Charge controller and battery bank size recommendations for 860w of PV on Sprinter

[Sunking]

Cool, so, since I have 2 series in parallel, should I have a 30 amp breaker coming in to the controller (after they have been T'ed together)? How about from controller to they battery?

Again there is NO REQUIREMENT to install fuses or breakers between the Panels and Controller. You are permitted to add them if you want, but it you are going to use a 30 amp breaker means the minimum size wire you must use is 10 AWG. You cannot apply a 30 amp breaker by electrical codes to smaller wire than 10 AWG It must be 10 AWG or larger.

From the OUTPUT of the CONTROLLER to the BATTERIES, and from the BATTERIES to the LOADS you are REQUIRED TO USE OCPD (over current protection devices). Try looking at the drawings I provided you as it answers your question in great detail.

I'm second guessing my choice of the 150/85 mc4. It has three pairs of mc4 connectors. Seems ideal for when i have 3 panels, but, until then, can i run both series in parallel into a single pair of ports?

You should be because you have not read the manual now have you? The 3 inputs ARE NOT FOR 3 PANELS, they are for 3 STRINGS of panels. Its a clever design idea so you are not forced to use combiners and fuses which cost big dollars. If you had read the manual you would have that question answered in detail;

MC4 models: Several splitter pairs will be needed to parallel the strings of solar panels. Do not exceed the maximum current rating of 25A per connector pair.

What that is telling you is the Controller can accept up to 3 String of Panels, and thou shall not exceed 25 amp input current.

I suggest you try reading the manual.

[Withalligators]

Cool, so, since I have 2 series in parallel, should I have a 30 amp breaker coming in to the controller (after they have been T'ed together)? How about from controller to they battery?

I'm second guessing my choice of the 150/85 mc4. It has three pairs of mc4 connectors. Seems ideal for when i have 3 panels, but, until then, can i run both series in parallel into a single pair of ports?

I've looked for a 12v adapter for it. Doesn't exist, unfortunately.

[SupraLance]

Regarding that laptop usage, you should look around for a car charger for it and eliminate the inverter loss altogether when you are using the laptop.
Regarding blue solar/smart solar, only difference between the models is the built in bluetooth vs needing a separate dongle to interface with bluetooth.
Regarding charging a 24v battery with a 12v alternator, there are converters that can step up the 12v output of the alternator to 24v to charge those batteries.

[Mike90250]

...... No breakers required with 2 strings. ......

Except, having breakers or a switch is very handy to compare string 1 vs string 2, and for the times you have to turn the controller off, you need to remove PV power , and restore it, in the proper sequence to battery power.

[Sunking]

How do I wire it all up properly?

I think I'll wire it in 2 pairs in series, running in parallel. Is that correct?

How many panels? 4 panels? If correct 2S2P

Do I need a breaker on each positive lead? Even between panels? Or each series? Or just one coming into the controller, between the controller and batteries, and between the alternator and batteries? The data sheet for the panel has a 15A series fuse rating so I'll have one inline for each series.

What size should the breakers be?

No breakers required with 2 strings. You will need fuses or breakers between the controller and batteries, between alternator and batteries, and between the batteries and load. Something like this. Only thing that will be different is fuse and wire sizes.

[Withalligators]

OK, I'm think I'm going to go with the Smartsolar 150/85-MC4. https://www.victronenergy.com/solar-...150-85-150-100

How do I wire it all up properly?

I think I'll wire it in 2 pairs in series, running in parallel. Is that correct?

Do I need a breaker on each positive lead? Even between panels? Or each series? Or just one coming into the controller, between the controller and batteries, and between the alternator and batteries? The data sheet for the panel has a 15A series fuse rating so I'll have one inline for each series.

What size should the breakers be?

What am I missing? I'm doing so many projects at once, I'm worried I'm going to screw something up with my old and addled brain.

And of course, 3 days after I drive 4 hours to get the panels I was setting for, (4 x 215w) 327w Sunpowers that are the same width show up on CL. UGH.

[Withalligators]

What do you guys think about the Victron stuff? They have a bunch of 150/85 controllers that are rated for 1200W input. If I wire 2 pairs in series, I'd never exceed that, even with 3 x 370w panels (if I ever find them).

https://www.victronenergy.com/solar-charge-controllers

There are a few variations, I'm not sure which is best for my setup. The three options are the Bluesolar MPPT 150/85, SmartSolar 150/85, and then a different Bluesolar unit (which looks like an outdoor unit not applicable to me.

Which would you guys prefer? Bluesolar or Smartsolar? I can't find any real difference, but I can find the Smartsolar easier, and it looks more premium, whatever that's worth.

[Mike90250]

Inverter input (DC) voltage is only a minor contributor to efficiency. Quality of design is a major factor (Moringstar suresine 300)

Size of inverter is also a large factor, 5% loss in a 300w controller is much less than 5% of a 3,000w controller. Keeping all the big electronics warmed up eats power.

The PT-100 looks to be a decent product, I installed one, it went well, and the connections were well laid out

http://www.magnum-dimensions.com/pt-100-mppt-charge-controller

[Withalligators]

My question about inverters was more about efficiency. My understanding is such that at 12v to 120v, there is about a 10% loss to inverter size. So, my 330w laptop on a 400w inverter is actually using 330w + 40w. First off, is that true?

This is why I have a number of inverters. Try and match usage of commonly used items to maximize efficiency.

But I can't find any small inverters that work on 24v. They're all huge. But, at 24v, is there half as much loss to the inverter? ie ~5%? If so, it would still be a 40w cost to using an 800w inverter at 24v? Or am I going to be throwing away 80w on an 800w inverter at 24v? This is something I've wondered.

Anyway. Charging off the alternator with a 24v bank? How, DC-DC charger?

What about using step down converters from decent companies like Samlex for the 12v stuff? None of it is high draw. Or does the inherent inefficiency of step down converters mean might as well use 120 stuff off an inverter as loss will similar?

[Sunking]

If you are using an Inverter,, you can run battery voltage at whatever you want. Higher is better. Again simple math and this math will scream at your wallet. With a 80 amp controller you panel wattage limited by battery voltage.

1000 Watts @ 12 volts
2000 watts @ 24 volts
4000 watts @ 48 volts.

So if you have 1000 watts of panels which is more expensive

80 amp controller for 12 volt system
40 amp controller for 24 volt system
or
20 amp controller for 48 volt system.

ITS EASY MATH.

[Sunking]

Anyway, I appreciate you taking the time to explain this, but it's thrown a bit of a monkey wrench in my works. I thought I could wire in series or parallel to keep my voltage or amps down. As in, if I wired the whole thing in series, I would have max 5.8A and ~200V for 4 panels. If I did them all in parallel I would have 48.5V and ~24A. A 30A controller is way more palatable than an 80A one if I do 860W/12V=~72A.
What am I missing?

Simple math

Watt Hours = Battery Voltage x Amp Hours
Amp Hours = Watt Hours / Battery Voltage

So lets say you need a battery capacity of 2400 watt hours. What is the capacity required at 12, 24 and 48 volts

2400 watt hours = 12 volts x 200 AH
2400 watt hours = 24 volts x 100AH
2400 watt hours = 48 volts x 50 AH

Lots of ways to build the 2400 watt hour battery at any of these voltages. Example you could use 4 x 12 volt 50 AH batteries. To do any of the three configurations.

4P = 12 volts @ 200 AH
2S2P = 24 volts @ 100 AH
4S = 48 volts @ 50 AH

However you would only use 50 AH batteries to make the 48 volt battery. You would not use them for 12 or 24 volts. If you need 12 volts @ 200 AH, then you buy 200 AH batteries like 2 x 6-volt golf cart batteries rated at 200 AH and wire them in series.

Now go back to the first formula I gave you.

Charge Amps = Panel Wattage / Battery Voltage.

1000 watts / 12 volts = 84 amps
1000 watts / 24 volts = 42 amps
1000 watts / 48 volts = 21 amps.

Seeing a pattern?

[Withalligators]

Are 24v inverts running at half the loss? Is an 800w inverter as efficient at 24v as a 400w inverter at 12v?

After a bunch of searching, I can find everything I want at 24v except exhaust fans and decent interior LEDs. If I can get better inverter efficiency, and save on cabling and a controller, I may consider 24v.

Actually, what about charging a 24v bank off of a 12v alternator, and topping off the starter with solar when the bank is getting high current? This seems like the crux.

[Withalligators]

Can I run a 24V battery bank, run the fridge/freezer/compressor off that, and use a step down converter to run my fans/lights/USB charging stuff/400W pure since inverter off of that? This would half my inverter and cabling cost (hyperbole, but you get what I mean), or is it just not worth the cost savings?

[Withalligators]

My current vehicle has a Midnite solar classic kid and a 310w panel. I don't think I've ever seen the thing output more than 16A. It's bananas to think I need to worry about almost 5x that amperage with less than 3x the wattage.

I was planning on designing a tilting mechanism to maximize collection, especially in the winter months (I'm in Southern California). Also, I was think about the possibility that I find the larger output sunpower panels down the line, and buying a controller that can handle up to 1110W.

But it seems that 100A controllers are much more scarce. What do you guys think about the outback power flex max 100a charger? Or magnum? I can't find a Morningstar rated over 60a.

EDIT-That outback doesn't work at 12v. Dammit.

My field season is starting soon, and I'd reaaaalllllyyy like to be lined out by then, so I'm forced to ask for lots of help and make quick decisions.

I appreciate you guys answering all my questions.

[Mike90250]

But you are eventually ending up at 12v for the house battery, and charge controllers are rated for output amps, regardless of the input. Most of the better controllers have a PV voltage limit of 150V, that you must never exceed, so designing a string for 100v is usually pretty safe.
60A @ 12V is 720watts, so you could go up to about 1,000w in panels, and not max things out, unless you park on the equator, or on a 30degree hill, to get perfect panel alignment.