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Thread: How do you test a regulator/rectifier?

  1. #1
    Baby Twin
    Join Date
    Jun 2013

    How do you test a regulator/rectifier?

    Hello everyone - I'm new to this particular forum. I hope someone out there can help

    I have a problem with the battery on my RSVR not charging

    I have checked the output from the generator and I don't think that is at fault (20V dc at 3-4000rpm on each of the 3 wires)

    It seems to me that the next thing I should check is the regulator/rectifier

    Does anyone know what voltage I should expect on the output side of the regulator/rectifier? Or are there any other tests I can do to work out what the problem is?


  2. #2
    Superbike Twin Dr_D's Avatar
    Join Date
    May 2013
    East Yorkshire
    This is nicked from UKMOC but Ducati electrics are similar to Aprilia. Good guide anyway.

    First a basic troubleshooting process to determine whether you have a charging system failure.

    A good Multi-meter is a pre-requisite.

    Record your battery voltage under the follow conditions
    1) Ignition off, unloaded battery.
    2) Ignition on, headlights on, not running
    3) Bike started, running at idle

    Condition 1, should be at least in the high 12.x range if fully charged.

    Condition 2, your voltage should not drop much below 12.0 at worst. (It may continue to drop – hopefully slowly! – As your lights will be discharging it. However this should be a slow decline)

    If it does drop immediately into the 11’s, your battery is insufficiently charged – if it was just charged from a battery charger however, then it indicates your battery no longer has sufficient capacity to retain charge/supply current to load and should be replaced.

    Condition 3 is what we are most interested in with respect to charging capability.
    Voltage should be at least in the 13’s at all engine rpm. You may detect it will fall off slightly as you raise engine rpm. This is not atypical performance. A simple mod that can enhance your charging voltage to the battery can be achieved by this modification outlined in this thread. That should give you performance in the 14V+ range.

    What if you have less than 13V?
    First thing to check is the fuse in the charging circuit.

    Next, examine the wires and connectors between the R/R output and the R/R input – are these charred/melted due to excessive heating? This is fairly common result of poor connection between the terminals.

    A ‘cold’ resistance check for shorted diode/SCR:
    Unplug both input & output plugs from R/R;
    With your meter set to read resistance (use a diode test if the your multi-meter has one), test from each pin of the three pin plug, to both the red & green wired pins NONE of these should read short circuit (zero resistance); depending which way you bias the test leads, you may get some reading (from the forward bias) but it must absolutely not be a short. If you see a short on any of these readings the R/R is defective.

    Next, do a resistance check on the stator (check at the cable connector going back towards the stator itself).
    Measure between the three respective combinations of the three pins:
    This time each of these should measure almost short circuit (very low resistance in order or about 1 ohm)

    This next check is probably the simplest/quickest way of determining a stator problem - in majority of cases a bad stator will be indicated by failing following test:
    Check resistance from any one pin to the engine earth – this should not read any indication – maximum resistance or open-circuit.
    If you read ‘short’ in that last test, then your stator is .
    (if open, it is not quite guaranteed your stator is good however - but in majority of cases a failed stator will fail this isolation test)

  3. #3
    Baby Twin
    Join Date
    Jun 2013
    Thanks for the reply Dr

    I followed that series of tests and couldn't find anything wrong. However, the battery is still not charging

    So, I decided to have a further poke around with the voltmeter and got the following results -

    With the engine running the output side of the reg/rect shows 12.3V (ie not high enough to charge the battery)

    With the input side connector block taken apart the supply from the generator shows 10V ac at idle rising to about 20V ac at 4000rpm on each of the 3 wires (healthy generator surely?)

    Now, here's the strange bit (at least to my mind) - with the connector block joined together again, and the meter probe stuffed down the side of the wire to get to the copper terminal, and the engine idling, I get 9V ac on 2 of the terminals BUT only about 1V ac on the other

    Can anyone explain why I'm getting a different reading in the same place depending on whether the connector is joined together or not? Does this imply that the reg/rect is faulty in some way?

    Cheers, Ian

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