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Why every caravanner and camper NEEDS a clamp meter

Batteries draining too fast? 

Trailer lights flickering? 

Solar panels not working their best?

Why every caravanner and camper NEEDS a clamp meter!

Camping and caravanning is great, without a doubt.  The great Australian past time.  Especially when all your gear and equipment is working perfectly, the way it should.  You get to relax, unwind, and enjoy being in the outdoors…

But what about when everything isn’t working perfectly?

Have you ever noticed that your batteries are draining faster than what they used to?  Or maybe that they’re not charging as quickly as they once did?  Perhaps you’re needing to know how long your batteries are going to last before they’ll need charging again?

Maybe when you’re out camping, you’ve noticed one of your lights flickering a little?  Or maybe not working at all?

And solar panels are brilliant, when they’re working at their best…  have you ever wondered if yours are producing the charge they should be?

And most caravanners and campers have struggled at one point or another with trailer lighting not working as it should.

Did you know that a clamp meter could help you with all this?  Potentially saving you hours of frustrations, and hundreds of dollars in auto-electrician fees!

Knowing a few basic ‘tricks’ and having the correct tools on hand to do your own problem solving is imperative for those travelling and camping often - particularly if you’re frequenting places off the beaten track!  Help is not always immediately available, and even when it is, it can cost you hundreds of dollars in fees!!  Read on to find out how having your own clamp meter in your tool box can help...


WHY a clamp meter?

Flir CM46 Clamp Meter
A clamp meter is going to be far more suitable in your travelling toolbox than your standard multimeter. 

Unlike a multimeter, a clamp meter can measure current travelling through a wire, without having to touch the bare wire inside or having to break into the circuit. 

This allows you to safely measure the current draw on any device in your camping setup, and the current your charging systems are putting back into your batteries, within just a few seconds.  And you do not have to pull apart any wiring to measure these currents.
As there is no need to break into any circuits, a clamp meter allows you to measure these currents easily and safely, and while all the devices are in use.

Further, a clamp meter usually has all the functions of a multimeter, such as voltage, resistance and continuity, so it allows you to troubleshoot a host of electrical issues you may experience while off the beaten track.


Current Measurement

WHAT can you measure with your clamp meter?

A clamp meter can measure how much current is being drawn by your:

  • Fridge
  • Microwave
  • TV
  • Radio
  • Lighting system
  • Fans
  • Water pump
  • Satellite receivers

You can even measure how much current is being drawn when all devices are being used at the same time.  


You can also measure how much current is being replaced by your:

  • Solar panels
  • Wind turbines
  • Towing vehicle
  • Mains power battery chargers


If the current going into your batteries is less than the current coming out, your batteries are going to go flat.  (Not necessarily a bad thing, as some charging systems are only there to prolong the battery cycle).  But if you expect the battery to remain fully charged, then input must be equal to or greater than output.  So it’s worth checking!!


HOW to measure with your clamp meter

A quick bit of theory...   For the purpose of this explanation we are talking about direct current, aka DC.  In particular, a 12V system that you will usually find in a caravan or camper that supplies all of the 12V apparatus.
When a current travels through a conductor, a magnetic field emanates from that conductor.  The strength of that magnetic field is directly related to the amount of current running through the conductor.   A clamp meter has a special circuit in the clamp that detects the strength of this magnetic field.  After a few calculations in the meter, the equivalent current that would cause a magnetic field of that strength is displayed on the meter. 
Further to this, the magnetic field has a particular polarity (North or South) in a circular direction around the cable which is determined by which way the current is flowing in the conductor.   
The reason I mention this is because the positive and negative conductor placed side by side, will have opposing magnetic field directions around each of them as one current is going from the battery to the equipment, and the other is returning from the equipment to the battery. In effect the magnetic fields cancel each other out, leaving no net magnetic field.  With zero net magnetic field, a clamp meter cannot measure current.  
So, to measure current you need to make sure to place the clamp around one conductor only, not both.  It doesn’t matter whether it is the positive or negative conductor, as the same current value will be measured in each.  What’s going out the equipment should be coming back.

To measure the current in a cable, find a place in the cable where the positive and negative (usually red and black wires) can be separated. 

This often occurs at the origin or end of the cable.  If this is not possible because positive and negative are well concealed in insulation, or are very difficult to get to then there is a work around which I will explain a bit further on.

Let’s say you want to know how much current your fridge is drawing from your battery.  Simply find a place in the supply cable to your fridge where you can get a clamp around the positive or negative conductor. 

Ensure your clamp meter is set to DC Amps.  (If your meter does not have auto ranging you may have to set it to a suitable range, in which case, 20A range or thereabouts, would be a good start for this measurement). 

Clamp your meter around one conductor, and read the result on the screen. 

It’s that simple. The same goes for any other device that you wish to check.  

The measured current may give a negative result. This just means that the meter is expecting the current to be going the other way, based on which way you put the clamp on. If you turn the clamp over and measure again, you’ll see the current changes back to a positive value. 

The clamp should have markings showing which way the current should flow for a positive result.  

Showing positive symbol on Flir CM46 clamp meter



Flir CM46 clamp meter testing current draw in caravanIf you cannot separate the positive from the negative supply to a device, or the cables are difficult to get to, there is a work around. 

Turn every other device off and measure the current draw at the battery.  You should be able to clamp onto one conductor here as they are naturally separated in order to be fixed off to the battery terminals.

What if you cannot turn everything off?  eg. You're working at night and need the lighting!  You can turn the device you want to check off, measure the current at the battery, turn the device on, and measure the current at the battery again. 

The difference between the two measurements is the current being drawn from the device you just turned on.  

Finally, as already hinted above, you can measure the total current of all devices that you have running simply by measuring the total current being drawn from the battery. 

Using clamp meter to test charging current in caravanTo measure the current supply to the batteries from whatever charging device you have running,  just do exactly the same as above. 

Find a place in the supply cable from the charging device where you can separate positive and negative, and use the clamp to measure one of the wires.   It is unlikely that you won’t be able to find a place in the cable to measure, as these cables will usually go straight to the battery.



Using your Clamp Meter

Use the clamp meter to work out how long your batteries will last

If the drawn current from your battery is more than the generated current recharging your battery, (as is often the case with solar generation), your battery charge is being depleted.  The difference between the generated current and the drawn current can be used to calculate how long the battery should last before going flat.  If you are not generating, then obviously the only value you will use is the current drawn from the battery.

Here’s how -

Your battery will have an amp hour rating on it. eg 100 Amp Hours (100 Ah).  If you divide this figure by the difference between generated current and drawn current, the result is the amount of hours your battery should last (assuming the battery is fully charged to begin with, and in good order). 

Let’s say you have measured the total current being drawn at 10A, and the current being generated at 8A.  The result is 2A being drawn from your battery. Divide the rating of your battery, by the resultant current draw.  In this case divide 100Ah by 2A. You could reasonably expect your batteries to last for around 50 hours at this rate.  

If you’re relying on solar power to charge your batteries, then keep in mind that you won’t be receiving any charge once the sun has gone down!  Here the maths gets a little bit trickier, because you're only generating power during sunlight hours, and not at night.  One way to work it out is by taking individual measurements for current draw during generation and at night, and use these values to track battery use. 

To calculate, estimate how many hours of generation your solar panels will give each day. Multiply the net current draw during generation by the the number of hours of generation. This will give you the amount of Amp Hours being used during the day.  Do the same for night time. Multiply the current drawn at night by the number of hours there is no generation. This will give you the Amp Hours being used at night.  Start adding these values up for each day and night.  When the total reaches the Ah rating of the battery, this is when your battery will go flat. There is obviously a fair bit of estimation here, but it should give you a ball park figure.


Use the clamp meter to confirm a supply cable or circuit

Using Flir CM46 clamp meter to prove wires in a circuitIf you need to find out which cable is for what, for instance you want to change a circuit in your set up, you can easily determine what cable is supplying what device.  

Simply place your clamp around a circuit you think might be the one you're looking for and turn the device on.

If the current increases, then you are on the right circuit.  Turn it on and off a few times just ''to be sure, to be sure''.  The current should instantly rise and fall in unison. 



Using the Multimeter Functions on your Clamp Meter

Now you've seen how handy a clamp meter can be, but it doesn't stop there....  clamp meters can also have a range of other functions.  Ideally, for travelling, you should have one with at least the additional functions of voltage, resistance and continuity.  A temperature function would also be very handy.


What you can do with the Voltage function

Check battery levels

Figuring out how long your batteries are going to last is great, but these calculations only work out if you know the charge level of your battery to begin with.  The voltage function of your meter allows you to check the volts of your battery.

Using Flir CM46 clamp meter to test caravan battery voltage


Set your clamp meter to Volts.  If your meter has autoranging you won’t have to set a range, however if it doesn’t, you’ll need to set it to the range higher than 12 volts (eg. 20 volts).

Using the probes, which you will have plugged into the Volts and Common ports on the clamp meter, place the red probe on the positive terminal of your battery, and the black probe on the negative terminal of your battery.  Your meter will display the battery voltage. 

A fully charged 12 volt battery should be sitting around 12.68V or higher.  Anything less than 12V indicates your battery is already flat.  And in between indicates your battery has lost some charge. 





Check for faulty circuits

* In appliances…

Let’s say your fridge isn’t working.  You need to investigate whether the problem is with your fridge itself, or the supply to your fridge.

Using Flir CM46 clamp meter to check fridge supply plugWith your clamp meter still on the volt setting,  and the leads in Volts and Common ports, unplug the fridge, and check for voltage where the fridge was plugged in.  Insert the probes where the positive and negative pins would be.  (Don’t touch the probes to each other whilst doing this, or you could short circuit the plug.) 

The reading should be the same as the battery voltage.  If so, the problem is with the fridge itself or the lead on the fridge.  If there is no voltage, the problem is with the supply, somewhere between the battery and the plug.  There could be a break in the circuit, or it could simply be a blown fuse (so check the fuses!).

If it’s a break in the circuit, you can systematically check along the circuit for voltage wherever you can get the probes on.  When the voltage disappears the part of the circuit that has the break is between where you had voltage, and where you didn’t.


* In trailer lights…

You can also check voltage to trailer lighting this way.  Narrowing down where the break is, makes the process of fixing the problem a lot quicker and easier!

Corroded connections are a common thing with trailer wiring.  Chances are there is a crook connection in the part of the circuit you found the break in. 


What you can do with the Continuity Tester function

A continuity tester is very simple in its operation.  It tries to complete a circuit in the meter between the probes.  If the circuit is not completed, nothing happens.  If a circuit is completed, the meter gives off a sound. 

So, if you place something between the probes, for example a conductive wire, this will allow the circuit to be completed and a beep will sound from the meter.   If there is a break in the wire, the circuit cannot be completed and no sound will come from the meter.  The continuity tester is used with the power off or disconnected (eg disconnected battery).

Always test your meter when nothing happens to ensure its working.  To do this all you have to do is touch the probes together to complete the circuit. If the meter  beeps, your good, if not, you’re on the wrong setting, or your meter is faulty.   99 times out of 100, you'll be on the wrong setting.  The usual mistake is being on just ohms instead of continuity.


Check for blown fuses

Using clamp meter Continuity function to test fuseWith a continuity tester you can check fuses on any appliance.   

Just place the meter on continuity function, which usually has the symbol that looks like emanating sound. Remove the fuse from it’s housing, and place the probes on each terminal of the fuse.  If the meter beeps, you're good.  If nothing happens, the fuse is blown.


Check cables and wires for breaks

Easily check your appliance cables, or trailer wiring, for breaks. There's a few different ways to check for continuity in a cable. The main difference between each method is how you reach each end of the wire you want to test.

Before you begin testing a wire for continuity, disconnect the wire at each end.  This takes away any possibility of a test gaining a return path through another route. 

You'll notice that the leads on the multimeter are not very long, so you need a way to reach both ends to test. An easy way to think of it is that you need use something to extend one of the probes to reach the other end of the wire.

What can you use?

Firstly, the wire you want to test is likely to be in a cable with other wires. You can use one of these other wires as an extension for one of your your probes.

Join the end of the wire under test that you can't reach to another wire that also goes to both ends.  In the example below, we have joined the red and yellow wires, which is left hand indicator and brake light on a camper trailer plug connection.

Showing 7 pin trailer plug connections   Shorting two wires in trailer plug connections to extend test probes    

Now you can put your probes on both these wires at one end. The circuit route for the meter will be down one probe, into the wire under test, back up the wire you used as an extension, and into the other probe. If there is no break in the wire the meter will beep.

Using clamp meter Continuity function to test trailer light wiring

In the example shown, we have removed the globes and are testing between red and yellow wires, at the light cluster of the trailer.

There is an anomaly that may pop up if there is no beep, and that is the possibility of there being a break in the extension wire. There are a few different things you can do to take this possibility out of the equation.

You can simply use another wire in the cable that you know was fine before you started testing. 

You can get a separate piece of wire altogether and use it to literally extend your probe.

You can use the chassis of the caravan, trailer, or camper as a wire. Just fix the end of the test wire you can't reach to the chassis. Under an existing screw or bolt head is the usual method. Then at the other end you place one probe on the wire and the other on a bare piece of metal or screw head on the same chassis.  If there is no break in the wire, the meter will beep. Try and use clean metal or clean bolt heads so that you get a good conductive connection. You may have to clean it up a bit first. 

The continuity function allows you to not only check for breaks in wires, but also shorts in wires, or a short to the ground.  That is, if you measure between two wires or between a wire and bare caravan frame/bolt and you get a beep when you shouldn’t have one, then there is a short circuit somewhere. 


Check faulty connections

If you suspect a faulty connection, you can use the continuity tester to test across each side of the connection.  You should get a beep if the connection is good.


Check switches are opening and closing correctly

With the power turned off disconnect one wire from the switch and turn it on. Measure across the switch terminals. It should beep.  Leave your probes there and turn the switch off, the beep should cease.   


What can you do with a Temperature Probe

If your clamp meter has the added option of a temperature probe, this function can be very handy.   The probe usually consists of a separate wire that plugs into your voltage and common inputs on your meter.  At the end is a very small metal ball.  This is the sensor for your temperature.   You place this ball on a surface or within a space that you wish to measure, and it very quickly takes on the temperature of that surface or space, allowing the meter to measure that temperature.   

Using Flir CM46 with temperature probe to check temperature of camping fridge

You can use this for...

*  Testing your fridge temperature

*  Testing your air conditioner output

*  Testing hot water output.

*  Testing how hot it is today!

*  Testing for high fever if you’re sick!  (I recommend under your arm, not in your mouth.  It’s not actually medical apparatus, or hygienic, but it can be effective if it’s all you have on hand!)




So you can see that having your own clamp meter with you when you’re travelling is helpful for a whole host of reasons.  It can be used in a multitude of ways to determine problems you may experience with cabling, connections, supply and generation.   I haven’t even mentioned troubleshooting motor vehicle electrics, or looking at individual pieces of equipment that have failed that a reasonably handy person may resolve with some simple testing. 

Plus, doing your own trouble shooting is fun and satisfying.  Even more importantly however, it can easily save you hundreds of dollars in trade fees!

Do you have a clamp meter in your travelling tool box?  Don’t head off on your next trip without one! 

Here are 4 clamp meters that Delta Pro recommend, that are suitable for this kind of troubleshooting.  These are quality meters that are industrial standard, will last for years, and are very affordable.  They have all of the functions mentioned above, and more.  

Lutron CM-6155C

Flir CM46

HT Instruments HT9015

Prova A11


By all means, if you are looking for something different, you can check out our full range of quality clamp meters.  Be sure to use the search filter features to help reduce your search to only the meters with the specific parameters you’re looking for.   

Happy travelling,