I have been told that an EV may use 200wh per mile at a certain speeed and that that means the power needed to maintain that speed is 200w.
The above is in error; I will try to clarify.
First, assume that speed is 30 mph which will make arithmetic simpler. Getting a measure of the energy used in an hour will allow us to both determine average power and allow us to determine total distance that can be traveled on that energy. At 30mph, a car travels 30 miles in an hour. If each mile consumes 200wh, the total energy consumed in an hour is 30 x 200 = 6000 wh. If that 6000wh was consumed uniformly over the hour, power supplied during that hour was 6000 watts.
This is of interest because of a contention that playing a radio can significantly reduce EV range. The contention is that a radio can consume up to 1kw. AND that an EV might have it's motion powered by as little as 200 watts. That type of audio system requires additional amplifiers and speakers to consume that additional power. The practical upper limit for audio power is determined by the DC-DC converter that converts (typically) ~400vdc from the main/"traction" battery to "auxiliary battery" voltage of 12-14vdc. That level of audio power is possible. But, I contend that typical radio powers are 10-20 watts. Maybe 100-200 watts if played at max level.
So, according my my estimates, playing a radio at normal levels might reduce range by about 1/3 of 1%. That effect will lessen as speed and motive power increases. Increasing speed will increase the 6kw necessary to keep the car at a constant speed thereby lessening the fraction of total power consumed by a radio.
I don’t think that you’re going to change his mind, but I applaud your effort.
ReplyDeleteWhile there are car sound systems that draw considerably more than 1KW, that is the exception - by a massive margin. Your 10 to 20 watts is far more typical for most people. A few people might get into the 100 watt or so range, but even that will be rare.
ReplyDeleteJust as a reference, my son is into the really high power (massively loud) car sound competition. The really high end people in that world are running on the order of 50 KW. Ever wanted to know what 50KW of a 40 Hz tone sounds like in a car - go to one of their competitions (bring hearing protection).
If one is to get ~50kw out of an EV traction battery, another connection to that battery will be required. That is, in parallel to the existing DC-DC converter.
DeleteReading your older blog about micro-grid augmentation, with a link to https://www.travisllado.com/2019/05/tesla-model-3-stereo-part-9-summary-and.html
ReplyDeleteThe author reports his system in the Model 3 is drawing about 200 amps (protected by a 250 amp fuse)for good high volume audio. Drawing 200 amps from the 12 volt DC-DC converter for an hour would consume 2400 Wh. Using your number of 6000 Wh for the 30 miles, plus 2400 Wh for the Audio, yields only 60% of expected range. 40% of the power went into the audio system!
As usual, the logic of your argument escapes me. The debate is over whether a normal radio, played at normal volumnes (10-20 watts, maybe up to 100 watts) can significantly reduce the range of an EV.
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