So why are NiMh 1.2 volts?

[spookyspiff]

Hi. I really like my NiMh batts but it would be great if they gave off 1.5 instead of 1.2 volts. Why don't they make them at 1.5? I realize alkalines don't stay at 1.5 for very long (so maybe this is pretty silly), but what's the issue here?

 

[darkzero]

if your looking for 1.5s there are some rechargeables on the market that are 1.5v, called "alkaline rechargables". I don't know how great they perform and what sucks is the charger is not backwards compatible. Must use their charger which is not recommended in charging NiCads or NiMhs & you can't use your existing charger to charge the "1.5 rechargeable alkalines" Also not sure if they are affected by "memory" nor do I know if they have low internal resistance like NiMhs which would be great. Anyone know? txs

 

[Empath]

They don't make NiMH cells 1.5 volts because they can't make them 1.5 volts. The voltage is a property of the chemical reaction, and not a variable that engineering or designing "more of" or "less of" something can change. It's the same with your primary cells; the 1.5 volts are a property of the chemical reaction, and not something designed into the cell.

Regarding the so-called rechargeable alkaline cells, they aren't rechargeable at all. They do have designed into them a means of overcoming some of the hazards and drawbacks of attempting to recharge them. All "charging" does is temporarily delay the growing internal resistance that results from their use in order to permit more of their full potential to be used. The chemical change is not reversible through electrolysis.

 

[CNC Dan]

[ QUOTE ]
spookyspiff said:
Hi. I really like my NiMh batts but it would be great if they gave off 1.5 instead of 1.2 volts. Why don't they make them at 1.5? I realize alkalines don't stay at 1.5 for very long (so maybe this is pretty silly), but what's the issue here?

[/ QUOTE ]

Chemistry. The chemical action in NiMH cells produces 1.2 volts nominal.
The chemical action in alkiline cells produces 1.5 volts nominal.

 

[shiftd]

Alkaline rechargeable SUX!!!!! big time. First off, it is not as rechargeable as it may sound. you do can recharge it, but the charge that it holds is no where near half of NiMh. In addition, they love to leak and i mean big time leaking. I just opened one new from a package and i notice some spill happened in the plastic enclosure. the others leak after a few charge.

In conclusion, if you want rechargeable, go with NiMh or whatever else. if you want 1.5V, go with alkaline. Never, ever use the rechargeable alkaline, unless that is your last resort. !

 

[eluminator]

Yep. Actually NiMH should be called 1.25 volts. They start out above 1.3 volts. By the time they are down to 1.2 volts, almost all of the usable energy is gone. At least that's what my MiMH/NiCad battery analyzer says.

 

[spookyspiff]

Ah ha. Thanks!

 

[Kevin Tan]

Or you could try the lithium-ion rechargables for 3.7v and 1600mah for the 17670 which has the same dims as 2xcr123a. Self discharge of less than 5% a month(ymmv).

 

[Wildcat]

I have a question along this line. I'm a newbie so please speak in laymans terms.

I have some used AA alk's that read 1.4v and they run my Lambda Illuminator, but it is much dimmer than the 1.6v ones. Is this normal? Is all the useful energy in the first @ 1/10th of a volt? Then I put an AAA that read .8v in my Dorcy and it still ran for another 10 hours before I finally took it out. It was, IIRC, .2 or .3v and it leaked inside the light.

Why are Lithiums 1.75v and how far do they get down before they are drained.

 

[eluminator]

Disposable batteries like alkaline are apt to leak if completely discharged. You should remove dead batteries from whatever equipment they are in. I wonder how long it took for them to leak. hours? days? weeks?

I use a battery analyzer to measure the voltage of my NiMH.
The analyzer puts a load across the battery when measuring the voltage. What load, or to put it another way, what current draw, I don't know.

When you measured 1.4 volts, I'm guessing that was with no load. If you used it in the flashlight, or put a proper size resistor across it, I think you would have seen a smaller voltage.

I guess just measuring with no load like you did may give some indication of it's condition. Putting a resistor of say 20 to 100 ohm across the battery would probably show a more dramatic drop in voltage as the battery was depleted.

I wouldn't go below 10 ohms or so unless you know what your are doing. A hot resistor could be painful. A hot battery could be worse.