12v? 24v? 36...48v????

[TurnThePage]

I'm very near to picking up a new travel trailer that I intend to pack with solar and LiFePO4 batteries. It's a 30A 120VAC RV. I understand the electrical wiring advantages of the higher DC voltage configuration, but what does everybody do with their 12v appliances?

I'm hoping for around 1500 watts of solar and no less than 1000Ah of 12v batteries. Is there a good reason not to stick to a 12v configuration?

[2oldman]

Grit dog wrote:
Hope this helps! Cheers!

Nothing you say helps, but you are quite the comedian.

[Cptnvideo]

FYI, my Victron 150/100 allows me to choose between 12,24,36 or 48 volt output. I have 8 200 watt panels, 4s2p. My Victron typically shows between 92 and 101 max voltage from the panels each day. I have a 12 volt system, 5 206 ah SOK LFP batteries. Controller, batteries and 3k inverter are within a few feet of one another. A whopping 16 feet of 4-0 cable.
I have a 20cf residential fridge and 3 A/C units, with 1 having soft start. My 12 volt system will run any one of the A/C units, probably 2 for an hour or two, although I've never tried it.

[2oldman]

StirCrazy wrote:
I haven't seen a 30amp mppt that will take a 48v input,

That would be unusual. Many controllers will take up to 150vdc input. It's the output at 48v that might be a little more difficult to find.

[3_tons]

Per StirCrazy : “also at 0 degrees F SiO2 only have 60% of there rated capacity, where LFP has 80% so even in cold situations you have more power available, just have to warm them up to charge, oh wait they have built in heaters also.... “

Sage points spoken…..What Say PianoTuna??

(Note that StirCrazy owns both SiO2 and LiFePO4…).

3 tons

[pianotuna]

Morningstar 30 amp allows up to 150 volts input.

[StirCrazy]

afidel wrote:

StirCrazy wrote:

afidel wrote:
Personally I'd run the 12V stepdown converter into a 12V battery, either lithium or SLA. That way peak loads for the slide motors and compressor motor get taken up by the 12V battery and the 12V converter can just top that off. I know there are folks that team a couple of 12V stepdowns together to supply the loads, but it has to be much more stressful on the components in them than if there was a decent pool of ampacity there. Since you aren't actually using it for storage capacity a 50Ah 100A LiFePO4 would work great and they're like $160.

The big advantage of 48V is you can use a much cheaper MPPT controller since they're basically priced on output amps and 48V is 4x lower amps for the same watts. Wiring costs are also much lower since you get to drop down to wire gauges which are commonly available instead of double 0 or triple 0 cables.

but thats like I said, keep the battery side all 12 volt and use a MPPT charger (more expensive by the way not cheeper) and stack the panels to 24v. you could probably spend a little more and get one that will handle a 48 volt input, but I don't know if it would be worth it for most people in a rv setting. the one problem you do run into with a all series run is shading.. in a home system where you have solar out in the open it isnt an issue, but for a lot of camping it is. I guess you would have to look at the price increase to a 48v input MPPT VS the upgraded wire size for the 24V setup. wiring is going to be an issue anyway you look at it with the size he wants to run so it will have to be resized.

edit, I did look at my brand and a MPPT charge that wil handle a 48V input is only 160.00 more canadian (one size biger) so it will be tight as to which way is cheeper, but I would go that way myself four 24V panels in a 48V series / parallel set up get the smaller wire size and you get some protection from shading.

What I was saying is that a 30A MPPT can put ~1,500W into a 48V system, to accomplish the same with a 12V battery system requires a 120A MPPT controller which are 3-4x the cost and several times the size and mass.

I haven't seen a 30amp mppt that will take a 48v input, but I am sure there are, my 40Amp will only take 24V input so if I want to add another panel to my camper which I am planing on I have to do parralell, or buy the 60amps controler which will take 48V of panel input, and that is only 100 bucks more than the 30 amp 24v one. so ya I get where you coming from, i just don't see that much of a price increase. my little 40amp will handle 1040 watts of 24V input, which to be frank is more than I will ever use in my little camper, but I will have to put them in paralell as it won't handle 48v haha, but my 5th wheel is getting upgraded to 12 to 1400watts of panels so if I get the 60amp verion of my mppt it will take 48V so I would still have to do a series/paralell setup using 24v panels and I'll just pull new wires down and mount the charger right at the batteries. but if there are reasonably priced 30amp 48v mppt controlers let me know that might be another way for me to go on the 5th wheel. doing 4 smaller 24v panels and still be around 1000watts and more efficient than that 480 watt pwm set up it has now lol. its funny I get more AH of charging from my 325 watt MPPT on my camper than I do on the 480 watt pwm on the 5th wheel in a day.

[StirCrazy]

pianotuna wrote:
StirCrazy SiO2 make lifepo4 look bad when truly large draws are needed. So why would I get a battery that has essentially a "limiter" (otherwise known as a BMS) on it at 1 C????

that all depends on the size of the battery and the brand, the dragonfly 270AH LFP have a 300A continuious discharge and peak up to 500A, and thats just having one. if you have 4 of them that gives you 1080AH available and a continuious discharge of aproximatly 1200A if you need it. how many people draw that much?

also at 0degrees F sio2 only have 60% of there raited capacity where LFP has 80% so even in cold situations you have more power available, just have to warm them up to charge, oh wait they have built in heaters also....

[StirCrazy]

CA Traveler wrote:
StirCrazy Serial panels with bypass diodes which all large panels have is more shade tolerant than parallel panels and this is especially true when there is shade like a A/C involved. It's a factor but not necessarily hugh.

I wanted a more efficient system but adding another panel may be a better price performance option.

For me 1500W solar systems "require" the larger 60/72 cell panels and MPPT. 12V panels for 1500W is certainly possible but last time I looked more panel cost and more panel square footage.

yup I have the 72 split cells on my camper (24V) which is what I recomended. I don't think I'll ever use 12v panels again. and I don't ever recomend a PWM controler even if you just have 1 12v panel. so much more effiency in a MPPT. I think what I said before (whith out going back and checking would be four 400 watt panels if there is the room giving your 1600 watts, depending on the controler you can do two series strings in paralell wich will keep the input voltage at 48V and the controler will convert that to 12V high amp charging. because you can place the solar controler right beside the batteries the cost of thick cable will be minimal and you won't need to spend the extra 1 to 2K on a step down converter to make it 12V again for powering the rv.

[TurnThePage]

2oldman wrote:

Cptnvideo wrote:
I don't see any benefit to adding components (that can possibly fail) to convert back to 12 volts when a 12 volt system is adequate for what the OP is trying to do.

I don't know what the OP is trying to do. He's been a bit vague.

Sorry. Don't mean to be vague. I'm closing in on retirement, and intend to adventure a LOT. I'm considering adding a small (8-9000 BTU) mini-split, which should run quite nicely on the system I'm planning. When I started this post, I wasn't specific about my needs, I just wanted other points of view on the various options. I'm still leaning toward keeping it 12v, but am also learning along the way. I could easily change my mind before I've even acquired a single component. This discussion is probably as good as I've seen about this subject. Thank you all for that.

[3_tons]

I would only add that for those worried about 12v voltage sag ‘when under a SUDDEN HEAVY load’, Lithium is your battery of choice…Example, a lone Aims 100a/hr Li is capable of 200a for up to 10 sec - Because of this (from only one battery !!), and the relatively stable voltage under load, it’s a bit of a stretch to imagine a real world amperage deficit scenario (despite PT’s belabored ‘fear’ campaign - lol)…

3 tons

[pianotuna]

Cptnvideo,

Charge controllers are more efficient and cheaper at 48 volts.

Inverters are more efficient at 48 volts.

Inverter / chargers are more efficient at 48 volts.

At about 600 watts of solar, MPPT controllers start looking extremely attractive.

For the OP with 2.5 times that amount it is a no brainer.

If a dc 48 to dc 12 converter failed, the OP could easily reconnect the OEM converter to power 12 volt loads. In my case, that is exactly what I did when my Magnum inverter/charger decided to burn up.

Even a tiny 12 volt battery would be enough to supplement the OEM converter for use when operating slides.

The chances of both the converter and the dc to dc device failing at the same time is pretty small.

[Cptnvideo]

From what I have interpreted, he wants a helluva solar setup for a 30 amp RV and he has heard of 24 & 48 volt systems.
While there are advantages to those systems, I just don't think they would apply in his case.
My limitation is my 3kw inverter output. My 12 volt batteries can supply more than the current the inverter needs to produce 25 amps.

[Grit_dog]

Cptnvideo wrote:
Old man, I didn't say anyone was incorrect. If you're quoting me, please quote all of the post.
I don't see any benefit to adding components (that can possibly fail) to convert back to 12 volts when a 12 volt system is adequate for what the OP is trying to do.
My 12 volt setup works very well in my 50 amp RV and the OP is buying a 30 amp RV.

I’m with ya…

[2oldman]

Cptnvideo wrote:
I don't see any benefit to adding components (that can possibly fail) to convert back to 12 volts when a 12 volt system is adequate for what the OP is trying to do.

I don't know what the OP is trying to do. He's been a bit vague.

[Cptnvideo]

Old man, I didn't say anyone was incorrect. If you're quoting me, please quote all of the post.
I don't see any benefit to adding components (that can possibly fail) to convert back to 12 volts when a 12 volt system is adequate for what the OP is trying to do.
My 12 volt setup works very well in my 50 amp RV and the OP is buying a 30 amp RV.