從再生(sheng)能(neng)源（如光電池(chi)面板或風力(li)發(fa)電機）接收能(neng)量(liang)(liang)的(de)(de)系統(tong)一般會將能(neng)量(liang)(liang)保(bao)存在可(ke)充電電池(chi)中,再提(ti)供(gong)給負載(zai)(zai)。通常情(qing)況下,兩個過程是(shi)同時發(fa)生(sheng)的(de)(de)。對電池(chi)剩余(yu)電量(liang)(liang)的(de)(de)周(zhou)期性評估(gu)可(ke)以保(bao)證延長(chang)電池(chi)的(de)(de)性能(neng)和壽命,同時控制(zhi)電池(chi)供(gong)給負載(zai)(zai)的(de)(de)電流。電池(chi)的(de)(de)剩余(yu)電量(liang)(liang)包(bao)括(kuo)前次計算的(de)(de)充電量(liang)(liang),加上(shang)新增電量(liang)(liang),或者減去消耗的(de)(de)電量(liang)(liang)。根據Coulomb定(ding)律,可(ke)以用(yong)下式計算出累積充電量(liang)(liang)：

　　其中QACC是電池(chi)最新的累(lei)積電量,i表(biao)示在時(shi)間間隔Δt期(qi)間累(lei)積的電流量。

　　在不連(lian)續的(de)情況下(xia),該式(shi)變成

　　其中n表示在(zai)時(shi)間間隔(ge)Δt內電流(liu)Ik的(de)測量次(ci)數。雖然Δt值可以任意選(xuan)擇,但選(xuan)等于一小(xiao)時(shi)的(de)值比較方(fang)便,因為電池制造商標定容(rong)量的(de)單(dan)位是安培小(xiao)時(shi)。

　　為(wei)了簡化(hua)微控制器的硬件(jian),降低(di)算(suan)術(shu)運算(suan)所需(xu)內存數(shu)量(liang),可以(yi)將1小(xiao)時劃分為(wei)128個測量(liang)周期(qi),并用寄(ji)存器移位方(fang)法完成(cheng)公式中(zhong)所需(xu)的分割。可以(yi)從32個電(dian)(dian)(dian)(dian)(dian)流(liu)采樣取(qu)平均值(zhi)作為(wei)每(mei)次充(chong)電(dian)(dian)(dian)(dian)(dian)測量(liang)值(zhi),采樣值(zhi)經微處理器內部ADC轉(zhuan)(zhuan)換(huan)。一個ADC的輸(shu)入(ru)通道用于轉(zhuan)(zhuan)換(huan)充(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu),另一個ADC用于轉(zhuan)(zhuan)換(huan)放電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)。因此,剩(sheng)余電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)量(liang)的公式就簡化(hua)為(wei) QREM=QPREV±QACC,其中(zhong)QREM 是(shi)(shi)剩(sheng)余電(dian)(dian)(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)(dian)(dian)量(liang),QPREV是(shi)(shi)前次計算(suan)的充(chong)電(dian)(dian)(dian)(dian)(dian)量(liang),加號表明(ming)是(shi)(shi)凈充(chong)電(dian)(dian)(dian)(dian)(dian),而減號則(ze)表明(ming)是(shi)(shi)凈放電(dian)(dian)(dian)(dian)(dian)。

　　如圖1所(suo)示,電(dian)(dian)(dian)路(lu)包括一個(ge)8腳的(de)(de)(de)飛思卡爾(Freescale)公(gong)司低(di)成(cheng)本MC68HC908QT2微控制器(qi)(qi)IC3。電(dian)(dian)(dian)流(liu)采樣電(dian)(dian)(dian)阻(zu)R1兩端的(de)(de)(de)電(dian)(dian)(dian)壓會(hui)根據電(dian)(dian)(dian)池充電(dian)(dian)(dian)還是放(fang)電(dian)(dian)(dian)而(er)轉換極性(xing)。IC2A和IC2B分別(bie)接(jie)(jie)成(cheng)相(xiang)同(tong)增益的(de)(de)(de)非反相(xiang)和反相(xiang)放(fang)大器(qi)(qi),用(yong)于檢測R1兩端的(de)(de)(de)電(dian)(dian)(dian)壓。非反相(xiang)放(fang)大器(qi)(qi)IC2A只響應(ying)充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)產生(sheng)的(de)(de)(de)正向電(dian)(dian)(dian)壓,而(er)對放(fang)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)產生(sheng)的(de)(de)(de)負輸入(ru)(ru)電(dian)(dian)(dian)壓則提(ti)供(gong)零輸出。反相(xiang)放(fang)大器(qi)(qi)IC2B則只響應(ying)負輸入(ru)(ru),而(er)對正充電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)提(ti)供(gong)0V。兩個(ge)運放(fang)的(de)(de)(de)輸出都是正的(de)(de)(de),范圍從(cong)0 V至約5V,從(cong)而(er)簡化了與(yu)ADC多路(lu)輸入(ru)(ru)的(de)(de)(de)接(jie)(jie)口設計(ji)。IC2采用(yong)德州(zhou)儀(yi)器(qi)(qi)(Texas Instruments)公(gong)司的(de)(de)(de)TLC277,它(ta)的(de)(de)(de)優(you)點是占(zhan)用(yong)印制電(dian)(dian)(dian)路(lu)板(ban)面積小,并有低(di)的(de)(de)(de)輸入(ru)(ru)失調(diao)電(dian)(dian)(dian)壓。

　　確定了最低、最高期望的充、放電電流后,就可以計算出檢測電阻R₁的值(zhi)和放大器增益G,公式(shi)如下：

　　其中I_MAX是最大放電電流,V_IN(MAX)是最大ADC輸入。在本例中,最大充、放電電流均約為1A。

　　因此,對1A充電或放電電流和最大ADC輸入為5V時,可以選擇0.5Ω的R₁,增益為10或100。一旦計算出了電池的充電能力,就可以通過單線接口SIP、I²C、CAN（控制器局域網絡）或其它工業標準方法,將數據發送給主控處理器或其它目標（參考文獻1）。為使電池壽命最長,可以用微處理器的輸出來控制外部負載吸入的電流。

　　制造商一般交付充滿電的鉛酸電池,這是為了防止出現硫酸鉛沉淀問題,本設計假定一塊電池開始時處于滿充電狀態。如要將此電路用于鉛酸電池以外的其它化學性質電池,必須修改電池最大可充能量值(zhi),該值(zhi)保存在一個專用的硬件寄存器內。