Check Your Portable Generator Output Safely (Using a Cheap Voltmeter)

Last Updated on August 2, 2020 by Matt

how to test a generator with a multimeter

A portable generator can be a great tool for a variety of situations.

Whether using it as an emergency backup power source, for powering tools in a remote location, or for improving your tailgating or camping experience, it’s important that your generator is producing the correct voltage.

How can you tell? A cheap voltmeter is all you need. 

Safety First

When using a voltmeter to test your generator’s output, it’s important to follow a few safety rules.

Ideally, you should stand on a rubber mat and wear shoes with non-conductive soles. This is just a precaution, but it is a good idea. Although it is unlikely, you could end up getting seriously injured.

It is also imperative that you don’t touch the voltage regulator or other wires at any point—or you could get a big shock.

Testing your generator’s output is really quite safe, but an abundance of caution doesn’t hurt.

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1. Start your generator and turn on the voltmeter

Get the generator running. Turn on the voltmeter and make sure it is set to the “AC Voltage” position.

If you don’t have it in this mode, you’ll risk blowing a fuse.

2. Ground your meter

Using the black lead, ground your voltmeter by attaching it to the generator’s frame.

The lead should have an alligator clip you can use to attach it to the frame.

3. Touch the red lead to the output plug

Take the red lead and touch it to where you would plug in a tool or appliance.

Read the voltage displayed.

This is your generator’s current voltage output.

Troubleshooting an AVR

If the voltage wasn’t the number you were expecting, there are a few steps you can take to figure out where the problem is.

First, if your generator has an automatic voltage regulator, or AVR, this is likely the cause of your lack of voltage.

To test this, locate the AVR and remove the two leads.

Next, remove the red and black leads going from the AVR to the brush set.

Cover the red and black leads with electrical tape so they cannot touch each other or the housing.

Grab a 12-Volt DC power source (like a car battery) and some alligator clips. Hook the alligator clips to the brush set you just removed the leads from.

Then, hook the positive line you just attached to the brush set to your battery.

The positive line should always be toward the bearing. Don’t do anything with the negative line just yet.

At this point, start up the generator.

After the generator has been running for at least 10 seconds, hook the negative line from the brush set to your battery.

Now, grab your voltmeter and use it to test those first two leads that you first detached from the AVR.

You need it to read at least 60V. Often, this 12-volt battery test actually resolves the problem.

It helps restore the residual magnetism that the generator needs.

If this doesn’t work, you will likely need to replace the AVR. If the AVR isn’t the problem and your generator is still failing to produce electricity, chances are good that another more complex part has gone bad.

At this point, you should take the generator in for servicing from a manufacturer-approved technician.

Conclusion

Ultimately, checking your portable generator’s output is an easy and safe endeavor. A cheap voltmeter is all you need, and the process is quite simple. If you get an unexpected reading on the voltage meter, the basic troubleshooting process is a bit more complicated but still doable and safe.

Does this guide make sense to you? Do you have any unanswered questions? Do you have any other questions about portable generators?  Please ask away in the comments!

Last update on 2020-10-20 Affiliate links & images from Amazon Product Advertising API

8 comments

  1. I have a storm plus 5500. When it’s plugged up to our camper, the circuit breaker kicks in a few moments. any suggestion why this this happening. Could it be the AVR?

  2. Check to make sure that you do not have anything switched on in your camper circuit that pulls an immediate load. An example of this would be the electric side of the water heater or one or both AC units left on. All of these require a starting voltage that is more than the genset can handle until up to speed and loaded incrementally.

  3. Hi
    I have just checked my Strong line MEG4000 powered by Yamaha; On three phase the voltage is 265volts per phase (I am in Europe so a little high but ok) however the Hz are all over the place. Hz Phase1 320-370 range; Hz Phase 2 165-200 range; Hz Phase 3 265-320 range. My chargers on my solar system wont work with these Hz levels and I have no idea if this is normal or whatever. Advise would be helpful.

  4. Hello, I have a generator with 3 x 220 v output =0 volt
    1 x 400 v output =0 volt
    1 x 12v output =0 volt
    bud how di I teste the AVC/AVR;
    I have dismantled the AVC
    he is entitled to 80x38x34 mm
    it is wiht 1 jellow and 1blau + cabel on richt site
    on the left a plug with 2 x jellow_ 1 brouwn _1 blau

  5. My Generator runs fine for about an hour, and then suddenly the voltage output stops (Engine still running)
    An hour or so later, start it again, runs OK for a period of time, and then again the voltage output stops.
    Any idea what the cause of this could be?

  6. I need to get a 6dm14 battery for a model TG72B12 and I’m having no luck. I have tried Batteryplus Lowe’s and Home Depot. Any suggestions?

  7. I have a 5000 watt old jc pennys gas generator and have a cheap jx avr replacement. When I run it with my voltmeter I’m only getting 13 volts output that should be 120v. Can I adjust the small screw clockwise on the backside of the avr with everything isolated to prevent shock up to at least 110 volts?

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