鎳鎘電池智能充電器的研制
蓄電池作為能量的(de)轉存(cun)裝置或備用(yong)電源被廣泛地(di)應用于各種自動化(hua)設(she)備(bei)中(zhong)。使用普(pu)通的充電器對(dui)蓄電池充電容易發生過充電或充電不足的現象。過充電,可使蓄電池發熱,電解液失水;充電不足,可使蓄電池內化學反應不充分,并且長期充電不足會導致蓄電池容量下降。以上兩種情況都會降低蓄電池的使用壽命。由此可見,充電器性能的好壞直接影響到蓄電池的使用效果和使用壽命。本文采用恒流限壓、實時監測的智能控制充電方法設計了一種對講機所使用的8.41V3Ah的鎳鎘智能充電器一原理完全可設計出用于其他不同類型、不同容量的蓄電池的充電器。
1 鎳鎘電池的發(fa)展(zhan)及特(te)點
1899年(nian),Waldmar Jungner首先在開(kai)口型(xing)鎳(nie)鎘蓄電(dian)弛中(zhong)使用了鎳(nie)極板,同時,Thomos Edison發明了用于電動車(che)的(de)鎳(nie)鐵(tie)電池。但是.由(you)于(yu)當時這些堿性(xing)蓄(xu)電(dian)池(chi)的(de)(de)極板材料比其他蓄(xu)電(dian)池(chi)的(de)(de)材料貴(gui)得多,其實際應(ying)用受到了極大的(de)(de)限(xian)制。直到1932年,鎳(nie)鎘電池經(jing)歷了最重(zhong)要的(de)改進(jin):科學家在鎳(nie)電池中(zhong)開始(shi)使(shi)用活性(xing)物質。1947年,密封型鐮鎘電
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池研制(zhi)成功。
鎳鎘電池的特點是效率高、循環壽命長、能量密度大、體積小、重量輕、結構緊湊、不需要維護,因此在工業和消費產品中得到了廣泛應用。
2 鎳鎘(ge)電池的充(chong)電方式及(ji)充(chong)電特性曲線(xian)
充電器能否達到最佳充電效果由所選擇的充電方式和充電特性曲線共同決定。近年來,蓄電池充電器大致可以(yi)分(fen)為連續電(dian)流充電(dian)和脈沖電(dian)流充電(dian)兩(liang)大類。
連續(xu)電(dian)(dian)(dian)(dian)流(liu)(liu)充電(dian)(dian)(dian)(dian)因放電(dian)(dian)(dian)(dian)容量(liang)受到(dao)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)接受能(neng)力(li)(li)的(de)限制和(he)受到(dao)在(zai)充電(dian)(dian)(dian)(dian)過(guo)程中電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)極化所(suo)產生氣(qi)體的(de)阻(zu)力(li)(li),使得在(zai)大(da)電(dian)(dian)(dian)(dian)流(liu)(liu)充電(dian)(dian)(dian)(dian)的(de)情況下(xia),電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)放電(dian)(dian)(dian)(dian)容量(liang)下(xia)降和(he)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)發(fa)熱;若用(yong)小電(dian)(dian)(dian)(dian)流(liu)(liu)充電(dian)(dian)(dian)(dian),雖可克服這個缺點,但充電(dian)(dian)(dian)(dian)時間過(guo)長。
脈(mo)(mo)沖(chong)電(dian)(dian)(dian)(dian)(dian)(dian)流充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)在充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)過程中是(shi)(shi)斷(duan)斷(duan)續(xu)(xu)續(xu)(xu)的(de)。采用這(zhe)種(zhong)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)方式可以提高電(dian)(dian)(dian)(dian)(dian)(dian)池的(de)接受能力(li)、消除(chu)電(dian)(dian)(dian)(dian)(dian)(dian)極化(hua)作用、縮短(duan)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時間(jian)、增大放電(dian)(dian)(dian)(dian)(dian)(dian)容量、減少電(dian)(dian)(dian)(dian)(dian)(dian)池發(fa)熱和提高充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)效率。但是(shi)(shi)目前的(de)脈(mo)(mo)沖(chong)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)器的(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)脈(mo)(mo)沖(chong)寬度(du)和間(jian)歇(xie)時間(jian)都是(shi)(shi)固定的(de),不(bu)能根據(ju)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)狀(zhuang)態改變充(chong)(chong)、放電(dian)(dian)(dian)(dian)(dian)(dian)的(de)時間(jian)參數以及適應快速充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)的(de)要求(qiu),因此充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)效果受到(dao)了限制。
結合以上兩點,本設(she)計采用了(le)一(yi)種更好、更優化的充(chong)電(dian)方式(shi),即恒流限壓與實(shi)時監(jian)測的智能控制(zhi)充(chong)電(dian)方式(shi)。該充(chong)電(dian)方式(shi)對主回路(lu)開關電(dian)源進行數字控制輸出(chu)電(dian)壓和電(dian)流。
鎳鎘(ge)電(dian)池充(chong)電(dian)特性曲(qu)線如圖1所示。當恒定電流(liu)充(chong)入剛放完(wan)電的電池時,由于電池內阻產生壓降,電池電壓很快上升至A點(dian)。此后,電池(chi)開始接(jie)受電荷,電池(chi)電壓以較低的(de)速率(lv)持(chi)續上升。在(zai)AB之間,電化(hua)學反應(ying)以一定(ding)的(de)速率產生氧(yang)氣(qi)(qi),同時(shi)氧(yang)氣(qi)(qi)也以同樣(yang)的(de)速率與氫(qing)氣(qi)(qi)化(hua)臺,使電池內部的(de)溫度和氣(qi)(qi)體壓力都很低。經過一定(ding)時(shi)間至C點,電解(jie)液中開(kai)始(shi)產生氣(qi)泡,這些氣(qi)泡聚集在極板(ban)表面(mian),使(shi)極板(ban)的(de)有效面(mian)積減小(xiao),電池的(de)內(nei)阻抗增(zeng)加。電池電壓開(kai)始(shi)較快(kuai)上升。這是(shi)接近充足電的(de)信號。
充足電(dian)(dian)(dian)(dian)(dian)后,充入電(dian)(dian)(dian)(dian)(dian)池的(de)電(dian)(dian)(dian)(dian)(dian)流不是(shi)轉換為電(dian)(dian)(dian)(dian)(dian)池的(de)儲能(neng),而(er)是(shi)在正極板上(shang)產生氧(yang)(yang)氣超(chao)電(dian)(dian)(dian)(dian)(dian)位。氧(yang)(yang)氣是(shi)由氫(qing)氧(yang)(yang)化(hua)鉀和水組(zu)成(cheng)的(de)電(dian)(dian)(dian)(dian)(dian)解液電(dian)(dian)(dian)(dian)(dian)解而(er)產生的(de),不是(shi)由氫(qing)氧(yang)(yang)化(hua)鎘(ge)還原為鎘(ge)而(er)產生的(de)。由于從大(da)量的(de)氫(qing)氧(yang)(yang)離子中比(bi)從很少的(de)氫(qing)氧(yang)(yang)化(hua)鎘(ge)中更容易分解出氧(yang)(yang)氣,所以(yi)電(dian)(dian)(dian)(dian)(dian)池內(nei)的(de)溫(wen)度急劇上(shang)升,使得(de)電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓(ya)下降。因此電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓(ya)曲線出現峰(feng)值D點。電(dian)(dian)解液(ye)中,氧(yang)氣的(de)產生和復合是放熱反應,電(dian)(dian)池過(guo)充電(dian)(dian)即E點,不停地(di)產生氧氣,從而使電池內的溫度(du)和(he)壓力(li)升高。
3 硬(ying)件電路
該(gai)智能充(chong)電器采用(yong)單片機AT89C2051進(jin)行控(kong)制,使(shi)用了開關電源及A/D、D/A等技術(shu)。實(shi)現了鎳鎘電池(chi)的智能充電。其硬(ying)件電路如圖2所(suo)示,整個電路(lu)分為開(kai)關電源部(bu)分和以單片機為主的控制(zhi)電路(lu)部(bu)分。
此開(kai)關(guan)電源屬(shu)于復合式(shi)開(kai)關(guan)電源,采用(yong)TL431的(de)精密基準和PC817組成(cheng)反饋(kui)電(dian)路(lu)。整(zheng)個工作過程:交流輸入經濾波、整(zheng)流后(hou)成(cheng)為直(zhi)流高壓,再由功率開(kai)關管斬(zhan)波、高頻(pin)變壓器降壓后得到高頻矩形(xing)波電壓,最后經過輸(shu)出整流濾(lv)波器,獲得所需要的直流輸(shu)出電壓。此(ci)開關電源達到了:交(jiao)流輸(shu)入電壓范圍為90~270V,能同時輸出(chu)+5V(作(zuo)為控制部分(fen)電(dian)源(yuan))及4.4~11.3V(主回路)的電(dian)壓,輸出電(dian)流為1A。其電路如圖3所示。
控制(zhi)電路部分主要(yao)由(you)AT89C2051、ADC TLC0832、運放(fang)LM358及數字電位(wei)器X9C102、分壓(ya)電阻、電流采樣電阻組(zu)成。單片機(ji)對(dui)正在充電的電池進行實時電壓、電流取樣(yang),經A/D轉換后(hou)輸入單(dan)(dan)片(pian)機。單(dan)(dan)片(pian)機根據電(dian)池不同(tong)的充電(dian)狀態采取不同(tong)的充電(dian)算法,通過數字電位器對開關電源的輸出(chu)電壓進行控制(zhi),通過(guo)改變電池組端電(dian)壓來達(da)到(dao)控制(zhi)充(chong)電(dian)過程的目(mu)的。
電(dian)(dian)(dian)(dian)路接(jie)上蓄電(dian)(dian)(dian)(dian)池后,充電(dian)(dian)(dian)(dian)過程開始,當檢(jian)測(ce)到(dao)電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓(ya)在正常范(fan)圍內時(shi),充電(dian)(dian)(dian)(dian)器軟啟動(dong),充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓(ya)、電(dian)(dian)(dian)(dian)流(liu)逐漸增加到(dao)額定恒定充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu)值,進(jin)行恒流(liu)充電(dian)(dian)(dian)(dian),“正充電”LED燈閃爍(shuo),同時開始計(ji)時。此(ci)后不(bu)斷檢(jian)測電(dian)(dian)池電(dian)(dian)壓,當電(dian)(dian)池電(dian)(dian)壓大于或達到規定的最大值(該電(dian)池規(gui)定(ding)的最大值為10.5V)或充電時間等于5小(xiao)時后(hou),單片機(ji)發出(chu)指令,減小(xiao)數控輸出(chu)值大小(xiao),使充電電流(liu)減小(xiao),轉為涓流(liu)充電(0.1A),“已(yi)充滿”LED指示燈(deng)亮。這(zhe)樣就避免了因(yin)電(dian)池(chi)溫升過(guo)快(kuai)或嚴重極化,影響充電(dian)質量(liang)、降(jiang)低(di)蓄電(dian)池(chi)的使用(yong)壽命甚至產生事故,從而快(kuai)速、安全、高質量(liang)地完成充電(dian)過(guo)程。
4 軟件智(zhi)能控制
在程序(xu)的初(chu)始階段(duan)首先應(ying)對(dui)單片機進行初(chu)始化,然(ran)后判斷電(dian)(dian)池是否連接正確,根據電(dian)(dian)池電(dian)(dian)壓判斷應(ying)該進入哪(na)一(yi)個(ge)充(chong)電(dian)(dian)階段(duan),即恒(heng)
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流(liu)或者涓(juan)流(liu)充電(dian)方式。恒流(liu)方式:不斷檢(jian)測流(liu)過電(dian)池(chi)的電(dian)流(liu)是否達到(dao)恒定電(dian)流(liu)(1A),如果小于lA則抬高電(dian)池兩端(duan)的電(dian)壓使之達(da)到lA(在電(dian)池兩端電(dian)壓(ya)小于電(dian)池的最(zui)大充(chong)電(dian)電(dian)壓(ya)10.5V的前(qian)提下)。涓流(liu)方式(shi):在電(dian)(dian)池(chi)兩端電(dian)(dian)壓(ya)達到最大值后進入涓流(liu)充電(dian)(dian)模式(shi)。程(cheng)序(xu)結構(gou)圖如圖4所示。
本文(wen)提出一種(zhong)恒流限壓、智能(neng)控(kong)制的充(chong)(chong)電(dian)(dian)(dian)(dian)方(fang)案,能(neng)很好地解決鎳鎘蓄電(dian)(dian)(dian)(dian)池(chi)組(zu)在充(chong)(chong)電(dian)(dian)(dian)(dian)過程(cheng)中存在的過充(chong)(chong)電(dian)(dian)(dian)(dian)、充(chong)(chong)電(dian)(dian)(dian)(dian)不(bu)足、發熱等問題。該充(chong)(chong)電(dian)(dian)(dian)(dian)器(qi)已批量生產(chan)并投入使用,效果令人滿意(yi)。同(tong)時(shi),在已有的基(ji)礎上(shang)針(zhen)對不(bu)同(tong)種(zhong)類的電(dian)(dian)(dian)(dian)池(chi),只要根據不(bu)同(tong)電(dian)(dian)(dian)(dian)池(chi)的最佳(jia)充(chong)(chong)電(dian)(dian)(dian)(dian)曲線對控(kong)制器(qi)中的程(cheng)序(xu)進行相應(ying)的調整,就(jiu)能(neng)對不(bu)同(tong)類型的電(dian)(dian)(dian)(dian)池(chi)進行充(chong)(chong)電(dian)(dian)(dian)(dian)。