rcgldr Posted June 30, 2023 Share Posted June 30, 2023 (edited) If I brake moderately hard at around -10 amps or so peak current, I see reported peak voltage higher than pack voltage, more than the difference in reported voltage when charging at 3 amps versus not charging. With harder braking, I get reported peak currents around -15 amps, no hint of overlean or beeps, so clearly only part of that 10 to 15 amps is being used to charge the batteries, and something is dumping the rest of the current. I'm wondering what the source for the reported peak voltage is. I see a similar issue with reported current and reported peak current. The average current x ride time is less than charge current x charge time, so reported average current is high. Based on pack voltage drop being less than what battery tests show, reported peak current is also high. Edited June 30, 2023 by rcgldr Quote Link to comment Share on other sites More sharing options...
alcatraz Posted July 3, 2023 Share Posted July 3, 2023 (edited) I don't yet understand the principal of this circuitry but... We have fairly good braking ability even at a full battery (it's not noticeably less than with a depleted pack). That means that the motor or control board is able to convert the motor generated power into a high enough voltage (well over the max pack voltage) so that the battery can act as a resistance/buffer and soak up the energy. When a wheel overbrake alarm goes off it doesn't appear to be because there's no braking ability, but that the pack voltage is too high and pack damage will follow if you continue to brake. What I'd like to know more of is when/how braking transitions between a resistive load to a pack charging load. Apparently there are these two modes. On the MSP the resistive load appears to be applied when you overpower the charging circuit. So when you pull back like an animal, hanging off the back, then the pedals dip and the wheel enters a different braking mode. Brake force is still applied, however differently. Edited July 3, 2023 by alcatraz Quote Link to comment Share on other sites More sharing options...
alcatraz Posted July 3, 2023 Share Posted July 3, 2023 (edited) I suspect that this resistive load is the control board shorting out the motor. I suppose this would quickly result in an overheated motor if done long enough. Not sure though... Edited July 3, 2023 by alcatraz Quote Link to comment Share on other sites More sharing options...
alcatraz Posted July 3, 2023 Share Posted July 3, 2023 Everyone has felt how wheel acceletation get "soggier" as the pack depletes. Specially at low battery. Inversely, braking at full battery isn't noticeably soggy. Quote Link to comment Share on other sites More sharing options...
mrelwood Posted July 3, 2023 Share Posted July 3, 2023 There are much more knowledgeable people on this forum than me. But based on what I know and understand: There is no resistive load of any kind in EUCs. Regenerative braking happens when the motor behaves like a dynamo, with magnets moving through the magnetic field of the motor coils that act as electromagnets. Though the coils actually generate some energy when the tire is rotated even when the wheel is powered off. When riding at a steady speed, the motor also acts like a dynamo, and creates a back-EMF voltage (“dynamo voltage”) that gets higher the faster you go. Once the bEMF voltage reaches the controller output voltage, there is no longer any power (voltage difference) to accelerate even at 100% PWM. When you accelerate, the coils are switched on at specific times where they pull the magnets forward towards them. When braking, the magnets are being pulled back. (I don’t think they actually short the coils, since like @alcatraz said, that would overheat the motor fast.) I would assume that the time periods when the coils are active are such that they cause the bEMF voltage to be much higher during braking. On 6/30/2023 at 8:13 PM, rcgldr said: clearly only part of that 10 to 15 amps is being used to charge the batteries, and something is dumping the rest of the current. Braking on an EUC also uses energy, since the motor coils still need to be activated. It’s only the difference between the bEMF voltage and the momentary battery voltage that charges the batteries. And a lot of the current is absorbed as heat. On 6/30/2023 at 8:13 PM, rcgldr said: The average current x ride time is less than charge current x charge time Does the ride time include the time spent at zero speed (and powered on)? Some of the charge current is also absorbed as heat. There are losses everywhere! Quote Link to comment Share on other sites More sharing options...
varamontelo Posted July 3, 2023 Share Posted July 3, 2023 When the wheel is in descending road, battery get a little charge ; and with wind in back too. The intensity is low, logic. The result is fun if the distance is large, and minimal if short. we can't have a real quantity for a moment. Inmotion produced a fantastic model because the driver board on V8 and V8F are safe ; not on the last inmotion models with others priorities or profits. I like V8F, V10F, after it's different. Quote Link to comment Share on other sites More sharing options...
rcgldr Posted July 4, 2023 Author Share Posted July 4, 2023 (edited) On 7/2/2023 at 8:04 PM, mrelwood said: Braking on an EUC also uses energy, since the motor coils still need to be activated. It’s only the difference between the bEMF voltage and the momentary battery voltage that charges the batteries. And a lot of the current is absorbed as heat. With the pack around 75 volts, voltage when charging at 3.1 amps is about +1.2 volts. When braking at -10 to -15 amps I'm seeing about +4 volts. This is most likely due to where the voltage is being sensed and reported by my V8F. I doubt the charge current to the pack during braking is higher than 3.5 amps. On 6/30/2023 at 10:13 AM, rcgldr said: The average current x ride time is less than charge current x charge time, so reported average current is high. Based on pack voltage drop being less than what battery tests show, reported peak current is also high. On 7/2/2023 at 8:04 PM, mrelwood said: Does the ride time include the time spent at zero speed (and powered on)? Some of the charge current is also absorbed as heat. There are losses everywhere! If ride time includes time spent at zero speed, that would increase ride time x average current, but ride time x average current is more than charge time x charge current. The difference is charge current is reported by the charger, while average and peak currents are being reported by my V8F. Based on the voltage drop I see, reported peak current is also high. Edited July 5, 2023 by rcgldr Quote Link to comment Share on other sites More sharing options...
mrelwood Posted July 4, 2023 Share Posted July 4, 2023 6 hours ago, rcgldr said: I doubt the charge current to the pack during braking is higher than 3.5 amps. Why is that? 6 hours ago, rcgldr said: The difference is charge current is reported by the charger, while average and peak currents are being reported by my V8F. Well, there’s no point in comparing them then. There are large differences with the voltage and current calibrations even between the exact same wheel models, let alone completely different products at completely different circumstances. Wheels generally don’t even report the instant values, but smoothed ones over x period of time. So you aren’t seeing the actual peak values, or getting a usable picture of the peak nor average values. Quote Link to comment Share on other sites More sharing options...
rcgldr Posted July 5, 2023 Author Share Posted July 5, 2023 14 hours ago, rcgldr said: I doubt the charge current to the pack during braking is higher than 3.5 amps. 7 hours ago, mrelwood said: Why is that? Because the cells are 3500 mah cells, and generally not charged at greater than 1C. 14 hours ago, rcgldr said: If ride time includes time spent at zero speed, that would increase ride time x average current, but ride time x average current is less than charge time x charge current. The difference is charge current is reported by the charger, while average and peak currents are being reported by my V8F. Based on the voltage drop I see, reported peak current is also high. That should have been ride time x average current is more than charge time x charge current (missed an edit). Quote Link to comment Share on other sites More sharing options...
mrelwood Posted July 5, 2023 Share Posted July 5, 2023 10 hours ago, rcgldr said: Because the cells are 3500 mah cells, and generally not charged at greater than 1C. It has two parallel packs, so 1C would be 7A. Either way, a short term large charging current is not that harmful for the cells. And the braking process isn’t as controlled in that sense anyway, the wheel has to stay upright by any means necessary. Nobody wants to drop on their ass because the wheel decided not to exceed the manufacturer recommended charging rates. Quote Link to comment Share on other sites More sharing options...
rcgldr Posted July 5, 2023 Author Share Posted July 5, 2023 3 hours ago, mrelwood said: It has two parallel packs, so 1C would be 7A. Brain fade on my part. It is a single pack, 20S2P (21 wires on V8F BMS to sense the 20 voltages of the 20 cell pairs), so 7A max would make sense based on battery cells, but eWheels states to limit charge current to 3 amps instead of 5 amps when using their charger on a V8F. So the issue must be the controller board. It does appear to limit voltage to +4 volts over pack voltage, as I saw +4 volts for -12 amps and -15.5 amps braking current in separate braking tests. I'm not sure what circuitry is used to bleed off the rest of the current. - - - Update to my prior post: ride time x average current is more than charge time x charge current (missed an edit), so reported current is high. Quote Link to comment Share on other sites More sharing options...
Chriull Posted July 5, 2023 Share Posted July 5, 2023 16 minutes ago, rcgldr said: I'm not sure what circuitry is used to bleed off the rest of the current. I'm sure - none. 1 Quote Link to comment Share on other sites More sharing options...
rcgldr Posted July 6, 2023 Author Share Posted July 6, 2023 12 hours ago, rcgldr said: I'm not sure what circuitry is used to bleed off the rest of the current. 11 hours ago, Chriull said: I'm sure - none. The voltage and current are controlled by the regenerative circuitry, normally by controlling the duty cycle of the MOSFETs, for example a 3 phase MOSFET bridge. What I'm not sure of is how much heat the MOSFETs dissipate during braking. Quote Link to comment Share on other sites More sharing options...
Chriull Posted July 6, 2023 Share Posted July 6, 2023 2 hours ago, rcgldr said: The voltage and current are controlled by the regenerative circuitry, normally by controlling the duty cycle of the MOSFETs, for example a 3 phase MOSFET bridge. What I'm not sure of is how much heat the MOSFETs dissipate during braking. During regenerative braking the controller works as step up converter - the "lower" mosfets control the voltage by their duty cycle/frequency, the "upper" mosfets rectify the output voltage. And the battery "consumes". So 9x% of the power is dissipated in the battery, some of it charges the battery. Quote Link to comment Share on other sites More sharing options...
Chriull Posted July 6, 2023 Share Posted July 6, 2023 2 hours ago, rcgldr said: What I'm not sure of is how much heat the MOSFETs dissipate during braking. The lower mosfets are switching - so they dissipate nothing while off and a small amount during on (10mOhm x 15A² ~ 2W). Switching losses should be way below that. The upper, rectifying mosfets dissipate more if their body diode is ("mis")used - could be some 1.5Vx15A. Used as "active" rectifier they should just dissipate about the same 10mOhm x 15A². But the battery dissipates some 15A x 80V... There is no other component big enough to be able to dissipate such power repeatedly for some time/seconds. (besides the motor - but he already dissipates some additional power not regarded here) 2 Quote Link to comment Share on other sites More sharing options...
rcgldr Posted July 6, 2023 Author Share Posted July 6, 2023 2 hours ago, Chriull said: But the battery dissipates some 15A x 80V... My pack is usually around 76 volts. Doing a hard braking test, the reported peak braking current was -15.5 amps, and reported peak voltage was 80 volts. I'll need to test again, but I think I saw a +4 volt increase at -12 amps. Since this is peak voltage, the lack of difference in peak voltage increase could be related to duty cycle. Quote Link to comment Share on other sites More sharing options...
Chriull Posted July 6, 2023 Share Posted July 6, 2023 7 hours ago, rcgldr said: think I saw a +4 volt increase at -12 amps 4V/12A~0.3Ohm sound feasible for some 20s2p config - 20*30mOhm/2=0.3Ohm. Li Ion cells seem to be very efficient taking a charge from the little reading i have done. Using some "braking chopper" (https://en.m.wikipedia.org/wiki/Braking_chopper) to reduce charge current to 7A would mean to heat a resistor with ~8.5A x 80V ~ 700W. Which needs to a big resistor... 1 Quote Link to comment Share on other sites More sharing options...
rcgldr Posted July 8, 2023 Author Share Posted July 8, 2023 (edited) On 7/6/2023 at 7:31 AM, rcgldr said: +4 volt increase at -12 amps. Since this is peak voltage, the lack of difference in peak voltage increase could be related to duty cycle. On 7/6/2023 at 3:15 PM, Chriull said: 4V/12A~0.3Ohm sound feasible for some 20s2p config - 20*30mOhm/2=0.3Ohm. I also see +4 peak voltage at -8 amps, so the peak voltage increase is apparently fixed, and apparently it's the duration of each cycle that changes depending on braking current. Edited July 8, 2023 by rcgldr Quote Link to comment Share on other sites More sharing options...
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