System design question?

[carib_sun]

Hi all,
I am new to the forum, doing some reading and research, looks like a great group for information.
I have installed several grid-tie and off-grid syystems at my own places and for friends over a few years but never done any technical education. I have a specific system in mind to install in a 5th wheel trailer I keep in the UK but with US electrical system which I would like to keep as we live mostly on the left side.
Looking at the relatively new Midnite Solar MN3024DIY as a base, with room for four panels on top. I'm wondering if there's any reason I shouldn't use this inverter/ charger on the rig, being it is *generally* a static trailer, not mobile. I am thinking I could add a US (120V/60Hz) 12vdc charger for the house 12v battery that runs the DC lighting and water pump and keep separate, using the inverter system with a decent 24vdc battery bank to power the 120v appliances. Any thoughts or suggestions on this and suggestions on battery type and configuration also welcomed. Thanks in advance.
Dave.

 

[Vigo]

I guess my first question would be whether you need to power enough of an AC load to justify not just sticking to a 12v system?

 

[carib_sun]

I guess my first question would be whether you need to power enough of an AC load to justify not just sticking to a 12v system?

Fridge/ freezer, TV and enetertainment, there's an electric heater though I think I'll be installing a diesel heater. There will be a heated electric blanket in the colder months, so yeah, I think so.

 

[Vigo]

Im not exactly encouraging you to make it a 12v system but of those items the only things that would require a 1000w inverter would be the fridge (briefly during compressor starts) and the electric heater (which i would just encourage you to do the diesel heater and not run electric heat off inverters as an intentional design choice). So i would say keeping the system 12v is definitely an option for you. But if you want to run 24v that is no problem either, you would simply have to have a 12v battery charger involved.

As far as it being a mobile application i dont think it matters at all. I think one of the only real issues there is that some devices make a ton of fan noise and in an RV it's a bit harder to 'get away' from the noise source given all the space constraints. Other than that, i'd just say the devices need to be mounted in a way that they don't shuffle or bounce around when the vehicle moves. You can screw them down to anything and it should be fine. Nothing else about an RV can withstand the same G-forces as that inverter probably can. It's mostly about the rate of change.. bolting it to something limits those accelerations to how fast something can smack your 5000lb trailer around (not very fast), while if you let something slide and fall off of a shelf or slide along until it bangs into a wall, that's actually much worse. But no real worries about using it in a mobile app as long as it's mounted securely and not in danger of banging into things or other things banging into it.

 

[carib_sun]

Thanks Vigo, I appreciate your input. Do you think then, that I will find a better 12v inverter for the AC and would it have to be 2kW or under? Any suggestions on a quality inverter/ charger? I have only ever installed residential, 5-6kW and 48vdc systems before so I'm very limited in knowledge on these components. A big part of the reasoning looking at the Midnite Solar box was I've used their components and felt they are well built. This box has MPPT charge controller and 24v charger included, so it seemed like good value for money at $550 and at 17lbs is something I can easily pack in my luggage. Is there a reason to keep to 12v, other than cost of a split system? I would like to install Lithium batteries so a 110/12v charger is a minor cost to keep the house battery at 12v but open to your advice if there's better reasoning to stay at 12 for eveything. I also have rom for possibly four full sized panels on top so it's possible I could get 1300W+ up there. Again, your input is appreciated amigo. D.

 

[Vigo]

No big advantage to 12v other than not needing to have two ‘systems’, but its mot enough to make me have much opinion one way or another here. It would probably matter more if it were a motorhome aka ‘caravan’ ? with a 12v charging system you could make use of. 12v all-in-one options are limited to fairly small inverter sizes which would practically force you into a separate ‘component’ system of inverter/mppt/grid charger and if you aren’t being super specific about your requirements that’s mostly a downside in terms of complicating your design and install phases.

24v goes up to 3kw with numerous all in one options such as the one you showed. I have no personal experience with their quality but the internet leads me to believe they are one of the ‘old hands’ of the game and generally to be trusted. I dont see any problem with your original plan. In fact if the trailer doesnt already have a 120v to 12v ‘converter’ onboard which you trust to maintain the 12v battery, another thing you could do which is extremely cheap both in terms of money and energy consumption, is just to use a PWM solar charge controller with your 24v batteries as the ‘solar panels’, to maintain your 12v house battery. They consume almost no energy, dont require the inverter on or ‘shore power’ hooked up to function, and are adjustable in terms of voltage setpoints. I have done that with several different models and the one real distinguishing point between all the cheap models is that a very few have a current limit setting which allows you to set it not to ever run at its max current, which i consider is likely to extend its lifespan. Ive bought one like that for $23 although i couldnt find the exact model. You can get a 24 to 13.8v step down converter for the same money but you lose any adjustability to it. Either of those would not require you to run your inverter in order to charge to ur 12v system, although if you can program that inverter to only invert for certain hours of the day while you’re away it would accomplish the same main goal of not spending 40-60w continuously 24/7 just for the privilege of powering a 12v charger which might not even be doing 40w of charging to begin with.