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LTC4060 slow charge

Dear,

I want to build NiMH/NiCd battery charger for 3 cells series connected. I found LTC4060 but it allows fast charging only. My battery pack of NiCd batteries is 3.6V/800mAh. I want to charge it with 80 mA current, but I have read that –∆V termination doesn't work very well when the charge current is less than 0.5C. Should I use external NTC and other full battery termination method in this case, or you can recommended some other solutions?

Best regards

  • Hello,

    In general, slow charging NiCd cells makes termination a little more difficult.

    You are correct that –∆V termination is less reliable when charging slowly. Unfortunately, so is temperature-based termination. Your concern with –∆V termination may have come from this Battery University article, and there is some information there on why temperature-based termination is more difficult when slow-charging as well.

     

    You should employ a form of 'absolute' temperature termination where you terminate charging if the battery reaches a certain temperature. The dT/dt termination scheme described in the Battery University article may not work well at low charge rates and the LTC4060 does not offer this feature anyway.

     

    It can also help to reduce the charge voltage to ensure that the batteries do not get over-charged. Unfortunately, LTC4060 does not watch the charge voltage and only looks for –∆V, which may not work in your case.

     

    Furthermore, LTC4060 is not designed for fast charge currents <400mA. The 80mA that you want would essentially fall into 'fast charge' when using this part, because fast charging is a necessary phase of the LTC4060's charge cycle.

     

    All this seems to indicate that LTC4060 may not be the best part for the job if you want to charge at such a low current.

     

    LTC4079 is not specifically geared towards NiCd, but it could be made to work since it is flexible in terms of charge voltage, outputs current in your desired range, and still has temperature termination and and either C/10 or timer termination. Perhaps with a combination of all of these features, you can safely terminate charging of your NiCd batteries at the currents that you need.

     

     

    Regards,


    Zack

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