preventing accidental charging of alkaline batteries

[larryg]

Hi all,

I'm in the process of designing a battery powered device to be used in the car. The plan calls for rechargeable batteries with 12V from the car to provide charging. However, I would also like the option of using alkaline batteries. The problem arises if a customer has inserted alkalines in the device and connects the charger.

How can you determine what type of battery you have? I had thought about internal resistance since alkalines have a much higher impedance than NiMH or NiCD, but measuring the impedance doesn't seem trivial. I have seen some battery chargers on the market that determine the type of battery, but I'm not sure how they go about doing that. Perhaps they develop a quick charge-discharge profile?

Any thoughts? Thanks for all your inputs.

Regards,

Larry G

 

[itsmoked]

It is a subtle difference. I don't remember exactly but you check the voltage apply the charger for x seconds turn the charger off and check the battery. Alkali batteries respond differently than a NiMH or LIon battery. I will cogitate on this, maybe a neuron will fire and I can be more specific.

 

[sdmays]

If the number of batteries per device you are designing is constant (for example a design that runs off 4.8V from four rechargeable cells) you can determine what kind of cells are installed by looking at the battery voltage...Back to the example above:

4 X 1.5V (alkaline) = 6.0V
-as opposed to-
4 X 1.2(5)V (NiCd (NiMH)) = 4.8V

 

[larryg]

Sdmays,

Thanks for the feedback. I could see that working with fresh batteries. However, I think the larger problem will be as as such:

The customer will insert alkaline batteries in the unit and use it until they deplete. At which point, they will plug in the charger, forgetting that they used alkalines. Since NiCD and NiMH flat-discharge at around 1.2 volts and have a EOC of about 1V compared to an alkaline's EOC of about .8V, I don't think that method will be effective. Also, I have no control over when the customer plugs in his charger. The voltage could be anywhere between fresh and dead.

Thanks,

LarryG

 

[dwftx34]

The dual battery type devices i have. Use a propritary rechargable battery type but allow for alkalines with a secodary battery post which is not part of the charging circuit. I think many others have tried to over come this problem also and the trouble is making it idiot proof.
BTW the device is a Fluke Electrical Meter 860B

 

[VEBill]

There are also 'Rechargeable Alkalines' to consider...

Sounds like the simplest approach will be warning lables and clear instructions.