直流減速電機的功率，應根(gen)據出產機(ji)械(xie)所需求的功率來挑選(xuan)，盡量使電(dian)(dian)動機(ji)在額外負(fu)載下作業。挑選(xuan)時應留(liu)意以下兩(liang)點(dian)：如電(dian)(dian)動機(ji)功率選(xuan)得過(guo)小(xiao)．就會呈現(xian)“小(xiao)馬拉大車”表象，形成直流電(dian)(dian)機(ji)長時間過(guo)載．使其絕緣因發熱而損壞．乃至電(dian)(dian)動機(ji)被焚毀。

②假如直流電機功(gong)率(lv)(lv)選得過大．就會呈現“大馬拉小車”表象．其輸出機械功(gong)率(lv)(lv)不能(neng)得到充分利(li)用(yong)，功(gong)率(lv)(lv)因數和功(gong)率(lv)(lv)都不，不但對用(yong)戶和電網晦氣。并且還會形(xing)成電能(neng)浪費。

要準確挑選電動機的功率

此外(wai)．常用(yong)的是(shi)(shi)類(lei)(lei)推法來挑(tiao)選電動機的功率(lv)。所謂(wei)類(lei)(lei)推法。即是(shi)(shi)與相似出(chu)產機械所用(yong)直(zhi)流電機的功率(lv)進(jin)行比照。

具體(ti)做法是(shi)：了解本單(dan)位或附(fu)近其他單(dan)位的相似(si)出產(chan)機(ji)械(xie)運用多大功(gong)率的電動(dong)機(ji)，然(ran)后選(xuan)用附(fu)近功(gong)率的電動(dong)機(ji)進(jin)行試車(che)。試車(che)的意圖是(shi)驗證所選(xuan)電動(dong)機(ji)與出產(chan)機(ji)械(xie)是(shi)不是(shi)匹配。

驗證的(de)(de)辦法是：使電(dian)(dian)動機(ji)股動出產機(ji)械作(zuo)業(ye)，用(yong)鉗形電(dian)(dian)流(liu)(liu)表(biao)測(ce)量直流(liu)(liu)電(dian)(dian)機(ji)的(de)(de)作(zuo)業(ye)電(dian)(dian)流(liu)(liu)，將測(ce)得的(de)(de)電(dian)(dian)流(liu)(liu)與該電(dian)(dian)動機(ji)銘(ming)牌上(shang)(shang)標(biao)出的(de)(de)額外電(dian)(dian)流(liu)(liu)進行比照。假如(ru)電(dian)(dian)功機(ji)的(de)(de)實(shi)踐作(zuo)業(ye)電(dian)(dian)流(liu)(liu)與銘(ming)脾上(shang)(shang)標(biao)出的(de)(de)額外電(dian)(dian)流(liu)(liu)上(shang)(shang)下相(xiang)差不大．則標(biao)明所(suo)選電(dian)(dian)動機(ji)的(de)(de)功率(lv)

適宜(yi)。假如直(zhi)流電(dian)(dian)(dian)(dian)機(ji)(ji)(ji)的(de)(de)(de)實(shi)踐作(zuo)業電(dian)(dian)(dian)(dian)流比銘(ming)牌上標(biao)出(chu)的(de)(de)(de)額外(wai)電(dian)(dian)(dian)(dian)流低(di)擺(bai)布(bu)．則(ze)標(biao)明電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)(ji)的(de)(de)(de)功(gong)率(lv)(lv)選得(de)過大，應(ying)互(hu)(hu)換(huan)功(gong)率(lv)(lv)較(jiao)小的(de)(de)(de)電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)(ji)。假如測得(de)的(de)(de)(de)電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)(ji)作(zuo)業電(dian)(dian)(dian)(dian)流比銘(ming)牌上標(biao)出(chu)的(de)(de)(de)額外(wai)電(dian)(dian)(dian)(dian)流大以上．則(ze)標(biao)明電(dian)(dian)(dian)(dian)動(dong)(dong)(dong)機(ji)(ji)(ji)的(de)(de)(de)功(gong)率(lv)(lv)選得(de)過小，應(ying)互(hu)(hu)換(huan)功(gong)率(lv)(lv)較(jiao)大的(de)(de)(de)直(zhi)流電(dian)(dian)(dian)(dian)機(ji)(ji)(ji)。

實踐上應該是思考扭矩（轉(zhuan)矩），電機功率(lv)和轉(zhuan)矩是有(you)核算公式的。