No charge from tow vehicle

theoldwizard1 wrote:

Katdaddy wrote:

ppine wrote:
Experience suggests that it is difficult to rely on your truck alternator to being your batteries on your trailer back up to full charge.

I wasn't expecting full charge. But I was expecting some charge.

Maybe yes, maybe no.

Try the following test. Disconnect the positive lead to the house battery. Measure the voltage of the house battery bank. Plug the trailer into the tow vehicle and start the tow vehicle. Have some one hold the engine speed at high idle (about 2000 RPM). Check the voltage at the disconnected positive lead and ground.

If you are LUCKY, the voltage will be above 13.0V. Good, but not enough to charge the batteries. You need a minimum of 13.8V and even that is really low. Cleaning all of the contacts, including grounds will help a little.


Read this DC-DC Battery charging

Right on the money

"
Thanks for this. Looked in junction box under kingpin. No fuses there. I will try cleaning the terminals and checking grounds and see what that gets me."

Yes, but did you stick an actual voltmeter there to see if it was doing truck (when running) 13+ volts or only the same voltage as when you put the voltmeter on the trailer batteries with no 7-pin connected?

Never mind for now about getting a proper full charge on the trailer batts from the7-pin. You just want to know if you are getting at least 13.x at the trailer batts with the truck running and the 7-pin connected.

Need to use the voltmeter place to place along the way to find where you lose the truck's 13.x volts on the trailer's side.

Interesting information. Thanks.

Katdaddy wrote:

ppine wrote:
Experience suggests that it is difficult to rely on your truck alternator to being your batteries on your trailer back up to full charge.

I wasn't expecting full charge. But I was expecting some charge.

Maybe yes, maybe no.

Try the following test. Disconnect the positive lead to the house battery. Measure the voltage of the house battery bank. Plug the trailer into the tow vehicle and start the tow vehicle. Have some one hold the engine speed at high idle (about 2000 RPM). Check the voltage at the disconnected positive lead and ground.

If you are LUCKY, the voltage will be above 13.0V. Good, but not enough to charge the batteries. You need a minimum of 13.8V and even that is really low. Cleaning all of the contacts, including grounds will help a little.

Read this DC-DC Battery charging

ppine wrote:
Experience suggests that it is difficult to rely on your truck alternator to being your batteries on your trailer back up to full charge.

I wasn't expecting full charge. But I was expecting some charge.

Experience suggests that it is difficult to rely on your truck alternator to being your batteries on your trailer back up to full charge.

BFL13 wrote:
First suspect is the pin connections (pin #4) Scrape out any corrosion, wiggle them together hard, and try again. You can also take the plug apart and clean it all up.

With the trailer plug not connected to the truck's, stick the multi-meter probes into pin 4 and ground pin--should get trailer battery voltage.

If no joy, your multi-meter search starts again at the terminals where the 7-pin cord is attached on the trailer. (on a 5er under by the kingpin, not sure where with a TT)

Sometimes the 7-pin positive on the trailer is spliced into another positive such as for the jacks and it is fused.

Of course you do this with the truck running so you can see the voltage is 13 or 14 something and not 12.x battery voltage.

Thanks for this. Looked in junction box under kingpin. No fuses there. I will try cleaning the terminals and checking grounds and see what that gets me.

With 12 volt DC, first thing is check the grounds. clean the grounds on the batteries and at the converter. Just a little corrosion can insulate them.

Iraqvet05 wrote:
What brand and model of truck? GM is notorious for not providing the fuse required to power the charge circuit for the 7 pin connect plugs.

The OP wrote: I checked the plug in the truck and I have charging voltage there.
So it sounds like that isn't the problem.

What brand and model of truck? GM is notorious for not providing the fuse required to power the charge circuit for the 7 pin connect plugs.