HF NiMh batteries

[Donald]

Originally Posted By: eljefino
Originally Posted By: DBMaster
I found pretty much all rechargeable standard battery sizes to be of limited usefulness due to the 1.2 Volt issue. A standard AA is 1.5 volts. While a rechargeable AA may have more capacity, the item you are powering needs to be able to run effectively on 1.2V per cell rather than 1.5. For a lot of applications (my nose hair trimmer, for example) I have to toss the battery once it drops below 1.3 or 1,4 volts. The motor just can't spin fast enough with the lower voltage.


I wonder what the "under load" voltage of the half-dead alkalines were. NiMH has less internal resistance so they keep their open cell voltage better under load... short to say, they drop less, which helps with their lower starting point.

Though its more than plausible that a lot of stuff is designed around getting rechargeables, your robot nose picker excluded.

It might be a good idea to modify your robot nose picker to allow you to monitor the battery voltage while the robot is in motion.

 

[DBMaster]

Robot nose picker? Hmm. You guys laugh, but when I invent the thing and it makes me a millionaire we'll see who's laughing.

 

[JHZR2]

Originally Posted By: eljefino
Originally Posted By: DBMaster
I found pretty much all rechargeable standard battery sizes to be of limited usefulness due to the 1.2 Volt issue. A standard AA is 1.5 volts. While a rechargeable AA may have more capacity, the item you are powering needs to be able to run effectively on 1.2V per cell rather than 1.5. For a lot of applications (my nose hair trimmer, for example) I have to toss the battery once it drops below 1.3 or 1,4 volts. The motor just can't spin fast enough with the lower voltage.


I wonder what the "under load" voltage of the half-dead alkalines were. NiMH has less internal resistance so they keep their open cell voltage better under load... short to say, they drop less, which helps with their lower starting point.



Exactly. That internal resistance, the ability to actually flow current at a practical level is key. NiMH is good for that.

The problem with cheapo NiMH batteries for applications that sit, like cameras, is that they have high self-discharge. You will lose 50+% of the stored charge in a pretty short time, like days.

The only NiMH batteries I would buy, and I do use them, is the Sanyo Eneloop, or equivalent variants by Sony or Energize (cycle energy and precharged variants respectively). They have very low self discharge, which is key.

Junk like those HF ones are OK if youre charging and using right away, but they are no good if youre going to use them intermittently.

At that point, Id only count on them being about 600mAh of accessible energy.

For those who need higher voltage, you can buy AA rechargable NiZn batteries, which have an OCV of around 1.6V.