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Automatic Ni-MH battery charger woes
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VanMarco:
Hello. I built this pcb for this.

r6 and r7 are just bridges.
I have changed the pot to 10K because i dont have a 5K one, and replaced the 2.2k resistor with a 1k one, as this circuit was designed for lead acid, voltage didnt want to go to 5V to charge 4x AAA batteries. One thing happened. I connected the batteries and switched on, the led turned on briefly and then died. voltage at the batteries is 5V. I am not sure it is charging.
Did i break something>?
VanMarco:
well, batteries are technically charged, now i want to see how long they last.
Conrad Hoffman:
NiMH batteries really need several redundant systems to determine when to cut the charge. The voltage slope can be hard to detect, so it should be combined with a temperature sensor at a minimum. A timer is good, plus a total charge limit. That's why it's usually better to buy a decent unit. You can also charge at a lower rate for a specified time, so long as you don't let the battery stay on the charger after the time limit.
MarkF:

--- Quote from: VanMarco on February 02, 2020, 02:38:23 am ---Hello. I built this pcb for this.

--- End quote ---

Nice.
Here is the layout I did:




--- Quote from: Conrad Hoffman on February 02, 2020, 04:18:57 am ---NiMH batteries really need several redundant systems to determine when to cut the charge. The voltage slope can be hard to detect, so it should be combined with a temperature sensor at a minimum. A timer is good, plus a total charge limit. That's why it's usually better to buy a decent unit. You can also charge at a lower rate for a specified time, so long as you don't let the battery stay on the charger after the time limit.

--- End quote ---

The NiMH battery chargers are constant current sources that will (if the charging isn't terminated) will charge
the batteries to a voltage higher than their rating. (i.e. You don't set the voltage.) 
That is why they need to check the temperature and/or voltage drop to know when to stop charging.

This charger NEEDS to have it's charging voltage set at the batteries full voltage.  This will prevent over charging.
It will charge at the set constant current value until it nears completion. 
As it reaches the set voltage, the charging current will decease and stop when the set voltage is reached. 
(The LED goes out when charged.)

I believe the charging current is somewhat exponential.

Whether this is good or bad for a NiMH battery, I don't know.
VanMarco:
I think my cells are rubbish. You know those china batteries that come in bright attractive colour like redd, orange and have written on crazy values like 1,800mah and the like, and cost like 5 bucks for 16pcs? those. I think those are 130mAh each, or something along those lines. When i put 3 into a flashlight (led) they last around 15/20 mins or so. MarkF can you show me the underside of your circuit?
That's mine.

thanks
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