MC4 branch connectors vs combiner box questions

[lorettaboy]

So i've been doing some research on connecting multiple solar panels in parallel, and most people seem to advise using a combiner box rather than MC4 branch connectors. But i've also seen quite a few youtube videos that show the MC4 connectors. Also, Renogy sells a 400w kit that uses the MC4 branches and no combiner box: https://ca.renogy.com/renogy-400-watt-12-volt-monocrystalline-solar-starter-kit/. Is it safe to use the branch connectors?

 

[snoobler]

Most MC4 branches are rated for 30A. Since they're joining MC4 wires, your joined wire is only going to be 10 and sometimes 8awg. This may be too thin for some situations (high current arrays, long wire runs, etc.).

A combiner box can readily handle larger currents on the output.

 

[lorettaboy]

Most MC4 branches are rated for 30A. Since they're joining MC4 wires, your joined wire is only going to be 10 and sometimes 8awg. This may be too thin for some situations (high current arrays, long wire runs, etc.).

A combiner box can readily handle larger currents on the output.

My setup will be 3 195 watt panels on a small camper trailer. Do you think the branch connectors will suffice? They are rated at 30amp.

 

[snoobler]

What is the Isc value on the panels?

 

[lorettaboy]

What is the Isc value on the panels?

9.87A

 

[snoobler]

3 * 9.87 = 29.61A

10awg wires and MC4 branch connectors should be fine.

What is the Voc & Vmp?

What charge controller are you using?

 

[lorettaboy]

• Rated power: 195W
• Voc: 22.41V
• Vop: 17.9V
• Short circuit current (Isc): 9.87A
• Working current (Iop): 8.89A

I'm going to get the victron 100/50, hooked up to 2 6v t105's.

 

[snoobler]

Are those name-brand properly labeled panels? Their specs are inconsistent with the claimed rating.

Rated power is typically Vmp * Imp = 8.89A * 17.9V = 160W

You're clearly planning parallel, why not series? If shading and partial shading are not a concern, a series connection to the MPPT is likely preferred. Panels flat on a roof will perform slightly better with a higher working voltage.

In that case your current will only be 9.87A max. No branch connectors needed.

 

[lorettaboy]

Here is a link to the panels: https://www.amazon.ca/dp/B00ZOOGVOQ/ref=cm_sw_r_cp_apa_i_3MQCQBS1BW3ERB142T37
I'm going with parallel connection due to shading issues on various campsites.

 

[lorettaboy]

Would there be an advantage to instead using 6x100 watt panels, paired in series and then connected in parallel?

 

[snoobler]

Here is a link to the panels: https://www.amazon.ca/dp/B00ZOOGVOQ/ref=cm_sw_r_cp_apa_i_3MQCQBS1BW3ERB142T37
I'm going with parallel connection due to shading issues on various campsites.

When you click over to the 100W and multiply Vmp * Imp, you get 99.9W, so the math works on the 100W, but it doesn't on the 195W.

I would challenge that those panels meet claimed spec, or there is a typo on the webpages. If you have the panels, check the label.

If they really do meet spec, then it's likely their Isc is OVER 10A. Three in parallel would be > 30A.

Series/parallel decision is more influenced by PARTIAL shading, i.e., where one panel might be partially shaded. If you anticipate all 3 panels will be completely shaded or partially shaded, series might be the better choice.

Would there be an advantage to instead using 6x100 watt panels, paired in series and then connected in parallel?

First and foremost, I'm confident that the specifications on the 100W panel and the published specs meet the rating. The inconsistent numbers (even on ECO-Worthy's own site), give me pause on the 195W. I would not spend $ on those panels without resolving.

A 2S3P would definitely be equal to or better than the 3P 195W. You'd get the benefit of 200W per series but at 2X the voltage for some MPPT benefit. You would also have the same shading tolerance and about an 18A peak current.

A 3S2P would reduce current and increase voltage at the expense of partial shading tolerance.

Personally, if partial shading is a big concern, I'd go 2S3P 100W given the options discussed.

 

[HRTKD]

I went with series connections. The way my luck goes, if one roof panel is in shade then everything on the roof is in shade.

To hedge my bet, I also have portable panels that I deploy on the ground. That way I can usually find a sunny spot away from the trailer.

 

[lorettaboy]

When you click over to the 100W and multiply Vmp * Imp, you get 99.9W, so the math works on the 100W, but it doesn't on the 195W.

I would challenge that those panels meet claimed spec, or there is a typo on the webpages. If you have the panels, check the label.

If they really do meet spec, then it's likely their Isc is OVER 10A. Three in parallel would be > 30A.

Series/parallel decision is more influenced by PARTIAL shading, i.e., where one panel might be partially shaded. If you anticipate all 3 panels will be completely shaded or partially shaded, series might be the better choice.



First and foremost, I'm confident that the specifications on the 100W panel and the published specs meet the rating. The inconsistent numbers (even on ECO-Worthy's own site), give me pause on the 195W. I would not spend $ on those panels without resolving.

A 2S3P would definitely be equal to or better than the 3P 195W. You'd get the benefit of 200W per series but at 2X the voltage for some MPPT benefit. You would also have the same shading tolerance and about an 18A peak current.

A 3S2P would reduce current and increase voltage at the expense of partial shading tolerance.

Personally, if partial shading is a big concern, I'd go 2S3P 100W given the options discussed.

I'm leaning towards the 2S3P option as well. My roof deck is 25' long, so i'd be able to space each series pair out decent enough. My next question is which Victron MPPT is right for my needs. I'm thinking the 150/35 should suffice, but when i use the Victron Calculator it suggests the 150/45 which seems like overkill to me? My calculations show my solar will bring in 18.51 amps and 43.2 volts. Am i missing something?
Panel specs are:

• Maximum Power: 100W
• Open Circuit Voltage (Voc): 21.6V
• Max Power Voltage (Vpm): 17.3V
• Short Circuit Current (Isc): 6.17A
• Working Current (Iop): 5.78A

 

[snoobler]

The 100/50 you mentioned should be fine unless it lacks features you want (I can't keep straight which have bluetooth). You'll only be at 44Voc vs the 100V limit, and 600W into a 12V only needs a max of 50A.

 

[lorettaboy]

I went with series connections. The way my luck goes, if one roof panel is in shade then everything on the roof is in shade.

To hedge my bet, I also have portable panels that I deploy on the ground. That way I can usually find a sunny spot away from the trailer.

Do you have a second charge controller for the ground panels?

 

[HRTKD]

Do you have a second charge controller for the ground panels?

Yes. 1280 total watts between the roof and the ground.

 

[lorettaboy]

Yes. 1280 total watts between the roof and the ground.

Nice. I'd like to do the same.
Side question: I have 6 40w panels that are each rated at 2.3A 17.1V. Wondering how i should connect them to maximize the charge. Was thinking of wiring them all in series to maximize voltage, or to do them up in a 3S2P configuration to get the amps up.

 

[HRTKD]

Nice. I'd like to do the same.
Side question: I have 6 40w panels that are each rated at 2.3A 17.1V. Wondering how i should connect them to maximize the charge. Was thinking of wiring them all in series to maximize voltage, or to do them up in a 3S2P configuration to get the amps up.

If you do 6s you may need a bigger solar charge controller due to the limitation on max input volts. 3s2p would allow you to use a smaller solar charge controller, as long as its amp output isn't leaving power on the table.