See this thread: https://www.f150forum.com/showthread...=375885&page=1

I think one of the big points taken from that thread is to not ground at the battery so that the battery management system can properly "see" the load you are adding.

 

Then you don't need to worry about an isolator. Take +12 off the battery and ground off the frame (somewhere the current sensor can see the load) and knock your lights out! The BMS will see this as an aux load.

Amen. Glad to see another brother on here.

 

Thanks, tvsjr.

I appreciate that!

Good, glad to know I can just old-school it direct like that.

I see some marine 8 AWG in my future with a simple fuse-block!

 

Just make sure you consider the power draw. If you simply parallel the batteries, if your rear battery is rather discharged, you will see a substantial inrush current. If the trailer battery bank is sized fairly large, 8AWG may not be sufficient. At that length, 8AWG is only good for about 40A. If you had, say, 200AH of battery capacity, you would exceed that substantially for long enough to cause things to light up. You also have the potential for the front battery to go bad and the rear battery to try to supply power to start the truck... this would get very interesting.

The problem with diode/FET/relay isolators is they allow power to flow both directions when the truck is running and the alternator charging. This is what pisses off the BMS. You basically want the secondary battery to look like just another accessory... not have it contributing power back into the vehicle system.

The Right Answer(tm) would be a DC-to-DC battery charger. That would provide current limiting, and also (with a good enough unit) 4-stage charging for battery equalization, etc. Such devices are commonly found in solar systems and in the marine world... which means they aren't cheap.

 

Yeah, what I am thinking is just wire to a fuse block and it is easy enough to run any size wire... not like I'd need a ton of 8 or 6 AWG to get there.

I believe that is a 200A alternator there..... I don't want any fires!

From the fuse block I will run a DC/DC charger and isolate it from the starter battery with a switch when I am not under way.
You beat me to the punch but, you know, great minds and all that.....

The fuse block will allow me to add a few things that I am sure I will just have to have at some point.... what they are, quien sabe, but I am sure they will pop into my head as soon as I see somebody else having something cool I want!

Honestly, the solar module should keep things charged up pretty well with the Blue Sky CC so relying on the engine to charge is only for backup and not regular duty.

My only concern would be more than a few days of no sun but that module is pretty good in low light, too, so I will realize something unless it is raining.

 

Sterling

I like how simple it is to wire and I also like the 30A charging if it needs it along with the charging profile.

It will mount easily to whatever box I choose to install my solar PV charge controller.

I am going to make everything as plug and play as possible for easy installation and removal as needed.

However, THIS is a great price and waterproof..... options.....

 

Have you looked at the Sterling Pro Charge B? It seems waterproof, cheaper than the one first one you linked to, and appears to have some isolation features. Thanks for bringing attention to their products.

Your second link takes me to an empty shopping cart, so I'm not sure what you were referencing there.

 

Oops! Fixed the link, thanks. Yes, that is what I linked to and their price was around $230.

Are you affiliated with Sterling?

Seems like a perfect product for my application.

 

I am not affiliated them, just another guy interested in project like yours

And great find in your link! It has the data sheet which should help determine if it is in fact appropriate for the application.

 

[QUOTE=tvsjr;5317731]

The problem with diode/FET/relay isolators is they allow power to flow both directions when the truck is running and the alternator charging. QUOTE]



Umm, isn't the point of a diode is that it only allows current to flow in one direction?


di·ode
ˈdīˌōd/
nounElectronics

noun: diode; plural noun: diodes

1. a semiconductor device with two terminals, typically allowing the flow of current in one direction only.