Portable Generator Producing Low Power - or Power is Fluctuating

The information contained in our websites is designed as a guide only, for assisting Repair Professionals. By using our information you are agreeing to our T&Cs.

Turn off the Generator immediately and do not run if you have high voltage output as this might cause damage to the Alternator!

***If there was any smoke, or electrical burning smell from the alternator, please run the tests at the bottom of the page before replacing any Parts!

If you replace the AVR/Capacitor or Brushes for a second time, this is a sure indication of an alternator or overload  issue.

**If your engine stops when you turn on the breakers or you are getting approximately half power,  please submit a support ticket for more help at the bottom of this page. 

If there was no smoke or electrical burning smell coming from the alternator, then the majority of the time** (over 85%) it is the just the AVR or Capacitor beginning to fail, depending on which is fitted to your Generator. Replacing this should fix your problem, but please be aware that a blown AVR/Capacitor may not be the fault, but may indicate a fault within the alternator or an overload surge.

If you replace the AVR/Capacitor for a second time, or wish to confirm this is not a result of an underlying problem within the alternator, please run the tests at the bottom of this guide.

Fluctuating power

A) The engine should run at a constant and steady speed, this determines the generator’s voltage output. If the engine speed varies, this will cause the voltage output to vary along with it – as a direct result of an engine problem. In this case, the engine problem should be addressed first. Solving the problem with the engine speed should also fix the output problem. If your engine speed is varying, please Click Here to investigate the issue with your engine.

B) If the engine speed is steady but the output varies, it is the alternator that needs to be looked at in more detail. There are two main causes of varying outputs from the Alternator, a faulty AVR or a short circuit occurring in the Stator.

The most common reasons for alternator parts failing:

1) Overloading the generator – Breakers do not protect you from overloading, only from surges.

Be sure to take surges into account when calculating what can be run on your generator. Please be aware many things with a motor could have as high as a 100% surge value to their running watts (i.e. Fridges/Freezers, Compressors, non-soft start AC). Also, be aware, most things that produce heat are at least 1500w (i.e. coffee maker, hair dryer, kettle). Also, welding often requires higher currents than portable generators will produce, it is better to use a welder generator than to power a welder with an ordinary portable generator where overload is very likely.

2) Starting the generator with equipment plugged in and breakers on – Turn off all Breakers and unplug all the equipment when starting (This is a very common reason for overloads!).

3) The Generator was not grounded. All generators should be grounded during operation as per instructed in the manual. If there is a surge it needs to go to ground to prevent damage to the alternator and prevent electrocution!

4)  Equipment powered by the generator has an electrical fault and is surging beyond the capacity of the alternator.– All equipment should be tested on a regular basis. If you can smell the electrical burning scent around equipment, or issues only happen when certain equipment is plugged in, this is a good indication of an electrical fault within that equipment, or the equipment may require more power than the generator can produce.

5)  Generator was manufactured or fitted with an inferior quality Capacitor/AVR and this has degraded – Not uncommon, especially on budget versions.

6)Your generator is unbranded, rebranded, and is not actually the Wattage it has been marketed to be – This is common with cheap generators bought on eBay, Amazon, random small websites or from “on the side of the road” independent vendor types. If you think the generator is small in size or very cheap compared to other similar wattage generators, there is a good chance it has been incorrectly labeled as a larger generator. Please contact us for more info and we may be able to identify it for you.

7)You have a single phase generator that has been rebranded as a 3-phase generator – Again, common with cheap generators bought on eBay, Amazon, random small websites or from “on the side of the road” independent vendor types. A common feature for some of these incorrectly marked generators is a red socket on the control panel. Please contact us for more info and we may be able to correctly identify it for you.

Only replace the part with a quality Grade "A" replacement that is built for your Generator

Anything else could cause damage to your Alternator, resulting in the Alternator needing to be replaced Cheaper parts could surge and cause damage to your Alternator, resulting in the Alternator needing to be completely replaced, a very, very expensive repair! This is why we only sell maintenance quality grade “A” products.

Do I have an AVR or a Capacitor?

Use the table below to determine where to find the part on your Generator. Also, check for burning on the Stator windings or electrical burning smells while locating the AVR/Capacitor. If you have either of these problems, run the Alternator Test at the bottom of the page before replacing.

Once you remove the AVR/Capacitor you can identify it with this table:

2 or 4 wires = Capacitor and Brushless alternator. Search our Capacitors or search by Generator Brand

5 or more wires = AVR and Brushed alternator. Search AVR by Generator Brand and Model

Once you have identified if it is an AVR or a Capacitor, look up and purchase your replacement parts on our website

If you have an AVR on your Generator we also suggest you check the Brushes (tests below).

Where to find the AVR/Capacitor

Framed Generator

If your Generator sits in a frame, it is most commonly behind the end cover of the alternator. In rare cases, it can be found behind the control panel, follow the wires up from the alternator. It will be held on with either 2 bolts or a cable/zip tie. Replacing this should fix your problem.

Super Silent Generator

You can usually find this behind the rear panel of super-silent units. In rare cases, it will be located at the end of the alternator, if so you will need to remove the exhaust system to access it. It will be held on with either 2 bolts or a cable/zip tie. Very occasionally, manufacturers run very long wires to position the AVR so it is accessible through the service panel. Replacing this should fix your problem.

2 Stroke/Cycle Generators

In most cases, the part will be found behind the control panel. To locate it, remove the fuel tank. It will be a black box with 2 wires going to it and may be held on with 1 bolt. On some occasions, you will find a white cylindrical Capacitor instead. Replacing this should fix your problem. 

Alternator Testing on a Portable Generator

If you had burning, smoke, electrical smells from the alternator, replaced the AVR/Capacitor for a second time or just wish to test your Alternator to be sure there are no other faults, our founder invented a new easier way to test all modern Portable Generators! No need for manufacturer’s expected readings with “The Beagley Alternator Testing Technique.”

We have created this training video to teach you the technique. It will guide you through testing and allow you to diagnose any other problems which might exist in the alternator. 

For Capacitor (brushless) Alternators, please skip the brushes parts of the test.

If you have run these tests and want feedback from an engineer, please use the form below to submit a ticket with the full results. We are always happy to help.

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