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Battery Sparking and Blown Fuses

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    Battery Sparking and Blown Fuses

    Hello All!!!

    I recently built an electric bike (or at least in the process of) and I am having some trouble when completing the circuit.
    I purchased a hub motor from amazon rated for 1000w and it needs 48V to run. I have four 12v SLA batteries (in retrospect, not the brightest due to weight but was on a budget when I was buying parts).
    The hub motor comes with a motor controller and a fuse on the connecting line (I will have to find what fuse size later on today and will update) which is set up with your standard 3-prong plug like you would find in most electronics as well as an on/off switch on the throttle.

    What I was doing before was connecting all four of my batteries in series and then plugging in the 3-prong connector. I would notice I would hear a small spark, but so long as I made the connection quick and smooth, everything would work out just fine. I once attempted to plug in the 3-prong connector and didn't manage to seat the plugs right away and heard a more considerable spark than previously and I blew my fuse out and also corroded my connection beyond repair.

    I clipped the connectors and simply spliced the wires together, but now every time I go to complete the connection on my batteries I see a large spark and my fuse blows every time.

    Does anyone know how I can prevent this arcing when I complete my connection? I am pretty desperate to get this thing running since I have been working on it for quite a while and haven't gotten it to the point where I consider it a 'working e bike'. I've read a few posts regarding adding a resistor and some others showing people have used an on/off switch as their solution (but my controller already has a push-button on/off).


    EDIT: Corrected from XT60 to XT90

    There is a 2 pin connector called XT-90AS, anti-spark. Luna had them last time I needed some.....still do, I bet.

    It has a pre-charge resistor in it, so if you plug in slowly, that resistor completes the circuit first, limiting inrush current. But, that can't carry enough current for riding, so there is a 2nd stage, without the resistor. All built into the pins design of the connector. Try one of those on your battery connection.

    If your motor/controller kit is damaged/shorted, it won't help, but if it is functional and this is just inrush current, it will help. Again, it connects in 2 stages, go slowly when inserting the connector, to give it time to pre-charge.

    Good luck!
    Last edited by JPLabs; 09-29-2018, 11:14 AM.
    Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.


      Thank you so much for your help! So I went looking around on Lunacycle for an XT-60AS but I was only able to find an XT-90 Anti Spark plug kit. From what I can tell, the only difference is the rating of the plug that is being used, so paying a little bit extra for the 90 doesn't bother me at all. It also looks like this part incorporates the pre-charging circuit that I have been seeing so much about, so this looks very promising!

      So from what it looks like I should be able to simply splice/solder this connector into my pos/neg lines between the battery and the motor controller and I'm good to go, right?

      I am going to order some of these and install and I'll post again with updates!

      Again, thank you so much for your insight, this is a huge help! I know my bike can use a few improvements in some other areas, so when I get everything up and running hopefully I can post with a few pictures and details and see what the community thinks!


      • JPLabs
        JPLabs commented
        Editing a comment
        Good! I meant XT90, actually, you got the right ones. Post above has been corrected, thanks for pointing that out.


      XT90 plugs arrived about a week or so ago and I have installed them and have since ridden my bike without problems. THANK YOU SO SO MUCH!!! I cannot tell you how relieved I am to know that this was such a simple fix and that my bike is up and running. Rode to work and back the other day and it seemed like I was able to hit a decent speed (a bike app clocked around 27mph and didn't manage to hit full speed, but I take that with a grain of salt). The bike works great!!!

      Now I can focus on making the design more robust, next step is to figure out a more sturdy mount for my 4 12v 22ah (each) SLA batteries.... (man I wish I had waited and bought LiPo....)
      I still might get a Lithium battery in the near future, but they all seem quite expensive and I am worried that 12 or so amp hours won't be very much (even though that is what I am seeing on most e-bikes).

      Thank you again!!!


        Great! This example shows that, even if the answer is not crystal clear, trying the "best guess" is worth a try.

        Thanks for reporting back with your success in fixing your bike. Feels great, eh?
        Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.