Combining different sized Zamp solar panels

[RMNummi]

I'm installing a Zamp Obsidian suite of panels on an Airstream 25FBT w Zamp roof pre-wire box. Here is my plan:

2 90w Long Panels on either side aft of Trailer.
2 100w Panels on either side forward of Trailer
2 45w panels on either side midships of Trailer

Forgive my ignorance at the outset.

In a perfect world I would install all identical panels. There are obstructions that restrict this and I have to install different sized panels to fit.

Is it better to connect both the same wattage panels (i.e. port and starboard) together with a Y adapter and then a single extension cable to the roof box? (90 to 90 then to open port A on box, 100 to 100 then to open port B, 45 to 45 then to open port C)

or

Is it better to connect all three different watt panels together on each side using Y adapters and then a single extension to the roof box? (All the Portside panels 100 to 45 y adapter to 90 then y adapter to open Port A on box, same on Starboard side)

or

is the roof box incapable of handling the wattage and leave off a pair (45s) of panels? (so just the 90s and the 100s). (AS and Zamp tech both say no problemo with 4 90 W panels to Zamp roof box).

Or Does either way matter as they all are joined in the Zamp roof box.?

[vanderwielen]

looks like you have 2020 FBT. So, the wiring from the roof should be #10 gauge or good for 30 amps.

You have two technical concerns. First, the VOC, or open circuit voltage for all the panels needs to be the same if you intend to parallel them. If you are staying with the Obsidians, odds are that you're good.

Since you want to include 45 watt panels, you can't place the larger panels in series these. The current producing capacity of a series string of solar panels will be limited by the smallest panel in the string. So, a series connection essentially de-rates the larger ones.

Your option to parrallel combine the 45s, 90s and 100s into three feeds to the roof top solar will work and will produce the maximum solar harvest. The VOC of those panels with about 21 volts. So, your maximum current would be 450/21 and would be fine for your #10 wire.

Your final concern should be to size or verify that your MPPT charger can handle the approx. 37 amps of battery charging.

rick (E.E.)

[Mollysdad]

Nate on YouTube has good videos on installing panels. It's possible to add a panel and reduce the total output.

https://www.youtube.com/watch?v=jejro4zkl8I&t=1s

[tominphx]

Out of curiosity, how much voltage variation is acceptable in panels of differing wattage and of the same mfg? As an example, Zamp Obsidians have the following:
100W OCV 24.32V and 5.1A output
90W OCV 23.8V and 5A output
45W OCV 26.15V and 2.37A output

Also, even if you parallel panels by wattage groups you aren't just dumping the sum of all panel voltages and amperage outputs into the combiner box then to the charge controller?

I think this is why its best to have all panels by the same mfg. and wattage.

Cheers, Tom

[RMNummi]

Thanks amigos. Best video and advice ever. I’m going to ditch the 45s. 90s and 100s are close enough for government work.

[waninae39]

i have a similar situation

i used multiple MPPT controllers

i used one controller for each type of panel
when using one controller, the output was much lower

this is the display from the Victron VRM monitor
output is low as the SUN has not come up yet this AM

[RMNummi]

Well heck. I see the logic in the multiple MPPTs. Walk me through your wiring from the roof. You pull the Zamp box, you’ve got a single pair of wires running from box to trailer right? You had to run 2 more wires going into interior…

Question is…. How did you do pull the wires? Original “pre-wire” run or through the traditional fridge roof vent route?

[waninae39]

yes. the roof box combines all into one 10Ga wire pair.

i didn't want to add any addl holes in the roof

it was NOT easy, but is was able to get another 10ga pair from the under the zamp box, across to the Bath roof vent pipe. the tricky part was drilling a hole in the vent stack pipe, running the pair down the pipe, then out again. Not an easy task, but very rewarding when done. sorry no pics taken

another option is drill a hole and run the cable in a small cable trough on the inside roof

[vanderwielen]

Originally Posted by tominphx

Out of curiosity, how much voltage variation is acceptable in panels of differing wattage and of the same mfg? As an example, Zamp Obsidians have the following:
100W OCV 24.32V and 5.1A output
90W OCV 23.8V and 5A output
45W OCV 26.15V and 2.37A output

Also, even if you parallel panels by wattage groups you aren't just dumping the sum of all panel voltages and amperage outputs into the combiner box then to the charge controller?

I think this is why its best to have all panels by the same mfg. and wattage.

Cheers, Tom

generally, try to stay within 1/2 a volt or no more than 1 volt. Interestingly that Zamp panels of the same family are that far apart.

[RMNummi]

The plan as outlined above is to combine the same type panels ie. 90 port to 90 stbd with a Zamp Y adapter then run an extension to the Roof Mount. I’ll hold off on the 45’s for now? I did like the earlier comment… 90 to 90 then “Y” to Roof port then 100 to 100 then Y to roof port. That leaves an open port on the Zamp roof box. Showing my absolute ignorance… those (the 90s and the 100s) would all be classified as “parallel” right? They are all magically combined somehow in the Zamp roof box to the two wires running from roof to MPPT?

[tominphx]

The Zamp "combiner box" regardless of the number of ports is nothing more than a "junction box" each ports +/- pairs are spliced together into a single +/- pair exiting the box. It's been awhile since I've been in mine but from memory all the Zamp wiring in the box is 10ga.

I'm not sure what your charge controller sees with your intended 2 sets of parallel feeds!

Cheers, Tom

[RMNummi]

So if I’m running everything to the Zamp Box I’m Parallel no matter the “Y” connections… the 90s and 100s are so close there shouldn’t be an issue.

[tominphx]

Not sure I can answer that. Are you saying that you would like to parallel one 100W and a 90W as a pair and ditto for the other pair. I guess it would work but I'm not sure what your charge controller would see. Also depending how you are parked and your orientation to the sun, may cause each of the 100W/90W pairs to produce different outputs (one pair more toward the sun, the other pair slightly away from the sun).

Cheers, Tom

[JCRC]

On my 75 Argosy 24ft, I have all Zamp panels. 2 170 watt panels, 2 100 watt panels, 1 90 watt and 1 45 watt. I did a lot of research to make it work. I run 2 Zamp combiner boxes running to 2 mppt controllers. I run each panel to the combiner box, 170 100 90 and 170 100 45. The voltages are close enough, and I get really good return off my total watts, usually 80 percent or more. I wish I could show you my victron history, but my trailer is currently in Baja, and I'm not...
We fulltime in the Argosy and have over 3 years on the system with a 3000 watt inverter and 400ah of batteries. Do I wish I could put the same size panels on like all the cool kids, sure. But it works, and works well all over the US and Mexico.

[RMNummi]

So…initial observations.. installed a pair of 100s on the front of the 25FBT. These are joined by a Zamp Y adapter. This co-joined pair is then routed to the roof box. Same with a pair of aft Zamp 90 longs. Same with a midship pair of 45s. Ordered the standard Zamp Obsidian feet that come with 2-3” feet as opposed to the Zamp AS specific mounts. Easy to Pre-bend the mounts to fit the curved AS roof. Without pre-bending each mount plate wouldn’t be flat against roof. Used Zamp supplied VHB strips w 3M “adhesion promoter”. Because I’m paranoid about trusting the VHB I bought self tapping stainless machine screws, wrapped each in butyl tape and screwed down the feet. Peace of mind achieved. Sikaflex over each of the feet. Notes: could have gone w 100s on both fore and aft. Only thing that would have fit in the midship position was the 45s due to bath vents and sewer vent and fridge vent positioning. The forward 100s…one will always be in the AC shadow unless it’s high noon. I don’t know if mounting the 45s with the Zamp y adapter was the right move. Need to research/ask the forum whether these 45s should be wired in a series (to get 90) and then to the port instead of the Y adapter like the others. So all the panels are plugged into the roof box w Y adapters. On a 2020, the roof box uses 10ga. From roof to Sunexplorer MPPT. Installed a solar cutoff switch in the rats nest under the pax side head of bed. Swapped out Sunexplorer to Victron 100/50.

[tominphx]

RNNummi, 45s in parallel will retain panel voltage and double the amperage.

Cheers, Tom