Ok, new thread. What is the ideal regen? I'll start with some thoughts. Here are two premises:
1. saftey is a major concern - there needs to be a reliable, automatic way to disengage regen during an emergency and let braking (or ABS) take over. 2. regen should account for 100% of the deceleration in other conditions (except when current to battery is too high or the battery is too full). Given that, I'd like to see: 1. When I let my foot off the accelerator, the speed should stay constant to the extent no power is applied to the motor. For example, if you are on the level, the car should simply coast. If going down hill, regen should engage to the extent necessary to not increase your speed. 2. When braking, regen should ideally apply 100%. However, if deceleration is greater than some threshold, regen starts smoothly blending with braking, one linearly increasing, one linearly decreasing until a 2nd threshold is reached. At that point, braking is 100% mechanical. A comment on #2. By using a deceleration measurement, one avoids triggering mechanical brakes while going down a steep hill. For example, the Leaf appears to use some sort of braking force as a threshold, which means the physical brakes seem to apply nearly 100% on grades over about 10%. Peri -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Buddy Mills Sent: 20 March, 2014 12:04 AM To: 'Electric Vehicle Discussion List' Subject: Re: [EVDL] Regen efficiency,was: How can regen be a reason to buy or not? So much math...it hurts my head. Regen good. It kicks in, the amp gauge goes positive. As for the setup; I have a switch on the dash. Position 1, it only works when the brake is applied. Second position. it work when I let off the accelerator. Third position it is turned off. I also have a disengage switch on the clutch to keep the motor from coming to a dead stop when it is working off the accelerator and trying to shift gears. And last but not least my BMS turns off regen if my SOC is above 80% as to not overcharge the battery pack. Buddy Mills [email protected] Look mom, no gas. http://www.evalbum.com/2887 Disclaimer: No animals were harmed or killed in the process of writing this email. Any stories to the contrary are, for the most part, either fictional or greatly exaggerated. Cor van de Water wrote: > you have a total efficiency of: > 90%(batt) x 95%(controller) x 85%(motor) x 90%(drivetrain) = 65% Excluding the battery efficiency for simplicity and considering the situation from the point of view of energy provided by or received by the battery: Consider a 1000kg (approx. 2200lb) vehicle travelling 50km/h (approx. 30mph); it has a kinetic energy of 96450.6J. Using your numbers above, 96450.6J/(0.95 x 0.85 x 0.90) = 132715J were provided by the battery to achieve this. Regenning to a complete stop provides 96450.6J * (0.95 x 0.85 x 0.90) = 70095.5J to the battery. So, (0.95 x 0.85 x0.90) = 72.7% of the available kinetic energy is provided to the battery, however only 70095.5J returned / 132715J consumed = 0.528, or 52.8% of the battery energy consumed in achieving that kinetic energy level is recovered. Joules aren't a unit that means a lot to some of us (though SI units are easy to work this example in ;^), so let's convert it to something more familiar: 1J = 1W-second, so 70095.5J = 19.47Wh. If we assume that you accelerate to 50km/h and then regen to a stop every 500m (so you start from a stop at 0m and are again stopped at 500m), then out of every 500m travelled you recover 19.47Wh. So, how much does this extend your range? If your vehicle consumes 200Wh/mi (=200Wh/1609m) at 50km/h, then every 500m you recover enough energy to travel a further 156.6m: 156.6m/500m = 31% increase in range. Another way to look at it is that accelerating to speed after the stop consumes 132715J from the battery; this is 36.86Wh, or enough energy to travel 296.6m at constant speed. So, regenning to a stop allows you to recover enough energy to travel another 156.6m, but avoiding the stop in the first place saves you enough energy to travel 296.6m further. Obviously, the shorter the distance between each start and stop, the greater the % range increase appears. How high can we push it? Let's assume it takes us 5s to accelerate to 30mph (50km/h) and 5s to regen back to a stop. Let's assume that we accelerate to speed and then immediately regen to a stop, and continuously repeat this pattern. During each acceleration we travel 34.7m and during each deceleration we travel another 34.7m. So, for every 69.4m travelled, we consume 132715J to accelerate, plus about 31055J (69.4m @ 200Wh/mi) = 163770J. We recover 70095.5J, which is enough to travel (70095.5/163770) = 42.8% further in this inefficient driving pattern. _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
