Maximum wire gauge for WFCO power center

[Archicamper]

During this stay at home period, I have been working on my camper to get ready for some off-grid national park adventures whenever that may happen. To date, I have replaced my battery with a pair of Trojan T105 6 volt batteries and replaced the WFCO converter/charger section of power center with a Progressive Dynamics4600 Series converter/charger.

Upcoming projects include adding a battery monitor, a small inverter for the television and upgrading the wire size between the charger and the batteries. I am not in a position to add solar at this time. I have a generator and would like to minimize the run time to charge the batteries.

To this end, I want to increase the wire gauge between the charger and the batteries. The run is about 20 feet between the charger and batteries. From what I have seen on this forum a #4 gauge wire appears to be the largest gauge that will go into the lug on the WFCO power center. I want to verify this before I order wire.

So after all this background, can some confirm that a #4 gauge wire is the largest size I can connect to the WFCO power center?

Thanks

[TitanMike]

Tale a look at the WFCO fuse circuit board where the main battery wire is connected. It has a marking next to it that I believe indicates wire size the lug will accept. On mine it was 1/0. I only used #4 awg wire (welding cable works great) on mine.

To be sure, remove the existing wire and measure the lug's ID.

A #4 wire (conductor) is .204" in diameter and a 1/0 is .325

#2 is ,258 and #1 is .289.

If you use welding cable and find it hard to get all the strands into a lug, consider "tinning" the end which is an old term for just adding solder to get all the strands to stay put.

On that, I've found the easiest (meaning least frustration" is to get some non corrosive/rosin based soldering flux, dip the end of the wire in it, then using a good sized soldering gun (not torch), heat it well and then touch your rosin core solder to it. You just need enough solder to coat all the strands, no globs.

I'd use the largest wire you can squeeze into the lug.

Another method if you have the room you could also use one of these:






It will allow you to connect up to a 1/0 wire to a smaller terminal.

[Archicamper]

Do I need to replace the existing cut-off and inline circuit breaker? It doesn't seem that the draw on the batteries has changed.

[TitanMike]

Originally Posted by Archicamper

Do I need to replace the existing cut-off and inline circuit breaker? It doesn't seem that the draw on the batteries has changed.

When I upgraded my wire size I also added a 100 amp ANL type fuse (replacement fuses are sold at most Auto Parts Stores).

The fuse is to protect the wire should it be shorted to the frame for any reason and everything connected to the electrical system has it's own protection either in fuse panel or an inline fuse somewhere. I could go as large as 125 amp for the #4 wire I used but except for a 1 Kw Inverter mostly the max current on the line is 60 amps when batteries are charging.


The main circuit breaker installed is now as useful as nipples on a male.


BTW, when upsizing the main wire (Positive) don't forget to upsize the ground (negative) wires at both battery and converter. Make sure the connections to the frame are sound. I used some panel lugs and attached them to the frame with self tapping bolts. I prepped frame where lugs were to be mounted by sanding off all paint and applied some "No-Ox-Id" paste when I bolted the lugs down. I then attached the wire to the lugs, again using the same paste.

Original connections on my TT were crimped connectors secured with self tapping screws. No frame prep, just screwed down over the paint.

[01tundra]

When I replaced the WFCO converter with our new Wildkat converter I reused the factory fuse panel.

The most I could do is dual feed positive and negative with 6 AWG, I don't see how you would make 4 AWG work personally...

Below is an old picture, I've since replaced the two white negatives with another 6 AWG.

[SailorSam20500]

Originally Posted by 01tundra

Do you have a link for those posts.

Looks like some of these: https://www.walmart.com/search/?quer...auge%20reducer

[01tundra]

Originally Posted by SailorSam20500

Looks like some of these: https://www.walmart.com/search/?quer...auge%20reducer

Yeah I found them on Amazon as well -

https://www.amazon.com/Gauge-Reducer.../dp/B07R24MLXY

[TitanMike]

Originally Posted by 01tundra

Yeah I found them on Amazon as well -

https://www.amazon.com/Gauge-Reducer.../dp/B07R24MLXY

I've used the ones from Amazon and they're great for use with welding cable that have all the fine strands to corral. I used them to make connections to a negative bus that would only accept #8 wire.

[TARVIDSON]

I am curious how much charging time improvement one can expect to get from increasing the wire size between the converter and the batteries? I only have three to four feet of wire between the two.

[01tundra]

Originally Posted by TARVIDSON

I am curious how much charging time improvement one can expect to get from increasing the wire size between the converter and the batteries? I only have three to four feet of wire between the two.

You can use this calculator to compare voltage drop with factory wiring vs. larger AGW.

My battery is about 18" from the converter and I have 1/0 cable. I am getting a full 55 amps when I start recharging my BattleBorn battery.

https://www.calculator.net/voltage-drop-calculator.html

[TARVIDSON]

Thanks Tundra for the voltage drop calculator. I am not sure what size wire the motorhome has presently. I will check it out and see how much difference an upgrade would make. I do have the PD converter replacement for the WFCO 5500 and the WFCO fuse panel and two 12V lead acid batteries They have been adequate for 2-3 day boondocks.

[Larry-NC]

I just happened to have a WFCO 8955 laying around in the basement, with distribution board. The terminal diameter is 7.2mm, as measured with an internal vernier caliper. That corresponds to .283 inches. Tough to read as I've been having double vision.

I also test-fitted some drill bits. 9/32" fit loosely. 5/16" did not fit. So I'm guessing 19/64" or .297"

[Archicamper]

Originally Posted by TARVIDSON

I am curious how much charging time improvement one can expect to get from increasing the wire size between the converter and the batteries? I only have three to four feet of wire between the two.

I have over 30 feet of total run between my battery and converter including a short distance on the negative side. Wire size does make a difference.

[Archicamper]

Boy, I just priced out wire and it is expensive! If I was to use 1 gauge for my camper, it would be over $100. If I use 4 gauge it would be around $50.

1 gauge is recommended for my run but that is a tough pill to swallow!

Looks like I need to save up either way!

[TitanMike]

Originally Posted by Larry-NC

I just happened to have a WFCO 8955 laying around in the basement, with distribution board. The terminal diameter is 7.2mm, as measured with an internal vernier caliper. That corresponds to .283 inches. Tough to read as I've been having double vision.

I also test-fitted some drill bits. 9/32" fit loosely. 5/16" did not fit. So I'm guessing 19/64" or .297"

That means that #2 awg wire should fit with a "few thous' to spare". It's only .254".


{for the OP}
According to a wire size calculator, at full output of your converter #2 awg wire would be good for 32.1 feet yielding only a 2% voltage drop. Put 13.8 Volts in at the converter and get 13.55 at the batteries at 55 amp. #4 awg will only yield 13.4 volts at the batteries with same input/current.

Something else that doesn't often get discussed when talking about wire upgrades is the number of connections as well as the quality of the connections.

Every connection is a potential source of voltage drop. Make sure that ALL are "shiny metal" clean and even consider using a good electrical "grease" like No-Ox-Id to prevent any corrosion from degrading the connection. Keep connections to a minimum and if possible utilize something like a bus bar for any connections that are usually made to the battery. Avoid stacking connectors on a positive post. Run the main cable directly to the battery disconnect switch which is connected to the battery. Run a separate wire from disconnect switch to the bus bar and make all other connections like slide, awning, tongue jack, etc, to the bus bar.

When all done take out your multimeter, turn on every 12 volt appliance and accessory you can and measure the voltage from the connector swaged to the wire and the bolt is's connected to. Record the voltage drop for each connection. If they'e more than .1 volt, clean again and re-connect.

This is also why keeping connections to a minimum is important as the voltage drops add up.

[TitanMike]

Originally Posted by Archicamper

Boy, I just priced out wire and it is expensive! If I was to use 1 gauge for my camper, it would be over $100. If I use 4 gauge it would be around $50.

1 gauge is recommended for my run but that is a tough pill to swallow!

Looks like I need to save up either way!

How long a run"

Here's a 50' piece on Amazon of Welding Cable which is great for RV's as it's extra flexible. Only $90.

This offer is black but some red tape on each end would identify it as a Positive cable.

https://www.amazon.com/Gauge-Premium...motive&sr=1-15

[Larry-NC]

Originally Posted by TARVIDSON

I am curious how much charging time improvement one can expect to get from increasing the wire size between the converter and the batteries? I only have three to four feet of wire between the two.

Let's look at numbers instead of just arguing.

Let's compare, for example, 10 feet between battery and converter, AWG 6 vs AWG 0, and 55 amps charging current to a flooded lead-acid battery. Let's also assume that the negative lead has four feet of copper and the rest is through the frame (0 ohms).

Resistance of AWG 6: 14 ft. * .3951 ohms/1000 ft. = .005531 ohma
Resistance of AWG 0: 14 ft. * .0983 ohms/1000 ft. = .001376 ohms

Voltage drop across AWG 6: 55 amps * .005531 ohms = .304 volts
Voltage drop across AWG 0: 55 amps * .001376 ohms = .076 volts

Now that doesn't seem like much voltage drop, and it isn't. But because of the sleazy way these converters are designed, it makes a huge difference. The charging range of the battery isn't from 0 to 12.6 volts. The important range is really from around 12 to 15 volts. To completely charge a battery optimally different levels of voltage must be applied at different stages:

• Bulk mode is the fast charge applied up to 80% of charge.
• Absorb mode starts at around 14.5 volts. The current is lowered and the batteries charge more slowly. The Absorb mode ends when the current drops to a set level or a fixed time elapses. It is generally considered that the batteryis 100% charged at this time.
• Float mode is then entered. It maintains the charge without overcharging.
• Equalization mode is actually overcharging periodically for short time intervals. It serves to extend the life and performance of the battery.

Let's look at the cutover from Bulk Mode to Absorb Mode.
With AWG 6 wire, the cutover takes place at 14.5 volts at the converter. It's only 14.2 volts at the battery. The cutover takes place way too early. The battery will eventually fully charge but it will take much longer than necessary.

With AWG 0 wire, the voltage at the battery will be 14.48 volts instead of 14.5. an almost insignificant difference.

The resistances are tiny, but they are significant, given the huge current involved.

[Begin Rant]
The real problem isn't the cable size or converter-battery distance. It is the fact that the charging voltage is measured at the converter, not at the battery terminals. Inside the guts of the converter is a voltage sensor that measures and regulates the charging voltage. That sensor is connected internally to the two cables going to the distribution board and battery.

There's a notion called 4-wire design. The converter output is two heavy cables to the battery, as before. Two light-gauge wires run with these, from the battery to the sensor in the converter. The sensor is high-impedance so almost no current flows in them and hence there is no voltage drop. The sensor remotely senses the voltage at the battery so it changes states at the correct time, regardless of the amount of voltage drop in the cables.

This scheme has been around for decades. It was old-hat when I was in engineering school in the 1960s. It was available on every lab supply I ever used. But for some unknown reason it is not used in RV converters.
[End Rant]

[Larry-NC]

Originally Posted by Archicamper

Boy, I just priced out wire and it is expensive! If I was to use 1 gauge for my camper, it would be over $100. If I use 4 gauge it would be around $50.

1 gauge is recommended for my run but that is a tough pill to swallow!

Looks like I need to save up either way!

I wonder why it's not a design consideration to install the converter in close proximity to the battery. In our 2008 Forest River Cherokee, the converter i right up against the front wall of the trailer. The cable distance is maybe five feet, including the stop at the resettable breaker. (I could move the breaker and recover maybe two feet of that.)

In our 2002 SOB Nash which is a 22 foot unit, the converter is under the sink, 2/3 of the way to the back. The bed is in the front and there is room under it. The 120 v entrance is halfway between the converter and bed. I've considered relocating the converter all the way forward. It would be pretty easy to cut a few vents into the bed platform.

[TitanMike]

Originally Posted by Larry-NC

I wonder why it's not a design consideration to install the converter in close proximity to the battery. In our 2008 Forest River Cherokee, the converter i right up against the front wall of the trailer. The cable distance is maybe five feet, including the stop at the resettable breaker. (I could move the breaker and recover maybe two feet of that.)

In our 2002 SOB Nash which is a 22 foot unit, the converter is under the sink, 2/3 of the way to the back. The bed is in the front and there is room under it. The 120 v entrance is halfway between the converter and bed. I've considered relocating the converter all the way forward. It would be pretty easy to cut a few vents into the bed platform.

There are lots of "floor mount" converters that can be mounted close to batteries. Just need 120 v power routed to them.

I'm guessing that factories prefer the All in One power centers to just simplify wiring. Once the unit leaves the factory they only care that it charges the batteries, not how fast.

Considering that the majority of purchasers don't boondock (just a guess) they figure charging from shore power or tow vehicle/coach alternator is adequate.

[Jay2504]

Based on my own experience, trying to charge 3 group 31 FLA batteries with a WFCO 55 amp converter, the best I saw was 24 amps, but I didn’t check every time the batteries were low. What I would recommend to the OP to get the “most bang for the buck” is to simply buy enough #6 wire to run alongside the existing charge wire thereby cutting his voltage drop in half. Using the picture that 01 Trundra showed, hookup would be easy. The OP could add a complete #4 ground cable from the batteries to the frame for another $5. Also double the ground #6 wire from converter to frame. I did this with #8 wire that I had laying around and saw a pretty big improvement compared to the #6 positive wire by itself from the converter to the battery cut off switch. Not as good as what bigger cable would provide, but a significant improvement. Jay