btl Posted February 17, 2021 Share Posted February 17, 2021 (edited) Hi i am thinking about modifying my battery packs of the MSX and MCM5 84V from the stock "charging protection and balancing only" BMS to a better "balance, charge & discharge protection" BMS with bluetooth and app support to be able checking individual cell voltages. The MSX has two 84V, roughly 800Wh battery packs with integrated simple BMS in the shrinkwrap. Max. continous motor power is 2000W. Lets assume 4000W to include peaks, that makes 47A max current, divided by two (parallel battery packs). Thats 23.5A per pack (No idea why apps like the Gotway app or EUC world report much higher amps, i frequently trigger the overcurrent alarm set to 120A...). Therefore i conclude two 30A continous current / 20S BMS should be okay to not let my wheel cut out, but trigger the overcurrent protection in case of a mainboard failure and short curcuit. Did i make some mistake in my thinking? Let me know before i order. Greets, Stefan Edited February 17, 2021 by btl 2 Quote Link to comment Share on other sites More sharing options...
Chriull Posted February 17, 2021 Share Posted February 17, 2021 7 minutes ago, btl said: Therefore i conclude two 30A continous current 20S should be okay to not let my wheel cut out, but trigger the overcurrent protection in case of a mainboard failure and short curcuit. Don't know the overcurrent protection chatacteristics of your choosen smart BMS, but i'd choose the current protection much higher to avoid in _any_ case a cut off by some spikes... 12 minutes ago, btl said: No idea why apps like the Gotway app or EUC world report much higher amps, i frequently trigger the overcurrent alarm set to 120A... The reported value is the motor (phase) current and not the battery current. Looking at the "estimates" in https://forum.electricunicycle.org/topic/7855-anatomy-of-an-overlean/?do=findComment&comment=281335 i'd tend more to some 50A per BMS. Maybe even a bit higher - shall be a short circuit protection and not inflict a nasty faceplant by accident. 1 Quote Link to comment Share on other sites More sharing options...
btl Posted February 18, 2021 Author Share Posted February 18, 2021 Thanks for your comment. So motor phase current x battery voltage gives me these fake 10kW peak power i see in the EUC world log, i see. Surely enough, i want to prevent triggering the overcurrent protection while riding in any situation. I don't ride the beeps, but i do torque it over roots and rocks sometimes. In that diagram the battery current peaks at about 55A, which is still less than 30A per battery pack. But you're right, 50A per BMS gives a better safety margin. 1 Quote Link to comment Share on other sites More sharing options...
Chriull Posted February 18, 2021 Share Posted February 18, 2021 22 minutes ago, btl said: So motor phase current x battery voltage gives me these fake 10kW peak power i see in the EUC world log, i see. As this are unrelated values and by this no power. So not even a fake value 22 minutes ago, btl said: Surely enough, i want to prevent triggering the overcurrent protection while riding in any situation. I don't ride the beeps, but i do torque it over roots and rocks sometimes. Imho low speed high burden situations are very inneffective and can, beside "normal" real high power/burden situations lead to higher battery currents. 22 minutes ago, btl said: In that diagram the battery current peaks at about 55A, which is still less than 30A per battery pack. But you're right, 50A per BMS gives a better safety margin. And battery current is calculated with some assumptions, estimates and approximations and should be taken only as rough figure of whats happening! Quote Link to comment Share on other sites More sharing options...
btl Posted February 18, 2021 Author Share Posted February 18, 2021 Perhaps i measure real battery current before ordering new BMS. Much better than calculating with some assumptions. Quote Link to comment Share on other sites More sharing options...
Chriull Posted February 18, 2021 Share Posted February 18, 2021 15 minutes ago, btl said: Perhaps i measure real battery current before ordering new BMS. Much better than calculating with some assumptions. Of course - could just be challenging to get reasonable values! Even modern EUCs still do not like (longer) high burden situations at low speeds/standstill. Quote Link to comment Share on other sites More sharing options...
RagingGrandpa Posted February 18, 2021 Share Posted February 18, 2021 17 minutes ago, btl said: MSX has two 84V, roughly 800Wh battery packs Perhaps i measure real battery current I did 50A per pack sounds great- one pack could become faulted, and you'd still have ample current from the 'good' pack to ride safely. 3 Quote Link to comment Share on other sites More sharing options...
Brendan "nog3" Halliday Posted February 18, 2021 Share Posted February 18, 2021 1 hour ago, RagingGrandpa said: I did 50A per pack sounds great- one pack could become faulted, and you'd still have ample current from the 'good' pack to ride safely. I wonder how similar this would be to 16X current consumption. I had done the math around it and was looking at a 50A BMS per side pack for mine. Quote Link to comment Share on other sites More sharing options...
RagingGrandpa Posted February 19, 2021 Share Posted February 19, 2021 16 hours ago, Brendan "nog3" Halliday said: 16X current consumption Kingsong packs have internal fuses already. 16x has 2x30A fuses (~60A effective) in each 20s3p pack. Quote Link to comment Share on other sites More sharing options...
btl Posted February 19, 2021 Author Share Posted February 19, 2021 Thanks you for your comments! So the MSX draws up to 50A (with peaks sligthly above that) in stillstand overpowering events. You both agree that those will be the most current the wheel will ever draw? What about landing with a slightly tilted backwards case (thus spinning backwards wheel) after some air time? I'd expect that shock to be even more... On the other hand, a 30A fuse in the 16x battery packs is nice to see. Maybe adding a 50A fuse to each pack of my wheel can ease my mind enough already. Are these two 15A fuses in parallel? I was about to add something like this to my MSX: https://www.ebay.de/itm/DC-10-50-100A-100V-LED-Voltmeter-Amperemeter-Spannungsmesser-Strommesser-Volt-DE/313411549863 But with your measurements in hand, that might be unnessecary. Quote Link to comment Share on other sites More sharing options...
RagingGrandpa Posted February 19, 2021 Share Posted February 19, 2021 (edited) 31 minutes ago, btl said: MSX draws up to 50A (with peaks sligthly above that) in stillstand overpowering events. ... most current the wheel will ever draw? Yes. The stall current (e.g.: stillstand) is the highest current a motor can ever accept. 31 minutes ago, btl said: What about landing after some air time? I agree that landing a jump could require a huge balancing force. But the limit is always there- the motor (and firmware) can only allow a certain maximum current. If that (50A) does not provide enough balancing force, balancing will be unsuccessful and the EUC will 'dip' / crash. This happens frequently when landing jumps, especially on skate park ramps (personal experience). 31 minutes ago, btl said: 30A fuse in the 16x battery packs is nice to see. Are these two 15A fuses in parallel? You misunderstood. Each KS-16X pack has two 30A fuses in parallel. Parallel fuses don't behave consistently, but the hope is that electric current will be shared evenly by the fuses, for a total rating of about 60A. (And because there are two packs in the 16X, this means >120A available to the motor controller. Far more than it could ever handle.) 31 minutes ago, btl said: Maybe adding a 50A fuse to each pack of my (MSX) can ease my mind enough already. Go for it! Edited February 19, 2021 by RagingGrandpa Quote Link to comment Share on other sites More sharing options...
meepmeepmayer Posted February 19, 2021 Share Posted February 19, 2021 On 2/17/2021 at 9:50 PM, btl said: Max. continous motor power is 2000W. This is just a motor characteristic. It tells you exactly nothing about what the battery does, or anything about any battery currents. It just means "we claim you can run this motor continuously with 2000W input without it overheating". Just saying because a lot of people treat motor power numbers like they mean something... - Also something that comes up with EUC BMSes: make sure it does not shut down on undervoltage (apparently, usually BMSes do that). You don't want to crash because a short spike causing a too low voltage. No undervoltage protection! 2 Quote Link to comment Share on other sites More sharing options...
Chriull Posted February 19, 2021 Share Posted February 19, 2021 10 minutes ago, meepmeepmayer said: Also something that comes up with EUC BMSes: make sure it does not shut down on undervoltage (apparently, usually BMSes do that). You don't want to crash because a short spike causing a too low voltage. No undervoltage protection! Great point! As almost every serious BMS has this protection included - just for EUCs after way too many faceplants it was canceled! Be sure the BMS is smart enough so this protection can be canceled. Quote Link to comment Share on other sites More sharing options...
btl Posted February 19, 2021 Author Share Posted February 19, 2021 Thanks a lot! Quote Link to comment Share on other sites More sharing options...
alcatraz Posted February 20, 2021 Share Posted February 20, 2021 (edited) Don't blow the fuse doing an emergency stop. I'm also interested in one of these smart bms retrofits. I don't want the output to be controlled by it. I just want it to take control of charging, balancing and monitoring. Throw in a few temperature sensors, a programmable crazy loud alarm, done. And it needs to be really compact so we can actually fit it inside most eucs. Programmable 90% charge limit. Deluxe version with heating element output for winter riding. Bluetooth. Decent balancing current. What a dream. It should probably be designed in two modules. This so that the "balancing module" can be replaced when it breaks. There are tons of bmss out there with broken balancing circuits. It might even be useful for scaling large and small packs alike. They just use different balancing modules. Edited February 20, 2021 by alcatraz Quote Link to comment Share on other sites More sharing options...
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