Adding an appliance on a DC circuit

Snoblett · September 2021

Hi all. We have a 2021 Tab400 BDE.
We acquired low volt/ low amp portable dog perimeter. It draws 0.7 amps and has an 120V AC plug with an 18V DC converter. We indent to ditch the AC plug and would like to hard-wire the device.

We want the flexibility of being able to run this unit off the battery. So, we would like to add another DC circuit that operates just like LED lights and Fan operate.

Assuming we have a 12V to 18V transformer, can we add a new DC circuit to the system?

Does anyone have experience doing something like this?

thanks!!

BrianZ · September 2021

Do you have an inverter you can plug it into?

Snoblett · September 2021

Well, there’s factory installed AIMS Power DC to AC power inverter.

I actually have not quite figured out where that is located.

We opened up under the bed and viewed the batteries and the solar controller. Also viewed the battery power switch and fuses that are otherwise accessible via the outdoor storage compartment.

please forgive as we are extremely newbie camper owners. I’m still trying to get an understanding of how all the stuff works that is from the factory, let alone upgrades.

We are handy and capable people, just brand new.

pthomas745 · September 2021

The "inverter" in your trailer: takes your 12V battery power, changes it to "regular" household current. One of the "outlets" in your trailer will work with your device when the inverter is turned on. Then you just have to manage how to run whatever cables from the trailer's outlet to the "perimeter."

There are trade-offs for inverter use: the inverter itself needs battery power to do its electrical magic. The AIMS inverter uses about twice as many amps as your fence does. It is a large, powerful inverter. You might be better off using a smaller inverter. It would require much less power to make the electrical conversion.

I have a couple of inverters that I use in my 320. They plug directly into the "12V ports" (what used to be called "cigarette lighter" ports.) I run laptops, battery chargers, etc. The trailer's 12V ports with an inverter are only good for items less than "roughly" 150 watts, but it still works well. I pay close attention to my power use when I use my inverters this way.

The most efficient way to use your 12V ports in the trailer is if the device itself has a 12V plug. This eliminates the "middle man" of the inverters power needs.

So: you can use the trailer's plug attached to the inverter to run your device. It will not be very efficient, so power monitoring will be important. A smaller "portable" inverter may be a better choice.

And: no apologies necessary! What would we have to do around here is people didn't ask questions?!

Snoblett · September 2021

Thank you @phtomas745

We are looking to hard-wire the device like as though it was factory installed. The device is already DC and we don’t plan to use the 120V plug with 18V converter that came with the device.

I guess another way asking the question might be if I wanted to add another light or another outlet or another fan (or something) and have it hardwired to work like the other items that run off the battery

Does that make sense?

we could “hack it” and just wire it directly to the battery itself, I suppose, but I’d rather it be done such that it operates like the other items like the fan and lights, etc.

Snoblett · September 2021

By the way, I can’t figure out WHERE the AIMS inverter is! 🤦🏻‍♀️🤷🏻‍♀️

-I have the on/off switch in the cubby at the head of the bed.
-I know where the WFCO switch box is, but no clue where the inverter is mounted

I’m running out of places to look!

Snoblett · September 2021

Could the answer be as simple as tying into the open spots for #10 & #11 fuses to the DC side of the power panel and running the wires directly to my device?

BridgerSunset · September 2021

On our 2021 400 BD, the inverter is under the rear bed, aft from the batteries, in that narrow compartment. It is blue in color (although it was replaced once even prior to us taking delivery). The Victron solar controller is located in the rear of the closet (driver's side, just in front of wheel well) & is accessed by pulling out & removing the drawer.

pthomas745 · September 2021

@Snoblett Now I get it. There have been projects where owners ran power from the junction box on the trailer all the way to things like backup cameras and different rear lights. So, I'm sure it can be done. But, that is way above my pay grade. There will be more responses to this I'm sure.

Snoblett · September 2021

@BridgerSunset
im not sure if my wiring is the same. We have a 3 way fridge which means I don’t have that lovely wardrobe! 😩

I thought the blue thing aft of the batteries is the Victron solar panel controller. But I could be wrong! If this is the AIMS inverter, then I have no clue where the Victron is.

I had no idea the learning curve involved in buying a camper! Lol

Heres what mine looks like:

Grumpy_G · September 2021

If there are open fuse locations that would be the best place to run a new circuit from. You'd need to use a DC-DC converter to bump the voltage to 18V as transformers work for AC not DC voltage. I would use one of those universal car laptop chargers and either hardwire it or just add another 12V outlet and plug it in there.

On another note, is that 0.7A @ 18V or is that the current draw of the power plug ? In the latter case that comes out to over 80W which would be quite the drain on the battery.

AnOldUR · September 2021

@Snoblett … Try running it on 12V. I have a 18V Bluetooth amp that’s hardwired into my 12V system. Works great on the lower voltage. For your fence, the level settings may be different than when using the transformer, but it might work fine. You may be able to use your 12V cigarette outlet.

edit to add:
As @Grumpy_G said, be sure to check to actual amperage draw with a meter so you know how long you can use it without serious drain on your battery.

Snoblett · September 2021

@Grumpy_G and @AnOldUR
thank you both for your insights

As I am rapidly meet the boundaries of my electrical experience…

What kind of tool can be used to measure the actual draw of the fence device?

you’re right, it may be just fine on the 12V, we were just trying to replicate the output from AC power cord that came with it. I attached a pic of the power cord.

also, a pic of the device says Input 18V DC , 350 mA

My fence dealer says it draws “very little power” but we all know that is a highly subject reference, especially when counting every last drop of power from a battery

AnOldUR · September 2021

Snoblett said:

What kind of tool can be used to measure the actual draw of the fence device?

I've used a multimeter in the past. Cheap one's are easy to find. I recently purchased a Fuse Buddy. Not cheap, but makes checking the draw through different circuits easy.
https://www.amazon.com/gp/product/B083TCDQBH/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1

AnOldUR · September 2021

Not sure of my electronic math skills, but I believe that if the draw is .35 amps at 18V it would draw .53 amps at 12V. Not a lot, but enough so that you should be monitoring your consumption (which you should be doing anyway).

note:
It looks to me like the power supply draws .7 amps on shore power, but the device draws .35 amps at 18V.

edit to add:
I hope someone more educated comes along to confirm or tell me I'm full of sh--.

Snoblett · September 2021

I need to find a print an Electricity Math Cheat Sheet. I am feeling sooooo dumb about this stuff.

I feel like I have electric experience because my husband and I wired all the circuits of our house when rehabbing it. But that was limited in scope because the circuits were all nice and tidy on 120 V AC. Understanding of the circuit was required rather than an in depth analysis of draw.

The minutia of DC battery consumption is a whole new ball of wax for me and I’m pretty sure we didn’t cover it in 4th grade DC electricity circuits curriculum with switches and lightbulbs! Lololol

Grumpy_G · September 2021

350mA @ 18V for the device itself is not much so no problem there. The DC-DC conversion is going to add some losses but total current will likely be under 1A on the 12V side. Should work just fine.

Snoblett · September 2021

@Grumpy_G and @AnOldUR

You guys are the BEST

thank you!

Horigan · September 2021

@Snoblett
Does your T@b have a solar port either by the battery switch door or on the tub? If so, that's a 12V source you could plug a 12V to 18V converter into, then plug in your fence. I would add a fuse to the converter wiring. If no port, you can add one wired from the junction box under the tub.

Snoblett · September 2021

Hi @Horigan
we do have an extra 2-pin connector solar port on the outside of the camper. It’s mounted just under the 30A shore power plug-in port. I have read different testaments of how that may be wired to the battery and whether or not it runs through the Victron solar controller as the factory installed solar panel does.

I’m new to camper lingo, so I don’t know what you mean by “tub”

The transmitter device for the fence needs to be kept indoors, so we plan to mount it internal to the camper, probably on the wall just behind the TV.

pthomas745 · September 2021

The "tub" is the place the propane tank sits. In this file, there is an "Unofficial Tab 400 Resource Guide." Written by an owner here, it is just full of good info to help decode trailer "names of things." Look for the file by Awca12a.

https://tab-rv.vanillacommunity.com/discussion/comment/113652/#Comment_113652

The solar port (I call it an SAE port, you will also hear it called a "Zamp" port) is wired directly to the battery. Designed specifically for connecting a solar panel. Since it does go direct to the battery, you can make a connector that can use 12V power (usually through an inverter). Test it with a multimeter to show yourself the proper polarity.

Snoblett · September 2021

Oh! That tub. Lol
thank you for the reference guide and for your thoughts!

Denny16 · September 2021

The electric fence should work directly off the battery, the one I have does. Get a SAE connector from Amazon and wire up an adapter to connect to the doggie fence.
cheers

Snoblett · September 2021

Thanks @Denny16
where do you plug in the 2-pin SAE in your camper?

Denny16 · September 2021

The SAE (solar panel connector) is next to the rear outside storage door, so it is on the passenger side, which is convenient. The SAE port, as previously mentioned, is connected to the battery, not the Victron controller, which is why any portable solar panel using this connection, needs its own solar controller.

Your SAE port is on the driver’s side, not sure why nüCamp moved its location, so not as convenient to use for 12VDC accessories on the passenger/door side of the trailer. Your battery connection junction box is on the back of yout TaB 400 outside access storage locker, behind the ply back panel.

You could connect a standard 12VDC outlet using no 8 wire to this battery connection point, and tun the wire along the back a d side of the compartment and mount it just inside the door. Open the door and plug in your accessory. Be sure to add an appropriate size fuse on the positive wire, which is provided on some the accessory outlets sold on Amazon or an RV parts outlet. Here is one with wire and fuse, ready to connect to the battery junction box: https://www.amazon.com/SPARKING-Cigarette-Lighter-Terminals-Extension/dp/B07RMH3R8P/ref=sr_1_4?dchild=1&keywords=12+VDC+accessory+outlet&qid=1632767678&sr=8-4
cheers

BrianZ · September 2021

Maybe this would do it?..
SMAKN Waterproof DC/DC Converter 12v (10~17V) Step UP to 19V/2A Power Supply Module https://www.amazon.com/dp/B00ORHHTIS

Or this..
DC DC 12V to 19V 4A 9V-13V to 19V Voltage Regulator,Step-up Module,Boost Converter,Waterproof Power Adapt 76W 19V Volt Transformer Module(12V to 19V 4A) https://www.amazon.com/dp/B097GRPXFD

Snoblett · September 2021

@BrianZ
oooo, that might be a good solution for the Volt conversion.

So, testing my understanding, with the scenario of hard-wiring:

I can tie into an open fuse in the WFCO fuse box and create a new DC circuit

The new wires coming out of the WFCO would connect to the DC-DC converter, and then a set of wires between the DC converter and my dog fence radio transmitter device which will mounted on an inside wall of the camper, )probably near the TV for me because it’s easy use the same wire drop as the TV is already using.)

BrianZ · September 2021

Sounds like a plan, @Snoblett. Use at your own risk, but I would expect this to work better than trying to run the device at lower than the rated voltage, which might cause it to fail.
You really should buy a multimeter, just an inexpensive one so you can check the voltage coming out of the transformer before hooking it up, and maybe ask the manufacturer if that voltage is ok. A meter can allow you to check continuity in wiring, and if it has an audible beep that's easier to use, otherwise the resistance measurement (ohms) can be used.
For basic multimeter lessons, you can try the following link and look at the videos list for Multimeter 101, 102 and 103..
https://youtube.com/channel/UCRdKCLh2lKFl_dNBNaLTnWw

Snoblett · September 2021

Thank you so much @BrianZ
We had a multi meter kicking around, but my son snagged it. 🙄

But you are right, they are cheap enough.

MuttonChops · September 2021

@Snoblett ; Dogwatch Support says unit should work OK on 12VDC.

After reading your initial question/post I send an email to Dogwatch Customer Support asking for clarification on the power supply operating range of the MB-2.
Two replies were:

1}    You can operate the MB2 off the 12V supply. As its not a
       full 18V supply you will likely have reduced range (this is how
       far the signal is projected off the unit or wire.)

2}    I check with our engineer he said – “It will work with possibly
       different range” - want to be sure you get the polarity right.

       Hope this answers your question - if not give us a call

So sounds like you should try in on the T@B "as is" and see if the area coverage works for you. Might not have to invest in a DC-to-DC step up convertor.

Snoblett · September 2021

@MuttonChops
omgosh, you’re so awesome. We talked about just contacting DogWatch and I mixed the idea being a skeptic thinking that they wouldn’t say anything different than what is printed because of warranty or liability, etc.

thank you for investing the time to contact them. 🙂

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