Travel trailer - 24v battery - buck converter question

[chrisski]

Looks like that battery runs the breakaway system in addition to the dc panel.

From the research I've done that buck converter only puts out 12.2 volts and therefore won't even come close to charging that battery.
I suggest you try powering the converter via the inverter.

I wonder how you power a 12 volt brake and brake away once you step up a fifth wheel to 24 VDC, and would like to hear form people who’ve done it.

Although I am still putting together my first PV system which is 12 volts with 600 watts of panels, I would like to someday go to 24 VDC and add more panels so I can run more watts in an inverter at less amps.

I’m stuck at the breakaway battery, and the best solution I could come up with is to let the inverter power the converter which would charge the 12 volt battery and that would operate the breakaway.

I‘m told the trailer breaks will operate off the 12 volt through the 7 pin, even without a battery, but the two times my trailer batttery died, I got an error on my brake controller, said trailer disconnected. Once the 12 volt battery was charged, which was removed and placed on an auto battery charger then put back in, the brakes work. I’m not Done looking into it. Could be my error was because there was no brake away battery, so the brake controller did not want me to drive.

I looked at the Victron step down convers and saw The 24 VDC to 12 VDC were not designe to charge batteries, and no matter what amps I got, I don’t know if it supplies enough amps to operate the breakaway.

So for the breakaway, the only thing I would feel comfortable doing with the 24 VDC I’m putting together is to keep the 12 VDC battery in charged by the inverter, but I think this could be a very wasteful way to charge the 12 volt system. When I do upgrade to 24 volts, I will spend a good long time going over some calculations and reading up.

 

[Master Dalor]

Ok, I try to follow.

 

[John Frum]

I decided to try powering the legacy converter via the new inverter charger.
As far as the trailer is concerned it's on shore power.
That is the extent of the integration.
If the legacy converter is too inefficient then we can integrate a victron dc 2 dc converter.

 

[HRTKD]

Wiring into the legacy distribution panel is quite easy.

On the left side of the photo there are two terminal blocks that have two wires going into them. One on top left (negative) and the other on the bottom left (positive). Remove the wires from these terminal blocks and cap them off (see caveat below for the negative wires). The wires from your 24v->12v converter will go into these terminal blocks.

The terminal block labeled as +VCC is where your 12v converter's positive wire comes into the system. If the converter is the old old one with a lead acid charge profile you may want to remove this lead (and cap it off). There is also a negative lead coming off your 12v converter that goes into the top terminal block. If you are not going to use the 12v converter then you might as well remove this lead also.

There should be a large negative bus bar behind the distribution panel. It could be mounted to something or it could be flopping around loose in the compartment where the distribution panel is located. Mine was (and still is) flopping loose. I ran a negative lead from my new system into both the distribution panel AND the negative bus bar.

As a side note, my distribution panel looks identical. Mine is a WFCO, from 2006. My positive terminal block (lower left in the photo) had TWO red wires going into it. One was live and was routed from the battery, to the 12v cutoff switch, down below the trailer, then back up into the trailer and to the distribution panel. What a tortuous route. There had to be some voltage drop on that. The other wire terminated in the distribution box near the tongue of the trailer where the 7-pin came in. However, the wire wasn't connected to anything! It was just cut off and left in the wire loom. No tape or cap on it.

As mentioned by @schmism, I separated out the trailer's existing electrical system into two distinct systems. The instructions I provided above will do that. My system looks like this:

Secondary system
12v batteries on the tongue (dual Trojan T-105 6v in series - soon to be replaced by a single, smaller battery)
Power In
--7-Pin power coming in from tow vehicle
--150 watt solar panel with a GoPower PWM controller
Power Out
-- Generator starter
-- Tongue jack
-- Trailer breakaway brake system

Primary system
Two 280 Ah 12v LiFePO4 batteries
Power in
-- 640 watts of fixed solar panels mounted on roof
-- 640 watts of portable solar panels deployed on the ground
-- IOTA Engineering 12v 55 amp LiFePO4 converter (AC->DC)
Power out
-- Everything else!