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Old 10-17-2016, 02:29 PM   #1
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Who is charging who?

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!
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Old 10-17-2016, 02:37 PM   #2
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Quote:
Originally Posted by Loosenuts View Post
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.
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Old 10-17-2016, 02:38 PM   #3
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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.
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Old 10-17-2016, 03:38 PM   #4
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Thanks Mike, that's what I figured was likely the case. I figured someone here would know for sure.
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Old 10-18-2016, 10:00 PM   #5
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Quote:
Originally Posted by mike837go View Post
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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Old 10-19-2016, 10:39 AM   #6
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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.
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Old 10-19-2016, 11:14 AM   #7
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Quote:
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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.
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Old 10-19-2016, 11:15 AM   #8
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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.
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Old 10-19-2016, 06:43 PM   #9
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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.
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Old 10-19-2016, 11:47 PM   #10
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Quote:
Originally Posted by mike837go View Post
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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