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Old 05-29-2024, 11:25 PM   #1
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Battery to Inverter cables

In doing a Group 24 Lead Acid to 200Ah LiFePO4 upgrade, my battery location will move from the tongue to under the bed. A short negative battery cable can connect it to nearby inverter. (I'll be abandoning the long negative line coming from the battery box on the tongue.)

From the new battery position I plan to to run a new 10’ positive cable out to the 100A fuse on the tongue, where the old battery currently connects. The positive line from battery to inverter will end up around 24’ long in total.

** Is there any issue with having a short (18*) negative cable and s long (24') positive cable connecting the battery to inverter? **

If the positive and negative lines must be kept similar in length, I will buy a new 10’ negative cable to run from the battery and splice it to the existing negative cable at the tongue... but is it necessary?
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Old 05-29-2024, 11:29 PM   #2
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Moved thread from the Modifications and Updates section to the Electrical and Charging Systems sub-forum since the OP's questions are specific to that sub-forum.
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Old 05-30-2024, 06:27 AM   #3
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Quote:
Originally Posted by g.spalding View Post
In doing a Group 24 Lead Acid to 200Ah LiFePO4 upgrade, my battery location will move from the tongue to under the bed. A short negative battery cable can connect it to nearby inverter. (I'll be abandoning the long negative line coming from the battery box on the tongue.)

From the new battery position I plan to to run a new 10’ positive cable out to the 100A fuse on the tongue, where the old battery currently connects. The positive line from battery to inverter will end up around 24’ long in total.

** Is there any issue with having a short (18*) negative cable and s long (24') positive cable connecting the battery to inverter? **

If the positive and negative lines must be kept similar in length, I will buy a new 10’ negative cable to run from the battery and splice it to the existing negative cable at the tongue... but is it necessary?
Any chance you could sketch out your layout? As I type this I fear I am missing something . The wires from the battery to the inverter should be the same distance or close to the same distance.

If the negative battery terminal is a short distance from the inverter negative then why can't then positive be the same? Your wires from inverter to the battery are two independent wires within your system. A second set of wires from the battery to the RV grid will take care of the grid.

Your stated methodology would in itself require 4/0 wires for a 1000 watt inverter.
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Old 05-30-2024, 06:30 AM   #4
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Quote:
Originally Posted by g.spalding View Post
In doing a Group 24 Lead Acid to 200Ah LiFePO4 upgrade, my battery location will move from the tongue to under the bed. A short negative battery cable can connect it to nearby inverter. (I'll be abandoning the long negative line coming from the battery box on the tongue.)

From the new battery position I plan to to run a new 10’ positive cable out to the 100A fuse on the tongue, where the old battery currently connects. The positive line from battery to inverter will end up around 24’ long in total.

** Is there any issue with having a short (18*) negative cable and s long (24') positive cable connecting the battery to inverter? **

If the positive and negative lines must be kept similar in length, I will buy a new 10’ negative cable to run from the battery and splice it to the existing negative cable at the tongue... but is it necessary?
Are you talking about using the frame as a ground? If the new location is closer to the power center why are you running wires back out to the tongue?
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Old 05-30-2024, 06:55 AM   #5
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As stated above, you'll need a very large gauge and expensive cable for this length. Why not move the fuse block to the new battery location?
FWIW, here's a quote from a WFCO manual: "A fuse is required by the National Electrical Code (NEC) to protect the battery and cables. A UL listed 100 Amp DC rated slow blow fuse or circuit breaker must be installed in the Positive battery cable within 18 inches of the battery."
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Old 05-30-2024, 07:09 AM   #6
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I moved a battery under the bed and will be putting my inverter right next to it under the bed. My distance between the battery and inverter will be about 16 inches max. At the battery (new location), I connected the existing 6 AWG wires that ran to the original battery box and connected to my WFCO power center.

The distance forward of the bed cavity to the old battery box was about 6 feet which easily allowed me to run the wires into the bed cavity from a point on the frame opposite the bed cavity.

The rule for installing inverters is to install them as close to the battery as possible. The wire should be sized predicated on the number of amps (max) that the inverter will be drawing from the battery plus some. Also, install a breaker on the positive to limit the amperage.

Inverters can generate heat, so the proper wire gauge and breaker are very inportant.
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Old 05-30-2024, 07:28 AM   #7
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Originally Posted by PhilFromMaine View Post
I moved a battery under the bed and will be putting my inverter right next to it under the bed. My distance between the battery and inverter will be about 16 inches max. At the battery (new location), I connected the existing 6 AWG wires that ran to the original battery box and connected to my WFCO power center.

The distance forward of the bed cavity to the old battery box was about 6 feet which easily allowed me to run the wires into the bed cavity from a point on the frame opposite the bed cavity.

The rule for installing inverters is to install them as close to the battery as possible. The wire should be sized predicated on the number of amps (max) that the inverter will be drawing from the battery plus some. Also, install a breaker on the positive to limit the amperage.

Inverters can generate heat, so the proper wire gauge and breaker are very inportant.

The OP stated that the inverter is already under the bed. He is moving the new batteries to the same location, but asking if he can leave the high-current fuse on the tongue. The fuse is between the battery and inverter, so he's asking if it's OK to loop a positive cable to the tongue and back to keep the fuse inline. I don't understand why he can't just relocate the fuse block to the location under the bed.
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Old 05-30-2024, 07:35 AM   #8
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What Phil said .... ^ x 3

Take the existing wiring/cables from the battery tongue box... It took me 10 minutes to do it
feed it to the new battery location... It does NOT need to be upgraded in any way as the wire LENGTH stays the same.

Put the Inverter next to the battery and size the cable and any fuse from battery to Inverter based on maximum amps your Inverter can pull .

Your Inverter user manual will have guidelines on cable sizing
BUT .... if your inverter came with cables they will be the cheapest nastiest cables they can get away with. Spend the money on decent cables and lugs from a known supplier.
Get either welding wire OR marine grade which have more strands and are much more flexible ... Keep the length and joints to a minimum

Use busbars where necessary to avoid adding more lugs to a battery terminal


Battery paralleling cables ... the cables that connect the batteries together in parallel will need to be UPGRADED (most likely) to work with the inverter's increased load
ONLY the cables for the paralleling connections...
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Old 05-30-2024, 07:38 AM   #9
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PS missed the mention of fuse on tongue

MOVE it too the new location
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Old 05-30-2024, 07:40 AM   #10
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Find where the battery cables attach to on the RV before they reach the original battery position. Usually a resettable circuit breaker that looks like a relay box. (Mine was on the back of the front crossmember) Drill a hole through the RV flooring and pull them up through to the new battery area. Best to use a buss bar at this point for the ability to add other stuff. You can shorten the cables if desired.
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Old 05-30-2024, 08:18 AM   #11
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Originally Posted by jlankford View Post
The OP stated that the inverter is already under the bed. He is moving the new batteries to the same location, but asking if he can leave the high-current fuse on the tongue. The fuse is between the battery and inverter, so he's asking if it's OK to loop a positive cable to the tongue and back to keep the fuse inline. I don't understand why he can't just relocate the fuse block to the location under the bed.
I think you are probably correct, except he called it a 100 amp fuse while most likely he means 30 amp catastrophic fuse. A 100 amp fuse more than likely would be a small amperage inverter fuse thus the confusion.

In any event, I didn't have any issues gaining the 6 or so feet needed from the existing wiring to run the wires to the under bed area and interfering with the main battery catastrophic safety fuse. As I remember, I have a two stud buss bar on the frame just prior to my 30 amp fuse device.
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Old 05-30-2024, 08:27 AM   #12
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I think you are probably correct, except he called it a 100 amp fuse while most likely he means 30 amp catastrophic fuse. A 100 amp fuse more than likely would be a small amperage inverter fuse thus the confusion.

Right. I have inferred that he has a 1000W inverter from the fact he stated he has a 100A fuse between his battery and inverter. A larger inverter would require a larger fuse.
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Old 05-30-2024, 08:52 AM   #13
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When I moved my LiFePO4’s from tongue to under bed position next to the inverter I added bus bars at the new location. I abandoned the 100a breaker on the tongue and installed a 100a fuse between the batteries and bus bar. I ran new 2/0 cable to the 1000w inverter ( approx. 1.5’ run) and used the existing 2awg cable that previously fed the inverter from the tongue position to run power back to the battery switch for the camper 12v stuff. It allowed me to move the batteries without drilling holes for new wiring, and seems work OK.

My understanding is you want as short a run as possible between battery and inverter, with cables close to the same length. Others with more knowledge may have better advice.
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Old 05-30-2024, 01:33 PM   #14
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No feedback from the OP yet.

I, too, disagree with running the positive out to the tongue and then all the way back.

You have two goals.
1) Feed battery power to the main distribution "hub" if you will at the tongue...OR rewire all of that "stuff" that connected to the group 24...WITH THE EXCEPTION OF THE INVERTER.
2) Simultaneously, in parallel, feed the inverter. 100 amp DC fuses/circuit breakers are cheap. Get a new one to install between the new battery bank and the inverter. Keep the cables between the battery bank and the inverter as SHORT AND FAT AS POSSIBLE, because a 1000 watt load at 120 volts means 83+ amps between the battery bank and the inverter. (In the calculator, ALL CALCULATIONS are based on 12 volts, because that's the source of your power...the battery bank.) As PhilFromMaine (and perhaps others) said, the place to locate that inverter is inches from the battery bank, and then run a 12/3 romex to the converter to feed whatever circuits you intend to feed.

WHILE WE ARE AT IT. Don't forget the automatic transfer switch!! This can be in the inverter, but you absolutely must have one to avoid the disaster that would happen if you fire up the inverter while connected to shore power.

With a transfer switch, you could essentially feed your entire converter with the inverter and then just carefully manage your loads to stay within the capacity of your inverter. If you have shore power, your transfer switch will keep things from blowing up.

If you upgrade to a 2000 watt inverter, you'll be pushing 170 amps through your connecting cables. So any thought of the monkey motion of running long cables all over hell and gone to feed the inverter through connections on the tongue will require cables the diameter of your thumb. That much copper alone will eat 100 pounds out of your CCC.

You have the makings of a great system. Do this right, or you'll regret it. I have a 500 watt inverter about 18 wire feet from my battery bank, and I ran #8 awg to feed it....and that's not heavy enough to run continuously. Use the calculator in the link above and use this wire gauge table. ALSO NOTE that with DC, wire gauge calculations are based on the total length OUT AND BACK. Not just one way as with AC power. Be sure to choose a DC WIRE GAUGE TABLE for our calculations.
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Old 05-30-2024, 03:34 PM   #15
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Head spinning

Thanks to everyone for sharing your expertise, for your willingness to help. You all have good points; most of it makes sense. I wish I had a better understanding of the electrical components and their intricacies. It will come in time.

On my trailer, after the fuse on the tongue, the positive wire goes to a main shut off switch. On the back of the switch is not only the main positive cable back to the inverter, but a couple other wires which go into different wiring harnesses. I'm not qualified to sort this all out and move it inside.

If I understand Jim Moore correctly, I would move the battery inside and power a positive bus, first going through the 100A fuse which I would relocate from the tongue. Then I would feed two things from the bus:
- the inverter via a short cable
- the existing wiring on the tongue via a 10' cable. (Of course I'd disconnect its red cable going back to the inverter.)

This would mean the inverter would no longer be under the main shut-off switch, which is probably why there is a switch. If that's acceptable, this would be simple enough for me to do.

Jim, I'm afraid your comments about the transfer switch / feeding the converter are over my head at the moment. Maybe I could leave this part out for now to research later. I don't plan to use inverter anyway; it doesn't seem all that useful and I understand it's a battery hog.

I suppose my other option is to abandon the battery move and just put the new battery on the tongue in place of the old one. I don't like having an expensive battery outside, but everything would then remain as designed and under the master switch.
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Old 05-30-2024, 04:12 PM   #16
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This would mean the inverter would no longer be under the main shut-off switch, which is probably why there is a switch. If that's acceptable, this would be simple enough for me to do.

Jim, I'm afraid your comments about the transfer switch / feeding the converter are over my head at the moment. Maybe I could leave this part out for now to research later. I don't plan to use inverter anyway; it doesn't seem all that useful and I understand it's a battery hog.

The inverter is usually factory wired directly to the battery bypassing the disconnect switch, so this plan is fine. You can simply run a smaller gauge wire from the new positive bus back to the battery side of the disconnect switch and leave everything else in place.

The inverter model pictured includes a built in automatic transfer switch (called a pass-through in the manual), so you are set. Typical configuration is that the 120VAC circuit for the outlets will run from the power center first to the inverter, and then the output from the inverter proceeds to the outlets. The outlets will automatically receive shore power when it's available, and can be powered by the inverter when not. You should keep the inverter powered off most of the time. It will still pass through shore power when off, and when not on shore power it will waste a lot of battery sitting on but idle.
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Old 05-30-2024, 04:38 PM   #17
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a good auto electrician can have it setup in a very short time...

Make your fingers do the walking .. find a local auto sparky.
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Old 05-31-2024, 09:05 AM   #18
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I installed a Samlex EVO-3012 Inverter/Charger in 2019 with 4/0awg cable. It can power boost 140% (4200W/300A) for 30 seconds. I used 4/0awg cables and a 400a fuse within 7 inches of the positive terminal. I have a spare 400A Class T Fuse, but have never needed it.

You may need to increase your cable size. The total feet is the distance to & from the Inverter. My Inverter/Charger is three feet from the battery bank. My total run is under ten feet.


Samlex CFB2-400 Fuse Block
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Old 05-31-2024, 12:52 PM   #19
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Very helpful comments and advice; thanks to you all! Here's my plan:

- Turn off Master Switch
- Disconnect and remove the old battery
- Disconnect existing + and - cables from Inverter
- Disconnect existing + cable (to inverter) from back of master switch

- Run a new #2 AWG 18" black cable from battery - terminal to inverter -
- Use existing ground wire (from old battery) to ground new battery - terminal to frame

- Move the existing 100A fuse and 16" red cable (from old battery) under the bed, and connect the cable to battery + terminal
- Run a new #2 1' red cable from fuse to a new + bus bar
- Run a new #2 1' red cable from + bus bar to Inverter +
- Run a new #2 10' red gable from + bus bar to existing + wiring on tongue
(I realize using #2 here is overkill, but I already ordered it)

- Set the Solar Controller to LiFePO4
- Run down the battery to < 30% so Converter resets itself to LiFePO4

Sound OK?
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Old 05-31-2024, 01:30 PM   #20
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Don’t forget to buy a new battery disconnect and install that inside near the battery bank where you can easily reach it.
Looking at that original battery disconnect. A little scary to me with the terminals exposed mounted in a cutout on the frame. Corroded looking, too.
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