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 Post subject: A battery is a battery
PostPosted: Wed Sep 22, 2010 10:11 pm 
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Robbie The Botkiller
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Well that is a bit too simple I guess.

But still, a lot of brands are the same.

The most used battery are disposable alkaline penlites. I've been testing a number of alkalines from different brands. Turns out there is very little difference. You can buy those expensive Duracells, but for a fifth of the price you have the Ikea house brand that will perform only 10% less. So it'll give you 90% of a Duracell for 20% of the price.

Obviously there's a big difference between the various types: zinc-carbon, alkaline, lithium.

I took a number of penlites and had them give 200 mA for four hours every 24 hours until the voltage dropped below 0.9. The voltage was constantly monitored by a small laptop computer with an AD card attached to it. It gave me graphs like this:

A disposable alkaline:
Image


A rechargable NiMH:
Image

You see why a rechargable battery suddenly fails without warning when it's empty. The graph is more or less horizontal, while the disposable battery gives a voltage that drops slowly, so you can see the end coming.

If you want to know more, take a look on this page of the batterijvergelijker (battery comparator): http://www.batterijvergelijker.nl/index.php?page=wegwerp. The explanations are in dutch but the table is readable in any language.

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PostPosted: Wed Sep 22, 2010 11:50 pm 
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No More Coasters!
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that's pretty cool research.


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PostPosted: Thu Sep 23, 2010 10:14 pm 
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Robbie The Botkiller
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Yes it is.

I made a little switch board containing a battery holder, a voltage indicator, a few switches to connect or disconnect resistors, and the AD card. The card can measure voltages from 0 to 4.095 V in steps of 0.001 V. In the circuit is a power supply that is limited to 200 mA, so I'm sure that is what the battery has to give. When a battery lasts for 10 hours it has given 10 h x 200 mA = 2000 mAh, which is a typical value for alkalines.

I'm now testing a few rechargeables. Consumers will not as often as with disposables be interested in the technology because most of the times the capacity is written on the battery. The goal is to see whether or not the battery lives up to its expectation.

I was doing a test some time ago with a cheap recharcheable. The specs said 2000 mAh. I charged the battery and it gave 960. A test implies a complete discharge, so I charged it again and tested. The second time was 1560 mAh, and a third was 1580. The memory effect becomes visible. Cool huh.

Oh and Lithiums are a class of their own. I tested an Energizer Ultimate Lithium penlite, which gave 1.806 volts new. Pulling 200 mA out of it, the voltage dropped gradually (in about half an hour) to 1.45 volts and stayed there for hours, as if the graph was drawn with a ruler. This means the battery will recharge your camera and flash much quicker than an alkaline, which in my opinion justifies the price. And the weight is less: 24 grams for an alkaline (0.85 oz) and 14 grams (0.49 oz) for a lithium. For survival applications that use 4 penlites (flash light, radio, gps) this is a difference of 40 grams or 1.41 oz, which can be interesting.

It's fun, I learn a lot and I have new ideas for testing.

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PostPosted: Fri Sep 24, 2010 9:22 am 
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My experiments have shown that if not completely discharged from time to time , nickel-cadium batterys develop a "memory" and will not accept a full recharge after many partial recharge cycles.

Nickel-Metal-Hydride (NiMH) rechargeables , do not seem to suffer from this quirk .

I would like to see the type or schematic , data sheet or chip number of the A/D converter .

msg

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PostPosted: Fri Sep 24, 2010 12:05 pm 
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Robbie The Botkiller
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It's a H-Tronic HB627, containing the PIC18F2553 that does the AD conversions. The chip can do a lot more, but on the HB627 it's configured for 8 analog input channels. The AD conversion has a resolution of 12 bits, giving 212 = 4096 steps. One step is 1 milliVolt, so I can measure from 0 to 4095 mV with an accuracy of 1 mV.

I recently bought an HB628, which has the same features but as an extra it has 8 digital open collector outputs. What I want to do is fully automate periodic discharges of a battery, by sending on/off signals to relay switches that opens or closes the discharge circuit. I can also automatically terminate a load if the voltage drops below a threshold level, which makes this kind of experiments a lot safer (imagine what could happen if an empty cell continues to get 200 mA pushed through it in discharge direction).

The software I use now is basically only monitoring software: realview 3.0. The software I will be using on the fully automated measurements is Profilab Expert. It's an electronics simulation program with an enormous amount of components, and it's very flexible and easy to learn. It supports a lot of real-life hardware, like the two cards I just mentioned.

If you're interested in what the software looks like: both softwares can be downloaded in demo versions here.

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PostPosted: Tue Mar 29, 2011 12:52 am 
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<nerd>
In the meantime, I built a new switch board using the HB628 with analogue inputs and digital outputs.

I built the controller in Profilab Expert, a great product. It measures the voltage of the battery and switches automatically for a periodic discharge. It also switches off when a threshold in voltage is reached. So I can discharge a battery fully automated and directly read the capacity it has given.

On the PC, the operator console looks like this:

Attachment:
screen.JPG


On top obviously is the graph that shows how voltage depends on time.

At the bottom, from left to right:

Discharge period (7200 seconds = 2 hours)
Discharge time per period (3600 seconds = 1 hour)
Time in a period
Total testing time

Plotter start to get it running
Plotter stop to stop it and save data
Mail switch: on means that some of the data is mailed to a specific mail address every minute so I can watch from anywhere

Threshold: below this voltage the battery is considered empty, so the measurement stops
Auto reset: when switched on, the measurement will continue when the battery is revived to the specified voltage

Status: reset button will restart the measurement and the load of the battery
Load: battery is being discharged
Running: measurement is running (in any step of the period)
Idle: measurement is not running but threshold is not (yet) reached
Halted: measurement stopped because of reaching the threshold

Measurement: actual battery voltage, minimum voltage thusfar, voltage change per second

Capacity: 200 mA specified for discharge current, total time of discharge, discharged capacity (which is the end result when the measurement is halted)

And a few more meters on the right showing the voltage and the change in voltage.

Cool huh. :)

</nerd>


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PostPosted: Tue Mar 29, 2011 3:03 pm 
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Has Been To Cheeseland
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Robbie wrote:
<nerd>

Cool huh. :)

</nerd>


You truly make me smile sometimes, Big Cheese. 8)


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PostPosted: Tue Mar 29, 2011 7:10 pm 
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JM wrote:
Robbie wrote:
<nerd>

Cool huh. :)

</nerd>


You truly make me smile sometimes, Big Cheese. 8)



Well, Robbie´s skills are really impressive!

Andreas

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PostPosted: Tue Mar 29, 2011 7:13 pm 
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Indeed they are. :)


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PostPosted: Tue Mar 29, 2011 7:24 pm 
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JM wrote:
Indeed they are. :)

... and if you know him personally, you will be even more impressed about this smart man!

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PostPosted: Tue Mar 29, 2011 8:12 pm 
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He came to my house and ate all my cheese.!!!!
(Come to think of it, I didn't have much coffee left when he went home.)

What he left behind was much more important. Friendly advice.
The man is a gentleman.
Dave.


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PostPosted: Tue Aug 02, 2011 1:17 pm 
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Robbie The Botkiller
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In the meantime I'm testing more rechargeables. I tested the Eneloop

Image

and the performance is 114% of what is specified. Brilliant result!

The regular Sanyo 2700 also lives up to its promise scoring 104%.

I'm now testing the new Eneloop XX (2500 mAh).

The GP ReCyko also delivers 105%.

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PostPosted: Fri Apr 18, 2014 4:35 pm 
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Robbie The Botkiller
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I saw a documentary about disposable batteries. It's in dutch but I still post it here as I think Dirk will be interested: http://derekenkamer.kro.nl/seizoenen/seizoen_6_2014/afleveringen/17-04-2014

The conclusion is exactly like mine: there is no real difference between brands. A battery is a battery, the only difference in the price. When you buy Duracell, the only thing you pay for is marketing strategy. It costs around 4 dollarcents to produce a battery and obviously logistics, margins and wages have to be added. A spokesperson of the only German battery factory stated that 70% of the cost of the battery is materials, so for let's say 25 cents you should be able to buy a set of 4 penlites. Yeah right :lol:

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PostPosted: Fri Apr 18, 2014 6:27 pm 
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This is the first time I've seen this thread. It's very interesting to see that bit about the rechargable batteries failing suddenly. That is my experience also. And useful info about lithium batteries recharging the flash faster - all useful stuff Robbie. Give that man some cheese... =D>

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PostPosted: Fri Apr 18, 2014 9:13 pm 
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All I use anymore is rechargeables. NiCad, NiMH, lith-ions, and lead-acid. They've saved me mucho money over the years. Got my first taste for them when I flew R/C many years ago. The Lith-ions are nice for a lengthy charge, but when they lose that charge it's virtually instantaneous...At least the NiCads drew it out enough to give warning.

I carry three 9-volt niMH rechargeables with my active bass rig, keep them marked so I know which one I pulled out last. I also cycle them every couple months (run them all the way down, then recharge) to maintain capacity. Cycling is more necessary with the NiCads, but I do it with the NiMHs just to be safe.

On a side--I used to know a girl who worked as a floor engineer for Duracell, I believe in N. Carolina. She told me once that when their production supplies were low they would simply take the "skin" off of Evereadies and replace them with their own label. This could be a myth, but she did work there and I never had reason to disbelieve...


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PostPosted: Fri Apr 18, 2014 10:08 pm 
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I once did this girl named Battery. But it ended quickly because she overcharged me.

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PostPosted: Fri Apr 18, 2014 10:15 pm 
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RZ wrote:
I once did this girl named Battery. But it ended quickly because she overcharged me.


Yeah, but did she unwrap you and put her own label on?


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PostPosted: Tue Apr 22, 2014 8:42 pm 
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I believe Eric, but not Ron.

Wait, I believe Ron, but not Eric.

Wait...


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PostPosted: Tue Apr 22, 2014 9:05 pm 
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JM wrote:
I believe Eric, but not Ron.

Wait, I believe Ron, but not Eric.

Wait...


She told me to wait. I couldn't.

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PostPosted: Wed Apr 23, 2014 12:40 am 
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Robbie The Botkiller
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:dontknow:

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