为什么直流电动机线圈中电流变而外部电路中电流却不变呢，换向器到底是怎样办到的啊？
推荐回答（3个）
电动机线圈每当跃过平衡位置时就改变电流方向的原因： 反证法：若不改变会怎样？线圈跃过平衡位置后受力方向不变却成了阻碍转动的力（力与转动方向反向）线圈最终返回到平衡位置摆几下后停下来。 为了使线圈转动能沿一个方向持续必须及时变阻力为动力！即改变磁力的方向，只改变电流方向的方案最好！.
对换向器的简单认识：结构上即两个铜（半）环，分别与线圈两端相连 故会随着线圈转动（隶属转子）；换向器外部搭着正负两个电刷A\B；半环中间绝缘（否则外部AB相连电源短路）；当转动时换向器内部的线圈两端不断改变着与之间接接接触的正负电刷AB 比如ab端一会与A电刷（负）接…一会又….
所以电流一会从ab边出来一会从ab边进去,即线圈中的电流方向发生了变化（注直流电动机外部电流方向不变）换向器把外部的直流电（由直流电源提供）变成线圈内部交流电
换向器功能： 把直流变交流（应用直流电动机） 也能把交流变直流（应用直流发电机）
希望你能明白
直流电动机中有几个线圈绕组!它几个绕组通过电刷或霍尔元件来转换线圈轮流接通电流，所以它线圈中的电流是有、无、有、无间断的，或：正、反、正、反方向的。而外面的电流是以一个方向向内部几个线圈供电的，所以它基本上是不变的，实际上在换向的瞬间是会有变化的，不过时间很短，且被外面的电容滤掉了。
利用电机旋转的惯性，换向器一会将正连接到L端、负连接到N、一会将正连接到N端，负连接到L端。
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