Lithium polymer batteries.

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Lostgallifreyan
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Lithium polymer batteries.

Post by Lostgallifreyan »

I mentioned in another post, the use of rechargeable LiPo (Lithium polymer) batteries in a Psion Organiser II, and while I think there's a good chance that people still using organisers know enough to make best use of them, it's worth making a detailed explanation for this battery choice.

Lithium batteries, unlike zinc/carbon cells or even alkalines, survive best when left in a partially discharged state, so in an Organiser left idle a lot of the time, this is an ideal battery to use. A fully charged LiPo battery will also hold its charge for as long as an alkaline (up to 10 years) when unused or on a very light load, so they can be used in smoke alarms, where the load over long periods is very similar to an Organiser left idle with a battery in it.

Lithium batteries have one 'disadvantage', you don't get much warning when they fail, their voltage won't change much for the entire lifetime of a charge. This is not a disadvantage, it's what people used to complain that batteries did NOT do! :) If the charge lasts a long time, then we're not going to get caught short very often. Better yet, even if we do, LiPo batteries will not leak and damage a device when we're not looking, as the other types do.

Two things give long charge life. The most obvious is the extra capacity, more than is easily had in a PP3 9V battery. The other is the voltage, which also helps keep the Organiser healthy for a long time. The main voltage used in the Organiser is 5V DC. The normal voltage of an alkaline PP3 goes from about 10.5V down to 7V a short time before it dies. The LiPo battery starts at 8.4V (if the charger is accurate) and drops to about 7V before its internal protection disconnects it to keep it safe till it can be recharged.

Either battery will end charge life at about 7V, but the voltage regulator in the Organiser is what makes the difference. It's not a new switchmode type so is not as efficient. It's linear, so input current is the same as output current. There is power lost in the regulator as it maintains a steady 5V output. A new alkaline wastes more than half of all the power it can supply. This doesn't improve much as its voltage falls because by the time it's near-efficient it's near dead! There is a minimum voltage the regulator needs as overhead, probably about 2V, which is why low battery warnings tend to happen at about 7V.

The LiPo battery spends all of its time close to the most efficient voltage a linear regulator can accept while giving a 5V supply, so it is a very good choice. This is not the only way the Organiser gains either. The voltage drop across the regulator causes power loss, as heat. Electronics don't like heat. By running the Organiser on a LiPo battery, there is less heat in the regulator, so its semiconductor reliability and lifetime are extended. This also applies to the capacitors, which will last longer at lower voltages. That matters because they are often the first things to fail!

One thing to consider is what might happen if a strong load causes the voltage to sag for a moment. If it's already close to safe margins, in theory it might be risky to use it if you're using 'top slot' devices, or using large capacity RAM or Flash packs. In practise it IS safe, because the internal resistance of a LiPo battery is low, unlike that of alkalines, so even though it's a narrower margin, it's a safer one. Unlike with older battery types, EPROM formatting is safe if the LiPo battery is recently charged, which is useful if you're away from mains power but have some spare batteries with you and need to format a pack. The only older type that could do this reliably is NiMH or NiCd, but those don't have much capacity, or hold a steady voltage for long, and when they leak the result is usually heavy and destructive corrosion of metals nearby, even the tracks on circuit boards protected from direct physical contact.

That leaves only two choices: alkaline, or LiPo. The second wins in most if not all critical requirements, but most of all the efficiency and safety for long term use make them ideal because unlike ALL other types, they are equally effective for long term light loads, or short term heavy loads. They're the only battery type that we can use while rarely having to think about it beyond remembering to check them and charge them at times. In an Organiser with no external loads that might be once a year. I usually do it when the clocks change because it's when I check the condition of all Organisers I have. Sometimes I used to find one dead but that hasn't happened since I started using LiPo batteries. They are also the best choice for multimeters and test gear that isn't used often.

The biggest problem with LiPo batteries is losing them. I have one unaccounted for, somewhere, in something. I'm sure it's still alive but I have no idea where...
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MartinReid
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Lithium polymer battery charge port

Post by MartinReid »

I see... there are some with the charger port on the bottom and some with it on the side... do you charge yours 'in-situ'... how do you make sure the charger port is the correct side when fitted... where did you get yours from... there are non in CPC....

As for loosing batteries... I bet you can't read this without smiling... We once went to help out an old dear whose hubby had put a false ceiling in the living room without taking the battery out of a smoke detector that was now trapped in the ceiling space.... it was fine for years but then... the beeping was driving her crazy...

Always sincere
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Lostgallifreyan
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Re: Lithium polymer batteries.

Post by Lostgallifreyan »

That must have been a royal pain! I hope the new ceiling had panels to make it relatively indestructible when stopping the thing.

I found my lost battery, it was in a small Maplin project box. And it was at 8.0V so fine, which is good because it had been in there for at least two years and probably wasn't fully charged when it went in.

Mine have a makers name 'EBL' on them, and a nominal capacity of 600mAH, and no charging port, but they plug to any standard NiMH charger because they have the extra circuitry for strict voltage limit and final disconnect built into them to make them adapt to the standard charger. I didn't trust the idea at first, and even now, I never charge ANY lithium battery unsupervised, but these have proved their worth many times now.

The one I lost has a nominal capacity of 900 mAH, but it's not true, some shyster labelled it wrong to sell it. It was cheap enough to try, the battery is still good, just not what was claimed. I suspect that 700mAH might be the highest capacity for now, in an available PP3.

Having ports in them to charge in-place is a neat idea, but might be trouble because modification of the Organiser is needed to satisfy what will be a fragile and specific connection. Also, because of the strict 4.20~4.22V DC per cell (there are two cells in the PP3's), it is best if there is NO load at all during charge, to prevent misreading of that voltage. Charging batteries in-place always has some risk that they will be loaded during a charge, and that could be unsafe. In theory all it has to do is compensate and keep the voltage stable, thus providing for the load rather than have the load drain the battery, but there's no guarantees that a cheap charger is that stable. I like to give them a simple life. :)
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Lostgallifreyan
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Re: Lithium polymer batteries.

Post by Lostgallifreyan »

I did once try to charge in-place in an Organiser, with a method shown in detail in the image here "Failed charge line.jpg". That should have worked, with an LED to indicate charging current present, a diode to block DC in case the LED failed, and a 2.2K resistor to limit current to a level that is safe for the battery. This failed because a transistor in the Organiser's voltage regulator burnt out! I'd miscalculated something, obviously... That Organiser still works off a battery, it just can't take top-slot supply unless I fix the regulator.

That idea is NOT safe, so I urge that no-one copies this! I just put it here because it may be that some small re-think by someone who understands the Organiser circuit better might lead to a viable in-place charger that can work when 10.5V is used for the top slot. It may even be that I failed by using 12V. That works in normal cases, but I may have been asking too much that time.

A more successful test is in the other picture. I really did NOT trust those LiPo batteries at first, so I set up a full test of voltage and current. It shows that the voltage is safe, those readings were the latest values shortly before the battery's internal electronics cut off the charge current (and the UniRoss NiMH charger's red LED went out). The charge was on a new battery, supplied partially charged. It took two hours and twenty minutes, and stayed at about 24 mA throughout. The voltage never topped the absolute 8.44V limit, and the battery voltage stabilised at exactly 8.40V after charging stopped.

Since then I have found that some batteries stop at a lower voltage, but not by much, and it means if it is a 'fail', it's a safe one. Any errors found err on the side of caution and safety, so I trust them now, even though I still charge them only when I'm there to see fair play... So far no LiPo battery has died inexplicably here, as some normal Li-ion cells do at times.

EDIT: Ignore the masking tape. That was only there to identify the battery as having been tested in case I wanted to test it again sometime. The picture is just about clear enough to identify exactly which battery I bought.. I got 10, and still have 5 unused. They come in very nice boxes too! Some kind of semi-clear shatterproof plastic...
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Charging Test.jpg
Failed charge line.jpg
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MartinReid
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Supplier...

Post by MartinReid »

When considering these LiPo batteries.. and looking for a UK supplier I've found...

(1) in Lancashire.. iPowerUS Ultra Li-Polymer 9V 800mAh Rechargeable Battery Model IP9V-800 (here) £22.95 each. The description states you MUST use the dedicated charger - iPowerUS Li-Polymer Fast Smart 9V Battery Charger FC-9V4LN 4-Way UK Plug (here) £42.95

(2) in Devon.. UNIROSS 9V PP3 Lithium Polymer Rechargeable Battery (here) there is no price and no memtion of 'special' chargers..

Any thoughts and comments would be appreciated before I invest in these..

Always sincere
Martin
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Lostgallifreyan
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Re: Lithium polymer batteries.

Post by Lostgallifreyan »

Avoid the expensive one! Not just because it's expensive, either. They want you to remain trapped into using their charger! They could hide a multitude of sins in an arrangement like that. I'm not saying they are, and I certainly don't want to libel anyone so I won't.

The better approach is to go with known standards, and sellers who are willing to make devices and offer safety guarantees when allowing OTHER firms devices to work with them, MUST adhere to standards. That is why the Uniross batteries are a safer bet by far.

Testing stuff is also what matters, and how could you do that when the only context is an expensive one forced on you the moment you pay into the contract? That's why the expensive dedicated system is a bad idea. Can't set up any viable comparisons, let alone cheap ones!

The batteries you get need not be Uniross either, but why not, if the deal is right? Ask them what they want for ten, because they talk of minimum order quantities. Bear in mind that the ones I got were on Ebay from a UK seller, and cost me £28.09 including postage, for ten of them. The specs are almost certainly identical. There's a good chance the maker is the same, and Uniross get their own branding because they pay the maker to do it.

Sellers come and go on Ebay, but there's usually one or two, they do it despite the exorbitant fees because the reach, and the feedback system, are often worth more to the firm than other forms of advertising. Just check out the credentials of the seller as best you can. Registered business seller with an openly published physical address and a website that sells direct as well as their Ebay presence. Sellers like those are usually a safe bet because if they do people over their feedback record won't last long! They're more likely to keep it at very close to 100% because the advertising value of that score is beyond price.

Whatever you do, you don't have to pay for ONE, more than TEN should cost. :) A decent NiMH PP3 charger might cost £10 to £15 extra but if it's one that also handles large single 1.2V cells it's a good investment.

I noticed a claim of 800 mAH for the expensive one, and a claim for 800 as a 'pulse' rating on the Uniross battery. There's a good chance that the expensive one is rated with the biggest number, and it may not be a constant-drain value. I can't claim against the expensive one, I really have no idea for sure, certainly no proof, but it IS worth questioning these things cautiously. For one thing, a 'nominal capacity' implies they have no test results to back a claim, else they'd produce some.

The Uniross 800 mAH pulse rating is acceptable because that little pulse every twenty minutes or so is exactly what the Organiser does during its long idle periods. This helps to back up the notion that these battery types are ideal. (Actually all Lithium cells as far as I know have this extra pulse capability, even some of the very early non-rechargeable ones).

There was something else I forgot to say earlier, and I still can't remember for sure, but it may well have been price-related, or supplier-related. If so I just covered as much of that as I know how to do.


EDIT:
I just tried an Ebay search: EBL 600 mAH
I got a load of results, prices various, some with chargers. Try that and pick your best shot. :) The best price break looks like being in small multiples, which is why I went with ten. Having multiple sources to choose from is always nice..
hawsey
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Re: Lithium polymer batteries.

Post by hawsey »

I think I will try these lipo batteries out, thank you for the detailed info @lostgallifreyan

Martin the smoke alarm beeps made me laugh, many a time over the years as a Telephone engineer, I've had calls to fix " beeping Telephones" which almost always turned out to be smoke alarms that people had forgotten about: almost a thing of the past now as land lines continue to disappear.
( I will send you a chip for Ham log on Monday)
MartinP
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Re: Lithium polymer batteries.

Post by MartinP »

My concern with the PP3 LiPo batteries is that they probably have a boost circuit which holds the output voltage to a fixed level during the discharge with a steep drop in power at the end. This may not trigger the low power warning with enough time to respond, causing data loss. But this may vary depending on the battery manufacturer. What are people's experience of this? Is it a problem or not?

As an alternative, I think a simple 2 cell LiPo with a nominal voltage of 7.4 V should work fine and wouldn't have such a steep discharge at the end, here's an experiment:
2S LiPo for Organiser.jpeg
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Lostgallifreyan
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Re: Lithium polymer batteries.

Post by Lostgallifreyan »

The EBL PP3's I described in my first post don't have a boost circuit, they decline slowly. The one I lost, then later found in a Maplin kit box, had declined to about 6V, so it's probably safe to assume that this low a voltage, after so long a decline, might give far better warning than an alkaline would. It recovered fairly well on recharge, though slightly low, about 8V instead of 8.4 as usual.

I agree that a boost circuit would be bad, but I think those would come with far more expensive batteries, and those would not only have a 'Joule thief' but also a Watt watcher. :) This being necessary because that might be the only way that a user of one could ever have to gauge the state of discharge or the lifetime of charge left for any given constant load.

Those EBL ones seem to come under the general rule of nominal 7.4V dual-cell types. I saw the innards of one once. A picture.. Two blocks, so not a solid metal wall, so not a standard Li-ion. The Wikipedia article suggests that defining 'LiPo' is a bit murky because of the types and purposes of polymers used, but it seems to me that the EBL-type batteries are to standard cylindrical Li-ions what AGM batteries are to flooded lead acid. They use an absorbent polymer to hold the electrolyte, so they are safer against heat and pressure, and have a much lower risk of explosion or leakage.

They may have flaws (some seem to charge back to a bit less than the full 8.4V that most will reach) but in general, compared to others, I find it hard to see the down-side.

To prevent data loss I always keep the internal RAM as a working space, backed up to RAM pack then, when code is more stable, to a Flash pack on the same machine. The only things I lose if power fails suddenly is the clock time and the main menu and some test programs used for small samples to be sure something there is fit to add to something bigger elsewhere.

One risk with any battery that gets low, is spikes in load on the Organiser's power system resulting in data loss on an attached RAM pack. The EBL lithium PP3 batteries reduce that risk compared to an alkaline, because the lower internal resistance means that there is a limit to how low the voltage can drop in some instant of high drain. I used to get that problem a lot when testing a GPS module and Organiser based GPS data display. That was with 'Procell' alkalines. I got better results with the lithium batteries, more stable when loads change a lot. It's possible to get that with alkalines too, but only if a capacitor were added across the terminals, and I don't like modifying things if I can avoid it.
MartinP
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Re: Lithium polymer batteries.

Post by MartinP »

It's good if most PP3 LiPos have 2 cells in them without too much circuitry that could cause a problem, and some features like short circuit protection and charging from USB would be useful to have. And even if they have a boost circuit (I've found a couple that do), this might not be that bad, it just depends how they cope with a current load when the battery gets low. This is because the Organiser doesn't actually monitor the battery voltage, it checks the voltage of its own regulated 5 V supply. The 5 V is maintained by controlling the current, so the low power warning is triggered when the battery can't supply enough current for the load.
The LiPo I showed in my previous post has an extra connector with 3 pins to allow balance charging of the 2 cells. It can be charged with a standard LiPo charger of the type sold for radio controlled models. These chargers vary in design and cost, but they often have some useful features such as monitoring the charge in mAh. The batteries are quite cheap, only about £4 each when bought individually. They have the advantage of being simple, standard and cheap, but they are not as convenient as a PP3. The PP3 connector in that Organiser of mine had broken, so I had to try something else anyway.
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