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Old 01-16-2021, 10:59 PM   #1
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Wire gauge from battery to charger

Hi all, looking for some ideas here for my new travel trailer. I have a WFCO 8955PEC converter charger. Iím moving from one AGM battery to 3 Lion Engergy UT 1300 LiFePo4 batteries I therefore would like to upgrade the charger. Iím looking at the PD9100 series and would like to go as high of amperage model as I can. The Lion Energy batteries are spec for charging as high at 100A. I know that I need the appropriate gauge wire going from the battery to the charger. This distance is approximately 10ft.

On the existing battery posts it is 2 AWG wire on the posts. When I look under the cover of the WFCO at 12V battery pos and neg, it is 8 AWG wire. What gives? I was expecting that the same gauge would be used from the battery to the charger converter. What am I missing here?

I donít think they are related, but the TT also has a solar controller and a 1000w inverter.

Thanks!
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Old 01-16-2021, 11:25 PM   #2
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You need to use a wire gauge at least the smallest size rated for the amperage over the distance needed. That being said, if 6 or 8 gauge will do the job, bigger is always better. If your terminal connections will handle 2 gauge, go with 2 gauge. The thicker the wire gauge (lower number) the less resistance loss in voltage you will have over a given distance. 10' is not very far of a wire run, so I would go with 2 gauge to get the largest benefit possible. Might as well use the best wire size since you are spending money on LiFePo4. Welding cable is commonly used and is very durable and not super expensive. You can also get a hydraulic crimp tool to install the cable ends on Amazon (also not super expensive). I bought my welding cable on eBay by the foot and you can get it with different size outer insulation.

I have been buying all my terminal connectors and battery terminals from "Genuine Dealz" in Georgia. They also sell tinned marine grade wire. I highly recommend them.

https://www.genuinedealz.com/

AC/DC Wire & Supply also has a store on eBay. This is also where I've been buying my welding cable and my copper core large crime terminals. Again I recommend them, never had issues with them.

https://www.ebay.com/str/acdcwireandsupply

This is a decent video on using a 16 ton crimper on a 4/0 battery terminal. They then seal with heat shrink tubing to finish the job of a custom cable.

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Old 01-17-2021, 09:32 AM   #3
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Thank you Dward. I do have a hydraulic crimper and am familiar with making the connections. The trailer has a fully enclosed bottom, so I cannot trace the battery run. I just see 8 awg at the WFCO DC board and 2 awg at the battery.

I know that 8 awg will not allow the 80A charging Iím hoping for, so I need to upgrade it. I guess Iím just confused as to what may be happening with the wiring to the battery.

Thanks
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Old 01-17-2021, 02:19 PM   #4
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With the new "Lithium" batteries the charge current will be all your new converter can put out so bigger is better for wire size.

Two things to consider:

The distance from converter to battery;

The maximum size wire you can attach to the terminals of your new Converter.

Here's a wire size calculator that works well for selecting wire size based on distance. Measure BOTH the wire length from converter to batteries and wire length from Battery to frame ground AND wire length from Frame ground to converter negative terminal.

https://www.wirebarn.com/Wire-Calculator-_ep_41.html

Add all together and use that length for your calculations.

When I upgraded wire size in my TT for Lithium batteries I didn't bother with the current wire routing as it was way too long to begin with. I merely went down into the underbelly and ran my new wire that I'd encased in a piece of reinforced rubber hose for chafe protection straight to the batteries new location. Only opened the underbelly cover at both ends.

On my converter the max wire size the converter would accept was #2 Awg. If there is room an adapter for larger wire, like 2/0 awg can be used for the connection.


An even better way is to abandon the WFCO converter section by disconnecting it on both ends (120v connection and 12v fuse board) then install a "Deck Mount" converter near the batteries. Then run a piece of Romex (12-2 w/ground is OK) from the converter's circuit breaker to the new converter location. This will charge the batteries as fast as it can and the old #8 awg wire will be more than adequate to run the 12v accessories so leave it alone.

If you want, you could merely fasten some conduit to the bottom of the frame and run your new circuit through it using weathertight fittings. Doing that you'll need to run THHN type wire and transition at each end with a junction box. No Romex in conduit.
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Old 01-17-2021, 02:57 PM   #5
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My thoughts, 2 awg at the battery goes to load center. The 8 awg from converter also goes to load center. Or there is a buss bar somewhere they meet.
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Old 01-17-2021, 05:56 PM   #6
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Being LFP batteries, they don't need to be mounted outside. If they are, is moving them closer to the converter an option? The wire requirements may drop a lot, if you can.
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Old 01-17-2021, 10:32 PM   #7
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Many thanks to you all for your responses. Definitely learning here. Much appreciated.

So despite the snowy weather here I crawled under the trailer and found the 2awg positive from the battery runs to the battery disconnect switch and from there continues as 8 awg, presumably all the way to the converter charger.

In line with suggestions here, my current plan is to change the battery location to inside the front storage compartment, next to the inverter. I will disconnect the wfco 8955 but leave it in place. Then I will locate the new PD9180 next to the batteries. From there I can run one set of 2 awg wire to the inverter and another from the battery pos to the 9180 and the negative to the chassis (or at this proximity is it just better to connect the negative fro the battery to the negative of the charger?). Both the inverter and the charger will be within 2 feet so I think all good there I terms of gauge.

For the 12v run from the 9180 charger to dc fuseboard, I think I can just repurpose the existing 8 gauge wire that used to run from the battery pos to the DC fuseboard. Make sense?

For 120v going into the 9180 there happens to be a 120v outlet plug right there for the inverter. Thatís a 15a circuit but the inverter is only 1000w, so I think I could also connect the 9180 right there and thereby avoid running any new wire to the power center/AC breakers.

This all sound correct?

One last question. It appears to me that the solar controller is connected to the battery at the disconnect switch. When I disconnect, the solar remains on, which I guess makes sense as itís then able to continue charging the battery. I think this will be okay to leave as is, but just want to make sure no issues.

Thanks
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Old 01-17-2021, 11:22 PM   #8
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Originally Posted by Bisquick2 View Post
Many thanks to you all for your responses. Definitely learning here. Much appreciated.

So despite the snowy weather here I crawled under the trailer and found the 2awg positive from the battery runs to the battery disconnect switch and from there continues as 8 awg, presumably all the way to the converter charger.

In line with suggestions here, my current plan is to change the battery location to inside the front storage compartment, next to the inverter. I will disconnect the wfco 8955 but leave it in place. Then I will locate the new PD9180 next to the batteries. From there I can run one set of 2 awg wire to the inverter and another from the battery pos to the 9180 and the negative to the chassis (or at this proximity is it just better to connect the negative fro the battery to the negative of the charger?). Both the inverter and the charger will be within 2 feet so I think all good there I terms of gauge.

For the 12v run from the 9180 charger to dc fuseboard, I think I can just repurpose the existing 8 gauge wire that used to run from the battery pos to the DC fuseboard. Make sense?

For 120v going into the 9180 there happens to be a 120v outlet plug right there for the inverter. That’s a 15a circuit but the inverter is only 1000w, so I think I could also connect the 9180 right there and thereby avoid running any new wire to the power center/AC breakers.

This all sound correct?

One last question. It appears to me that the solar controller is connected to the battery at the disconnect switch. When I disconnect, the solar remains on, which I guess makes sense as it’s then able to continue charging the battery. I think this will be okay to leave as is, but just want to make sure no issues.

Thanks
You are on the right track. I would definitely connect the negative wire directly to the battery, preferably to the non battery side of the shunt for your battery monitor you should be also installing. Move the ground wire to the chassis to the same side of the shunt as only the battery negative should be attached to the battery side (of shunt).

This way you really won't need to mess with the chassis ground connections other than to make sure they are clean, good, connections.

Mounting the converter next/near to the batteries cuts way down on the expense of the wire as some heavy gauge wires can run ~$5 per foot. Youch!


BTW, the outlet right next to the new inverter location is most likely on the same circuit as other outlets. Charging batteries and running a heater might be a problem. Just so you know.
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Old 01-17-2021, 11:50 PM   #9
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You are on the right track. I would definitely connect the negative wire directly to the battery, preferably to the non battery side of the shunt for your battery monitor you should be also installing. Move the ground wire to the chassis to the same side of the shunt as only the battery negative should be attached to the battery side (of shunt).

This way you really won't need to mess with the chassis ground connections other than to make sure they are clean, good, connections.

Mounting the converter next/near to the batteries cuts way down on the expense of the wire as some heavy gauge wires can run ~$5 per foot. Youch!


BTW, the outlet right next to the new inverter location is most likely on the same circuit as other outlets. Charging batteries and running a heater might be a problem. Just so you know.

Thanks TitanMike. I think this is the lowest cost but more importantly for me, the easiest install and fastest charge times.

Yes, planning on a Victron 712. Iíll wire the shunt and negative to chassis like you suggest.

For the 120v supply, it looks like the 1000w inverter and small outdoor kitchen refer are on that 15a circuit. I guess worse case I could wire it this way and if I start popping that breaker, then run the new wire for the converter? Would that make sense??
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Old 01-18-2021, 09:17 AM   #10
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Thanks TitanMike. I think this is the lowest cost but more importantly for me, the easiest install and fastest charge times.

Yes, planning on a Victron 712. Iíll wire the shunt and negative to chassis like you suggest.

For the 120v supply, it looks like the 1000w inverter and small outdoor kitchen refer are on that 15a circuit. I guess worse case I could wire it this way and if I start popping that breaker, then run the new wire for the converter? Would that make sense??
Just remember, the ONLY wire connected to the battery negative terminal should be the one going to the shunt. Converter negative and chassis ground should be attached to the other end of the shunt. Important so worth mentioning.
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Old 01-18-2021, 01:58 PM   #11
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Right and this is so the battery monitor measures all, correct?
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Old 01-18-2021, 03:55 PM   #12
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Originally Posted by Bisquick2 View Post
<<SNIP>>

On the existing battery posts it is 2 AWG wire on the posts. When I look under the cover of the WFCO at 12V battery pos and neg, it is 8 AWG wire. What gives? I was expecting that the same gauge would be used from the battery to the charger converter. What am I missing here?

I don’t think they are related, but the TT also has a solar controller and a 1000w inverter.

Thanks!


They ARE related.
The 2 AWG wire is feeding your inverter from the battery bank. 1000 watts at 12 volts = 83+ amps.
This calculator is handy: https://www.rapidtables.com/calc/ele...alculator.html

Your factory-installed charger is probably NOT delivering anything close to 83 amps to the battery bank, thus the 8 AWG wire to carry something closer to 30 amps +/- from the WFCO to the battery. It just so happens that some of that charging power is traveling on 2 AWG. No problem.

I'll hazard a guess that the inverter is essentially in series between the WFCO and the battery bank, and when it was installed the wire was upgraded only where it needed to be.

Furthermore, if your inverter has an automated transfer switch, the WFCO to Inverter wiring is also "signal" wire to notify the inverter that shore power is interrupted and to switch on the inverter. All loads on the inverter would be supplied with 120 volts (also from the converter to a second circuit in the inverter) until shore power goes away, then the transfer switch triggers the inverter to supply 120 volts to the attached appliances/house circuits, with that power sourced from the battery at 12 volts and very high current.

The wiring from the WFCO to the Inverter is probably a bit more complex than I described, but conceptually that's what's happening.

If you're going to upgrade your charging system to deliver 100 amps from the converter all the way to the battery, you'll need to use the AWG/length/current tables cited by others to replace all the wire from the new converter to the battery. The inverter won't mind being fed by heavier wire from the battery bank.
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Old 01-18-2021, 05:01 PM   #13
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At the distribution board

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My thoughts, 2 awg at the battery goes to load center. The 8 awg from converter also goes to load center. Or there is a buss bar somewhere they meet.
They meet at what I call the distribution board, the board with all the 12v fuses and the reverse polarity fuses. I think that's what you are calling the load center.

That printed circuit board, maybe 5" x 4", has four big clampdown connectors, two to the converter and two to the battery (via the hidden circuit breaker).
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Old 01-18-2021, 05:05 PM   #14
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They ARE related.
The 2 AWG wire is feeding your inverter from the battery bank. 1000 watts at 12 volts = 83+ amps.
This calculator is handy: https://www.rapidtables.com/calc/ele...alculator.html

Your factory-installed charger is probably NOT delivering anything close to 83 amps to the battery bank, thus the 8 AWG wire to carry something closer to 30 amps +/- from the WFCO to the battery. It just so happens that some of that charging power is traveling on 2 AWG. No problem.

I'll hazard a guess that the inverter is essentially in series between the WFCO and the battery bank, and when it was installed the wire was upgraded only where it needed to be.

Furthermore, if your inverter has an automated transfer switch, the WFCO to Inverter wiring is also "signal" wire to notify the inverter that shore power is interrupted and to switch on the inverter. All loads on the inverter would be supplied with 120 volts (also from the converter to a second circuit in the inverter) until shore power goes away, then the transfer switch triggers the inverter to supply 120 volts to the attached appliances/house circuits, with that power sourced from the battery at 12 volts and very high current.

The wiring from the WFCO to the Inverter is probably a bit more complex than I described, but conceptually that's what's happening.

If you're going to upgrade your charging system to deliver 100 amps from the converter all the way to the battery, you'll need to use the AWG/length/current tables cited by others to replace all the wire from the new converter to the battery. The inverter won't mind being fed by heavier wire from the battery bank.
And it's strongly suggested to use the lowest percentage of voltage drop the "tables" have so you maximize the charge current.

The biggest problem with WFCO converters is that they switch from Bulk to Absorption, and then Float charge voltages way too soon because of the voltage drop in the small wire used by the factory.
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Old 01-18-2021, 05:06 PM   #15
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Right and this is so the battery monitor measures all, correct?
That is correct. Only way a battery monitor can accurately measure current in/out of the battery is if ALL current passes through it.
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Old 01-18-2021, 05:09 PM   #16
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They meet at what I call the distribution board, the board with all the 12v fuses and the reverse polarity fuses. I think that's what you are calling the load center.

That printed circuit board, maybe 5" x 4", has four big clampdown connectors, two to the converter and two to the battery (via the hidden circuit breaker).
??????

Usually the negative wire goes from the Fuse board to the frame and the positive wire is all that goes directly to the battery via the hidden circuit breaker. Circuit is essentially two wires but the frame plays the role for most of the distance of the negative side of the circuit.
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Old 01-18-2021, 05:24 PM   #17
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Electricity & wire size, 1st, I would say cable size, the bigger the better.
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Old 01-18-2021, 05:46 PM   #18
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Or...

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The biggest problem with WFCO converters is that they switch from Bulk to Absorption, and then Float charge voltages way too soon because of the voltage drop in the small wire used by the factory.
Or you could say that the big problem with WFCO chargers is that manufacturers mount them too far from the batteries. On our Cherokee 38P, the WFCO 8955 was mounted at the front wall. The batteries are on the opposite side of that wall. Probably around five feet of cable run.
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Old 01-18-2021, 06:01 PM   #19
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Or you could say that the big problem with WFCO chargers is that manufacturers mount them too far from the batteries. On our Cherokee 38P, the WFCO 8955 was mounted at the front wall. The batteries are on the opposite side of that wall. Probably around five feet of cable run.
I don't think that is a WFCO problem, or any converter problem. That is an RV design problem.
My converter is about 30' from my battery bank. I thought about moving it closer when I changed the converter out, but why? It has worked just fine for almost 10 years where it is! Would it work better for charging if moved closer? I'm sure it would, but not enough difference for me to worry about.
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Old 01-18-2021, 06:02 PM   #20
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Or you could say that the big problem with WFCO chargers is that manufacturers mount them too far from the batteries. On our Cherokee 38P, the WFCO 8955 was mounted at the front wall. The batteries are on the opposite side of that wall. Probably around five feet of cable run.
Yes, that could be said. On my TT the WFCO was under the refrigerator which is above the rear axle. It actually worked and if you consider the average current that is involved, the #8 awg wire is OK. Just OK however and since us boondockers want to charge our batteries as quick as possible, it's totally inadequate. Especially with LiFePo4 batteries which CAN cause a 100 amp converter to attempt to send 100 amps down the wire.

I ran a #4 awg wire initially but will probably move the converter eventually. Old WFCO 8955 converter was replaced with a deck mount PD9160L that I just installed in the space vacated at the bottom of the power center.

When I get in the mood (and warmer weather arrives) I'll just run some conduit along the frame rail and extend the converter 120 V circuit to my battery compartment where the converter will end up living. LiFePo4's don't off-gas so no worries about keeping it away from the Lead Acid batteries and there being an explosion hazard.
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