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Do I need a DC-to-DC controller for vehicle to teardrop battery

NORTH53OVERLAND

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Hi everyone, i'm new to this.

I know that a 7-pin harness will do some charging of my trailer battery. I have a semi-custom trailer being built but have asked that they leave the super basic battery out so I can add my own 12V system.

This is my idea;
- For now I will use a single 230ah 12V AGM battery (eventfully upgrade to Lithium)
- Xantrex Freedom XC 1000 to provide shore power charging to the battery and DC to AC pure sine wave inverter
- Renogy 40A MPPT solar charge controller
- 200w renogy suitcase style solar panel

My big question is, should I or do i need to have a DC to DC charger as well? If so why, if not, why not?
 
Cool, I have often wanted a teardrop trailer. Here are some comments:

- You only need 200W / 12V = 16.67A, 40A seems unnecessary.
- You only need a DC/DC charger if you want to charge your battery from your car alternator
- You might want a DC/DC regulator to power DC loads in your trailer, if any of them require a different voltage than the 12-14V that your battery provides. If the manufacturer builds it for 12V then probably everything runs on 12V (lights, fan, whatever else is on a teardrop trailer, etc?).
 
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Cool, I have often wanted a teardrop trailer. Here are some comments:

- You only need 200W / 12V = 16.67A, 40A seems unnecessary.
- You only need a DC/DC charger if you want to charge your battery from your car alternator
- You might want a DC/DC regulator to power DC loads in your trailer, if any of them require a different voltage than the 12-14V that your battery provides. If the manufacturer builds it for 12V then probably everything runs on 12V (lights, fan, whatever else is on a teardrop trailer, etc?).

Thank you Paul. I figured I would just go with overkill at once for the input for the solar controller in case I add more in the future.

My confusion concerning DC/DC charger is that I believe if I got the factory 12V system from the trailer builder that they would have beein charging the battery from the 7-pin and no addtional Dc/DC charger. As such, is there a particular reason why some people have one and some dont?

The rest of the system is 100% 12-14V.
 
My confusion concerning DC/DC charger is that I believe if I got the factory 12V system from the trailer builder that they would have beein charging the battery from the 7-pin and no addtional Dc/DC charger.
Ah yes for car batteries like lead-acid / AGM, I think they just hook up the battery directly to the alternator. For LiFePO4 you wouldn't do that. I'm not that knowledgeable in automotive stuff like that; I suggest you ask one of the "mobile" / "RV" / "car" forums for that. But yeah it seems plausible to me.
 
Take the voltage at the hitch and at the battery connection point in the tear drop.

13.9 to 14.4 is what most alternators output when the vehicle is going zoom zoom.

You need a dc-dc booster charger to raise the voltage if it is sagging a bit.
 
Just a couple of comments first:
I applaud you jumping right in. I DIY just about everything.
If you are still in the building stage, may I suggest...
1. Rethinking your inverter choice. It is expensive and not Lithium battery compatible. If you up grade to lithium batteries, you'll also have to upgrade to a compatible inverter/charger. Get one that's already selectable.
2. The wiring for connecting/disconnecting that portable panel to the Renogy MPPT would take the same time and energy to put a 200 watt panel on the roof. If you set on using the portable panel for now, wire up the trailer for the MPPT while you're in the construction phase, but use a temporary portable controller for now too.

The 7-pin is mainly for keeping your trailer break away battery topped up.
If all your using now is that one battery, you'd be fine.
You might get 10 amps from the line, which is all you for charging lead batteries at anyway.

If you upgrade to lithium batteries, I think you would need to spend hours regularly on the road with the trailer, and boondock a lot to justify the cost of installation as opposed just plugging in some where for an hour or two.

Just my frugal opinion, good luck.
 
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Hi everyone, i'm new to this.

I know that a 7-pin harness will do some charging of my trailer battery. I have a semi-custom trailer being built but have asked that they leave the super basic battery out so I can add my own 12V system.

This is my idea;
- For now I will use a single 230ah 12V AGM battery (eventfully upgrade to Lithium)
- Xantrex Freedom XC 1000 to provide shore power charging to the battery and DC to AC pure sine wave inverter
- Renogy 40A MPPT solar charge controller
- 200w renogy suitcase style solar panel

My big question is, should I or do i need to have a DC to DC charger as well? If so why, if not, why not?
200 watts of panel will get you...
200 watts / 14 volts * .9 conversion factor = ~13 amps
230 amp hours * .5 depth of discharge / ~13 amps = ~9 hours for a full charge.

That battery probably shouldn't be charged much harder than .1c or 23 amps which will take 5 hours.
If you have the spare alternator capacity you could get the 20 amp version of this.
RNG-DCC1212-20-CA
 
Hi everyone, i'm new to this.

I know that a 7-pin harness will do some charging of my trailer battery. I have a semi-custom trailer being built but have asked that they leave the super basic battery out so I can add my own 12V system.

This is my idea;
- For now I will use a single 230ah 12V AGM battery (eventfully upgrade to Lithium)
- Xantrex Freedom XC 1000 to provide shore power charging to the battery and DC to AC pure sine wave inverter
- Renogy 40A MPPT solar charge controller
- 200w renogy suitcase style solar panel

My big question is, should I or do i need to have a DC to DC charger as well? If so why, if not, why not?
If your plan is to eventually go with a DC to DC charger for a LFP bank, you should have a separate circuit run using an Anderson connector and not run it thru the 7 pin. Too much VD thru the 7 pin and it's wiring. It would be wise to have it ran now from the hitch into the camper while it is being built.

In the meantime, you could run the AGM without the DC to DC charger and run the wire on tow vehicle with the opposing Anderson connector. This way you are already wired for a DC to DC charger on tow vehicle as far as the cable to rear and it gives you the ability to charge your AGM. Be forewarned though, without a DC to DC charger or isolator, you can drain the vehicle starting battery dead. You have a few choices, 1 either install the isolated DC to DC charger now; 2 unplug the Anderson connector when you're parked for the day; 3 install an isolator. Choice 1 is preferable, then you would be all set for the switch to LFP.

If you do run the circuit only, be sure to know what DC to DC charger you intend to install and it's amp output to size the cable correctly.
 
My confusion concerning DC/DC charger is that I believe if I got the factory 12V system from the trailer builder that they would have beein charging the battery from the 7-pin and no addtional Dc/DC charger. As such, is there a particular reason why some people have one and some dont?
North53: When a normal 12v trailer is put under load (e.g., running a fridge on '12v' electric for safety, while towing), it will typically pull its own Trailer Battery down to about 60% State-Of-Charge, before power pulled from the towing Vehicle (through the 7-pin "Bargman" connectors and cable begins to dominate the power consumption. And you don't really get much actual CHARGING through that cable, unless you reconfigure (to either a DC-->DC Boosting Battery charger, or a much larger cable).

What happens without a DC-->DC boosting battery charger, and without a separate large cable: Right at engine startup, your Tow Vehicle Alternator adjusts under-the-hood voltage (under the control of the "engine control module" computer which monitors and corrects for Voltage issues) quite high, up to about 14.2 Volts. That's to recharge the Starter Battery within the Tow Vehicle (hereafter "TV"). But shortly after the Starter Battery is "recovered" to being nearly full (as measured by ECM), the ECM will direct the Alternator to maintain only a much lower "Float Voltage" Voltage value under the hood - typically in the range of only 13.4 - 13.6 Volts. When such a low "charging Voltage" is applied, Lead-Acid batteries will only charge very slowly.

Three other things happen through the very thin "Trailer Battery Charge" wire within the Bargman cable. #1, because it is relatively thin, it has "Voltage Drop" power loss - which further reduces the amount of Voltage seen at the teardrop Trailer battery(s), when you are powering loads or trying to recharge the Trailer batteries. (They will accept even less input charging power, because the Voltage falls even lower than the TV "float Voltage" when current begins to flow at a significant rate of Amps.) #2, the TV's "Engine Control Module" doesn't see that Voltage drop - because it mostly occurs within the wire. And #3, because the batteries are not sucking in much power - the ECM again sees no excessive "accessory loads" pulling down the Voltage under the hood.
- - -
With a DC-->DC boosting battery charger (normally installed within the Trailer where it can monitor the Trailer Battery "State-Of-Charge" a lot better), the DC-->DC Booster pulls HIGHER current along the Bargman, ignoring the "Voltage Drop" and raising the Voltage back up to a value which the Trailer batteries "want" to see. (Typically 14.2V, for lead-acid batteries which need considerably charging). Only when Voltage Drop falls much too low, typically around 11.2V, will the DC-->DC charger "give up" on sucking power in from the Bargman.
- - -
With a much bigger add-in cable, you can also avoid the 3 problems of running "charge current" through the Bargman Cable. With the much larger cable, the Voltage at the Trailer Batteries and the TV Starter battery is kept nearly identical, with almost no Voltage Drop and with High Current capability. If the Trailer batteries are low, they begin to pull substantial balancing current from the TV Starter Battery and Alternator (through the big cable, with almost no Voltage Drop along the cable). The ECM directly sees low voltage in the engine compartment, and will boost Alternator output "to bring the Starter battery back up to 100%" - with BOTH batteries TV and Trailer, being charged together, by the higher Voltage, until they are BOTH near 100%.
 
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should I or do i need to have a DC to DC charger as well?
You don't need a DC-DC charger if you are charging an AGM battery. The AGM charging profile is similar enough to a FLA tow vehicle battery.

You should run a DC-DC converter when running a lithium battery mainly to limit current draw from the tow vehicle. It also allows you to fully top off a LFP battery
 
do you have the agm battery yet? if not you can go lithium much cheaper
 
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