hi I'm Nick, my mission is to make solar energy understandable to everyone. in this video I'm
going to talk about fusing solar panels. when we want to add solar panels to our house or vehicle
we can wire them in several ways. these are series, parallel or a combination of both.
I did a video about this, check out my video about how to wire solar panels.
in this video, i will only talk about the size of the fuse and where to put them.
first we need to understand that the fuse is there mainly to protect the wire.
in a parallel connection, it also protects the solar panel.
Most of the time you will be wiring your panels in series. This is because MPPT
charge controllers have a high input voltage and it's cheaper to wire them in series.
in that case, you only need to have one fuse on the positive wire coming from
the solar panels. the maximum fuse size will be indicated on the back of the solar panel.
if we use the formula Isc times 1.56 to calculate the minimum fuse size it will be 6.2 amps times
1.56 equals 9.6 amps. in this case i would use a 10 amp fuse. we can use a general inline mc4 fuse.
if you use a PWM charge controller you will most likely wire in parallel.
you need to fuse every parallel panel. as you can see in the following image
every parallel panel is fused. just like the previous example, we will use a 10 amp fuse.
we now need to calculate the fuse size for F4.
we need to use a short circuit current and multiply it by three panels.
then we multiply it by the safety factor of 1.56 and we become 29 amps. we will use a 30 amp fuse
for f4. if you have a larger system you might want to combine series and parallel.
here the same rules apply: fuse every series string as indicated in the example. this is
an example of a 3s2p system. there are three panels in series and two parallel strings.
we need three fuses in total. one for each series string and one for the combined parallel array.
fuse 1 and 2 will be 10 amps like our previous examples. fuse 3 will be 6.2
amps times 1.56 times two parallel strings equals 19.3 amps. we will use a 20 amp fuse.
as you might already know, in series the voltage gets added up and in parallel the currents get
added up. that means we can use a small wire size in series, and we need to use a bigger wire size
in parallel. if we want to calculate the wire sizes of the last system, we can do so as follows:
the wire from the solar panels to the charge controller needs to be calculated according to
the short circuit current of the solar panel. this is 6.2 amps times 1.56 equals 9.6 amps.
the combined voltage of the three solar panels is 52.5 volts.
if we calculate this for the voltage drop we can see that a 14 gauge or 2.5-millimeter square
wire is good for 25 feet length. the other wire from the combiner box to the charge controller
needs to be thicker because it combines the current from two series strings. 6.2 amps
times 1.56 times two strings equals 19.3 amps. the voltage is the same at 52.5 volts.
let's say the length is 25 feet, then we need a 12 gauge or 4-millimeter square wire.
i did a separate video about voltage drop in solar systems.
if you are interested you can watch it after this video.
you can use parallel branch connectors up to 10 gauge. this is because solar cable doesn't
go bigger than this. if you have properly sized system, you shouldn't go bigger than 10 gauge.
you need to install a solar disconnect switch between the solar panels and the charge controller.
this can be a sore disconnect switch or a circuit breaker. if you choose a circuit breaker it's
best to place it near your charge controller. then you don't need a separate combiner box.
make sure the voltage is high enough for the solar panel voltage.
a battery disconnect switch is not suited because it's high current low voltage.
i hope this video answered your questions about fusing solar panels.
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and if you want to learn more about off-grid solar power check out my book on the subject.