Cutoff Quandary D-cell Ni-Mhy

VidPro

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I have made a battery pack with CTA 12A D-cells, its a 12v battery pack with 20 of them 10x2 10 in series by 2 in parellel.
Charged it as a Whole (14.3v) then discharged it 2 times as seperated cells, to do an initial cycling, and the setup is not lasting the time i expect it to (low capacity).

Because my charge method is SLOW (not smart) and i dont have a CBA (battery analiser) i want to stick a few of them on the LaCrosse thing to test them, and to charge them with a cutoff.

and that is where my question comes in.
a "cutoff" especially the one on the lacross is not going to show up unless the charge rate is well over the overcharge rate, so the thing might not cutoff. but i really want to test at least 2 of the batteries and see what the capacity would be if it reached a cutoff.

there is not #$%@& (short for poopey) specs on the battery package, or on the site for the battery CTAdigital.com , so i dont know 2 things.
what would the charge rate have to be to get a V-Drop
What would the max voltage be for them off the charger charged, or what is the max voltage i should set the power controller to be for a charge of the series set.
how they sell a battery , and no charger for it, without providing some sort of specs or parameters is beyond me?

so far, i got them putting out about 9A at a 1.5A discharge rate :-( actually 3A discharge for 2 sets. a very poor capacity.
Charging at a voltage controlled 14.3v for the set, they got warm when they reached about that voltage, so i assume from that they were mostly charged.

so i am a bit limited in charger stuff, as i dont have a triton or a D-Cell "smart" charger, and after initial testing , it will mostly be charged easily as a single 12V unit, so i only need to test a few times.

If i wire it up to the LaCross, would i be better off to use 1000ma setting, it wont reach overcharge and wont cutoff, and then it wont ever be ruined
or
set it for 1800ma and hope IF it doesn't SEE the cutoff, it also doesn't blow up the cheap china battery?

at 1000ma it SHOULD be an adequite overcharge rate, and therein it should never get ruined, but not cutoff.
at 1800 it SHOULD be an adequite rate to see a voltage drop at the end of charge (or overcharge occurance) BUT if it doesnt SEE the V-drop, it would ruin the battery.

so now you see my quandry. run it at 1000, and a cutoff might not be spotted, run it at 1800, where a cutoff SHOULD exist, but if it didnt then i would have to go buy 2 more just to test what the REAL capacity is vrses the claimed BS.
 
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The problem is you're charging by current. Connect all 24 in series, then charge in a setup like this:
You'll need a 5A rated bridge rectifier and a light fixture that holds two 100W bulbs.
chargetj8.png


Do this on a well isolated surface, away from kids, pets, etc and obviously don't TOUCH ANYTHING until you unplug it.

Put the battery pack where the oval is.
Place light fixture in place of coil inside red box.
Plug the whole thing into 120v outlet.

If you set it up light, both your 100W light bulbs should light up, but not at full brightness. Let it charge for 16 hours like this. If you have an ammeter, monitor the current on AC side and try to maintain roughly 1.2A by changing the combination of two light bulbs. (if 100+100 is too little, try 100+150 or 150 + 75).

This setup should be able to charge as many as 36 cells in series. The more cells you connect, the more efficient it is. Incandescent bulb maitains current better than a pure resistor due to its property, so it tends to hold the current quite well with some variation in state of charge. You can charge as little as one cell, but 99% of energy is diverted to lighting up the light bulb if you charge one cell.

Aside from shock hazard(which you can avoid by common sense), this setup is quite safe. If something was to short out completely, the current will be limited to 1 2/3A and both light bulbs would light up brightly.
 
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VidPro

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Handlo, your just trying to get me shocked :) it doesnt even make me flintch anymore :)

i need to TEST it, with meter things, something that provides me with the total capacity, i got enough charger junk without having to rig one. somehow i need to get reality SPECS on the battery.
 
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VidPro said:
Handlo, your just trying to get me shocked :) it doesnt even make me flintch anymore :)

i need to TEST it, with meter things, something that provides me with the total capacity, i got enough charger junk without having to rig one. somehow i need to get reality SPECS on the battery.

I am aware what you'd like to do. No worry about cut-off. Your batteries won't be damaged at 1.2A charge rate (C/10) as long as you don't leave it charging for two weeks.

Well, you do need to charge them up at ~C/10 for ~16hrs first before testing.

Since you don't have a CBA, whole thing should be rested for about an hour and discharged at ~2.4A until 0.9/cell into a suitably large resistor while logging the voltage across the resistor. For the discharge test, Don't use a light bulb, because the resistance is not constant from cold to hot.

do you have a logging DMM?
Using the voltage points, you can make something like this
https://www.candlepowerforums.com/threads/119022
 
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VidPro

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no i have 2 dmm things, and a bunch of timers, but resistive discharges change rate by a bit.

i was using a 12v light bulb and one of the dmms set up as a ammeter. that is how i got my first few discharge specs, and they are to low in capacity :-(

it takes to long, and i am not positive i am getting a full charge without some cute smart charger.
potentially i could slow charge it and assume its fully charged, but i dont even know the overcharge rate, or the charge rate, because there is no specs.
with the lacross it is supposed to cutoff when fully charged, but its not specifically designed for 12A batteries.
 
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VidPro said:
no i have 2 dmm things, and a bunch of timers, but resistive discharges change rate by a bit.

i was using a 12v light bulb and one of the dmms set up as a ammeter. that is how i got my first few discharge specs, and they are to low in capacity :-(

it takes to long, and i am not positive i am getting a full charge without some cute smart charger.
potentially i could slow charge it and assume its fully charged, but i dont even know the overcharge rate, or the charge rate, because there is no specs.
with the lacross it is supposed to cutoff when fully charged, but its not specifically designed for 12A batteries.

Charge cut off is NOT necessary at C/10 rate. This is why you call it forming charge. You basically force that rate for 16 hours for the first few cycles. That AC powered light bulb based charger will get your cells fully charged, but just like any battery, it will take you perhaps half a dozen cycles before full capacity is reached.

C/10 means (A-hr)/10hr. Hrs cancels out and you get amps. C/10 for 16 hrs is universal and is industry standard charging method for testing capacity. I really don't have the funds/need to own a lab power supply that can sustain 1.200A w/ varying voltage, but if you have a charger superior to the light bulb design, feel free to set it to force 1.200A through your pack and have it shut off at 16hrs.
 
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VidPro

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from the other thread

Handlo says:
The difference is probably due to a different charge algorithm. Dumb charging does not suffer premature termination and even though it might not offer the best cycle life, it offers the most consistent, full charging.


Silver says:
You can get away with parallel charging if you charge at low currents and follow the charge with an extended trickle charge, or if you use cells matched on capacity. The balancing occurs during the trickle charge phase.


I say:
and that is exactally what i will be doing with the PACK, I will slow dumb charge it, with voltage and current control , as a 12V set of series pack. that will balance out the cells, and so i dont have to dissasemble it anymore.
but right NOW, i am cycling it (they call it forming) as single cells, and i am getting horrible capacity rating :-(
SO
i would like to test it on a computer machine thing.
 
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VidPro said:
from the other thread

Handlo says:
The difference is probably due to a different charge algorithm. Dumb charging does not suffer premature termination and even though it might not offer the best cycle life, it offers the most consistent, full charging.


Silver says:
You can get away with parallel charging if you charge at low currents and follow the charge with an extended trickle charge, or if you use cells matched on capacity. The balancing occurs during the trickle charge phase.


I say:
and that is exactally what i will be doing with the PACK, I will slow dumb charge it, with voltage and current control , as a 12V set of series pack. that will balance out the cells, and so i dont have to dissasemble it anymore.
but right NOW, i am cycling it (they call it forming) as single cells, and i am getting horrible capacity rating :-(
SO
i would like to test it on a computer machine thing.

There's not a drastic difference in capacity between discharge rates of C/5 and C/3. All you need is a known value resistor that draws APPROXIMATELY C/5 rate. The value of resistor doesn't really matter as long as you know the value exactly and the draw is ~C/5. So for a 12v 12Ah pack, two 11 ohm resistors in parallel (5.5ohm) is good enough. Just connect your ammeter in series and measure the voltage across it and take both readings. Use Ohm's law to figure out the exact resistance.

Once you know that, all you gotta do is use something to log the voltage across the resistor every minute and you've got all the info in the world you need to get the Ah and Wh capacity. The closer the data points, the better your accuracy.
Well made RC car packs are quite expensive. Good pack assemblers capacity test EACH cell out of thousands of cells they have, then cells are cherry picked by capacity, so all six cells in the 7.2v pack is matched. If you only got 24 cells and you want to make two 12v packs, there isn't a whole lot you can do to capacity match.
 

VidPro

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Handlobraesing said:
Charge cut off is NOT necessary at C/10 rate. This is why you call it forming charge. You basically force that rate for 16 hours for the first few cycles. That AC powered light bulb based charger will get your cells fully charged, but just like any battery, it will take you perhaps half a dozen cycles before full capacity is reached.

C/10 means (A-hr)/10hr. Hrs cancels out and you get amps. C/10 for 16 hrs is universal and is industry standard charging method for testing capacity. I really don't have the funds/need to own a lab power supply that can sustain 1.200A w/ varying voltage, but if you have a charger superior to the light bulb design, feel free to set it to force 1.200A through your pack and have it shut off at 16hrs.

ok i know that formula, are you sure these cheap 12A d cell things are going to handle a 1/10th charge rate?
i am just a wee bit paranoid, because the pack replaces the one i , , , ummm, , , i overcharged just a bit , , , umm, ok i blew the dang thing up with the car charger. :) patience isnt one of my virtues, 16 hours to charge Bah :)
 

wptski

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Handlobraesing said:
Charge cut off is NOT necessary at C/10 rate. This is why you call it forming charge. You basically force that rate for 16 hours for the first few cycles. That AC powered light bulb based charger will get your cells fully charged, but just like any battery, it will take you perhaps half a dozen cycles before full capacity is reached.

C/10 means (A-hr)/10hr. Hrs cancels out and you get amps. C/10 for 16 hrs is universal and is industry standard charging method for testing capacity. I really don't have the funds/need to own a lab power supply that can sustain 1.200A w/ varying voltage, but if you have a charger superior to the light bulb design, feel free to set it to force 1.200A through your pack and have it shut off at 16hrs.
I've seen C/10 mentioned many times but only refered to as shown or C divided by 10. I've seen it written as being the same as .1C as not to be confused with 10C. Your the first person that I "can" remember refering to it as C/10hrs. The "hrs" may been dropped from the equation too! :D

The Sirius Pro Former that I use suggests 24 hrs charging.
 

SilverFox

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Hello VidPro,

With what you have...

Start with empty cells and hook them up to the outside slots of the La Crosse charger. Select 1800 mA charge rate and set a timer for 10 hours.

I don't know if the La Crosse can handle that high a capacity or that length of time, so keep an eye on things. I also am not sure you will get a correct display.

You should be getting around 10+ Ah out of those cells.

Tom
 

VidPro

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Thanks silver, darn, if i had known , and i should have known, they were that overrated, i should have got some sanyo Ds instead.

darn, aparentally it doesnt TEST at the 1800 :-( it will only charge at the higher rates, and when the voltage on the battery goes up, the total MA shows less than 1800.

so it wont run in test mode (above 1000ma)
and it might not be at more than ~1200ma when it gets time to discover a cutoff.
mabey the clipleads are not helping by adding more resistance.

basically it doesnt look like it is going to work.

i wonder what "smart" charger i could get for less than 70$ so i can singularly test and cycle them with some basic info.
 

SilverFox

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Hello VidPro,

Check out the new Maha Wizard One C9000 charger. William, the engineer responsible for the design of this charger, has indicated that you can use it to analyze C and D cells provided you can figure out a way to hook them up.

I believe the pre-sale at Thomas Distributing has the price at around $60.

Tom
 

VidPro

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i saw that thing, the only thing i wondered about it was if it would take longer to access the data, the display difference looked like you would have to manually cycle through each unit to see final specs.
wheras the 900 is displaying specs of each unit side by side, easy to compare the 4 for a odd one.

other than that, i didnt notice anything that was different, as in mabey they use the same chip? wonder if they use the same cheap switches, no light, no on/off switch, and other things that would be nice but not nessisary on the 900.
 

VidPro

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Handlobraesing said:
Someone pointed out BC-900 auto shut off at 3.7Ah

ahh, you mean capacity.
yup its a waste of time, and it was a bad idea. that is 2 times now i tried that, and it didnt work, once with the 4000ma Ni-cads.

ok dumb idea number 1789456 , dont try and charge high cap D cells with a B-900.
 
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