Two resources that I have found helpful are @FilterGuy 's "DC Fuse and breaker Sizing and Placement" and the "Wire and Fuse Selection Quick Reference (Blue Sea Systems)". Others may be better at directly linking to those.
Have spent way too much time looking at those and wondering if I've got it right.
I like your resources and have move I've come across downloaded.DC Fuse and breaker Sizing and Placement
To get the paper, click on the orange button at the top of the page The attached presentation gives the fundamentals for picking fuse/breaker sizes and describes where in the circuit they should be placed. You can download the presentation by...diysolarforum.comWire and Fuse Selection Quick Reference (Blue Sea Systems)
This PDF is a good quick reference guide for wire size and fuse selection. The wire size chart is based on 12v DC, but is safe to use for higher voltages (in which case it will be more conservative). It should be noted that circuit length is the...diysolarforum.com
I am trying to pick through the various comments to understand the set-up.I like your resources and have move I've come across downloaded.
Something I'm curious on is what size ocpd would be recommended for my hybrid inverter that has this in the description.
"Maximum Charging Current: 40A when Utility/Grid Charging, 0-80A when PV Charging."
From that I take that when plugged into AC and charging from the mains it can charge at a max of 40a, and I can set the PV charge 0-80a.
By using the 1.25 rule in your document on the most current the charger can provide, 80a, it suggests a 100a fuse which is what I have planned and will match my 4 wire. Since the bank will be charged and discharged by the same wires and at 3000w/29a ac gives me 80a dc @ 48v the 4 wire with a 100a fuse also matched my needs there I think. Bms is also a 100a.
Should I set the PV charge profile for my setup to match the 40a that it can provide when using the mains or it wont matter? Bank will be 16s 310ah.
On page 2 of the Overcurrent Protection Devices (OCPD) on Solar Arrays document it says fuses become necessary when "3 or more Parallel Strings of 1 or more series panels". My intention is to use 6 250w panels in a 2s3p configuration giving me around 74v and 28a. If I understand it correctly I don't fall within the above parameter as I only have 2 in series not 3. Or am I way off?
Awesome, thanks!I am trying to pick through the various comments to understand the set-up.
It sounds like it is a 48V, 3000W system with a capability of charging at 80A from PV or 40 from AC Mains. Is that correct?
Assuming a 90% efficientcy of the inverter, it could draw up to 3000/.9 = 3333W. If the battery is low that works out to be 3333/48V = 69A.
The driving factor for sizing the fuse and wire is the largest current source which is the 80A PV charge. Consequently, the fuse size should be 1.25 x 80 = 100A. You had it correct. ?
I'm ambivalent and have no real preference other than what you think would be better. I've been told that 2s3p or 3s2p should preform somewhat similar through a mppt. Your thoughts or recommendations on 2s3p or 3s2p?3 strings in Parallel need to have OCPD on each string as shown above.
If, on the other hand, you had 2 strings of 3 panels in series, OCPDs would not be required.
I'm ambivalent and have no real preference other than what you think would be better. I've been told that 2s3p or 3s2p should preform somewhat similar through a mppt. Your thoughts or recommendations on 2s3p or 3s2p?
The 2s3p would give me 74v and 25a and the 3s2p would be 111v and 16v roughly. The 2s3p would need the fuse because the amperage is increased and the fuse is for the amps not the voltage?
I do have some shade but not a ton. So more parallel might be the way to go.more Parallel strings are better if you have shading issues
Yea the max is 145 but Im planning for six panels not 4. I suppose I could just get 8 and do 4s2p. Giving me voltage around 148 at 16 amps. Wasn't really sure and how hard of a number the 145 was but I was advised another threads to stay under it always.usually have a fairly high max PV input voltage. Can you do all 4 in series? You appear to have panels with 37V Voc so 4 in a series would be 148V before temperature compensation.
Yea so looking like three is the max I can do in series to stay within my voltage and amperage parameter.Your controller probably has a 150V limit so now that I have done the math I am guessing 3 in series is the most you can do.
ThisIf, on the other hand, you had 2 strings of 3 panels in series, OCPDs would not be required.
yes That looks reasonable. You have (145V-111V)/111V = 30.6% Voc headroom for low temperature conditions so you should be good for even extreme cold tempsSo to confirm I'm a safe with 3s 2p. Giving me voltage around 111 and 16 amps. And not needing a fuse in that array?
It does not take much shade to really mess things up. Your panels probably already have bypass diodes. You may want to consider a blocking diode on each string so if one string is shaded it won't impact the others.I do have some shade but not a ton. So more parallel might be the way to go.
Correct.And not needing a fuse in that array?
Awesome thanks. Depending on when I buy my panels I may end up getting 8 if they're the right price. If that happens I'll just be sure to stay within my v and a input parameters. And if I bust over on the v side and have to go in parallel more than one string I will refer to the above and put in the correct fuse.yes That looks reasonable. You have (145V-111V)/111V = 30.6% Voc headroom for low temperature conditions so you should be good for even extreme cold temps
Correct.
Fusing & Wire Sizing guidelines for solar panels
To get the paper, click on the orange'' button at the top of the screen. This resource is intended to help the user understand when they need to add Over Current Protection Devices (OCPDs - Fuses or Breakers) to the solar panel array and what...diysolarforum.com
With 2 parallel strings of 3-Serial panels. No fuses are needed. However, you should put a disconnect switch in before the charge controller. Some people use breakers as disconnect but a regular 2 pole switch would work as well.Referencing this post again as I'm about to buy my panels tomorrow. They're 8 yr old 250w photon solar brand panels for $40 each with mounting rails and brackets. Short circuit current is 8.7 and max fuse rating is 15. If I stick to my 3s2p like I wanted to above will I need 2 fuses since I'll have 90 or so v @ 16.6a?
Thanks
Very good thank you. I don't understand it all but I appreciate it.With 2 parallel strings of 3-Serial panels. No fuses are needed. However, you should put a disconnect switch in before the charge controller. Some people use breakers as disconnect but a regular 2 pole switch would work as well.
I plan on 10' my run isn't long at all. 15' maybe 20.The current you should use for wire sizing is 8.7 x 2 x 1.56 = 27.144. I would use a minimum of 10AWG. However, if your run is long, you should go to 8AWG.
So even though my hybrid inverter can take in up to 50a still use a 30a as it's unlikely 6 250w panels in a 3s2p config can put out 50a? Trying to understand why 30a.If you decide to use breakers as the disconnect, make it a 30A breaker.
The breakers are just being used as switches. The panels will never produce 30A even with a dead short in the most optimal solar conditions. Consequently, anything over 28A will work. In fact, A dual pole switch is acceptable. People use breakers as solar disconnects because they are an easy and cost-effective way to do the disconnect.So even though my hybrid inverter can take in up to 50a still use a 30a as it's unlikely 6 250w panels in a 3s2p config can put out 50a? Trying to understand why 30a.
Makes sense now thank you. Nearing the end of my questions unless when I put this together Saturday something goes arie.The breakers are just being used as switches. The panels will never produce 30A even with a dead short in the most optimal solar conditions. Consequently, anything over 28A will work. In fact, A dual pole switch is acceptable. People use breakers as solar disconnects because they are an easy and cost-effective way to do the disconnect.
However, since they are breakers, I like to make them small so if something weird happened they would pop sooner than later. (The only weird thing I could imagine where they would pop is some kind of short through the SCC that dumps the full battery current through the SCC output... That seems highly unlikely, but why NOT use the smaller breaker)