Electronics > Projects, Designs, and Technical Stuff
Looking to (re)build a circuit to discharge my lipo batteries to like 3.9-3.7
not1xor1:
--- Quote from: magic on December 31, 2019, 08:34:42 am ---They claim 500mW discharge power.
https://www.hobbyrc.co.uk/lipo-suction-4s-xt60
So I wasn't that far off but they also claim overtemperature protection so perhaps it's not TL431 after all. And 3.9V rather than 3.2V termination so I'm not sure how they are doing it with so few components. And low leakage.
Maybe OTP is a polymer fuse ::)
--- End quote ---
The resistors divider is calculated for 3.8V and in any case 4.2V * .1A = 420mW so just a minimal difference.
In any case I never pretended to exactly replicate that circuit.
BTW here is a new simplified version with just one BJT and 150mA of average discharge current. Due to the BJT saturation voltage the resistor value should be adjusted.
(The BJT may still be replaced by a P-MOSFET)
Siwastaja:
--- Quote from: not1xor1 on December 30, 2019, 04:44:42 pm ---Apart that you are re-quoting Siwastaja's plain nonsense,
--- End quote ---
Not nonsense - no capacity was originally defined, so it could be anything. I was thinking a pack somewhere around 10Ah, and discharging down to somewhere around 30-40%, this would be days. Your calculation also slightly increased the discharge current from the schematic you posted first.
Your calculation is correct with your assumptions. Increase the resistor divider values to further decrease quiescent current, and the circuit is fairly good for your example case.
gilligan:
Awesome stuff guys... I'm certainly learning things.
FYI, these are LI-PO batteries not LI-ION just for clarity sake in the need to properly store them at the proper voltage.
not1xor1:
--- Quote from: gilligan on December 31, 2019, 05:18:55 pm ---Awesome stuff guys... I'm certainly learning things.
FYI, these are LI-PO batteries not LI-ION just for clarity sake in the need to properly store them at the proper voltage.
--- End quote ---
to be sure you have to check the cell manufacturer datasheet
not1xor1:
--- Quote from: Siwastaja on December 31, 2019, 04:39:32 pm ---
--- Quote from: not1xor1 on December 30, 2019, 04:44:42 pm ---Apart that you are re-quoting Siwastaja's plain nonsense,
--- End quote ---
Not nonsense - no capacity was originally defined, so it could be anything. I was thinking a pack somewhere around 10Ah, and discharging down to somewhere around 30-40%, this would be days. Your calculation also slightly increased the discharge current from the schematic you posted first.
Your calculation is correct with your assumptions. Increase the resistor divider values to further decrease quiescent current, and the circuit is fairly good for your example case.
--- End quote ---
OK... I may have been too rude
please accept my apologies and ... BTW have a happy new year :)
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