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"Expert in regulator rectifiers" 

Problem with the rectifier?

What should I do if the charging of the regulator rectifier is not good? (The ideal charging is between 14V - 14.7V). What are the signs of a faulty regulator rectifier? In our next article, we will explore this topic.

It is important to know how to use a multimeter at least at a basic level to perform the measurements. If you are not familiar with it, seek help from a mechanic or at least from a friend with experience.

The following diagram will also help visually identify the problem, and after the image, you will find a detailed explanation of each (numbered) point.


0. Let's talk a few words about the battery:

  • Sealed batteries (AGM, absorbed glass mat with gelled acid) prefer a charging voltage above 14.5V (but it should never exceed 15V).
  • For conventional/flooded lead-acid batteries with caps (open batteries), the ideal voltage is below 14.5V (but above 14V). If the voltage is higher, the water loss due to electrolysis needs to be replenished more frequently, meaning you have to top up with distilled water. Never use tap water or battery acid!

1. Overcharging (above 14.9-15V) likely indicates an issue with the regulator rectifier.

1.1 However, it is also worth checking if the voltmeter (multimeter) you used for the measurement is running low on battery (the battery of the multimeter). A multimeter with depleted batteries can display readings 2-3V higher than the actual voltage! In most cases, the device will indicate this with a "LOBAT" message or a low battery icon.

If the overcharge value displayed by the multimeter is relatively stable, it can also be a sign that the batteries are starting to deplete. For example, if the multimeter consistently shows 15.8V regardless of whether the measurement is taken with or without the headlight on, and regardless of the engine speed. In such cases, the multimeter might not yet indicate that its batteries are low, but the measurement is no longer accurate (and the voltage regulator is not actually overcharging).


2. Undercharging (below 13.7-13.9V): It might not necessarily be an issue with the voltage regulator. Before you immediately order a new voltage regulator, it is worth checking a few things, as it is possible that the voltage regulator is not at fault and something else is causing the problem.


Can the engine speed (RPM) affect my charging?

If your charging is low at low engine speeds, while it increases when the engine speed is raised and reaches the appropriate (above 14V) voltage range, then suspicion may arise that the magnets of the alternator/generator have weakened. It may be worth investigating this as well! 

It's actually advisable to perform the following measurements anyway if one of the components of the regulator rectifier - battery - alternator/generator triumvirate malfunctions. It may happen that the fault is caused by another component, not the one that has failed (e.g., a short-circuited alternator/generator causing the regulator rectifier to fail due to the short-circuit current). 

2.1 Check if there's any voltage drop in the motorcycle's wiring harness:

Loose, corroded connections can cause low, insufficient charging. If the connector has melted, replace it.

Inspect the sliding contacts. Dirty or oxidized sliding contacts can also cause voltage fluctuations.

Check the fuse (most motorcycles have it next to the starter relay) to ensure there's no melted plastic around it. 


TIP, especially for older motorcycles:

With proper care (and expertise), only for a test, connect the regulator rectifier current leads directly to the battery (even using extension wires if the voltage regulator wiring is short). When making the connection, loosen the battery terminals, place the wires underneath, and then tighten them back securely. 

If the voltage in the system is appropriate during the test (it should be between 14.5 - 14.7V), then the fault (voltage drop) is clearly somewhere in the motorcycle's wiring (typically such "weak points" are poor connections or crimped joints anywhere in the wiring). Maintenance and repair are necessary in such cases.


In this case (if your voltage is correct during the test), even if you replace your regulator, the new regulator will also undercharge, since the current regulator is already regulate the correct voltage, but it's not reaching the battery. This is NOT a voltage regulator issue.


It is crucial to emphasize the necessity of professional expertise for this test.

Strict attention must be paid to the correct polarity during the connection, as reverse polarity will damage the regulator rectifier!! This test connection should only remain for the duration of the measurement; the wiring fault must be repaired!!



2.2 Disconnect the voltage regulator from the motorcycle and use a voltage meter (multimeter) to check the diodes. Set the multimeter to diode test mode. You can find a video for measuring the voltage regulator diodes at the following link: https://www.youtube.com/watch?v=NTjumDgixkQ&t=215s . 

Here we are checking that if even one diode is faulty (its value deviates from the measurements), then it's certain that the regulator is bad!

Even if the diodes are good in the regulator, it's still possible that the regulator is faulty. But checking the diodes is the most you can do (and in a significant portion of faulty regulators, the cause of the issue is the diode). So, if the diodes are fine, then let's go through the other components of the charging system:


2.3 If after checking the above points the charging issue hasn't improved (or the fault hasn't been identified), then check the alternator/generator:

When measuring the alternator/generator, stop the motorcycle and disconnect EVERY wire (can't go wrong with that).

Check for a short circuit in the alternator/generator: Place one end of the multimeter on the metallic body of the motorcycle (avoid painted surfaces as they insulate!!), and with the other end, test each of the three generator leads individually. In each case, the multimeter should display "1" or "OL".

If it beeps or shows a value, there's a short circuit in the alternator/generator winding, no need to look further because it's already bad!

If the previous measurement is fine, you can start the motorcycle. Set the multimeter to the AC ("waveform" symbol) 200V measurement range and measure between the phases. There should be three measurements, and they should all be the same. The value depends on the idling speed, typically ranging between 15-25V. The key is that they should all be consistent!

In some motorcycles, magnets may be glued to the alternator/generator. In this case, check to see if they have slipped. The gap between the magnets should be of equal width.


2.4. After this, check the battery as well:

Charge the battery fully with an automatic charger. Then, wait for 10-15 minutes, and measure its charging voltage: If the voltage is around 12.5-12.6V, then the battery is fine. If the result is lower (below 12V), there might be a cell blockage, and replacing the battery may be necessary.


If the above measurements have been conducted and the fault remains unidentified, then it's highly likely that the voltage regulator is causing the low charging.