5mm cable will take at least 25 amps safely (using the x10 rule of thumb) so there cannot be a safety issue. The safety fuse is at the battery because THAT can deliver 100s of amps.

A fuse between the panel and the controller is there in case the controller goes faulty and feeds battery power up to the panels. Yes the blocking diode will prevent current flow but what if that diode is faulty? maybe a nearby lightening strike induced a high voltage in the cable runs and fried the diode and knackered the charge controller.
You would imagine the battery end fuse would protect the circuit......

You do it for the same reason as your house has a fuse in the plug of a device, but inside the device it will also have another fuse.

To be fair, a fuse underneath the solar panel and on the output of the solar controller is probably not needed for the vast majority of failure modes. But in real world engineering you put 2p protection in place wherever there is even the slightest possibility of a failure mode that could cost you more than the cost of the fuse.

 

[Richard n Ann]

So many ifs and buts. I suppose it's down to what is your acceptable level of risk. If my van got struck by lightning, the LAST thing on my mind would be "I wonder if my solar panel fuse has blown" lol
Each to their own.

PS fuses and their connections introduce a small voltage drop.

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[Gromett]

So many ifs and buts. I suppose it's down to what is your acceptable level of risk. If my van got struck by lightning, the LAST thing on my mind would be "I wonder if my solar panel fuse has blown" lol
Each to their own.

PS fuses and their connections introduce a small voltage drop.

I didn't say a direct lightening strike I said a nearby one which induced a voltage. Believe me this happens, I have lost devices to this. As an electrical engineer I won't reduce protection for the sake of a 2p fuse.

The resistance of a vehicle style fuse is negligible and would cause little if any noticeable voltage drop.

 

[Richard n Ann]

I think you've pretty much lost the argument when you start to talk about lightning. At first you said every source of electricity needs a fuse, so you seem to be changing your explanation to fit your beliefs.
Anyway it's fine if anybody wants to fit a fuse in the solar panel cable it won't do any harm and it can be used to isolate the controller.

 

[Richard n Ann]

It also won't do any harm to put a fuse in your TV coax... just saying

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