Question on how batteries work in this ACR+Solar situation

[dwh]

For my campervan, I just ignore the 50% rule and replace my deep cycle aux battery every couple years. I also don't buy expensive deep cycle batteries. I buy the cheap ones.

Cost works out the same over the years, but I get double the energy budget without having double the lead to haul around.


I do buy good cranking batteries, but I don't abuse those.

 

[jeegro]

Rhwat, interesting experience. I guess it will just be something I have to experiment with. I'll stick with a lead acid for now to get my feet feet. Should I decide to go to lithium, it shouldn't change my setup at all. In conclusion, my setup:

Panels: 2x50w 12v panels wired in series. Either a Renogy or preferably a flexible type panel. Maybe an extra 100w suitcase panel to setup onsite.
Controller: Morningstar sunsaver MPPT 15a
Isolator: Blue Sea 7622 ML-ACR
Starter Batt: TBD, something group 34 lead acid. Odyssey's are nice.
Aux Batt: TBD, a deep-cycle AGM or flooded, group 34
Monitor: Victron BMV-702 or a Blue Sea M2 1830
Shore charger: CTEK 4.3
Inverter: TBD, whatever works

I know how to do the wiring pretty well. I already have a Blue Sea 12 circuit split panel, wired up for 6x constant, 6x switched. I have some cool Auber gauges setup on that panel, to monitor coolant temp, oil temp, and oil pressure.

This should give me a top-of-the-line compact setup with room for expansion (bigger batteries, more panels, etc). If anyone has some advice on my product choices, please let me know!

 

[DaveInDenver]

Solid. But then again I run the SunSaver MPPT 15, ML-ACR, Odyssey PC1400-25/35 pair... My hole is a portable solar panel. I have a 24V/240W Sanyo but it's much too awkward and heavy to use portable. It goes with me to Field Day and what-not, but that's really it.

 

[jeegro]

That seems like a lot of money to spend for a 65 aH battery. What's your thinking? Are you winching?

 

[DaveInDenver]

That seems like a lot of money to spend for a 65 aH battery. What's your thinking? Are you winching?

Mostly it's because I got a deal on the pair and they fit nice in the tray I'm using.

 

[jeegro]

Nice setup.

If I can find a good deal on the PC1500, it looks like a good choice: https://www.amazon.com/Odyssey-34-PC1500T-Automotive-LTV-Battery/dp/B00249CSS2

For panels I'm currently looking at these flexible 50w 12v options.

https://www.amazon.com/KINGSOLAR-Fl...&sr=8-42&keywords=50+watt+12+volt+solar+panel

https://www.amazon.com/ALLPOWERS-Be...id=1480150676&sr=8-6&keywords=50w+solar+panel

https://www.amazon.com/gp/product/B017TPHTLG/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=A2D22KZJD14Y8Y

a 24v 100w panel is another option, but 24v panels seem much harder to find. I think the problem if I go with 2x50w panels in series, is that I can't add another single 100w 12v panel, right? I'd need to add another 2x 12v panels in series, and then parallel them with the flexibles above. Hmm....

 

[dwh]

a 24v 100w panel is another option, but 24v panels seem much harder to find. I think the problem if I go with 2x50w panels in series, is that I can't add another single 100w 12v panel, right? I'd need to add another 2x 12v panels in series, and then parallel them with the flexibles above. Hmm....

Perhaps another misconception involved here...

You seem to think that you need to rig the 12v 50w modules in series.

Probably based on the mistaken idea that you have to do that to get some extra benefit from the MPPT.

Not true. The MPPT benefit will be exactly the same no matter if you rig the modules in parallel or in series.

So rig the two 12v 50w modules in parallel, and you can just parallel another 12v 100w module later.

 

[jeegro]

OK. In that case, I can get a 100w panel that fits nicely on top of my FrontRunner bag (21x37") instead.

 

[DaveInDenver]

You can run the SunSaver up to any array of 36V and there is an advantage to higher voltage, lower cable losses for a given power transfer.

The downside to series wiring is the array will be the lowest panel current. The disadvantage to parallel is the array depresses to the lowest panel voltage. Either way unless all the panels are matched there's potentially some loss of possible energy.

My preference is running the array at the highest practical voltage and lowest practical current. But either way the SunSaver MPPT 15 is limited to an input power of 200W for a 12V system, so be aware of overall configuration. With mismatched panels the controller will try to find the max power point for each panel when it can. But it will be happier not bucking excessive voltage, so parallel is easier on the controller.

 

[jeegro]

Thinner wire was a factor in my series decision, yes. I also watched a youtube video - and while it wasn't exactly the scientific method - it seemed that MPPT controllers are more efficient when converting higher volts/lower current into more amps to the battery compared to 12v.

But it looks like I've found a 120w panel that will just perfectly fit ontop of my roof rack bag... so I think thats going to be the way to go.

Dang, I thought the Sunsaver could do at least 300w of panels? I probably expect myself to end up somewhere between 200-300w.

 

[DaveInDenver]

It can do 400W into a 24V battery. It's limited to 15A in either case and it's got a max regulated voltage of 15V on a 12V system, so that's the 225W max. Anything beyond that is wasted as heat and potentially damaging to the controller.

 

[jeegro]

Not a lot of juice for a $180 piece of equipment, eh? Oh well. 225 should be fine. Not doing anything crazy.

 

[jeegro]

Found a really good deal on a 120w panel. https://www.solarblvd.com/product_info.php?products_id=3082

Does anyone see anything wrong with this? Other than it being flexible.

This plus a 100w suitcase style panel would be perfect.

Compared to this 120w panel, for over double the price: https://www.amazon.com/KINGSOLAR-Flexible-Solar-Panel-Black/dp/B00R8SMVC2/ref=sr_1_42

 

[dwh]

it seemed that MPPT controllers are more efficient when converting higher volts/lower current into more amps to the battery compared to 12v.

The MPPT does a periodic check to find out what voltage gets the most watts out of the solar, and then operates the solar at that voltage until the next time it does the check.

So say you rig two 12v modules in parallel and the MPPT figures the Vmp right this minute is 17v. If you had it rigged in series, the Vmp would be 34v.

Either way the PV is operating at Vmp, so it doesn't matter which way you rig it, you still get the max watts the array can produce.


As for the buck conversion, it doesn't matter if you down convert from 17v 6a, or from 34v 3a...you still end up with 100w in from the solar and 100w out to the battery.


Wiring in series to raise the voltage and lower the amperage is very important when rigging a house for solar - it can save you a couple grand buying thinner copper wire.


But wiring a car with 5a of solar? Please, even with 10a of solar, you could use lamp cord and it would work just fine...and the "power lost due to inefficiency" would probably be measured in milliwatts.


As for a mis-match in Vmp of you two 50w modules vs. your 100w module, don't sweat it. The MPPT is just going to average out the whole array when it picks an optimal operating voltage.

It won't be the holy grail of perfect efficiency, but it'll be close enough.


And the truth is, with such a small system, you're not really going to see much benefit from the MPPT anyway.

So don't sweat it.

 

[dwh]

So say you down convert from 17v 6a to 13v 8a. That looks like a 2a "boost".

How about down convert from 34v 3a to 13v 8a? Woo, that looks even better - 5a boost instead of 2a boost.

But actually, there is no "boost" to begin with - that's marketing hype - it's still just 100w in, 100w out.

Edit: And either way, you end up with 8a to the battery.