RV 48V to power 12v Loads

[Ozark]

Whenever you have your 48V inverter running, or shore power just use one of these :

https://www.amazon.com/gp/product/B085RXS63Q/

The last 12V 100Ah LiFePO4 battery I bought was just over $170 with tax, delivered. Add the charger and you’re still under $200 for everything.

Also, there are many MPPT’s that can charge both 12 and 48V nominal LFP.

Your choice but dismissing a 12 and 48V system often costs more. Remember that step down converters draw power when idle also but a simple switch can solve that issue with minimal additional complexity.

Hi Jo,
A little charger would be fine for a couple of lights, but 30w is a little frugal even for me.
The point of a bigger charger is to be able to get off shore power or the generator faster.

I'm not dismissing a 12/48v system, as mentioned, it's what I have. I'm merely pointing to some of the considerations getting there:

1. check your house 120/12v converter for LFP compatibility,14.4 volts (etrailer has info) It might be cheaper/easier to just switch to a 12v LFP
2. If you are combining, check your loads. Use an clamp meter to check YOUR draw from jacks etc. to find how big/how may converters you might need (I know Victron says theirs can run parallel) My setup uses much less than others report.
3. check any appliances or equipment for minimum voltage requirements. For example my fridge wants 12.2 or alarms even tho actual cutoff is 10.something volts. The converter I bought puts out a steady 12.1 and the fridge puts out a steady beep beep beep. Probably better in my case to have purchased THIS 13.8v. Or the Victron Orion 48/12 30a with I think 10-15v adjustable, and 40a surge

 

[JoeHam]

Perhaps I don’t understand your use case, here is mine :

I run 12V nominal ham radios in an off grid setting in a 20ft steel shipping container. They pull 20 Amps plus on an intermittent basis (like your jacks are intermittent). Over a contest weekend I will use 100Ah.

I also have a 48V inverter running to power the computer, lights, a small heater or fan as needed. Since the inverter is already on, with power to spare, I continuously run the small +/- 30W charger on the 12V system. Over a 48 hour contest weekend that is plenty to keep the 12V battery topped up for the intermittent use.

IF you are going to have shore power, OR a 48V inverter running anyway this is an inexpensive way to keep your 12V needs satisfied. Especially if those needs are intermittent use of leveling jacks and low draw lighting.

In addition, my solar panels can charge either my 48V or my 12V system depending on which needs it most. IF the little/cheap charger gets behind I just direct solar power to the 12V system.

Your system, your choice. Just another way to approach it.

 

[Ozark]

Hi Jo

My main concern is running a 12v fridge as I am a type 1 diabetic and insulin likes the cool. I hope to do lots of dry camping as we transition to full-timing for a while. Hopefully be on shore power <50% of the time.

Fridge pulls about 100w when running. How much it runs of course depends on the season. Summertime it probably runs a good percentage of the time. 100w x 24 hours = 2400 w/h a day (throwing in misc pumps, jacks, etc).

2x 100Ah 12v FLAs is what I tried last year and they didn't fare well. This kinda surprised me because I would top them off daily either from shore or by "plugging in" the house cord to my 48v system. I had kept it seperate electrically and just provided a 30A outlet.

I only have 1200 nameplate watts of PV at this point and since they are flat unless I'll be in place a while I net much less. I hope to pick up some used or blems down at SanTan to ground deploy for the other charger. The reason I used the 6548 is it can use all the power my little Honda inverter can produce and I can taylor the charger to take the most efficient amount.

 

[JoeHam]

Well now I have to change my caveat to : your system, your health, your choice .

My rationale for my system choices is above and I can’t add anything more.

I’m sure you’re aware that insulin loses potency when not refrigerated so as long as you’re titrating administration amounts to your blood sugar levels it wouldn’t be life threatening of course. You would use a slightly larger volume for the same effect.

Here is some information about unrefrigerated insulin storage that you probably know :

https://www.goodrx.com/conditions/diabetes/how-long-can-insulin-be-out-the-fridge

Good luck with whatever choice you make.

Joe

 

[OffGridInTheCity]

I do 48vdc -> 120vac (MPP Solar 3048LV) and use a 120vac -> 12vdc @ 80a converter for my 12vdc subsystem. I have AC on all the time as I use a mini-split for heat/cool and all electric kitchen etc. The 120v -> 12vdc draw/efficiency-losses are negligible.

There are many to choose from, not pushing anyone in particular, but here's a random 50a example on AMZ - https://www.amazon.com/12V-50A-600W-Power-Transformer/dp/B09NJLNYKH/ref=sr_1_6 - with voltage adjustment. I set mine to 13.5v (or something like that) for the Maxx Fan but not sure it mattered.

Surprisingly (in a good way) the units have held up over very rough roads (washboard and gaps in pavement) type of thing - no issues at all.

 

[Ozark]

Thanks for the link Joe. I have a "supply" of insulin I've built over time. As you say, it doesn't spoil as rapidly as advertised at room temp, but likewise it's shelf life is longer than the 2 years in the notice. Bu to last it wants to be cool.
Sorry for the OT.