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</TD> </TR> </TABLE>	 </DIV> 	 <DIV ID="centerDoc"> 		  		  		 <A HREF="/index.html"><IMG HEIGHT="29" WIDTH="251" SRC="/z/logosm.png" VSPACE="0" HSPACE="0" ALIGN="BOTTOM" BORDER="0" ALT="PowerStream Power supplies, battery chargers, batteries and packs, dc/dc converters, injection molding"></A>&nbsp;&nbsp;&nbsp;<a href="/cgi-powerstream/sb/order.cgi?storeid=*2094b0595d034953e3f31f4e68d1999fb64b&amp;function=show"><img class="shopcart" src="/z/cartgsss.png" alt="View Shopping Cart" width="50" height="50"></a><script src='https://www.google.com/recaptcha/api.js'></script>		<TABLE> 		  <TR VALIGN="TOP" ALIGN="LEFT"> 			 <TD HEIGHT="19"></TD> 			 <TD HEIGHT="19">November 17, 2017</TD> 			 <TD HEIGHT="19"></TD> 			 <TD WIDTH="148" ALIGN="LEFT" VALIGN="TOP" HEIGHT="19"></TD> 		  </TR> 		  <TR VALIGN="TOP" ALIGN="LEFT"> 			 <TD HEIGHT="87"></TD> 			 <TD> 				<H1>NiCad Battery Charging Basics</H1></TD> 			 <TD></TD> 			 <TD WIDTH="148" ROWSPAN="2" ALIGN="LEFT" VALIGN="TOP">				<A HREF="NiCad-NiMH-Catalog.htm"><IMG SRC="z/5730ss.jpg" BORDER="0"				ALT="Wall mount chargers 3 cell to 12 cell versions" WIDTH="118"				HEIGHT="93"></A> <BR> <A HREF="NiCad-NiMH-Catalog.htm">NiCad/NiMH charger				catalog page</A> </TD> 		  </TR> 		  <TR VALIGN="TOP" ALIGN="LEFT"> 			 <TD COLSPAN="3" HEIGHT="1"></TD> 		  </TR> 		  <TR VALIGN="TOP" ALIGN="LEFT"> 			 <TD></TD> 			 <TD WIDTH="561" COLSPAN="3" ALIGN="LEFT"> 				<H2 ALIGN="Left">NiCad (NiCd, Nickel Cadmium) Battery Charging</H2>								<H2 ALIGN="Left">Nickel Battery Charging Basics</H2> 				<P ALIGN="Left">NiCad and NiMH batteries are amongst the hardest				  batteries to charge. Whereas with lithium ion and lead acid batteries you can				  control overcharge by just setting a maximum charge voltage, the nickel based				  batteries don't have a "float charge" voltage. So the charging is based on				  forcing current through the battery. The voltage to do this is not fixed in				  stone like it is for the other batteries. </P> 				<P ALIGN="Left">This makes these cells and batteries especially				  difficult to charge in parallel. This is because you can't be sure that each				  cell or pack is the same impedance (or resistance), and so some will take more				  current than others <I>even when they are full.</I> This means that you need to				  use a separate charging circuit for each string in a parallel pack, or balance				  the current in some other way, for example by using resistors of such a				  resistance that it will dominate the current control. </P> 				<P ALIGN="Left"><FONT COLOR="#000000">The coulometric charging				  efficiency of nickel cadmium is about 83% for a fast (C/1 to C/0.24) charge,				  and 63% for a C/5 charge. This means that at C/1 you must put in 120 amp hours				  in for every 100 amp hours you get out. The slower you charge the worse this				  gets. At C/10 it is 55%, at C/20 it can get less than 50%. (These numbers are				  just to give you an idea, battery manufacturers differ).</FONT></P> 				<P ALIGN="Left"><FONT COLOR="#000000">When the charge is complete				  oxygen starts being generated at the nickel electrode. This oxygen diffuses				  through the separator and reacts with the cadmium electrode to form cadmium				  hydroxide. This causes a lowering of the cell voltage which can be used to				  detect the end of charge. This so-called minus delta V/ delta t bump that is				  indicative of end-of-charge is much less pronounced in NiMH than NiCad, and it				  is very temperature dependent. Many of the chargers listed here use a				  sophisticated algorithm that uses the -deltaV to accurately charge NiMH and				  NiCad packs <A				  HREF="NiCad-NiMH-Catalog.htm">/NiCad-NiMH-Catalog.htm</A></FONT></P> 				<P ALIGN="Left"><FONT COLOR="#000000">As the battery reaches				  end-of-charge oxygen starts to form at the electrodes, and be recombined at the				  catalyst. This new chemical reaction creates heat, which can be easily measured				  with a thermistor.. This is the safest way to detect end-of-charge during a				  fast charge. This method is often used with multi-cell packs and the 20, 30,				  and 40 cell pack chargers here use a thermistor				  <A HREF="NiCad-NiMH-Catalog.htm">/NiCad-NiMH-Catalog.htm</A></FONT></P> 				<P ALIGN="Left"><FONT COLOR="#000000">Nickel cadmium battery				  chargers should cut the charge off when the temperature exceeds the maximum				  charging temperature, typically 45 degrees C for a controlled fast charge, and				  50 degrees C for an overnight or fast charge.</FONT></P> 				<H2 ALIGN="Left">Overnight Battery Charging</H2> 				<P ALIGN="Left">The cheapest way to charge a nickel cadmium battery				  is to charge at C/10 (10% of the rated capacity per hour) for 16 hours.. So a				  100 mAH battery would be charged at 10 mA for 16 hours. This method does not				  require an end-of-charge sensor and ensures a full charge. Cells can be charged				  at this rate no matter what the initial state of charge is. The minimum voltage				  you need to get a full charge varies with temperature--at least 1.41 volts per				  cell at 20 degrees C. The best charging practice is to use a timer to prevent				  overcharging to continue past 16 hours. An example of this kind of charger is				  shown at <A HREF="Ni-6-200.htm">/Ni-6-200.htm</A> . This charger uses a				  microprocessor to report the state of charge via an LED as well as performing				  the timing function. </P> 				<H2 ALIGN="Left">Faster Charging</H2> 				<P ALIGN="Left"><FONT COLOR="#000000">Some nickel cadmium cells are				  designed to be "quick chargeable." This is just a timed charge at C/3 for 5				  hours, or C/5 for 8 hours. This is risky because the battery should be fully				  discharged before charging. If the battery still has 90% of its capacity when				  the timer starts you would have a good chance of venting the battery. One way				  to ensure this doesn't happen is to have the charger automatically discharge				  the battery to 1 volt per cell, then turn the charger on for 5 hours. The				  advantage of this method is to eliminate any chance of battery memory.				  PowerStream does not currently have such a charger, but the microprocessor				  board used in the C/10 charger <A				  HREF="NiMH-NiCad-solar-charge-controller.htm">/NiMH-NiCad-solar-charge-controller.htm</A>				  could easily be modified to do the discharge. A power dissipating package would				  be needed in order to dissipate the energy from a partially charged battery in				  a reasonable amount of time. </FONT></P> 				<H2 ALIGN="Left">Fastest Charging</H2> 				<P ALIGN="Left"><FONT COLOR="#000000">If a temperature or voltage				  monitor is used NiCad batteries can be charged at rates up to 1C (in other				  words 100% of the battery capacity in amp-hours for 1.5 hours). The PowerStream				  battery charge controller shown in <A HREF="Product3.htm">/product3.htm</A>				  does this, as does the battery management board shown in <A				  HREF="Product5.htm">/product5.htm.</A> </FONT></P>The termination can be done				with minus delta V, when the battery voltages drops -10 to -20 mV per cell. To				terminate the charge on temperature requires a temperature slope				measurement.<BR><BR>This board also has the ability to sense voltage and				current for more sophisticated algorithms required for ultra-fast charging.				These algorithms require constant monitoring of the voltage, temperature, and				sometimes pressure, to actively determine the amount of current a battery can				take without damage. This is sometimes called a smart charge, or a controlled				fast charge.<BR><BR>A cheaper version of the fast charger can be made by just				monitoring absolute temperature. The charge rate is set at C/2 until 45 degrees				C is reached, then switched over to a C/10 charge to complete the charge. This				is the most common NiCd fast charger of the 1960's through the 1980s because it				could be controlled by a simple bi-metallic thermostat switch mounted on the				battery.<BR><BR> 				<H2>Trickle Charging Nickel Batteries</H2><BR>In a standby mode you				might want to keep a nickel cadmium battery topped up without damaging the				battery. This can be done safely at a current of between 0.05 C and .06 C. The				voltage required for this is dependent on temperature, so be sure to regulate				the current in the charger.<BR> 				<P ALIGN="CENTER">Custom design and manufacture of state-of-the-art				  battery chargers, UPS, and power supplies for OEMs in a hurry!</P> </TD> 		  </TR> 		</TABLE> 		<DIV>  <TABLE BORDER="0" CELLSPACING="0" CELLPADDING="0"> <TR > <TD  COLSPAN="2"> </TD> </TR> <TR> <TD></TD> <TD > <P ><BR>  <A HREF="/index.html" TARGET="_top">[Home]</A>


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