Simple Vandweller Low Voltage Cutoff Design For House Battery

Being an Electronics Engineer in my past life, and being a Vandweller, having had over the last 7 years a Class C, Prius, and Popup Truck Camper I have designed my own 12 volt systems.

The single problem I hear from vandwellers is how they killed their house battery by running it down too low to many times.  Even lead-acid batteries are expensive, so this year I have designed a simple 10 amp low voltage disconnect, commonly referred to as LVD.

The following is for simple one battery systems where the maximum usage at any time is 10 amps.  That’s 120 watts.  To make this simple for people that charge devices like cell phones, tablets, iPads, or laptops.  Or a single circuit equaling 10 amps.  

It makes no difference if you have lead-acid batteries or lithium batteries, as this only controls the output of the battery.

The best part is this a cheap solution vs buying a new battery.  The second best part is most people can get the parts and do it yourself.

Here are the basic parts above.

1. Plastic case

2. LVD circuit board

3. Corded 12V plug

4. Corded 12V outlet

You can even use 12V cords you have around provided the caution about having a fused circuit.

That’s it folks!

Build and plug it in and it reads your battery voltage.

One button to the left below the display to set the low voltage cutoff.  I recommend 12.0 or 12.1 as this is about 50% depletion of lead acid battery and point of recharge.

Another button to the right of the lower display to set the offset that regulates the voltage when circuit turns on.  

In the example above 12.1 cutoff + .4 turns circuit back on at 12.5 volts

You can make these settings anything you want within the specifications of the LVD, that has a wide range.

In the picture above I placed a on-off-on switch on top of the box to sleep I left room to mount it to the cover.  The switch may be handy if you wire it into a dedicated circuit.  The switch, when wired would give you the ability to; 

1. Bypass the circuit board if the board ever failed.

2. Turn it off to shut circuit down.

3. Circuit is on.

Note: My simple circuit design above assumes you have the circuit you plug this into with a 10 amp or smaller fuse or use a 12v plug with fuse in it like my picture above and it’s 10 amps.  If you don’t have a10 amp circuit or a fused 12v plug it is best to use the parts below as the 12v in and out cord are fused but you need to ensure that they are 10 amps or smaller.

Above is the LVD circuit board on Amazon. The instructions for programming like I listed above are in the product description.

Here is the plastic box.  I chose to set the circuit board on bottom of the box and to do this I needed to cut the mounting posts a bit to set it inside them and then used shoe goo to glue the four circuit board corners.

I used a small drill to drill through the side of the plastic box to route the wires in and outZ. The size of the drill bit will depend on your wire size.

Here is a heavy duty plug 12V cord rated for 15 amps.  Change fuse to 10 amps or use a less heavy duty cord but rated for no less than 10 amps.  I do favor heavy duty cords for wear and less loss of power in the cords.

Note: you will need to cut the ring terminals off the cord above to put into the box.




Like the plug above the 12V receptacle cord rated for 15 amps, change the fuse to 10 amps or use a less heavy duty cord but rated for no less than 10 amps.  I do favor heavy duty cords for wear and less loss of power in the cords.  You can see on the Amazon picture above, you can select the length of the outlet cord.  Plan ahead where you mount the box and how long a cord you will need.  

Note: you will need to cut the ring terminals off the cord above to put into the box.

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So, for less than $40 using heavy duty parts you can have a plug and play Low Voltage Cutoff for your house battery.  If you have old cords around you can save money but use cords rated for no less than 10 amps.  If you already have a circuit and have enough space and wire you can shut off the voltage to the circuit and cut the red and black, strip the ends and wire in the LVD saving more time and money.

Always work with circuits disconnected from the power to prevent mistakes.  You can see from my simple designed using some parts I have that I put colored tape on the leads before installing. Not all products use red and black cords.  You may need to test what wire is the + and -.  Do this before you start.

Use proper fusing. If you don’t understand how to do something ask someone that does.  There are lots of resources out there and your friends may have the skill.  

Best wishes with your LVD project.

Brent

macaloney@hotmail.com