Replacing Trailer DC2DC with Inverter - Thoughts?

[bedpan]

Hey Folks.
I cobbled together a power system last year in an 18' cargo trailer I am converting to a Travel Trailer. The Initial build was cheap/quick and mostly just stuff I had on hand. I did order a Renogy 50A DC2DC charger. I had to overcome a few hurdles but it actually worked quite well. The biggest hurdle I had was the old 1000W inverter I was using inside the trailer. The fans are quite noisy everytime the fridge kicked in.

Now I have ripped it all apart and I am working on insulating and actually building out the interior. I stumbled on a used deal for a Victron MultiPlus 12/2000/80 . This fixes one problem we had with the old inverter.

The next problem with the rebuild is the Power wall is moving from the front of the trailer to the back. This will add an extra 36' of cable to my already 45' run for the DC2DC. Its running fine on the current 4 gauge wire but I suspect it will all have to be upped in size with a 80' run (round trip). This got me thinking again about using 120AC to run from the truck to the trailer. I can install the 1000W inverter I have under the hood and run an extension cord to the bumper. I can install the AC input for the trailer on the front and we are done! Well not really done and here are the questions that are coming up in my brain.

1) I need to look but thinking of putting the inverter under the hood. I would need it to be switched with the ignition. I have a 90A Solid State isolator I can use that I think would suffice. Am I missing something here (beyond fuse, switch and 12 gauge extension cord to bumper)? Is there a better option then an Isolator?

2) Thoughts on the power input on the trailer. I was going to go 30A but then I would need a dogbone to connect the 15A extension cord from the truck to the 30A receptacle on the trailer. Being in the weather I was thinking it might be best to avoid extra connections. Any suggestions here?

3) Am I missing something obvious here? On paper I can feed 80A to my batteries using the Victron instead of 50A with the Renogy. I will likely have to scale the Victron down to maybe 60A to not overload the inverter. It removes a piece of kit from the trailer and adds AC to the truck which could be handy for other things.... It seems like more people should do this and are not.. So what am I missing... Its ok call me stupid ;-)

Cheers guys and thanks in advance!

 

[FilterGuy]

You might find this usefull

Wiring the connection at the trailer hitch

The Hitch in Trailer Wiring. When working on a trailer, the electrical interface between the trailer and the tow vehicle can present special issues that must be understood and delt with in order to prevent problems The 7-Pin connector can not...

diysolarforum.com

 

[bedpan]

You might find this usefull

Wiring the connection at the trailer hitch

The Hitch in Trailer Wiring. When working on a trailer, the electrical interface between the trailer and the tow vehicle can present special issues that must be understood and delt with in order to prevent problems The 7-Pin connector can not...

diysolarforum.com

Amazing article! I learned a few things and has given me a few ideas moving down the road as I wire things up. Thanks very much for sharing

 

[bedpan]

Anyone? Thoughts or concerns with using an Inverter in the truck and stringing an extension cord to a trailer to charge while driving?

 

[fratermus]

Anyone? Thoughts or concerns with using an Inverter in the truck and stringing an extension cord to a trailer to charge while driving?

I haven't had coffee yet this morning but it doesn't seem to be a crazy idea. I'd thought about something similar for a different reason: the ability to put a heavily-paneled tow vehicle in the sun and run 110vac to the trailer in the shade. Ended up with a van build so I didn't pursue the logic further.

Following with interest.

 

[HRTKD]

An inverter installed under the hood may not like the heat generated by the engine. Victron inverters will derate as the heat increases. Plus, not all inverters are rated for exposure to the elements.

Installing the inverter in the cab would work better.

My RV trailer does not use the charge current from the tow vehicle at all. The solar panels provide enough power that I don't need anything from the tow vehicle.

 

[bedpan]

An inverter installed under the hood may not like the heat generated by the engine. Victron inverters will derate as the heat increases. Plus, not all inverters are rated for exposure to the elements.

Installing the inverter in the cab would work better.

My RV trailer does not use the charge current from the tow vehicle at all. The solar panels provide enough power that I don't need anything from the tow vehicle.

Thanks Jim,

Under the hood and heat issues makes sense.. I may investigate it further as the cabin will be a lot more work.. But I think you are likely right.

I could go solar, but for my usage charging while driving is just easy. We don't typically stay anywhere long and drive 3-5 hours many days. Solar is in the plans this just solves the problem cheaper and quicker until I am ready for the solar project.

Anyone else have any thoughts or concerns?

 

[HRTKD]

There was a forum member a couple years back that used DC-DC converters to take the truck's 12 volt to 48 volt, then run smaller wire to the trailer (as 48 volt) and then a converter in the trailer to go from 48 volt to 12 volt. The cost in cabling to run high amp 12 volt is prohibitive. 48 volt requires ~25% of the size of cable.

 

[bedpan]

There was a forum member a couple years back that used DC-DC converters to take the truck's 12 volt to 48 volt, then run smaller wire to the trailer (as 48 volt) and then a converter in the trailer to go from 48 volt to 12 volt. The cost in cabling to run high amp 12 volt is prohibitive. 48 volt requires ~25% of the size of cable.

Interesting idea.. I guess going to 120v is even better ;-) If I have enough 4 gauge I might try adding it to my DC2DC just to see how it does. AC is cheaper for me as I have 3 or 4 inverters I have collected kicking around the garage. If I can avoid buying another DC2DC it would be best..

I have lots of expenses coming up on the Cargo Trailer Conversion so if I can avoid extra hardware it would be good.

 

[Aussieguy]

what battery in the trailer ?
lead acid.... upgrade the wiring and add a voltage sensing relay
---------------------------------------------------------------------

Lithium
I would go the solar route.. the normal 7pin trailer power will add some amps
along with the solar at the same time.
you can look for some good used panels to keep the cost down.
+ one or two panels for a ground array.
------------------------------------------------------------------------------------------------------------------
Inverter in truck?
if you can set the inverter's low voltage (battery) cutoff to be just under the charging voltage so it won't drain the battery while engine not running
or add a voltage sensing relay in front of the inverter

you will always loose some power at the inverter and the converter back to 12v

I was wondering if it would work too....... so also following.

 

[bedpan]

what battery in the trailer ?
lead acid.... upgrade the wiring and add a voltage sensing relay
---------------------------------------------------------------------

Lithium
I would go the solar route.. the normal 7pin trailer power will add some amps
along with the solar at the same time.
you can look for some good used panels to keep the cost down.
+ one or two panels for a ground array.
------------------------------------------------------------------------------------------------------------------
Inverter in truck?
if you can set the inverter's low voltage (battery) cutoff to be just under the charging voltage so it won't drain the battery while engine not running
or add a voltage sensing relay in front of the inverter

you will always loose some power at the inverter and the converter back to 12v

I was wondering if it would work too....... so also following.

Lithium. Right now I have access to a few 100AH Renogy's. I am using those.
I will buy two 200 or 300 AH batteries in the coming bit.

Again not super driven to go solar just based on how I use it..
I can always start my truck and charge, sun can be a problem with shadows and weather.

I was planning on using some older 1000W inverters I have kicking around. As I read a little I might maybe look at a newer one. With built in cut offs it would save having to put in an isolator (although I already have one)

 

[bedpan]

I will likely wire this up in the coming weeks/month. I am working on insulating now then wall panels and furniture. Wiring will be mostly after that.

Really the next piece to sort out is how to set this all up. Specifically how to ground it all, GFI's etc... So I have some reading to do. Anyone have any advice or suggestions? I plan on going back and reading FilterGuys white papers again this weekend as well!

 

[HRTKD]

Any device with a ground connector should be grounded to the chassis and the battery should (eventually) be grounded to the chassis also.

 

[12VoltInstalls]

dogbone to connect the 15A extension cord from the truck to the 30A receptacle on the trailer.

A 12ga cord is 20A

Being in the weather I was thinking

I would hardwire from the truck’s inverter to one of these setups, and hardwire that to an A/B 3-pole 120V transfer switch that chooses the RV 120VAC inlet or the truck 120VAC (or just use that kind of weatherproof inlet and skip the transfer switch).

Installing the inverter in the cab would work better

how to ground it all, GFI's etc... So I have some reading to do. Anyone have any advice or suggestions? I plan on going back and reading FilterGuys white papers

A 20A GFCI immediately inline of the multiplus 120VAC output is what I would do, then feed your breaker panel from that.

Use breakers that are minimal- a 20A breaker on a 2000W inverter will never protect anything. 15A max.
A 10A breaker for smaller circuits will allow you to use 14ga or maybe even 16ga romex and save a few bucks for free. A 65W running load fridge doesn’t need a 15A circuit for example.

will likely have to scale the Victron down to maybe 60A to not overload the inverter.

80A at 12V nominal is 8A at 120V, 960W; plus whatever (40% more?) that inefficiency contributes from the charger. So yes, 60 may be appropriate.

 

[bedpan]

Any device with a ground connector should be grounded to the chassis and the battery should (eventually) be grounded to the chassis also.

I was reading @FilterGuy guides. Pretty handy. I learned a few things on the resi stuff and clarified a few things for me on the mobile stuff.

But ya.. More less ground the grounded stuff and hook up the batteries to ground as well..

More thinking about GFCI and grounding points with a AC system that spans two vehicles.

All said though I might give the DC2DC a test to see how it does at 80' of 4 gauge. I know that is close to 10% loss.. It really should work though I think.. I like the idea of the inverter but short of buying a new quite inverter I don't have one that I can install in the cabin of the truck. So I will try and make do with what I have..

 

[bedpan]

A 12ga cord is 20A

I would hardwire from the truck’s inverter to one of these setups, and hardwire that to an A/B 3-pole 120V transfer switch that chooses the RV 120VAC inlet or the truck 120VAC (or just use that kind of weatherproof inlet and skip the transfer switch).



A 20A GFCI immediately inline of the multiplus 120VAC output is what I would do, then feed your breaker panel from that.

Use breakers that are minimal- a 20A breaker on a 2000W inverter will never protect anything. 15A max.
A 10A breaker for smaller circuits will allow you to use 14ga or maybe even 16ga romex and save a few bucks for free. A 65W running load fridge doesn’t need a 15A circuit for example.

80A at 12V nominal is 8A at 120V, 960W; plus whatever (40% more?) that inefficiency contributes from the charger. So yes, 60 may be appropriate.

I was thinking a large gauge of wire for the extension cord from the truck inverter to the trailer more for physical protection then need of wire size. Saying that though I realized that I would be far better off with some loom and a cheaper cable.

As I read @FilterGuy 's guides I realize that all inverters in a mobile app should really be on a GFCI. I would likely add one to my inverters I have kicking around.

I will run wire size calculators for the rest of the build come that time. I was thinking I might get away with some 16 gauge as my longest internal run in the trailer should be under 20'.. But had not run the numbers yet...

Thanks for the ideas!