| Electronics > Projects, Designs, and Technical Stuff |
| Automatic Ni-MH battery charger woes |
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| Conrad Hoffman:
You need to set a higher voltage than "nominal" or the batteries will never be fully charged. The problem is, if you do that, you need those better methods of stopping the higher current charge. Or, you suffer with a longer charge time at lower current and rely on time, usually 16 hours or something. Modern NiMH is better at tolerating a trickle charge, but it still isn't recommended. No idea on the inexpensive batteries. The best seem to be the Eneloops, but they aren't cheap. OTOH, they don't self-discharge much over time, so you can use them in clocks, remotes and flashlights. I'm still using some ten year old "old tech" NiMH AA batteries in my electric tooth brush and they work well because I change them frequently; they don't have time to self-discharge before I run them down. The cells with a high leakage rate would be a bad choice in a flashlight because they'll be dead when you need it most. |
| MarkF:
--- Quote from: VanMarco on February 02, 2020, 10:48:55 am ---MarkF can you show me the underside of your circuit? That's mine. thanks --- End quote --- Here you go: |
| VanMarco:
it still puzzles me how is it possible that discharged batteries go in there and immediately voltage is the same as the charging voltage. Also is it normal that I get battery voltage on the DC input when the dc input is disconnected? |
| NiHaoMike:
--- Quote from: VanMarco on February 02, 2020, 04:40:41 pm ---it still puzzles me how is it possible that discharged batteries go in there and immediately voltage is the same as the charging voltage. --- End quote --- A lot of batteries have a "hysteresis" effect where the charging voltage is significantly more than the open circuit voltage. --- Quote ---Also is it normal that I get battery voltage on the DC input when the dc input is disconnected? --- End quote --- No, that means you forgot to include a blocking diode. |
| Buriedcode:
Using a CC/CV charger for NiMH is not a very good idea. The peak voltage per cell depends on the cell, and the charging current. Arbitrarily setting it to whatever voltage you feel like will mean either the cells don't get charged much at all, or worse, over charged, reducing their life, possibly damaging the cell. VanMarco: Please post a schematic of the charging circuit you are building/using/testing, along with the parts you used for it. A layout means nothing if we don't know what the circuit is or the values used. Some might be confused because you provided a link to one charger in the original post, but then said you had built a different one later on. |
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