Can I use one MPPT unit connected to a fixed roof solar panel and a removable foldable panel?

[Johnny Nova]

Hi
Not sure this is possible as the little research I have done seems to point to using 2 separate MPPT units...............Is it possible to have just one Victron MPPT unit connected to a fixed 200W solar panel on a van roof and when required plug in a portable 200W or 400W foldable solar to boost charging power?

If the above is possible how would one build a branch connector from the solar terminals on the MPPT unit to 2 Anderson plugs?

 

[Rednecktek]

Adding in a second 200w panel is easy, just put a splitter somewhere in the line between the panels and SCC where it's easy to reach. The SCC will just see parallel panels.

If you wanted to use 3 panels, you might want to mount a combiner box outside you can add panels in and out. That way you can go from 1s1p to 1s2p to 1s3p at will.

 

[Johnny Nova]

Adding in a second 200w panel is easy, just put a splitter somewhere in the line between the panels and SCC where it's easy to reach. The SCC will just see parallel panels.

If you wanted to use 3 panels, you might want to mount a combiner box outside you can add panels in and out. That way you can go from 1s1p to 1s2p to 1s3p at will.

Thanks for your reply
Apologies for questions as I try an understand
Would a 400W portable blanket also work in conjunction with the 200W fixed panel?......or do need to keep wattage the same as the fixed panel?
I'm planning to run 6mm2 wire (10 AWG) from the 200W fixed panel to the SCC unit........is this splitter an off the shelf item that I can purchase or I need to build?

 

[Rednecktek]

Whenever you're putting multiple panels to a controller you'll want them to be as matched as possible or your larger panel will be nerfed by the smaller one.

Hit up amazon for "solar y splitter" and you'll find dozens of splitters. 6mm wire will be fine.

 

[Rocketman]

The real question is what are the electrical specs for each panel:
Voc
Vmp
Imp
And which Victron mppt do you have.

If they are different there will be a penalty for hooking them up together- how much of a penalty depends on how close they are.

The way to figure out the penalty…
Using Vmp (voltage) and Imp (amps).

If hooked up in series - volts add - use the lowest amps.
If hooked up on parallel- amps add - use the lowest volts.

Then volts *amps = watts.

Figure it out and post the specs both panels and we will double check the math.

 

[Johnny Nova]

Whenever you're putting multiple panels to a controller you'll want them to be as matched as possible or your larger panel will be nerfed by the smaller one.

Hit up amazon for "solar y splitter" and you'll find dozens of splitters. 6mm wire will be fine.

Does attached sketch show what you mean by parallel setup and I think I would need 2 of the Y connectors if understood you correctly?

By adding Anderson plugs into the line I would then be able to run off one MPPT unit when I need to place the portable solar panels in the sun.

 

[Johnny Nova]

The real question is what are the electrical specs for each panel:
Voc
Vmp
Imp
And which Victron mppt do you have.

If they are different there will be a penalty for hooking them up together- how much of a penalty depends on how close they are.

The way to figure out the penalty…
Using Vmp (voltage) and Imp (amps).

If hooked up in series - volts add - use the lowest amps.
If hooked up on parallel- amps add - use the lowest volts.

Then volts *amps = watts.

Figure it out and post the specs both panels and we will double check the math.

Hi
The 200W fixed panel spec.s (already purchased)
Voc=24V
Vmp=20.5V
Imp=9.76A

The 225W solar blanket I am considering has the following specs
Voc=23.3V
Vmp=19.8V
Imp=11.36A

My calc using your advise is as follows for parallel setup:
(9.76+11.36) x 19.8 = 418.2 Watts

Does this mean the 200W panel will drag down the 225W unit slightly?

I have not purchased a MPPT solar charge controller but was considering the Victron brand .......maybe 100 / 30 unit but will need to check when I settle on the final solar panel setup

 

[Rednecktek]

Does attached sketch show what you mean by parallel setup and I think I would need 2 of the Y connectors if understood you correctly?

Yup! That's exactly how it works. The splitters come in pairs, one for the negative and one for the positive.

Does this mean the 200W panel will drag down the 225W unit slightly?

Very little, they're so close it's not worth worrying about.

The real question is what are the electrical specs for each panel:
Voc
Vmp
Imp
And which Victron mppt do you have.

Fortunately his panels are so small that even the cheapest version can handle a 2p setup. The controller amperage is probably the bigger issue as the first panel is wanting to pump 20a-ish on its own. With 2 panels he'll need a 40a controller.

 

[Johnny Nova]

Yup! That's exactly how it works. The splitters come in pairs, one for the negative and one for the positive.



Very little, they're so close it's not worth worrying about.



Fortunately his panels are so small that even the cheapest version can handle a 2p setup. The controller amperage is probably the bigger issue as the first panel is wanting to pump 20a-ish on its own. With 2 panels he'll need a 40a controller.

My initial thoughts were to use an equal or greater wattage portable solar panel on the ground (ie: bigger than the fixed 200W panel I already have) and try and run it off just one SCC unit but understanding better now the issues it would cause it makes me think I should maybe go back to 2 x SCC units and use a larger portable foldable solar panel to get max charge back into a 200AH lithium battery.
ie: The fixed 200W solar panel can run off a Victron 75 /15 SCC
and run maybe a 400W foldable panel on the ground with its own SCC unit probably Victron 100 /30

 

[Rednecktek]

15a on a 200w panel maxes out that SCC, you'll need either a larger controller or multiple controllers.

 

[Johnny Nova]

15a on a 200w panel maxes out that SCC, you'll need either a larger controller or multiple controllers.

What calculator or formula do you use to check for the size of the SCC (MPPT type) ?
I used the calculator on the Explorist website

 

[Rednecktek]

Rule of thumb for a 12v system is 100w = 10a of SCC. So 200w would want 20a, 400w would want 40a, and so on.

 

[richard cabesa]

Rule of thumb for a 12v system is 100w = 10a of SCC. So 200w would want 20a, 400w would want 40a, and so on.

Victron recommends 220w max on the 75/15 and 440w mX on the 100/30.
I have three of the 75/15 running 200w each and one 100/30 running 400w.
Everything runs great

 

[Rocketman]

If you look at the data sheet for the Victron mppt you are considering it will tell you the max watts it can output.

For example the mppt 100/30 says 420w (if I remember correctly). You can have more solar watts going into it than that - that is called over paneled.
Both arrays on my MotorHome are over paneled. I have 800w of solar going into a Mppt 100/50 - it says the max is 700w. I seldom see 700w because my panels are usually flat and conditions are not ideal.
I also had an array with 400w going into a mppt 100/30. I needed more solar when conditions were not ideal - but the OEM wiring could not handle a bigger charge controller. So I added another 200w to that array. Because it is very over paneled it spends a lot of time maxed out at 30amps going to the battery (420w). I am fine with that. It does heat up more than I would like.

Good Luck