DaveThomasPilot

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About DaveThomasPilot

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  • Birthday 12/14/1954

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    Norh Carolina
  • Interests
    RC Helicopters, PCB design, Flyball, Private pilot, scuba diving, skiing

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  1. Page 62 of the STM32F103VBT6 spec states input leakage current of +/- 1ua. That corresponds to a voltage delta of +/- .75 volts. That's a typical maximum input leakage specification. Frequently, it's the result of an ESD protection diode on the input. Typical leakage is normally well below the specification. On the other hand, a bit of flux left on the board after the soldering operation or other contaminants can cause leakage currents of sufficient magnitude to cause unacceptable voltage accuracy errors when large impedences are used. I understand this is not the KS14C design, but is a representative example of a poor analog design on what should be a simple circuit. I'd consider trying to find a similar divider on my KS14C and "fixing" it. But, it has that coating all over it. I wonder about that coatings resistance---could be a source of leakage too.
  2. What is the processor?
  3. Yes, I saw that in the schematic. But where does STM32_PA3 go? I don't think you could get a valid measurement meter with your meter. You'd need to use a bridge. Besides, a given part on a specific card might not be leaky, while others could be in spec but too leaky for an accurate voltage measurement. Consider that a leakage (or input bias current) of just 1 ua would cause .75 volts of error in the input measurement. It seems pretty dumb to use a very high value resistor to scale an analog voltage value in a design where power dissipation isn't critical. With 65 volts, the resistor would dissipate about 5.5 mW. On a card that will be dissipating many watts! Seems like it could be an order of magnitude (or more) lower.
  4. C21 looks like a ceramic cap. Close enough to zero leakage. I checked the schematic, but couldn't figure out where it goes. Input leakage current of that part would have to be very low to not cause an error through 750K.
  5. So, a resistor divider for the scaling. Increased leakage on a bypass cap on the lower side would make the scaled voltage measure lower than it should. What kind of cap? Is it poloarized? If so, it's leaky (prob. aluminum electrolytic or tantalum) and shouldn't have been used with a high value resistor like 750K. We could look up the leakage spec if you have a P/N for the cap.
  6. I use processors in many DIY projects. They have sleep states where they dissipate much less than 1 uA (that's 1/1000000 of an amp), but still can be awakened from the sleep whenever the voltage on a specified pin changes. So, a single pull-up resistor to that one pin is all that would be required to wake the processor, which could then turn on pass device to allow battery power to be applied to the control board. You'd be surprised how many young electrical engineers lack very basic analog circuit design skills. I would NOT be surprised to see some poor circuit design in the circuits that scale the voltage down do the analog to digital conversion.
  7. I'm probably at about the same stage you are. I can get on and off the wheel, though sometimes it takes a couple of tries to get going. Turns to the right are easy now, turns to left getting better. I was struggling with foot pain, when I rode more than a few minutes without dismounting. Today, I tried using very thin socks and not tightening the shoe straps on my hiking boots so tight. I wanted to be able to "squirm" a little in the boots to shift weight. It worked! Moving my feet at all is very scary at this stage in my learning, but with the thin socks and looser fit boots, I can move them just enough inside the boot to relieve pressure points. I guess at some point, I'll actually be able to move my feet around on the pedals while riding, but I'm not there yet. Good luck and keep the progress reports coming!
  8. I've had to remove and re-insert the control board in my KS14C too many times while trying out potential replacement boards. Every time I removed the board, I had to bend the leads on the 2200 uF aluminum electrolytic capacitor out of the way to access one of the four screws that attach the control board to the wheel's housing. When the replacement boards wouldn't work, I went back to the original board to make sure something else in the wheel was not causing the problem. Then back to the replacement board to see if it really was bad. Then the orignal control board was inserted Finally, one of the cap leads on the original control board broke. This is likely a common problem, since there's no way to remove the board without bending the leads and then bending them back when the board is replaced. I decided to document how I repaired it so maybe it will help someone else having the same problem. I found a replacement cap on Digikey, but I didn't want a place an order for the single $4 part. I order from them frequently, so I decided I'll wait until I place my next one and meanwhile implement the repair using the broken one. I don't think all four screws are needed to attach the control board to the housing. If only three are used, it might not be necessary to bend the leads to remove the board (or at least not as far). The remaining lead length on the broken pin was too short for a 90 degree bend, so I soldered header pins in pcb through holes instead of soldereng the cap directly: Then, I soldered the leads of the capacitor to these pins: I still may have to unsolder the cap to remove the control board next time, but I think that's better than continuing the fatigue the cap leads until they break again. Also, rather than use what seemed like a silicone glue on the screws that attach the pcb and the motor wire screws, I used blue thread lock. The original glue KS used gets in the screw heads and has to be picked out with tweezers before the screws can be remove. We always used blue thread lock (don't use red!) for all screws when we built RC helicopters. We'd clean each screw with alcohol, then use a toothpick to put a tiny amount of thread lock on the screw threads. They never came loose, despite the extreme vibration to which they were subjected.
  9. Also, if many people are using the ChargeDoctor and terminating the charge early to preserve battery life, they wouldn't know if this issue existed in their wheel or not. But, the low voltage tilt-back warning might not occur in time to prevent an accident. At least, that is my worry.
  10. Yes, I slow charged once and rode immediately after the charge and had no issue. Best I can recall, I rode on that charge for miles, but still got tilt-back going down hills. But, my feet really hurt a lot and it just wasn't fun riding more than a few minutes. I fully charged it using the fast charger Jason sent me. I don't recall if I tried riding immediately after that charge, but I did check to make sure it wasn't doing the tilt back thing immediately after being fully charged with the fast charger. Then, it sat for several months. When I powered it on again, I got beeping and tilt-backs and had to leave it on for days before I could get on it. Before the Charge Doctor arrived (I ordered it from France before I knew Jason distributes them in the US), I added wires inside the fast charger to measure its output voltage. I expected the charger voltage to be higher than what the wheel reported, since it's on the anode side of a protection diode, but it was lower. Which said something was clearly wrong. When I got the ChargeDoctor, I did open up the wheel so it measured the battery voltage. I did that for the discharge curve, but didn't bother for the charge curve (I would have needed to build another connector adapter). The reason to use the Charge Doctor is to have it automatically cut-off the charge at a specified voltage. You have to figure out what voltage (or current) will do that for your specific wheel (and hope it doesn't drift a lot). Absolute accuracy isn't really important--you just need to determine the cut-off voltage needed to prevent tiltiback. Aluminum electrolytic caps are leaky by nature. They also dry out over time. But, I don't know if they could get significantly more leaky sitting in a relatively hot garage. The analog circuity designer should not have a circuit where the leakage current of a cap is important to the voltage measurement accuracy, but it seems like it must be something like that going on. I think I've seen four reports on this forum with the same symptoms. I'll try to go back through and find them.
  11. Your comments about the differences in charge and discharge curves make sense. I checked the accuracy of the Charge Doctor voltage measurement using DVMs, but not the current. However, given how close the charge current was to an even 5 amps, gives me confidence in the current measurement accuracy. I didn't check the math for running integral of volts * amps for the watt-hours, but I'm sure you got that right. I'm very happy with the Charge Doctor! Agree. But, the idea is to test the tilt back thresholds on a replacement control board Good to know. That says you don't really need a "fuel gauge" once you have enough experience? But, besides being just a beginner, I'm trying to keep my speed down to just above walking speed. I really don't trust the wheel's overall reliability when there's what's probably a design issue with an unknown (to me) root cause. I'm not sure one could detect battery voltage at slow speeds?
  12. Jason first sent me a replacement charger when the issue first happened last fall. That was after the wheel had been idle after the initial purchase for about 6 months (I broke my back in an aircraft accident and couldn't ride the wheel for several months). First he sent a slow charger. That didn't overcharge and we thought the problem was solved. I rode on that charge, but my feet hurt so bad if motivated me (along with other things) to loose weight. I've lost over 30 pounds so far and wanted to start riding again last month. That's when I noticed the tilting again. I compared the voltage reported by the app to the output voltage of the charger and noticed the inconsistency. Then, I bought the charger doctor and found the voltage delta to be still worse (over 3 volts!). So, something is drifting. No component drifts that fast unless it's over-stressed in the design (3X rated power dissipation in a precision resistor, for example). But, I can see the design using very high resistor values to scale the relatively high battery voltage and failing to recognize the impact of stray, leakage, and input bias currents on a high impedance nets voltage.
  13. Was this a KS14C? I have same problem. Wheel thinks the voltage is higher than it is. Too high, so it does the tilt-back thing. Mine has gotten worse. Check out this thread, about 1/2 way down. And today's post:
  14. It took my three days to discharge enough to start riding, with the lights on the whole time.
  15. I've seen three instances of these failure symptoms on this forum (besides mine). I'd love to get a schematic so I could figure out how they are measuring voltage. Surely, they are not using a resistor divider to scale the voltages with high resistance values and failing to account for input bias current... The parasitic current would drift over time and cause this type of issue. But, that would be pretty naive design.