newbie questions, solar/lithium in a 5th wheel, where to start?

[sunshine_eggo]

For us, it came down to simplicity of use. The original, complex system did everything we wanted, but it was a cluge. Now that we have the MPII powering the whole AC distro panel powered via the MPII, the user experience is identical to being on shore power with the exception of load management while on batteries. Not much different than when we are at a campground with only a 30A hookup.

As far as brand, I got the blue disease. Once I got the Cerbo, I wanted everything on that slick panel. The only way to do that was to go all blue. I am even going to convert my tank monitors over to work on the Cerbo display.

The fever is WORSE than cowbell!

 

[Scycle]

Here's my diagram for my MPII install:

View attachment 79247

On your previous diagram with bus bars instead of the Lynx dist. you were fused 250A at the battery and now at 400A, so I was wondering the reason? I'm starting to sketch my system and fusing and wire gauge is my big hang up-where, what size fuse & wire.

 

[corn18]

On your previous diagram with bus bars instead of the Lynx dist. you were fused 250A at the battery and now at 400A, so I was wondering the reason? I'm starting to sketch my system and fusing and wire gauge is my big hang up-where, what size fuse & wire.

I only had 2/0 wire going to the MPII for a short period. 2/0 is good for 250A. Once I switched to 4/0, I went to the 400A class T.

 

[Scycle]

I only had 2/0 wire going to the MPII for a short period. 2/0 is good for 250A. Once I switched to 4/0, I went to the 400A class T.

I posted this in a different forum, but wondered if you would take a look at it and critique it?

 

[DonPhillipe]

Are you starting to see the picture?

No, I'm not seeing it for my own personal environment. The reason that mfgs go to higher voltages is as you pointed out, to save money on copper. (Plus there's the inherent advantage of an ignorant public that believes e.g. a 18V rechargeable drill is twice the device a 9V rechargeable is and will buy the high voltage unit over lower voltage every time.) What we are doing in upgrading is a one-shot and to save a few dollars on copper is not worth adding and dealing with the additional number(s) of a fiiniky buck converter(s) or a single one running all appliances which also hopefully assumes people are using 12V appliances and not running an inverter 24x7 like in a large home installation and thus using everything powered off 120V. Something also I have not seen anyone talk about here is as I have just done, going from 230Ah (115Ag) usable lead/acid, once I switched to lithium I found the overhead of all my fancy new equipment rendered my old 480W solar array incapabile of supplying my previous daily requirement of energy and that is because when you add fueling the additional overhead of "intelligent" BMS, "intelligent" solar charge controllers and all the additional blue tooth radios, and new interface devices, you've shot yourself in the foot due to the limited real-estate of the vehicle rooftop needing to be expanded just to keep up with the new amp-demand of all the monitoring equipment. Also regarding the concept of the base battery voltage not mattering, in a house, it's true that most people ignore and don't care what voltage level is on the feed line to the massive house inverter. In a vehicle, all your 12V appliances will be best run off direct battery connect and thus minimizing the points of failure and reducing the very hungry losses of a constantly running inverter or the lower but still notable energy loss through one or more buck converters. Also if you travel to remote areas, the least components to fail, the better off you are.

 

[DonPhillipe]

I spend more time designing things thinking what happens if something goes wrong

Always good to find a kindrid spirit. Don't loose the positive "negative attitude" I always say. Cheers to you my friend! You and I have shared bread with our fellow Murphy ;-)

 

[DonPhillipe]

purpose of adding a DC-DC

Another option if you have a high performance alternator, e.g. a Sprinter 150a has a common steady 30A commitment to keep the chassis components energized (45a if the A/C is going), so it makes a lot of sense to tap off that extra 120a that is just dormant with no need for a B2B/DC-DC If you then want to shut down the charge after you reach 90% capacity with that alternator "boost" and let the solar setup later "baby" the top-off routine, you can. Otherwise how much would someone be spending to add a DC-DC that would handle that extra 120A? Not sure if a 120a DC-DC is available but it's likely expensive. Secondly, most RVs have at least 2/0 going through a 200A solenoid to charge the "house/leisure" battery so if the alternator has the capability, the batteries take that much current, and the alternator is not of the modern/smart where coasting turns it into a electric brake category then that extra 120A is a lot of resource to be wasted stifling it down via a 30A DC-DC that most people can afford.

*** EDIT: My apologies, the topic is on a "5th wheel", there is no practical way to get that much DC current from an alternator to a vehicle towed behind. Therefore I retract my statement. A DC-DC or B2B will be required and for this I'd hope for one that used the highest internal voltage. In fact what I recommend to many 5th wheel drivers is assuming they have already laid out a sizable cash sum for an extremely elaborate 120VAC charger for the LiFePo4 in their rig, it makes a lot of sense to just put a heavy duty 120VAC inverter near the truck chassis battery and to run 120VAC back to the trailer, where the equipment you have already paid for can do it's normal job