New install Comments

Hi, I'm changing over to lithium batteries and adding a 2000W inverter in a travel trailer. Looking for any feedback/comments on my proposed install.

In order to keep power for the electric trailer brakes , I'm splicing into the 12V line from the power distribution center (WFCO) that goes out to the trailer junction box. One side of the splice will come from the battery to power the brakes all the time. The other side of the splice will send 12V power to the WFCO via a switch.

Thank you

Conjuring @HRTKD, who knows quite a bit about trailer brakes from what i recall.

That may work, but I’d be sure that the biggest loads are less than 30 amps. Leveling jacks will exceed that and slide outs will come close. I’d like to look at a wiring diagram first, but that is likely impossible, so with no diagram, I’d test for continuity between the positive and negative at the breaks with power off.

I am spliced in through my 12 volt system for my RV to include DC power and RV Brakes at the old 12 volt battery box.

Also, by splicing, I hope you actually mean using some sort of post or busbar and not actually splicing.

chrisski said:

That may work, but I’d be sure that the biggest loads are less than 30 amps. Leveling jacks will exceed that and slide outs will come close. I’d like to look at a wiring diagram first, but that is likely impossible, so with no diagram, I’d test for continuity between the positive and negative at the breaks with power off.


Also, by splicing, I hope you actually mean using some sort of post or busbar and not actually splicing.

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Hi, small travel trailer, no slides or leveling jacks. Yes, all loads are less than 30 amps.

Not sure I need a bus bar. The line from the WFCO will go directly to the switch. The other side will be connected to the 12V line that comes from the trailers junction box where the 12V line for the electric brake is located. I plan just to crimp connect the wires since there are only 2 ends.

Thank you,

You'll want your inverter negative wire on the other side of the shunt. Battery on one side, everything else on the other.

TacomaJoe said:

You'll want your inverter negative wire on the other side of the shunt. Battery on one side, everything else on the other.

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tks..good catch. I missed that.

Just to point out, splicing is not a qualitative term. Every vehicle wiring diagram is riddled with splices. They are well executed, tucked safely away and generally far more reliable than any connector that a filthy human can easily grab with their big stupid hands and screw up.

It’s true that ‘amateur’ splices are generally terrible, but a splice, or splicing is not inherently bad just because people who are bad at it make bad splices!

Curious to why you wouldn't install a DC/DC charger? You wouldn't have to mess with the trailer brakes.

fault_tolerance said:

Curious to why you wouldn't install a DC/DC charger? You wouldn't have to mess with the trailer brakes.

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Hi,

A DC to DC charger is used to be able to charge your batteries while on the move. I'm not installing one at his time. I'm using my WFCO and solar to keep them fully charged.

I'm moving my batteries from the front of the RV to inside. I needed a way to keep power to my trailer junction box position #6 where the line for the emergency electric trailer brakes is located. When the batteries were in front, the 12V wire from the batteries ran to position #6 and then back into the RV. Since I no longer have the batteries there, I needed a way to keep position #6 hot all the times. Hopefuly that makes sense.

tks

@Chaucer have you already purchased everything?

Yes, I'm almost done with my install. I noticed the other poster used 2/0 wire from his switch where I'm using 10 AWG to my WFCO from the battery. I'm almost certain it's fine...but it made me wonder.

One change from my diagram is my Class T fuse is 250 amps not 200 amps.

Well, it's fine as far as safety because it shows a 30 amp fuse on it. But if it blows the 30a fuse, it won't be fine as far as usability. It kinda depends on how the original 30a rating on the WFCO was arrived at. If it has some kind of current limiting onboard set to 30a then you are probably fine. But if it was rated based on something like 'it can do 30a continuously without breaking' or 'it will do 30a into the typical IR of a single discharged lead acid house battery' then it might not be ok because the drastically lower IR of a couple of lithium batteries in parallel might take its output way above 30a, for as long as that lasts.. I believe this is a somewhat similar problem to charging lithiums with alternators directly, which is possible but has some potentially parts-killing pitfalls.

I wouldn't bother running something as big as a 2/0 unless you plan to majorly upgrade the charge amps potential of the onboard converter at some point. But, i would consider running something larger than 10ga, especially if the distance is long and the install (and re-install if you have to upgrade later) is tedious.

Hi,

The WFCO by design is limited to 30A or 600W. They make different sizes/capacities, my small RV doesn't have a lot of demand. The larger circuits on the AC side is the Air Cond., microwave and heat, which are 20 A. each. (Can't run two at the same time). Everything else is 15A. Same on the DC side.

The distance for the 10 AWG wire is only 5 feet.

Thank you for taking a look.

The 5 ft run sounds pretty easy to upgrade later if you feel the need. If you already have the wire i would just try it and see.

Vigo said:

The 5 ft run sounds pretty easy to upgrade later if you feel the need. If you already have the wire i would just try it and see.

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Just curious why you suggested to run larger than 10 AWG?

tks

Well, if it were 25ft i would suggest to upgrade it. But I probably should have just asked about the distance and the difficulty of running that wire, before saying what i would or wouldn't do about it. Given a short run and easy access i think the 10ga is fine!

I don't know enough about electronics design to know whether a given device has good 'limiting' on its output side or not. I do know a wide variety of 'charge sources' will just decide not to work if the initial resistance of the circuit they are energizing is too low. I have messed around with bench psus, wall warts, laptop chargers, 'actual battery chargers' etc and i have not noticed a solid pattern as to which will safely (for the device) charge into a lower resistance circuit than designed for (i.e. large lithium bank vs lead acid).

However, i have also charged my lithium with the converter in my rv and have not been able to 'overcurrent' it in spite of hooking it to ~`5kwh of lifepo4 in parallel. I have seen a max of about 45 amps out of mine, but i forget what its actual rating is. Regardless, it works.. but mine seems to peak at 13.9v no matter what, so it will only contribute very much if the lithium are discharged below half. It slows to a semi-useless trickle well before the lithiums are fully charged. Which is fine! I just don't count on it for much in my total charging strategy.