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Old 05-01-2016, 06:40 PM   #1
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Voltage from Converter

I've been reading up on the whole RV electrical genre lately and was convinced due to the location of my power center (mid coach, WFCO 8955PEC) and my batteries (tongue) that my batteries were on their way to certain death due to such a long feed and likely improper size wires from the factory. I started this project assuming I was going to be running some new wire to the batteries from the power center....all the while wondering why with a brand new, 2016 TT, this is still an issue.

I found a 6AWG wire at the front of my TT, attached to one of the batteries and an identical 6 AWG wire inside my power center, hooked to the battery feed post. I did some real rough math based on an estimated length (I went with 25 feet) and of course became again mad that would need to fix an issue that should not be an issue with a brand new TT.

Imagine my surprise when I found the following readings at these two spots. I tried to take these photos so you could see I was not making anything up. Seriously, no foolin'.

This photo is from the power center. I used the very point of the leeds, touching the wires as they come through the connectors.
Note the voltage is 13.66.


This photo is from the batteries. I have the loop of the connector on the 6AWG wire touching the leed. The negative is touching the negative post on the battery. The voltage kept bouncing between 13.66 and 13.67.


How does this make sense? There should absolutely be a voltage drop...right? This testing was done while plugged into my 30AMP connection at home.
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Old 05-01-2016, 06:49 PM   #2
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I don't know about voltage drop but amount of amps could maybe?
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Old 05-01-2016, 06:51 PM   #3
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You do have to remember that the convertor just puts a low amper charge to recoop lost battery juice and top it off when plugged in . The convertor supplies 12 volt to all the campers system when plugged in, not the battery
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Old 05-01-2016, 06:51 PM   #4
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That's why it's 6 gauge wire, to minimize voltage drop. Generally maximum converter output on the battery charging stage is only around 8 amps and 6 gauge is more than sufficient to handle that.
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Old 05-01-2016, 07:03 PM   #5
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The wires won't have a voltage drop if there is no current draw. Voltage drop comes from line loss. The longer the line, the more voltage drop will occur depending on the how much current is being drawn. Voltage drop is different for every wire size and is calculated by volt/foot (millivolt/foot or microvolt/foot).

Link to voltage drop calculator http://www.calculator.net/voltage-drop-calculator.html
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Old 05-01-2016, 07:14 PM   #6
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To measure the voltage drop you need to unplug from the shore power source, let the battery rest for a few hours, then take your readings from the same points. If you have the controller putting out 13.6 volts and your battery is close to 13.6 volts your not going to read much of a difference.

My TT has a 10AWG from the main 30 amp fuse (by Batteries) and the TT's battery charge controller.

6AWG is not going to show a big voltage drop.

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Old 05-01-2016, 07:15 PM   #7
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Hoppers is correct there's no voltage drop when there's no current draw. AWG 6 is the correct size and strokes with the minimum requirement. Seems you have the 55 amp WOF. If you are planning to install a inverter do it as close to the batteries with the correct size wire.
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Old 05-01-2016, 07:22 PM   #8
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Quote:
Originally Posted by pman1088 View Post
I've been reading up on the whole RV electrical genre lately and was convinced due to the location of my power center (mid coach, WFCO 8955PEC) and my batteries (tongue) that my batteries were on their way to certain death due to such a long feed and likely improper size wires from the factory. I started this project assuming I was going to be running some new wire to the batteries from the power center....all the while wondering why with a brand new, 2016 TT, this is still an issue.

I found a 6AWG wire at the front of my TT, attached to one of the batteries and an identical 6 AWG wire inside my power center, hooked to the battery feed post. I did some real rough math based on an estimated length (I went with 25 feet) and of course became again mad that would need to fix an issue that should not be an issue with a brand new TT.

Imagine my surprise when I found the following readings at these two spots. I tried to take these photos so you could see I was not making anything up. Seriously, no foolin'.

This photo is from the power center. I used the very point of the leeds, touching the wires as they come through the connectors.
Note the voltage is 13.66.


This photo is from the batteries. I have the loop of the connector on the 6AWG wire touching the leed. The negative is touching the negative post on the battery. The voltage kept bouncing between 13.66 and 13.67.


How does this make sense? There should absolutely be a voltage drop...right? This testing was done while plugged into my 30AMP connection at home.
I am a little unclear what you are attempting to prove/disprove. In particular I am unclear what you are actually measuring in the last picture. If I were doing this I would have everything connected and then measure at the convertor, and then again at the battery itself. The difference is the loss through the wiring.
Voltage drop is a function of current. If there is very little current through the wires, there will be little or no drop. With 6AWG wiring I would not expect to see much voltage drop until you were drawing 10-15 amps.
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Old 05-01-2016, 07:34 PM   #9
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Voltage from Converter

I am trying to understand why I'm not seeing any voltage drop in my wiring. In the second photo, I'm connected to the battery wire coming from the converter/charger...minus all other drawing or adding connections, my thinking was this would be the closest to what the converter is giving the batteries. I now understand thanks to hoppers4 and Mustang65 that there needs to be some draw to see this drop. I will let some parasitic draw drain my batteries for a few days and then try again when the batteries are actually taking in some juice....I'll post my findings. Thanks for the help!


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Old 05-02-2016, 09:10 PM   #10
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Voltage from Converter

This evening my batteries were measuring around 12.4V (roughly in the 80% range) so I plugged in the shore power. 13.66V at the power center and 13.48V at the batteries.....that puts the drop around 1.24%


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