Slidein Camper

Digital Multimeters and Trimetric Meters


Jim Tomblin says that using digital multimeters is important


Jim Tomblin’s trimetric meter installed in his camper


Jim Tomblin’s 12-volt battery minder

In this article Jim Tomblin is going to teach us how to use digital multimeters  and trimetric meters.  Our first battery story with Jim Tomblin, “Camper Batteries 101: The Basics” covers the 12-volt systems in truck campers and educates us about camper batteries.  Specifically, we learned about charging batteries, replacing batteries, and maintaining batteries.

The response to his article was very positive so we’re following up with Camper Batteries 102.  In this article, Jim gets more in-depth about batteries and introduces us to using digital multimeters and trimetric meters with our campers.

TCM: If you need to change your old batteries out for new batteries, how do you do it?

Jim: First, if you have two batteries, they need to be the same.  You can’t have an AGM battery and a deep cell battery at the same time.  Second, they need to both be new.  You can’t have an old battery and a new battery together.

Before getting a new battery, you need to check your storage compartment’s dimensions.  Battery dimensions are different, so you want to determine where they will fit.  You will need to disconnect your old battery and connect your new one.  You are dealing with heavy wires that will need to be crimped.  And you need to make sure that it is properly connected.  There is some skill in doing that because you are making connections in the wires.  You can always ask a local RV dealer to do it.

TCM: What’s the difference between a 6-volt and a 12-volt battery?

Jim: It all has to do with the size of the battery.  12-volt batteries are Group 24 or 27.  A 6-volt battery is also called a golf cart battery.  They give you a lot of capacity.   When you hook them together, it’s the same as a Group 27.  They occupy a little bit less space than two twelve-volt batteries, but not much.  You can get them from Costco or Walmart.  The advantage to having two 12-volt batteries is that if you lose one you’re okay, but if you lose one of the 6-volts you’re dead and you have to go home.  I suggest that everyone uses digital multimeters to monitor their batteries.

TCM: What is a digital multimeter?

Jim: It’s a trouble-shooting aid.  Digital multimeters are a tool that you can check the voltage of DC, the voltage of AC, the amps of DC, the amps of AC, and the resistance in ohms.  You can get a digital multimeter online or at Home Depot.

Learning to use a digital multi-meter is important because it gives you a quick reading of your battery.  You should measure your batteries when you’re plugged into shore power.  When your camper is charging it should read above 13 volts.  If you have a good converter and you measure your battery at 12 volts, then it’s possible that the wire could be broken or a fuse blew.  You have to be cautious in how you measure the voltage in batteries.  If you are not careful you could create a situation that could be dangerous.

Another use for the meter is the resistance reading.   Say a light bulb in your camper goes bad, set the meter on resistance for a low value, like two, and then measure the light.   It should read zero.  If the meter doesn’t jump, then you know light bulb is open or blown inside.  Learning to measure resistance is something you practice.  You could even practice with your household light bulbs.

TCM: How does the digital multimeter work?

Jim: It’s the same as when you check the monitor in your camper to see if your battery is good, fair, or poor.  With a digital multimeter, you get a more exact reading of where the battery is really out.  If you are having trouble with your battery, you can see if you have more than 12 volts in your battery.  When you test your battery, your battery should read at least 12.6 volts.  If you have 12 volts then your battery needs to be charged.

TCM: How do you learn to use a digital multimeter?

Jim: You should have someone show you how to use it and you need to practice.  I usually tell people to go get a bunch of batteries they use in their home like AAA batteries.  When you are ready to get rid of a battery, see what the voltage is.  This is just to get used to measuring the battery.  AA and AAA batteries should be about one-and-a-half volts.  When they are just about out, they are at one volt.

The same is true for a 12-volt battery.  You should see a reading of 12.6 volts when it is charged.  If it reads 12 volts, it is nearly dead.  It doesn’t take much when it’s been sitting there.

TCM: What if you think you have a problem with your camper converter?

Jim: If you were thinking that you had a problem with your converter and you are plugged in, a trimetric meter would come in handy.  The trimetric meter can actually tell you the voltage of the converter in your batteries.

TCM: So, the trimetric meter is a good tool for truck campers as well?

Jim: One of the greatest tools for a camper is the trimetric monitors.  With a punch of a button, it will tell you by looking at it real quick that you’re in trouble.  When you charge it up you will get a 100% reading.  The trimetric monitors are helpful when you are boondocking and you use your battery.  If you think you should have used 15 amps at the end of the day and you look at your trimetric monitor and it says, 14 amps, then you can say, “Right on”.

Remember, two Group 27s have about 80-90 amps available, so using up fourteen amps means you still have a strong battery.

TCM: What does the trimetric meter display look like?

Jim: There is a display panel (see picture at the top of the page) that you can hang up on the wall of your camper that’s about four inches by five inches.  On the display there are a couple of buttons.  It tells you how many volts, amps, and the percentage of capacity.  After using it, I figure we use about fourteen to seventeen amps a day when we boondock.   It does take a little bit of skill to install.  You could get it installed at a RV appliance repair place.  I also recommend

TCM: So, if I’m bookdocking and I’m worried about using too many amps, what could I do?

Jim: Use your lights only when you need them.  The heater fan in the camper uses a lot of amps.  I’ve had friends who have a catalytic heater that they put in their camper that runs on propane.  You can mount it or get a hanger for it so that it can be on a door.  By using it, you don’t use as much of your battery power.  When using a catalytic heater, you need to crack a window open to circulate air a bit.  You would set your thermostat on fifty, turn the catalytic heater on low.  Your catalytic heater will reduce the run time on the camper furnace by a lot.

Also, don’t run your refrigerator on DC while you are boondocking.  It takes at least ten amps per hour to use the refrigerator.

TCM: Should we be testing our batteries all the time?

Jim: Using digital multimeters should only happen if you suspect that something is going on.  Over the years, as you use your batteries, you will learn what to do.

Click here to go Jim’s first article, Camper Batteries 101: The Basics.



Truck Camper Chooser
To Top