One of the members on the private SR FB group let me know that some of the newer members whose bikes are the more recent models may be having their bikes exhibiting the following symptoms (the procedure below is written by Seb of Luna Cycle):

  • Dashboard, head lights, tail lights, USB port flashing ON & OFF five times after switching the
    ignition to ON and dies completely, then 30 second pause and it flashes again and again in a
    endless loop. The flashes are quick in a constant pulse, about 1 sec per ON/OFF cycle.
  • It’s also possible that the Dashboard, head lights, tail lights, USB port will only flash once and
    shuts off completely. That symptom can be also a bad BMS but best is to try that procedure to
    see if the issue can be resolved with it.
  • If you measure the voltage from the charge port and unplug the battery once the BMS is
    tripped you will monitor the voltage go down (can be 0V up to 40V) for about 30 secs and then
    it should go back to were it was depending on your state of charge.

The procedure is simple and can be done with basic tools and electric knowledge. Here is Seb’s procedure to fix it (thank you Seb!):

Tools needed:

  1. 2.5mm hex key
  2. Philips head screwdriver
  3. Wire cutter and stripper (capable of stripping 22 & 26 awg wires)
  4. Plier, Vise grip, long nose, any plier will do.
  5. Adhesive (can be RTV, Silicone, hot glue) to replace the adhesive on the battery post.

Parts needed:

• The Luna Sur-Ron battery hack kit (just ask for one)
• Or just a piece of wire, a fork or ring terminal, butt crimp and piece of heat shrink.

Procedure:

Note: The battery can be at any state of charge for this procedure, while the wire is “live” you cannot
get shocked by it. But if by mistake you short-out the positive and negative terminals of the battery (the
2 buss bars where the 3 red and 3 black wire are secured to) then you will get a good spark, so pay
attention to not put any metallic tools inside the battery!

Steps:

Remove the 10 hex screws around the top of the battery

Gently pull the top off and make sure that the gasket does not get ripped or damaged

Put the gasket back into the BMS top cover groove

Locate the 7 wire ribbon cable and separate using a utility knife/blade the last 2 wires on the
left from the rest. Pay attention not to cut the insulation off the wires. If it happens use some
electrical tape to re-insulate the wire. Do not pull the wires from the connectors.

Locate and cut the second to last wire off the ribbon cable. This wire from now on will be
called the B16 wire. Make sure to leave an inch from the connector as it be easier to insulate
this wire later.

Remove the adhesive from the first positive battery post (red wire, left side on the previous
photo)

Loosen the Philips head screw enough so the fork terminal will fit in between the battery
main positive wire and the washer. Tighten the screw back.

Strip 1cm (3/8”) of the end of the gray ribbon B16 wire, be gentle it’s easy to cut the copper
strands and end up with not enough strands to make a good connection.

Strip 1cm (3/8”) of the end of the 20awg wire you received

Twist both ends (gray B16 and loose wire) together and put the crimp over it. Make sure no
copper stands are exposed. Use a plier to compress the crimp make sure you don’t break the
insulation.

Take the heat shrink and put it over the B16 wire, leave a few millimetres off and use heat
to shrink it down, after a few seconds press on the heat shrink tip with your fingers. Now this
wire is isolated and can’t short out on anything.

Put adhesive on the battery screw like it was before. The goal is to lock it in place but also to
prevent the screw from falling into the battery and shorting cells.

Make sure the gasket is still in the track and you can put the top back on. Don’t over tighten
the top screws.

You’re done!

Thanks again to Lee and Seb. If you’ve had this issue and this little hack has worked for you, please do other owners the favor of leaving a comment below about your experience with this procedure. Thank you.

A visitor asked what this ‘hack does’ so I asked Seb from Luna. Here’s his explanation: “The hack is a bypass… it bypasses the B16 wire from the cell to the BMS.. you keep the same protection as before.. just get rid of the issue.”

17 Comments

  1. Thank you so much. This fixed my flashing dash/no run condition. I preformed this fix at the race track and it was a life saver. Great tutorial.

    • Glad it helped you. This process was authored by Seb of Luna Cycle and I was allowed to post it here.

  2. Just curios, what did this fix do? Does it bypass something? Thx

    • Ralph I’m not sure so I’ve asked Seb from Luna for an answer and will post it here once I find out.

    • Hi Ralph I followed up with Seb and added this to the post. Here is his explanation: The hack is a bypass… it bypasses the B16 wire from the cell to the BMS.. you keep the same protection as before.. just get rid of the issue.

  3. hi mark, i just did this but now my battery indicator stays on 99% , check the voltage its 66v its more like 95%..

    • Sorry barney can’t help you with that. Best to contact Luna help desk to get your answer.

  4. Thanks u so much guys!!! I’m from Russia, same problem!! 5 minutes.. SOLVED!!)))

    • Nike, so glad it helped and for letting me know. Take care.

  5. Mark, is this the only solution for this fault? Would a dealer just replace the battery pack or would they replace the faulty BMS?
    Are there any negatives to this MOD? I have read that disabling the BMS on the discharge side, can lead to the battery being damaged.

    • Bryn I’m not certain whether or not this is the only solution for that issue. To find out if the dealer who you bought your bike from would replace the pack or just the BMS you’d need to contact them. As far as any negatives to the mod I cannot speak first hand as I have never had to perform the modification. I got the procedure directly from Seb who works for Luna’s customer service. I trust Seb and he knows his stuff on many of the electrical components of the SR. I make it my own policy on this site to not post things for which I’ve had no direct experience, EXCEPT from people like Seb.

  6. Is that the bms discharge bypass? Cause i have a new controller bac4000 and im looking how do the discharge bypass plz someone tell me thx

    • Kev I cannot tell you. I do not have, or do I know anything about the BAC4000.

    • Kev, this is not a BMS bypass. It just bypasses a soldered joint that sometimes fails.
      I had this confirmed by Seb at Luna Cycles, He said:

      “the BMS wire hack is not a bypass by any means. it’s just a way to fix a solder connection that can go bad. you do not loose any protection against any possible problem by doing this, the BMS wont loose any protections!”

      • So for bms bypass i need do this?? B

        basically you unscrew the top lid and cut the thick black wire that goes form the main connector into the BMS and make an extension connecting that connector black wire directly to the pack (cells) negative.

  7. I have a 2019 Sur-Ron and just wanted to say thank you. Was pretty frustrated when the bike started cutting out this past weekend. I am in Vancouver Canada and there are not a lot of these bikes around so I was on my own to fix it.
    Performed this “hack” last night, problem is gone. THANK YOU!

    The exact symptoms were as follows in case anyone wants to know.
    -This past weekend it just started cutting out all together after anywhere from 5 minutes of riding to 20 minutes. All lights and displays worked fine, just no throttle response. Cycle the key on and off and when you hit the throttle it would cut out again as soon as it tried to move the bike. Using the LED jumper it would flash 24 times. If you waited (anywhere from 5 minutes to 30 minutes) eventually it would start to work again.
    The hack fixed the issue.

    • Hi Mike you are more than welcome. Seb from Luna Cycle gave me permission to post the hack here on my site so I’m happy it helped. Even more that YOU listed the symptoms you ran into in order to help other owners, thank you for that effort. Nothing is worse then to be out enjoying your ride to have a malfunction occur. BTW Vancouver is a gorgeous town, I’ve visited my friends many times who live in Richmond, BC. Gyoza King is one of my fav hole in the wall places to eat in your town. But due to COVID19 they have permanently closed their doors. FUCK!

      I am right there with you on being the “Lone Ranger” as two years ago the SR community was tiny to say the least. I’m running into that right now with the Cake community which is EVEN SMALLER than the SR community was two years ago.

      My Cake site is just about done, but much more content to add. Hearing back from members like you motivates me to do the work to support other owners so thanks again Mike, much appreciated.


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