Testing the Waters "Solar"

[homelesshartshorns]

Thanks for the feedback.

[Randyretired]

Wiring the solar panels in series will increase the voltage and decrease the amps.  The voltage that the controller can handle is critical.  If the open circuit voltage is higher than the controller is designed for that is often catastrophic but if the voltage is within limits, series is often preferred. The fuse that is causing the problem is not needed IF the wire is sized to handle the current.  The NEC suggests fusing unless the wire is sized to carry approximately 156% of the maximum panel current.  

[homelesshartshorns]

This is a 400 watt Renogy kit with a 40 amp mtt controller.  10 gage wire witch I added 10 foot to reach the array. 

[Randyretired]

The spec's I found on the 400 watt Renology kit are

VOC 24.3

ISC 5.21

Controller maximum voltage.  100

The VOC and ISC are listed on the back of the panel and you should check those spec's to be sure.

Based on those spec's if the panels are wired 2 in series and 2 of that combination, then 10awg meets the NEC requirement for unprotected (no fuse) service.  These panels should NOT be wired 4 panels in series as that could exceed the maximum voltage during cold temperatures. 

If the spec's on the back of the panels match and the panels are wired this way, I would remove the fuse.  However, a means to disconnect the panels for service is required or should be considered.  I often use a DC breaker for this but size the breaker at least as high as the wire can carry.  In this case I would use 30 amps or more.

Edited February 5 by Randyretired
To add disconnect requirements

[homelesshartshorns]

So you seemingly have way more experience than I do, witch is Zero! I did take the blown 10 amp fuse out of the line and seen the array does put numbers on my app indicating the array is hot. So your sugestión is stick with parcial un protected and not do all four in series?

[Randyretired]

Yes.  That is what I would do but you should check the spec's on the panels.  Based on these numbers 10amp fuse is to small.  It is good to see your array actually providing full power.  It must be setup correctly.  I don't consider myself an expert but I do have experience in solar. If you are not comfortable with my suggestion please get another opinion.

[homelesshartshorns]

55 minutes ago, Randyretired said:

Yes.  That is what I would do but you should check the spec's on the panels.  Based on these numbers 10amp fuse is to small.  It is good to see your array actually providing full power.  It must be setup correctly.  I don't consider myself an expert but I do have experience in solar. If you are not comfortable with my suggestion please get another opinion.

My only uneducated question is why would a kit come with a fuse that seems to small? Would me adding 10 foot of cable be an issue? Other than that I have everything set up accoriding to instructons for the partial array.

[Randyretired]

That is a good question. The spec's that I found show a working amperage of 4.91.  With the way yours are wired that is 9.82 amps. Nearly 10amps and solar panels under certain conditions produce more than rated.   Typical design requires wire to be sized at 125% of load but solar panels produce more than spec's now and again do to reflection, including off of clouds.  10awg wire meets this and if a fuse is used it should be sized for the wire.  10awg is rated to carry 30 to 40 amps depending on conditions.  You could also safely use a larger fuse with this wire but it is also safe in this instance to not provide over current protection. 

[homelesshartshorns]

Thanks for you input. Has given me food for thought and suggestions are always helpful. Ill let you know if I burn the house down.

[homelesshartshorns]

I finally stumbled on my issue I think.

 New 400 Watt 12 Volt Solar Premium Kit | Renogy Solar

On this page I set my system up in partial configuration. And put the 10 amp fuse in line where is says 30 AMP Fuse not included!!! What a Deal!!!

So according to these two configurations in series I only need the 10 amp fuse and in the partial seem to need a 30 amp fuse.  So my next question is do I still need a fuse at all? It looks like if I was to go series I might get away with no fuse? 

[Randyretired]

Fuses are added to protect the wire.  In your situation the panels can not produce more power than the wire can handle.  A fuse won't hurt anything but is not needed.  Looking at the spec's the maximum controller voltage is listed as 100v.  All 4 of your panels in series would produce a VOC of 98.2v.  Solar panels are typically rated at 70F.  As the temperature falls the voltage produced increases.  Most controllers will fail when the voltage capacity of the controller is exceeded.  I would never suggest a VOC of 98.2 is an acceptable voltage for a controller rated for 100v.  From you comments it seems Renology endorses this but based on the advertised spec's I certainly can not. 

[homelesshartshorns]

I appreciate you comments. Your thoughts are not to go with out a fuse if I rewire my array ln series?

[Randyretired]

I know that sounds like a simple question but if I just answer it it may not make sense.  Let me try to explain.  Fuses are to protect the wire and are based on amps.  When solar panels are wired in series the voltage is multiplied by the number of panels but the amperage stays the same.  When panels are wired in parallel the amps multiply but the voltage stays the same. Your panels produce 5.2 amps and 24.3 volts.  So in series the voltage is high but the amps are still 5.2.  Wire size is based on amps and fuses control the amps.  In series the amps are low and the wire will easily carry the current.  So in series the wire will most easily handle the current.  So yes in series I would not recommend a fuse.  However, since fuses control only amps, fuses will not control voltage.  So adding a fuse will not protect the controller from high voltage which is why based on advertised spec's I can not recommend series wiring.  In any case a properly sized fuse of 30 amps should not cause any problems no matter how the 4 panels are wired.  If Renology endorses series wiring you can probably get away with it and a fuse will make no difference either way.

[homelesshartshorns]

9 minutes ago, Randyretired said:

I know that sounds like a simple question but if I just answer it it may not make sense.  Let me try to explain.  Fuses are to protect the wire and are based on amps.  When solar panels are wired in series the voltage is multiplied by the number of panels but the amperage stays the same.  When panels are wired in parallel the amps multiply but the voltage stays the same. Your panels produce 5.2 amps and 24.3 volts.  So in series the voltage is high but the amps are still 5.2.  Wire size is based on amps and fuses control the amps.  In series the amps are low and the wire will easily carry the current.  So in series the wire will most easily handle the current.  So yes in series I would not recommend a fuse.  However, since fuses control only amps, fuses will not control voltage.  So adding a fuse will not protect the controller from high voltage which is why based on advertised spec's I can not recommend series wiring.  In any case a properly sized fuse of 30 amps should not cause any problems no matter how the 4 panels are wired.  If Renology endorses series wiring you can probably get away with it and a fuse will make no difference either way.

I think I'm getting it.  Series will produce more power than the 40 A Controler can handle, in cool weather! But if I stay in Partial and get the 30 A fuse, wires are big enough for the power produced and the fuse will keep the controller safe. 

[Randyretired]

Yes.  If this were my system I would wire it the way yours is currently and remove the fuse.  If the fuse would make you more comfortable you can leave it but with a 30 amp fuse.  Either way should work.

Edited February 6 by Randyretired

[Chad Heiser]

For the two panels in series, the voltage doubles and the amperage stays the same.  For example two 25 volt panels at 4 amps in series would produce a 50 volt at 4 amp output.  When two additional series connected panels are added in parallel, the voltage will remain the same and the amperage will double.  With the four panels in this example in series parallel (2S2P), the end voltage will be 50 volts and the end amperage will be 8 amps.

I am not a fan of the in line fuses like you found on your set up for the reasons your system is having issues.  They tend to blow at very inconvenient times.  Most that I have found are typically installed incorrectly as well.  They tend to be installed  in the wrong place in the string and end up getting more amperage than they are rated for as a result and blow.  I had to remove one from someone’s system the other day for this exact reason.  It was installed in the wrong place in the array and was getting more amps than it was rated for.

I prefer a DC rated breaker down by the solar controller.  Not so much for the circuit protection ( for the reasons Lou Schneider explained), but to be used as a shut off when I want to isolate the panels from the system for testing or service or whatever.  Plus a circuit breaker is resettable rather than having to replace a fuse.

[homelesshartshorns]

4 hours ago, Chad Heiser said:

For the two panels in series, the voltage doubles and the amperage stays the same.  For example two 25 volt panels at 4 amps in series would produce a 50 volt at 4 amp output.  When two additional series connected panels are added in parallel, the voltage will remain the same and the amperage will double.  With the four panels in this example in series parallel (2S2P), the end voltage will be 50 volts and the end amperage will be 8 amps.

I am not a fan of the in line fuses like you found on your set up for the reasons your system is having issues.  They tend to blow at very inconvenient times.  Most that I have found are typically installed incorrectly as well.  They tend to be installed  in the wrong place in the string and end up getting more amperage than they are rated for as a result and blow.  I had to remove one from someone’s system the other day for this exact reason.  It was installed in the wrong place in the array and was getting more amps than it was rated for.

I prefer a DC rated breaker down by the solar controller.  Not so much for the circuit protection ( for the reasons Lou Schneider explained), but to be used as a shut off when I want to isolate the panels from the system for testing or service or whatever.  Plus a circuit breaker is resettable rather than having to replace a fuse.

You mentioned putting the fuse in the wrong place in the array! Is the right place near the controller or is that location just more convenient than the right place? Or is the best option no fuse. I have ordered a 30A fuse.

[Chad Heiser]

16 hours ago, homelesshartshorns said:

You mentioned putting the fuse in the wrong place in the array! Is the right place near the controller or is that location just more convenient than the right place? Or is the best option no fuse. I have ordered a 30A fuse.

Those in line fuses are best installed with each solar panel at the positive pigtail coming off the solar panel.  This way the fuse is protecting the single panel it is connected to rather than a line of solar panels (that they often aren’t sized properly for).  This means using one fuse for each panel.  A lot of budget kits try to get away with one fuse for the entire array, but then don’t specify how the array is to be wired (to keep the amperage within spec for the fuse) or simply supply the incorrect sized fuse for the application.

Edited February 10 by Chad Heiser

[homelesshartshorns]

8 hours ago, Chad Heiser said:

Those in line fuses are best installed with each solar panel at the positive pigtail coming off the solar panel.  This way the fuse is protecting the single panel it is connected to rather than a line of solar panels (that they often aren’t sized properly for).  This means using one fuse for each panel.  A lot of budget kits try to get away with one fuse for the entire array, but then don’t specify how the array is to be wired (to keep the amperage within spec for the fuse) or simply supply the incorrect sized fuse for the application.

I have two 30A inline fuses comming and with what I understand I am trying to protect my 40A controller from my cheap array, that occasionally overheats. So thinking to put a fuse in each of the two series panels. Is this a good plan.

[Randyretired]

A 30amp inline fuse will not protect the controller.  The 40 amp rating is based on the output.  Part of what a MPPT controller does is change the panel voltage to the battery voltage and change that excess voltage to amps.  For instance the VOC on your panels is around 24.3v and 2 wired in series produces 48.6v.  The MPPT converts the amps at 12v by a factor of 4.  So 30amps at 48v becomes 120 amps at 12v.  The limiting factor here isn't the fuse.  It is the panels that are not capable of producing that much.  More importantly though is fuses should be sized to protect the wire.  This is basic engineering.  Each component should have internal protection and in this case the controller will not accept more power than the 40amp output.   In fact it is common and even suggested by many MPPT manufacturers to purposely over panel an a MPPT.  Since solar only rarely outputs full power only a small amount of the power will be clipped.  Allowing this clipping is a way to save money on controller's with very minimal loss.  Your panels will never put out more power than this 40 amp controller can use.  MPPT's typically produce heat while working.  If you are more comfortable with the 30amp fuses they won't hurt anything but they are not needed

 

[homelesshartshorns]

9 minutes ago, Randyretired said:

A 30amp inline fuse will not protect the controller.  The 40 amp rating is based on the output.  Part of what a MPPT controller does is change the panel voltage to the battery voltage and change that excess voltage to amps.  For instance the VOC on your panels is around 24.3v and 2 wired in series produces 48.6v.  The MPPT converts the amps at 12v by a factor of 4.  So 30amps at 48v becomes 120 amps at 12v.  The limiting factor here isn't the fuse.  It is the panels that are not capable of producing that much.  More importantly though is fuses should be sized to protect the wire.  This is basic engineering.  Each component should have internal protection and in this case the controller will not accept more power than the 40amp output.   In fact it is common and even suggested by many MPPT manufacturers to purposely over panel an a MPPT.  Since solar only rarely outputs full power only a small amount of the power will be clipped.  Allowing this clipping is a way to save money on controller's with very minimal loss.  Your panels will never put out more power than this 40 amp controller can use.  MPPT's typically produce heat while working.  If you are more comfortable with the 30amp fuses they won't hurt anything but they are not needed

I wondered why a 10 amp in line fuse failed? The 10A fuse blowing is why I went with 30A!! We are talkin 30' of # 10 wire between the array and the controler.

 

[Chad Heiser]

On 2/10/2024 at 5:20 AM, homelesshartshorns said:

I have two 30A inline fuses comming and with what I understand I am trying to protect my 40A controller from my cheap array, that occasionally overheats. So thinking to put a fuse in each of the two series panels. Is this a good plan.

Putting a 30 amp fuse on each series string will not hurt anything (assuming you have at least 10 AWG wire).  The fuses are there to protect the wire, not the equipment.  You do not want a fuse rated for more ampacity than the wire is rated for because then the wire itself becomes the fuse (the wire will fail before the fuse).