Question about power station providing back-up to trailer battery.

MadCityJack

I have a TAB 320 teardrop trailer with a 3 way fridge that runs fine on propane with minimal draw on my 90 ah wet battery.

I do have 135 watts of solar panels for charging, but I often am in forested/shaded areas and get minimal sunlight for charging of the battery.   My multimeter indicates that I am getting down to 60% SOC, which creates a bit of anxiety about the fridge.   As of yet, I am not ready to purchase a Lithium battery but it is on the horizon.  

However, I recently purchased an EcoFlow River Pro (720 watts) and I wondered what would happen if I plugged the 12v regulated output (8 amp max output) of the River Pro into the 12v output socket of the trailer battery (I would make a two male plug connector).  I should point out there is no easy access to the 12v wires to the fridge for directly connecting to the River Pro.  

My first, likely naive,  thought is, I would charge the wet battery (BTW: I am not connected to the tow vehicle at this point), but wonder.   Thanks in advance for your input.  

VictoriaP

Is there a reason you don’t want to use a smart charger? Most of us just put a pigtail on the battery and hook up something like a NOCO Genius between the powerbank and the trailer. 

MadCityJack

VictoriaP said:

Is there a reason you don’t want to use a smart charger? Most of us just put a pigtail on the battery and hook up something like a NOCO Genius between the powerbank and the trailer. 

I didn’t mention that this would occur while boondocking.  No AC.  

VictoriaP

Does the EcoFlow not have a 110 outlet then? Every battery pack I’ve seen that’s big enough to provide supplemental power to a trailer has an inverter and 110 outlets built in. I’ve used my Goal Zero Yeti in exactly this way before. I’ve also just used a 30 amp to 15 amp adapter and plugged it into the GZ without the charger.

MadCityJack

I know that DC to AC conversion results in loss of efficiencies due to the inverter, so I was wondering if there was a work around just using DC to DC.  I do appreciate that direct charging DC (power station) to AC (out from inverter) to DC again (converter/Noco) will likely be inefficient but I do not know the extent.  However, in an emergency, definitely yes.   Thank You.

Denny16

If the battery in the power unit has a higher voltage than the TaB battery, it will charge the TaB, and run the 12VDC circuit.  But if the TaB battery is a higher voltage, then they will both power your TaB 12 VDC circuit.  That said, if the TaB 12VDC 
load from the TaB exceeds the capacity of your portable system, or it could damage it, or the unit will just shut down.
cheers

MadCityJack

@Denny16 Well that was straightforward.  Thank you.  After some reading I learned that while the regulated output of the portable unit I am using is at 13.6 v, (10 amps) likely adequate for bulk charging of a lead acid battery, the current (10 A) would not go down after a 70%-80% charge.  That is, unlike a dedicated charger (e.g. NOCO) the portable unit doesn’t allow for the required drop in amperage at 70-80% charge associated with the absorption and float stages for optimal battery lead acid functioning.  I am speculating that in an emergency the direct DC transfer from a regulated portable power station to the TAB battery, could be helpful, minimizing the inefficiencies associated with going through the portable unit’s inverter to a NOCO (or similar charger) and then to DC again.  However, regular use of the portable power station is to be avoided because it would lead to sulfation and premature battery failure.  Also, the NOCO and similar devices would be sensitive to temperature changes, modulating voltage for optimal performance.  Do I have this right?

Denny16

Yes, yes you do.  I agree with that assessment.  The portable power stations are not designed to be a house battery charger, rather a power source for devices running off 12 VDC, camping lights, lphones which are self regulating during charging, etc and 120VAC appliances.  It could also power other DC devices, like a CPAP machine, the TaB TV monitor, a DC portable cooler, etc.
cheers

ScottG

I don't know the answer to the original question regarding charging the battery via the 12V "cigarette lighter" but am also curious to know as I encountered the same question recently with regard to an unrelated matter.

My suspicion is that this will not work. It can work in an automobile because the circuits are more direct, but in an RV the circuit passes back through the mysterious innards of the converter.

MadCityJack

@ScottG Perhaps the safest approach, if necessary, would be to use a 12v cigarette plug DC out from the portable power station to alligator leads to attach to the house battery; disconnect house battery from camper.  With my Eco Flow River Pro, output v is 13.6 and amps are limited to 8 (which is higher than my old 6 amp Schumacher charger).  It would be slow charging nonetheless.  

Denny16

Jack, that would charge the battery quicker, but not any safer, as you are only eliminating the trailer circuit loads.  It will get more energy to the battery connecting directly, but it is still going to be a trickle charge anyway…
cheers

Pschwalb

@MadCityJack sorry to resurrect an old thread. I've been trying to do the exact same thing and think I've got a solution. Optimate makes a portable dc to dc charger. Using an adapter, you can plug one end into the power stations dc out (cigarette lighter) and the other end direct to the house batteries. It's only 2 amps, but avoids the conversion loss and provides a regulated charge. 

Viajero

Pschwalb said:

@MadCityJack sorry to resurrect an old thread. I've been trying to do the exact same thing and think I've got a solution. Optimate makes a portable dc to dc charger. Using an adapter, you can plug one end into the power stations dc out (cigarette lighter) and the other end direct to the house batteries. It's only 2 amps, but avoids the conversion loss and provides a regulated charge. 

We do this with our Tesla. A DC to DC converter connected from the aux port in the trunk of the Tesla to the T@Bs 7 pin. Works well. We added a couple meters and installed it in a little tool box just for giggles.