Who is charging who?

Loosenuts · 10-17-2016, 01:29 PM

I know that my truck will supply 12v to PIN 4 of the pigtail and that this assists in keeping the battery on the trailer charged while running down the road.

Now:

If my trailer (2016) is plugged to shore power.
And if my truck (2010 2500HD) is plugged into my trailer via the 7 pin pigtail.
And if pin 4 on my truck is hot all the time.
Will the charger on the trailer keep my truck battery topped off too?

Thanks!

mike837go · 10-17-2016, 01:37 PM

Quote:

Originally Posted by Loosenuts

I know that my truck will supply 12v to PIN 4 of the pigtail and that this assists in keeping the battery on the trailer charged while running down the road.

Now:

If my trailer (2016) is plugged to shore power.
And if my truck (2010 2500HD) is plugged into my trailer via the 7 pin pigtail.
And if pin 4 on my truck is hot all the time.
Will the charger on the trailer keep my truck battery topped off too?

Thanks!

Nope!

There is a relay in the Breakaway Battery Charging Circuit. When you turn the key off in your truck, Pin 4 is disconnected.

abarkl · 10-17-2016, 01:38 PM

Most likely not but check in with a volt meter.
Chances are there's a diode only allowing power to flow from the truck to trailer.

Loosenuts · 10-17-2016, 02:38 PM

Thanks Mike, that's what I figured was likely the case. I figured someone here would know for sure.

ctbailey · 10-18-2016, 09:00 PM

Quote:

Originally Posted by mike837go

Nope!

There is a relay in the Breakaway Battery Charging Circuit. When you turn the key off in your truck, Pin 4 is disconnected.

As with so many things, the answer is "it depends."

The factory 12v accessory jumper provided by GM under the hood of my chevy leaves the 12v lead hot whether keys are in the ignition or not.

I had this same conversation this past weekend, while camping, with my friend.

To prove it, I used a signal probe on the pin... and lo and behold! 12v with the truck just sitting there.

When the truck was purchased, I did not have 12v, and after searching the chevy forums... the GM techs told me where to find the factory pigtail that was still wrapped from factory, and where to plug it into the engine compartment fuse panel.

So, the correct answer would be: you should go check with a test light... you might be surprised.

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Loosenuts · 10-19-2016, 09:39 AM

Ok so then back to my original question.
If pin 4 was hot all the time (unswitched) would the charger on the trailer charge the battery in my truck or is there a diode or circuitry that would prevent it?
I should have check this when I was replacing the battery in my truck this past weekend. I guess the only way to know would be to disconnect the battery from my truck, plug into the trailer and see if I get 12v at the battery leads.

mike837go · 10-19-2016, 10:14 AM

Quote:

Originally Posted by Loosenuts

Ok so then back to my original question.
If pin 4 was hot all the time (unswitched) would the charger on the trailer charge the battery in my truck or is there a diode or circuitry that would prevent it?
I should have check this when I was replacing the battery in my truck this past weekend. I guess the only way to know would be to disconnect the battery from my truck, plug into the trailer and see if I get 12v at the battery leads.

Checking for +12 when truck's battery is disconnected would be a valid test.

If there is no diode, relay or resistor between the truck's battery and pin-4, then the trailer's charger will charge the truck's battery whenever you are on shore power or running the generator.

-------------

I would like to state that it was poor advice the Chevy Tech gave to leave pin-4 powered at all times. I feel that the two electrical systems should be isolated whenever the tow vehicle is shut down.

Pfflyer · 10-19-2016, 10:15 AM

You could check the voltage of your truck battery before you plug into shore and after you plug in. Before you plug in your should see about 12.7v. If your charger is charging your truck battery when plugged into shore it should read 13+volts depending on your charger profile.

3'senough · 10-19-2016, 05:43 PM

On this point. I once connected the shore power when the TV was connected and running. Sent my P3 into all kinds of fits and I had to unplug it and do a reset on it.

I never made that mistake again.

Point is, don't turn your key on when the shore power is connected.

ctbailey · 10-19-2016, 10:47 PM

Quote:

Originally Posted by mike837go

Checking for +12 when truck's battery is disconnected would be a valid test.

If there is no diode, relay or resistor between the truck's battery and pin-4, then the trailer's charger will charge the truck's battery whenever you are on shore power or running the generator.

-------------

I would like to state that it was poor advice the Chevy Tech gave to leave pin-4 powered at all times. I feel that the two electrical systems should be isolated whenever the tow vehicle is shut down.

You should look into a battery isolator, these are common devices for just this purpose, and they are also useful when the truck has a secondary battery for plowing and other equipment.

Chevys that come with the trailering package have the factory-supplied line to light up pin 4.

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ctbailey · 10-19-2016, 10:55 PM

Quote:

Originally Posted by Loosenuts

Ok so then back to my original question.
If pin 4 was hot all the time (unswitched) would the charger on the trailer charge the battery in my truck or is there a diode or circuitry that would prevent it?
I should have check this when I was replacing the battery in my truck this past weekend. I guess the only way to know would be to disconnect the battery from my truck, plug into the trailer and see if I get 12v at the battery leads.

Every truck is different. And if the truck was purchased used... all bets are off. Just hook up your multi meter to the line that feeds the pin4... and trace it toward the battery. If it runs through an electrical block, it will actually be difficult.

The best thing to do is unplug the 7-pin, then there's no question.

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mike837go · 10-20-2016, 07:08 AM

Quote:

Originally Posted by Pfflyer

You could check the voltage of your truck battery before you plug into shore and after you plug in. Before you plug in your should see about 12.7v. If your charger is charging your truck battery when plugged into shore it should read 13+volts depending on your charger profile.

Having 2 charging systems connected together WILL drive each other nuts!

After jump starting, disconnect the cables as soon as possible, unless you know that a failed charging system is what led to the dead battery.

Somebody mentioned having the truck engine running while the TT was plugged in. Last time I made that mistake I ripped the TT's power cord. Now unplugging and safely stowing the cord is part of the pre-movement checklist.

Dustdevil · 10-20-2016, 07:15 AM

Many Chevy and Ford pickups with towing option have the circuitry connected, but not the fuse/relay. It is usually in a small plastic bag in the glove box, or in the box surrounding the power fuse block under the hood. I had my 2003 Chevy Crew Cab diesel for 14 years before I discovered that the relay/fuse for the power pin in the 7 pin connector was not plugged into the socket, and I did research on it. I thought it had been there the whole time. It wasn't, and typically is not from the factory.

Camper_bob · 10-20-2016, 09:07 AM

I have often wondered how "smart" the 12V in the 7-pin actually is. If you're plugged into shore power and your trailer is plugged into your truck that is running, what happens? The truck is sending 13.XX volts through the 7-pin, and thus to the battery, and the converter is sending 13.XX volts to the battery. Would the truck see the voltage from the converter on the trailer and dial back the output voltage? Would the converter see the truck's voltage? Or is the charge line in the 7-pin at the mercy of the charge controller in the truck and just putting out the same voltage the chassis battery is calling for?

And what about the other direction? Can the trailer battery drain the truck's chassis battery through the 7-pin? Like if you leave the trailer hooked up and plugged into the truck (but NOT shore power) over night? I would hope not. In most modern trucks, there is "battery saver" technology that wouldn't allow something like this? Right? I always get a little nervous and make sure my 7-pin is unplugged from the truck unless we're on the road.

I can say that I have had the truck plugged in and running while the trailer has been connected to shore power and had no ill-effects that I'm aware of. Now, granted, I don't leave it like that for long, but it happens. I usually will fire the truck up to get it cooled down and finish up by unplugging and stowing my shore power cable. Sometimes it's 2 minutes, sometimes it's 10 minutes.

I do know (or at least I'm pretty sure) that my 7-pin is dead if the truck is off. Looks like I'll be breaking out the VOM this evening just to be sure.

Dustdevil · 10-20-2016, 10:18 AM

Almost every tow vehicle that has the towing package from the factory has a battery isolator circuit. When the engine is turned off, with the key in the "off" position, the tv batteries are isolated from the 7 pin connector. A homebrew system may not be that sophisticated, depending upon who wired it. Unless that system fails, you're fine keeping the trailer plugged into the truck overnight, and it won't suck the truck batteries dry, by design. However, the moment you turn on the key or especially start the engine, with your trailer plugged into 120 vac, all bets are off. The charging systems will both attempt to put over 13 volts on the same wiring, which is now connected, and you'll likely eventually screw up your charger, your alternator, your tow vehicle's on-board computer, or some combination of the three.

mike837go · 10-20-2016, 10:31 AM

Quote:

Originally Posted by Camper_bob

I have often wondered how "smart" the 12V in the 7-pin actually is. If you're plugged into shore power and your trailer is plugged into your truck that is running, what happens?
...snip...
I do know (or at least I'm pretty sure) that my 7-pin is dead if the truck is off. Looks like I'll be breaking out the VOM this evening just to be sure.

The regulators from each charging system start switching irrationally.

One activates its charging current (on the truck, +12V (approximately) is applied to the rotor) which puts up to MAX AMPS + MAX VOLTS (depends on engine speed) on the output stud of the alternator. The regulator monitors electrical system voltage, when the voltage goes too high, the power to the rotor is disconnected. Once the voltage drops, the rotor is repowered. This cycling happens several times per second. With just 1 battery in the circuit everything is cool.

Now, insert a 120VAC powered battery charger; It supplies about 14V for several seconds, stops, samples the battery voltage and pushes Bulk, Top-up or Maintenance voltage again. Cycling several times per minute.

So, when the battery charger is sampling, the alternator will cycle, then the battery charger will go into Maintenance mode. Unless the sampling occurs during an off cycle of the alternator, then the charger will go into Bulk mode for a cycle.

All in all, nothing will probably get damaged from a minute or so of this 'confusion'. But why abuse perfectly good electronics in this fashion?

My procedure and my advice:
1) Disconnect the truck before going on shore power.
2) Disconnect shore power and stow the cord before connecting to the truck.

Simple. Easy. Safe.

Camper_bob · 10-20-2016, 01:07 PM

Looks like I'll have to change my process then. I have a well ingrained process for hooking up the truck (which includes plugging in the 7-pin), and a well ingrained process for final prep for departure (the last step of which is to disconnect shore power, and conduct a final walk-around on my way back to the driver's seat).

Looks like I'll have to make a couple adjustments to those processes. My biggest concern is forgetting to connect the trailer to the truck. But then, I could just make that my very last step during my final walk-around. But I guess I would discover my error pretty quick, like right about the first time I went to stop and the trailer brakes didn't engage!

Subaru297 · 10-20-2016, 01:08 PM

My solar panels are never disconnected and as long as the sun is shining they are charging the batteries. Up to 14.7 volts at times.

That should not be any different than the converter trying to charge a battery.

I have not suffered any failures of the truck or trailer from them both being plugged in and trying to charge each other.

You can make the same argument for someone who has solar and is also plugged into shore power. Two chargers can be attached to the same battery without any ill effects.

Loosenuts · 10-20-2016, 01:25 PM

The reason I brought all this up was because the battery on my truck decided it was time to die last weekend. Fortunately we were at home. If we had been camping, the truck would have been backed up to the trailer. So the thinking was, if my truck battery went dead while camping, would I be able to plug it into the trailer and charge the battery enough to get the truck started (as I did at home by putting a charger on it for a few minutes).

It looks like the answer is a resounding MAYBE with a lot of qualifiers.
I do appreciate everyone's input on this. It would appear the best course of action would be to use a V/O meter and find out if that pin 4 is hot all the time.

EDIT: So I went and checked and mine is live with the key off.

And by default one of the first things I do when I pull in is unplug the trailer from the truck. Mainly because I don't want one killing the other.

Camper_bob · 10-20-2016, 01:35 PM

Quote:

Originally Posted by Loosenuts

The reason I brought all this up was because the battery on my truck decided it was time to die last weekend. Fortunately we were at home. If we had been camping, the truck would have been backed up to the trailer. So the thinking was, if my truck battery went dead while camping, would I be able to plug it into the trailer and charge the battery enough to get the truck started (as I did at home by putting a charger on it for a few minutes).

It looks like the answer is a resounding MAYBE with a lot of qualifiers.
I do appreciate everyone's input on this. It would appear the best course of action would be to use a V/O meter and find out if that pin 4 is hot all the time.

And by default one of the first things I do when I pull in is unplug the trailer from the truck. Mainly because I don't want one killing the other.

In that case, I would simply dismount the battery from the trailer and carry it to the front of the truck and use it to jump the truck. But then I have a crappy old Interstate dual purpose that's on its way out. So if I killed it and needed to get a new one, that wouldn't break my heart.

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