Voltage from Converter

[pman1088]

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.

[Paintinfool3]

I don't know about voltage drop but amount of amps could maybe?

[Paintinfool3]

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

[Roy W.]

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.

[hoppers4]

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

[Mustang65]

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.

Don

[ALJO]

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.

[DanNJanice]

Originally Posted by pman1088

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.

[pman1088]

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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[pman1088]

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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[DanNJanice]

Originally Posted by pman1088

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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13.66V seems right in line with what I would expect. Since the batteries were down to 12.4V, your charging current was most likely fairly high to start off, I would think about 15Amps. 1.24% looks to me like a reasonable voltage drop. As the batteries charge the current will continue to drop and the voltage drop will decrease as well.
If you really what to find out what is going on invest in a clamp-on DC amp meter so you can see what your current draw/source really is.

[Seann45]

Try the test again with the RV UNPLUGED..(no 30 amp service)

[Mustang65]

Originally Posted by Seann45

Try the test again with the RV UNPLUGED..(no 30 amp service)

x2
Use only the battery as the voltage source

Don

[Levinehikeski]

That drop will only be there with that sort of charge(like you said, 80%), and will change (be higher drop for lower percentage of battery and lower drop when approaching 100%). In the current (no pun intended) condition I wouldn't worry about that small amount of drop, if there is more draw...

What is the largest conductor your power center can take? If you are that worried, change it to a heavier gauge and report your findings here, I don't think you will see that much of a difference.

[SkyBound]

I just tried this with my trailer. My PD 55amp converter was putting out 13.68 volts and my batteries (Trojan 6V) were reading 13.2 volts. This was after letting the batteries drain down to 12.4 volts and plugging in. My wire from battery to converter is 6 gauge and the converter is about 1/3 of the way back from the front of the trailer. I was somewhat surprised to see that much of a drop.

Is this going to harm my batteries? It seems like the converter is trying to give them 13.7 and they're only getting 13.2.

[pman1088]

Originally Posted by SkyBound

I just tried this with my trailer. My PD 55amp converter was putting out 13.68 volts and my batteries (Trojan 6V) were reading 13.2 volts. This was after letting the batteries drain down to 12.4 volts and plugging in. My wire from battery to converter is 6 gauge and the converter is about 1/3 of the way back from the front of the trailer. I was somewhat surprised to see that much of a drop.

Is this going to harm my batteries? It seems like the converter is trying to give them 13.7 and they're only getting 13.2.

Based on the manufacture specifics for your batteries, I would say they are never going to get the recommended voltage during the bulk phase of the charge. I would venture to say this will cause a shorter life.

[SmokerBill]

Originally Posted by pman1088

Based on the manufacture specifics for your batteries, I would say they are never going to get the recommended voltage during the bulk phase of the charge. I would venture to say this will cause a shorter life.

I agree. Here's a screenshot from the Trojan T-105 data sheet. It calls for 14.8 VDC for the bulk charge period.
http://www.trojanbattery.com/pdf/dat...ata_Sheets.pdf
I'm pretty sure that the low charging voltage my onboard converter supplies has caused my Trojans to deteriorate faster than they would have than if they were charged with the recommended voltages.

[Mustang65]

Originally Posted by pman1088

Based on the manufacture specifics for your batteries, I would say they are never going to get the recommended voltage during the bulk phase of the charge. I would venture to say this will cause a shorter life.

You may or may not hit 14+ VDC for the charge voltage if the batteries are near fully charged. If so, it may for a brief time, then the charge controller will drop the voltage. If you want to see if the battery controller will hit 14+ Volts, pull your shore power connection, put your ceiling fan on, all the interior lights on, radio on, for about 4 to 6 hours (or the battery voltage discharges to 12.0VDC), then plug in to shore power. (monitor the battery voltage during the discharge so the battery does not drop below 12VDC) Check your battery voltage level. It should hit 14+ volts then. If not, check the charger specifications...

Don

[pman1088]

I left the Fridge and lights on last night, planning to put significant drain on the batteries for some more testing. This AM the voltage at the batteries read 9.67V (Bad batteries....blah blah blah, I blame the four months the trailer spent at the dealer). Upon plugging in I had 13.6 at the converter, and 13.06 at the batteries. 24amps was the draw the batteries were getting at first plug in.

Three times the external breaker attached to the outside of the trailer popped. I never saw the type of voltage that should be coming with a "bulk charge" from the WFCO (14.4) as advertised.

Should the charger immediately go to 14.4 with Battery levels that low? When does the 14.4 mode turn on?


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[pman1088]

Did a battery box project this weekend, which forced me to do some rerouting of wires. Low and behold, the charge wire was running through a 20amp auto-rest breaker on the front of the trailer.



I replaced it with a 40 amp, since it was always popping on and off when I would first add shore power after running the batteries down. Upon powering up, I'm at 14.56v at the converter and 14.22v at my batteries. Pushing about 24 amps 15 minutes after plugging in.


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