Fuses on the PVmodules

fca1

Hi,

i'm now upgrading my system and i will add a midnite 150 + 3000w of pv modules...

i will will have 4 strings of 3 modules or maybe 6 strings of 2 modules still deciding because of the voc

The modules will be the Luxor LX-250M/156-60+ with a VOC of 37.41V and an ISC of 8.61 amps...

So going for the 4 strings will have on each string ~112V and 8.61 amps..

So i should put a fuse on each string will a 15amp fuse be ok or should i go for a 10amp ?

i after some inline fuse that i can put inside my combiner box (very simple water proof box with some bus bar) any recommendation on the fuse

i was thinking on something like this but this more for auto/boat environments

Attachment not found. ?
or
4 of this that have a 12awg cable and a led that show when blown...

Attachment not found.


regards

inetdog

Re: Fuses on the PVmodules

fca1 wrote: »

...after some inline fuse that i can put inside my combiner box (very simple water proof box with some bus bar) any recommendation on the fuse

i was thinking on something like this but this more for auto/boat environments

The biggest caution is that some automotive type fuses are not rated for voltages in the area of 40 volts DC and can arc and maybe catch fire if they blow under load.
As for the size of the fuse, the manufacturer's ratings should include a "Maximum Series Fuse" rating. You may want to go all the way to that value to reduce the chances of nuisance blowing when the combiner box gets very hot in the sun. (Automotive fuses are less likely to be affected by that, while circuit breakers may be more sensitive to temperature than regular fuses.)

Cariboocoot

Re: Fuses on the PVmodules

Auto fuses are not designed to work with over 32 Volts, so they wouldn't work safely with even one of those panels let alone three in series.

Be safe: get the right equipment for the job.

BB.

Re: Fuses on the PVmodules

Those types of autofuse holders--Wayne had a similar model and even running well under its current rating toasted the holder and could have started a fire if not in a metal box.

waynefromnscanada wrote: »

In my opinion a few volts won't make a lot of difference. I know of one case where they were used on a 1Hp 240 VAC motor that didn't have internal overload protection. Added after having motor re-wound several times. After that, only the fuse blew if the motor got stalled. That said, the current was already limited to what the windings would pass before burning up. On a more serious note, I nearly had a fire with the combination of one of those 30A fuses and it's plug in holder, where there was continuous 20A or so current.

Seems a resistance built up between the fuse blade and the holder clip. Melted the holder, blackened the fuse leg, ate part of the blade away with arcing, still the fuse didn't blow! When I found it by accident when checking voltages and discovering a drop where there shouldn't have been any, the whole mess was welded together. Had to cut it open to see what had happened.

After that, I soldered the wires directly to the fuse blades and have had no more problem. Used to have similar electrical problems with 12 volt motorbike systems years ago, at points where the wires were crimped into connectors. Just something to consider.

It turns out that many automotive and boating type switches and safety devices are not really designed to run at rated loads (i.e., light duty use). Get good quality and pay attention to them over time.

-Bill

fca1

Re: Fuses on the PVmodules

inetdog wrote: »

The biggest caution is that some automotive type fuses are not rated for voltages in the area of 40 volts DC and can arc and maybe catch fire if they blow under load.

that's my main concern also and will be ~112V don't know if that fuses are ok for these voltages...

inetdog wrote: »

As for the size of the fuse, the manufacturer's ratings should include a "Maximum Series Fuse" rating. You may want to go all the way to that value to reduce the chances of nuisance blowing when the combiner box gets very hot in the sun. (Automotive fuses are less likely to be affected by that, while circuit breakers may be more sensitive to temperature than regular fuses.)

The Panels didn't arrive yet, so can't see the labels, on the online documentation luxor don't have info on the recommended fuse size, i'm afraid of 10amps its to close to the 8.61 amps probably i will go with 15 amps ...



other point is if i go with parallel connections using these kind of mc4 connectors i will have to put inline fuses in red marks right ?

Attachment not found.

Cariboocoot

Re: Fuses on the PVmodules

fca1 wrote: »

that's my main concern also and will be ~112V don't know if that fuses are ok for these voltages...





The Panels didn't arrive yet, so can't see the labels, on the online documentation luxor don't have info on the recommended fuse size, i'm afraid of 10amps its to close to the 8.61 amps probably i will go with 15 amps ...



other point is if i go with parallel connections using these kind of mc4 connectors i will have to put inline fuses in red marks right ?

If all panels are in parallel each and every one must have a fuse on it before it connects with any others.

I know; I have got to make the drawings.

fca1

Re: Fuses on the PVmodules

Cariboocoot wrote: »

If all panels are in parallel each and every one must have a fuse on it before it connects with any others.

I know; I have got to make the drawings.

In the example modules are in strings of 2 ..
And following your recommendation I must put a fuse as on pic in red , between each string ..
If auto uses not ok , any recommendation for a inline fuse holder/ fuse ?
Regards

Cariboocoot

Re: Fuses on the PVmodules

fca1 wrote: »

In the example modules are in strings of 2 ..
And following your recommendation I must put a fuse as on pic in red , between each string ..

Yes, but your drawing shows a fuse on the first string, then the next fuse on two strings together, then no fuse for the third string.

A panel string needs to be constructed like this:

(-)PANEL(+)--(-)PANEL(+)--FUSE--COMBINER

If auto uses not ok , any recommendation for a inline fuse holder/ fuse ?
Regards

You may not like this answer but ... in-line fuses for that sort of Voltage would be few and far between. For four or six strings you should use the proper commercially-available equipment:
http://www.solar-electric.com/sopawiinco.html

Some have made their own boxes, but you have to have fuses/breakers rated for the Voltage and current and the combiner box needs to be weather tight if it is outside.

fca1

Re: Fuses on the PVmodules

I want to make it right and with correct solutions, safety is very important for me..
But to use a din fuse holder and fuse like the midnites I can't use that mc4 parallel connectors ...right ?
I will have to bring each string to the combiner box ..
I'm I right ?

Cariboocoot

Re: Fuses on the PVmodules

There are a couple of options available. One is to use one of MidNite's pre-wire boxes which has the MC4 connectors right on it: http://www.solar-electric.com/prpvcobo.html

Another it to buy MC4 "extensions" and cut them in half, giving you a positive and negative connector that can be spliced to standard wiring or tightened into a terminal: http://www.solar-electric.com/incaforsoelp.html

NorthGuy

Re: Fuses on the PVmodules

Cariboocoot wrote: »

Another it to buy MC4 "extensions" and cut them in half, giving you a positive and negative connector that can be spliced to standard wiring or tightened into a terminal: http://www.solar-electric.com/incaforsoelp.html

When you move these into the box, positive and negative wires look exactly the same. It is very important to connect them with correct polarity. It might be a good idea to mark positive ends with red tape before routing them into the box.

niel

Re: Fuses on the PVmodules

NorthGuy wrote: »

When you move these into the box, positive and negative wires look exactly the same. It is very important to connect them with correct polarity. It might be a good idea to mark positive ends with red tape before routing them into the box.

excellent point as you don't want to get the wiring mixed up as you could damage panels as well as create a fire hazard.

ggunn

Re: Fuses on the PVmodules

fca1 wrote: »

that's my main concern also and will be ~112V don't know if that fuses are ok for these voltages...





The Panels didn't arrive yet, so can't see the labels, on the online documentation luxor don't have info on the recommended fuse size, i'm afraid of 10amps its to close to the 8.61 amps probably i will go with 15 amps ...



other point is if i go with parallel connections using these kind of mc4 connectors i will have to put inline fuses in red marks right ?

Attachment not found.

As others have said, each string of two modules must have its own fuse, and you cannot combine them as you have drawn it. All three strings must come together at a single point and all the fuses must be between the combining point and the modules. You are right about the fuse size, however. The minimum fuse size is Isc X 1.25 X 1.25. In your case that is 13.4A, so a 15A fuse is appropriate.