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Ban of non-rechargeable batteries
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SiliconWizard:

--- Quote from: Zero999 on July 04, 2020, 01:24:45 pm ---I think there's a lot of badly designed products out there, built down to a price.
--- End quote ---

Very true.


--- Quote from: Zero999 on July 04, 2020, 01:24:45 pm ---I've seen LM78L05 regulators used in devices powered by 9V alkaline batteries, when a low-dropout regulator should have been used instead. Quite often this increases the cost of ownership, compared to spending a little more on the device itself.

--- End quote ---

I suppose you're talking about the case where the user uses rechargeable 9V batteries instead? I don't quite remember how low a typical 9V NiMh battery can go for instance? Something like 6V or 6.5V? Then yeah, a 78L05 wouldn't cut it.

A better approach (although a bit more expensive usually due to the inductor and more expensive regulator) is to use a buck converter, instead of typically dissipating almost 50% in the regulator itself: (9V-5V)*I. Loosing almost half of the capacity of the battery just to shave maybe one dollar, probably less? Eek.
Rick Law:

--- Quote from: SiliconWizard on July 04, 2020, 06:25:28 pm ---...
I suppose you're talking about the case where the user uses rechargeable 9V batteries instead? I don't quite remember how low a typical 9V NiMh battery can go for instance? Something like 6V or 6.5V? Then yeah, a 78L05 wouldn't cut it.
...

--- End quote ---

Hard to remember because some NiMH 9V manufacturer (TEnergy Centura line for example) use 7 cells and some use merely 6 cells.  So you have a mix of nominal voltages.

At 7 cells, nominal NiMH cell total voltage is 8.4V.  So my 7-cell  TEnergy Centura (which is in my UT61E) can happily delivery most of it energy at around 8.4V and it stays around 8.4V until remaining capacity is below 10%.  When it does go below, it crashes down like a rock since most of it energy is delivered.  That is the behavior I want, keep going till near death.

At 6 cells, , nominal NiMH cell total voltage is 7.2V.  It is half-dead coming off the gate.  I would imagine it wouldn't reach 6V for a while, but 6V to 7V is not a happy range.  Too bad 6 cells seem to be the rule rather than the exception.

I did a mini-review of the TEnergy Centura 9V long time ago (2013) when the cells were new - it didn't drop below 8V until 94% to 96% of the energy was delivered at 1/10 C discharge.  At a higher 1/3 C discharge, it kept above 8V till 92% of the energy was delivered.  Once I get my bench cleaned up (and found that two load resisters I used for the tests), I may do a follow up and see how that same 6 years old Centura is holding up these days - it has been in my UT61E since the test so it is kind of an old man of a battery now...
https://www.eevblog.com/forum/reviews/tenergy-centura-9v-and-tn141-mini-review

EDIT: Rather than using numbers from memory, I reworded a bit to use the actual numbers I had -- since I found my old post
james_s:

--- Quote from: SiliconWizard on July 04, 2020, 05:47:04 pm ---https://en.wikipedia.org/wiki/Nickel–metal_hydride_battery

The low self-discharge type has been introduced in 2005, so that's 15 years ago, not 25. Those cells are pretty good indeed, although with a slighly lower capacity as a trade-off. But even to this day, not all NiMh batteries on the market are of LSD type, far from it (and the average joe is likely to buy non-LSD batteries, because those are cheaper and because they just don't know... or even just because they will tend to go for the highest capacities, which look attractive, which are likely NOT to be of LSD type.) As an example, a typical capacity for NiMh LSD AA batteries is 2500mAh, whereas you can find NiMh AA batteries up to 3000mAh, which are unlikely to be LSD IMHO.

Standard NiMh batteries OTOH still have a relatively high self-discharge rate.

--- End quote ---

Where can you even buy standard NiMH batteries anymore? Maybe random China sellers? I haven't seen them in years, all the ones that the local stores around here carry are pre-charged (LSD), all of the Amazon branded ones, all of the Ikea ones, even the cheap stuff like Tenergy is LSD, albeit not as good quality as the Japanese stuff. It's a complete non-issue, yes I'm sure if you look hard enough you can find garbage, just like if you can easily find junk alkaline cells that leak (Duracell, Kirkland, etc) but excellent quality NiMH cells have been widely available mainstream products for over a decade, I literally have not bought a single disposable AAA, AA or 9V battery in more than 10 years and this has not required any extreme measures or sacrifices. It surprises me that anyone still buys them, I can only assume they are either "penny wise and pound foolish" or they are not aware that technology has progressed.
Zero999:

--- Quote from: SiliconWizard on July 04, 2020, 06:25:28 pm ---
--- Quote from: Zero999 on July 04, 2020, 01:24:45 pm ---I think there's a lot of badly designed products out there, built down to a price.
--- End quote ---

Very true.


--- Quote from: Zero999 on July 04, 2020, 01:24:45 pm ---I've seen LM78L05 regulators used in devices powered by 9V alkaline batteries, when a low-dropout regulator should have been used instead. Quite often this increases the cost of ownership, compared to spending a little more on the device itself.

--- End quote ---

I suppose you're talking about the case where the user uses rechargeable 9V batteries instead? I don't quite remember how low a typical 9V NiMh battery can go for instance? Something like 6V or 6.5V? Then yeah, a 78L05 wouldn't cut it.

A better approach (although a bit more expensive usually due to the inductor and more expensive regulator) is to use a buck converter, instead of typically dissipating almost 50% in the regulator itself: (9V-5V)*I. Loosing almost half of the capacity of the battery just to shave maybe one dollar, probably less? Eek.

--- End quote ---
I'm talking about alkaline batteries. If your device won't work at 7.2V, then it's wasting a large proportion of the battery life of a 9V alkaline.

Here's some tests showing the discharge curves of some 9V alkaline batteries.
https://www.powerstream.com/9V-Alkaline-tests.htm

Always design for a lower cut-off voltage of 6V and not only will the device work off NiMH, but it will also make full use of ordinary alkaline batteries.
all_repair:
One does not have the luxury to test or to know how a device going to draw on its 9V battery before owning one.  My LSD NiMH 9V batteries are being replaced by 9V rechargeable lithium.  Save quite a bit of time and hassle in troubleshooting is it power or insufficient voltage problem.
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