The charge supply voltage must be higher than the battery terminal voltage. Then you put a current limit resistor inline with the supply to achieve what charge current you need. You thenmonitor the battery voltage to either cut it off at a predetermined voltage, or look for the 'peak'.
If you just put a 12v DC supply onto a flat battery pack you might have damaged the battery pack.
If you just put a 12v DC supply onto a flat battery pack you might have damaged the battery pack.
sreten said:
Hi, i presume they are not lead acid batteries,/sreten.
he said 10 1.2V cells so they are either Ni-Cd or Ni-MH cells.
either way, they need to be charged constant current and the current depending on the cell Ah rating.
detecting full charge is different on both cells but the Ni-MH is a little easier to detect. the cells heat up when they are fully charged. leaving them to overcharge will lead to cell damage or explosion though so you should be careful.
I was refering to Ni-MH 1.2 batteries at 2600mah, but have also lead acid batteries.
It seems that I have damaged the lead ones, because just have conected 12V power supply to them, and now they have very low capacity
Well, I understood the current setting, if I would need 260 ma, isn´t?
So, I= V/R where V=12V and I 0,26A, so the R I need is 46 ohm?
Are not avaible chargers for 12V operation? I have one for charging the indidual batteries, but have not found on electronic stores one to can charge a 12V pack..
And what voltage should I use? 13V? 14V?
And what about the led to know when is charged?
If there is avaible a 12V charger for sale would be really nice, and better if is voltage variable. 10.8 V etc..
It seems that I have damaged the lead ones, because just have conected 12V power supply to them, and now they have very low capacity
Well, I understood the current setting, if I would need 260 ma, isn´t?
So, I= V/R where V=12V and I 0,26A, so the R I need is 46 ohm?
Are not avaible chargers for 12V operation? I have one for charging the indidual batteries, but have not found on electronic stores one to can charge a 12V pack..
And what voltage should I use? 13V? 14V?
And what about the led to know when is charged?
If there is avaible a 12V charger for sale would be really nice, and better if is voltage variable. 10.8 V etc..
ah, ok, but still there is the issue of the when to stop, I think would be better buying a smart charger. I have found afordable at 20$ + shiping on ebay for any voltage from 9.6 to 18v. It detects automatically the voltage. Current draw selectable.
But there are two types for NIMH/ NICD and for Li-ON.
The thing is that I have some cells of a laptop broken battery at 10.8 V, and also have bought 12 battery AA size batteries for 10 euro. They are 2600 mah. So each 12V pack for 2600 mah would be only 10 euro.
But I would need more mah, and need to buy more batteries. But what do you think is the best capacity/price ratio, Li-ion batteries, or NI-MH ones? I should better buy all the same to can use just one charger.
But there are two types for NIMH/ NICD and for Li-ON.
The thing is that I have some cells of a laptop broken battery at 10.8 V, and also have bought 12 battery AA size batteries for 10 euro. They are 2600 mah. So each 12V pack for 2600 mah would be only 10 euro.
But I would need more mah, and need to buy more batteries. But what do you think is the best capacity/price ratio, Li-ion batteries, or NI-MH ones? I should better buy all the same to can use just one charger.
it must be noted that Li-ION cells are the least forgiving in charge method.
if you don't follow the charging scheme for a Li-ION cell, the least that would happen is instant damage to the cell. and the worst, well, explosion is one.
I would suggest to stick to Ni-MH since they are a bit more forgiving and simply require a constant current charging method.
I would like to vote for a thread discussing battery types, charging methods, and possible risks in different types..........what do you guys think?
if you don't follow the charging scheme for a Li-ION cell, the least that would happen is instant damage to the cell. and the worst, well, explosion is one.
I would suggest to stick to Ni-MH since they are a bit more forgiving and simply require a constant current charging method.
I would like to vote for a thread discussing battery types, charging methods, and possible risks in different types..........what do you guys think?I think a thread for batteries would be a great idea. I see a lot of misinformation posted in various battery topics on most forums. Most of it is unintentional, but having a single thread with all the info could be a great service to DIYAudio.
I would be happy to contribute to a thread like this, I've been a battery technology engineer in the mobile phone and laptop industry for the past 6 years. I've really only worked with NiMH and Li-Ion, but have done thousands of hours of testing, failure analysis, and design of fuel gauging and charge algorithms.
Now back on topic. I would be wary of buying broken or old stock laptop batteries. Lithium Ion battery packs that have been in storage for a long time may have self discharged to a point where the safety circuitry has disabled the pack. You might be able to recover the cells in this case with a proper trickle charge, but if you don't know what you are doing, or the cells are too deeply discharged it can lead to a very dangerous situation.
Old NiMH stock might not work as well as fresh cells (or at all), but there won't be the same safety risk as with Li-Ion.
I would be happy to contribute to a thread like this, I've been a battery technology engineer in the mobile phone and laptop industry for the past 6 years. I've really only worked with NiMH and Li-Ion, but have done thousands of hours of testing, failure analysis, and design of fuel gauging and charge algorithms.
Now back on topic. I would be wary of buying broken or old stock laptop batteries. Lithium Ion battery packs that have been in storage for a long time may have self discharged to a point where the safety circuitry has disabled the pack. You might be able to recover the cells in this case with a proper trickle charge, but if you don't know what you are doing, or the cells are too deeply discharged it can lead to a very dangerous situation.
Old NiMH stock might not work as well as fresh cells (or at all), but there won't be the same safety risk as with Li-Ion.
Everything you wanted to know about NiMH batteries and charging here: www.hardingenergy.com/pdfs/NiMH.pdf
Making a smart battery charger to keep these in good condition seems to be quite envolved, may be better, quicker, cheaper just to by one.
However I'd like a smart NiMH charger design so that the bats could be charged in circuit from a wall wart rather like mobile phones. Saves all that battery swapping. I imagine doing it with a PIC or AVR microcontroller and a temp sensor. Any ideas out there or existing designs ?
Given all the stories about exploding laptops recently, I'd stay well away from those batteries.
Making a smart battery charger to keep these in good condition seems to be quite envolved, may be better, quicker, cheaper just to by one.
However I'd like a smart NiMH charger design so that the bats could be charged in circuit from a wall wart rather like mobile phones. Saves all that battery swapping. I imagine doing it with a PIC or AVR microcontroller and a temp sensor. Any ideas out there or existing designs ?
Given all the stories about exploding laptops recently, I'd stay well away from those batteries.
" ... Making a smart battery charger to keep these in good condition seems to be quite envolved, may be better, quicker, cheaper just to by one. ..."
Absolutely. The effort and costs of a DIY battery charger are considerable compared to the >> US$10 chargers available from numerous sources ... and there is no reason to try to "re-invent the wheel".
For larger lead/acid batteries = same, same ...
Absolutely. The effort and costs of a DIY battery charger are considerable compared to the >> US$10 chargers available from numerous sources ... and there is no reason to try to "re-invent the wheel".
For larger lead/acid batteries = same, same ...
The Ni-MH and even the Li-Ion charge circuits inside mobile phones are quite simple, and could easily be implemented with a PIC or AVR. In mobile devices there are generally a few redundant systems in case either the hardware breaks or the firmware locks up.
For Ni-MH you would need a uC with an available ADC, FET, temp sensor, and not much else to implement an on-board charge circuit.
For Ni-MH you would need a uC with an available ADC, FET, temp sensor, and not much else to implement an on-board charge circuit.
You sure guys?? Do you really want to get into battery charger design for metal Halydes and Lithium??
Searching Electronic Design Magazine for "battery charge" produces:
http://www.elecdesign.com/Articles/Index.cfm?ArticleID=1299
http://www.elecdesign.com/Articles/Index.cfm?ArticleID=10319
http://www.elecdesign.com/Articles/Index.cfm?ArticleID=8244
http://www.elecdesign.com/Articles/Index.cfm?ArticleID=8493
... and about 50 more just the last two years ...
...
... 
... 
... ... ...
Best buy one.
Searching Electronic Design Magazine for "battery charge" produces:
http://www.elecdesign.com/Articles/Index.cfm?ArticleID=1299
http://www.elecdesign.com/Articles/Index.cfm?ArticleID=10319
http://www.elecdesign.com/Articles/Index.cfm?ArticleID=8244
http://www.elecdesign.com/Articles/Index.cfm?ArticleID=8493
... and about 50 more just the last two years ...
...
... ... ... ... ...Best buy one.
Well this is a DIY site, so understandably peopl want to do things themselves. I think there are a few reasons to not use pre-built chargers, they aren't always ideal for your goals with the batteries, or if you want to use built in batteries.
While I generally recommend using off the shelf charge control ICs, for NiMH I don't see any reason not to experiment because you can really customize the charge control to what you are trying to get out of the battery. For example if your main goal is fast charge times you can implement it in such a way to do that, if you want to really maximize your cycle life, you can implement charge controls that will help extend the life of the battery. It's also important to realize what happens with the batteries over their lifetime and how an off the shelf charger may not be able to adequately handle the changes.
I won't recommend someone to roll their own Li-Ion charge circuit for a few different reasons, but the safety aspects I'm sure are quite apparent given the recent incidents and recalls. Most places won't sell Li-Ion battery packs that don't include at least basic protection circuitry, but even with those you still must take great care in designing the charge circuit. With that in mind, you should also take great care in selecting a pre-built charger. When dealing with Li-Ion a difference of 50mV can make a huge difference.
While I generally recommend using off the shelf charge control ICs, for NiMH I don't see any reason not to experiment because you can really customize the charge control to what you are trying to get out of the battery. For example if your main goal is fast charge times you can implement it in such a way to do that, if you want to really maximize your cycle life, you can implement charge controls that will help extend the life of the battery. It's also important to realize what happens with the batteries over their lifetime and how an off the shelf charger may not be able to adequately handle the changes.
I won't recommend someone to roll their own Li-Ion charge circuit for a few different reasons, but the safety aspects I'm sure are quite apparent given the recent incidents and recalls. Most places won't sell Li-Ion battery packs that don't include at least basic protection circuitry, but even with those you still must take great care in designing the charge circuit. With that in mind, you should also take great care in selecting a pre-built charger. When dealing with Li-Ion a difference of 50mV can make a huge difference.
jc2 said:
I built one using a dual op amp, transistors, a fet, and passives. I used a datasheet that tells the charging requirements of a Li-ion cell and followed from there. the charger has the threshold for trickle->normal charge, the constant voltage level and the cut-off current all variable with multiturn trimmers so they can be tailored to suit most cells.
I have been using it for a month now and it works perfectly. the only thing its missing is a cell balancing feature and a case. I'm using the old cells from a dead laptop and recently, I measured the cells and they measure with EXACTLY equal voltages so I would think it may not be needed.
Generally application circuits will require multiple NiMH cells in series for 4.8 volts or whatever but cells should be charged individually as far as I can tell. So for my in-circuit charger with microcontroller there must be a way to reconfigure them for charge/discharge. Looks like relays are required.
I have read somewhere that puting too many cells in series can lead to failure if the cells are not closly matched, anyone know a sensibe limit to how many or how to prevent failure? Is this only true for charging in series or discharge as well ?
I have read somewhere that puting too many cells in series can lead to failure if the cells are not closly matched, anyone know a sensibe limit to how many or how to prevent failure? Is this only true for charging in series or discharge as well ?
You can charge NiMH in series, all the cell phones, power tools, laptops that have used NiMH packs have done it this way. It actually works in you favor if you are doing a -dV end of charge detection. Instead of looking for a 10mV change, you can look for a 40mV change. The one problem with series connections is that over time as the cells degrade the -dV peaks won't always happen at the exact same time with all the cells, so you might not get that full 40mV change. So some chargers may not detect the full charge and will overcharge them.
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