hello all. going to kejimikujik national park this weekend, and i've got a new (to me) tug this go around. I've finished setting up my trailer lights and connection, but now i'm going to set up the 12v so that i can charge the trailer with the tug. the boler is already wired for that in the 7 pin round connector, I just never got around to doing it on my previous tow vehicle.

so, are people connecting their +12volt right straight to the battery (with fuse of course)? I had the idea to use a 2nd battery switch, or an isolator like this:

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which is basically a heavy duty relay: when the key is in the run position, it' will turn the relay on, and connect the batteries to charge the accessory, or trailer. when the key is off, the current is disrupted so the tug battery cannot be drained by the accessory. I asked my father who's towed all his life - he has a stick built truck camper, with much the same amenities, but his charging wire goes directly to the tug battery.

i'm confused because nobody talks about this, but do people ever worry about not being able to start their tug in the morning? I know in my old van i had a dual batteries under the hood, and one was isolated in this fashion. is it overkill, or a good idea?

anybody? i suppose I'm going to go ahead and use the relay, as I have now got the wire from the battery to the rear bumper loomed, taped and cable-tied.

I have mine charging while driving only.
No relays ect ect.

Works perfect.

so what does that mean? does it mean you have a wire running straight from + on your tug battery straight to + on your trailer Battery? do you just disco the umbilical cord when you park?

We have a direct charging line running from the battery on the tug with fuse between to the 7 pin connector and then straight to the trailer battery when connected. Yes, the 7-pin connector is disconnected when we arrive, and some folks put a battery disconnect switch so they can disconnect that way and leave the connector hooked up.

The relay will do the same thing, disconnect the battery on the trailer when then ignition is off. I have one but never wired it in because we just unplug the tow when we get there.
But if I forget I always have that handy jump-it.

I paid to have my charge line installed at Camping World. They installed blocking diodes near the Honda's battery which allow current to flow to the trailer's battery when the car is running but not when it is shut off. They used different hardware, but it does the same thing your setup does.

Hello, Here is the setup I use with great success. I used it with my
last 13' Trillium keeping the battery charged up and allowing the
refrigerator to run on 12 VDC while traveling. With the isolator
there is no need to worry about disconnecting the trailer hookup
saving a fancy switch and some effort. When I stop for over an
hour I switch the refrig to propane.

Parts:
Sure Power Industries Multi Battery Isolator Model 9523A (95 Amp Max)
-- Note: The Model 9523A has an extra terminal "E" to use with GM vehicles.
-- A Model 952 would have sufficed for this application.
50AMP DC circuit breaker
# 6 wire - 30 feet (#6 instead of #8 for long run to rear of truck)
MISC: terminal lugs, heat shrink tubing, solder, etc.

The output of the alternator (RED) was disconnected and a New (RED) wire
run to the isolator input terminal A.

Isolator # 1 connection to (BLACK) wire that was hooked to the wire originally on
Alternator output going to vehicle battery.

Isolator #2 output goes to a 50 AMP circuit breaker and then #6 wire (WHITE) back to
battery connection on the trailer receptical.

Also, a #6 Wire was run from the alternator case to the frame rail in the
engine compartment and off the frame rail to Ground on Trailer connector.
This helps ensure a low resistance path for the ground, too.

Hope this helps some fellow FRG owners. If anyone has any suggestions
to help improve this setup, please post as I am looking for a new tug and
want a similar setup on it. Larry H

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ahhhhhh - it didn't occur to me that people unplug the umbilical cord. I always leave it connected which is why i couldn't wrap my head around a direct connection.

thanks to all that responded - I grew up with truck campers, it's a hassle to disconnect the umbilical cord so by force of habit i always leave it connected on my boler.

For what it's worth, i did end up using the dual battery switch, and I also ran a ground line from the neg on the tug to the back, grounding it to the frame, hitch, and right in to the 7-pin. boler taillights are brighter now...guess after 18 years, my toyota's grounds have fizzled a little!

Once I get the interior cleaned up a little, I'll throw some pics of my Boler up finally!

We use a Blue Sea automatic charge relay (ACR) as pictured. It senses the tow vehicle voltage and only switches on when the engine is running, triggered by the higher voltage present with alternator output. It may be overkill, but it has worked great for two years on two different vehicles. It just goes in series with the power lead to the house charging line and uses one short sensing lead to get the TV's charge system voltage. It's even adjustable, but I've never felt the need to change it. http://bluesea.com/category/2/productline/overview/386

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Parker

By "#6" do you mean 6 ga. wire? This may be the most important aspect of running from tug battery to camper. I paid a trailer hitch place to hook me up that way and they used 14 ga. wire, which later on I found out is not adequate to push the current all the way to the back end of my 13' Trillium where the battery is. So, now I'm faced with doing it right. Please confirm proper wire gauge or size. Thanks.

Marv. W.

Evening Marv... by #6 I meant 6 Guage. Larry H

That's exactly what I have(right on the batterie box cover).

I used 8 gauge wire, as that was what was on the trailer from the batty to the tongue, so I met it with the same from the tug. 14 is awfully small for the task, i would'nt go any smaller than 8.

I did pretty much the same as Larry.
Thought I'd be smart and run pin 7 on the connector as an extra +ve from the truck back across the umbilical since the wiring was lighter. Stupid me forgot and wired pin 7 up as an extra -ve from the trailer. Needless to say when it was all connected there was a funny smell and smoke.

My advise is to leave pin 7 (the center one) empty unless you really know what you are doing

Steve_L almost fired me as his new "apprentice trailer electrcian" after that attempt at playing with fire. Melted the connectors real good though.

You mean I'm not the only one to do this?

Smoke? Check! Who's got the Mirrors?

So THAT was what happened! I was a little worried that we messed up something with the brake controller install.

Back to the topic, in my opinion and in my experience, using the tow to recharge the trailer battery is at best a miserably slow process.

If you just took both batteries out and connected them together, then the two batteries would seek a common level. The tow battery would drop and the trailer battery would rise.

Installed, the same thing happens except that the alternator would would continue to keep topping off the tow battery as charge slowly moved from the tow to the trailer. A little like trying to water the lawn by keeping a leaky swimming pool topped up.

I've never tested this, but I'm inclined to believe it would be quicker and more efficient to just buy a 5 or 10 amp battery charger and run it from an inverter plugged into a cigarette lighter in the tow vehicle. (Size depends on the current the lighter socket is designed to handle) (Being sure to account for the inverter inefficiency.) The charger would send more current, quicker and more completely.

My brief encounter with running our laptop from the house battery while at only 12V would lead me to wonder whether there would still be an issue with low voltage. As you say, by the time the electrons find their way to the trailer, they're running out of steam, so the voltage back there is probably going to be less than what the inverter is happy with....I bet they want to see 13.8V. Mine got pretty hot and started switching on and off when powering the laptop. Admittedly, it was sized barely large enough for the laptop, so many a larger inverter wouldn't have this problem if running off less than 13.8V.

I bet Pete has some experience with this....

Parker

One thing I found out after reading the fine print LOL.
My 300w pure sine wave inverter puts out 180w through power outlet.
300w connected directly to the battery 300w

My laptop draws 204w the inverter was not real happy plugged into an outlet.

Bill K.

I'm doing another of my "test boxes". This one is inserted between the tow vehicle and the trailer. It measures the voltage and current leaving the tow to the trailer. Plus other shiny bits.

In a proof of concept prototype (I was fussing with different ways to get at the amperage. In the end there will just be access to either the charge or ground line for a Fluke 336 clamp meter.) I had it hooked up and the F150 idling while I turned on various 12v appliances in the trailer then went out and looked at the amp readings to see if they were consistent with what I had measured in the past.

Everything looked good except when I turned on the reefer on 12v. I know the reefer takes 10A DC. the F150 was only supplying about 7 to 8 amps. That meant that, at idle, the alternator wasn't getting the job done.

My past experience has shown that at highway speeds the alternator on my Ford with the tow package just keeps up with demand but doesn't replace amp hours.

I'm not saying that there isn't some way to configure things to make it work...but I am skeptical of most schemes I've seen.

Still waiting for some misc. pieces before I can assemble the final box. More toys for boys...

Yes, that was it. I don't remember what was what, guess that happens when one wires up 2 halves of a circuit over two years forgetting to write things down.

My gut says that since the wires in the umbilical are 10 Ga or smaller, I ran an extra +ve through pin 7 from the trailer battery thinking the hitch connection would provide for extra grounding. When I wired up the truck end my mind said if I kept pin 7 as the ground, no harm could be done. (yeah right, I forgot about the idiot that wired the trailer end) The worst damage was my ego, but I did learn a lot from the apprenticeship, thank you.

Once I resolved that problem and replaced the melted components the brakes worked just fine. It was a noticable difference driving home from MI.

OK, I see I have contradicted myself in this thread. I believe post 21 above is the way I wired things. This confirms the need to follow convention and write things down. All I know now is that pin 7 is empty on both ends because I will never know what I'll be towing or what will tow the trailer. Lesson learnt and grateful there was not more damage.

Well maybe there was, my solar charge controller seems to be on the fritz. And that was not cheap. Hopefully it will bounce back with a new battery.

Nate, I have used an isolator (relay) like the one in your picture for 10 years. It was simple to hook up and is automatic. Key off, isolator is off. You can't forget to do it.

Someone wrote to one of these forums that he unplugged his umbilical, forgot it and dragged it to death on the pavement. I never unplug unless I am unhitching.

The more expensive diode type isolators do the same job, but you lose a little bit of current in the diodes.

i understand the theory about how to do this, but maybe someone could make a part list and step by step instructions on how to wire a simple tug to trailer charge line. I would really like to do this before my next trip. So many people do it slightly different it gets kinda confusing. .. thanks to anyone that wants to run through an easy set up or a link to one. Also i have a flat 4 from my truck, is there a 7 pin harness that i can plug the flat 4 into and still have it wired for power to the trailer? I'm having a hard time finding one. I can find lots of flat 4 to a 7 blade adapter but those wont allow me to add the auxiliary power correct?

Here is the best wiring diagram I have seen. It comes from Don on the Casita forum.

Click to view attachment

Some good info here
http://www.powerstream.com/battery-isolator.htm
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thanks i got it figured out now. i just needed a wiring diagram i guess. I really like deans. hehe i got the 7 blade figured out too.

Maybe this Scamp wiring schematic will help?
Wiring Diagram - Scamp

I read this thread with interest. It is an example of the rules:

Write everything down

Mark it

Don't ever trust to memory

Measure twice before cutting once.

Working with electrical circuits for a local aircraft company, I learned that you never trust anyone else's work, always double check. Electrical things go together easily, it is when you turn the current on that you discover you have problems. "Houston, we have a problem." Check again.

I was told when I took delivery of my trailer, to not worry when stopping for an hour or two, but for parking overnight, always unplug the trailer or it will draw the tug battery down.

As far as dragging the plug end, I have two systems:

1 - I physically attach the plug to the trailer

2 - My Brake controller will not show "c" if the trailer is not hooked up.

Happy Trails

i think I'm just going to use the unplug it method to start with. i almost always unhitch anyway. So what size fuse should be used? or circuit breaker? thanks