Designing Victron System for Keystone RV Travel Trailer

[John Frum]

The legacy DC 12V system has return wires on all circuits which go to a common 12VDC Neg Bus Bar with one exception: The legacy battery negative terminal is grounded directly to the chassis and uses the chassis to return from the 12VDC Neg Bus Bar. (As shown in that image with the floor plan).

Are you getting rid of the legacy battery?

 

[SendIt]

I'm disconnecting the house electrical system from the legacy battery, but leaving it installed because it's also used to run the cutaway brakes. (e.g. if the trailer falls off the ball while in motion, it pulls a wire that triggers the trailer brakes).

From what i've read online, other owners have done this when adding solar to this model of trailer with no issues.

 

[John Frum]

I'm disconnecting the house electrical system from the legacy battery, but leaving it installed because it's also used to run the cutaway brakes. (e.g. if the trailer falls off the ball while in motion, it pulls a wire that triggers the trailer brakes).

I'm aware.

From what i've read online, other owners have done this when adding solar to this model of trailer with no issues.

Yep.
How are you charging the legacy battery?

 

[SendIt]

I'm aware.

Yep.
How are you charging the legacy battery?

Tow vehicle via the aux power pin on the trailer 7-pin connector.

 

[SendIt]

Hey thanks for the help everyone. I've got everything installed and wired up and just getting ready to do a full charge cycle test. Here are some pics (wiring still needs to be cleaned up)


(It's -14F here, so the light is in the battery box to keep everything warm.)

I have a quick question about the ground relay in the multiplus. Should I disable it to prevent a ground loop? Here's the description in the multiplus settings:


Thanks!

 

[John Frum]

There should be always be exactly one neutral/ground bond.
When you are connected to shore power the bond is upstream of the pedestal.
When you are inverting ac from dc the neutral/ground bond is created by the relay in the Multiplus.

 

[SendIt]

Thanks, that makes sense

 

[HRTKD]

Before you hit the road, I recommend that you install strain relief for every wire/cable in that system. The bigger cables especially will use use road vibration to come loose.

Even the cables going into my Cerbo GX have strain relief. The connections to Cerbo GX didn't feel very solid to me, hence the strain relief to make sure the connections stayed connected.

 

[SendIt]

I’m in the process of cleaning up the wiring. Got a box for the battery and working on the heater circuit.



Will post the final results here when complete. For anyone coming across this in the future, I started a new thread for the solar portion: https://diysolarforum.com/threads/sizing-solar-cells-for-couple-full-time-boondocking.54957/

 

[Ryan23]

Did you opt for the Victro SmartShunt anyway? Looking at the photo above, it looks like it. I’m building a similar system for my RV and was wondering if the SS provided some sort of functionality you couldn’t get with a BMS tied into the Cerbo. Looks great, thanks!

 

[SendIt]

Yeah, I couldn’t get the BMS to talk to the Cerbo. After some testing, it looks like the two disagree on SOC by quite a bit as well. I imagine the shunt is more accurate, but that’s just a guess…

 

[Powderday]

Yeah, I couldn’t get the BMS to talk to the Cerbo. After some testing, it looks like the two disagree on SOC by quite a bit as well. I imagine the shunt is more accurate, but that’s just a guess…

I've got my BMS (Overkill Solar 8S 120A on a 8S EVE280 bank) talking to my Cerbo through dbus-serialbattery. There is a noticeable difference between the two, I've going to investigate further next month (I have a slight battery imbalance that I have to check out as well) but I did notice that the consumed AH was fairly close. I have set DVCC on and set Battery Monitor to use the BMS as the master control so it doesn't try to charge the batteries below 0oC (which happens without the batt heaters on). See attached screenshots... it's in my trailer at the moment (in storage through the winter, so it hasn't seen a load cycle in about 6 months).

 

[SendIt]

Yeah, I ended up going with an alibaba BMS and it's so poorly documented that I didn't even want to attempt it. Good job with the overkill solar hack though!

 

[Powderday]

Yeah, I ended up going with an alibaba BMS and it's so poorly documented that I didn't even want to attempt it. Good job with the overkill solar hack though!

Thanks, I'm still chasing the problem with the difference between the two, it seems they are off by about 0.1A.

I glanced back at your battery photo, are you tapping a 12V connection off your cells here?

 

[SendIt]

Thanks, I'm still chasing the problem with the difference between the two, it seems they are off by about 0.1A.

I glanced back at your battery photo, are you tapping a 12V connection off your cells here? View attachment 144545

No... that would be a really bad idea. I'm monitoring midpoint voltage with the aux lead on the smartshunt.

 

[EBKRV]

What about power tongue jack? Running off the old FLA 12v? The 7 pin charging that battery only does it last sitting for 2 weeks...most don't none ever have had. I would have went straight from the dc-dc 24 to 12 converter to the factory wiring on the tongue and dumped the FLA myself.

Tow vehicle via the aux power pin on the trailer 7-pin

 

[justinm001]

What about power tongue jack? Running off the old FLA 12v? The 7 pin charging that battery only does it last sitting for 2 weeks...most don't none ever have had. I would have went straight from the dc-dc 24 to 12 converter to the factory wiring on the tongue and dumped the FLA myself.

An FLA should only lose like 3% a month if no loads. Are you thinking the tongue jacks consume power when not in use or something else?

I have an enclosed trailer i take maybe once a month I added an electric tongue jack, lights and a 100ah SLA battery. Mainly worried about leaving lights on and draining battery, didn't think about the jack using idle load. My idea was to use some device that'll cut voltage off when it's like 12.65v (80%) incase I forget to turn lights off

 

[HRTKD]

I'm not aware of a tongue jack having an idle consumption. My Husky tongue jack is rated for 25 amps, but I've never tested that.

 

[EBKRV]

An FLA should only lose like 3% a month if no loads. Are you thinking the tongue jacks consume power when not in use or something else?

I have an enclosed trailer i take maybe once a month I added an electric tongue jack, lights and a 100ah SLA battery. Mainly worried about leaving lights on and draining battery, didn't think about the jack using idle load. My idea was to use some device that'll cut voltage off when it's like 12.65v (80%) incase I forget to turn lights off

No I didn't mean the power tongue jack has an idle consumption whatsoever I meant using that and breakaway only for the FLA and it never getting a charge other than from the 7 pin...In my 24 yrs of owing RVs I've never had an FLA sit idle for more than 2 weeks without needing a good full charge. Whether they were new or old I've had them all Interstates, Deka's, East Penn, etc etc and that's with taking the best care of them as well. To me in 24 yrs all FLA's are garbage and with your system I'd just dumped it and tied it all together like most do...but hey to each there own.

 

[justinm001]

No I didn't mean the power tongue jack has an idle consumption whatsoever I meant using that and breakaway only for the FLA and it never getting a charge other than from the 7 pin...In my 24 yrs of owing RVs I've never had an FLA sit idle for more than 2 weeks without needing a good full charge. Whether they were new or old I've had them all Interstates, Deka's, East Penn, etc etc and that's with taking the best care of them as well. To me in 24 yrs all FLA's are garbage and with your system I'd just dumped it and tied it all together like most do...but hey to each there own.

99% of trailers with electric brakes only have a mini sla battery that just charges off the 7 pin including those with a power tongue jack. Not travel trailers but just everyday flat or enclosed trailers. If your chassis battery isn't lasting more than a couple weeks you have something else connected to it draining the load. It's not an issue with FLA it's an issue with whatever is pulling a load when off