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Battery charging

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yelvington View Drop Down
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Post Options Post Options   Quote yelvington Quote  Post ReplyReply Direct Link To This Post Topic: Battery charging
    Posted: 21 Nov 2020 at 10:23am
If I swap the lead-acid battery for a Lithium battery, do I need to also replace the built-in battery charger? Where is it? We have a 179 Hood River Edition. 


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offgrid View Drop Down
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Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 21 Nov 2020 at 10:33am
Yes. It is just below the breaker panel. WFCO makes a direct replacement charger set up for Lithium batts.  If you want to also charge from your tow vehicle while driving you will need to add a dc/dc converter to the circuit from your 7 way connector as well. One other consideration is to move your battery inside the trailer so it stays warm if you want to do any winter camping, Li batteries don't like to be charged in sub freezing weather. If you do a search for StephenH's rpod mods you will see what all is involved. 
2015 Rpod 179
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StephenH View Drop Down
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Post Options Post Options   Quote StephenH Quote  Post ReplyReply Direct Link To This Post Posted: 21 Nov 2020 at 5:36pm

This is the one that is needed. As Offgrid stated, it is a direct replacement. Since you have a 179, my LiFePO4 battery mod would be directly applicable. It isn't only the converter though. To charge it on the road, the standard auto charging system will not work since it will not put out the correct charging voltage. I put in a DC to DC charger and ran a dedicated charging circuit in my Frontier. While I was at it, I also put in a battery isolator solenoid and ran a heavy wire to a dedicated outlet on the rear of the Frontier. A new power cable from the RPod plugs into that. You can't just tap into the RPod's wiring directly because then you would be trying to charge by using the battery as the source. Since there is no free energy or perpetual motion, it just won't work.

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offgrid View Drop Down
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Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 21 Nov 2020 at 7:27pm
StephenH, you could take the existing +12V  from the 7 way and run that through a dc/dc to the Li battery. You don't have to add a new connector from the tow vehicle if you do that, unless you want to charge at a higher current rate than the existing circuit can handle, which is typically 30A.  
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Post Options Post Options   Quote StephenH Quote  Post ReplyReply Direct Link To This Post Posted: 21 Nov 2020 at 9:03pm
Not really. I tried that. You can't have the same power feeding the DC to DC charger as running through the RPod's circuits. The DC to DC charger (at least the one I have) is 20A output, so input is higher. It has a 30A circuit breaker. The Frontier would not have supported that and would still have required disconnecting the umbilical's DC connection which I did anyway to keep from feeding power back through to the Frontier, and running a dedicated wire from the umbilical to the DC to DC charger. Since the Frontier did not have a heavy enough wire for that kind of load to begin with, running a new wire from the Frontier battery though the isolator solenoid and to the dedicated power outlet like I did made the most sense. If I had gotten the 40A DC to DC charger, it would have been necessary. In a way, I future-proofed it as I can just change the DC to DC charger for a higher capacity model and still be okay.

Before I got the DC to DC charger, I tried using the umbilical's 12V power, but what ended up happening was that the power to run the charger was coming from the battery. Since the battery can't charge itself, I quickly realized that I needed to separate the circuit that powers the charger from the trailer's wiring. That keeps everything operating as it should and doesn't try to violate any physics laws.
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Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 22 Nov 2020 at 8:12am
StephenH, I think you are perhaps misunderstanding my suggestion. I am not suggesting connecting the output of the dc/dc to the 7 way connector. Right now, you are not using the original +12V pin on the 7 way connector for anything. I am suggesting that that pin be used to supply the input of the dc/dc, and only the input of the dc/dc. That eliminates the requirement for a second umbilical. Everything else stays the same as what you have. 

The 7 way connectors are rated at 30A and most folks have a 30A fuse at the tow vehicle battery and a 10 gauge conductor to supply it. That is plenty for a 20A output dc/dc.  You are correct that if you wanted a higher output dc/dc than about 25A you would need a higher rated connector and wire, but that isn't needed for an rPod unless you are planning for an electrical system upgrade that can supply much larger loads such as an inverter to run the a/c. 

If you want to do that then you should also consider going to 24 or 48V to keep the wire gauge smaller,  current and resistance losses down and inverter efficiency up. Locating the boost dc/dc for this in the tow vehicle near the battery would also help keep the copper losses lower. In this scenario a different connector would be required because the 7 way Bargman is only rated for 12V. You would also most likely need a custom wound alternator to handle the increased load without overheating, particularly if you are trying to maintain battery charge from a idling tow vehicle while running the a/c. 

Or you could just stay with the standard alternator, the Bargman, a small dc/dc for light duty charging while on the road, and use a generator and a bi-directional inverter/charger to cycle charge the battery bank while running the a/c. 

Anyhow, back to yelvington's orginal question, I think your posting is a great starting point for someone wanting to substitute a Li battery for lead acid in a 179 with an otherwise standard electrical system. The only thing I would change is that I'd use the +12 pin on the 7 way to feed the dc/dc input rather than a separate new connector. 

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Post Options Post Options   Quote StephenH Quote  Post ReplyReply Direct Link To This Post Posted: 22 Nov 2020 at 5:32pm
And I think you are misunderstanding my point. Unless the 7-way 12V connector is disconnected from the RPod, using it to supply the DC to DC charger puts it in the same circuit as the RPod's 12V system. I did write above that it would be possible to just disconnect the 7-way's wire from the RPod and to take it instead to the input of the DC to DC charger, but I guess I was a bit unclear. I still like the idea though of a battery isolator solenoid and the heavier 6 AWG cable I ran to minimize power loss which is what I did. Unless the 7-way's power is disconnected from the RPod, in effect, both the input and output of the DC to DC charger would be in the same circuit which does not work. We both are saying the same thing, but in different ways.
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Post Options Post Options   Quote offgrid Quote  Post ReplyReply Direct Link To This Post Posted: 23 Nov 2020 at 7:17am
For sure you can't connect the input and output of the dc/dc together and expect it to function. I just want to make it clear to anyone contemplating conversion to a lithium battery that a separate connection from the TV is not a requirement.

To summarize, I think the simplest practical conversion for an rPod owner who is not looking to also increase their electrical loads and already has a fused 30A supply to their 7 way would be:

1) replace the WFCO battery charger with their compatible lithium model.
2) install the lithium battery in an unused interior space
3) install a 50 fuse or circuit breaker at the battery + terminal
4) run 6 gauge wire from the breaker to the load center battery terminal
5) install a 20 to 25 amp output boost dc/dc converter in a ventilated location near the battery
6) run 6 gauge from the breaker to the + output of the dc/dc
7) run 10 gauge from the +12V pin of the 7 way to the + input of the dc/dc
8) run 6 gauge from the - terminals of the dc/dc and the battery to chassis ground
9) if using solar be sure to use a lithium compatible charge controller
2015 Rpod 179
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