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rectifier max output voltage?

Discussion in 'The Garage' started by marp68, Sep 29, 2018.

  1. marp68

    marp68 XS650 Addict


    What is the max output voltage from the rectifier when revving the bike 3000 and above? If I understand it correctly it shouldn't output more than 14.5 V. Or?

    BTW, is the regulator and rectifier the same unit?

    My old battery was unexpectly drained, so I kickstarted the bike and went out for the planned ride. The battery didn't seemed to charge though. So I recharged it during the night. Forgot to use the meter before unmounting it. However, the day efter it showed only12 v and then quickly dropped to below 11 during a few hours, so I guessed the battery was in really bad condition and didn't bother to mount it and see how it behaved when starting and idling.

    I bought a new one, charged it fully up to 13.5 v. During a few days it dropped just slightly down to 12.5. When starting the bike, it dropped to 10.5 and then went up again, so that seemed fine. When idling it read around 13.5. When revving to around 2500 it went up to 14-14.5, so that was also fine.

    But when revving higher up to 4000 it jumped up to between 15 to even 17 v once. Is that really okej? I thought the max output of the rectifier is around 14 V. Otherwise higher voltage will fry the battery. Could that be what happened to my old battery?

    If there is a problem, does it have to do with the regulator/rectifier or could it even have to do with the generator?

    What's the next step would you say?

    Thanks for any feeback
    Last edited: Sep 29, 2018
  2. pamcopete

    pamcopete Ride.Enjoy.Life is Simple

    The regulator senses the Voltage on the brown wire from the ignition switch, not the actual battery Voltage. The difference is the voltage drop across the contacts of the ignition switch and any other connection or fuse from the red wire on the ignition switch to the battery. What this means is that the regulator can "see" 14.5 Volts on the brown wire but if there is, say, a 1 Volt drop from the brown wire to the battery, then the battery Voltage will be 15.5 Volts. This is because the output from the rectifier goes directly to the battery, not to the brown wire from the ignition switch that the regulator is connected to.
  3. 5twins

    5twins XS650 Guru Top Contributor

    No, the regulator and rectifier are not the same thing. The regulator regulates the alternator's output based on what voltage it reads in the system on the brown wire, as Pete said. The rectifier is fed the output from the alternator, which is AC, converts it to DC, and feeds it to the battery.
  4. Ozboy

    Ozboy XS650 Addict

    Did i read somwhere that it might be a good idea to run this brown wire from reg/rec thru a relay to battery? Maybe 5t mentioned it in a post. I am getting 14.5v at battery but this sounds like a good mod to do. Is it recommend?
  5. mrtwowheel

    mrtwowheel Honda Etched On Brain Top Contributor

    I run voltmeters to battery, using a relay, switched by ignition. I've done this with coils too.

    Yeah, why not. Even clean switches and connections loose some juice on the way back to the battery.

    Ozboy likes this.
  6. 5twins

    5twins XS650 Guru Top Contributor

    That was Pamcopete's idea and mod. Instead of having the regulator sense the system voltage through the brown wire, have it do so at or very close to the battery, like at the starter relay. You will get a better reading of what the battery voltage actually is. Often the voltage on the brown wire is less than the actual battery voltage because of all the connections and switches it's passed through to get there. This makes the regulator think the battery needs more charging than it actually may need. So, run the brown wire from the regulator through a relay to the battery (or close to it). Use the brown wire in the harness that was going to the regulator to trip the relay.
    Ozboy likes this.
  7. Ozboy

    Ozboy XS650 Addict

    Cool. I have my coil running thru a SPDT relay so i have a spare pole i can use for this. I have been chasing a volt drop for ages now and got it to .3v now with out replacing the wiring harnes. Taking the coil off the ignition wire thru the relay got me from .6v to .3v.
    Good riding weather coming up so will sort the harness out later.
  8. pamcopete

    pamcopete Ride.Enjoy.Life is Simple

    Running the coil power through a set of relay contacts sounds like a good idea, and I used to do that myself, but the problem is when the battery Voltage is low when starting, the relay may drop out thus cutting the power to the coil. Running the regulator brown wire through a set of relay contacts directly to the battery is a good idea, however, and I do that on all of my bikes.
  9. Ozboy

    Ozboy XS650 Addict

    Yeah It was a problem that I took into account. I tested the relay and it closes at 9v but I can access this relay easily so I keep a small jumper wire if I need to do so.
  10. marp68

    marp68 XS650 Addict

    Thanks for feedback. Haven't been able to reply earlier. Problem solved I think. Now it doesn't go higher than 14.5 at around 3000 rpm.

    Is it possible that the regulator sometimes for one second leaves higher V when revving up very quickly, but then quickly adjust the V down to 14.5 again?

  11. Was reading through this post. I have a .4 voltage drop at my brown wire off the reg/rec. How exactly would I do the relay mod? What relay would I need and how would I wire it? Any insight helps! Thanks
  12. Ozboy

    Ozboy XS650 Addict

    Hey Rob
    I was chasing a volt drop for a few months. Cleaning all your connections really well plus some silicone grease after. You must clean your ignition swtich contacts as well. Red wire into switch is battery then it come out on the brown to supply the fuse box to power all of the bike with key on.
    Get a cheap volt meter meter set up for testing with clips on the battery reading batt volts start going thru all connections to find out where the drop maybe with a DMM or automotive tester
    I was having .6v drop and now down to .2v drop.
    Getting a cheap jump starter battery pack helps or hook a larger car battery as it cam take some time to work thru it all.
    Link to the tester i have used for many years. This is Aussie website tho
  13. Hey thanks for the info. I desperately need a re-wire. Im getting a .6 V drop at yhe ignition switch. Tried cleaning the contacts and put some dieelectric grease on and still the same readings. I want to wire my bike up properly. Do you knoe where I could get my hands on those white wire block connectors? I cant seem to find them in any store.
  14. Ozboy

    Ozboy XS650 Addict

    Yeah that brown wire does do alot all over the bike but has to be somewhere.
    Doesnt Mikes XS have them? They are 6.8mm locking tab terminals.
    Or try here they have some great gear
  15. Im trying to figure out how I can get my brown wire to feed power to the other wires. My bike currently has the brown wire and the other electronic wires connected using those twist connectors with the wires shoved into it. How is your brown wire feeding to the other wires? I want to make good solid connections.
  16. Ozboy

    Ozboy XS650 Addict

    Check out Wire Splicing on Youtube. Best method is to use thin copper wire wrapped around your two splices to hold it all together when soldering. I got mine from an old battery cable i took the insides out and wrap with that. Make sure you get the correct lay of the wire you dont want to bend it back on it self if you get the lay wrong. Heat shrink needs good prior planning but failing that the cloth type Tesa electrical tape and heat shrink on the very end wraps. It is alot better than PVC rubbish.
  17. Ozboy

    Ozboy XS650 Addict

    Also check out short video from Revival Cycles on bike looms. The split wire loom stuff is awesome and so easy to use.Check out the shop too as they only sell qualiity they use and recommend
  18. Thanks man. Appreciate the insight. I'll try and tackle this later today and through the weekend.
  19. 5twins

    5twins XS650 Guru Top Contributor

    Yes, pretty much every one of these bikes needs their wiring gone through and cleaned up. That includes wiring AND all the connections. If doing all that doesn't solve your voltage drop issue and you still want to do the regulator relay mod, here's how to wire it up .....


    Pulling the power from as close to the battery as possible is best so that you avoid as many connections (and possible voltage drops) as you can. Do take a voltage reading at the positive battery terminal and then again at the solenoid connection. You only have a short (maybe 6") battery cable there but it could be bad, or maybe it's connection points are.

    As far as relays go, there are several types. Here's a link that will educate you about them .....


    Any of the common types you'll need are readily available at most auto parts stores for a couple bucks.

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