checho Posted February 17, 2016 Share Posted February 17, 2016 I need help troubleshooting a problem. I recently bought a ks-18a with a 1200w (1100w) motor, and 1360wu battery pack. Everything was working fine for a few hours, until suddenly i lost all power, good thing I was going very slow and did not get hurt. After troubleshooting, I can see that the batteries are fine, and the batteries deliver power to the motherboard, the battery voltage that the motherboard receives is 65.2V. however the fuse that comes from the battery to the motherboard is blown, when replacing the fuse with a king song fuse about 1 or 2 seconds after turning the wheel on the fuse blows, and the wheel moves a little back and forth, I tried other fuse 5A and 10A and they blow immediately and the wheel does not move, the highest rating fuses I have found are 30A but I have not tried them since it might be a fire hazard. I am not sure the rating on the king song fuse it is pink, I guess it is around 20A, maybe 25A since it is not labeled. It is always the same fuse that blows, the one that goes directly to the motherboard, the other fuses have never blown. I took a picture of the motherboard and it looks clean, no burn spots. The wheel moves freely, but the resistance in moving without power is now much higher than when it was working and turned off, I am not sure if this is normal now that the wheel does not have power to the motherboard, or if it is an indication of a problem. Any help troubleshooting this problem will be greatly appreciated. Link to comment Share on other sites More sharing options...
OliverH Posted February 17, 2016 Share Posted February 17, 2016 The fuse blows because of load over spec or a short. It's a protection. You need to find the issue rather than higher the A value of the fuse. Link to comment Share on other sites More sharing options...
checho Posted February 17, 2016 Author Share Posted February 17, 2016 I will be getting a new control board from King Song, they think it is the control board. yes it is a short, but when changing a fuse and you think it is a short it is always better to start by a lower spec fuse than a larger one. Lets hope that the motor is fine, and it is only the control board. I will post an update after replacing the control board. Link to comment Share on other sites More sharing options...
Cloud Posted February 17, 2016 Share Posted February 17, 2016 The fuses on 14" are 40A. I dont see them being less amperage on the 18. Theoretically you can use two 20a fuses in parallel instead of 1 -40a but 2 fuses will not fit into the socket and would need soldering. You can order 40a fuses online from china Link to comment Share on other sites More sharing options...
esaj Posted February 17, 2016 Share Posted February 17, 2016 The tire not moving freely (resisting turning) even without power would suggest a short in the mosfet-bridges, so likely it's the control board. It's probably also that same short that burns the fuse. But really just guessing. Link to comment Share on other sites More sharing options...
Cloud Posted February 17, 2016 Share Posted February 17, 2016 By the way, the fuse rating will be imprinted on the top edge of the fuse. If you look closely you will see it Link to comment Share on other sites More sharing options...
checho Posted February 18, 2016 Author Share Posted February 18, 2016 Cloud you are correct, the 40A rating it is engraved in the fuse without ink, it is hard to see at first. But the fuse it is rated at 40A. Esaj, I will be getting a new control board, it is the control board shorting the fuse. Is there a link where I can read in regards the tire not moving freely (resisting turning) since I would like to know why this happens when there is no power? because when the wheel is working but powered off from the control board it moves more freely than now, but when the mosfet-bridges have problems it does not, that is something I really do not understand why it happens and would like to read about, a link on the subject would help. Tina will be sending me a new control board, once I get it I will post back. Link to comment Share on other sites More sharing options...
esaj Posted February 18, 2016 Share Posted February 18, 2016 8 hours ago, checho said: Esaj, I will be getting a new control board, it is the control board shorting the fuse. Is there a link where I can read in regards the tire not moving freely (resisting turning) since I would like to know why this happens when there is no power? because when the wheel is working but powered off from the control board it moves more freely than now, but when the mosfet-bridges have problems it does not, that is something I really do not understand why it happens and would like to read about, a link on the subject would help. Tina will be sending me a new control board, once I get it I will post back. I'm not sure if there's any page explaining it in detail, but here's what happens according to my limited understanding: A mosfet (a certain type of transistor) can fail (break) into two states: "conducting" (ie. letting current pass through them freely) or non-conducting (acting like a break in the circuit). Based on peoples experiences on this forum, it seems they usually are in the "conducting" state after they fail. An electric motor actually can (and will) always also act as a generator. When the motor is turning, the coils and magnets passing each other inside the motor will cause a varying voltage (called back-EMF), and current, if there's a closed circuit, to manifest. If you put a multimeter or oscilloscope between the motor phases and turn it by hand, you will see some voltage being generated. Simplified again, when the motor is being "fed" a voltage that is larger than the voltage produced by the motor itself, it will speed up (the current and thus acceleration will depend on the voltage difference, larger difference causes larger current). If the motor itself is producing a larger voltage, the motor will slow down (and the current will flow in opposite direction). When the voltages "match", the motor will turn at constant speed (and no current will flow, zero torque). Of course in real-life, there's always some friction etc. which try to slow down the motor, so actually the voltage being fed is likely slightly larger than back-EMF. When it comes to braking a motor, there are a few different ways to do it. Our motors use regenerative braking, where the voltage produced by the turning motor is higher than what is being fed from the batteries (I believe this also called "super-synchronous" speed). A detailed explanation using regenerative braking with a single half-bridge is in the answer to this question here: http://electronics.stackexchange.com/questions/56186/how-can-i-implement-regenerative-braking-of-a-dc-motor I haven't (yet) tried it, but I believe the basic idea is the same with 3-phase motors and 3 half-bridges; by "pumping" charge into the motor coil and then "shooting" it off to the battery. But how this all relates to the motor resisting turning when a mosfet has failed, lies in the part of that answer that talks about braking the motor by causing a short over the motor itself: Let's redraw our schematic with that model, with values as if our motor is spinning at high speed: This motor is running at full speed. We have a small current to overcome the friction in the motor, and the back-EMF is the supply voltage, less the voltage drop over R1. Not much current flows because the back-EMF cancels most of the supply voltage, so L1 and R1 see only 100mV. Now what happens when we switch the bridge to the low side? At first, nothing. L1 prevents an immediate change in current. However, this doesn't last long, and very soon (defined by the time constant of L1/R1, not more than a couple ms ms typically) the back-emf (V1) has reversed the current, and now it's going in the other direction. It's also pretty huge, since now L1 and R1 don't see the small difference of VB1−V1VB1−V1 (it was 100mV), but now they see the full 9.9V from V1 alone: We now have a large current flowing in the opposite direction. Torque is proportional to current, so now instead of applying a gentle clockwise force, just enough to overcome friction, we are applying a hard counterclockwise force, and the mechanical load is rapidly decelerated. As the speed of the motor decreases, so does V1, and consequently so does the current, and the torque with it, until the load is no longer spinning. Where did the energy go? The kinetic energy of the mechanical load is energy. It can't just disappear, right? Right. If you look at the circuit again, we have 9.9A flowing through R1. PR1=(9.9A)21Ω=98.01WPR1=(9.9A)21Ω=98.01W. The kinetic energy of the load was converted into heat in the motor's winding resistance (and in a practical circuit, also the H-bridge transistors). That's the basic theory in a very simplified and short form. So, when mosfets on the same "side" (low or high) of their respective half-bridges have failed, they will short two (or all three) phases of the motor together. Even when the wheel is not otherwise powered up, turning the motor (by hand or by pushing it along the floor) will cause the motor to act as a generator, but at the same time that short-circuit through the bridges will cause the braking action. Basically your motor is braking all the time while turning (or 2/3rds of the time if only 2 phases are shorted together). Your battery pack fuse probably blows when the wheel is powered up, because that same short-circuit through a bridge will also short the battery with itself. Probably someone more knowledgeable can correct any mistakes I made in the above Link to comment Share on other sites More sharing options...
Cloud Posted February 19, 2016 Share Posted February 19, 2016 4 hours ago, esaj said: Probably someone more knowledgeable can correct any mistakes I made in the above Correcting mistakes would be easy. Problem is finding someone more knowledgeable!! Link to comment Share on other sites More sharing options...
esaj Posted February 19, 2016 Share Posted February 19, 2016 16 hours ago, Cloud said: Correcting mistakes would be easy. Problem is finding someone more knowledgeable!! I think there are a number of people in these forums alone that know a hell-of-a-lot more than me about these, but won't bother answering these... not that I blame them, probably they have a lot of better things to do. Most of my conclusions are more like best guesses, any real electronics engineer knows a lot more than me Link to comment Share on other sites More sharing options...
Chriull Posted February 20, 2016 Share Posted February 20, 2016 On 18.2.2016 at 2:49 PM, checho said: Cloud you are correct, the 40A rating it is engraved in the fuse without ink, it is hard to see at first. But the fuse it is rated at 40A. ... Tina will be sending me a new control board, once I get it I will post back. You have more original king song fuses as replacement, once you install the new motherboard? Or Tina will also send you an original fuse? The amperage is just one parameter which defines a fuse - different 40A fuses can behave very diverse. 14 hours ago, esaj said: I think there are a number of people in these forums alone that know a hell-of-a-lot more than me about these, but won't bother answering these... not that I blame them, probably they have a lot of better things to do. Most of my conclusions are more like best guesses, any real electronics engineer knows a lot more than me Imho there is no "absence" of answers - just all the answers and sound guesses for the given facts are given so far. Just a little bit of irrelevant "smartassing" could be added to some minor details , like: On 18.2.2016 at 10:55 PM, esaj said: ... So, when mosfets on the same "side" (low or high) of their respective half-bridges have failed, they will short two (or all three) phases of the motor together. ... Could also be, that only one halfbridge, or just one mosfet failed (and makes a short circuit) - once the back-emf with the right polarity reaches the forward voltage of the body diode of the corresponding second mosfet he will start to conduct and so the wheel breaks too. If @chechois somhow "electronically" experienced and wants a second spare motherboard he has good chances to revive it by replacing the (failed) mosfets - they should be quite cheap to get and it should not be too much work. Someone sometime ago in a thread here reported, that he succeded by doing so. But of course with the mosfets some other components could have died, too - so there is no guarantee for success. You can gather more evidences, to be sure that the mosfets are the reason: - The resistance of the wheel should increase, the faster you try to turn it. - Measuring the mosfets with an ohmmeter (regard polarity of the ohmmeter, whether the coils of the motor are still attached,...) Link to comment Share on other sites More sharing options...
checho Posted February 24, 2016 Author Share Posted February 24, 2016 Thanks Esaj, for the very detailed explanation. Chriull, if you could provide instructions on how or where to get replacement mosfets I will definitely give it a try at repairing the control board, and ideally if possible to replace them by better mosfets with higher amperage and temperature ratings if possible. In regards the troubleshooting: The resistance of the wheel will not increase any more since it is already very hard to turn, now that the control board is bad. "- Measuring the mosfets with an ohmmeter (regard polarity of the ohmmeter, whether the coils of the motor are still attached,...)" Ohmmeters do not have polarity, ohms do not have polarity, voltage has polarity. I heard about reading the ohms with a meter, but what should I expect? Same resistance among all 3 cables going to the motor? In regards my knowledge with electricity it is basic to moderate, I took 1 course of electricity under college part of Engineering physics., and one course of digital circuits a very long time ago. Link to comment Share on other sites More sharing options...
Chriull Posted February 24, 2016 Share Posted February 24, 2016 5 hours ago, checho said: ...Chriull, if you could provide instructions on how or where to get replacement mosfets I will definitely give it a try at repairing the control board, pfff... Lets see Just to start with - you know that replacing the Mosfets is no 100% guarantee to get your board repaired. Still could be something else/additional - which presumably is not repairable (at least not per "long distance forum connection"). And you have experience in soldering and "electronics work"? You are touching the "high power" interface between battery and motor - so your soldering should be solid and clean. Any shortcomming can lead to some future faceplant, if the connections get loose/bad by vibration or other burden. And of course any short circuits/"?blotchiness?" can result in a nice fireworks when powering on... 5 hours ago, checho said: and ideally if possible to replace them by better mosfets with higher amperage and temperature ratings if possible. Pleas not. Stick with exactly what was in there! You can easily indroduce malfunctions by changing to different Mosfets - the design is (should) be tailored to the used Mosfet. So you should have detailed knowledge of the design and the Mosfets to make an adequate upgrade! You should even try to get the Mosfet from the same manufacturer. For example for the 75NF75 (used in some Ninebots) exists data sheets from EStek and from ST. Both Mosfets with the same Name have quite some differences... So any number/letter beside the "main name" could be important - or also not You have 6 of them or 12, organized in two banks of 6? Can you identify the names of _all_ of them? 5 hours ago, checho said: In regards the troubleshooting: The resistance of the wheel will not increase any more since it is already very hard to turn, now that the control board is bad. Ok - is a "good" sign, that we are on the right track... 5 hours ago, checho said: "- Measuring the mosfets with an ohmmeter (regard polarity of the ohmmeter, whether the coils of the motor are still attached,...)" Ohmmeters do not have polarity, ohms do not have polarity, voltage has polarity. no, yes, yes. Ohmmeters do not measure the resistance directly - the apply an voltage on the probes and look what current is flowing -> so they can conclude on the resistence. So ohmmeters are in reality amperemeters with an dc supply (and an adopted scale). 5 hours ago, checho said: I heard about reading the ohms with a meter, but what should I expect? Same resistance among all 3 cables going to the motor? Getting the resistances between all three of them, for each in both directions is the easiest measurements (without any changes to the board/cabling). If you get all six values in the same range its just no ?message/statement/evidence?. So then the second step would/should be to disconnect the motor (cut/unsolder the 3 motor wires - just the 3 thick ones near the Mosfet, not the other wires to the hall sensors) and measure the Mosfets "directly". (If the motor can be disconnected easily you also can start with step two ...) Just do get you an idea of whats going on there, a schematics of the Mosfets and Motor: (reused from http://www.kellendenny.com/2014/11/bldc-motor-and-controller-theory.html - did not read this side, but could be a nice indroduction to this topic) And presumably you have for of each of this mosfets a second one in parallel (the mentioned 12 pieces above) 5 hours ago, checho said: In regards my knowledge with electricity it is basic to moderate, I took 1 course of electricity under college part of Engineering physics., and one course of digital circuits a very long time ago. And a last note regarding the work to be done, so you can take your final decision whether or not you want to start the operation: The Mosfets have to be electrically insulated from the heatsink and thermically coupled as good as possible. So in the "ancient times" one used to take "?mica plates?" for the insulation and thermal paste for the thermal coupling. Nowadays there exist many plastic/silicone foils/plates which take both tasks. But i have no actual experience which of this choices is "state of the art" and recommandable ... And since the Mosfets are (should be) screwed to the heatsink, you'll need some plastic pieces to insulate the screw from the heatsink/mosfet. Link to comment Share on other sites More sharing options...
Chriull Posted February 24, 2016 Share Posted February 24, 2016 Had quite an off-topic answer here... 8 hours ago, checho said: Chriull, if you could provide instructions on how or where to get replacement mosfets I will definitely give it a try at repairing the control board... Look at you local electronics shop, online electronics shop, aliebaba, ebay,.... Depends on your location, your preferences and who has the items available... And here an addition: 8 hours ago, checho said: The resistance of the wheel will not increase any more since it is already very hard to turn, now that the control board is bad. If you disconnect the motor from the mainboard (see above), then the motor should turn easy again. If not your motor has a problem (?additionally?). Link to comment Share on other sites More sharing options...
Mistagear Posted February 24, 2016 Share Posted February 24, 2016 All good this talk of repair, however I'm nearly certain that KS would require the board returned to them as part of warranty Link to comment Share on other sites More sharing options...
Chriull Posted February 24, 2016 Share Posted February 24, 2016 54 minutes ago, Mistagear said: All good this talk of repair, however I'm nearly certain that KS would require the board returned to them as part of warranty Could be, but since On 17.2.2016 at 7:05 AM, checho said: I will be getting a new control board from King Song, they think it is the control board. and 9 hours ago, checho said: ... I will definitely give it a try at repairing the control board... i assume, KingSong did not require the board returned - however @chechowill know. Another addition (question i did not answer before): Quote I heard about reading the ohms with a meter, but what should I expect? Same resistance among all 3 cables going to the motor? Depends on your Ohmmeter and the kind of damage, that occured. As said above same resistance among all 3 cables would be a "no message", but there could be a short circuit or siginificantly lower resistance shown... Then in the second step (the three motor wires disconnected) you measure each Mosfet (parallel pair) from Drain (positive Probe) to source (negative Probe) and get an extremely high resistance (overflow/no connection) shown. If not, you found one of the bad Mosfets (parallel pairs). Maybe you can also identify them already optical by discolorations on the casing/thermal compounds... Once you have identified dead Mosfets (to conclude the cause) i would recommend you to exchange _all_ Mosfets. They do not only die once they exceed a certain fixed temperature but also age/worsen by high/over temperatures. And also looking for a short circuit only lets you see, if the Mosfet is absolutely dead - to check if the Mosfet is really ok, one would need much more tests... Link to comment Share on other sites More sharing options...
Kingsong-France Posted February 25, 2016 Share Posted February 25, 2016 Hello, About fixing the mother board, There are different critical point. 1st take off the vernish on motor's screw and take picture of the order yellow, blue, green. The mother board have 4 screw, take them off and put in on the new mother board before placing into the emplacement. 2nd point is the bipper, you will need to access to the screw under the Green capacitor, if you are affraid to break it on the new MB, it's not an obligation to do it, there are two screw, One is enough. After putting all stuff and fix the screw of the motor you will need to put some vernish on each screw. If you don't do it and ride it under the rain, you could have electric arc and you will kill you MB again. This is typical vernish, ask Tina if she can give you some, if not, you will to go find some. Wish you a good day, good luck Link to comment Share on other sites More sharing options...
checho Posted February 26, 2016 Author Share Posted February 26, 2016 Thanks for the information on replacing the motherboard, I am currently waiting for the replacement. In regards the varnish, what type of varnish is used on the control board, and only on the screws? is the purpose of the varnish to prevent a short in case water gets on the control board ? will liquid electric tape work for that purpose? Link to comment Share on other sites More sharing options...
Kingsong-France Posted March 1, 2016 Share Posted March 1, 2016 @Checho, I think liquid electric tape could be enough, please watch how high the temperature can go. The mother board connection to motor, can go on high temperature and soon it will be summer. Have a good day Link to comment Share on other sites More sharing options...
Keith Posted March 1, 2016 Share Posted March 1, 2016 58 minutes ago, Kingsong-France said: @Checho, I think liquid electric tape could be enough, please watch how high the temperature can go. The mother board connection to motor, can go on high temperature and soon it will be summer. Have a good day Surely the varnish is there to ensure the screws do not come undone, not as insulation. Locktite would not work well on an electrical connection, especially if it gets hot. There is plenty of electrically open points on the board; insulating just the screw heads would achieve little. On the other hand, one of 3 phases coming loose would be dangerous if riding as the motor would very suddenly stop and also be likely to burn out the motor or controller. Link to comment Share on other sites More sharing options...
checho Posted March 2, 2016 Author Share Posted March 2, 2016 I got a bottle of this vanish: http://www.mgchemicals.com/products/protective-coatings/insulating/red-insulating-varnish-4228/ Red GLPT Insulating Varnish 4228 what do you guys think, will this Varnish work well? Today I got the control board, soon I will start working on it, just want to check if the varnish I got will work well if not let me know what type of varnish it is recommended. Locktite blue will probably not work well since the control board probably gets very hot, and the hot temperature locktite it is for permanent connections and for that reason it is also not good for the job. Thanks, Link to comment Share on other sites More sharing options...
Keith Posted March 2, 2016 Share Posted March 2, 2016 17 hours ago, checho said: I got a bottle of this vanish: http://www.mgchemicals.com/products/protective-coatings/insulating/red-insulating-varnish-4228/ Red GLPT Insulating Varnish 4228 what do you guys think, will this Varnish work well? Today I got the control board, soon I will start working on it, just want to check if the varnish I got will work well if not let me know what type of varnish it is recommended. Locktite blue will probably not work well since the control board probably gets very hot, and the hot temperature locktite it is for permanent connections and for that reason it is also not good for the job. Thanks, @checho, that should work fine, the varnish is primarily there to prevent the screws coming loose, not for insulation, although what you have purchased will do both. As you quite rightly say (and I said before) locktite would not be usable with electrical connections, both due to heat softening all but the permanent type and it isn't electrically conductive. Link to comment Share on other sites More sharing options...
checho Posted March 3, 2016 Author Share Posted March 3, 2016 It was the control board. Replaced the control board and the wheel is now working fine, now I will apply the varnish to the screw heads and let it dry, I will apply 2 coats, second coat after first coat dries. It appears that it was the MOSFETs since once the control board was removed the wheel no longer had a high resistance in turning. The strange thing is that the old control board shows no signs of burnt spots. Tina provided great service shipping the control board and fuses. The most difficult part in replacing the control board was removing the existing varnish from the screws. Thanks everyone for the support. Link to comment Share on other sites More sharing options...
esaj Posted March 3, 2016 Share Posted March 3, 2016 5 hours ago, checho said: It appears that it was the MOSFETs since once the control board was removed the wheel no longer had a high resistance in turning. The strange thing is that the old control board shows no signs of burnt spots. That's the problem with electronic components; you can't always tell from the outside if they're faulty or not. A single static discharge from your fingers can destroy the gate of a mosfet, yet from the outside you couldn't tell it. Link to comment Share on other sites More sharing options...
Jeffrey Scott Will Posted March 15, 2016 Share Posted March 15, 2016 On 3/2/2016 at 9:44 PM, checho said: It was the control board. Replaced the control board and the wheel is now working fine, now I will apply the varnish to the screw heads and let it dry, I will apply 2 coats, second coat after first coat dries. It appears that it was the MOSFETs since once the control board was removed the wheel no longer had a high resistance in turning. The strange thing is that the old control board shows no signs of burnt spots. Tina provided great service shipping the control board and fuses. The most difficult part in replacing the control board was removing the existing varnish from the screws. Thanks everyone for the support. Indeed! I had to replace my control board on my 14c, and that was the most puzzling part. I tried taking a knife, melting it, etc... but eventually just took some needle nose plyers and just pulled it off. I really thought I was at a dead end for awhile. Link to comment Share on other sites More sharing options...
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