RV 48V to power 12v Loads

[mkgolfer]

Hi All,
I am just starting my journey into "off griding' my RV. To start, I need a battery or batteries to power my 12v loads. I was looking at Will's upgraded DIY EG4 hand cart vid and noticed he used a 48V server rack battery with a 48v to 12 step down. In Will's video, he said you could power 12v loads doing this. I was wondering, can I use a 48v battery, attach a 48v to 12v step down and attach the 12v side of the step down to my RV 12v loads? Perhaps attach the 12v step down side to a bus bar and attach my RV 12v load to that bus bar?

If I can do that, would I need to disable/shut off my on board RV converter/charger? Is this even possible?

Thanks A;;

 

[justinm001]

First check if your on board converter/charger can support LFP batteries. If so and you're not planning a lot of amperage then it makes more sense to just keep 12v.

 

[McKravitts]

There are numerous 48 volt DC to 12 volt DC converters out there. Most are rated low wattage, like around 100 watts.
You might have to use more than one, but they should work.

II've been using a small low power one and I never shut down my inverter charger.

 

[HarryN]

If you have a lot of 12 volt loads, there are some higher power converters out there.

For a rugged, wide temperature range converter, secamerca makes some - not cheap but bullet proof.

 

[Scoob]

Make sure you check all the loads. The electric jacks or the hydraulic pump for the jacks and slides pull a LOT of amps.

I tested a hyd pump and it peeked at 130 amps and pulled 60 amps loaded.
The electric leveling jacks I checked peeked at 85 and pulled 35 loaded,

 

[Ozark]

Same situation here, 2-48v EG4 batts, 6548 all-in-one, Renogy PV on the roof, Daygreen 400w 48-12v converter to run trailer stuff.
The converter puts out a solid 12.1v at the terminals and runs everything fine...
...except the Norcold 12v fridge that wants 12.2 or it will beep incessantly.
So now I have to buy another converter, 48v to 13.8v, not a bank buster but a pain nonetheless
so check your loads

 

[Dave in AZ]

With the huge 12v dc loads on an Rv for jacks, leveling, like scoobs mentioned above, the 48>>12v converters don't look to provide enough power, 100 to 400W. I would think you could keep a single 12v battery though to supply those large loads, then have it constsntly recharged from a converter. Then you could get by with a larger drain on your single 12v, knowing it would recharge in a few hours.

 

[Ozark]

Hi Dave
My rig is only 25', 7k lbs, the tongue and stabilizers pull less than 13amps, so 150w on a 400w converter. Not sure what others might need.

Lead acid as we all know is terrible (my 2 brand new100ah deep cycles would run down overnight running the fridge which probably killed them). Most older and I guess many new RVs (mine is only a couple years) have chargers with output too small for lithium which needs 14.4v. You can get a replacement charger for $300 - this one would fit my load center: # PD9160ALV But after killing my batteries last season it didn't make sense to replace the charger AND buy new 12v Lithiums for however many more hundreds when I have 10kWhrs of 48v.

I had purchased the 48v setup for an off-grid situation that is yet to materialize so started from that.

 

[RvNaut]

I have this in place. below is a diagram of the system (not final design).

I used a Victron 48/12 converter. It prevents back flow of voltage. Note I have left a 12v battery in line so as to not hammer the converter and it give run time if/when I need to shut own the 48v.

 

[justinm001]

I'm hoping Victron releases an Orion XS 48/12 as it's very efficient and has current limiting plus vedirect so you can automate.

Even better if they do a 12/48 also. I could then have both setup so can go both ways and keep battery banks at even levels.

Just think, we could have solar charge 48v bank then it send to the 12v bank and not need 4x the mppts. Perfect use case for lead acid 12v and LFP 48v as you can quick charge from mppts then the XS will slow charge the LA all night

 

[rustythorn]

I'm hoping Victron releases an Orion XS 48/12 as it's very efficient and has current limiting plus vedirect so you can automate.

Even better if they do a 12/48 also. I could then have both setup so can go both ways and keep battery banks at even levels.

Just think, we could have solar charge 48v bank then it send to the 12v bank and not need 4x the mppts. Perfect use case for lead acid 12v and LFP 48v as you can quick charge from mppts then the XS will slow charge the LA all night

i'm hoping for more options too, i've not yet settled on how to deal with my 12 volt needs. originally i wanted to eliminate all of them and run everything on 48VDC or 120/240VAC but i realized i could save some power [eg 50-100 watts a day] by having a 12v system to run items that are optimized for 12v. especially since i already have a 12 volt system being lazy in the van. my plan is to beef up the existing 12v system either with dual deep cycle lead acid or lithium. right now, i'm considering giving the 12v system its own SCC and dedicated solar panel [50-100 watts] that plus vehicle charging should be enough but i wouldn't say no to a better system.

 

[justinm001]

i'm hoping for more options too, i've not yet settled on how to deal with my 12 volt needs. originally i wanted to eliminate all of them and run everything on 48VDC or 120/240VAC but i realized i could save some power [eg 50-100 watts a day] by having a 12v system to run items that are optimized for 12v. especially since i already have a 12 volt system being lazy in the van. my plan is to beef up the existing 12v system either with dual deep cycle lead acid or lithium. right now, i'm considering giving the 12v system its own SCC and dedicated solar panel [50-100 watts] that plus vehicle charging should be enough but i wouldn't say no to a better system.

Well I went all out. Have 48v with dual Quattro 5k in split phase, then AC to the 12V Quattro 5k. 1500w solar on 48v and 300w on 12v. Then have alternator splitting to both the 12v and 48v. I realized I can save 80w idle load by shutting off my 48v inverter and putting all main loads on 12v, then turn on the 48v inverters for most of the ACs and cooktop and such.

Couple things I learned:
It doesn't make much sense to have solar on both.
It's much better to have 1 bank always fully charged then the other low instead of both at like 80%.
It's nice to have things auto shut off so when I get to 50% 1/4 of my outlets don't work then 3/4 shuts off then all dead. This way if I leave a dehumidifier on pulling 700w it'll shut off at 50%.
The DC to AC losses aren't that much and so much stuff is easier to just run off 120v. I have a backup 120v to 48v and 120v to 12v 8n my lighting area so if 12v is dead I can run that and it'll give me lights. (or precharge inverters

 

[rustythorn]

Well I went all out. Have 48v with dual Quattro 5k in split phase, then AC to the 12V Quattro 5k. 1500w solar on 48v and 300w on 12v. Then have alternator splitting to both the 12v and 48v. I realized I can save 80w idle load by shutting off my 48v inverter and putting all main loads on 12v, then turn on the 48v inverters for most of the ACs and cooktop and such.

Couple things I learned:
It doesn't make much sense to have solar on both.
It's much better to have 1 bank always fully charged then the other low instead of both at like 80%.
It's nice to have things auto shut off so when I get to 50% 1/4 of my outlets don't work then 3/4 shuts off then all dead. This way if I leave a dehumidifier on pulling 700w it'll shut off at 50%.
The DC to AC losses aren't that much and so much stuff is easier to just run off 120v. I have a backup 120v to 48v and 120v to 12v 8n my lighting area so if 12v is dead I can run that and it'll give me lights. (or precharge inverters

yep, dual separate solar systems is a bit silly and i hope to find something better but my situation is a little different; i don't have an alternator so unless i use a DC/DC from the 48v to the 12v i would have to rely on the small amount of power from the native 12v system in the van. i could of course use a DC/DC from the 48v to charge the 12v but that would be just as inefficient as DC/DC from the 48v to power the 12v items directly. plus by beefing up 12v system i can add a little more to the total storage of the van with very little additional room or space. i figure run about 100-200 watts of per day from the 12v system. that plus the 50-100 watts of power savings results in a total off loading of 150-250 watts per day from the main house battery. but all of that is still in the drawing board stage

 

[justinm001]

yep, dual separate solar systems is a bit silly and i hope to find something better but my situation is a little different; i don't have an alternator so unless i use a DC/DC from the 48v to the 12v i would have to rely on the small amount of power from the native 12v system in the van. i could of course use a DC/DC from the 48v to charge the 12v but that would be just as inefficient as DC/DC from the 48v to power the 12v items directly. plus by beefing up 12v system i can add a little more to the total storage of the van with very little additional room or space. i figure run about 100-200 watts of per day from the 12v system. that plus the 50-100 watts of power savings results in a total off loading of 150-250 watts per day from the main house battery. but all of that is still in the drawing board stage

The new OrionXS is like 98% efficient. If they only make a 48/12 you'd be all set. That makes it as efficient as voltage drop on 12v cables over 48v

 

[Ozark]

I used a Victron 48/12 converter. It prevents back flow of voltage.

Thanks.
Can you tell me where this is documented?

 

[Dooug]

Definitely gaps in the 48/12 market. 24 volt more options for power conversion. But the 24v market has it own quirks as well.

 

[JoeHam]

It might be much easier to add a 12V LiFePO4 battery and be done with it

 

[Ozark]

It might be much easier to add a 12V LiFePO4 battery and be done with it

Depends on the rig, the charger needs to be capable of charging a LFP. My fairly new trailer can't do it stock, it would need a $300 upgrade, plus the cost of the battery. The upside is it would still be outwardly "stock".

 

[millsan1]

On my electric UTV, i have a 2000 watt inverter connected to my 48V batteries to power 120 loads.

 

[JoeHam]

Depends on the rig, the charger needs to be capable of charging a LFP. My fairly new trailer can't do it stock, it would need a $300 upgrade, plus the cost of the battery. The upside is it would still be outwardly "stock".

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.