Why not mount an MPPT solar controller inside for portable solar panels?

[PCMcE]

I have a 2015 25' FC RBQ that has dealer(?) installed solar. I'm having an external facing solar port installed so I can augment the 200W of installed roof-top solar with some portable panels - esp. important if/when parked such that the roof top solar is ineffective.


I've talked to a couple of places about this and both seemed to assume that the external port would be wired straight to the battery - requiring that the portable solar panels would need to have their own solar charge controller. I understand this would work no problem and as many portable solar panels come with their own solar charge controllers, I can see this being a reasonable default.


However, I'm curious why I shouldn't have the install include an solar controller *inside* the trailer between the port and the battery bank. There may be a bit more work involved and I'd have to buy a dedicated solar controller (and buy portable panels without an SCC). But this would seem to be a cleaner solution.



The reason I'm tempted is a dedicated (inside mounted) SCC would be positioned near the batteries (I read where this is important so that SCC and batteries sense the same ambient temp). Also, if I do a Victron I get a good bluetooth capability and honestly the extra $50-75 dollars for a dedicated (but good, bluetooth enabled) SCC would be worth it. I could then go with portable solar - some now, maybe a bigger array over time - without essentially purchasing multiple (lower quality?) SCCs - one for each portable panel set.



Anything I'm missing? Any reason to not go in this direction - buying/mounting SCC in the trailer as part of installing the solar port?



Thanks in advance!

[lewster]

Sounds right! I would ge a Victron large enough to handle any potential increase in your solar wattage in the future.

[PCMcE]

Originally Posted by lewster

Sounds right! I would ge a Victron large enough to handle any potential increase in your solar wattage in the future.

Yes - exactly. I'll probably try 200W-220W portable solar initially - expanding to 2x that if needed in future. So I'm tempted toward the 100v/30a Victron BlueSolar controller ($112 on Amazon). Seems plenty 'future proof' enough.


Thanks!

[richard5933]

I tackled this differently, using one solar charge controller for both the rooftop and portable panels.

What I did was install a Victron large enough to handle all my rooftop panels AND the portable panels that we sometimes carry. There are four panels on the roof, wired in series/parallel. The portable panels, when connected, are just another bank of panels which connect in parallel to the rooftop panels.

To control switching back and forth, I've got a Blue Sea battery disconnect between the panels and the charge controller - this is a A/B/A+B input switch, meaning that it can be set to allow just the rooftop panels, just the portable panels, or both.

[PCMcE]

Originally Posted by richard5933

I tackled this differently, using one solar charge controller for both the rooftop and portable panels.

What I did was install a Victron large enough to handle all my rooftop panels AND the portable panels that we sometimes carry. There are four panels on the roof, wired in series/parallel. The portable panels, when connected, are just another bank of panels which connect in parallel to the rooftop panels.

To control switching back and forth, I've got a Blue Sea battery disconnect between the panels and the charge controller - this is a A/B/A+B input switch, meaning that it can be set to allow just the rooftop panels, just the portable panels, or both.

Thanks! I thought about this way as well - in fact I'm going from AGM to Lithium so I need to update my original (Zamp) SCC anyway. It is tempting esp with a selector switch. But I expect (don't know for sure) that the wiring might be a bit more complicated - although maybe only marginally. But I thought a 'one SCC to rule them all' approach would require uniformity between the solar panels? I have 2x100W Zamp flexible solar panels on the roof and want flexibility to get 220W or (if needed) 400W portable solar suitcase. Honestly I didn't know if the mix-and-match set of panels would even work together in the A+B config. Does it?


Also was reading that separate SCC is good if one set of panels is in the shade (or if the panels are facing different directions even) although with the A, B or A+B switch that is potentially mitigated. Even if I could switch it, any switch I put in will be a bit of a pain to get to - not bad (remove the bench cushions and reach through an access panel) but still something esp if required during the day to get optimum input. If two SCC working in tandem "just works" in all (most?) configurations, that is worth it to me.



But please educate me if I'm thinking about this incorrectly!



Thanks!

[rodsterinfl]

I am similar to Richard on the solar.

I have two suitcases w/controllers and two ports outside that I originally had hooked directly to the batteries and an internal controller for the roof mounted panels. I ran all of it by two solar engineers that said it would work.

It did, but...

There was a lot of loss as the controllers would sense current and shut down early. So, I redid/rethought the system. I bought a bigger internal controller (morningstar) and disconnected the controllers on the suitcases but left them on the units for potential other uses (have a backup lithium power station) and wired one port to the controller- left the other to the batteries just in case I want to use suitcase controllers that way (options).

So, in effect, there is one controller for solar with camper and no conflict even with different panels. The only catch is that based on specs, one panel can only produce 93% of its capability due to varied panel voltage.

[vanderwielen]

ive done exactly this on the last 2 conversions in my now empty battery box.

[PaulBristol]

There are good reasons why each portable panel should have its own controller.

1) Each panel may be in a different location and therefore output differently. If you want to harvest all the power that each outputs, then you need a separate controller or controller circuit.

2) All solar panels are not the same. Again each panel type needs a controller that maximizes harvest. Even the same make and model panel may be different due to age and changes in manufacturing.

3) Charging power loss is most critical for high current charging. A 100 watt panel may output peak power of 8 amps. A small 14 gauge wire is twice the size needed for charging. Some portable systems use 10 gauge wire. That is maybe 4 times the size needed. So, unless you have 300 watts or more of portable, small remote controllers are fine. That allows for small long cables to place the panels where they need to be.

Many external solar connector kits are rated for 10 amps. If you are planning more than that, make sure you get one rated for 15 amps or more.

When cable sizes get above 10 gauge, they become difficult to manage. Using internal controllers with multiple smaller wires to each panel may make sense. Higher voltage panels with internal controllers near the battery can improve harvest through smaller wire.

[Malia20]

Good discussions...I found that when my portable (with PWM) mixed with my rooftop (MPPT) with lead-acid batteries every thing was good during Bulk charging, but one would drop out during Absorption. I figure they were trying to absorb at slightly different voltages, so one would give up as it thought voltage was too high (from the other controller).
I switched to the portable feeding the one internal controller (MPPT). What I lose because the panels are not absolutely identical and positioned the same I more than gain from the portable feeding the MPPT (about 30% more from the portable).
PaulBristol is correct, a controller for each panel is best ...OR use the Victron Smart Controllers that talk to each other, one controller controlling the others. This way (it would seem) they would not fight over the absorption voltage as isolated controllers would.

Fred

[tominphx]

May as well add to this, 2 100w Zamp Obsidian on roof, 3 100w unregulated Zamp Obsidian portables all through 40A Zamp PWM controller and 1 400Ah lithium battery. We are strictly 12V and propane therefore ours is a very simple system not requiring MPPT monitoring or efficiency.

If you do something similar, I'd suggest using all like size wattage, manufacture of panels and carefully size wire for the portables length of run to minimize loss. Your choice on controller either MPPT or PWM of sufficient capacity and which fits your needs.

Cheers, Tom

[jeffb831]

The problem is having unmatched panels flowing through the same controller can result is in issues with how the power is added together from the panels.

• Series wiring increases the voltage of the solar array but keeps the amps the same.
• Parallel wiring increases the amps while keeping the voltage the same.

In both cases "same" means the lowest one.

Here is an explanation of what can happen: https://explorist.life/using-mismatc...r-panel-sizes/

It is even possible to reduce the power to below what was originally there when adding an extremely mismatched panel.

[uncle_bob]

Hi

Any time you have multiple controllers trying to feed the same battery bank, things can get "fun". If you go to multiple Victron MPPT's, you really want to set up some sort of "master control" to manage them. There are multiple ways to do this.

Once you go to lithiums, the value of the temperature sensor for charging is not as great as for lead acids. The internal BMS on the lithiums takes care of a lot of things. Also lithiums do not "move voltage" quite as much over temperature.

As others have noted, matching up whatever portable you have to an internal controller is important. Since most portable panel setups come with a controller, it's not clear you will save a lot of money doing this. You will have better control on the charge process with a Victron compared to the typical "included" controller.

Since roof panels and portables likely will not see the "same sun" simply wiring them all together is not something I would recommend.

Bob

[Glen Carter]

For the time being, I ran a cable outside for portable solar and Anderson connector (same as my portable solar panels). I have 6 100W portable panels I can take with me. I use a portable Victron SmartSolar 100/30 to connect to the Airstream battery and without to connect to my Lion Energy Safari solar generator.

[richard5933]

Originally Posted by PCMcE

Thanks! I thought about this way as well - in fact I'm going from AGM to Lithium so I need to update my original (Zamp) SCC anyway. It is tempting esp with a selector switch. But I expect (don't know for sure) that the wiring might be a bit more complicated - although maybe only marginally. But I thought a 'one SCC to rule them all' approach would require uniformity between the solar panels? I have 2x100W Zamp flexible solar panels on the roof and want flexibility to get 220W or (if needed) 400W portable solar suitcase. Honestly I didn't know if the mix-and-match set of panels would even work together in the A+B config. Does it?

Also was reading that separate SCC is good if one set of panels is in the shade (or if the panels are facing different directions even) although with the A, B or A+B switch that is potentially mitigated. Even if I could switch it, any switch I put in will be a bit of a pain to get to - not bad (remove the bench cushions and reach through an access panel) but still something esp if required during the day to get optimum input. If two SCC working in tandem "just works" in all (most?) configurations, that is worth it to me.

But please educate me if I'm thinking about this incorrectly!

Thanks!

It all depends on how you plan to use things.

Typically, we just use the roof solar. The 400w on the roof is more than enough on a good sun day to keep things topped off before early afternoon. Of course, we're not running the a/c from the batteries, so YMMV if you are or if you're using lots of power overnight and have a huge battery bank.

The times that we use the portable power are typically when the trailer is parked in the shade and we still want to get some solar recharging. Boondocking, for instance. If we don't have power to run the a/c unit, then we want to be in the shade. But if we're in the shade, then the rooftop solar is useless. This is when the 50-foot cable (4ga) to the portable panels helps - we can park in the shade but still have our panels in the sun. Since they can be aimed & tilted to maximize collection, they do just fine.

The only time we run both the rooftop and the portable is when we're in a hurry to get the batteries charged, or if we're at the end of the season when the sun is not too strong. It's true what's been said about having a bank of panels in the shade bringing down the whole works to their (lower) level, so when we're running both rooftop and portable we aim to have them all in full sun.

Our rooftop and portable have similar voltage profiles and are wired in parallel to maximize this. We have to sets of two panels on the roof. Each set is in series and both rooftop sets of two are in parallel to each other. When we use the portable as well, they are another two panels in series which get connected to the rooftop in parallel. All the controller sees is three pairs of panels connected in series - the controller doesn't care if they sit on the roof or the pavement as long as the voltage is similar.

[davidz71]

I purchased a Renology 200 watt solar suitcase because I had to move my trailer to a different area during the turkey hunting season last year. Batteries were running lower in the early morning before sunup. To combat partial loss of direct sun, I bought the suitcase. I mounted a 30 amp Epever waterproof mppt controller inside a waterproof stainless box and plan to mount the box to the outside of my aluminum battery box on the tongue. The stainless box will be insulated from the battery box by use of stainless bolts, lockwashers, washers and rubber washers. They will be oversprayed with Flexseal before putting the batteries back in the box. The remote monitor that came with the controller will probably be mounted near the mppt controller inside behind the folding couch. I've had Trojan SCS 200 12 v. flooded batteries for around 8 years and one has started using water in 3 ot the 6 cells at a faster rate in one of the batteries. I suspect I will have to replace both this summer at close to $270 each. I will take more measurements this coming weekend to see if I can shoehorn in two SCS225 150 amp hr batteries rather than the 115 amp hr in there now.

[waninae39]

i have 3 victron MMPT for slaor.
all on inside. under the bed for our FC 25 fb

[PCMcE]

Wow - great insight and very helpful discussion. Thanks for all the replies!


Here's what I think is best for my set up and why. Note: I want to be able to generate up to 150ah on a good day to (mostly) match my expected power usage. I'm planning to upgrade to ~324ah of lithium so i'd still have a couple of days off grid even if less-than-ideal conditions.



Currently I have 2x100W Zamp solar panels on the roof. They are relatively old - I replaced them myself when I bought the trailer circa 2019. (Kudos to Zamp who honored the warranty on the original solar panels so I just did the like-for-like swap.). The trailer has been mostly in covered storage when not in use and the roof panels still produce power but they, like me, are not getting any younger over time.


Based on a later generation(?) but similar Zamp flexible panels, I would expect these panels to have produced 17.8V and 5.6A when brand new. This is likely on the high side given my panels are an earlier generation (I think) and are ~5yrs old. They are wired (in parallel) to a Zamp 30A SCC. Under absolute ideal conditions and assuming no degradation over time, that would be 17.8V and 11.2A at the SCC.



If/when I add a 220W portable solar suitcase, the specs on that are 20V and 11A (220W). If I wire in parallel to the same SCC it would work - I land at a combined (albeit ideal) output of 17.8V and 22A - the lower voltage of the older panels brings down the voltage of the newer portable a bit. Still the combined would provide a total of 391W of power out of 420W - 93% efficiency. Given all the caveats I could live with that except...


If the old panels have degraded, maybe down to 15V, my 93% efficiency starts to drop (~78% at 15V for the old panels) and I'm getting less bang-for-the-buck by combining the portable suitcase on the same SCC as the "old" panels. (Note: this degradation is a SWAG - I haven't measured the old panels and don't know what is expected degradation over time so this could be way off in either direction).



If I want to add 400W of portable solar to the "old" panels. The 400W suitcase puts out 40V and 10A according to its spec sheet. Wired to the same SCC even the ideal voltage of the 'old' panels takes a huge chunk out of the 400W portable. Through the same SCC I would get (ideally) 17.8V and 21.2A netting 377W out of a potential 600W system - or a 63% efficiency and *less than* the 220W portable system config. (I certainly may have done the calculation wrong as this seems incredible. Maybe it is a worst case scenario and the 400W portable I picked is just not designed to work-and-play-well-with-others due to it generating 40V. So please correct me if I'm doing something wrong here!)


So that's not good. With a second SCC handling the portable panels all is well I believe. The 'old' panels are walled off from whatever I add for the portable (so the lower voltage they produce doesn't drag anything else down) and both charge the battery bank directly as best they can given current conditions. I understand this set up will have some hiccups too - as mentioned above multiple SCCs can get "fun" due to wire gauge/length and charge profile settings, etc but this would be back into the margin of error that I can live with. If I can get the majority of the collected solar energy pumping into the batteries in 'bulk' charging stage, I'm happy. I can live with the two SCC entering/exiting absorption stage a little ahead/behind each other, esp. if I can minimize this by tweaking each SCC's charging profile.


Whether to mount the additional SCC 'inside' or 'outside' the trailer is more of a 'pick 'em'. Using the empty battery box would work of course but given the rest of the rewiring that has to happen, fully 'inside' (under the lounge) seems the cleanest option. Panels to external facing port, port to 'inside' mounted SCC, SCC to lithium batteries (also 'inside').


No doubt, other configs with different constraints (e.g. not trying to milk some additional life out of some old roof top panels like I am) would work super well too. Definitely not asserting this as one-size-fits-all config. Mostly sharing in case I've gotten this garbled or the calcs horribly wrong. Would greatly appreciate any/all corrections if I have!

[JeffKim]

@PCM, I have a pretty strong opinion on this and I think you might have arrived at the correct solution of two separate controllers (as others have stated). This topic comes up a lot.

Assuming the goal is to maximize electron gathering, we have two 100|30 Smart Victron MPPT controllers since our 300W rooftop panels more often than not have a different solar exposure than the 420W portable panels. The MPPT controller optimizes the array voltage to get the most power. If there are two different arrays wired to the same controller then the controller won't optimize to the maximum power point. I'm not sure what it will do. A separate controller for each to me is the only way to go.

Also, they aren't all that expensive and with Victron they will play with each other. If you have a Victron shunt installed it will communicate the true battery voltage and the controllers will account for wire resistance in their output. (See VE.Smart Networking). You can monitor solar charging with Bluetooth which is fun to amuse disinterested parties, like my spouse.

I use 10AWG from the Zamp plug to the controller and use 10AWG for the 25' portable panel cable. I have a 40A fuse going to the positive bus bar. Temperature isn't important with lithium batteries, but you can add a Victron battery temperature sensor to shut down charging if it's too cold.

[PCMcE]

Thanks again for all the feedback and insight. I feel like I have a much better handle on this project now then when I started!


One additional question. I've noticed many (most?) of the upgrades include one (or more?) master 'on/off' switch as part of the build out. Sorry if this is a newbie question but what does that provide (and what, specifically, does it switch)?


The 'Store' mode will disconnect the current batteries from (most) everything else in the trailer. (I believe there is still a small draw for carbon monoxide detector and smoke alarms? even in 'store mode' but everything else is disconnected). Is a master on/off switch just a better/more complete 'Store mode'?


Or is the on/off switch to disconnect the SCC(s) from the battery - maybe for safety reasons while doing work on the trailer? If not that - then what? I've had the trailer for ~5 years (even did replacement for rooftop solar panels) and never wished I had a master on/off switch. But then again I'm also not competent enough to do electrical work in the trailer itself so I could see that it would be valuable for those that do such work (esp. with the batteries mounted inside such that manually disconnecting the batteries by removing the + or - wires from the battery terminals would be a big pain).


So, is a master on/off switch critical or more a convenience?


Thanks in advance!

[richard5933]

Simple answer - installing a manual disconnect switch that actually disconnects EVERYTHING from the battery bank enables you to leave a trailer with lithium batteries for a few months and come back to the batteries in virtually the same state of charge. They self-discharge at such a slow rate that there is no need for trickle charging or any other maintenance if they are totally disconnected and the temps are above -15F.

For lead acid batteries you'll have a similar advantage - much longer time in storage without the need for trickle charging or maintenance. Not as long as with lithium but noticeably longer when totally disconnected.

There are enough phantom loads on a trailer that a week or so is all it takes to reduce the charge to a problem level.