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Battery to powerful for controller???

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    Battery to powerful for controller???

    Hello everyone,

    I am new to ebikes and I'm currently attempting to build my first one. I went the cheap route and bought all my parts off Aliexpress. My parts are listed below....



    Front Hub Motor (29er 750w)---

    The first mistake I made was buying each part from 3 different companies... and I realize that now. The battery and the controller have different connectors (xt60 for the controller) and (some triprong for the battery but only two wires). I figured I can just splice any kind of matching connectors on them and things should work. So I did as you can see in PHOTO #1 below. You can probably notice it didn't go well since the male prong on the controller connector is burnt down. When I plugged in the battery to the controller sparks started flying and I quickly unplugged.

    ********My problem is that I'm not sure why this happened. I did notice that the wire gauge sizes are different from the battery and controller. The battery wire gauge reads 12 awg while the controller wires connecting to the battery are about 18 awg. Could this be the problem? Is the amps from the battery to much for the controller? I read the controller and it reads a max amp limit of 25 +/- 1. Since the battery is 36v and 1000w I'm assuming the amps are at 27.7 (1000w% 36v = 27.7a). Do I need to upgrade to a controller that can handle a higher amp load like this?>>>

    I appreciate any help and advice. Hopefully I was clear enough with my question. Thank you!

    Higher amps don't occur until you'er out riding. There is a short or possibly a accidental mis-wire. Looks like you suffered a catastrophic failure and will need to be carefully looked over.


      Are you sure you had the polarities right?


        Are all 36v?


          Were the red to red and black to black?


            The polarities are correct, color matching and same symbol. I should also note that I do know everything works because before I spliced the new connectors I used somewhat thin copper wire to test the controller and battery connection. There was an initial spark but nothing crazy and I was able to operate the LCD screen and throttle and made the wheel spin at 53.2 km an hour. with the bike upside down. I didn't feel any extra heat when I touched the controller or battery during this motor test.

            Perhaps the inside of one of these new connectors has the positive and negative wires slightly touching?


            • Mstroup
              Mstroup commented
              Editing a comment
              The battery is rated at 38v with my multimeter. Didn't know if that was worth mentioning.

            Have you used a DVM to check for a short between the controller wires, now, despite the fact that you think it's fine since it spun before? That's absolutely necessary, now. Should be a check before ever connecting a new system.

            You had a short, and arcing. We just don't know what kind of short. It's possible to create a short WITH an arc, in a circuit with no 'hard' short you can detect with a DVM. Circuits test good, but the voltage spike when connecting can create a plasma path between closely spaced conductors which carries high current and self-sustains until something stops it. Wires very close but not touching, on the controller side, for example, might do this. (I'm not totally confident on this, in this case, to be honest, I'm extrapolating from other training at higher voltages which I didn't totally understand, inductive kick and other EE voodo, so I'd welcome input if anybody knows better or can contribute).

            We don't know if you checked it...If you measured and did not detect a short across the red and black on the controller, before connecting it, maybe this secondary arc is why it happened? If you measure now and don't detect a short, though, it's perhaps just because whatever caused it isn't touching anymore. Moved, burned away, whatever. I'm not saying that's what happened here, but consider it as you try to diagnose further.

            To me, that connector looks like it simply kept arcing as you unplugged it, until the arc length was long enough to extinguish the 'flame'. Current flowing through the plasma, between connectors of the same polarity, as opposed to a short ACROSS the plug from + to -. Is that accurate?

            That could happen simply from unplugging a circuit with enough current flowing through it, from a hard short like touching wires on the controller side, etc. Maybe you just have a hard short now, which you will be able to measure. It could fit the evidence, I think. We will know more after you do a resistance test.

            Since you tested before and it worked, you have the right wires. And since all you changed is the connector (right??) then that is a highly suspect part.

            Do a careful check with a DVM now, do you get a short (low resistance? No? Then I'd try it again, but with the original wiring method that worked for you. Still work? Use an appropriate connector that has insulation protection between the terminals to discourage arcing! The one you use is pretty unsuitable, with both conductors exposed, side by side, during connection. Short arc path, and vulnerability of physically shorting the contacts while partially connected. Both are undesirable.

            If we hadn't seen the result, I think a lot of people would say it's nothing to worry about, low risk, to get a serious arc at 36V. Congratulations in reproducing a failure mode that most don't encounter, I guess?

            Use appropriate safety equipment. Please! Very dangerous trying it again, you know what might very likely happen. Again. So be extra careful.

            There is a thing in the EV realm called KFF. That stands for Kentucky Fried Fingers. Don't Google that on a full stomach. But maybe do, if you are casual about safety gear. Our batteries are low enough voltage we tend not to see as much danger as higher voltage guys, but you just found a way to get a nasty arc, so get careful, fast.

            I realize this is kind of vague and not the best written post, but I wanted to reply pretty quickly with what I can contribute, before you try again.

            Sorry to scold you, too, but we all want you to be safe!
            Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.


              Assuming you have not shorted anything out and you have verified this is still working by removing that connector and temporarily hardwiring it with wire nuts or whatever you have handy..

              You are using connectors produced for AC, not DC. These connectors are not built the same.

              See how the same circuit has way more arc when it is using DC? That is why you need connectors built for DC.


              • calfee20
                calfee20 commented
                Editing a comment
                "Scrutiny" I wonder if 50 to 80 volts DC would be as bad.

              Thanks for all the advice!

              So I took the proper safety measures...( goggles, insulated gloves and I removed the connectors I had on. Then I tested if things were still compatible with a pair of alligator clamp wires. There was a very small spark but everything ran as it should.

              Guess I was overthinking with wire size and ampacity. To my understanding based on my research volts/ current is pulled (not pushed) from the battery. If that is the case then everything in this setup should work properly even if I start to ride the bike at higher speeds.I'm not saying im going to be full throttle everywhere I go but the battery has more than enough power (1000w) to handle the motor and controller loads (750w).

              Since it appears the issue was the connectors I will head out and pick up some xt90 spark resistant wires and keep you guys updated.

              Thanks again!


              • JPLabs
                JPLabs commented
                Editing a comment
                "So I took the proper safety measures".......

                Not if you didn't confirm no short, before reconnecting it. Gear, or not.

              I suppose you could say the DC juice is pushed from the neg and pulled into the pos. The current being the same through the load components so not sure it matters unless you use an old analogue meter.


                Hello everyone,

                I know it's been a while since I've posted any updates which was due to online shipping. I managed to complete my 36v 750w ebike!

                The problem that I mentioned earlier was whether the controller wasnt strong enough to handle to handle the battery.

                Turns out the issue was the connectors that I chose. They were connectors you would find on an extension cord in a garage. This type of connector is not best suited for a DC circuit as we saw in the video posted above by paxtana. The short happened within one or both of the connectors.

                The item I ended up buying was the XT90 no spark connectors which took a month to ship to me..

                I plugged everything in and drove it around and everything is working great! nothing overheating or sparking.

                I appreciate all the advice and help from everyone. This is a hobby I plan to enjoy a long time.

                Thank you!


                  Great! Thanks for the update with your solution, too, much appreciated.
                  Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.