Adding Dissimilar Panels

[jor_tucson]

Just want to make certain my figuring is correct. I just installed 800 watts on my RV with 4 Rich Solar 200 watt panels in a series parallel-configuration.
I call them S1 and S2. The 10 gauge wire from these is paralleled in a combiner box on the roof. Everything works fine. Now I would like to add two 100 watt panels in a series-parallel configuration and run that to my combiner box.

S1 and S2 at the combiner box are the same with 40.8v and 9.8a each so my current setup is 40.8v and 19.6a to my controller.
S3 at the combiner box will be 43v and 4.54a.

So... in that these three are paralleled at the box I use the lowest voltage number which is the original 40.8 and add the 4.54 amps so my new numbers are 40.8 and 24.14. Have I got this right? Thanks.

 

[sunshine_eggo]

Sorta. The mismatch will result in operation somewhere between them, but likely coser to the 40.8V. Overall, the entire array will experience a % penalty about the same as the Vmp difference - about 5.4% in your case.

With a third string, you will need fuse protection on all three strings. A single suitable MC4 in-line fuse on the (+) of each string is fine. The panels have a max fuse rating on the label. That's the best number to use.

 

[Rocketman]

Yep, you got it right.

Now because of 3 strings in parallel- each string needs fuses - they make Mc4fuses.

 

[jor_tucson]

Whoa, you guys are fast with the replies! Thanks a million. I just ordered three 20a fuses. No more room on the roof so this should do it. I'm long in the tooth so this should keep me off the roof which will make my wife happy. Thanks again.
jor

 

[sunshine_eggo]

Whoa, you guys are fast with the replies! Thanks a million. I just ordered three 20a fuses. No more room on the roof so this should do it. I'm long in the tooth so this should keep me off the roof which will make my wife happy. Thanks again.
jor

That's probably too high for the 100W string. those are likely 10 or 15A max.

 

[jor_tucson]

That's probably too high for the 100W string. those are likely 10 or 15A max.

Oh, sure. Forgot about that. My 200w panels show a 20a fuse rating but the 100s don't have that info (they are old). I do have a 10 amp MP4 fuse so I'll use that for S3. Thanks.