Running a cordless phone on alkalines instead of NiMH?

[more_vampires]

Back on topic, not sure I've seen a cordless phone that could run on lithium ion. Most I've seen are nimh aaax2. Though I've seen 3-cell phones before, that's 1.2v x 3 = 3.6v. Hot fresh lions are 4.2, so

Wouldn't try it, unless you don't care if the phone fries. Besides, nimh is so much safer for a device that might get thrown around or coffee spilled upon it, dropped into the sink or toilet, accidentally left in the dishwasher, etc.

 

[Kurt_Woloch]

The difference is not as great as you think... as explained above, NiMh's are rated at 1.2 V, but their voltage will mostly be above that. Keep in mind that the phone is also being charged on its cradle while being turned on listening for an incoming call, and the charging end voltage might be between 1.45 and 1.5 volts per cell, so the electronics will have to cope with a voltage of 4.35 to 4.5 volts here as well. Thus I don't think it would go poof when subjected to 4.2 volts from a Li-Ion. Even if you go to use the phone, it might be taken fresh from the cradle when it rings, so at least in the first minutes of talking, there still may be 4.2 volts from the batteries before the voltage slowly goes down... which it does for lithium ions as well.

By the way, I actually think that the Li-Ion batteries are the reason why cordless phones tend to be equipped with 3 (not 2 or 4) NiMh cells, because the voltage is roughly the same as for one Li-Ion cell, so part of the electronics can be reused from mobile phones using Li-Ion cells.

Oh, and mobiles run on Li-Ion as well, so why should they be unsafe for cordless phones?

Back on topic, not sure I've seen a cordless phone that could run on lithium ion. Most I've seen are nimh aaax2. Though I've seen 3-cell phones before, that's 1.2v x 3 = 3.6v. Hot fresh lions are 4.2, so

Wouldn't try it, unless you don't care if the phone fries. Besides, nimh is so much safer for a device that might get thrown around or coffee spilled upon it, dropped into the sink or toilet, accidentally left in the dishwasher, etc.

 

[more_vampires]

The difference is not as great as you think... as explained above, NiMh's are rated at 1.2 V, but their voltage will mostly be above that.

Devil's in the details, as always. There are flashlights that fry over the difference between 3.0 (cr123a primary) and 4.2 (lion.) Quite possible to make a device that tolerates it, certainly.

Keep in mind that the phone is also being charged on its cradle while being turned on listening for an incoming call, and the charging end voltage might be between 1.45 and 1.5 volts per cell, so the electronics will have to cope with a voltage of 4.35 to 4.5 volts here as well.

Excellent point, sir. Reppans showed me a neat picture of AAX3 nimh connected in series charging off of a lithium ion charger. One more point for 3 cell phones maybe working with a lithium ion. You're likely very right, I agree.

Oh, and mobiles run on Li-Ion as well, so why should they be unsafe for cordless phones?

Paranoia. I check CPF to see if anyone has tried lion in a "non-lion" maker-rated device before frying my own brand new precious. It's a mixed bag. Kills some lights, some lights turn into Superman. I guess the point is that if it actually worked "well," then a maker (of a flashlight) would say it's fine if it were so. One more marketing bullet, right?

I prefer low self discharge NiMH where possible due to safety, low maintenance, and low concern.

 

[magellan]

Guys, I'm a little confused here after all the learned discussion. How could an NiMH run at over 4V? If it were a lithium ion that could be 10-12V and trying to charge it to that voltage would probably burn your house down. I know NiMH is a lot more forgiving than lithium ion but still...How is that possible? Are you saying the usual 2-cell AAA cordless phone has the batteries in series? Even so, plugging in two lithium ions would bump the voltage to about 7.2V if they were ICRs.

 

[more_vampires]

Guys, I'm a little confused here after all the learned discussion. How could an NiMH run at over 4V?

Easy up, friend. Not all companions in this journey we call life have the same experiences. If so, life would be rottenly boring.

NiMH, aka nickel metal hydride, is a simple acronym for a massive bit of technology developed over quite a very, very long time. Untold fortunes have been thrown at this, when engineers said "well, maybe that's it..."

Oh wait, it improved. The problem is that the incremental improvement for a mature tech is a super slow game. NiMH is getting pretty mature. No more leaps and bounds, but you never know!

People "count out" a technology, then forget that the first computers were partially based off of silk weaving technology. Yes, I'm talking about "punch cards." I'm also talking about the "wheel of technology." A good old trick always seems to come back, somehow. If you want a new idea, as the old saying goes, read an old book.

If it were a lithium ion that could be 10-12V and trying to charge it to that voltage would probably burn your house down. I know NiMH is a lot more forgiving than lithium ion but still...How is that possible? Are you saying the usual 2-cell AAA cordless phone has the batteries in series? Even so, plugging in two lithium ions would bump the voltage to about 7.2V if they were ICRs.

"Forgiving" and "electrical engineering" can't play nice together in the sandbox. I am normally loathe to try to make EE statements as something I say might start a fire, ruin some equipment, and hurt some innocent people.

Tough game.

If you could possibly electrocute yourself with NiMH batteries, you did it on purpose these days. Otherwise, stop eating them and get into the padded room where you belong!

Oh, God, do bizarre corner cases annoy me!

Have a blessed day, all!

Short answer, aka "TLDR;" : Any battery stacked "in series" adds voltage, but the particulars about those batteries dramatically alter the situation. If you don't know enough about their condition, you cannot predict what will happen.

 

[Kurt_Woloch]

As far as I know, yes, the usual 2-cell AAA cordless phone probably has the batteries in series, as has the 3-cell AAA cordless phone and most of the other devices that take multiple batteries. Of course, you can't use the same number of lithium ion cells because they have three times the voltage. So running a 2-cell AAA cordless phone on 2 lithium-ion cells probably won't work (if you can fit them in at all), even running it on one won't work because the voltage is still too high, but running a 3-cell AAA cordless phone on 1 lithium-ion cell should work... there's only the question if you can fit it in and if you get the charging right, because a charging circuit for 3xAAA NiMh's might well severely overcharge a lithium-ion cell.

Guys, I'm a little confused here after all the learned discussion. How could an NiMH run at over 4V? If it were a lithium ion that could be 10-12V and trying to charge it to that voltage would probably burn your house down. I know NiMH is a lot more forgiving than lithium ion but still...How is that possible? Are you saying the usual 2-cell AAA cordless phone has the batteries in series? Even so, plugging in two lithium ions would bump the voltage to about 7.2V if they were ICRs.

 

[magellan]

As far as I know, yes, the usual 2-cell AAA cordless phone probably has the batteries in series, as has the 3-cell AAA cordless phone and most of the other devices that take multiple batteries. Of course, you can't use the same number of lithium ion cells because they have three times the voltage. So running a 2-cell AAA cordless phone on 2 lithium-ion cells probably won't work (if you can fit them in at all), even running it on one won't work because the voltage is still too high, but running a 3-cell AAA cordless phone on 1 lithium-ion cell should work... there's only the question if you can fit it in and if you get the charging right, because a charging circuit for 3xAAA NiMh's might well severely overcharge a lithium-ion cell.

Thanks! That was exactly what I needed to understand.

 

[magellan]

Easy up, friend. Not all companions in this journey we call life have the same experiences. If so, life would be rottenly boring.

NiMH, aka nickel metal hydride, is a simple acronym for a massive bit of technology developed over quite a very, very long time. Untold fortunes have been thrown at this, when engineers said "well, maybe that's it..."

Oh wait, it improved. The problem is that the incremental improvement for a mature tech is a super slow game. NiMH is getting pretty mature. No more leaps and bounds, but you never know!

People "count out" a technology, then forget that the first computers were partially based off of silk weaving technology. Yes, I'm talking about "punch cards." I'm also talking about the "wheel of technology." A good old trick always seems to come back, somehow. If you want a new idea, as the old saying goes, read an old book.



"Forgiving" and "electrical engineering" can't play nice together in the sandbox. I am normally loathe to try to make EE statements as something I say might start a fire, ruin some equipment, and hurt some innocent people.

Tough game.

If you could possibly electrocute yourself with NiMH batteries, you did it on purpose these days. Otherwise, stop eating them and get into the padded room where you belong!

Oh, God, do bizarre corner cases annoy me!

Have a blessed day, all!

Short answer, aka "TLDR;" : Any battery stacked "in series" adds voltage, but the particulars about those batteries dramatically alter the situation. If you don't know enough about their condition, you cannot predict what will happen.

Thanks! Interesting history for sure!

 

[more_vampires]

but running a 3-cell AAA cordless phone on 1 lithium-ion cell should work...

2 cells in parallel = same voltage as one cell, but double the capacity. A 3 cell series AAA cordless phone may very well work 3 cell 10440 wired parallel.

The big uncertainty: Will the charge subsystem choke or cause a potentially dangerous situation?

 

[magellan]

2 cells in parallel = same voltage as one cell, but double the capacity. A 3 cell series AAA cordless phone may very well work 3 cell 10440 wired parallel.

The big uncertainty: Will the charge subsystem choke or cause a potentially dangerous situation?

Cool. Okay, I understand the series vs. parallel setup, but it seems most cordless phones are series types? Is that because of, compared to a flashlight, you have all the extra electronics in the handset that the small PCB in a flashlight wouldn't have and you have to worry about more resistance losses?

As to the charging situation, good question. If the charging system is expecting NiMH and gets LiIon, that could get interesting. NiMH need dV/dt termination, but aren't that sensitive to overcharge compared to LiIon. LiIon don't require dV/dt termination, but are more sensitive to overcharge. Also, the LiIon would be charging at about 1.5V or at least less than 2V given internal impedance losses in the battery. In that case is it even possible for the LiIon to overcharge? I'm sure there are other issues but that's all I know. I'm no expert.

A bit of a story about series vs. parallel, years ago a friend's big Ford truck wouldn't start, and I was still a college student and driving this little compact car with a small battery. Another college friend was there and he had a similar small battery. We tried jump starting the big engine with one battery, but it wasn't strong enough. I knew that we could double the amps by hooking up both smaller batteries in parallel. So with two sets of jumper cables (which we fortunately had) hooked in parallel we were able to start the big truck engine with the two smaller batteries.

 

[more_vampires]

Cool. Okay, I understand the series vs. parallel setup, but it seems most cordless phones are series types? Is that because of, compared to a flashlight, you have all the extra electronics in the handset that the small PCB in a flashlight wouldn't have and you have to worry about more resistance losses?

AFAIK, 2 and 3 cell series phones are to:

1. Skip having a boost driver
2. Dramatically increase talk and standby time as you're not heavily drawing a single cell. Spread the load, as it were.

We tried jump starting the big engine with one battery, but it wasn't strong enough. I knew that we could double the amps by hooking up both smaller batteries in parallel.

Excellent thinking, sir.