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Thread: R1150RT 2nd Load Relay for Twin Spark

  1. #1
    Registered User roger 04 rt's Avatar
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    R1150RT 2nd Load Relay for Twin Spark

    The early twin-spark R1150RTs connect all three ignition coils (2 stick coils for the primary plugs and one conventional coil for both secondary plugs) to the battery, directly through the contacts of the key switch. Later R1150RTs added a "2nd Load Relay", which connects the stick coils directly to the battery through a relay. Why did they do this?

    From reports, the measured resistance of the secondary coil is less than 2 ohms. My measurement of the stick coils shows a primary resistance of less than 1 ohm. That means that the saturation current (maximum current flow) through each stick coil is 12 amps (24 amps total) and for the lower-plug coil is 6 amps--those current levels are only achieved momentarily, for a few thousandths of a second. At saturation current, the total momentary current is 30 amps. The parallel resistance of all three coils is about 0.4 ohms.

    I measured the contact resistance of the key switch on my twin-spark at about 200 milli-ohms, or 0.2 ohms. Do the electrical engineering math on this and knowing that it takes time for an inductive coil to charge and reach saturation current, if the battery voltage was 12V and when all three coils reach saturation, the voltage at the top of the coils will be 8V and it will be 8 volts for anything connected to the key.

    What is connected to the key circuit:

    --two stick coils
    --the lower plug coil
    --Fuse 1
    --Load Relief, Fuel pump, & Motronic Relay control coils
    --Kill Switch
    --Tachometer
    --other relays and indicators

    Looking at the list there isn't anything that is going to be too seriously upset by the voltage spikes. But during the initial moment of cranking, when the coils are momentarily left on for maximum dwell and the starter has dropped the battery voltage to 9-10 volts, the voltage dips, at the key switch could reach 6 volts. Far from ideal.

    When some engineer at BMW realized that adding the stick coils had increased the current 5X through the key switch, and that some starting and running problems could be traced to it, they decided to reengineer the wiring harness and add a "2nd Load Relay" and then route the stick coils through that relay, directly to the battery. I don't know why they didn't also route the lower plug coil at the same time.

    My plan is to build a wiring harness and relay (done), switched by the key, that connects all three ignition coil directly to the battery. The next step is to find connection point X9450 where the 5 green wires for the above list of connects come together.

    If anyone knows where all the green wires come together it would be a big help.
    Last edited by roger 04 rt; 06-17-2015 at 03:49 PM.

  2. #2
    Registered User roger 04 rt's Avatar
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    The key to this project was finding the place where the green wire from the Key (which is switched +12V) connects to the three ignition coils and the other 8 wires that are powered when the key is switched on. Thanks to MFOL the photo below which helped me find the "connector point" and Dirtrider for several workmanship tips.

    Looking at the photo below there are two groups of connection points. One group is exposed in the photo and you can see the bundle of green wires. The other is in a black tape stub in the photo, circled in red.

    The project to add the 2nd Load relay has a few parts, none complicate, total cost for the relay and wire about $15:

    --find the bundle of green wires, remove the three wires for the ignition coils (find them by using an ohmmeter after the green wire connection is opened). And group those three wires into a new bundle. Then connect the control coil from a new relay (from euromotoelectric $6) to the original bundle of now 9 green wires. The original bundle is switched +12V.

    --ground the other side of the relay control coil to battery negative

    --connect one relay switch contact to the battery +12V

    --connect the other switch contact to the new group of three green wires going to the ignition coils.

    --take all the new wires, bundle them up and zip tie them along the left side of the frame, adjacent to the main wiring harness.

    --the new relay was located on top of the airbox next to the battery.

    One of the hard parts of the job after you've found the green wire connection point is removing the copper barrel that is compressed around them to create the new connections. It's tough and hard to remove. I ended up filing one side off.

    Status
    The relay and new wire harness has been built and laid in place, waiting for me to connect it to the two groups of green wires. Then I'll tape everything over and tie wrap the new harness to the old. Should be another hour tomorrow morning

    I'm working patiently because this involves the 12 primary switched power wires for the motorcycle. More tomorrow.

    Last edited by roger 04 rt; 05-13-2017 at 09:28 AM.

  3. #3
    Registered User roger 04 rt's Avatar
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    It wouldn't be like BMW to add a relay part way through a model run, in this case after shipping a bunch of twin-spark R1150s. But they did, so there must have been a problem without it--but that's getting ahead of the story.

    The install of the 2nd Load relay was completed late yesterday and took about 2 hours. To recap I disconnected all 3 ignition coils from the key-switched, green wire where they got their +12V, and connected all of them to a key-switched 40A relay, which in turn is connected directly to the battery. This creates a much lower resistance connection, which allows all three coils to charge more fully.

    Since there were 12 Green wires at the original X9450 connection point, I did a lot of checking to make sure they were all reconnected properly in the new design.

    Then I charged the battery, reset the Motronic and started it up. The first start after a reset can be sluggish but that was not the case. It fired right up and seemed to be idling smoother, which I ignored initially, believing that I had a case of "confirmation bias" (getting the effect I was looking for).

    This morning I buttoned everything up (noticing a crack in the right side plastic that I've got to fix now, darn) and started the bike for the second time. This time for sure I can say it started easier and idled more smoothly, from the moment after it caught.

    Went out for a test ride, and after getting a couple bars on the RID I pulled over and dropped the Fast Idle Lever to the off position. Normally if I do this before 4 bars, the idle is a touch rough and slightly low. Not so today. At two bars on the RID it idled as least as well as fully warmed up before. Once the RID was up to 6 bars the idle speed was 50-100 RPM higher than the last time I rode.

    Over the course of the next hour-plus I rode a wide range of speeds and loads. Wide-throttle high-RPM acceleration is more responsive as is low-RPM torque. Riding in 6th gear at 45 mph and up was good, noticeably better than usual even taking into account the richer mixture on my bike.

    When I pulled into the garage after the hour, the smoothness of idle was, no doubt about it, the best it's ever been. Overall, pulling all three coils off the key and onto their own relay has made a noticeable difference. Tomorrow I plan to log a cold start and ride to see if there is a measurable difference with the GS-911.

    To my initial question, "Why did BMW add this relay?", it seems to me that with three ignition coils on the key switch, the coils were being undercharged before they were fired. And the improvement now is most noticeable at start, idle and high engine load.

  4. #4
    Registered User roger 04 rt's Avatar
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    For anyone interested in trying this modification, below is a rough schematic which may be clearer than the written description. The added wiring and relay are highlighted in yellow.

    All of the original wires going into connection point X9450 are Green.


  5. #5

    2nd Load Relay question

    Hi... thanks for this... great piece of work... question is: Is there an easy way to tell if a bike already has an OEM relay fitted?

  6. #6
    Registered User roger 04 rt's Avatar
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    Quote Originally Posted by ninja View Post
    Hi... thanks for this... great piece of work... question is: Is there an easy way to tell if a bike already has an OEM relay fitted?
    Yes, the relay is mounted in the open space adjacent to and to the left of the Coding Plug socket. I will try to find a photo.

    I've ridden for a week or so now with the change. It makes a very solid improvement.

  7. #7
    Registered User roger 04 rt's Avatar
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    In the photo below, the 2nd Load relay is the yellow relay to the right of the pink coding plug (not the relay with the clip that's being pointed to).


  8. #8

    04 1150RT 2nd Load Relay

    Thanks for the quick response... looks like I'm good to go!... Last night I found the LH throttle stop screw in the bottom fairing so I will have the plastic off this weekend anyway and wanted to catch anything else that needed doing. It still runs surprisingly well with the throttle hanging off the cable, so I guess its not that far off... Thanks again.

  9. #9
    Registered User roger 04 rt's Avatar
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    Here's another report from a rider who made this mod.

    Quote Originally Posted by Boomer343
    Just an update. I finally got the old girl fired up tonight and found that it is a good idea to put a fuse into the fuse holder for the new hot wire to the relay for this circuit to work. That was the one deviation from Roger's diagram that I did. Having seen the aftermath of car stereo systems wired in with no fuses I like to have them in place.

    So .... was it worth the effort..... absolutely. There is no doubt my bike started quicker and went into a smooth idle. I am also using the axfied and have put new coils and spark plugs in previously. No other tune up procedures have been done by me.

    Compared to when I purchased the bike, it had the original coils still working and new standard plugs, the addition of the axfied and now this mod has made a world of difference. The new iridium plugs and new coils made a very small change, nothing like this.



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