I have an idea that came to me today while I was working on my RV. A little background first; I bought an Excursion and a 30' Rockwood Windjammer travel trailer. I'm a consultant and I work from home pretty much exclusively, so it doesn't really matter where home is. I plan on moving into the RV full-time and exploring the country while working from wherever I am.

The floor plan I have comes with a front bunkhouse. I removed the bunks on the left side and built myself a desk. I would like to be able to work without ground power, so that means having enough battery capacity to run my equipment for 24 hours without recharging (solar is in the near future).

I have 5 accessories that I currently have at my desk and wouldn't you know, every single one of them actually runs on DC. The DC-to-AC-to-DC conversion is obviously horribly inefficient.

I have:
2 laptops, each needs 19.5v DC. I can buy car adapters for both of them from Amazon.
1 USB hub that needs 5v DC. I will need to make/buy some kind of transformer for this one, or get a USB hub that takes 12v DC (not sure if they make them, kind of making this up as I go)
1 monitor that needs 12v DC
1 desk lamp that needs 12v DC

My plan is to use the under-bunk storage area on the other side of the bunkhouse to store a couple of AGM batteries and eventually a solar charge controller. I would like to be able to charge the batteries either off ground power or an external generator.

I would then run what would essentially be a 12v DC outlet power strip to my desk where I can plug my devices in. I would also like to have a bunch of powered USB outlets built into the power strip.

This would be a separate system from the rest of the RV electrical system. I don't want to run any of my 12v devices off the main RV system, and I don't want anything in the RV to run off the secondary batteries.

I have a basic understanding of electricity, but I've never done a project like this before. I know there are some things I'm probably overlooking, but does anyone see any glaring holes or problems? Any ideas for improvement?

Can I integrate the existing battery charger and use it to charge the secondary system? I don't even know where the charger and inverter are in this rig. There's an outlet in the very front of the RV, maybe I can draw ground power for the battery charger there and keep everything up front?

What about the tongue weight of the batteries? These things aren't light. The batteries I'm looking at are in the 100 lb range. Each.

 

Why don't use just get a generator and then you can use that to keep things charged.


You don't want those batteries on the inside of the trailer. The venting of the gases is not a good thing to breath.

 

I plan on that as well. However, solar is a lot cheaper in the long run.

AGM batteries are safe to run in low ventilation areas.

 

Having had solar in more than one rig including our current one, I would encourage a closer look. Even my friend who manufactures solar controller and sells systems says to buy the generator first. There are just too darn many limitations to solar including cost to get a system large enough to have reasonable amp output and the sun doesn't shine sometimes for days.


You are right. AGMs can be used in any position anywhere.


Yes, you can use your converter to charge both battery banks. Not much to it. Just a selector to choose which battery bank you are charging when.


To calculate your power needs you want to know watts or amp draw. Voltage doesn't tell you much.


I have 130 watts on the roof, a 2000 watt inverter/charger, and will be going to four AGMs in a couple of months, which is pretty much the typical minimum. And yes, 130 watts is just a basic system.


I would encourage anyone considering solar to do a lot of reading on it. Know your loads and where you are going to camp. Solar is much more common in the western states and less so east of the Mississippi.


My thoughts,


Steve

 

I will try to help in the one area I know a little about...

USB itself runs on 5VDC, so any USB car charger will put out the appropriate 5VDC you need. The only issue is getting that correct voltage into the HUB somehow since I'm sure the AC adapter has a round plug. Maybe take a USB cable and remove the end that goes into the device being charged and splice in a round plug. I also have an adapter in one of my vehicles made by Sony back in the Discman era that would put out multiple regulated voltages between 3 and 12VDC along with a polarity switch and 3 different sized plugs on the end. Kind of like a standard household multi-adapter, but for your car.

The only reason USB hubs normally need external power is to boost the USB power to acceptable levels for the multiple devices plugged in. If the devices plugged in don't use USB power (such as externally powered devices, i.e. printers or self powered External HDDs) or very little power (thumb drive), you may not need any external power on the HUB for it to work.

 

I never thought of that. That will work perfect, I'll just splice in the plug that came with the hub.

Unfortunately I have too much stuff plugged in. Two cell phones, a wifi hotspot, a mouse, two thumb drives, lync headset, etc.

Thanks for the tip on the car USB adapter. I can definitely use that trick.

 

Watching with interest as I will be doing something quite similar next year at this time.

I'm curious if you can use a battery isolator between your auxiliary batteries and the house batteries? This would allow your generator or shore power charger to charge all batteries simultaneously..

 

Yes, you can use an isolator, but it is even simpler to use a selector that gives you the choice of choosing to charge either one battery or both at the same time and also offers you the choice of linking them for use if the need arises without powering the isolator. A no brainer to wire and reliable to boot.


Just a thought,


Steve

 

Makes sense.. Thanks Steve!