D+ Signal question

[VanIsledave]

Hello Smart Peeps,

I'm installing a DC-DC Charger to charge LiPO batteries.

I've got the 12VDC from the tow vehicle bit also have to wire in a D+ Signal line so the charger won't operate unless the vehicle is running.

OK, I think that makes sense, that should help to prevent draining my TV battery.

But can I simply use the 12V from the 7pin connector as both the 12V input to the charger and the DC+ signal line? (My logic is that the 12V at the connector is only there when the vehicle is running, right?)

Thanks!

Dave

[tony.latham]

(My logic is that the 12V at the connector is only there when the vehicle is running, right?)

The wire should run from the battery to the 7-pin and thus always hot. Check it with a continuity light or a multimeter. But your DC-DC battery charger might sense when the vehicle is running by the increase in voltage???

What's it say in your instructions for the charger?

Tony

[VanIsledave]

Yep, you’re right, Tony. Just checked, the 12v is always hot. The need for the D+ Signal makes more sense to me now. Just gotta figure out an easy way to get it.

I also realized that there wasn’t really any way to use the 12v from the TV as the wire and connector are quite small and I’d probable have melted them if I tried.

Just another puzzle to work out. Thanks for your help.

Dave


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[JasenC]

The 12v off the 7 pin should be a 10 gage wire, you can get some more 10ga to run to your camper battery.

I just buttoned mine up today.

[RJ Howell]

On my past DC/DC unit the signal wire is only to turn the unit on. So using a small gauge wire was no issue. I connected it to my running lights since I always have at least them on. My new unit is internally switched (no separate signal wire). Have to say I like my old one better as I could shut off the DC/DC charger manually when we're not camping/traveling. Now I disconnect the house battery..

If you were thinking of using the pin wiring as a source.. I wouldn't. Gauge is far to small to carry enough current to do much good unless you are traveling all day and haven't drawn down all that far. 16g wire will only send about 5amps of power to the pin, then you have to add travel to your house battery, remember, travel of current is measured both ways. Fifteen feet to the pin is 30 feet of travel.

My situation is different than most of you folks due to I built a truck camper. So my run is only 20ft (10ft to the battery). #10 gauge wire is just right for as I have a 30a DC/DC unit (hybrid for alternator/solar). Most folks I have conversed with are using 10gauge back to a connection on the TV and 12 gauge back on the TT/TD. They getting ~12amps to the battery. Units are 20a charing units.

Hope some of this helps!

I love the way the DC/DC works. It fits our traveling style and rarely do we require setting up the solar panels.
Safe Travels!

[friz]

I usually tap into a fuse using a fuse tap for these kind of connections. I usually find the circuit for radio or 12v "cig lighter" outlets. Something non essential but switched with the ignition switch. Also, in modern cars , the BCM shuts these down first when low voltage from the battery is detected.

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[troubleScottie]

As others have said, run a separate connection.

Think high power stereo amplifier in car (do people still do that?)

Battery - fuse - solenoid disconnect (switched) - 4-8AWG wire to rear of vehicle - Anderson connector with cover/similar - Anderson connector - 4-8AWG wire to charging point
Ground would be straight run with Anderson connectors.

Assuming you are using a junction box, it would be nice to have these two wires on their own connection points. I would not mix with the other D+ wire. This is complicated if using all the original 7 pins plus possible separate stop, right, left (for LED light bar) Never seen a box bigger than 10. Then again, lots of room for yet another box.

The Anderson connectors are nice reliable connectors. They have covers to protect from road grim eg dust cover, environmental boot, rigid protective boot (powerwerx)

[VanIsledave]

Thanks a million for the replies! I think I've got an idea of how to get the D+ signal now - not sure if I'll take it from the running lights or another circuit, it's probably going to be the one that's most easily accessible. I think I'll run it along the 7pin wire and have add connectors so I attach and detach it when hooking up the TD.

I wasn't super clear in my original post but I do have a good access point for the +12VDC on the trailer. When our trailer was built the company added a junction box underneath that gives me access to all of the wires. Makes life much simpler. Looks like this:



@troubleScottie - thanks for the tip on the Anderson connectors.
@friz - I've never used fuse taps before, are they pretty secure?
@RJ Howell - Sounds like our unit works the same as your original i.e. the signal turns it on. And yep, probably not a good idea to send that much current down a small wire!
@jasenC - Great advice, it's 10ga all the way.

Dave

[friz]

I have never had one fall out.

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