Electronics > Beginners

NiMH Battery Pack Substitution Effect on Charging Circuit

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drussell:

--- Quote from: Rick Law on October 31, 2018, 01:45:38 am ---A 2200mAH battery may draw too much charge current - more than the charger circuitry can handle.
--- End quote ---

:bullshit:

A completely discharged 600 mAh pack will look like a very low impedance load, just like a 2200 mAh pack will.  It is the charger that limits the current, not the battery pack.  Many simple chargers are just a resistor from a voltage slightly above the Ni-MH "full charge" voltage.  Other cheap ways of doing it are just something like a LM317.  Unlike Li-ion chargers, many Ni-MH non-rapid chargers don't even have any kind of management or sensing, they just leave the voltage on there but limited to a small enough current that they don't blow up the cell / pack.  These won't care about the capacity.  If it uses a real Ni-MH charger charger that senses charge termination, it won't care either unless they've intentionally put a timer on it or something, in which case you would need to start the charge cycle more than once to get it to full charge.  It is still not going to burn up the charger.

ogden:

--- Quote from: drussell on October 31, 2018, 12:08:21 am ---
--- Quote from: ogden on October 30, 2018, 08:06:31 pm ---
--- Quote from: mvs on October 30, 2018, 07:48:06 pm ---It is not so easy... Lower relative charge current may affect NiMh charge termination (Negative Delta-Voltage detection). Some charge controllers also limit charging time.

--- End quote ---

Right. Better use 1000mAh AAA. It's still 1.5x capacity and most likely current capability as well.

--- End quote ---

Why would 1000 mAh be okay but 2200 mAh not?

Can you provide an example of somewhere that this is actually an issue?

--- End quote ---

Sure. Issue can be way too long charging time for car with 4x bigger battery. 4x increased capacity will result in 4x longer charging time which for dumb 0.1C charger is... 40 hours ;)

drussell:

--- Quote from: ogden on October 31, 2018, 02:58:32 pm ---Sure. Issue can be way too long charging time for car with 4x bigger battery. 4x increased capacity will result in 4x longer charging time which for dumb 0.1C charger is... 40 hours ;)
--- End quote ---

Obviously if you triple or quadruple the battery pack capacity, the charge time is going to triple or quadruple accordingly.  That doesn't mean it is going to burst into flames and burn your house down.   :palm:

ogden:

--- Quote from: drussell on October 31, 2018, 03:47:58 pm ---Obviously if you triple or quadruple the battery pack capacity, the charge time is going to triple or quadruple accordingly.  That doesn't mean it is going to burst into flames and burn your house down.   :palm:

--- End quote ---

 :horse:

Perhaps for you only burned-down house is an issue, but for others quadrupled charging time could be as well.

edy:
Thanks for the help, yes I agree it could be an issue... I don't want to wait that long to charge the battery. I have another potential solution to bypass the need for using the internal charger which is designed for the 600mAh battery pack. That is, I could just charge the batteries by inserting them into an external charger and then putting them into a 4-battery holder that I use for the car. The external charger may be more rapid. But here is another solution where I don't have to remove and replace batteries each time.... Let me know what you think....

Another option that I was thinking is to use one of those 5V Li-Ion cell-phone power packs. The car takes 4.8V but if I feed it a 5V output from a Li-Ion cell-phone charger, will it really care? I could attach the cell-phone power pack to the car permanently and charge it up by plugging it to 5V USB input. The output of the cell-phone power pack would be going to the battery input for the car. The car would see 5V and should be able to draw enough current out of the power pack to operate (most of these cell-phone power ups output 1-2A). Basically, this bypasses the need for using the built-in charger for the car, and in any case I am going to another battery chemistry, and I would still have the convenience of just "plugging in" quickly a charger cable for the car (in this case, the cell-phone power pack input instead of the car charging input), and not have to be removing and installing rechargeable batteries each time.

Thoughts?

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