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Pros/Cons of 120V only in new trailer build

hidiyguy

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I’m dreaming about the possibility of doing a full-size (28+ foot) cargo trailer to travel trailer conversion in a few years. A few reasons would be to build quality from scratch, better insulation, reduce likelihood of problems (solid water connections that are accessible, etc), no delamination to worry about, and to build split ductless ac, solar and LiFEPO4 batteries into the trailer without having to scrap some of what I paid for w/ rv purchase.

The purpose of this post is not to debate the wisdom of doing that, but to ask: What pros or cons am I missing of building a 120V-only system?

For my notional build, I would go with a 48V nominal LiFEPO4 battery pack to reduce inverter amp draw for major appliances (AC, Fridge, water heater), so adding 12V would require a 48V to 12V converter, adding another piece of hardware. Items that would typically use 12V (lighting, water pump) are readily available in 120V (can pick up lighting at any big box building supply store), so I’m struggling to come up with a solid reason why I would need 12V in the trailer (other than separate 12V tongue battery outside the trailer to power trailer brakes, brake and running lights, and jack). My build would not have powered levelers or slides.

Pros of 120V only:
- Less complexity in electrical system (no 48V to 12V converter or 12V distro panel)
- Lower gauge AC wiring possible vs 12V DC
- 120V components (particularly lighting fixtures, bulbs, outlets) readily available at big box stores
- USB charging outlets can be integrated into AC outlets (install AC outlets that include USB charging ports) vice separate i.e. not using 12V for USB
- Does not add significant sizing issue for inverter, as added 120V appliances (lighting, water pump) are not large draws

Cons of 120V only:
- Will need to up-size AC distro panel for a few more circuits
- Requires inverter to always be on, even for lighting (mitigated by fact 48V to 12V converter would have to be on to operate lighting on 12V, and fridge will be 120V and require inverter to be on anyway)
- Single source of failure for all electrical vs lighting and water pump separated on 12V (can mitigate by carrying a backup inverter and installing a few battery-powered lights for emergency use)
- Trades 48V to AC inversion loss in place of 48V to 12V (does not seem to be significant since inverter will be on anyway when trailer is in use)

What pros or cons of 120V-only am I not thinking about? Appreciate your thoughts, and huge thanks to all the contributors on this forum who have helped me envision this build as a real possibility--particularly DIY LiFEPO4 and split-ductless AC. Comfort of AC off-grid may give me a chance of actually selling this to my spouse over a pretty-looking purchased travel trailer with all the warts hidden from sight (and waiting to emerge after you drive it off the lot).

Hi from DiyGuy
 
Have not had coffee yet but which inverter{/charger} are you thinking of?
Are there any 48VDC ones that are targeted for mobile applications?

Edit: I see Victron has one.
 
Have not had coffee yet but which inverter{/charger} are you thinking of?
Are there any 48VDC ones that are targeted for mobile applications?

Edit: I see Victron has one.
Yes, although not all are marketed for mobile applications. Victron and Schneider Electric are two top contenders at this point due to ease of integration, but available options will likely change before I get around to building this.
I think the only "con" is a negligible efficiency loss via the inversion process.
I considered that, and while I haven't calculated the difference my gut tells me it won't be that much. Savings from not installating a 12V system could easily buy an extra panel which would more than make up for the difference
 
I run my home with 120V only, even my deep well pump 260' down is a 120V SoftStart Grundfos, can even run my Mig & Compressor (but they are quite impolite to solar, but had to try it) There is no difference to Inverter Efficiencies OR the interface between Inverter, SCC & Batteries, two sides of a kayak paddle.

Do NOT buy anything until you have a solid plan worked out, Failure to Plan is a Plan to Fail ! and it is COSTLY ! (not to mention angry spouse).
Conservation is Far Cheaper than Generation & Storage so carefully consider appliances..
a Hot Water Tank = Evil ! Powersucking killers ! Think of it like this, do you keep your car idling all day long in the driveway just because you may want to drive to the corner store for 15 minutes ? Well 15 Minutes of every hour a water tank is heating that water, "just in case you turn on a tap. On demand, even electric is far more efficient like Mini-splits, they make a world of sense. Cookstove, an Induction Cooktop is way more efficient than any other type of electrical cooking (except nukelators) BUT you have to be careful to get a properly EnergyStar rated one and not just something from WebStore cause it's cheap.

Soft-Start AC, fridges/freezers and High Draw motorised devices really take the "Hit" out of the equation on batteries which makes the entire system much happier & less stressed. Some can be bought this way (more coming available all the time) while many others (not all) can be retrofitted with a Soft-Start module to eliminate the Start Surge which can be up to 5X the Amperage Rating on the appliance/device. IE Compressor with pressurized tank, or any big electrical motor with heavy resistance.

BTW: Did you know that all LPG (propane) equipment can handle BioGas ? No need to modify burners or anything just a slightly different regulator and BioGas generator attached to it. People are using Biogas worldwide, even in North West Territories &, Yukon & Alaska, so if someone say it's won't work, hit Ignore, they are clueless. BTW, it can be ANY organic material like kitchen scraps to your own waste if you want. Not hard to DIY (done worldwide) or even a simple kit can be purchased. If using ONLY Organic waste (food scraps, lawn cuttings etc) the "residue" from the anaerobic digestion (AD) afterwards is also a Super Fertilizer the "Ultra of Compost Tea" to make your gardens grow like mad without chemicals ! Check into it, you might be quite surprised. (yeah, you can even run a genset (LPG Adapted one) with BioGas).

IMPORTANT NOTE: You mention a 48V to 12V converter. Mistake ! You would need a 60V->12V. Why 60V, because when charging 58.4V = 3.65Vpc per cell, this detail in CRITICAL, it is the fastest way to melt down a transformer/converter if it cannot take 60V and when they fail, they pass through the full voltage - imagine 48V hitting a 12V device... BtDt and NOT Pretty ! Fried my previous RV Furnace which was heating my powerhouse and in deep mid-winter no less so the building froze up, including my 50gal pressure tank (it's also my pumphouse).

AC-Socket + USB combo's are GREAT BUT... yep, there is a BUT... Do NOT buy offbrand or no name, seriously, there have been troubles. Eaton (Schneider company) or Leviton makes very good ones and worth the extra pessos. Now USB-2.0 and USB-3.0 are the way to go as USB 3 if more capable &higher power) and the newest standard.


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I also use Switched Plugs such as this from Leviton (they also make good AC-USB plugs too.

Codes Vary but this is basic, ALWAYS defer to your local electrical code !

AC Wire size is relative to the AC Side Only it doesn't care what is providing it or how. Therefore standard rue for gauges apply.
120V/15A=14/2 AWG, split 15A=14/3 AWG & two interlocked breakers.
120V/20A=12/2 AWG, Split 20A=12/3 AWG & two interlocked breakers.
!! Any wire used for any heating devices (water heater, baseboard and such) must be Red Jacketed.
240V/50A= #6/3 AWG 240V/30A = #8/3 pref but can goto #10/3 (not accepted by everyone..
verify to your local regional electrical code requirements.

Each 120V/15A circuit can have 10 devices (switches/plugs) same for 20A.
Kitchen plugs = 20A or Split-15A (3-wire & double breaker)
Any wet areas, bathroom, kitchen should also be CGFI. Some also require it in bedrooms now as well.
A separate Lighting circuit not attached to plugs is often suggested (some require it) and makes good sense to have lights if a plug pops a breaker.

48V@250A MAX = 12,000W = 100A AC power out (uncorrected for inverter inneficiency)
NOTE, 240V is only two 120V Legs at opposite phases. With 240V you can use a regular 100A Square-D House panels that have a 240V/100A Main breaker and then you solve two issues by not requiring a breaker between the Inverter & AC Panel. Then each leg powers the breakers at 120VAC but if you double the breakers you get a 240V Circuit (max 50A). In FACT, it is advantageous to have at least one 240V Circuit & plug which can be accessed... Call it Future Proofing, you may not think you'll need it but... I Regret not going that way because it limits options.... IE If I bought an EV with V2H (Vehicle to Home) capability (I'm offgrid so don't care about the pitiful grids) then I could charge / discharge from the EV as well... This is going to be quite common with EV's. Also having a 240V plus near an opening (window/door) you could run 240V extension if/when/as needed.
This would require #6/3 AWG from Inverter to Main AC Panel "Main Breaker".

I suggest Square-D "QO" series because they are simple, very good quality and quite affordable (all components) and parts (breakers etc) are available everywhere because they are so common. Check out the listings at Schneider-Electric Link Below.

NB: Surge & Lightning Protection is a MUST !!! I cannot understate the importance of this... One bad zot can fry everything, including you ! It's not funny, not a joke and Nothing to be Cavalier about. This is one area that is Woefully lacking in discussion & importance... More than likely because Will has never really addressed it in his vid's & tut's, but his Van-Life origins may have a lot to do with that. Use ONLY Top Quality protection devices like the ones Midnite Solar has,m for the AC & DC Sides. REF: Midnite Surge Protection Devices.

I have done house wiring in Renovations, restorations and new builds (my own) for a bit of time >30 yrs and always followed our codes & passed everytime without issue.

GROUNDING must be considered as well. AC & DC do NOT Share a Ground ! Imagine a 120/240V trip to the common ground and what that would do to the DC side... Just something to avoid... some might argue that, it's THEIR problem. Freedom of choice includes making Bad Choices.
The AC needs to be grounded and NOT to the trailer frame but to actual Ground. DC can be grounded to trailer frame. There are Code Rules related to this and they really are a wildcard pending where you are. RV's/Trailers and viewed & handled differently "everywhere" and some are downright mortifying ! AGAIN defer to your local codes or better ones if you feel they are loose. I'm not a mobile guy but have done much work on RV Trailers and it can be shockingly amazing what you find inside the high priced rolling coffins, some are gobsmakingly bad. Wiinnebego for one... Ohhh My.... And the older Terry Trailers are Gawd Awful !

I have schematics & diagrams of my 120V system in my "About my System" link at the top of my signature.
Hope it helps, Good Luck
Steve
 
When I have several cloudy days in a row, I like to hold off on using the 120 volt appliances I have enough extra panels that by doing this, the solar panels can charge the batteries back.

The idle draw of my inverter is 1 amp, which left on all night cam be 16 ah, and the most I’ve used overnight is 165 ah, so about 10% of production. Nothing turning a generator on for a bit and using the RVs converter to power up the battery bank won’t handle.

I find myself working on the RV a bit and its nice to plug a charger in without the need to turn the inverter on.

You’ve got a way to power the trailer breaks.

Those are the only reasons I can think of.
 
Thanks for the further comments. Will absolutely conduct an energy audit to size my system, and appreciate the reminder to size any 12V converter to the true voltage of the battery bank vs nominal. I'm really trying to anticipate how I would use the trailer and design the system to best meet that need (and planning 2-3 years out, so definitely not buying anything until I'm close to install time).

I had thought about the need to turn on the inverter just to use lighting as a drawback (such as when working on the trailer vs getting ready for a trip when the refrigerator also needs to be on); will have to more fully consider that or a workaround.

Steve- I have checked out your schematics...everyone posting their design is very helpful.

Thanks again for the continued comments to help me fully think this through.
 
The nice thing about using 12v DC devices, especially for lighting, is that they are made for what you're trying to do. Finding 120v AC devices that come in small formats may be more challenging. Everything should be LED for lighting, but you'll need a converter to step down to DC for most LED devices that would work well in a trailer. I'm thinking of LED strip lights here.

12v DC water pumps are much more readily available than 120v AC water pumps that fit well within a trailer.

Wiring for 12v DC is a lot smaller than 120v AC.
 
How’s this coming?

read this through

I’m an advocate of dual systems. It’s easy in my case because my inverter is 12V…

But basics for adequate lighting and convenience usb could outfit the whole thing at 12V for $100 including a bluesea fuse box, switches, and wire. And 12V dependable water pump will function.
I use shallow electric boxes with ‘normal’ household light switches for 12V lights. (In an emergency your 12V LEDs will still work at 9V…not as bright, but they will)

I like the redundancy- although my inverter’s on 24x7 because of the fridge now, I like the 12V simplicity. If you want more traditional-type light fixtures the RV market has a bunch of 12V stuff available.
 
A 240vac split-phase inverter usually does not put out its full rated power to a single 120v side.
 
This is for a future build, so I'm just using this time to plan. With a 120V fridge the inverter will always be on while camping in the trailer but I think I'm convinced of the benefit of having a 12v system for operating the lights independent of the inverter (while working on the trailer, as a backup so all electrical isn't down if the inverter fails, etc). Thanks for the inputs to help me think it through.
 
This is for a future build, so I'm just using this time to plan. With a 120V fridge the inverter will always be on while camping in the trailer but I think I'm convinced of the benefit of having a 12v system for operating the lights independent of the inverter (while working on the trailer, as a backup so all electrical isn't down if the inverter fails, etc). Thanks for the inputs to help me think it through.
If you add a manual transfer switch, you can always power the trailer from shore power when the inverter is down. Not trying to convince you of what to do one way or the other, but to add the 12v system for your stated reason only isn't necessary.
 
I am thinking about building a cargo conversion for much of the same reasons. I would be interested to hear more about that side of things. Maybe another thread, or forum?

Don't forget your trailer brakes will require 12v. This can be done with a small 12v battery that charges off the 7 pin connector. Or you can put in the 48-12v buck converter to run it for you.

I had not considered going 12v free until I read your post. Got me thinking a little about it. My knee jerk reaction is that it would be cheaper easier to stick with 12v for lights and maybe water pump. The low voltage is far safer easier to install and mount fixtures. Once you go 120 then you need junction boxes for splice and device.

Just my knee jerk thought process so far.
 
Don't forget your trailer brakes will require 12v. This can be done with a small 12v battery that charges off the 7 pin connector. Or you can put in the 48-12v buck converter to run it for you.
Not sure a trailer connector would provide enough power to recharge any RV battery. It’s a pretty skinny wire and things like Water pump and propane bower motor take up a bit more energy than a brake.
 
Not sure a trailer connector would provide enough power to recharge any RV battery. It’s a pretty skinny wire and things like Water pump and propane bower motor take up a bit more energy than a brake.

The 7 pin circuit rarely provides a lot of amps. 30 at the most, 20 on average. I tend to think of it as a maintenance charge. If the battery is depleted, it's not going to to bring the state of charge to 100% unless it's a small battery.

On a dual axle trailer, the breakaway system will draw about 12 amps if it gets activated. Power for the regular brakes is a different circuit that doesn't go through the trailer battery. My SeaFlo water pump is 17 amps max, but it's a step up from an OEM water pump.
 
had not considered going 12v free until I read your post. Got me thinking a little about it. My knee jerk reaction is that it would be cheaper easier to stick with 12v for lights and maybe water pump. The low voltage is far safer easier to install and mount fixtures. Once you go 120 then you need junction boxes for splice and device.
I’m weird in that I love being able to turn the inverter off- not that i do (refrigerator) but if things break I have lights and cell phone charger and my 300W pure sine inverter for soldering iron, whatever, while I fix stuff.
Some say it’s an unnecessary expense unnecessary ’pain’ whatever. It’s not that expensive and with the right parts-bin lighting you can have lights in the milliamp range quite inexpensively.

I will admit I like that my water pump is 12V, and I have a 3VDC converter to use with the tankless water heater.

Things look different now that I have an electric fridge. It’s a mind warp when you get to the point you don’t even think about that you’re 100% solar anymore and the inverter is on 24/7 but I like that I know I can take a hot shower even if the inverter calved out.

if I was 120V only I’d lose a level of redundancy that I find comforting
 
Not sure a trailer connector would provide enough power to recharge any RV battery. It’s a pretty skinny wire and things like Water pump and propane bower motor take up a bit more energy than a brake.
Absolutely. I point it out just to say regardless the OP will need a 12v system for the brakes.
He will either need to buck convert from 48-12 or maintain a small 12v system the brakes alone.
 
Absolutely. I point it out just to say regardless the OP will need a 12v system for the brakes.
He will either need to buck convert from 48-12 or maintain a small 12v system the brakes alone.
Was a brake system not already on it? I would hope so. With the professional conversions, don't they usually install a separate battery for the trailer brakes?
 
Was a brake system not already on it? I would hope so. With the professional conversions, don't they usually install a separate battery for the trailer brakes?
HRTKD mentioned it already but on RV trailers the house battery is your brake battery. To add a Cargo trailer (with brakes) will come with a small 12V battery already setup for the brake system. Its the reason I mention. Regardless you end up with a small 12v system regardless of going 120v/48V or not. You still have a 12V system albeit small.
 
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