MPPT Sizing

[MRA]

Astra came with 300W Solar and a Victron MPPT 150/35. This was more than adequate when the sun was shining bright - but as we all know; the sun doesn't always shine bright, so we added another 200W solar. All are connected in parallel.

From the Victron doc, this MPPT can provide up to 35amps to my battery - so it appears as if I am over paneled by 6⅔ amps (500W/12V=41⅔A) which is probably not a big deal - so 2 questions:

1) Am I correct or do I misunderstand the documentation/math ?
2) Is it worth buying a second MPPT (or a bigger one)?

Cheers,
MRA

[JeffKim]

With solar panels a typical 100W panel the OC amperage is around 5.2A. If you have 500W all in parallel then you're around 26A, so well within the controller's 35A.

At least with our 25' GT there isn't room for another 200W on the roof so I assume these are external panels that are plugged into the same controller? If so, then it's less than optimal since it's not likely the roof and the external panels have the same exposure. The controller can't optimize for both so it's likely some sort of compromise. With our camper we have two Victron 100|30 Smart controllers, one for the roof and one for plugin panels. The Smart makes it easier to monitor them via Bluetooth. I sold the stock 150|35 on eBay.

[uncle_bob]

Hi

As noted above ....

Unless all the panels are identical and in about the same orientation, they will struggle. You are unlikely to have them all hit max at the same time. Indeed with some combinations, one set will more or less shut down the other set.

What's the best way to handle mixed panels?

Get a second controller for the second set. Run them into it. Network that controller with the first. Let some sort of gizmo tell each of them what to do. This likely involves a shunt in addition to that controller.

Bob

[blacklab]

Following.

My memory may be off, but I believe this is the first time I've read that one needs separate controllers to manage roof top and portable panels.

On my existing RV, there is a single Victron controller that seems to manage the roof top Merlin panels + 2 x 100W Zamp Obsidian portables well. Sometimes the rooftop system is in partial shade and Zamps are in full sun and I'm getting full output from the Zamps and partial output from the Merlins (seems reasonable based on the shading). But, perhaps I'm oblvious to the limitations of this system.

BTW, with the Zamp Obsidian portables, I don't use the supplied Zamp controller (you can either use it or not). The portables are fed directly into the RV via a Zamp port.

Cheers,

Bryan

[JeffKim]

Originally Posted by blacklab

Following.

My memory may be off, but I believe this is the first time I've read that one needs separate controllers to manage roof top and portable panels.

On my existing RV, there is a single Victron controller that seems to manage the roof top Merlin panels + 2 x 100W Zamp Obsidian portables well. Sometimes the rooftop system is in partial shade and Zamps are in full sun and I'm getting full output from the Zamps and partial output from the Merlins (seems reasonable based on the shading). But, perhaps I'm oblvious to the limitations of this system.

BTW, with the Zamp Obsidian portables, I don't use the supplied Zamp controller (you can either use it or not). The portables are fed directly into the RV via a Zamp port.

Cheers,

Bryan

If you haven't rewired the Zamp port it connects directly to the batteries and not to the controller. If you don't use the controller in your Zamp panels then not good, the output voltage can be in the 20V range which can be damaging. It won't charge the batteries according to their charging parameters.

If you do have it rewired to the controller then it doesn't have any magical way to switch between panels, it sees the voltage coming in and tries to optimize the power output according to the battery chemistry it's set to. Battleborn has an explanation on how these work.

[JeffKim]

Originally Posted by uncle_bob

Hi

As noted above ....

Unless all the panels are identical and in about the same orientation, they will struggle. You are unlikely to have them all hit max at the same time. Indeed with some combinations, one set will more or less shut down the other set.

What's the best way to handle mixed panels?

Get a second controller for the second set. Run them into it. Network that controller with the first. Let some sort of gizmo tell each of them what to do. This likely involves a shunt in addition to that controller.

Bob

I was wondering about this in regard to Victron Smart controllers, so I looked it up in the VE.Smart Networking manual. A shunt isn't required, the controllers will talk amongst themselves:

Connect multiple SmartSolar charge controllers together in a VE.Smart network to make them charge the battery as if they were one large charger. The chargers will synchronise the charge algorithm between themselves, with no further hardware required. They will simultaneously switch from one charge state to another, for example from bulk to absorption./

Since it's election season, I was wondering how they campaign to select the master:

Synchronising the chargers works in a master-slave manner. The chargers will elect a master among them and that master will be the one to dictate the charge algorithm. As the master cannot be determined by the user, it is important to make sure all chargers belonging to the same network have the same battery settings.

Sounds like a lot of responsibility:

At the beginning of the day, the master will measure the battery voltage before any of the other chargers in the network start charging (to find battery idle voltage). This information is used to decide what should be the total absorption time for some types of batteries. The battery idle voltage is shared with the other chargers, as well as the total absorption time, and the elapsed time on the current charge state.

It does state that with a shunt the true battery voltage can be communicated (without voltage drop over the wire) to better optimize. Particularly with lithium it's a necessity in any case.

[uncle_bob]

Originally Posted by blacklab

Following.

My memory may be off, but I believe this is the first time I've read that one needs separate controllers to manage roof top and portable panels.

On my existing RV, there is a single Victron controller that seems to manage the roof top Merlin panels + 2 x 100W Zamp Obsidian portables well. Sometimes the rooftop system is in partial shade and Zamps are in full sun and I'm getting full output from the Zamps and partial output from the Merlins (seems reasonable based on the shading). But, perhaps I'm oblvious to the limitations of this system.

BTW, with the Zamp Obsidian portables, I don't use the supplied Zamp controller (you can either use it or not). The portables are fed directly into the RV via a Zamp port.

Cheers,

Bryan

Hi

Nope, that's not how it works.

The "Zamp port" is simply a couple of wires direct to the battery. It does not in any way feed into the onboard controller. You can actually use that port as a 12V power *source* if you wish. With the setup you propose, the portables are simply feeding the battery directly with no controller involved at all. That's not a good idea.

For portable panels you either need to rewire the onboard controller and bring out custom cables to feed in the portables *or* you need a separate controller.

Bob

[AlbertF]

Originally Posted by MRA

Astra came with 300W Solar and a Victron MPPT 150/35. This was more than adequate when the sun was shining bright - but as we all know; the sun doesn't always shine bright, so we added another 200W solar. All are connected in parallel.

From the Victron doc, this MPPT can provide up to 35amps to my battery - so it appears as if I am over paneled by 6⅔ amps (500W/12V=41⅔A) which is probably not a big deal - so 2 questions:

1) Am I correct or do I misunderstand the documentation/math ?
2) Is it worth buying a second MPPT (or a bigger one)?

Cheers,
MRA

The typical operating voltage of solar panels is about 17 volts, not 12. 500/17 = 29 amps. Assuming 90% efficiency, the controller will supply a maximum of 26 or 27 amps to the battery. I think you're fine.

Does the controller have a readout? My basic Renogy PWM controller does; it shows a maximum of 1.7 amps with a small 40 watt panel - 40/17*.73 = about 1.7 amps, which tells me that the solar panel is functioning as designed.

[blacklab]

AM Solar wired my Zamp port to the Victron Controller. It is not wired directly to the battery bank.

So, my Zamp Obsidian portables (uncontrolled) go to the Zamp port, then to the same Victron Controller that is managing the rooftop solar.

Cheers,

Bryan

[uncle_bob]

Originally Posted by blacklab

AM Solar wired my Zamp port to the Victron Controller. It is not wired directly to the battery bank.

So, my Zamp Obsidian portables (uncontrolled) go to the Zamp port, then to the same Victron Controller that is managing the rooftop solar.

Cheers,

Bryan

Hi

Ok, but, if the portables are getting more sun than the roof panels, then you get no power from the roof. If the roof gets more sun, then there's (essentially) nothing coming from the portables.

Even with the "same sun" there are multiple ways a panel can be set up. This one may still do the same "take things over" even with equal illumination.

Bob

[blacklab]

Bob,

OK, thanks.

I can't do it now, as my trailer is in storage, but I want to look at the "History" on my Victron Connect app for the Controller and Solar. I may be totally wrong, but I thought there were days where the Portables were fully in the sun and the roof panels only partially in the sun, yet I was getting more current than the portables can produce, suggesting to me that the roof panels were also contributing.

Cheers,

Bryan

[uncle_bob]

Originally Posted by blacklab

Bob,

OK, thanks.

I can't do it now, as my trailer is in storage, but I want to look at the "History" on my Victron Connect app for the Controller and Solar. I may be totally wrong, but I thought there were days where the Portables were fully in the sun and the roof panels only partially in the sun, yet I was getting more current than the portables can produce, suggesting to me that the roof panels were also contributing.

Cheers,

Bryan

Hi

It might not always be a total wipe out. You might get 80% out of one and 30% out of the other. A pair of controllers would give you 95% and 50% in the same case. Next time out, you do pretty much get a death spiral.

The fancy setups these days put a controller on each panel. They then network it all. The claim is that it roughly doubles the power under most real world situations. Can you trust that claim? I have no idea .... They typically are talking about dozens of panels.

Bob

[Mollysdad]

Since you have two sets of panels of various size, have you done the math of connecting 'series-parallel'?

This guy runs so many options my eyes glaze over.

https://www.youtube.com/watch?v=jejro4zkl8I

[uncle_bob]

Originally Posted by Mollysdad

Since you have two sets of panels of various size, have you done the math of connecting 'series-parallel'?

This guy runs so many options my eyes glaze over.

Hi

Even so, he doesn't get into *all* the grubby details.

Best to just go with matched panels. (or accept that you won't get as much power as you might otherwise).

Bob

[Mollysdad]

Originally Posted by uncle_bob

Even so, he doesn't get into *all* the grubby details.

Best to just go with matched panels. (or accept that you won't get as much power as you might otherwise).

Bob

I recall seeing a setup where you ADDED a 200w. panel and the total output went DOWN.

[uncle_bob]

Originally Posted by Mollysdad

I recall seeing a setup where you ADDED a 200w. panel and the total output went DOWN.

Hi

Same kind of problem when a 100W panel + controller shuts down a 400W panel + controller. You now get 1/5 the power for how ever many minutes / hours that condition persists.

Bob

[waninae39]

by using series and parallel wiring , you can setup you panels to best match the victron mppt maximums

[JeffKim]

Originally Posted by uncle_bob

Hi

Same kind of problem when a 100W panel + controller shuts down a 400W panel + controller. You now get 1/5 the power for how ever many minutes / hours that condition persists.

Bob

Despite my post #6 and drinking the Victron Kool-Aid, this got me to thinking what would cause one controller to compete with another or shut another down. It would seem that each is responding to the voltage it sees and supplying current appropriately assuming each has a similar charging algorithm.

So I went down a rabbit hole and found the definitive Will Prowse video which demonstrates that coordinating chargers is unnecessary and a myth. This IMHO explains a lot about solar controllers including why it's best to have multiple controllers and worth a viewing all the way to the end.

https://www.youtube.com/watch?v=rSj6-JSxoD4&t=655s

[uncle_bob]

Originally Posted by JeffKim

Despite my post #6 and drinking the Victron Kool-Aid, this got me to thinking what would cause one controller to compete with another or shut another down. It would seem that each is responding to the voltage it sees and supplying current appropriately assuming each has a similar charging algorithm.

So I went down a rabbit hole and found the definitive Will Prowse video which demonstrates that coordinating chargers is unnecessary and a myth. This IMHO explains a lot about solar controllers including why it's best to have multiple controllers and worth a viewing all the way to the end.

Hi

It's pretty simple if your chargers are set up properly. If they are set up some other way.... who knows.

With a charger that sees 13.6V and does not start charging ( = proper setup), all you have to do is get the wires to that voltage with *one* charger. Shade the other one. It comes back up and goes to sleep ....

Since we're talking about the wires and not the battery (so drop in the cabling does indeed matter), your battery voltage is likely something well below 13.6V when this happens.

Yes, it's worse with lead acids that spend a *lot* of time at the top voltage.

There are lots and lots of threads around here from folks actually having this problem with their Airstreams.

Bob

[JeffKim]

Originally Posted by uncle_bob

Hi

It's pretty simple if your chargers are set up properly. If they are set up some other way.... who knows.

With a charger that sees 13.6V and does not start charging ( = proper setup), all you have to do is get the wires to that voltage with *one* charger. Shade the other one. It comes back up and goes to sleep ....

Since we're talking about the wires and not the battery (so drop in the cabling does indeed matter), your battery voltage is likely something well below 13.6V when this happens.

Yes, it's worse with lead acids that spend a *lot* of time at the top voltage.

There are lots and lots of threads around here from folks actually having this problem with their Airstreams.

Bob

If the controllers aren't set up properly, yes who knows. And maybe what you describe is where neither controller has the "true voltage" at the battery so there's desparities in charging.

But for the relatively common scenario where there's the stock Victron controller connected to the roof panels and someone wants to add external panels with their own controller through the Zamp plug (wired to the battery), the controllers shouldn't conflict based on this video. They might not be totally optimal, but they both should supply current to the batteries.