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'79 special voltage regulator swap basic questions

Discussion in 'The Garage' started by pkovo, Apr 12, 2015.

  1. pkovo

    pkovo XS650 Enthusiast

    First off, HELLO. I've been on the forum in the past for help, but it's been years. Sadly XS650 has been neglected in a garage cocoon for the past several years, but I'm looking to get it back into shape. This is probably the first of many basic questions I'll have, and I tend to be long winded, so apologies in advance.

    For the impatient: On my '79 with points, If I do the VR115 regulator swap, and retain the stock alternator, do I need to add nylon screws to one of my brushes?

    Details for the patient readers: Bike is a '79 650 special. Mostly stock, other than items I've been forced to replace. Charging system has always been the part of the bike that gave me the most headaches...seems common. I probably should just pony up for a PMA kit, but not quite ready to, so here's where I'm at.

    Just put in new battery. Checked wiring and ended up replacing both battery cables, as they were corroded, and I rewired my fuses (in line auto fuses added yrs ago) because the connections were suspect. Getting good pull out of rotor with the slap test, not surprising as my rotor is a rewind I picked up sometime in the past decade and has little use. Rotor, points, brushes, plug wires, plug caps have all Ben replaced in the past decade and have little use.

    I fired her up yesterday. Sprang to life on second kick and it's been at least a year since the last time I started it (thank you stabil). Once warm, I checked voltage, and it's high when the revs are up, peaks at about 15.6 volts. I know this voltage regulator is adjustable, but I have very little faith in it. I've adjusted it in the past, which could account for it being high, and I remember it being a hassle and seeming like a part that could easily fail. Looking for an easy "plug and play" replacement and found the thread on the VR115 replacement. However I found some of the info confusing with regards to the when the nylon screws are needed. So...

    1. Do I need the nylon screws for one of my brushes if I run the stock rectifier and the VR115 regulator?

    2. If at some point later on I replace the rectifier with the DIY radio shack deal, does that change whether I need the nylon screws?
  2. 5twins

    5twins XS650 Guru

  3. pkovo

    pkovo XS650 Enthusiast

    Nice, thank you both!
  4. pkovo

    pkovo XS650 Enthusiast

    OK I swapped the regulator and tested it. Seems to have dropped the voltage by one volt. Wondering if it's still too high.

    Testing with two different multimeters, here's what I'm averaging with the revs up to about 2-3k

    Meter one: approx steady 14.6 v highest reading at 14.63
    Meter two: approx steady 14.7 v highest reading at 14.74
    Idle around 12.4v

    Tests done with a fully charged new AGM battery

    My old Yamaha manual shows that it should test 14.5v + or - .5v so it seems good to me. However I've seen some posts where people indicate anything beyond 14.5 is too high and could damage the battery. So, to you 650 Gurus, am I good with these readings?

    I thought I read something to the effect that the regulator is on the load side, whereas the alternator is not. So if I understand that correctly (I may not) then it seems a drop in voltage at either of my switches might create a higher voltage at the battery since the regulator would be trying to make up for it but the alternator would add it as extra voltage

    Does that make sense or am I way off? I've cleaned, checked, and repaired a lot of the wiring, but I didn't test the switches.
  5. TwoManyXS1Bs

    TwoManyXS1Bs Kablatta, kablatta...

    The mechanical regulator test for 14.5v (by the book) is done with the battery disconnected, while at 3000 rpm. Back then, batteries were the solid-plate wet-cell deep-cycle design. I prefer to set it with the battery connected, and measuring at the battery. I like 13.8-14.2v for those older battery types to avoid overcharge boiling. AGM is different, never worked with those. Probably need to research the battery manufacturer specs.

    Yes, good thinking. Power goes all the way forward to the switch, then back to the coils, continuing on to the regulator, and thru it to power the rotor. Poor connections along that path can create unwanted voltage drops, and influence the regulator...
  6. pkovo

    pkovo XS650 Enthusiast

    Thank you. Glad that it seems like I am finally starting to understand this thing.

    I just checked, and I seem to have approximately .5v drop on that brown wire at the regulator plug. I read that anything more than .3v should be considered unacceptable (from Curley's guide I think) so it looks like I'll be checking all the connections on that brown wire path. I guess that means the red from the battery up front too.

    If I'm understanding all this correctly, the extra .2 voltage drop I'm seeing, is in essence the extra charging output I'm getting.

    Curley's guide clearly says...."dirty connections and worn brushes account for most of the charging system problems"...and it's looking to be the case for me.
  7. TwoManyXS1Bs

    TwoManyXS1Bs Kablatta, kablatta...

    Yes, you now have a good grasp of the system.
    Might as well see if that voltage drop changes while exercising various accessories, lighting, horn, ...etc.
  8. XSLeo

    XSLeo XS650 Guru

    Often the voltage drops are in the main switch and fuses.
    If you have the stock 4 fuse block the clips are weak. They can't hold the fuses as well as when new.
    Swapping the stock box for the more modern blade fuses. In line or a block.
    The switch can be taken apart and the contacts cleaned.
    Another switch that causes trouble, not in charging but in ignition. The Engine stop switch. It gets dirty too. This voltage drop effects the coils. Low volts=low output=weak spark.
  9. pkovo

    pkovo XS650 Enthusiast

    Thanks guys. Unfortunately I can't carve out much time to work on it as a stomach bug is picking off my kids one by one this weekend.

    I did check a few things. No voltage drop at the main fuse. Not a surprise though as I rewired this a few weeks ago with inline auto fuses. I had done that long ago, but redid the connections recently because I was sloppy the first time around.

    I have full battery voltage on the red wire up to the plug at the key switch. Testing the drop between red and brown at that plug shows a drop of only .1 at the key switch. I thought it would be worse. The drop at the reg is coming up .54.

    Unfortunately I didn't have time to check or do much else.
  10. TwoManyXS1Bs

    TwoManyXS1Bs Kablatta, kablatta...

    I know how the brown feeds from the ignition switch to the regulator on the simpler '70-'71s.
    Yours being a '79 is much more complicated. Need the schematic for that...
  11. XSLeo

    XSLeo XS650 Guru

    The brown wire off the switch feeds the reg before it goes elsewhere. Your extra drop may be in the wiring connections. A bit of corrosion on the male and female parts in a plug will cause extra resistance, this causes the drop.
    You need to check everything.
  12. pkovo

    pkovo XS650 Enthusiast

    Thanks guys.

    XSLEO, You may have just answered my question before I had a chance to ask. I'm sitting here with a sick kid, looking at the wiring diagram in my manual. I see brown running from the switch, back to a fuse, then on to the regulator. I also show it going on to a host of other things after the fuse. So my question was going to be, do I have to hunt for a drop in the host of other things it runs to after the fuse, or am I just concerned with the path to the reg, since it appears that is "first in line" after the fuse on the diagram?

    Other things I see down stream of the fuse on the brown wire are:

    Neutral light
    Tail/brake failure
    Front stop switch
    Rear stop switch
    Flasher cancel unit

    What about the kill switch? I'm having trouble figuring out if that is in the path I need to check from this diagram.

    Also, did all of the xs650 models have an on off switch for the lights in the kill switch housing? My wiring diagram shows one, but my switch doesn't have one. I thought my unit was stock, but perhaps it was replaced at some point before I inherited the bike.

    Thanks again guys. I'm about on par with a sharp 12 yr old when it comes to wiring, so I appreciate the help.
  13. The Kill switch is not in the path to the regulator.

    !978 Special still had the "Lights" switch, but the switch was deleted in the 1979 Special. The 1979 headlight is turned on by the Safety Relay.
  14. pkovo

    pkovo XS650 Enthusiast

    Excellent, thanks!
  15. pkovo

    pkovo XS650 Enthusiast

    OK, not surprisingly, I'm confused. I dismantled and cleaned my ignition switch. Cleaned up some other connections. etc. Was still seeing a .5 volt + drop at the Brn wire at the regulator when I turned the key on.

    I decided to check my rotor and brushes....just because. By chance I took the reading at the brown wire to the regulator with the positive brush removed. When I did that I only saw a .2v drop.

    Now, what does this mean exactly? Seems liek I'm losing an extra .3v + drop due to the wire leading to the positive brush. Or, am I an idiot, and just testing this stuff wrong, or missing something obvious?

    Here are the readings I have now:

    **Battery voltage 12.7
    1) approx 12.5v at brown wire to reg with positive brush removed
    2) approx 12.2v at brown wire to reg with positive brush connected (why the .3drop?)
    3) approx 10.6v at positive brush if wire connected (too low??)
    4) approx 11.96v at wire to positive brush if disconnected

    While I was in there, I tested the rotor. Slip ring to slip ring, approx 5.10 Ohms, and either one to ground is infinity. So rotor seems fine. Brush length OK, but the positive brush will need rplacing soon, it's only about 3/8"

    Fired it up and ran some tests:

    -engine 2-3k at battery: settled in around 14.6-14.65V
    -idle, down about 12.5V
    -engine 2-3k at brn wire to reg: around 14.3-14.35V

    This was the first time I took that last measurement. This is what I would like at the battery, and it's down by .3v, which is the extra drop I'm seeing when I test the brown wire not running with key on

    I'm not sure what to check next. Is this poiting to something obvious? I feel like I have alot of pieces of a puzzle, but can't figure out what the picture is.

    I still have the original rectifier in there. I bought a new one, but it hasn't come in yet. I'll be replacing the old one as soon as I get the new one and time permits.
  16. pamcopete

    pamcopete Ride.Enjoy.Life is Simple

    The only way to eliminate the .5 Volts drop to the regulator, which results in a .5 Volt rise in battery voltage is to use a relay to connect the regulator directly to the battery so that the regulator will regulate the battery voltage instead of the load voltage.

    This is especially important for AGM or other exotic batteries because their tolerance to high voltage is not very good.

    I did this to all of my bikes, and all of them have an AGM battery. I also replaced all of the mechanical (relay) type regulators so now all of my batteries read 14.5 Volts at 2,500 + RPM. If the drop across the ignition switch or fuse or whatever increases, I can either fix it right now or just let it go because it doesn't affect the life of those expensive batteries.
  17. XSLeo

    XSLeo XS650 Guru

    The only volts you need to worry too much about is the one at the reg. The other things do draw on the voltage but won't have that strong an effect at the reg.
    Not all diagrams show the connectors. Looking in the Clymer book at the late 78 79 diagram If you trace the power path from the battery to the reg. It comes off the battery on a red wire to the main 20 amp fuse. Fuse up to the key switch. Along this red wire is a junction with the red wire from the rectifier. From there it comes up to a black rectangle with three wires in and three out. this is the connector in the headlight bucket. This could be a bit corroded.
    Any way power travels through a connection on the red wire, to the key switch. Through the contacts in the switch, out the brown wire back through connections in the plug. Again could be dirty.
    From this plug the brown wire goes back to the fuse box and links to all three 10 amp fuses. One fuse comes out a brown wire. From there it comes to a junction with the Light checker, the rear brake switch, horn, flasher canceler. Now the reg.
    I have had a couple wiring harness' apart. A lot of these junctions Are where they stripped the insulation off the main brown wire and crimped a brown wire to it. These added wires run to each item After the reg connection it goes on to power the front brake and some of the indicator lights.
    I don't recall for sure on the reg, if it is powered by the main wire or one of the add on brown wires.
    At this point the power flows to the reg through another plug. Again possible dirty.
    One thing you can check is the ohms along this brown wire. With one meter lead hooked at the brown wire at the red Check for continuity at each of the items along this path. Like the brown wire at the horn, brake light switches, Flasher cancelor, Light checker . If you get a consistent ohm reading at all these points then your brown wire
    should be ok. Might even want to check voltages as well.
    Sometimes even with everything right you just might not get things as good as you like.
    Yes, the charging voltage is a bit high. You may just have to live with it. If you are using a regular wet cell battery, keep a close eye on the water lever. Most loose some water, maybe once a month you might have to add a few cc's to each cell. But if it's much more than that I might worry.
    I might suggest adding a voltmeter to the bike so you can easily keep tabs on the system.
  18. TwoManyXS1Bs

    TwoManyXS1Bs Kablatta, kablatta...

    Just some rough numbers here.
    12.2 volts going thru a 5.1 ohm rotor is about 2.4 amps.
    That additional 2.4 amps produces an additional.0.3 volt drop.
    Which works out to a feedline resistance of 0.125 ohms.
    And an additional power loss of about 0.72 watts.

    At 4.016 ohms per 1000 feet,
    It would take 31 feet of 16 gauge copper wire to equal that drop.

    If the feedline were to act like 6 feet of 16 gauge wire (battery to switch and back to regulator),
    the resistance would be about 0.024 ohms,
    and produce a voltage drop of only about 0.06 volts...
  19. Yes, good idea to replace the original rectifier. Also replace the brushes if one is down to 3/8".

    If you're seeing 14.6 volts at the battery, with rpm at 3000, its a little on the high side, but is still acceptable. As mentioned the battery may require water addition occasionally, due to the higher voltage.

    Was the headlight and tailight both on when you measured 14.6 volts?

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