Rechargeable NiMH 1.2v batteries

[nicknorman]

51 minutes ago, Stilllearning said:

Back in the days of the Epilogue you turned off the tv and it actually was “off”. Now it is on standby and still consuming power, does anyone know how much?

Old CRT TVs, quite a lot. Modern flat screen LED TVs, virtually nothing. We leave our boat TV on standby 24/7. It has zero visible impact on the batteries.

[DHutch]

3 hours ago, Stilllearning said:

Back in the days of the Epilogue you turned off the tv and it actually was “off”. Now it is on standby and still consuming power, does anyone know how much?

I have measured various devices with a plug-through power meter and some are really quite good, once bought a self advertised 'low standby power' freeview box and they was actually very good. But the reason I bought it was the old one drew over 20w when 'off' and less then 30w when 'on' which I thought was awful. Somewhere in the middle is my computer monitors, which draw 2w each regards of if they are on 'standby' just turning of the computer or if they are 'off' by pressing each screens power button and turning off the led light.

 

With the pc that's about 5w continuous, which is obviously nothing compared to the amount of energy our gas boiler or a room heater gets thought in a year, but is also the equivalent of leaving a LED room light on all day everyday or by my calculations 40kWh per year, as much as a 2bar fire for a whole day. 

 

Daniel

[WotEver]

4 hours ago, Stilllearning said:

Back in the days of the Epilogue you turned off the tv and it actually was “off”. Now it is on standby and still consuming power, does anyone know how much?

I believe you’re missing the point. The argument that the mouse isn’t using any power because the pc is off equates to the TV isn’t using any power because BBC has stopped transmitting. 

[Stilllearning]

32 minutes ago, WotEver said:

I believe you’re missing the point. The argument that the mouse isn’t using any power because the pc is off equates to the TV isn’t using any power because BBC has stopped transmitting. 

I was in fact going off my own topic

On the rechargeable batteries front there have been various interesting responses, including yours. Mrs S is of the opinion that as the rechargeables that she uses are years old and the charger is too, there is no point in worrying about how fast the batteries go flat, the system is cheaper than buying new throw away alkalines. 

1 hour ago, DHutch said:

I have measured various devices with a plug-through power meter and some are really quite good, once bought a self advertised 'low standby power' freeview box and they was actually very good. But the reason I bought it was the old one drew over 20w when 'off' and less then 30w when 'on' which I thought was awful. Somewhere in the middle is my computer monitors, which draw 2w each regards of if they are on 'standby' just turning of the computer or if they are 'off' by pressing each screens power button and turning off the led light.

 

With the pc that's about 5w continuous, which is obviously nothing compared to the amount of energy our gas boiler or a room heater gets thought in a year, but is also the equivalent of leaving a LED room light on all day everyday or by my calculations 40kWh per year, as much as a 2bar fire for a whole day. 

 

Daniel

I suppose the best way to monitor what power is being used by all the equipment sitting on standby would be by having a smart meter?

[Chewbacka]

4 hours ago, nicknorman said:

Old CRT TVs, quite a lot. Modern flat screen LED TVs, virtually nothing. We leave our boat TV on standby 24/7. It has zero visible impact on the batteries.

Except if your tv is 240v AND leaving in standby prevents the inverter going to sleep, in which case instead of just a watt for the tv you may have 15w (give or take) for the inverter.

[nicknorman]

12 minutes ago, Chewbacka said:

Except if your tv is 240v AND leaving in standby prevents the inverter going to sleep, in which case instead of just a watt for the tv you may have 15w (give or take) for the inverter.

I don’t  have the inverter set to go to sleep - too problematical for iPhone and iPad chargers etc. The inverter uses 9w (~0.75A) when idling, which I can’t top excercised about.

 

TV uses less than 1W (0.08A) on standby, ditto,

Edited January 1, 2019 by nicknorman

[Chewbacka]

20 minutes ago, nicknorman said:

I don’t  have the inverter set to go to sleep - too problematical for iPhone and iPad chargers etc. The inverter uses 9w (~0.75A) when idling, which I can’t top excercised about.

 

TV uses less than 1W (0.08A) on standby, ditto,

In your case you have lots of batteries and a low quiescent draw inverter, but not everybody does.  In which case they may want to think about it.  That said, many seem to have inverters that don’t sleep, in which case as you say  power saving TVs use nothing in standby.

[DHutch]

2 hours ago, Stilllearning said:

I suppose the best way to monitor what power is being used by all the equipment sitting on standby would be by having a smart meter?

Yes an no, obviously it picks up things like your fridge and freezer kicking in an out and other non-parasitic base loads. But also does show some interesting things, although I must say as someone who as a reasonable handle on what items use, a three colour ten segment display that goes orange when the kettle is on and red if you out the kettle on with the microwave, wasn't as interesting as I thought it might be.

It sent meter readings to my energy provide for about three weeks, as by the time they forced me to have one I had already signed up to swap to another provider, who where then unable to support they type it was. 

 

Daniel

[aracer]

 

On 30/12/2018 at 23:44, Mac of Cygnet said:

So why are rechargables only 1.2v when full?  Can't they be made 1.5v like the ones they are meant to replace?

They aren't. Which is what bugs me about comments like:

On 30/12/2018 at 18:14, nicknorman said:

The problem with NiMh batteries (and NiCd) is that the nominal voltage is 1.2v. Whereas non-rechargeable batteries have a nominal voltage of 1.5v. So even with fully charged NiMh, the mouse will probably think they are partially flat and will probably give up with them before they are actually flat.

Because the nominal voltage of NiMH batteries cells (and rechargeable cells in general) means something different to the nominal voltage of alkaline cells (and single use cells in general). For NiMH and other rechargeable cells the nominal voltage is the mid discharge voltage. For alkaline and other single use cells the nominal voltage is the voltage when unused. The typical voltage of a fully charged NiMH cell is actually 1.4V - in reality alkaline are often 1.6V when completely unused, but that very quickly drops to 1.5V - so not hugely different. The mid discharge voltage of both is about 1.2V, the fully discharged voltage of both is about 1.0V. Unfortunately that doesn't tell the whole story - the discharge curve is somewhat different for the different chemistries, the most obvious difference being that for NiMH the main part of the discharge curve is very flat with a sudden drop off at the end, which can result in running out of power with little warning.

 

As for devices which specify only alkaline cells - in general they are poorly designed even when used with alkaline cells, as they will stop working when there is still a lot of energy left in the alkaline cells. Generally such a specification is a sign of cheap voltage regulation circuitry - somewhat surprising in an expensive bit of kit!

 

Finally, whilst most NiMH cells probably are still the type with fairly high self discharge, I think some people here are a bit behind the times - low self discharge NiMH cells are readily available nowadays for a similar price. Typically low self discharge cells have a slightly lower nominal capacity, but still as much as a NiMH cell from a few years ago. Personally I own a mix of both types, with the LSD cells being used in low power consumption devices where I expect them to last months - alkaline still seem poor value in any application where you expect to have to replace them at least twice, even if that is only once every year. I also feel the need to point out that self discharge certainly doesn't apply significantly to a lot of rechargeable cells in use in modern consumer devices - LiIon cells have very low self discharge rates.

[WotEver]

But the discharge characteristics of NiMH secondary vs Alkaline primary are very different. When an alkaline battery drops to 1.2V it’s more than 50% depleted. Compare that to a NiMH which will sit at 1.2V for about 60% of its life before suddenly dropping off a cliff. 

 

To simply say that the mid-point of both is 1.2V is to completely ignore the shape of the discharge curve. 

Edited January 2, 2019 by WotEver

[DHutch]

6 hours ago, aracer said:

Because the nominal voltage of NiMH batteries cells (and rechargeable cells in general) means something different to the nominal voltage of alkaline cells (and single use cells in general). For NiMH and other rechargeable cells the nominal voltage is the mid discharge voltage. For alkaline and other single use cells the nominal voltage is the voltage when unused. The typical voltage of a fully charged NiMH cell is actually 1.4V - in reality alkaline are often 1.6V when completely unused, but that very quickly drops to 1.5V - so not hugely different. The mid discharge voltage of both is about 1.2V, the fully discharged voltage of both is about 1.0V. Unfortunately that doesn't tell the whole story - the discharge curve is somewhat different for the different chemistries, the most obvious difference being that for NiMH the main part of the discharge curve is very flat with a sudden drop off at the end, which can result in running out of power with little warning.

 

As for devices which specify only alkaline cells - in general they are poorly designed even when used with alkaline cells, as they will stop working when there is still a lot of energy left in the alkaline cells. Generally such a specification is a sign of cheap voltage regulation circuitry - somewhat surprising in an expensive bit of kit!

 

Finally, whilst most NiMH cells probably are still the type with fairly high self discharge, I think some people here are a bit behind the times - low self discharge NiMH cells are readily available nowadays for a similar price. Typically low self discharge cells have a slightly lower nominal capacity, but still as much as a NiMH cell from a few years ago. Personally I own a mix of both types, with the LSD cells being used in low power consumption devices where I expect them to last months - alkaline still seem poor value in any application where you expect to have to replace them at least twice, even if that is only once every year. I also feel the need to point out that self discharge certainly doesn't apply significantly to a lot of rechargeable cells in use in modern consumer devices - LiIon cells have very low self discharge rates.

Thats very interesting, I must say it's been a good 15 years since I looked into it in detail, and that was mainly RC car racing. But I didn't know about the different voltage references, or that the curve for an Alkaline is more gradual and less of a flat line with a cliff but that makes sense. I have heard that a lot of devices fail to make effective use of all the energy in a cell. 

 

Daniel

[nicknorman]

7 hours ago, aracer said:

 

They aren't. Which is what bugs me about comments like:

Because the nominal voltage of NiMH batteries cells (and rechargeable cells in general) means something different to the nominal voltage of alkaline cells (and single use cells in general). For NiMH and other rechargeable cells the nominal voltage is the mid discharge voltage. For alkaline and other single use cells the nominal voltage is the voltage when unused. The typical voltage of a fully charged NiMH cell is actually 1.4V - in reality alkaline are often 1.6V when completely unused, but that very quickly drops to 1.5V - so not hugely different. The mid discharge voltage of both is about 1.2V, the fully discharged voltage of both is about 1.0V. Unfortunately that doesn't tell the whole story - the discharge curve is somewhat different for the different chemistries, the most obvious difference being that for NiMH the main part of the discharge curve is very flat with a sudden drop off at the end, which can result in running out of power with little warning.

 

As for devices which specify only alkaline cells - in general they are poorly designed even when used with alkaline cells, as they will stop working when there is still a lot of energy left in the alkaline cells. Generally such a specification is a sign of cheap voltage regulation circuitry - somewhat surprising in an expensive bit of kit!

 

Finally, whilst most NiMH cells probably are still the type with fairly high self discharge, I think some people here are a bit behind the times - low self discharge NiMH cells are readily available nowadays for a similar price. Typically low self discharge cells have a slightly lower nominal capacity, but still as much as a NiMH cell from a few years ago. Personally I own a mix of both types, with the LSD cells being used in low power consumption devices where I expect them to last months - alkaline still seem poor value in any application where you expect to have to replace them at least twice, even if that is only once every year. I also feel the need to point out that self discharge certainly doesn't apply significantly to a lot of rechargeable cells in use in modern consumer devices - LiIon cells have very low self discharge rates.

I used the term “batteries” because that is common parlance, even though you and I both know that a battery is technically a group of cells. Sometimes it is more helpful to use words people are accustomed to, even if they aren’t exactly correct, in cases where the misnomer doesn’t affect the meaning.

 

Anyway, regarding the discharge voltage of NiMh I think you paint an overly optimistic picture. A quick google of discharge voltage curves for NiMh found the sort of curve I was expecting, not the sort of curve you describe. Obviously it will depend on the discharge current, which isn’t specified in this graph.

 

Edited January 2, 2019 by nicknorman

[WotEver]

6 minutes ago, nicknorman said:

 

Oh look, 60% of its time at 1.2V...

[aracer]

17 minutes ago, nicknorman said:

I used the term “batteries” because that is common parlance, even though you and I both know that a battery is technically a group of cells. Sometimes it is more helpful to use words people are accustomed to, even if they aren’t exactly correct, in cases where the misnomer doesn’t affect the meaning.

Sure - I started off writing my post using the word "batteries", but got to the point where it was a clearly inaccurate expression and so corrected myself. I'm sure people on here can cope with me calling them cells.

17 minutes ago, nicknorman said:

 

Anyway, regarding the discharge voltage of NiMh I think you paint an overly optimistic picture. A quick google of discharge voltage curves for NiMh found the sort of curve I was expecting, not the sort of curve you describe. Obviously it will depend on the discharge current, which isn’t specified in this graph.

Hmm, I wrote:

7 hours ago, aracer said:

Unfortunately that doesn't tell the whole story - the discharge curve is somewhat different for the different chemistries, the most obvious difference being that for NiMH the main part of the discharge curve is very flat with a sudden drop off at the end, which can result in running out of power with little warning.

 

I think that fairly accurately describes that graph. Describing NiMH as having a nominal voltage of 1.2V and alkaline as having a nominal voltage of 1.5V paints an overly pessimistic and far less accurate picture to the layman, leading to the misunderstanding MoC had. As I pointed out, any device specifying alkaline only typically requires more than 1.2V, hence relying on the first part of the alkaline discharge curve and resulting in cells with lots of remaining energy being sent to landfill - yes there is a difference which can mean alkalines will work in situations where NiMH won't, but only in really badly designed kit.

[nicknorman]

4 minutes ago, aracer said:

 As I pointed out, any device specifying alkaline only typically requires more than 1.2V, hence relying on the first part of the alkaline discharge curve and resulting in cells with lots of remaining energy being sent to landfill - yes there is a difference which can mean alkalines will work in situations where NiMH won't, but only in really badly designed kit.

If we come back to the OP’s post, it was about how the mouse was reporting 50% battery life remaining etc. I think the NiMh discharge graph show why this is likely to be inaccurate for a system designed to use alkaline cells but powered by NiMh. You say “... only in really badly designed kit” and that may be true depending on what the design criteria are. But from the consumer’s point of view, he/she can’t know whether the kit is well designed by your criteria, or not, until after they have it and try to run it from NiMh. I suggest that if the NiMh doesn’t suit the mouse, the better solution is to revert to alkaline as opposed to buying a new mouse of a different make - which may or may not be “well designed” by your criteria.

[WotEver]

6 minutes ago, aracer said:

... any device specifying alkaline only typically requires more than 1.2V, hence relying on the first part of the alkaline discharge curve and resulting in cells with lots of remaining energy being sent to landfill...

Not necessarily. As 1.2V is more than 50% discharged for an alkaline, using NiMH batteries could result in the device’s ‘battery level’ display continuously reading ‘low battery’ or maybe ‘50%’. If using alkaline then that message would be correct. 

[TheBiscuits]

My favourite article on batteries dry cells:

https://simplelivingsomerset.wordpress.com/2013/11/10/poundland-are-cynical-con-artists/

[Stilllearning]

1 hour ago, nicknorman said:

If we come back to the OP’s post, it was about how the mouse was reporting 50% battery life remaining etc. I think the NiMh discharge graph show why this is likely to be inaccurate for a system designed to use alkaline cells but powered by NiMh. You say “... only in really badly designed kit” and that may be true depending on what the design criteria are. But from the consumer’s point of view, he/she can’t know whether the kit is well designed by your criteria, or not, until after they have it and try to run it from NiMh. I suggest that if the NiMh doesn’t suit the mouse, the better solution is to revert to alkaline as opposed to buying a new mouse of a different make - which may or may not be “well designed” by your criteria.

It would be interesting to find out if Apple expected their wireless mouse to have a rechargeable or one use then throw away battery.

[DHutch]

2 hours ago, nicknorman said:

 

 

Would be nice/interesting to see the same for an Alkaline cell overlaid. Seems simple but I'm struggling to find  a good one that shows both.

This appears to be a reasonable set of graphs at a glance.

https://www.powerstream.com/AA-tests.htm

 

Daniel

[WotEver]

1 minute ago, DHutch said:

Would be nice/interesting to see the same for an Alkaline cell overlaid. Seems simple but I'm struggling to find  a good one that shows both.

Here you go:

From here: http://www.stefanv.com/electronics/using_nimh.html

[WotEver]

28 minutes ago, Stilllearning said:

It would be interesting to find out if Apple expected their wireless mouse to have a rechargeable or one use then throw away battery.

Apple being Apple, I would expect that if they wanted rechargeable batteries they’d have built them into the device with a charging lead. 

 

I bought an Apple Bluetooth keyboard a few years ago (to make typing on an iPad easier)  and that specified alkaline batteries. 

[DHutch]

16 minutes ago, WotEver said:

... and that specified alkaline batteries. 

But then most things I find work fine on NiMH anyway. Sometimes I wonder if they are just trying to avoid zinc batteries!

22 minutes ago, WotEver said:

Here you go:

From here: http://www.stefanv.com/electronics/using_nimh.html

Happy days!

Certainly shows why a 1.2v NiMH works well in something designed for a 1.5v Alkaline. 

[nicknorman]

14 minutes ago, DHutch said:

But then most things I find work fine on NiMH anyway. Sometimes I wonder if they are just trying to avoid zinc batteries!

Happy days!

Certainly shows why a 1.2v NiMH works well in something designed for a 1.5v Alkaline. 

Well not necessarily. If it is expecting around 1.5v and stops working as well or at all at 1.2v, then not. There are certainly some devices around like that.

 

The problem with such a graph is that it doesn’t mention the discharge current. NiMh is pretty good for high discharge currents. Alkaline less so. So you could make the point at which the voltages cross over, move quite significantly by changing the discharge current. I suspect that the graph Tony just put up, is for a fairly high discharge current.

[David Mack]

7 hours ago, nicknorman said:

I used the term “batteries” because that is common parlance, even though you and I both know that a battery is technically a group of cells.

 

Reminds me of my school physics master who not only insisted on "cell" rather than "battery", but also required us to use the word "lamp", a "bulb" in his view being merely the glass envelope which was but one component of a "lamp". 

 

(Now who is up for a discussion whether Calor gas comes in "bottles" or "cylinders"?)

Edited January 2, 2019 by David Mack

[DHutch]

4 hours ago, nicknorman said:

Well not necessarily. If it is expecting around 1.5v and stops working as well or at all at 1.2v, then not. There are certainly some devices around like that.

 

The problem with such a graph is that it doesn’t mention the discharge current. NiMh is pretty good for high discharge currents. Alkaline less so. So you could make the point at which the voltages cross over, move quite significantly by changing the discharge current. I suspect that the graph Tony just put up, is for a fairly high discharge current.

Obviously all rules have exceptions I'm sure.

 

And yes, i think the page I linked to had the graphs for different discharge rates. 

 

 

Daniel