Tow Vehicle to Trailer Connections

[saltydawg]

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.

Yeah I think thats not a good idea. The wiring for stock lighting is way to small.

[saltydawg]

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

Okay the lithium charge from tow vehicle problem is simple. The lifepo4 battery will willingly take a 100 amp charge rate, the alt in your car might be rated to around 85 to 100 amps. So the battery will let the alt give its all trying to charge, and by its all I mean all of its life. A dc to dc charger ( or mppt solar charger ) will limit the charge rate to one your car can handle, ie 20 amps or less.

I am a huge supporter of lifepo4 batteries, but unless your buying the battleborn with the built in warming and cold charge protection buy the sok 100 ah battery. it has great reviews for a little more than half the cost. Or even better build one, it takes 15 mins, and you can do it very cost effectively, with a cold weather protection bms.

The main issue with lifepo4 is you cant charge it below 32F. But you can use it when its cold, there are ways to warm it, protect it etc. First just putting it inside the trailer will help, then you get into things like warming pads for when you need to charge and its below 32F.

I have simple bee hive heating pads controlled by a 10 buck thermostat that also activates a relay that blocks the charging current until the batteries warm up. Total cost was 30 bucks.

[Sparksalot]

I suppose it would overload the truck lighting circuit and blow the fuse.

Or drive the computer crazy with error codes. In some modern vehicles, just changing from halogen to LED lamps can causes errors, because the computer is expecting to see a specific resistance. The result is a lot of guys have to put resistors in line to keep the computer happy.

[MickinOz]

I suppose it would overload the truck lighting circuit and blow the fuse.

Or drive the computer crazy with error codes.

Its one of the things I love about my 16 year old truck. No computer.
Its still got mechanical fuel injection, no ECU.

The other day the cool weather started. It's like autumn was watching the calendar.
The hard to start when cold issue, that first manifested itself on Gillies Downs station a couple years ago in sub freezing temperatures, finally made its presence felt in more normal temperatures.
$20 set of Ebay glow plugs fixed it, no need to plug in a box and read and clear error codes.
But, I still suspect I'd have issues. Might try it one day, just to see, but I want to mull it over some more.

[Socal Tom]

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

The way I see it charging by TV should be a backup plan, in my case it supplies the power I use in transit to cover the fridge. Everyone should either keep the batteries charged at home, or make it part of prep to charge them. It a real emergency, hook up the TV to the TD battery with jumper cables and let it idle for a hour or so.
Tom

[Tom&Shelly]

The way I see it charging by TV should be a backup plan, in my case it supplies the power I use in transit to cover the fridge. Everyone should either keep the batteries charged at home, or make it part of prep to charge them. It a real emergency, hook up the TV to the TD battery with jumper cables and let it idle for a hour or so.
Tom

Well, in our case, we're planning on being away from home for 4-6 months at a time...

Tom

[John61CT]

Yes how many days at a time off grid is the key differentiator in driving overall design.

Once you get past say 3-4 nights then you're basically creating a system to sustain **living** off grid.

Then the next factor is, how many days staying put in one site, or put another way, how many hours of driving per 3-4 days?

If long stays in one place, then solar + genset are your main sources

and you maximise your solar to reduce gennie runtime.

[Socal Tom]

The way I see it charging by TV should be a backup plan, in my case it supplies the power I use in transit to cover the fridge. Everyone should either keep the batteries charged at home, or make it part of prep to charge them. It a real emergency, hook up the TV to the TD battery with jumper cables and let it idle for a hour or so.
Tom

Well, in our case, we're planning on being away from home for 4-6 months at a time...

Tom

Then you probably want some solar panels, or a generator. FWIW on my 2 hour drive home yesterday the combination of solar panels and Charging through the 7 pin connector fully recharged the 150 watts I used the night before, by 10:30 am here on a sunny.
This thread has sort of gotten off track. The OP is building a weekend rig, so I was responding primarily to his needs. But I still think the TV charging should be the back up plan in your case too.