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diy solar

diy solar

Adding solar controller to RV trailer

LobbyBoy

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Joined
Jun 4, 2024
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31
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milky way
I put together a DIY solar power system for use with my 16 foot Scamp trailer and used it successfully all summer this year. Because many of the elements were experimental (for me at least) I avoided doing anything irreversible with the installation. I just put my 12V 100 A.h LiFePO4 battery and MPPT controller in a plastic box that rode in the truck while traveling and lived under the trailer when parked. Well, I drilled a couple holes on the underside of the trailer to feed through 6AWG wires connecting battery with my 700W inverter, which was housed in a cabinet inside the trailer. This system was completely separate from the trailer's 12V system with its own lead-acid battery.

This worked well, but is kind of heathen-like, and I would like to make a nicer more finished installation, probably replacing the lead-acid battery completely. Here are a few questions, and I'm open to hearing about other questions I haven't thought to ask...

* The trailer is set up for 12V, so I think I just want to keep this as the voltage for the DC system.
* Electrical interface with tow vehicle alternator: I assume I need a DC-DC device for compatibility with LiFePO4 battery.
* Shore Power converter. Existing one is only compatible with lead-acid battery (annoying!) I know how to replace this. I kind of don't like the trailer wiring, which uses one 12AWG wire for one of the two conductors from back to front of trailer, and from what I can see a 6 AWG wire for the other conductor. For the time being I will just disconnect this as I usually achieve the desired charging from solar.
* The trailer has a closet area at the front that could be available for some electrical components (inverter, solar charge controller, DC-DC device interfacing with tow vehicle).
* Where do people install the solar charge controller? I can imagine in the battery box up near the trailer hitch (trailer exterior), or in a cabinet in the trailer interior. FWIW my existing battery box wouldn't be large enough, and may not be sufficiently waterproof.
* I see no way around installing at least some feed-through electrical connectors. I see something like Hang Ton LP20 or so that might make sense if the current stays within capability, maybe using 2 pins per conductor or something. 700W inverter could call for as much as 50 A so I'd love to hear thoughts on how to approach.
* Keep the solar panels "mobile" so I can separate shade for trailer from sun for PVs. I have 2 PV panels that operate in the 70s of volts when in series that work well and this should enable acceptably low losses in PV cable.
* What else should I be aware of?
 
* The trailer is set up for 12V, so I think I just want to keep this as the voltage for the DC system.
YES, 24v is common when you have high electrical needs, not for regular RV needs.
* Electrical interface with tow vehicle alternator: I assume I need a DC-DC device for compatibility with LiFePO4 battery.
Not interference, but that the Ltih batteries will try to draw more current than the alternator normally puts out. The save is that the wire run is so long to a trailer that this is not reality, but the DC-DC will limit the amperage to the RV batt. I highly suggest using DC-DC charging.
* Shore Power converter. Existing one is only compatible with lead-acid battery (annoying!) I know how to replace this. I kind of don't like the trailer wiring, which uses one 12AWG wire for one of the two conductors from back to front of trailer, and from what I can see a 6 AWG wire for the other conductor. For the time being I will just disconnect this as I usually achieve the desired charging from solar.
It is compatible. It will not fully charge your lithium battery, but will put enough voltage across that everything inside will work and will work without running your batts down any lower than the voltage that the charger puts out; 13.6 volts maybe.
Lithium chargers are so cheap on ebay why not just get one? I use a 20 amp charger, err, I have one, but have never used it bc I have enough solar so far.
* The trailer has a closet area at the front that could be available for some electrical components (inverter, solar charge controller, DC-DC device interfacing with tow vehicle).
* Where do people install the solar charge controller? I can imagine in the battery box up near the trailer hitch (trailer exterior), or in a cabinet in the trailer interior. FWIW my existing battery box wouldn't be large enough, and may not be sufficiently waterproof.
Near the battery. The solar will put out 18 volts but then the controller will drop the voltage to 13-14 volts, so make the longest part of the run use the highest voltage and keep the lowered voltage shorter.
Inside. Where you can look at it too.
If you cam put the batteries inside then that will eliminate some of the issues of charging when outside temps are below freezing.
Keep in mind to not weigh down your trailer tongue too much. Batteries can be sideways, upsidedown or whatever also, so your options are open.
* I see no way around installing at least some feed-through electrical connectors. I see something like Hang Ton LP20 or so that might make sense if the current stays within capability, maybe using 2 pins per conductor or something. 700W inverter could call for as much as 50 A so I'd love to hear thoughts on how to approach.
* Keep the solar panels "mobile" so I can separate shade for trailer from sun for PVs. I have 2 PV panels that operate in the 70s of volts when in series that work well and this should enable acceptably low losses in PV cable.
That sound great in theory but not in practice. Do you just love setting up stuff when you camp, is that the enjoyment of camping for you? to set up stuff? If not then have mounted panels on the roof, and have your mobile panels for when you are in shade and are not getting enough solar power. These batts might go for more days than you are parked in the shade so be realistic. Your losses in the shade might be a net loss, but the net loss might be small enough that you can get by just fine. example; you might use 15 amp hrs per day and only get 10 amp hrs of charge per day, so that is a net loss of 5 amp hours. On a 100 amp hr battery that gives you 18-20 days before reaching zero. How long will you camp in one spot?
* What else should I be aware of?
Roof penetration. Gland, search the word "gland".
LAP sealant, never silicone or caulk. It comes in self-leveling and non-leveling.
VHB tape is a wonderful thing for your fiberglass. It does not take much.
 
YES, 24v is common when you have high electrical needs, not for regular RV needs.

Not interference, but that the Ltih batteries will try to draw more current than the alternator normally puts out. The save is that the wire run is so long to a trailer that this is not reality, but the DC-DC will limit the amperage to the RV batt. I highly suggest using DC-DC charging.

It is compatible. It will not fully charge your lithium battery, but will put enough voltage across that everything inside will work and will work without running your batts down any lower than the voltage that the charger puts out; 13.6 volts maybe.
Lithium chargers are so cheap on ebay why not just get one? I use a 20 amp charger, err, I have one, but have never used it bc I have enough solar so far.

Near the battery. The solar will put out 18 volts but then the controller will drop the voltage to 13-14 volts, so make the longest part of the run use the highest voltage and keep the lowered voltage shorter.
Inside. Where you can look at it too.
If you cam put the batteries inside then that will eliminate some of the issues of charging when outside temps are below freezing.
Keep in mind to not weigh down your trailer tongue too much. Batteries can be sideways, upsidedown or whatever also, so your options are open.

That sound great in theory but not in practice. Do you just love setting up stuff when you camp, is that the enjoyment of camping for you? to set up stuff? If not then have mounted panels on the roof, and have your mobile panels for when you are in shade and are not getting enough solar power. These batts might go for more days than you are parked in the shade so be realistic. Your losses in the shade might be a net loss, but the net loss might be small enough that you can get by just fine. example; you might use 15 amp hrs per day and only get 10 amp hrs of charge per day, so that is a net loss of 5 amp hours. On a 100 amp hr battery that gives you 18-20 days before reaching zero. How long will you camp in one spot?

Roof penetration. Gland, search the word "gland".
LAP sealant, never silicone or caulk. It comes in self-leveling and non-leveling.
VHB tape is a wonderful thing for your fiberglass. It does not take much.
Useful. Thank you!
This morning I'm looking at DC-DC chargers and now have another question: Can I connect the DC-DC charger input to both the tow vehicle power and the shore converter output? (Assuming I only run one at a time.)
 
I have seen that discussed on here, search forum more. For that reason I do not know, seems like a DC source is a DC source, but not sure why it was discussed at length unless all DC is not the same.
The reason to use a DC-DC is to protect the alternator. Alternators do not put out X voltage all the time, they only put out what the vehicle/components ask for. A 120 amp alternator is meant to put out 60 or less amps most of the time, never 120 amps all the time, maybe for a few mins at most. Asking for full power from an alternator will burn the alt out. (yes, some alts, few, rarely seen, are 100% duty cycle, but guessing he does not have this).
Why would you want to use DC-DC between a charger and the battery anyway? neither need protecting.
 

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