Battery Extenders Based On Rechargeable Nimhs

[Seb]

hi there,

i'd like to power my c3100 with a battery extender based on 4 NiMH rechargeable batteries with 1.2 volts each, which should theoretically sum up to 4.8 volts

before connecting to zaurus i did some research and discovered the following:

in spite of a nominal voltage of 1.2 volts i observed a voltage of 1.41 volts for size AA rechargeable NiMHs and of 1.31 volts for size AAA ones, which sum up to 5.65 (AA; seems a bit too much) respectively 5.23 (AAA; seems within range)

how can that be?? i always thought that due to some scientific physical/ chemical reasons galvanic systems of the SAME type always have the SAME voltage (that's the reason why batteries of the same type always have the same nominal voltage or a multiple of that, like 1.2 volts, 2.4, 3.6, 4.8 etc. for NiMH or 3.7 or something for Lithium-Ions, or some 2 volts for lead/ lead oxide batteries used in cars [they use 6 cells of 2 volts each])

so i was rather surprised discovering different voltages  

the voltage of the 4 "freshly recharged" AAs dropped overnight to 5.57 volts, while the AAAs were recharged some time ago, which might be part of the explanation

however, the 5.23 volts of the AAAs seem to be fine, since the charger supplied by my german vendor provides 5.26 - 5.31 volts, which is a bit more

my questions now are:
- can anyone explain the observed different voltages?
- does anyone have experience with NiMH-powered battery extenders? have you gauged (i'm not sure about this english expression..) the voltage?
- has anyone from another country/ region gauged the voltage of his/ hers "original" charger so that we know, how much c3100 can stand?

regards
seb

[Da_Blitz]

Its normal trust me, after you attach a load the voltage should drop fairly quikly. however it would be a bad idea to do what you are thinking as the voltage would drop to rapidly as the battery discarges, i would add another battery then put a regulater between it and the zaurus

alos the zaurus is very specific about the voltage and it is posible to damadge it with 5.63v, even the 5.23 would have me worried

another method is old mobile phone battries, you get 3.6v per cell with a capacity of 900maH's have 2 in sereis that are in parralel with another 2 and you get 7.2V @ 1800maH's which will double your battery life.

the alternative is to buy a Litium ion battery pack for the psp, i have 2  that have a capacity of 6000maH, that gives me just over 3 charges a peice meaning i can go for about 38Hrs straghit without looking at a power point, this means about a week or more normal usage, i also use it when i plug my DVD burner into my PDA to power both devices

trust me just buy a battery pack, it will save you a whole lot of hassle

[Seb]

thanks for your answer!

it was only yesterday when i learned about regulators, before that i was trying with schottky diodes which let the voltage drop by some 0.3 volts each (with the problem, that the voltage of the NiMHs drops over time itself..)

yesterday i bought a "low-drop-regulator", meaning it has a slightly ("low drop") higher input voltage than the 5 volt output, i'm corrently testing it whith a freshly recharged battery pack of 4 NiMHs and a small light bulb, monitoring the input and output voltage over time as well as the temperature of the regulator itself, especially i'd like to know what happens, when the voltage of the NiMHs drops to 5.2 or 5.1 volts (currently it's 5.40 volts   )

i built a small box for it with sockets to connect to cables but since these regulators are very small (maybe 10 x 15 x 4 mm) i'm thinking of integrating it in the connector cable without a box so that i can simply connect it to standard battery packs

i'll post the results of my testing, i'm testing the LM2940CT low drop regulator from conrad electronics, germany, with 5V, 1A

regards seb

[Da_Blitz]

very nice, only 6 months fro me then i am a qualified Electrical/computer engineer

i still think you should get litium ion batteries, the power density is insane, chargings anoying but all you need is a 12F675 from microchip and a bit of programming

[Seb]

chargings anoying
[div align=\"right\"][a href=\"index.php?act=findpost&pid=117127\"][{POST_SNAPBACK}][/a][/div]

yep, thats what makes NiMHs so much easier, and concerning power density, if you get hi power NiMHs and but them in a battery pack you get 2500 mAh @ roughly 5 volts in a pack of 31 x 29 x 57 mm for a price of 9.90 €

preliminary testing results:

voltage of the 4 NiMHs dropped to 5.07 volts (without load),
with 100 mA load it drops to 5.02 volts, which is the input voltage for the regulator, which in turn outputs 4.92 volts now (it used to output 4.97 volts with fully charged NiMHs),
so the regulator seems to cut off some 100 mV (edited!    )

temperature of the regulator is fine, but it's only 100 mA in this run

i'll wait and see what happens to the output voltage when input drops further, after that i'll rerun the tests with more load, like 4 watts, which would equal some 800 mA, if both tests are fine i'll test it on zaurus

[Seb]

one more thing about connector cables to zaurus:

if you plan to buy one (4.0 x 1.7 mm for C3100, i don't know about the other zauri) realise, that there are different "types", some have plastic inside, which sometimes is a bit tight, so that you would have to apply some force to connect it to zaurus

since i don't know how much mechanical force the female connector in the zaurus can stand i thought it's probably a bad idea to test this, so i looked for other "types" of the 4.0 x 1.7 mm male connectors, which i eventually found: they don't have plastic inside, and plugging is as easy (mechanically) as with the "original" one from my vendor

since these connectors only cost some cents each, if you don't have a chance to test before, i'd advise to buy one of each from different makes and then try which one fits the zaurus best

[daniel3000]

one more thing about connector cables to zaurus:

if you plan to buy one (4.0 x 1.7 mm for C3100, i don't know about the other zauri) realise, that there are different "types", some have plastic inside, which sometimes is a bit tight, so that you would have to apply some force to connect it to zaurus

since i don't know how much mechanical force the female connector in the zaurus can stand i thought it's probably a bad idea to test this, so i looked for other "types" of the 4.0 x 1.7 mm male connectors, which i eventually found: they don't have plastic inside, and plugging is as easy (mechanically) as with the "original" one from my vendor

since these connectors only cost some cents each, if you don't have a chance to test before, i'd advise to buy one of each from different makes and then try which one fits the zaurus best
[div align=\"right\"][a href=\"index.php?act=findpost&pid=117165\"][{POST_SNAPBACK}][/a][/div]

They have well-defined inner and outer diameters.
I _think_ that iD 1.7mm and oD 4.0mm is correct. You can get these plugs form Segor Elektronik in Berlin for example. Conrad does not have these plugs.

daniel

[Seb]

They have well-defined inner and outer diameters.
I _think_ that iD 1.7mm and oD 4.0mm is correct. You can get these plugs form Segor Elektronik in Berlin for example. Conrad does not have these plugs.

daniel
[div align=\"right\"][a href=\"index.php?act=findpost&pid=117177\"][{POST_SNAPBACK}][/a][/div]

yep i can confirm that conrad doesn't have these - i found them in quite a few small electronic shops in the hauptbahnhof area in munich, in german they're called "DC stecker"

and yes they're well-defined, but still, some don't fit without applying force (what you probably don't want) due to the plastic inside with a diameter LESS than 1.7 mm although differently specified - i guess the plastic is simply supposed to widen and provide better hold by being "tighter", i'd go for the ones without plastic

voltage with 100 mA load is down to 4.90 volts input and 4.80 volts output from regulator, does anyone know the minimum voltage for various zauri? i guess this might drop down further with more load and less remaining battery capacity

[deluxe]

thanks for your answer!

it was only yesterday when i learned about regulators, before that i was trying with schottky diodes which let the voltage drop by some 0.3 volts each (with the problem, that the voltage of the NiMHs drops over time itself..)

yesterday i bought a "low-drop-regulator", meaning it has a slightly ("low drop") higher input voltage than the 5 volt output, i'm corrently testing it whith a freshly recharged battery pack of 4 NiMHs and a small light bulb, monitoring the input and output voltage over time as well as the temperature of the regulator itself, especially i'd like to know what happens, when the voltage of the NiMHs drops to 5.2 or 5.1 volts (currently it's 5.40 volts   )

i built a small box for it with sockets to connect to cables but since these regulators are very small (maybe 10 x 15 x 4 mm) i'm thinking of integrating it in the connector cable without a box so that i can simply connect it to standard battery packs

i'll post the results of my testing, i'm testing the LM2940CT low drop regulator from conrad electronics, germany, with 5V, 1A

regards seb
[div align=\"right\"][a href=\"index.php?act=findpost&pid=117077\"][{POST_SNAPBACK}][/a][/div]

You might be interested to know that my USB powered 5v regulated supply has worked fine for 15 or so chargings. Gives exactly 5v on my multimeter, generates no appreciable heat, so I think you could build it into almost anywhere.

[Seb]

yep! i'm thinking of something like that in "waterproof", maybe a constuction with some of these heat shrink tubes

do you have experience with zaurus and low voltage, say, below 4.8 or 4.7 volts?

[Seb]

results for second test run with zaurus:

c3100 battery was down to 10%, i put 4 freshly recharged NiMHs in the battery pack (see above) and connected it to zaurus, input voltage of the regulator with "zaurus-load" dropped from 5.7something to a little bit more than 5.4 volts, output was fine with 4.97 volts

but then voltage rapidly dropped, within 25 minutes output voltage was below 4.60 volts so that zaurus didn't recognize this anymore as being "plugged to ac"

further observations:
- temperature of regulator became high, if you touched it, it was almost too hot to touch, but in the process of doing this, touching with the fingers was sufficient to cool it down again
- whereas in the tests mentioned above the regulator "took" only 0.1 volts, i observed a voltage drop of 0.4 volts in the regulator in the "not-regulated area" (below 5 volts)

essentially the higher "zaurus load" led to a drop in voltage of about 0.3 - 0.35 volts, then, at the beginning of uncharging the NiMHS, the voltage drops rapidly, so that 5 volts input voltage for the regulator are quickly reached, then the regulator itself takes some 0.4 volts (with "zaurus load") so that very quickly you reach 4.6 volts which is the bottom end of charging zaurus!

how should i proceed?

increase input voltage by taking 5 instead of 4 NiMHs (in order to have higher voltage)?
increase amp supply by taking two parallel battery packs of 4 NiMHs each (in order to have a lesser voltage drop because the "load per battery pack" is lower)?
combine these and take 10 (two times 5)?

any suggestions are appreciated (i'd like to stay with NiMHs though)

[Da_Blitz]

add another battery, should solve your problems

if you add them in parrellel you will double the time before it stops recinising however you will never use the full charge of the battries,

besides adding 1 battery is better than adding 4

[kahm]

I've been using 4xNiMH and 8xNiMH (2 4 packs in parallel*) for quite some time. A couple of explanations for what you're seeing for the higher voltages are:

1) Freshly charged NiMH batteries are warm, and have slightly higher voltages.

2) Your multimeter needs calibration. It is common for cheap multi-meters to be off by a few percentage points.

3) Your batteries are weird, and/or different than mine. I use Energizer NiMH AAs.

I've never measured more than 5.3v on an unloaded pack, and I've used mine with the 5000, 5500, 860, 1000, 3000, and 6000. Now, putting regulation on a home-made back isn't a bad idea by any means. (It'd certainly save things just in case some joker decides to load it up with Alkalines), but I don't think it's something to worry excessively over.

*This is apparently a proble due to reverse charging the packs, because I don't have installed diodes.

[kopsis]

The down side of linear regulators is that you're going to dump 10 - 20% of your battery power into regulator power dissipation. Even with your LDO regulator, you need to keep input voltage nominally 0.5V above output voltage (and 1.0V above to cover the full operating temperature range at 1A) and that entire voltage differential is going to be dissipated as heat. Needless to say, you *must* have a heatsink attached (about 4 sq cm of copper should do it for the typical TO220 package) or you'll very quickly exceed the maximum rated junction temp (160 deg C) of your LDO.

If you're willing to stick to 4 NiMH AAs, you're unlikely to have any problems feeding the voltage straight in to the Z. If you want to be able to use disposable alkalines, you can simply add a diode (with the appropriate current rating and forward voltage drop) and it will drop the voltage just enough to get you back down to the safe range without adding extra power dissipation. I did that with a 4 C cell alkaline pack and it works like a champ. I even added a switch so I can bypass the diode when the cells get weak. That setup will run my Z pretty much indefinitely

[Da_Blitz]

use a zener diode