充電時,鉛酸蓄電池充電器的參數指標
-
電動車鉛酸蓄電池組充電時，有幾個關鍵參數：最高充電電壓、浮充電壓、浮充轉換電流、最大充電電流。它們應該是多少？如何制定？其中最主要的是最高充電電壓，多少為好？與析氣量、充入電容量和環境溫度又是什么關系？對此眾說不一，各電池生產廠家的要求也不一樣。最高充電電壓值相對誤差范圍是多少？我們不能脫離實際的工作對象，盲目制定出超常規的精度要求。我們接到某電動車售后服務部通知：充電器比(bi)規定(ding)(ding)電壓高(gao)0.1V，電池(chi)因此熱失控(kong)而充(chong)脹了；也(ye)接到通(tong)知說：電壓比(bi)規定(ding)(ding)定(ding)(ding)低0.1V，電池(chi)欠(qian)充(chong)，提前報廢。一個千分之(zhi)幾的(de)誤(wu)差造成如此嚴重后果(guo)，真(zhen)是失之(zhi)毫厘，謬之(zhi)千里之(zhi)外，鉛酸蓄電池(chi)果(guo)真(zhen)有這么(me)神秘嗎？為了解(jie)開困擾電動車充(chong)電中的(de)這個謎團，做如下實驗。
用(yong)一個(ge)水(shui)槽盛滿水(shui)，電(dian)(dian)池(chi)放在(zai)水(shui)中，在(zai)電(dian)(dian)池(chi)上方有(you)一個(ge)收集(ji)氣(qi)體用(yong)的倒(dao)扣的漏斗(dou)，漏斗(dou)頂端裝有(you)可(ke)以計量氣(qi)體容量的注(zhu)射針筒(tong)。充(chong)電(dian)(dian)用(yong)可(ke)調(diao)穩(wen)壓(ya)(ya)電(dian)(dian)源，用(yong)兩只(zhi)四位半數字萬用(yong)表測量充(chong)電(dian)(dian)電(dian)(dian)流(liu)和充(chong)電(dian)(dian)電(dian)(dian)壓(ya)(ya)。
試驗(yan)時間(jian)是(shi)在冬季，水溫5℃。實驗(yan)條(tiao)件是(shi)統一用(yong)2A電(dian)流(liu)充(chong)(chong)電(dian)，最充(chong)(chong)電(dian)電(dian)壓分別用(yong)43V、44V、45V輪循環依次(ci)進行(xing)，浮(fu)充(chong)(chong)轉換(huan)電(dian)流(liu)一律400mA，記(ji)錄下每次(ci)的(de)充(chong)(chong)電(dian)時間(jian)，包括充(chong)(chong)電(dian)末期(qi)隨時間(jian)電(dian)流(liu)下降各點數據、開始析氣電(dian)壓，按時間(jian)記(ji)錄析氣量(liang)。電(dian)池(chi)充(chong)(chong)完后，用(yong)萬分之(zhi)幾精度(du)的(de)電(dian)量(liang)臺記(ji)錄放電(dian)容量(liang)。充(chong)(chong)入電(dian)量(liang)是(shi)在計算紙(zhi)上讀出時間(jian)電(dian)流(liu)曲線與(yu)坐標之(zhi)間(jian)的(de)面積（電(dian)容量(liang)就是(shi)充(chong)(chong)電(dian)電(dian)流(liu)對時間(jian)的(de)定積分）。數據見下表(biao)：
充號
最高(gao)電(dian)壓(ya)
V
充電電流
A
浮充電壓V
切換電流A
充入電量Ah
放出電(dian)量
Ah
析氣電壓
V
析氣量
mL
溫度℃
1
43
2
41.5
0.4
6.35
6.30
42.6
10
5
2
44
2
41.5
0.4
6.41
6.38
43.0
22
3
45
2
41.5
0.4
6.33
6.31
43.5
160
4
43
2
41.5
0.4
6.52
6.37
42.5
10
5
44
2
41.5
0.4
6.57
6.38
42.5
18
6
45
2
41.5
0.4
6.43
6.39
43
135
備注：該電池組30℃時，放電容量為10Ah。
得到(dao)(dao)試(shi)驗(yan)(yan)數(shu)據后，最感到(dao)(dao)驚異的(de)(de)(de)(de)是(shi)(shi)：充(chong)(chong)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)量(liang)的(de)(de)(de)(de)多(duo)少幾乎與充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)無關。很多(duo)人(ren)認(ren)為(wei)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)低(di)(di)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)會(hui)充(chong)(chong)不滿(man)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)會(hui)提前鹽化(hua)報廢，特別(bie)是(shi)(shi)在冬季(ji)氣溫(wen)較低(di)(di)的(de)(de)(de)(de)時候。而這次(ci)試(shi)驗(yan)(yan)正(zheng)好是(shi)(shi)在冬季(ji)，水溫(wen)只有5℃，試(shi)驗(yan)(yan)的(de)(de)(de)(de)中(zhong)心電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)值(zhi)是(shi)(shi)44V，上(shang)下(xia)偏(pian)差1V，相對誤差是(shi)(shi)2.3%。在用43V和(he)45V充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)情(qing)況下(xia)，充(chong)(chong)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)量(liang)和(he)放(fang)(fang)出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)量(liang)相差無幾，與大(da)(da)家公認(ren)的(de)(de)(de)(de)看(kan)法大(da)(da)相徑庭，試(shi)驗(yan)(yan)是(shi)(shi)用的(de)(de)(de)(de)同(tong)一組電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)，同(tong)樣的(de)(de)(de)(de)充(chong)(chong)、放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)條(tiao)件(jian)，輪番做同(tong)樣的(de)(de)(de)(de)測試(shi)，實(shi)驗(yan)(yan)數(shu)據重復(fu)同(tong)樣的(de)(de)(de)(de)規律(lv)，可排除偶(ou)然因素干擾，試(shi)驗(yan)(yan)數(shu)據是(shi)(shi)準確可信的(de)(de)(de)(de)。從電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)原理上(shang)看(kan)，只要充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)高(gao)于電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)端電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)，都會(hui)給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，一直到(dao)(dao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)中(zhong)的(de)(de)(de)(de)活(huo)性物質轉換完成(cheng)。充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)最高(gao)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)，也(ye)就(jiu)是(shi)(shi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)開始(shi)由(you)恒流(liu)區轉變到(dao)(dao)恒壓(ya)(ya)(ya)區，這種轉變是(shi)(shi)由(you)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)自(zi)身(shen)充(chong)(chong)入電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)量(liang)多(duo)少、活(huo)性物質反(fan)應了多(duo)少決(jue)定(ding)的(de)(de)(de)(de)，充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)的(de)(de)(de)(de)高(gao)低(di)(di)，僅是(shi)(shi)能進行電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)化(hua)學反(fan)應的(de)(de)(de)(de)條(tiao)件(jian)，只要高(gao)于電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)開路(lu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)就(jiu)會(hui)給電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，多(duo)少物質能參與反(fan)應由(you)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)自(zi)身(shen)決(jue)定(ding)。從這個思(si)路(lu)理解，就(jiu)不難(nan)得出，充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)高(gao)低(di)(di)對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)容量(liang)沒有多(duo)大(da)(da)影(ying)響。
電(dian)(dian)(dian)(dian)池(chi)在(zai)(zai)42.5V～43.5V時(shi)開始析(xi)(xi)氣(qi),而析(xi)(xi)氣(qi)的速度與充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓(ya)有關(guan)。到充電(dian)(dian)(dian)(dian)結束時(shi)，總(zong)析(xi)(xi)氣(qi)量與充電(dian)(dian)(dian)(dian)最(zui)高(gao)電(dian)(dian)(dian)(dian)壓(ya)有關(guan)，43V與45V總(zong)析(xi)(xi)氣(qi)量相差10位（注：以單格(ge)允許(xu)極限失(shi)水(shui)10克，18格(ge)相當240公升氣(qi)體，該電(dian)(dian)(dian)(dian)池(chi)45V時(shi)失(shi)水(shui)并不大）。 在(zai)(zai)充電(dian)(dian)(dian)(dian)末期(qi)電(dian)(dian)(dian)(dian)流下降(jiang)(jiang)區時(shi)，只要降(jiang)(jiang)低電(dian)(dian)(dian)(dian)壓(ya)到42.5V時(shi)，析(xi)(xi)氣(qi)立即停止，這時(shi)充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流稍小一點，還會依(yi)著原來的規律下降(jiang)(jiang)。
這里對浮充電壓、浮充電流討論一下。對于長期處于浮充狀態下的鉛酸電池組，如后備電源上用的等，對浮充電壓要求是嚴格的。據國處文獻，浮充電壓有-0.2%溫度系數，浮充電壓偏差太大會造成電池鹽化。而電動車用的電池屬循環使用，不是處于這種狀態，不應該用套用浮充狀態使用的條件，充電器設(she)定(ding)浮(fu)充(chong)(chong)(chong)的目的僅是免于充(chong)(chong)(chong)電(dian)末期大量(liang)析(xi)氣(qi)失(shi)水，只要把電(dian)壓降到(dao)析(xi)氣(qi)點電(dian)壓以下，但也不能低(di)于電(dian)池(chi)端電(dian)壓而停止向電(dian)池(chi)充(chong)(chong)(chong)電(dian)。前面說過，在(zai)浮(fu)充(chong)(chong)(chong)電(dian)壓下，充(chong)(chong)(chong)電(dian)電(dian)流的走(zou)勢基本還是依著原曲(qu)線下降，一般還補(bu)足5%的容量(liang)。所以浮(fu)充(chong)(chong)(chong)電(dian)壓應在(zai)的范(fan)圍是低(di)于析(xi)氣(qi)電(dian)壓（42.5V），高于電(dian)池(chi)充(chong)(chong)(chong)足電(dian)以后(hou)的開路端電(dian)壓（約(yue)40V）。
浮(fu)充(chong)(chong)轉(zhuan)換(huan)電(dian)(dian)流，只不(bu)(bu)過(guo)是選擇在充(chong)(chong)電(dian)(dian)末(mo)(mo)期電(dian)(dian)池(chi)(chi)活性物質反應(ying)接近尾聲，充(chong)(chong)電(dian)(dian)電(dian)(dian)流自動下降到(dao)某一(yi)點時，切換(huan)浮(fu)充(chong)(chong)電(dian)(dian)壓的(de)(de)(de)記(ji)號，不(bu)(bu)少人以(yi)為浮(fu)充(chong)(chong)電(dian)(dian)流高了(le)電(dian)(dian)池(chi)(chi)會(hui)充(chong)(chong)不(bu)(bu)滿(man)是概念(nian)不(bu)(bu)清，充(chong)(chong)電(dian)(dian)電(dian)(dian)壓只要高于(yu)(yu)電(dian)(dian)池(chi)(chi)端電(dian)(dian)壓，都(dou)會(hui)對電(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)，只不(bu)(bu)過(guo)有用(yong)戶看到(dao)指(zhi)示燈(deng)紅轉(zhuan)綠后(hou)提(ti)(ti)前(qian)去(qu)用(yong)電(dian)(dian)池(chi)(chi)，這種(zhong)情況是不(bu)(bu)多的(de)(de)(de)，一(yi)般(ban)都(dou)是夜(ye)間充(chong)(chong)電(dian)(dian)，到(dao)早晨綠燈(deng)已(yi)亮了(le)多時。有的(de)(de)(de)廠(chang)家(jia)使用(yong)說明書上(shang)提(ti)(ti)醒用(yong)戶，在轉(zhuan)綠燈(deng)后(hou)繼續充(chong)(chong)電(dian)(dian)2小時，是很(hen)好很(hen)正確的(de)(de)(de)。所(suo)以(yi)沒(mei)有必要刻意去(qu)追(zhui)求浮(fu)充(chong)(chong)轉(zhuan)換(huan)點的(de)(de)(de)高低，一(yi)般(ban)新電(dian)(dian)池(chi)(chi)末(mo)(mo)期電(dian)(dian)流約(yue)為50mA，失水以(yi)后(hou)，酸比增高，那時可(ke)達500 mA以(yi)上(shang)。從析氣(qi)速率與電(dian)(dian)壓的(de)(de)(de)關系上(shang)來看（上(shang)圖），早點脫離析氣(qi)區為好，一(yi)方(fang)(fang)面，一(yi)方(fang)(fang)面可(ke)以(yi)減(jian)少析氣(qi)量(liang)，另一(yi)方(fang)(fang)面，電(dian)(dian)池(chi)(chi)用(yong)了(le)一(yi)段時間，末(mo)(mo)期電(dian)(dian)流增高，但還能低于(yu)(yu)我們設(she)定的(de)(de)(de)轉(zhuan)換(huan)點電(dian)(dian)流，否則電(dian)(dian)池(chi)(chi)一(yi)直在最高電(dian)(dian)壓充(chong)(chong)電(dian)(dian)下，大量(liang)失水，引發熱控(kong)(kong)，充(chong)(chong)脹充(chong)(chong)壞電(dian)(dian)池(chi)(chi)。有人固執地強調，浮(fu)充(chong)(chong)轉(zhuan)換(huan)點高電(dian)(dian)池(chi)(chi)會(hui)欠充(chong)(chong)，前(qian)面已(yi)討論過(guo)，切換(huan)到(dao)浮(fu)充(chong)(chong)電(dian)(dian)壓后(hou)，不(bu)(bu)是停止充(chong)(chong)電(dian)(dian)了(le)，還會(hui)繼續對電(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)的(de)(de)(de)，轉(zhuan)換(huan)電(dian)(dian)流適當高一(yi)點有利于(yu)(yu)避免過(guo)分失水和熱失控(kong)(kong)。
至于充電電流的大小設定，先看一下電池制造廠家對10Ah（12Ah）吸附式小型密封電池對充電時的技術要求，通常規定充電速率不要大于0.3C，相當于4A電流，而充電器充(chong)電(dian)電(dian)流在(zai)2A左右，遠離(li)極限充(chong)電(dian)電(dian)流。