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| tom66:
--- Quote from: fourfathom on January 20, 2024, 07:41:55 pm --- --- Quote from: pickle9000 on January 20, 2024, 06:20:41 pm ---EV efficiency reduces component count not to mention regen. No transmission, There's a reason diesel electric locomotives and heavy equipment exist. --- End quote --- And that reason is torque at zero RPM. There are other reasons (on ships, for example) but torque and low-RPM capability are (I believe) the big reasons, not efficiency. --- End quote --- That and a very flat torque curve. The typical EV power/torque curve looks like constant torque up to something like 30 mph, then constant power after that. The power only ramps down when Vmax is hit - motor speed approaches limits or inverter cannot drive motor efficiently any faster. Some hybrids take advantage of this; my GTE would use the electric motor to flatten the ICE torque curve, resulting in (besides between gear shifts) a relatively constant 375Nm of torque at the gearbox input. ICE and EV motor are in parallel in that car, with a clutch to isolate the ICE when not in use, and with the gearbox after both. That meant it shifted gears in electric mode, one of the few EVs to do so. An ICE varies its torque as speeds increase until it hits peak torque-rpm (somewhere around 2500-3500 rpm, lower for diesel). Note that for EVs it can actually be beneficial to have a gearbox; Porsche's Taycan has a 2-speed auto for the rear motor, and the BMW i8 PHEV had something similar. It adds weight but lets you optimise the motor for a smaller operating range. Tesla take the approach of differential gearing, at low speeds the front motor is dominant, and high speeds the rear motor takes over, with each being tuned for different speeds of operation. This reduces complexity, but means they can never have both motors operating at high speeds, reducing power and changing stability, and they have to make the rear motor capable of propelling the car at Vmax (but that's really only relevant for track usage). --- Quote from: Siwastaja on January 20, 2024, 06:40:26 pm ---When capacity is defined as charge (coulombs, Ah), you get full capacity out even at -30degC, if you can accept using low discharge currents near end of the curve to prevent voltage sagging below the under-voltage lockout levels of the loads like the drive inverter - this is exactly why EVs start limiting power at the end of discharge, finally entering a limb mode: they are making sure you get pretty much every Coulomb out. Then again, when capacity is defined as energy capacity (Wh), then you have capacity loss which is actually equal to the efficiency loss. Note that even if the loss doubled per each 10degC (which isn't true, but it's in the same ballpark, so let's play along), it's totally different from remaining efficienc (or energy capacity) halving. This is elementary school math: when loss doubles 1% -> 2%, efficiency (and thus energy capacity) doesn't halve, but goes from 99% to 98%, a 1.01% difference, not 50% as jonpaul is saying. The percentage of jonpaul being wrong is then 4950.49504950...%, which doesn't much differ from his usual contributions. --- End quote --- The interesting thing about well made lithium-ion batteries is that they are very close 100% efficient when discharged slowly (C < 0.1). In fact, losses in the battery are bad, as they signal unwanted reactions are occurring, which reduces the cycle life of the cell. There is an excellent video on coulombic efficiency of lithium-ion batteries here. What's interesting is how bad the Nissan cells are in comparison to most other manufacturers. |
| nctnico:
--- Quote from: tom66 on January 20, 2024, 10:02:47 pm ---An ICE varies its torque as speeds increase until it hits peak torque-rpm (somewhere around 2500-3500 rpm, lower for diesel). --- End quote --- It is not that simple. It depends entirely on how the ICE is 'tuned' / configured. For example, most turbo-diesels have a flat torque / rpm graph right up to where maximum power begins because that gives the sensation of the strongest accelleration to the driver. Try to race somebody with a turbo diesel with a manual gear and you'll notice most people will shift up once the torque 'runs out'. But this is the spot where the engine starts to develop maximum power and shifting up takes the engine to an RPM range with less power output... so you'll see their car getting smaller in the rear view mirror while you are keeping your foot down and let the engine run in the maximum power rpm range. |
| David Hess:
--- Quote from: coppercone2 on January 20, 2024, 06:16:48 pm ---I think I notice it before too it feels like sometimes when the drill batteries get hot some power tools have a really heavy torque . Like when you run a small drill on overload with a big hole saw. jam jam jam but if you finally get it hot you get a hole same thing with my cutoff wheel tool, when its cold you can easily get a jammed blade. But keep trying and when the battery feels hot you can get through a plate thats buckling a little and pressing on the blade and being a PITA. It seems the hot batteries provide enough juice to keep the wheel spinning and grind away the slight deflection that crushes it. I think I notice it the most with a M12 power drill and the M12 cutoff wheel and the variable speed 20v dewalt deburring tool. Angle grinders running flap disks too but usually if you have skill you won't stall those or benefit from the lower ESR if you got the light touch with the grinder. But for hole saws and linear abrasive cutting the extra current makes or breaks the tool. You can't really use skill to overcome a problem like slight pressure from the deflection or just bulk friction from hole saws. That is usually a question of impossible fixturing or just plain luck. --- End quote --- I had problems with the brushed M12 drill being under powered for drilling holes for wiring, and the M12 brushless circular saw was almost useless with the smaller normal output batteries. In both cases I managed to overheat a battery without any apparent benefit from lower ESR. The larger and higher output M12 batteries improved on this of course, especially for the M12 brushless circular saw, and I ended up buying the M12 brushless drill just for more torque for drilling big holes. That Milwaukee released "high output" M12 batteries implies that they also eventually saw it as a limitation. I really like the M12 tools for their compact and light form factors but it came with performance limitations. |
| EEVblog:
--- Quote from: tom66 on January 20, 2024, 06:31:47 pm ---The issue with lithium ion batteries in low temperature is their open circuit voltage falls and ESR increases and so less capacity is usable under low temperatures, the car must ensure that the cell voltage does not fall below the critical level. The capacity is not lost - just inaccessible. This is why EVs appear to reduce in available range and many EVs expend energy on heating the battery up as it makes this capacity accessible once the battery has warmed up. The loss of range in EVs in low temperatures is principally due to the reduced efficiency of cabin heating, battery, and tyres, and for vehicles without a battery heater the reduction can be greater. Usually winter weather carries other factors like heavier wind and rain which impact efficiency too, but having a heatpump makes a huge difference, which is why the majority of EV models have a heatpump as at least an option now. --- End quote --- If you can endure the cold within the car (i.e. no heater) you could maybe eek out extra range my putting it in ECO mode and driving slowly and carefully, thus reducing the impact of increased ESR. Not generally a problem in Australia though of course. |
| coppercone2:
what is madness is the picture that you would see to show the gasoline production chain with a red gas can at the end. begin with a 1000 meter drilled bore, a oil well, a oil tanker, a refinery, a gasoline delivery truck, a gasoline station, finally the red can. Typical distance traveled (excluding the highly windy refinery plumbing) is at least 2000 miles. the production montage would have the world map with the red dashed line arrows on it ;D. Or a disturbingly long time lapse of the ship traveling across the god damn ocean. Maybe it even get attacked by houthi pirates. the tree burning generator is a highly optimized solution. Like damn when you build it you can even recharge the battery operated chain saws with it. practically a von numan machine. Where is that from, pandora? |
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