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pedwards2932 View Drop Down
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Posts: 333 		Direct Link To This Post Topic: Charging while towing
    Posted: 18 Dec 2020 at 4:46pm
I have my pod in storage and needed to charge the battery.  I hooked my inverter to my Escapes 12v plug and used a charger I had.  It is a 10 amp charger and it draws 1.9 amps.  It worked perfectly so I suspect if I wanted to run a charger while underway I could do it easily with no additional wiring.  Not sure how much draw the inverter uses running the charger but it is not an issue when engine is running.
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offgrid View Drop Down
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Posts: 5290 		Direct Link To This Post Posted: 25 Oct 2020 at 4:34pm
Originally posted by StephenH

This is still counter productive. Why not just run on propane while not connected to shore power. That is what I have done until I recently completed the DC to DC charger for the LiFePO4 battery. I also had a problem with charging while the refrigerator was on 12V power. We ran with propane for 4 years with no issues.
+1, I already suggested that. Consider that 12V operation isn't even an option on the new rPods with the larger fridges, either your fridge is off while towing or you run on propane. Some folks just aren't comfortable with the propane on while towing I guess. 
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StephenH View Drop Down
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Posts: 6417 		Direct Link To This Post Posted: 25 Oct 2020 at 4:19pm
This is still counter productive. Why not just run on propane while not connected to shore power. That is what I have done until I recently completed the DC to DC charger for the LiFePO4 battery. I also had a problem with charging while the refrigerator was on 12V power. We ran with propane for 4 years with no issues.
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offgrid View Drop Down
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Posts: 5290 		Direct Link To This Post Posted: 25 Oct 2020 at 4:18pm
Ok, but you would have the same issue running a new 120Vac line, right? Plus that would need a mounted 120Vac rated receptacle in addition to your 7 way connector. And you'd need to work up a locking system for the plug running from that receptacle to the charger so it didn't fall out on the road. 

I really think that if you don't want to run a larger conductor you would be better off with a dc/dc converter. Simpler and more efficient, and you can use your existing 12awg line for it. Run that to the dc/dc mounted in the trailer and from there to the trailer battery. You might try something like this and see it it works for you:
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1995 RV6A Experimental Aircraft
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pedwards2932 View Drop Down
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Posts: 333 		Direct Link To This Post Posted: 25 Oct 2020 at 3:43pm
Running a large wire on the Escape would be impossible for me,  you have to jack the car up so I would have to take it in and pay to have it done....about $150.
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offgrid View Drop Down
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Posts: 5290 		Direct Link To This Post Posted: 25 Oct 2020 at 3:37pm
Ok, I think I get it now. 

Ultimately you would need to run a permanent 120Vac line to the trailer. So, if that is the plan, why not just run a heavier gauge 12Vdc line now and be done with it? 10 gauge is what I and I think most of us have and that works fine to run the fridge while on the road. The voltage drop from that is only about 0.5V at 12A. Since you already have 12 awg running you could also just add a second 12awg conductor in parallel with the one you have and that would even be a little better than one 10 gauge.

The absorption fridges require a continuous heat source so the 12Vdc element just stays on all the time. 

Re efficiency, if you run straight dc from the TV battery to the trailer battery, the only loss is the voltage drop in the wire.  If you proivide energy via an inverter and charger then the losses would be the voltage drop from the TV battery to the inverter (significant), the efficiency loss in the inverter converting 12Vdc to 120Vac (about 0.85), drop in the ac cable to the trailer from the inverter (insignificant), the efficiency loss in the charger converting 120Vac back to 12Vdc (about 0.85), and the wire loss between the charger and the trailer battery. You will wind up needing about 20A out of your alternator/TV battery to get 12A to the fridge.  Also, you will end up with no current flowing through the existing 12awg dc circuit because the charger would be trying to maintain the trailer battery at a higher  voltage so current would not end up flowing through the 12awg connector. 
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pedwards2932 View Drop Down
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Posts: 333 		Direct Link To This Post Posted: 25 Oct 2020 at 1:10pm
I must not be explaining this very well.  Inverter is powered by vehicle battery thru a cigarette lighter plug.  Charger plugs into inverter.  Charger connected to trailer battery.  I would run the AC cord from inverter thru back door.  This would be temporary setup to see how it works.  I am not sure how you are getting the inefficiency as I know the inverter is not efficient but if it supplies 300 watts at 120 volts the charger should be as efficient as if it were plugged into a house outlet?
I didn't realize the refrig draws constantly I thought with the thermostat it would shut on and off.
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Posts: 5290 		Direct Link To This Post Posted: 25 Oct 2020 at 12:00pm
Originally posted by pedwards2932

No I was saying use the inverter to supply AC to the 10 amp NOCO GENIUS10 that requires 150 watts so you could use a 300 watt inverter.  Noco puts out 10 amps of charge to battery and rolls back to 3 when charged.  So I would clip it to the trailer battery and plug it into the inverter hooked up to the  vehicle 12 volt.  Not sure the 85% efficiency would apply.  My thought is between the alternator and the charger that would keep the charge up.  The refrig doesn't run constantly does it?  I could be wrong I am just thinking outside the box.

Yes the 11-12A 12V fridge current is continuous. And yes two 80-85% efficiency multipliers would apply. How could they not, you are taking your TV alternator/12V battery output through the inverter and then through the battery charger. 

Where are you planning to connect the inverter to the TV 12V supply?  You would be doing this while stopped using a temporary connection? If so just use propane. If you are doing this while driving you would need to run a separate 120V line between the inverter ac output and the battery charger. Better to just run a heavier 12v dc line. 

Or are you thinking to mount the inverter in the trailer and connect it to the 12V supply from the TV there? If you do that you will have even more voltage drop in the 12V feed from the TV, because of the efficiency losses. You would also have to disconnect the 12V feed from the trailer battery, or you would be trying to charge the trailer battery from itself, losing energy in the process. That would be a form of perpetual motion. 

Like I said, TANF. 

I do think a dc/dc converter would work. You would have one efficiency loss (dc/dc's are around 90%), which the 12avg wire could handle and still supply 12A to the fridge.  The dc/dc would boost the supply voltage from the TV battery/alternator which would compensate for the voltage drop in the 12awg wire. You would disconnect the 12V TV supply to the trailer battery and run it through the dc/dc instead, just like StephenH has done with his Li battery installation. 
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1995 RV6A Experimental Aircraft
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pedwards2932 View Drop Down
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Posts: 333 		Direct Link To This Post Posted: 25 Oct 2020 at 11:10am
The charger looked like a pretty full featured charger and fairly small so it would be easy to mount at the battery.  Here is the link https://no.co/genius10
By specs it takes 150 watts to run it which is a pretty small inverter (300 watt)  
I looked at DC to DC chargers and again ther require large wire to implement.....the inverter would not. I may try it just to see if it will work....at worst i would end up with an 300 watt inverter and a nice charger.
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mcarter View Drop Down
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Posts: 3419 		Direct Link To This Post Posted: 25 Oct 2020 at 10:50am
They do make battery to battery charging systems that feed off the tow vehicle, charge a remote battery(RV/boat/etc). They do not interfere with the vehicle battery charge. Google "battery to battery charge" or "charging a remote battery". A lot of big motorhomes and RVs have them. They are not cheap at least for good systems. It also may give you ideas with your proposed solution. The problem with most vehicle systems is they are designed to take care of the vehicle battery. They monitor and provide based upon vehicle need, not a remote battery. If I travel with reefer on DC my TT battery will be somewhat discharged upon arrival and that is with a 12V battery source thru the 7 pin. If you really want to charge a remote battery with a vehicle system, you need to look at battery to battery systems that isolate your vehicle charge and have proper components to charge a trailer battery.
Mike Carter
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