Comparing “old” 160w panel to “new” 250w panel and other considerations upgrading to LiFePO4

[Impatient]

My first questions involve whether a high voltage panel makes sense in a 12v camper setup…whether it will provide the performance boost the numbers promise, or just cause new problems I don’t have today. I know there is another thread that seemed to focus on this, but my post there got no response, so trying new thread instead.

I have an overly-complicated setup in my camper van, but any help appreciated.

today: 160w Carmanah/GoPower panel (see specs below) running through an older-style Morningstar ProStar 15m PWM controller. Actually, I have a switch on the positive wire so I can alternatively run the solar through a CTEK d250s (MPPT but with odd 23v input voltage limit and DC-DC capability). I use both controllers (one or the other for solar) but favor the Morningstar because it has a digital display which gives me some insight. I don’t know if the CTEK provides much better performance (maybe), but appreciate its ability to charge while driving…especially at night. I also have 2 separate AGM battery strings, so actually, if driving during daylight, I can charge both strings simultaneously (Morningstar for solar, CTEK from alternator). If parked longer term, I need to switch back and forth to get both strings charged. But I really like 2 strings, more on that further below.

I’m considering replacing the single 160w with a single SunPower 250w high voltage, which will necessitate MPPT such as Victron 100/20 (or larger???…please comment if that controller seems inadequate). The CTEK won’t work with this panel either (Voltage limit). The SunPower is surprisingly small, and fits my tight roof real estate; it’s specs are also below. The physical size is what attracted me to this panel. Adding panels to my existing doesn’t work so well with space allotted.

Will I get the expected power gains, or is something I haven’t considered going to be the new limiting factor? And/or are there going to be greater challenges / risks posed by the high voltage***. There is nothing magical about 250w for me, but on paper, it seems it would provide a meaningful bump in charge power, without causing a roof-top real-estate problem. I would be REALLY open to suggestion if there were another panel ~60” x ~31” with lower voltage, say a 36v panel, despite lower wattage.

250 is obviously 56% larger than 160. but given I mostly use PWM today, the percentage increase might be even higher. Keeping current 160wpanel, but getting a good MPPT controller might give an extra 25%, which might mean the bigger panel & MPPT might give close to 100% greater power…twice the power I can harvest today…or not. That is the (1st) question. Plus I’ve read there is a point of diminishing returns running high voltage into a 12v MPPT (I don’t know where that point is though). Plus I’ll still have the same issue with shading and am scratching head over how much wiring, fusing, and switching will need to be changed.

Also in the mix is upgrading ONE of the battery strings to LiFePO. One string for now. Battleborn claims I can keep using my current controllers (which do not have Lithium profiles, but probably not optimal). Of course, upgrading only one string complicates switching back & forth when I do upgrade to a controller with Li profile. If it matters, the “string I am upgrading to Li is 100ah. The other string (under the van floor) is 186ah AGM and the form factors needed and environmental considerations made upgrading that string a bit more of a challenge. In a perfect “greenfield” situation, with no budget limitations, I would have put LiFePO in the under-the-van location first, but I sprang for a single Battleborn when they had their Black Friday sale…and I doubt it would fit there. Besides that 186ah string still seems to work well (unlike the 100ah string). I don’t have the money to do everything

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[MisterSandals]

considering replacing the single 160w with a single SunPower 250w high voltage, which will necessitate MPPT such as Victron 100/20

Why does this panel change necessitate an MPPT such as 100/20?

The morningstar says it will accept up to 60V:
Maximum Solar Input Voltage (12V/24V bat): 60Voc

Morningstar makes quality equipment so I'd be mighty surprised it would not work for a higher voltage (what voltage?).

A 250W panel / 14V charge voltage = 17A charging max

I see no reason that upgrading to the bigger panel would cause any issues. The PWM "may" be a little less efficient converting ~40V to 14V but that is likely insignificant. More significant would be orienting your panels towards the sun as opposed to flat on the roof, for example.

 

[Impatient]

MrSandals, first off thank you for reply. let me look again at my current Morningstar. I saw the 60v max for the newer ProStar, but so far, not for the older (if current is Gen 3, I have at best Gen 2: gray, white & red.). Plus I read a MS white paper on why their MPPT was better than some others, and it seemed to indicate panels could produce voltages way above the STC specification…I didn’t think I had that much room to spare…assuming their STC max voltage for the controller was consistent between PWM and MPPT. That said, the real reason I am looking is I never see more than 6-7 amp in the wild, usually 5 or less, sometimes way less if I’m in the woods. Most usage is in the PNW in the sunny summer, but sometimes at the coast it’s not sunny, and/or in the woods, and/or when days begin to shorten in the fall. Theoretically, I can get upwards to 20a using bigger panel (or more panels)…but I assumed any PWM would “squander” the higher voltage (the SunPower in question is low amp ~ 6 & high voltage ~ 42Vmp, so I could actually get less yield than with my current panel??? The panel ratings are attached in my OP.

But this is why I am uncertain this is the panel for me. I agree it’s not optimal to have a panel pointing directly up, not angled toward sun, but on a high-roof van, it’s not easy to adjust panel angle.

 

[MisterSandals]

I didn’t think I had that much room to spare…assuming their STC max voltage for the controller was consistent between PWM and MPPT

Getting the correct specs would help make a better decision or know if this is even an issue.

You posted 2 pages full of different panels. I could not tell which you are talking about. With the temp coefficient and your lowest possible temperature, its easy to do the math on Voc temp compensated.

Its not uncommon for panels laying flat, especially up where you are to produce meager amounts. You're not alone, there are many threads with people thinking their systems are the problem.

 

[Impatient]

1st: apology. When I posted a response in a different thread, I mentioned the panel I was considering was the 3rd from the bottom: the SPR-X20-250-bulk. I failed to include that when I revised the text to create this thread. Mea Culpa.

2nd: apology. I just found the max solar input voltage for MY Morningstar Prostar is the same 60v as the newer units. Sorry, but at least that is good news…though I still assume an MPPT will be better tying a 50v Voc panel to a nominal 12v system.

3rd: I am asking advice because I know only enough to get into trouble. I included the low irradiance table for the “proposed” SunPower because I was surprised at how low the output amperage was at the low irradiance, though I had no comparable info for the 160w GoPower/Carmanah. But I was fishing for advice on whether the higher voltage panel would somehow be worse in low light. Anyway, I went back to see if there was more comparable info available from Carmanah, and perhaps there is, but I now want to throw my hands up and say “I’m confused,” and “I barely know what I am talking about.” If you look at my original Carmanah screenshot, it has IV curves at various irradiances, but what hit me was these curves show voltages into the upper 30’s, even though the Voc is 22.74. WTF! Also I found a curve for the SunPower, so while not completely apples-to-apples, there is some comparability possible…I guess. See attached (this 250 panel in lower right). Perhaps further exposing my ignorance, you will notice the amperage is always lower than the Carmanah’s except at voltages above 30…which I assumed I couldn’t reach without an MPPT...and not at all with the Carmanah. So the paranoia here is that I might end up with less power than with the current panel. My understanding up to this point was watts are watts, and with MPPT I could “make amps” as the voltage was pulled down to system voltage (watts remaining equal, more or less, subject to efficiency).

4th: I will leave this alone for the moment but plan C (not even B) was to add a 2nd Carmanah CTI160 panel, which I already own, but which REALLY screws up my rooftop real estate…and although it is the same model number, it has slightly higher amperage, and lower voltage (by 1v), though arriving at similar watts. It is clearly a different panel (fake???). I won’t get into all the parallel vs series conundrums this scenario presents. And like I said, for real estate reasons, I REALLY don’t want to do this.

 

[MisterSandals]

fishing for advice on whether the higher voltage panel would somehow be worse in low light.

A higher voltage is often better because the SCC needs battery charge voltage (~14V) +5 volts before it starts charging. So in low light conditions, whether its cloudy, early morning or late afternoon, having enough volts for your SCC to BE ABLE to charge is often the difference.
Whether PWM and MPPT are more efficient has been debated. I like MPPT quite a bit but have quite a few PWM controllers too. If you have a PWM and can scrape out the rated watts from your panel in full sun, its probably as good as an MPPT in the same full sun. I have not really compared the two technologies side by side.

You will be better off with the bigger panel.

Why not keep the 160W panel and make a way to patch it into your system with some Y connectors. Get 25' of cable so you can carry your 160W deployable panel out to the sun, prop it up with a stick (or something more high tech) to get you even more. When its cloudy, more panels is mo better. And in the summer if you park in the shade when its hot, you can have your deployable panel out in the sun.

 

[Impatient]

My takeaway from your advice (much appreciated) is that this “bigger”panel will help. Thank you. Hopefully there won’t be any huge gotchas when I contact the seller (these are “surplus,” or “closeout,” hopefully not worse than grade B”). If I could find them “new, grade A with SunPower warranty, I would prefer that, but I can’t find them “new” anywhere else.

Yes, having an additional portable panel that can be well-positioned makes a lot of sense, so I need to not preclude that in any design changes. I may look for something physically smaller though for that purpose. I am typically parked in a semi-public parking area, and leave the vehicle unattended (think trailhead, or “boat ramp”), but when staying close by, I still might gain from being able to point this 2nd panel toward the sun…as you’ve suggested.

The other issue (entirely of my own making) is that I bought a single 100 ah LiFePO battery to replace a disappointing single AGM 105 ah. This is one of my 2 “strings.” The other string is 2x 93 ah AGM’s which are tucked beneath the van body. I believe they are still going strong, and they will be a b*tch to access and replace, so was trying to delay replacing those. Plus this string is in a more hostile environment (potential freezing, and close to muffler, though some buffering…but probably more extreme temps.) So optimal charge algorithm for each string is different…though probably only for a year or 2. Someday, both strings will be lithium, I presume. So I’m trying to research whether I am better off using AGM profile for both strings, or buying a new controller with LiFe profile, use it for both, or perhaps come up with a “custom” compromise profile that will do reasonably well with both (for example, an AGM profile but with a lowered Float voltage that would basically be ignored by the Battleborn, yet still help the AGM’s. ????). As often as I flip the switch between strings, I don’t think reprogramming the controller each time is feasible.

Further comments are welcome.

 

[MisterSandals]

for example, an AGM profile but with a lowered Float voltage

What are the details of your AGM profile?

I've seen people here recommend AGM when an LiFePO4 is not available. I use a standard lead acid profile in my RV when connected to shore power but that's not often. Seems just fine. AGM should give a full charge.

 

[Impatient]

You asked about profiles:

* Current Morningstar Prostar: see attached, note 3 modes for flooded, GEl, or sealed (AGM).
I frequently see 14.3v +- occasionally 14.5 on the readout while in Absorption. My guess is this has to do with temp compensation. I’ve even seen higher when it tries to equalize once a month or so…but I’m sure I’m confusing it because I switch which battery string is connected to it frequently (once, twice, maybe more times per day). I do not have any temp sensor leads attached to batteries. String 1 (100ah) is inside cabin of van, 3 feet from Morninstar controller…which has a sensor built in to the unit…I just don’t have a lead to either string to override that sensor.

*Current CTEK d250s: see attached…unofficial, but most “official” ones show oldest version which had max 22v solar input…mine was “gen 2” (but still d250s…not SA or SE) which has 23v max (woooh!). Best I can tell, float voltage is 13.7 (unofficial, never seen anything “official.”). I do have temp sensor leads to string 2 (2x 93ah), underneath the floor of the van where temp swings are no doubt wider.

So both these are not optimal for LiFePO from what I can tell, which wants lower or no Float, and perhaps a time limit on Absorption, and definitely no equalization…although, the Battleborn BMS might protect.

Victron 100/20 has multiple default profiles, one of which is for LiFePO, plus “user-defined. Sorry, I can’t find anything concise that shows all options, but was thinking SINCE I WOULD LIKE TO SWITCH IT BETWEEN STRING 1 (which will now be 100ah LiFePO) AND STRING 2 (186ah AGM), a compromise profile: for example, 14.2v with no time limit on Absorption (maybe), and 13.3 or 13.4v Float, which might be friendly enough to both chemistries. REMEMBER, I would only be charging one string or the other…they are never joined. If it takes more than 2-3 clicks on the app to change profiles, I’m not interested in changing profiles each time I switch which string is connected to the solar (several times a day). By the way, Victron mentions “tail current” which I am TOTALLY clueless about.

NEW QUESTION: is there some small cheap device I could wire in between the new 48v panel and the CTEK (which can handle only 23v) to limit voltage to ~22v? This would not be my primary charge method, but could be a backup if needed. I realize I would get only 30%-40% the power (if that). Primary charge would be through Victron which can handle the higher voltage. If so, then perhaps I could almost “dedicate” the Victron to the LiFePO and CTEK to the AGM…almost, though not completely. I think it has been good to be able to switch which controller gets solar, and which controller goes to each battery string…great redundancy and “parallel” charging capability while driving.

 

[MisterSandals]

Current Morningstar Prostar: see attached, note 3 modes for flooded, GEl, or sealed (AGM).

I think GEL would be preferable because there is no equalization stage. Otherwise they are nearly all identical.

*Current CTEK d250s: see attached… which has 23v max (woooh!)

Yea, exceeding the 23V with a panel Voc would be bad.

Victron 100/20 has multiple default profiles, one of which is for LiFePO, plus “user-defined

I have a 100/30 and its a REALLY nice SCC.

If it takes more than 2-3 clicks on the app to change profiles, I’m not interested in changing profiles each time I switch which string is connected to the solar

It would take a couple clicks but when you switch batteries to change profiles, it might be good to see what the state of the battery is in the app. Its a great app, one of the best user interfaces around.

My understanding up to this point was watts are watts, and with MPPT I could “make amps” as the voltage was pulled down to system voltage (watts remaining equal, more or less, subject to efficiency).

You are thinking about this more than you need to. The MPPT does the work of taking any voltage up to 100V and turning that into charging amps as well as possible. Tailing amps are like slowing down the filling so it puts a better charge on during the end of charging.

is there some small cheap device I could wire in between the new 48v panel and the CTEK (which can handle only 23v) to limit voltage to ~22v?

No.

Can you get both panels on your vehicle? Then you could have small panel and CTEK to your AGM and the big panel and Victron to your LiFePO4.

There is another option to have your big panel and Victron charge your LiFePO4. Then have a DC-DC charger continually charge your AGM (or as you turn it on/off with an app. The Victron Orion DC-DC comes in a few different sizes (works from alternator too... i've installed a couple of these).

 

[Impatient]

Good food for thought, but let me dig deeper on 1 item…your “no” answer to the question about “small, cheap device” between ~48v solar panel and the CTEK.

WHY couldn’t a Victron 48/12 (or 48/24) CONVERTER be inserted between the panel & the CTEK SOLAR input. These converters have adjustable input & output. I’m not sure which I would choose, but 15v 9a (max for the 48/12) or 20v 5a (min on the 48/24) might both be “compatible” with the CTEK’s SOLAR input … at least on paper. Could you tell me what I am missing? Probably something obvious. I realize efficiency might be abysmal.

Why do this? To “dedicate” the MPPT 100/20 to the LiFePO, and dedicate the CTEK to the AGM. On days with little or no driving, I could still get a charge to the AGM from the solar, after “filling” the LiFePO. So I would need a switch (probably) between the solar and the 2 Victron units…I assume it would be one or the other, never both. I would probably still want to connect the CTEK to the LiFePO for alternator charging in a pinch…so in addition to a proliferation of little blue boxes, there would be a kluge of switches.

 

[MisterSandals]

Could you tell me what I am missing?

A solar panel isn't the steadiest of power supplies. But give it a go, maybe you've discovered how to do something that has eluded the industry and thousands of electrical engineers.

 

[Impatient]

Well, remember, that was a “New question” just a day or so ago…it’s not like I’ve been thinking of doing that for weeks … it just popped into my brain as a possible workaround to ONE of the “negatives” to doing this high-voltage panel, so I thought I would ask. For all I knew, thousands of engineers had already proposed this very approach.

I’d been trying to figure out how to harvest more power out of the limited roof space but all my thinking was in the direction of running multiple panels in parallel or series, only to be disappointed with the size of the footprint on my van’s roof, and struggling with other aspects of combining dissimilar panels. This 48v panel may never make it onto my roof either, but it would be nice, especially if I could keep using my 186ah AGM string alongside the 100ah (LiFePO) string. There have been more roadbloacks and “plot twists” than I ever imagined.

 

[MisterSandals]

I’d been trying to figure out how to harvest more power out of the limited roof space

Yes, there are a lot of us doing the same.

This 48v panel may never make it onto my roof

I thought it would be a pretty easy decision to do this.

especially if I could keep using my 186ah AGM string alongside the 100ah (LiFePO) string.

This is a good goal. Not sure why you dismissed the DC-DC charger suggestion so quickly and quietly-it is simple and solves most of your (battery related) issues.

There have been more roadbloacks and “plot twists” than I ever imagined.

Yea we all have learning moments. Do you have a possibility of changing the 49V panel to one that works with all your chargers?
Its pretty easy to find (and sell) panels on craigslist.

 

[Impatient]

1st, I should have reacted differently: could you re-affirm that reason the Victron DcDc CONVERTER wouldn’t be good is the variability of a solar input??? In case I do “try” this, is there a way to predict what the output current might be? But this experiment may never happen.

I snubbed the Victron DC-DC CHARGER because it is “only” a DC-DC charger, and doesn’t solve the problem of how to charge both strings from solar. I already have a DC-Dc charger, elegant, simple, maybe too simple, but at the same time flawed…the flaw being it’s low solar voltage limit…but, was hoping that might be better than zero solar capability. Someday I may end up with one, but how many little blue boxes does that mean, to get 2 string reporting, simultaneously 2 string charging from solar & alternator?

I don’t own the 48v panel yet, and may never own it…shipping quote is twice the panel price…so 3x price all in. I wish it were a more common size panel, I’d just wait, and try a small (or portable) 2nd panel for as long as I have the AGM string. Once both strings are LiFePO, it becomes easier (I think) to charge both strings from same panel…though, I would like meaningful reporting, which switching back & forth probably screws up.

All LiFePO might make the Orion Charger more acceptable too.

 

[MisterSandals]

In case I do “try” this, is there a way to predict what the output current might be?

I could only guess, and maybe then only wildly. It gets discussed from time to time here but i could not find a thread, sorry i did look.

and doesn’t solve the problem of how to charge both strings from solar.

You charge your bigger LiFePO4 battery from solar and simultaneously charge your AGM battery with a DC-DC charger like a Victron Orion. So you are charging both batteries (am i off on this that you are talking about "charging both strings"?). Are you calling your batteries "strings"?

I already have a DC-Dc charger, elegant, simple, maybe too simple, but at the same time flawed…the flaw being it’s low solar voltage limit

That's not really a DC-DC charger as its normally referred to, if its a solar charger that is. What are you referring to as your DC-DC charger?

You can charge 2 batteries with a single SCC, i have a friend with one of these:

Amazon.com

I think you'd need the display to set it to 2 different battery types. I cannot remember what it took when we set it up. I know it was easy because my friend had 2 deep cycle lead acid batteries.

 

[mikefitz]

If I may step in and help MisterSandals with a reply to this situation, a different viewpoint perhaps?

DC to DC converter to a panel

Firstly the concept of fitting a DC to DC converter to a panel to lower the voltage will not be very successful.
The solar panel is a variable current source and its maximum power point changes with solar intensity. That's why MPPT solar controllers are used, they automatically track the maximum point. A reasonable MPPT solar regulator will not cost much more than a DC to DC converter and will operate correctly.

Using a 250 Sunpower panel with a PWM controller

With a PWM controller the panel power is not the factor you need to consider , its the current that matters.
Your existing 150 watt panel has a maximum current of 8.6 amps, perhaps giving 7 to 8 amps on a good day via the Morningstar. The 250 watt panel has a maximum current of 5.8 amps, perhaps giving 5 amps with good conditions.

With the 250 watt panel you need a MPPT controller, expected current output from a MPPT controller around 15 amps on a good day, in theory with a low charge voltage almost 20 amps could be available.
Suggested controller Victron 100/20, budget option Epever 2206N XDS2.

Ctek DC2DC/MPPT

Useful only with low voltage panels. Very poor charging with output current drop when warm. The MPPT action is primitive and a purpose designed MPPT controller will out perform this unit.
Keep as a means to charge from the alternator and to use with an auxiliary low voltage panel, perhaps a portable unit.

Battery setup

At the moment you have two separate AGM battery banks and switch charge input and presumably load output as needed. In almost all such installations its impossible to correctly charge both correctly without additional complex equipment, leading to the early failure/loss of capacity is one or both banks.

Lead acid and particularly AGM batteries take a long time to charge, its possible your separation and selective charging is not fully charging the batteries.

Upgrading your system.

Reconfigure the battery system to have all in parallel, junk the sick AGM and replace that with a lead acid. Sorting the battery issues is the first thing to undertake

Fit a MPPT solar controller.

More solar is useful, a bigger higher voltage panel with a MPPT will give you 3 times the power over your existing system.

Add lithium battery or batteries to your system. With modest power requirements a single 100 Ah may be enough. Because a lithium charges much faster and more efficiently than a lead acid the complete system becomes very efficient. Battleborn are an expensive option, there are alternative lower cost 'drop in' batteries.

If you want to keep the 180 AGM just add the lithium in parallel, charge everything with a lithium profile. You don't need anything special to charge lithium, providing you charge to target voltage, say 14.2 volts and then stop charging.

Comment

Its not very clear from your post if you are making changes or just thinking about making change to your system.

What is the objective and what are the issues with the existing system?

Mike

 

[Impatient]

Hi Mike (& Mr Sandals). 1st thanks.

For 6 yrs I’ve had solar in my camper van, and thought it was again time for some upgrades (it’s been “upgraded” 4 or more times…but this time may be more revolutionary vs evolutionary…or at least a major mutation. I live in this thing “full-time” for 3- or 4- month stretches, summer/fall, with some additional multi-week trips spring and winter.

Let me reset this conversation, as it’s strayed a bit. THE MAIN CONCERN IS HOW TO HANDLE THE HIGHER VOLTAGE OF A PANEL I MIGHT WANT TO BUY…IT GOES BEYOND JUST HAVING 1 MPPT CONTROLLER, IMHO.

Today:
* Alternator charging via a CTEK d250s (this was added ~ 4.5- 5 yrs ago)
* one panel: 160w, from the beginning with Voc 22.75, barely under the CTEK d250s maximum solar input voltage (nominally);
* 2 controllers: the Morningstar Prostar 15M PWM, and the added CTEK (20a Dc-Dc from alternator and solar…my solar can go to either controller, but not both simultaneously…however, simultaneous use is possible, given my wiring and switching, see below)
* 2 battery “strings”: one has a single battery (105ahAGM…VERY RECENTLY replaced with a 100ah Battleborn…which has yet to be used). The 2nd has 2x 93ahAGM’s (186ah total), which I think has a year or 2 more life in it. This 2nd one is crammed under the van, not just any battery (-ies) will fit there, and absolutely no flooded battery there, they need to be mounted on their sides to fit. For that matter, the 1st string is inside my living quarters, so I don’t want flooded there either, off-gassing away. The 2nd string is more subjected to freezing and heat (as it is near the vehicle exhaust).
* 2 load fuse blocks, which can be switched to either battery “string.” Both can be run off either string, but a fuse block cannot connect to both strings simultaneously. This isn’t essential, but shortened some wiring runs. Changing this costs money and time, with little benefit (or detriment), although it does allow me to run different loads off different batteries at night if both strings are getting “weak.”
* obviously there are lots of switches and fuses. So there is lots of “redundancy” and “failover” (and less “single point of failure concern”…although more that can go wrong) allowing either charging source to fill either battery “string,” either string to power any and all loads, and shut anything and “everything” down if needed. If driving during the daylight, either string can be charged via solar, and the other charged via alternator. If driving at night, theoretically, I can run loads effectively off the CTEK (alternator), potentially keeping both strings topped off. It’s been suggested the CTEK doesn’t handle this perfectly, I don’t know, possibly true.
* loads include fridge, multiple fans, furnace fan, charging/power outlets, and lights. since the loads may be active throughout the day (and night), charging cycles may be “interrupted.” I’m sure you’re familiar with the PSOC term, and how SOC calculations and algorithms get confused by PSOC usage. This last year I tried to “game the system” somewhat by keeping charge cycles as uninterrupted as possible (run loads off one battery string, while charging the other) though I’m not sure how much this actually helped…and there was obviously chance of “error.” It has required more “hands-on” than I want, but that has become the big motivation to have more power, so it’s not so dependent on me switching batteries in the middle of the night. I’ve been trying to baby the 186ah string because it will be such a hassle and expense to replace.
* By the way, I don’t really have shorepower capability, except I can “pre-cool” the fridge (DC compressor fridge with 110v AC capability) before a trip, and don’t have an inverter (YET). Rarely do I camp where I can even hook the fridge to shorepower, let alone run anything else off AC.

Moving forward from today:
* I recently I just bought the 1 100ah Battleborn..so the “smaller” string was upgraded to LiFEPO. This might not have been the best thing to tackle first but I was convinced the 105ahAGM was the weakest link…often it couldn’t support the fridge and some lights for 6 hrs without voltage sagging to near 12.0v…and there was 6 more hours of darkness before daybreak. So what do I upgrade next (wallet permitting)? I vote for more solar, which is my most-used source of power…and now I consider my “weakest link.” But this (and the mixed battery environment) have multiple ramifications. For the last month, I’ve been trying to figure out how to ADD solar panels, parallel vs series, switchable between battery strings, etc, but never happy with the options. I have a self-imposed physical size limit on the roof, and the only options that seemed to work were: add 1 or 2 flexible panels (which I am leery of for durability reasons), or replace the perfectly functioning high-quality 160w panel with something only slightly larger (physically). There are slightly more powerful options in the 60”x26” footprint, though most slightly “crept above” the CTEK’s max voltage rating. It was only recently I found something that “smashed way beyond” that voltage limit: the SunPower Spr-x20-250…providing substantially more power IF you had the controller(s), wiring, switching, and fusing to handle the increased voltage. At 50.2 Voc, it would be an entirely new ballgame for me. By the way, these are “refurbed” so on top of the “known” challenges (not that I fully comprehend them all), there are unknown question marks. As far as I can tell, SunPower does not sell these anymore, and no other panel tries to be that size (31”x61”) with that voltage and power. It’s a seam or wrinkle in the market…either go bigger, or go smaller (in multiples)…for better or for worse. THIS panel will fit on my roof (along with the other stuff: ceiling fan/roof vent, and potential standup paddle board…which is huge). There are many panels in the 40”x60” size but they just don’t fit given the paddleboard constraint. Portable panels are a plus, but my travel/use case does not lend itself to their frequent use. I admit, you can have the biggest panel in the world and not get squat out of it if you’re parked under big tree(s), but I move around so much setting up something portable outside the van, and leaving the van for extended periods while I hike, bike, or surf, doesn’t lend itself to much use of portable panels.
* I thought I would reach out to the forum to see if anyone else had advice. The advice I WANT is how to keep 2 strings, 2 controller/charger circuits to maximize charging and usage patterns…AND how to handle 50+volts in my switching and fusing. Otherwise, I may just need to drop the idea of getting one of THESE 250watt SunPower panels. They do add considerable complication. The news Friday that the seller wants and extra $200 to ship one panel didn’t help either. Plus I need more info on what they supposedly did to the diodes, and why. I suspect these originally had microinverters (on each panel) to connect to an AC grid, but this is just a theory, and has not been confirmed. Of course, this may be a real gotcha…as I really do not know my way around diodes in solar…today I have plain-ole plug-n-play.'
* SOOOO, the loose plan that was rattling around in my brain, if the total system could be whipped into compatibility, was to have: 1 250w 50v panel (or next best alternative), at least 1 MPPT controller (like Victron 100/20 or equivalent), a DC-DC charger (and it would really help if it could double as a solar controller, otherwise I might need a 2nd MPPT to charge both strings), 2 battery strings (one LiFePO, and the other AGM, for at least another year), with ability to charge either string from solar or alternator. Once both strings are LiFePO, in a year or so, things will get a little easier, as charge profiles would not have to be unique for each string, simplifying switching.

***again, since the SunPower 250w presents an opportunity to have more power in a compact space, if I am going to buy it, I will need to grapple with the ramifications of at least one 50v circuit segment…and not completely defeat the purpose of multiple battery strings.***

***One small advancement would be if someone could point me to a “safe” 60v switch so that I could switch this panel (during the day) between 2 MPPT controllers.***

 

[mikefitz]

THE MAIN CONCERN IS HOW TO HANDLE THE HIGHER VOLTAGE OF A PANEL I MIGHT WANT TO BUY…IT GOES BEYOND JUST HAVING 1 MPPT CONTROLLER, IMHO.

The only way you can effectively use all the power from a high voltage panel is with a MPPT controller that can handle the voltage. There is no other practical option. Nothing else significant needs changing.

the purpose of multiple battery strings.

This is not the way to construct your system. All you will do is damage your batteries. A diy technique of charging and loading two banks of batteries will end in disaster.
Parallel all batteries , even lithium and AGM. This is a proven technique if you don't want to give up your AGM.
( if you were to test the 180Ah AGM bank you will find the actual capacity is very much less). Consider forgetting about the agm batteries all together and just rely on the lithium.

SunPower Spr-x20-250…providing substantially more power IF you had the controller(s), wiring, switching, and fusing to handle the increased voltage. At 50.2 Voc, it would be an entirely new ballgame

Dont fix on this SunPower panel. I am based in the UK and can obtain a number of different makes of 250 watt panels with the required footprint, you may be able to find alternatives. Junk your PWM controller, its possible that using it with the lithium battery could cause damage.

General comment. Your system is over complex and not necessary. Only use a MPPT controller with any panel you use. Connect all chargers and loads to one battery bank.

Mike

 

[Impatient]

Mike, I appreciate your responses. And Mr Sandal’s. Having some additional perspectives is invaluable!!! Any others?? Some advice will take time to sink in. I’ve been known to balk at certain advice, then agree later.

One thing that has driven me toward 2 strings was the “advice” to not combine new batteries with old, batteries of different capacities (or even brands), and of course, not combining chemistries. Originally I started with a single 103AGM, 2 yrs later was offered the 2x93’s for free, but thought they should be kept separated as advised. The original 103ah wouldn’t fit in the space under the floorboard, let alone all 3, but the 2x 93’s would. So it’s been 2 strings ever since. But I’m surprised at your “parallel all batteries” advice…given we are now talking Li & AGM. Wouldn’t there be a considerable imbalance in charging the two chemistries, potentially ruining the LiFePO prematurely? I’m not sure about all this…maybe…but this may take time to sink in…or may need more explanation..

Mike, Please mention a brand of 250+- watt panel in the 31”x61” range other than this refurbed SunPower. I tried searching, but no success. That would seriously change my sense of urgency/desperation. I’m also curious if there is a modern ~31”x31” panel with over ~110 watts. If so, obviously I could fit 2 of them, and potentially kill more birds with fewer stones.

And unless there is new info, I vote for an MPPT…it’s marginal with current 160w panel, but gets very compelling anywhere above that. I’m still thinking of keeping the CTEK for DC-DC charging duty only, but still scratching head on how to charge both strings from solar. Yeah, if money weren’t an issue, I would probably have bought 3 ReLion 80w for under the floorboard, and ditched the 2 string approach. Would be great…until it wasn’t, someday. I considered some of the physically smaller (and cheaper) 100ah LiFePO’s but given the temp range for that location (near muffler, and outside heated cabin), I don’t trust any battery that does not have absolute top notch BMS temp protection. Another reason to have a 2nd string (in the heated cabin, not near muffler).

So what panel is still a major question??? And how to connect things? To what controller(s), to what batteries??? That’s all.

I’ve somewhat entertained 2 MPPT controllers, one for each string…one programmed for LiFe, the other for AGM…or only one MPPT with a profile friendly to both chemistries, switchable between both strings…lower float voltage, really not sure if should limit absorption time (sounds potentially better at the moment). Potentially waiting 1 or 2 yrs before replacing 186ah string also sounds good to me —$$$.