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Charging a Lifepo4 with an Lm2596 module
Tj80:
Hi,
I'm trying to build a project which includes a Lifepo4 battery to run a Wemos D1 Mini for many months using deep sleep. I also need a charger circuit to allow the battery to be charged when power is available.
I'm trying to use an LM2596 constant current module to do this, and although it charges the battery fine I am having trouble with the battery discharging through the LM2596 module at around 9mA when no power is being input.
I have tried putting a diode between the positive output of the LM2596 module and the battery positive and increasing the output voltage of the module to overcome the diode drop. This stops the discharge from the battery into the LM2596 module - but now the battery won't charge! Actually, it does charge - but only at 0.9mA compared to ~150mA at the current state of charge without the diode. I can't fathom out what's going on and why the simple addition of a forward biased diode is stopping the thing from working!
Any advice gratefully received!
Many thanks,
Tim
bin_liu:
LM2596 is constant voltage module,you need CC and CV circuits.
LM2596 can be completed with LM358. . .
Tj80:
Hi,
Thanks for the reply. The module I'm using is one of the commonly available CC and CV ones - same as this:
https://www.ebay.co.uk/itm/292139967286
I have set a 500ma current limit and 3.6v constant voltage, this all works fine to charge the battery without the diode but not with.
I'm wondering if the forward biased resistance of the diode is high enough to affect it?
Many thanks,
Tim
bin_liu:
The voltage setting is wrong. When the battery is not connected, it should be 4.2V. If a diode is connected to the output, must be 4.2V+VF.
NiHaoMike:
--- Quote from: bin_liu on August 18, 2020, 12:54:50 am ---The voltage setting is wrong. When the battery is not connected, it should be 4.2V. If a diode is connected to the output, must be 4.2V+VF.
--- End quote ---
LiFePO4 is only 3.6V fully charged. I actually recommend 3.45V since the extra charge you can get going to 3.6V is especially small with LiFePO4 but keeping the charge voltage lower increases service lifetime.
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