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  1. H

    Field Weakening VS Gear Box VS Higher voltage battery

    Designing a motor with a characteristic current (current when shorted) to the nominal rating allows the controller to just short the motor terminals in a fault scenario. The issue bobc mentioned just goes to show that "converter fault --> all switches open" is not always the best assumption...
  2. H

    turnigy multistar lipo batteries, are they good?

    I purchased 3 of these. 1 was puffed, and then 1 cell died after I left it connected to a small load for a week. All other cells were fine. I'm split on buying a replacement, since it was ~$160 for 3 4s, 16Ah shipped. Now it will be ~$100 for a single replacement 4s, 16Ah. So, good? if...
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    features for 4,8, or 12S li-ion manager

    Hi everybody. I've been using my 12S balancing manager for a few weeks now on my 1kW e-bike, and I'm about to do another board spin. Does anyone have any request for features? Here's the quick pitch: It makes sure you don't over-charge or over-discharge any cell in the batch, and has some...
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    Taking Charge: Let's Develop the Products That We Want!

    I should specify that when i offered to develop products for the ES community, that it would be as a separate venture. My current employer is not currently in a position to serve the enthusiast community. Im guaging market needs. There are currently many electric cars and bikes on the market...
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    Taking Charge: Let's Develop the Products That We Want!

    Hi all, I wanted to bump this thread, since it's been a few years. I used to have some EV projects that centered around making items that weren't easily or cheaply sourced. I imagine many of the people here have similar issues. I currently work for a electric vehicle manufacturer, but I, and...
  6. H

    Electric Miata/MX5.

    Yeah, I'd like to know as well. Did the lipo's last at all?
  7. H

    ARPA-E LiteCar Challenge

    The deliverable is a 7 page explanation with designs and material lists. With the right people together, this could take a weekend.
  8. H

    Motorbike Motor

    I would suggest doing a 2-piece (T-style including one face and half the core) that can be more easily machined if you go away from the solid construction. This would allow you to wind the copper separately and then insert the half-cores into the form-wound coil. I think a lot of their value...
  9. H

    Advice requested YZ 250 motorcycle to electric

    It would help to know more about what you're expecting from the project in terms of performance, available budget, time to completion, among other things, but I see you need a proposal quick. For simplicity purposes, I'd suggest a DC motor (PERM, AGNI, E-TEK) and a Kelly controller. I'm sure...
  10. H

    Advice requested YZ 250 motorcycle to electric

    What are the goals of your project? How much time do you have? What is the experience level of you (and your team)?
  11. H

    1000kW DC powersupply - Help

    This is very interesting to see that even at 340A, it falls off quickly, but then rebounds to 4V, presumably where ~80% capacity can be extracted. When they say 'burst 90C', they really mean it. At 300A, I calculate with rough numbers for weight from a 3.5Ah pack on HK, that this cell only...
  12. H

    1000kW DC powersupply - Help

    A battery fab facility is a hard thing to start up, so that's likely why there are few boutique batteries out there. Although, if you can tell from the growth of the RC hobby, they are demanding better and more powerful batteries, particularly in the competition sector. When conducting a test...
  13. H

    1000kW DC powersupply - Help

    Do you have any data points you could throw out at us? I see the test from the SAFT cells got 14kW/kg at 20C initial temperature, but considering a 3S, 2600mAh LiPo, rated at 130C max, (229g), the power density is 16.4kW/kg NOT considering any internal resistance. If you figure they rate using...
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    1000kW DC powersupply - Help

    What happened to the SAFT 200-400C cells we were discussing or other similar pulse-power cells? LiveForPhysics brings up a good point about the 50% rule (peak power from a cell comes at or above 50% of the open-circuit terminal voltage). Also, thanks for the 70% (30% sag) rule-of-thumb. Maybe...
  15. H

    RC motors, efficiencies, gearboxes and more?

    most motors will have significantly more force pulling the rotor to contact the stator, rather than move parallel to it. Typically that factor is 3:1 or 10:1, so the mechanics of constraining the rotor and stator become significant. There are tricks to balance forces, like maintaining equal...
  16. H

    1000kW DC powersupply - Help

    I didn't say there wouldn't be a gear reduction. What I did say was that the motor(s) could be mounted longitudinally to avoid the need for a right-angle pinion gear and the losses that are associated with them. If there was room enough, a planetary set would be optimal, but it's not likely...
  17. H

    1000kW DC powersupply - Help

    Maybe you're not familiar with motor controllers these days, but current regulation is torque regulation, and with a properly designed motor controller, you can regulate torque 16000 times a second with ease, which is likely more than a hydraulic clutch actuator response rate. So... there's an...
  18. H

    1000kW DC powersupply - Help

    Thanks for the info. Why a clutch or a diff though? To say this would be purpose-built would be an understatement, so mounting the motor(s) transversely would be entirely possible.
  19. H

    1000kW DC powersupply - Help

    including transmission and fuel tank or no? Transmission (including clutch and gear reduction/differential) would probably be around 100kg Fuel tank would be around 15kg at least.
  20. H

    Field Weakening VS Gear Box VS Higher voltage battery

    Brushes, in and of themselves, are not horrible. They can be designed to last a while, and particularly for DC brushes, the commutator will be simply a smooth ring that can minimize wear and have minimal current passing through it. The tone of this conversation, though, is quite interesting...
  21. H

    1000kW DC powersupply - Help

    Using round figures, with 5.5MW needed at the top speed, this means that only 12-16MJ are needed, depending if the vehicle is running 1000' or 1/4 mile. I know it's counter-intuitive, but due to the short duration (4.4-6 seconds) and the triangular power curve (if using a controller), the...
  22. H

    1000kW DC powersupply - Help

    I like the ejector seat idea, and I don't want to be too much of an efficiency zealot for no reason, as this idea would technically work, but the simple matter of rejecting the heat from the clutch and the fact that double the energy would be necessary for the trip are two reasons I don't like...
  23. H

    RC motors, efficiencies, gearboxes and more?

    By gearing down to 40, meaning a higher ratio, should allow the use of less current to get the required torque for this example we are talking about here. The majority of the time the bike would be used below 20mph so im not sure core loss would be that large of a percentage drain on the...
  24. H

    1000kW DC powersupply - Help

    I don't think anyone said this would be easy, or even plausible at the end of the day. Entertaining to think about. Would you qualify this as less or more dangerous than TF dragsters through the various years in the past where many engines and parts exploded? I agree that arc flash is pretty...
  25. H

    1000kW DC powersupply - Help

    Maybe there is an assumption that it is above 20C? The single value of power density is a little silly considering it depends on temperature and state of charge, but it's been shown that higher temperatures decrease chemical impedance.
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