Tow Vehicle to Trailer Connections

[John61CT]

As high as,

and, might be. . .

[saltydawg]

Don’t worry about fancy dc/dc charging unless your have lithium batteries o

Actually heres the funny item, you can use a solar mppt chargers as a dcdc charger. If your solar panels have diodes in them, you can just parallel them in to the solar input. This lets you use the charging profiles built into the mppt charger to charge your battery, properly. Just make sure the mppt can handle the input you expect from the alt.

[cwegga]

Actually, one other question, Swoody, the diagram you posted, shows a red marker light at the rear of the trailer and an amber in the front. Is there a reason one is red, the other amber?

John

Marker lights are red or amber to destinguish the front and back of the trailer from each other when it is dark and it can't be seen well. Same as cars having red tail lights and side markers at the back and white headlights/amber markers at the front. The lights indicate direction of travel. For example it helps you determine if a vehicle with trailer is turning off your road onto a side road or waiting to pull out and could be a hazard to avoid.

Your local government should have laws about how many lights you need, and their placement based on trailer size. In the US some requirements will likely be in state law and some in federal law. Both should be available online if you start searching for trailer lighting requirements.

Here's an example from where I am though it is always good to read the actual statutes and not just trust random websites. https://trailers.com/state-laws/montana ... ach%20side.

Sorry I got a little carried away there. TL:DR the color shows which way the trailer is facing.

[swoody126]

wiring for RV battery thru 7-flat prong plug on 29' travel trailer is 10ga w/ a 30 amp in line fuse from the factory

IMG_5134.jpg (400.19 KiB) Viewed 1480 times

sw

[Capebuild]

Actually, one other question, Swoody, the diagram you posted, shows a red marker light at the rear of the trailer and an amber in the front. Is there a reason one is red, the other amber?

John

Marker lights are red or amber to destinguish the front and back of the trailer from each other when it is dark and it can't be seen well. Same as cars having red tail lights and side markers at the back and white headlights/amber markers at the front. The lights indicate direction of travel. For example it helps you determine if a vehicle with trailer is turning off your road onto a side road or waiting to pull out and could be a hazard to avoid.



cwegga, thanks for clarifying that amber/ red light orientation,.

[tony.latham]

1) Vehicle battery to trailer battery for charging battery on trailer.

John:

Let me stir the pot a bit.

Have you decided what battery type you are going with? (I certainly don't think you want to charge a lithium directly from your Subaru. But I'm lithium dumb.)

Up until this last build, our teardrop had flooded lead-acid marine/RV batteries. Or FLA for short. I charged them from the stock Tacoma electrical system while towing and from the sun while in camp. Both systems worked great.

But with this last build, I chose an AGM lead-acid battery. They need a little higher voltage than car charging systems put out. Some folks solve this problem with a DC to DC charger. But they are expensive and I was upgrading to a full-time roof mount solar system. So did I need this?

If you Google around on this site, you'll find people that do fine charging an AGM from their automotive systems. But damn, they are about twice the cost of an FLA.

I installed a cutoff switch in my electrical panel to turn the vehicle charging line on/off --just in case the solar system wasn't enough.



That's the red switch in the pic. We've done about thirty nights with this 'drop and that switch has never been on. The solar system always tops it off.

I've got a 130-watt solar system and we use about 8-10 amps per night, mostly from my CPAP.



Tony

[Sparksalot]

The amps current flow might be as high as 50-60A

requires a separate fat wiring pair and Anderson connectors

He's trying to charge it, not cook it.

[John61CT]

Not everyone has a "tiny" electrickery setup, just because they might have a tiny trailer.

FYI I've got a client with a 13kW alternator charging an 1800Ah LFP bank 40+ feet away

00 AWG wiring still has to boost the output voltage by over 2V to overcome voltage drop.

I was just pointing out that - in contrast to blinky lights or the breakaway kit battery - these issues need to not be ignored when doing **any** serious charging over more than a few feet.

And even with a small bank suitable for a TT say 400Ah, will can get expensive enough to want to give it the precisely correct profile so that it lasts the 6000+ cycles it should.

[tony.latham]

And even with a small bank suitable for a TT say 400Ah

John61CT:

I know you don't have a camper. I don't think you camp. I know you are on a lot of forums.

Teardrops usually have a battery that is less than 50 usable amps.

Tony

[saltydawg]

I would bet the "standard" teardrop battery is a 100 amp hour or smaller lead acid either agm or fla. So even at the recommended charge rate of 10 amps, can you charge thru the 7 pin, yes you can. But your looking at a 5 hour drive to charge from 50%. Then you do run into issues with voltage drop ( minimal ), and the alt in the car is looking at the starter battery, and the trailer battery as a load on it not something it sees as needing a charge.

Spend the extra on a solar panel and charger or a dcdc charger. You can use a mppt as a dc to dc charger if you plan on going solar, just buy the charger now and use it, then the panel later. The best way is simply a solar panel and charger, esp if you are using a lead acid battery, as a good charger will keep it fully charged like it needs to be, even when parked and not being used.

If your using lithium a dc to dc or mppt charger is basically required as the lithium battery if it needs any real charge can kill your alt.

[Sparksalot]

Not everyone has a "tiny" electrickery setup, just because they might have a tiny trailer.

FYI I've got a client with a 13kW alternator charging an 1800Ah LFP bank 40+ feet away

00 AWG wiring still has to boost the output voltage by over 2V to overcome voltage drop.

I was just pointing out that - in contrast to blinky lights or the breakaway kit battery - these issues need to not be ignored when doing **any** serious charging over more than a few feet.

And even with a small bank suitable for a TT say 400Ah, will can get expensive enough to want to give it the precisely correct profile so that it lasts the 6000+ cycles it should.

That’s about enough to power North Korea. I really don’t care to light up Kim and the gang.

[saltydawg]

Oh since I just read the op, yes that 4 to 7 pin adapter would work. But I would not use it, because I hate extra connections to corrode under the car.

I would install one of the 7 pin plugs that also has a 4 pin built in, no extra connections to go bad.

[Tom&Shelly]

I would bet the "standard" teardrop battery is a 100 amp hour or smaller lead acid either agm or fla. So even at the recommended charge rate of 10 amps, can you charge thru the 7 pin, yes you can. But your looking at a 5 hour drive to charge from 50%. Then you do run into issues with voltage drop ( minimal ), and the alt in the car is looking at the starter battery, and the trailer battery as a load on it not something it sees as needing a charge.

As it happens, that describes our system as I designed it (with AGM battery), and meets our specs. Our plan is to do lots of driving (in parts of the continent that don't always have lots of sunlight), so we'll likely see 5-8 hour drives every few days. I don't think we'll often get the battery down 50% between the drives though.

Worse, for those who worry these sorts of things: Our PD 4045 (for when we park at camp sites with shore power, or near certain dams in Canada, where I hear they give their product away free) has a smart charger, but no way to switch between FLA and AGM.

Oh, and then, when the teardrop is "in hanger", it'll be in one without AC power, so that's when we'll use a solar panel on the roof, with PWM controller.

As a retired Electrical engineer, I looked on this forum and others, considered the pros and cons (and some of the less than accurate material presented by certain nameless "cons"), and decided the KISS principle does indeed make sense.

We're just starting to use our teardrop this Spring, so, I'll let you all know in a few years if our battery cries uncle. Perhaps I'm making a mistake, and abusing an innocent battery. But it appears DC/DC chargers cost as least as much as the difference between the FLA and AGM batteries.

Scott, I do like the idea of feeding the TV power through an MPPT controller. Thank you. If the system turns out to need a redesign, that's one to consider. Or maybe, by then, we'll be ready to put a panel on the teardrop roof and feed it to the PWM controller. We'll be older then, and perhaps ready to stick to the sunny west.

So John (who started this thread--not the other one), the only advice I have as you design your system is to consider how you plan to camp, make a rough inventory of the electrical devices you want and how much power you think you'll use, and your budget. There's more than one way to design these systems.

Tom

[Capebuild]

I'll say thanks all again for the comments and suggestions. Needless to say my head is a bit spinning from all this info and various approaches. Still trying to figure out the simple thing about how all these wires from the trailer funnel down to connect to the 7 pin connector (I suppose that's not a complex thing compared to the rest of the setup).

Anyway, Tony, you had asked what kind of battery I was considering. Even though it is expensive, I was considering a Battleborn 100 Ah lithium. The reason, from what I've read, is it can be used below the 50% drain threshold and it provides more use cycles, lasts longer than an AGM; which would be my fall back position. I did not consider, what others have commented on, the strain it might put on my auto's battery or alternator in order to charge it. So I guess I need to learn more about that.

Regarding solar, I was planning on a single 100 watt panel on the trailer's roof.

John

[MickinOz]

Actually heres the funny item, you can use a solar mppt chargers as a dcdc charger. If your solar panels have diodes in them, you can just parallel them in to the solar input. This lets you use the charging profiles built into the mppt charger to charge your battery, properly. Just make sure the mppt can handle the input you expect from the alt.

Now you've got me thinking.
My mppt controller says it can take a panel that delivers more than the rated 20 amp current, it just won't charge any more than 20 amps.
I wonder if I could tap into the tail lights, and just run with the truck lights on and let that charge the battery?
It's wired 5 pin like a lot of stuff in Oz, so no auxiliary power circuit. I suppose it would overload the truck lighting circuit and blow the fuse.

On the other hand, unless the battery is really flat, the terminal voltage is only a couple volts less than TV voltage, so current might not be that high, eh?
We are sort of planning to use the 'drop as a simple overnighter. Topping off the battery on the way there and on the way home without having a solar panel is kind of appealing.