The information contained in our websites and in our videos are designed for assisting trained Repair Professionals as a guide only and does not replace professional training. By using our information you are agreeing to our T&Cs. and acknowledge that the advice given is a general guide.
This article is NOT designed for Inverter Generators. Please see our this Repair Guide.
Please be aware that a blown AVR/Capacitor may not be the original fault, but may indicate a fault within the alternator or an overload surge.
If you replace the AVR/Capacitor or Brushes for a second time, this is a sure indication of an alternator or overload issue.
Unfortunately, testing Generator AVRs and Capacitors, without specialist equipment, is not possible. This is because AVRs and capacitors have a tendency to show as working correctly on the low voltages that Multimeters give out. They may test correctly, but when put under high voltage or heat the fault will be exposed.
But..... we have developed tests to rule out all the other faults with your generator, enabling you to pinpoint what needs replacing!
Please note: These tests do not rule out faults on equipment that has been plugged into the generator, or that an overload of the generator caused the problem. See this article to see how much power your Generator should give out on an ongoing basis. It might not be what you expect or as stated on the generator!
If there was no smoke or electrical burning smell coming from the alternator, then the majority of the time** (over 85%) it is 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.
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 on top of their running watts (i.e. Fridges/Freezers, Compressors, non-soft start AC). Also, be aware that 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) The generator was manufactured or fitted with an inferior quality alternator and this has degraded - This is not uncommon on budget generators.
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 labelled 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 three 240V sockets 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.
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. Once you have identified whether it is an AVR or a Capacitor, you can look up and purchase your replacement parts on our website.
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.
If you have an AVR on your Generator we also suggest you check the Brushes (see below for specific information on brushes).
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.
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. |
| 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 or Capacitor so it is accessible through the service panel. |
| 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. |
Brushes
Brushes are only found on alternators with an AVR (If you have a capacitor please go to the next section).
Be sure the Brushes are connecting to the Slip Rings correctly. They should have 13mm of the Carbon rod connections (both of them) protruding when removed from the alternator, be the same length and have a gentle curve to the end of them, to allow a good connection. If they are worn or not connecting correctly they will stop power from being produced, or create power intermittently. It is recommended to replace the Brushes at the same time as your AVR, especially if you had a high output fault, as any surge from your AVR may have softened the carbon connections. One thing to be aware of is possible carbon buildup, on or around the slip rings. The worn carbon, from the brushes, must go somewhere, cleaning this off may lead to better operation.
If your brushes have melted this is an indication of one of the following:
- Alternator overheating due to low airflow.
- Alternator overheating due to an overload.
- Alternator failure.
In each case, we highly suggest you run the test below as it is highly likely that the alternator has been damaged.
Alternator Testing on a Portable Generator
If your generator experienced any smoke or electrical burning smells from the alternator, or you have replaced the AVR/Capacitor for a second time, or just wish to test your Alternator to check there are no other faults. Our founder invented a new easier way to test all modern Portable Generators! No need for the manufacturer's expected readings with "The Beagley Alternator Test" Technique.
We have a training video to teach you the technique. It will guide you through testing and allow you to diagnose other problems that may exist in the alternator.
FYI... For Capacitor (brushless) Alternators, test across the two Capacitor wires instead.
If you need any Parts we sell them on our website.
If you need any further assistance or help to determine the results, please Click here to open a support ticket and tell one of our engineers the voltage results for:
1) Across the Brushes or Across the Capacitor Wires:
2) R1 & R2 :
3) L1 & L2 :
4) R1 & L1 :
We are always happy to help.
If you believe you have a damaged alternator, feel free to get in touch using the submit a ticket, and we can help you work out if this is the case.
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