variable voltage from TV 7-way AUX?

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variable voltage from TV 7-way AUX?

Postby southboundsnakes » Thu Mar 17, 2016 1:40 pm

Hello all,

Question: I am finding that I'm not getting a great deal of charge into my trailer battery bank (2 x marine 12v in parallel trickle charging via tow vehicle AUX lead in a 7-way round connector) :thinking:.

When using a simple voltage tester, I get the light indicating that the ring terminal attached to the battery bank is live.
When testing with a voltmeter, I get a variable reading both at the TV-7way AUX and at the ring terminal attached to the battery post. starts at zero, cycles up to 40v and then back to zero, over and over.

This may be a goofy newb electrical question but in my experience the only way to learn is to look foolish sometimes!

Thanks a bunch in advance!!

sss
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Re: variable voltage from TV 7-way AUX?

Postby GuitarPhotog » Thu Mar 17, 2016 1:57 pm

40 Volts sounds scary. Are you sure of your measuring methodology? Try disconnecting the trailer battery before measuring.

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Re: variable voltage from TV 7-way AUX?

Postby H.A. » Thu Mar 17, 2016 5:09 pm

I.
Last edited by H.A. on Sat May 14, 2016 5:28 pm, edited 1 time in total.
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Re: variable voltage from TV 7-way AUX?

Postby tony.latham » Thu Mar 17, 2016 5:54 pm

I can't understand how you could be producing 40 volts with a 12V battery system and car alternator. :thinking:

It has to be something that your doing wrong with the voltmeter.

Test your batteries (one at a time) while not hooked up to the TV. They should be around 12.6V. If you get that 40V reading, it's the way you're running your voltmeter. Then with the engine running and disconnected from your trailer, test the vehicle voltage. It should be somewhere around 13.5V (or up to 14.5V) while running.

Voltage output won't tell you how fast your charging though... You need either a higher amp alternator or a fatter wire or both. And it'll still read 13.5V or there abouts.

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Re: variable voltage from TV 7-way AUX?

Postby southboundsnakes » Fri Mar 18, 2016 1:21 pm

The batteries are reading at their correct float voltage (13.6v) with both the volmeter and the display on my solar charge controller...thus it must be my methodology. Red lead on the on the AUX pin on the tow vehicle 7-way round, and the black lead on the center pin? or should I be grounding the black lead (on the tow vehicle trailer hitch, for example?)

Thanks again and PFMI!

sbs
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Re: variable voltage from TV 7-way AUX?

Postby MtnDon » Fri Mar 18, 2016 4:20 pm

Red lead on the on the AUX pin on the tow vehicle 7-way round


I believe the reading should be taken from the terminal marked for 12 volts or battery and the ground. The aux is usually used for something like backup lights or something else other than left, right, tail, ground or electric brakes. There's no telling for sure what the aux is connected to on the TV; ??
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Re: variable voltage from TV 7-way AUX?

Postby GuitarPhotog » Fri Mar 18, 2016 8:59 pm

Measure from pin 4 (black wire) +12 VDC to pin1 (white wire) ground. Your wire colors may be different, but the pin numbers are standard. The center pin is most commonly used for backup lights.

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Re: variable voltage from TV 7-way AUX?

Postby Dale M. » Sat Mar 19, 2016 5:33 am

Believe this is how plug is wired.... Colors may not be same but pin designations are correct, so disregard colors...

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This is 7 pin RV connector (most common) not to be confused with 7 pin round pin heavy duty connector used on large trucks wired differently...

You should have approximately 12.8 to 13 .5 volts across pins 1 ( ground) and 4 (12 volts) and same voltage from pin 4 to TV chassis (ground)... Also on some vehicles 12 volt to pin 4 is constant and its also conceivable on some vehicles it may be controlled by ignition switch...

Not sure on your trickle charge statement as on my Chev PU the 12 volt lead (pin 4) is fused at 40 amp...

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Re: variable voltage from TV 7-way AUX?

Postby southboundsnakes » Wed Mar 23, 2016 11:15 pm

Thanks a bunch for your responses guys and gals. Much appreciated and always psyched to get sound and clear advice.

SBS :thumbsup:
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