Diy combiner with fuses (budget)

jimbuck · December 2017

Hi there, I’m installing a simple 400w system in a converted van. It comprises of a Morningstar pro star ps30 pwm charge controller . 4 100w panels (parallel) 1x 115ah battery (possible future upgrade to 220ah)
The panels will be mounted flat to the roof hence the over panelling for the 115ah battery. I am installing this system to a tight budget for a friend, she already has the panels and the pro star controller. My question is regarding the combining of the panels. I plan to do this up on the roof into an ip67 box using glands and busbars. This will be diy made. The budget doesn’t stretch to buying breakers. Can I use fuses? The isc of the panels is 5.7a so times 1.56 = 8.89a can I use a 10a blade fuse for each panel? I have drawn a diagram of what I plan to do. Can anyone advise me if this is ok? Any advice would be much appreciated. Thank you, Jim
England

mike95490 · December 2017

That "can" work, but

Blade fuse HOLDERS are often pretty cheaply made, and you will be running amps through them, so good heavy duty holders are required.
I've seen 30A holders melted with 5A fuses in them, the contacts are so bad, they heat up, melting the holder.

When powered up, you cannot remove a fuse, or it's likely to arc badly, which is way too much fun for being on the roof.

Eventually, cheap fuses and fuse holders will fatigue from thermal excursions, premium ones will last longer.

jimbuck · December 2017

Hi Mike, thanks for the advice. If I can source some quality components and better fuses do you think it is doable? Breakers are £20 a piece here. The current through each fuse will only be 5/6A and I would cover a panel before removing one. I will use a larger breaker down line before the cc as a disconnect also. I would use strip link fuses but they seem to start at 30A.

Thanks, Jim

Estragon · December 2017

Can't tell from the diagram, is there a breaker between the + bussbar and controller?

jimbuck · December 2017

Hi Estragon. It’s not in the diagram but yes there will be an appropriate sized breaker on the positive feed to the cc also to be used as a disconnect.
Jim

littleharbor2 · December 2017

The fuse rating should be on the data label on the panels back side.

Photowhit · December 2017

I, personally, wouldn't worry about 4 parallel 100 watt panels, at 12 volt nominal, they aren't likely to pose a danger of creating an arc and starting a fire. I actually doubt back feeding them would damage them, it is possible but unlikely.

You could use a fused power distribution block that would work with midget fuses, some thing like this;

Usually they are designed for high end car stereo's. Cost for this is $20 in US. The midget fuses come in AC and DC versions. be sure to get the correct amperage and type of fuse.

Looks like you could buy this 5 pack of din rail fuse holders;

https://www.ebay.co.uk/itm/5x-RT18-32X-AC-380V-32A-1-Pole-10x38mm-DIN-Rail-Mount-Fuse-Holder-Base-I1S-F7X2/282513180276?_trkparms=aid=555018&algo=PL.SIM&ao=2&asc=49569&meid=4efaa763477a471996a247dd39fa6614&pid=100005&rk=1&rkt=2&sd=172958786364&_trksid=p2047675.c100005.m1851

and then find the correct fuse, These are fast acting 10 amp fuses KLK;

https://www.ebay.co.uk/itm/BARGAIN-10-X-KLK-10amp-Midget-Fuses-quick-blow-ceramic-600VAC-10x38mm/222755564748?epid=2055821616&hash=item33dd442ccc:g:m7QAAOSw5cNYFmMW

and a small section of Din rail;

Image: https://i.ebayimg.com/images/g/3ckAAOSwzaJYAJH7/s-l1600.jpg

https://www.ebay.co.uk/itm/10CM-Din-rail-35mm/222281260424?hash=item33c0fedd88:g:3ckAAOSwzaJYAJH7

NANOcontrol · December 2017

As said before these panels are only a danger to themselves, three panels feeding into a shorted one. The panels are current limited. Current can never get above normal operating current even in a short. Breakers are just disconnects and test points in this size system.

jimbuck · December 2017

So in theory, with the correct sized cables between panels that can handle the current of the other 3 combined, there isn’t an issue. I would like to use some sort of protection hence the fuses but with the budget being tight I can justify anything over the top.
Photowhit: thanks for the ideas! I’m looking for suitable sized enclosures and fused power distribution blocks.

Jim

Estragon · December 2017

Even with big wire, a shorted panel itself is at risk of getting overcurrent from the other three.

Another way to do it would be to use 2-way paralleling mc4 connectors (no fuses needed for 2 in parallel), and run the two + wires to a pair of breakers next to the controller. Total cost may be close, and you don't have to mess with mounting box and fuses on the roof.

jimbuck · December 2017

That sounds good

jimbuck · December 2017

My last message was much longer but it only posted the lines above?

So a pair of Y branch connectors for each pair of panels wired in parallel. Two sets of cables coming down into the truck ++ - - the two ++ going into their own separate fuses and then combined together after the fuses and into the charge controller. Sounds much easier up on the roof and nicer to disconnect down in the truck. Thanks Estragon!

Estragon · December 2017

@jimbuck - yup, that's pretty much what I had in mind. I would use a pair of breakers (more user-friendly as disconnects) but fuses would do the job.

You will also want a fuse or breaker from controller (and inverter, if using one) to the battery. Note that pv should be depowered before battery, and repowered after battery, which is easier with breakers. Controllers should be booted up with stable battery voltage, as unstable pv voltage can cause some controllers to boot wrong.

jimbuck · December 2017

Thanks for all of your help! It’s a 30amp controller so I will use a strip link fuse between that and the battery and same with the inverter. It’s been a challenge due to the budget. I built my own system last year and bought the best I could and oversized all the wiring. I’ll attach a picture of my own system.

jimbuck · December 2017

Thanks for all of your help! It’s a 30amp controller so I will use a strip link fuse between that and the battery and same with the inverter. It’s been a challenge due to the budget. I built my own system last year and bought the best I could and oversized all the wiring. I’ll attach a picture of my own system.

Diy combiner with fuses (budget)

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