Running a laptop off eneloop AA's - Page 1
Forum section: electronics / projects

author: Simon
author_rank: Unknown
timestamp: March 06, 2012, 12:47:42 pm
content: no I'm not crazy ! (well that is what I keep telling myself)so my laptop battery died. and I'm getting fed up with this business of dodgy batteries (this one was not old or well used). so why not build a large pack of AA batteries and run my laptop off of that ? Now is it worth trying to hack into the old battery connector or just go in from the charging jack ?Should i be concerned about putting rechargeable in parallel ? (that is packs of batteries that are already in series)How do i charge NiMH batteries ? (I assume that is what eneloops are

author: shebu18
author_rank: Frequent Contributor
timestamp: March 06, 2012, 01:18:50 pm
content: I saw in a old laptop battery that it was made up of something like AA batteries, enough for the voltage and capacity. It should be possible.

author: Unknown
author_rank: Unknown
timestamp: March 06, 2012, 05:44:19 pm
content: I don't see why it wouldn't work, but power density is going to suck. There's a reason why everyone is using lithium-based chemistries these days. I would connect it to the external power jack, since this will probably expect some well-defined DC voltage, as opposed to the battery terminals that will be connected to some sort of LiIon charge controller. You could just use a boost converter to produce the correct voltage. You may unlikely that your laptop requires some sort of EEPROM to authenticate the charger, however.Eneloops are NiMH cells, so NiMH charge controllers (Maxim makes some) should be fine. Not sure if AA cells are the most economical option for larger capacities, try searching the RCgroups forums, plenty of people there should have experience with larger capacities batteries and how to charge multiple cells.

author: sorin
author_rank: Frequent Contributor
timestamp: March 06, 2012, 05:44:48 pm
content: Try google, NIMH chargethis is a examplehttp://www.ti.com/product/bq2004ebut...1pcs enelop is 2.2W and cost around 3.5$for 4$ you can buy 2pcs Lion with total capacity above 10W

author: Simon
author_rank: Unknown
timestamp: March 06, 2012, 05:49:58 pm
content: so where do i buy Lion without getting burnt ?I'm not too fussed about super portability, I want something dependable. at the moment 30 AA's with two strings of 15 in parallel will give me about the 18.5V and over 50W of power more than the 47W of the original battery, I could put another string in and get it to 75W.

author: Simon
author_rank: Unknown
timestamp: March 06, 2012, 06:04:07 pm
content: Quote from: Dave.S on March 06, 2012, 05:59:00 pmthe D cells cost more than the same power eneloops (@ £1.5/cell), the lithiums cost about 2/3 what the eneloops doo but are they reliable ? the whole idea of this is to dump the crap and get good batteries in that will last (and of course i can toss one cell when it breaks if i get one bad one)

author: IanB
author_rank: Super Contributor
timestamp: March 06, 2012, 06:09:31 pm
content: You really aren't going to find this easy to do. Laptop battery packs, chargers and battery monitoring circuits are designed as a system. If you try to substitute one part of the system you could (and probably will) undermine the whole system.I don't know what make your laptop is, but you would be better off buying an OEM or good quality replacement battery (don't go cheap 3rd party with Li-ion, it won't pay off).The problem with making an external eneloop battery pack is you will also need to obtain an external eneloop battery pack charger. It will be way more cost and inconvenience than just getting a new battery for the laptop.When you have the new battery, know how to look after it. For instance, if you mainly use the laptop on mains power, remove the battery while doing so (but don't remove the battery while the computer is powered up). Try to avoid keeping the battery fully charged when not in use. Keeping it at about 75% will extend the life significantly. If you use the laptop on battery power, try to run the battery through cycles of nearly empty to nearly full (if you can), and avoid either draining the battery entirely or charging it to 100%.

author: Simon
author_rank: Unknown
timestamp: March 06, 2012, 07:02:36 pm
content: I'm also hoping for longer battery life, if i can just drop more parallel packs in as i want I can expand capacity for when I want to or carry the minimum when needed. It looks like an 18.5V pack to replace the charger is best. As for charging this is why I asked how you charge NiMH's, do i just apply appropriate voltage until full and then trickle ?For the price of an original battery I can nearly double the capacity with eneloops and more if the lithium are that cheap. I'm guessing I should charge each "strip" of series cells individually and have a diode from each strip when putting them in parallel so that they don't interfere with each other on charge

author: IanB
author_rank: Super Contributor
timestamp: March 06, 2012, 07:29:02 pm
content: Quote from: Simon on March 06, 2012, 07:02:36 pmNo, unfortunately not. NiMH batteries can either have "dumb" charging (slow and reliable), where you apply a trickle charge for 12 hours or so and then stop; or they can have intelligent or "smart" charging, where you charge at high current and use various tests (temperature, voltage, rates of change of) to determine when charging is complete.Smart charging gets progressively harder to do robustly when you have many cells in series. If some cells get out of balance and become a weaker link they will get additional stress and will tend to fail prematurely.One reason the industry went to the more expensive lithium ion cells is that charging them is in many ways easier to manage.

author: Simon
author_rank: Unknown
timestamp: March 06, 2012, 07:38:56 pm
content: well using identical cells all bought at the same time would hopefully mitigate the changes of chronic failure of one cell. I'd be inclined to use battery holders so that I can easily swap out 1 cell if need be.I'd be happy to use lion batteries, if i can find reliable ones that will last. after all this is to replace a bunch of lion batteries that certainly did not last long and were not value for money

author: IanB
author_rank: Super Contributor
timestamp: March 06, 2012, 07:44:59 pm
content: Your simplest choice is to get something like this for charging and put the eneloops in battery holders for use:http://www.batteryjunction.com/titanium-md-1600l.html

author: Simon
author_rank: Unknown
timestamp: March 06, 2012, 07:54:50 pm
content: what about a reliable source of lion cells ?seems that are not so easy to find as cells as they are mostly pre-assembled battery packs

author: bfritz
author_rank: Regular Contributor
timestamp: March 06, 2012, 09:39:53 pm
content: Simon,I've designed battery packs and battery pack electronics for portable computers for over 16 years. So, I think I can give you a little guidance that may help, and perhaps help you avoid some of the pitfalls that are lurking.First, lets discuss realistic expectations for battery life. I would expect that from a well designed, well built Li-Ion battery, to get about 80% of original capacity after 300 cycles. If you run the battery down 50%, and recharge, you need to count that as 1/2 a cycle. Note that if the battery is exposed to high heat, or is charged when outside the 10C to 40C range, that will shorten life a bit. Note that some less well designed laptops, will get quite hot from heat produced by the portables processor, and power supply circuitry within the portable. Temps of 30-35C internally are quite common. If you do things like set a portable on a blanket that blocks vents on the bottom, or block vents by setting it directly on your lap, this can result in greater internal heating, and shorten battery life. In addition, some portables are smarter than others regarding maximizing battery life. For example some manufacturers just charge the battery if it is not 100% full. Lenovo for example, has a capability setting to "Maximize battery life", which lets the battery decline to the low 90% range, before it will charge it back up. In normal useage scenarios, I expect to get 2 years of use, anything beyond that and I'm really happy. A typical battery costs about $100USD, so that doesn't seem too bad, for an item that is expected to wear out.So, if you have not gotten that kind of life from your battery, I'd love to hear which manufacturer to stay clear of! Don't worry, no one else is listening, and I won't tell anyone.The issue with replacing your battery with a AA rechargeable is going to be related to "rate" and voltage swing. For example, many portables today have a peak power demand of about 60-65W. The input voltage at the AC adapter input depends on the portable, but they fall into a couple camps. There is one where the input is designed for 19-20Vdc, and another for about 14-15V. Actually for the AA's the higher voltage case is easier. If we look at that, at peak power your pack attached at the adapter input will need to supply, 60W/20V = 3A. This is a lot of current for a AA battery. But the battery should be able to do it, per the Sanyo website here:http://www.eneloop.info/home/performance-details/discharge-current.htmlNote that because you are discharging at much higher than the C/20 rate (C is capacity in mAh, while 20 is the hours for discharge, 20 is normal for alkaline batteries for rating purposes.), you will not get the nameplate rating of 2000mAh, but rather per the graph something a little below 1900mAh.Another important consideration, is that such a system will require 19V at the end of discharge of the battery. If you design the battery to have 19V at the end of discharge, then you would need to use 19 cells in series, as the cell voltage drops to 1V at the end of discharge. So the voltage when full will be 19cells * 1.45 = 27.55V This is the issue with the "swing" in the voltage from empty to full.That is likely to be a problem. I think a vast number of portables will have problems with input charger voltages that high. So, then you end up having to put a DC/DC converter between the cells and the AC adapter connector on the laptop. Even assuming a good synchronous step-down (buck) converter, at say 90% efficiency, that is 10% of the pack energy wasted in the converter alone. You will not get that much energy directly into the battery in the portable, as there is another buck converter in the laptop that is used for charging, and that will be about 90% efficient. So your overall efficiency of charging from the external battery will be 90% * 90% = 81%. So that means your external battery goes from 1900mAh to 1900mAh * 81% = 1539mAh.Another thing to think about is that some manufacturers (For example Dell) use a ID device on their AC adapter, and if the ID device is missing, they will refuse to charge the internal battery from the AC adapter, as it is worried the AC adapter is an off brand that might damage the rechargeable battery.So, not sure if you still think that is worth it. If you do, I'll try and answer any questions you may have.The other idea is to use it to replace the internal battery. The first challenge there is the mechanical challenge of connecting to the battery connector. Most of those connectors are proprietary, and getting one or two at a reasonable price is often quite difficult. Your best bet is to harvest them from battery packs that have died that fit the laptop.Note that the internal charger is going to be designed to provide the recommended charge profile for a Li-Ion or Li-polymer battery pack. This is normally 4.2V times the number of cells in the laptop. The charge current is normally limited to some peak current, but can decline while the system is being used, as the AC adapter typically has an input power limiting circuit. It knows the max power of the AC adapter and cuts the current to the battery back when the combination of system plus battery would exceed the power capability of the adapter. This is important, as it means current could cut back for short periods of time while the portable is running.So, assume you get a connector, most of the batteries in portables are SMBus compliant. They read the info from the battery over the SMBus (A very small change from I2C), and enable the charger when a battery is present and needs charge. So, you would need to design a system to act like an SMBus battery. Your best source is TI, they offer a number of IC's that implement SMBus systems for batteries.You still then have the issue that many manufacturers read info from the battery over the SMBus, and if they think the battery is not an original OEM pack, they will not charge it. I believe that current HP, Dell, Apple and some others do this. So, you'll need to figure out what they want to see and do it.Then the voltage and current supplied by the charger is what a Li chemistry cell wants, not the EneLoop. You will need to figure out how to terminate charge correctly, without terminating early if the current throttles back on your EneLoop due to input power limiting. This is a tricky problem alone, and I hold one patent on techniques to use to get around this issue.If you want to do this to save money... I think what I've told you will make you realize you are not going to save money, and will likely cost yourself well about the cost of a pack or two, in trying to figure this all out.I'm happy to answer questions, so if you do have an idea of which direction you want to go, give me some info, and I'll let you know what to watch out for.So, after writing all that, I looked back at your post...Quote from: Simon on March 06, 2012, 12:47:42 pmAre you still telling yourself that? LOL Just kidding with you.

author: Simon
author_rank: Unknown
timestamp: March 07, 2012, 07:00:20 am
content: Thank you bfritzYou make good points but I'm pressing on. This is not really about saving money although I might in the long run. My main aim is to have a more reliable battery and really if it lasts longer than the "original" ones i may even make a saving. I also want a longer battery life in the bargain. The last battery was off ebay - joking apart if i buy a HP one I'll spend as much as my project. As it is an NC4200 (made in 2005) there is no "funny business" on the charger side, infact my current charger is not original as I biught the laptop off ebay second hand.I take your point about the voltage swings, I guess I was shying away from it really but knew it was lurking. I could use a SMPS to keep things pretty regular.From what you say Li-ions loose capacity fast ? do I really want to consider using them ? where can I buy decent Li-ions like I can get eneloops ?

author: IanB
author_rank: Super Contributor
timestamp: March 07, 2012, 07:59:13 am
content: Quote from: Simon on March 07, 2012, 07:00:20 amIt is difficult to buy quality Li-ions loose. They are usually sold in bulk directly to the people who make and assemble battery packs. There are significant dangers with larger Li-ion sizes like the 18650 often found in battery packs. If mishandled or improperly charged they can catch fire with hot flames and do considerable damage.Single lithium ion batteries are sometimes used by enthusiasts in high power torches, but the batteries sold for this purpose are relatively expensive if from a trusted source like Panasonic, and are potentially of uncertain quality and consistency if bought from a cheap source like DealExtreme.Sometimes when people want a supply of high quality lithium ion cells for their own use, they get them by taking apart battery packs for power tools. But if you did that, you might as well just buy an 18 V power tool battery pack and charger and use the battery pack directly. No need to take it apart at all--it will be nicely assembled with protection circuit and charge control all ready to use.

author: Simon
author_rank: Unknown
timestamp: March 07, 2012, 08:01:13 am
content: so really ebeloops are the way to go for this sort of thing

author: Simon
author_rank: Unknown
timestamp: March 07, 2012, 12:58:14 pm
content: well i'm talking one bad apple in a batch. obviously i can check them periodically with a meter to check they are all running the same ish voltage, if one starts dropping then it will be dying

author: GrumpyDave
author_rank: Contributor
timestamp: March 07, 2012, 01:01:16 pm
content: Quote from: Simon on March 07, 2012, 08:01:13 amWell to be honest. No.If your dead set on this idea and assuming your laptop will accept a dumb supply I fail to see how you will significantly improve the life over an oem battery pack with standard AA Ni-mh unless your willing to lug a satchel of batteries around with you...I'm no expert on batteries but heres how I see it....Laptop batteries use multiples of 3 lithiums in series so thats 11.1V (3.7 * 3)Google says Dells 9 cell packs are around 8Ah and eneloops AA are 1.2V 2AI dont think you'll do the eneloops any good if you discharge em much lower than ~0.9VLets assume you have sorted the voltage regulation and use a battery pack of 11 eneloops..1.2 * 11 = 13.2V 2AhAlso assuming you have solved the problem of paralleling packs which i believe is quite difficult to do properly.To match the capacity of that dell battery you will require around 44 AA cells!! Just to MATCH the oem battery!Then when they are flat, you need to find a way to charge them..

author: Simon
author_rank: Unknown
timestamp: March 07, 2012, 01:04:50 pm
content: I'm hooping to make a bigger pack and yes I don't mind the weight. I could try lead acid but not sure if that is cheaper/lighter

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 07, 2012, 02:28:54 pm
content: Lead acid is still the cheapest for a given capacity. They just don't last long if discharged a lot so plan on using less than 50% of the charge. A better option might be to find some Prius battery cell assemblies (each one is 7.2V) and use 2 or 3 of them in series with a proper regulator. They can be charged very fast (100A rating) if the proper charger is used.

author: andyg
author_rank: Regular Contributor
timestamp: March 07, 2012, 04:06:59 pm
content: You could use a pre-built RC LiPo battery from say hobbyking.com (lots of different configs and capacities to choose from) and a nice balance charger.Downside is there is no protection for the batteries, you would have to deal with that on your end.

author: bfritz
author_rank: Regular Contributor
timestamp: March 07, 2012, 09:48:03 pm
content: Quote from: Simon on March 07, 2012, 07:00:20 amYou say you want a more reliable battery. If that is your goal, the technology has improved greatly since 2005. If you buy a more modern laptop, you will get both more reliability and greater runtime. But, I'm guessing that won't sway you. LOLSo, sounds as if the system will operate fine from any power source you supply it with. That is good news... you won't have to spend a bunch of time reverse engineering a charger interface.QuoteI would recommend choosing a number of cells in series that allows you to either use a buck converter, or a boost converter. Try and stay away from a configuration where the battery voltage transitions during discharge through the output voltage you want, as this complicates the design of the DC/DC, and requires more complex topologies. (For example try and stay away from a battery configuration that uses 12 eneloops, if you need 15 volts to the laptop, as the range of voltage for 12 eneloops is 12 - 18V, and part of the time you would need to boost, and others buck.)QuoteI think you will find the eneloops will have a shorter life than the Li-ions do. You will be using a large number of them in either series or parallel. In series, during discharge it is easily possible to drive cells into "reversal". In other words the cell voltage goes negative as you have depleted all energy in the cell, while others still have energy. Adding cells in parallel can result in large currents flowing unless you very carefully match cell voltages before connecting the cells. Even if you match the voltage of the cells, if the capacity is not matched in a parallel configuration, you will end up charging the cell with the least capacity from its parallel neighbor with higher capacity, and wasting some energy in the process. You can also end up with very large currents flowing between cells, that can cause heating and fires. If you look at the Sanyo website for the data on lifetime of the eneloop cells you will notice they say something like "up to 1500 cycles". This is pure marketing. I tested some cells in real conditions at 35C several years ago, and got about 72% at 300 cycles. My benchmark that I like to see for Li is 80% at 300 cycles, and see this kind of performace as the norm.To get decent Li cells, I would suggest the radio control hobbyist market. I know you can get A123 LiFePO4 cells. You could also then just buy a charger designed for the cells. You would then only need to design the output DC/DC, and monitor the cells to ensure you don't take them to too low a voltage.The other possibility, is to choose an off the shelf laptop battery pack, that already contains safety electronics, and use that to power your DC/DC converter. No need to monitor undervoltage or overvoltage then, as the electronics in the pack will do it for you.

author: sonicj
author_rank: Frequent Contributor
timestamp: March 08, 2012, 12:26:25 am
content: AA is a step backwards over 18650 li-ion. ncr18650a is the bees knees and is easy to find with or without tabs.vented NiCad has the longest service life of any battery technology afaik. strapping a string of 'em to your laptop might pose a challenge though...-sj

author: Simon
author_rank: Unknown
timestamp: March 08, 2012, 07:05:03 am
content: Well due to cost I'm swinging towards lead acid right now, can easily buy enough capacity to not have to discharge them too much and still get the capacity. maybe I can look at li-ions for the future. The laptop is actually a nice little laptop, small (12.1") yes with decent performance, quite portable but still useable as a main computer if I had to fall back on it (as i did when decorating my house and had to put my quad core PC away)

author: philbx1
author_rank: Regular Contributor
timestamp: March 08, 2012, 07:30:14 am
content: Simon, this might be getting into the 'danger Will Robinson' area, but I assume you won't be dropping your laptopfrom a great height, pounding the batteries with a hammer etc.How about Li-Po's?A good charger likeTurnigy MEGAand a pack (I assume you need around 18v) likeTurnigy 18.5 8aHand monitor for safety5S Battery MonitorOr more (22.2v)Turnigy 22.2 8ahNow these are fairly expensive, but with a lower amp/hour rating the price comes down significantly.Also, I'm not so much suggesting these as an option, moreso info about newer LiPo and charging technology.BTW, I pulled apart a Dell battery last week and it had 6 Li-Ion's which looked VERY similar to these (without the text)HK 18650's

author: philbx1
author_rank: Regular Contributor
timestamp: March 08, 2012, 07:44:38 am
content: Quote from: philbx1 on March 08, 2012, 07:30:14 amOOPS - Actually, it may have been 9 of these. but at 9 x 3.7 = 33.3 it seems a lot of volts.

author: Simon
author_rank: Unknown
timestamp: March 08, 2012, 07:47:26 am
content: I like the look of the nano battery but not the priceand it ships from america i guess ? so best not go there, I'll have to keep an eye on battery developments. will there be the day that Li-ion batteries make it into mainstream use ? or are they just to erm.... volatile

author: Simon
author_rank: Unknown
timestamp: March 08, 2012, 10:50:19 am
content: were they directly in parallel or was there some control circuitry to isolate them ?

author: IanB
author_rank: Super Contributor
timestamp: March 09, 2012, 03:58:49 am
content: Quote from: Simon on March 08, 2012, 10:50:19 amIt's completely OK to put lithium ion cells in parallel in a battery pack. For example if you put 3 x 18650 in parallel you would get something that behaves like a single cell with three times the capacity. It will charge and discharge just like one big cell.However, you cannot do the same with NiMH like eneloops. Attempting to charge NiMH cells in parallel is a big no-no. Damaged batteries will result unless you design a really cunning charger.

author: bfritz
author_rank: Regular Contributor
timestamp: March 09, 2012, 09:26:15 pm
content: Quote from: Dave.S on March 08, 2012, 04:31:37 pmEvery Li technology battery I have seen in my career that uses batteries in parallel, connects them directly in parallel.Regarding circuitry to isolate them, I have never seen a battery pack that uses circuitry to isolate cells in parallel. It is common to see areas in the conductive straps between the cells, where the strap was been made narrower. The idea is that if a high current above some level starts to flow, the necked area will heat, and the strap will fail open, stopping the high current.Most Li technology manufacturers will furnish a data sheet on the cells. You usually have to ask for it, and it is almost always provided only under an NDA. It will give details on the maximum number of cells that can be placed in parallel. It is quite common to see two 18650 cells in parallel, and fairly common to see three in parallel. I have not seen a manufacturer whose datasheet says configurations of more than four in parallel are allowed.

author: Simon
author_rank: Unknown
timestamp: March 09, 2012, 09:32:06 pm
content: I guess that if more than 4 were put in parallel and they started failing you would end up in a position where 1 cell could be required to deliver 4+ times the intended current

author: bfritz
author_rank: Regular Contributor
timestamp: March 10, 2012, 08:03:29 am
content: Having extra discharge current for one cell is not that big of an issue for Li, but having a charge rate above what they are designed for, can cause internal plating of metallic lithium... and that is very bad. It clogs the graphite matrix, and usually results in shortening of the life, and can even lead to shorting across the seperator, and fires.But, don't kid yourself that Li technology is the only cell with safety issues. I have see NiMH and NiCd packs catch on fire and cause major damage. I saw the entire passenger side of an auto burned out because a portable computer had been set on the seat, and charged from an inverter connected to the cigarette lighter socket, with the inverter connected to the AC adapter.The majority of safety issues I have seen, mostly stem from construction issues between the cells. The welded straps between the cells need to be insulated with abrasion resistant insulators anywhere that shorting could cause a problem. Failing to do this can lead to shorts developing over years as the packs are subjected to vibration. Such shorts can allow over 100A to flow. It doesn't take long with a 100A short to cause a fire. This can happen as easily with NiCd or NiMh as with Li technologies.

author: bfritz
author_rank: Regular Contributor
timestamp: March 11, 2012, 02:13:55 am
content: Quote from: Dave.S on March 10, 2012, 12:39:00 pmThat fuse is external to the cells, and only limits current being drawn outside the battery. Any battery technology can be wired with such a fuse.Such a fuse does nothing to stop internal shorts within or between the cells, which is the typical problem seen in manufacture of packs. This is often caused by inadequate insulation not designed for the abrasion that occurs over years of use.

author: amyk
author_rank: Super Contributor
timestamp: March 11, 2012, 12:35:22 pm
content: Quote from: bfritz on March 10, 2012, 08:03:29 amThe other thing is the voltage limit, 4.20V maximum (+/- 1%) for standard lithium-cobalt (3.6V for phosphate). Some cheap devices I've seen can't keep that voltage tolerance with their simple circuit and just go for a constant-voltage 4V charge which probably reduces the usable capacity (but prolongs the life a bit).

author: bfritz
author_rank: Regular Contributor
timestamp: March 11, 2012, 08:12:57 pm
content: Quote from: Dave.S on March 11, 2012, 10:42:09 amI've never seen a NiCd or NiMh with an internal fuse. I have seen some Li-Ion cells with PTC devices internal, but I don't consider that a fuse, it is a current limiting device. I have designed a lot of packs, and looked at lots of cell data sheets, so I believe this is the exception rather than the rule. Please point me at any datasheet that shows such a fuse. I'm not asking because I don't believe, I'm asking because I haven't seen it.

author: bfritz
author_rank: Regular Contributor
timestamp: March 11, 2012, 08:19:15 pm
content: Quote from: amyk on March 11, 2012, 12:35:22 pmThat is a perfectly acceptable practice. You give up some capacity per cycle, but end up getting a longer cycle life.It is important to remember that even with this practice, it is still necessary to monitor the individual cell voltages of the series connected cells for safety purposes. It is possible for the cells to be inbalanced, and one cell to become much higher in voltage during charge, as it has the least capacity. If that cell goes overvoltage while the others are still below the overvoltage, it is possible to cause a safety event with the cell in overvoltage.

author: G7PSK
author_rank: Super Contributor
timestamp: March 11, 2012, 10:29:54 pm
content: I have been following this thread with interest as I have often wondered about the pros and cons of various cell types and configurations. From what have read Lithium cells should not be run flat, The Panasonic toughbook's or at least the CF28 has a utility within the bios for refreshing the battery, which should be run about once a month, this discharges the battery pack and then recharges it, I have noticed that these units give very good battery life which I assume is partly due to this utility. Why don't other makes have something similar. Simon, on ebay you can get a power unit for laptops that runs on all voltages including a 12 volt input you could use one of these with a deep discharge lead acid battery.

author: sonicj
author_rank: Frequent Contributor
timestamp: March 12, 2012, 02:17:27 am
content: i run my macbook pro off of a 12V deep cycle lead acid during thunderstorms. pulls around 2.8 amps surfin' the net.-sj

author: IanB
author_rank: Super Contributor
timestamp: March 12, 2012, 02:37:59 am
content: Quote from: G7PSK on March 11, 2012, 10:29:54 pmLithium ion cells of the regular kind used in laptops have more energy per weight and per volume than nickel metal hydride cells. In power tools too the lithium battery packs have more energy (longer run time) than the cheaper nickel cadmium packs.QuoteIt is OK to run them flat, where flat is defined as the point where no more useful energy is available. For a typical lithium ion cell this would be a resting cell voltage somewhere around 3.2 V, give or take. However, it is harmful to take the voltage much below this level and it may cause irreparable damage to the cell or even create a dangerous condition on recharging. Lithium ion cells and batteries always come with a battery protection circuit that cuts off the battery if the voltage gets too low.QuoteThere is no advantage to discharging and recharging a lithium ion battery. The battery comes with a useful working life, and cycling the battery unnecessarily just drains a few more grains of sand through the life timer and advances the battery further towards the end of its life. There can, however, be value in doing this to re-calibrate the battery management computer so it has an accurate measure of the capacity of the battery.QuoteThe best way to achieve good battery life with lithium ion is to keep the battery voltage away from the extremes. Charging to 100% and discharging all the way to 0% will shorten the life compared to, say, charging to 85% and discharging to 15%. Laptops with good battery management will avoid topping up the battery unless it falls below about 90%, and they may even have a battery conservation mode where they will avoid charging the battery to 100% ever. Charging a lithium ion battery to 100% (a cell voltage of 4.20 V) and keeping it there constantly is the best way to shorten its life.

author: bfritz
author_rank: Regular Contributor
timestamp: March 12, 2012, 05:23:06 am
content: Quote from: bfritz on March 11, 2012, 08:12:57 pmQuote from: Dave.S on March 11, 2012, 08:20:33 pmDave, is the link above your answer to a NiCd or NiMH with internal fuse?That posting does not mention a fuse within a cell. That posting mentions that most NiCd's have a fuse within the pack. This is very different from having a fuse within the cell. A NiCd cell is cylindrical in shape. Multiple cells are wired in series to form a pack. Usually either the positive or negative lead that exits the pack, has a fuse placed in series. Note that internally it is possible for the metal straps between the cells to short, even though external shorts are protected by a fuse.See myBeautifuldrawing below.Note that the short shown in red, will not trip the fuse, as the short current does not flow through the fuse. This is why pack fuses do not provide protection against shorts within a pack, only those external to the pack.

author: bfritz
author_rank: Regular Contributor
timestamp: March 12, 2012, 08:15:27 am
content: Quote from: Dave.S on March 12, 2012, 05:46:02 amSo, you posted that link to show that NiCd's have internal fuses... Yet the link never talks about internally fused cells. And your explanation is that "...it does not mean most cell doesn't have..."In my over 25 years of experience designing battery packs, and battery pack electronics, I have never seen a Ni pack with an internal fuse. Most cells do not have fuses. I was willing to believe some could, so I asked for some evidence, so you send me on a boondoggle, to an article that doesn't back up anything that was in question.I'm sure you believe you saw a cell with one, have zero knowledge other than what you believe you saw, and were probably mistaken in your analysis. It is possible to make a cell with an internal fuse, but doing this would have very little benefit to the cell manufacturer, as they would then have to stock different cells with different fuse ratings. I just can't see a good reason to do it, can see lots of downside, and you offer no real evidence other than "I saw it".Can you understand why your argument isn't very convincing?By the way, I have quick access to cell data sheets from every major cell manufacturer. If you give me a cell manufacturer, and model number, I can look this up quickly. If most cells have this, as you say, then giving me a major manufacturer's model number for one, should not be difficult.

author: amyk
author_rank: Super Contributor
timestamp: March 12, 2012, 11:42:03 am
content: Quote from: bfritz on March 11, 2012, 08:19:15 pmI've only seen that simple circuit using a single-cell low-capacity lipo (~150mAh). It was in a cheap MP4 player and just used a current-limiting resistor and voltage divider to provide around 4V at 50mA from the USB 5V line.I've seen in the datasheets for a lot of battery charger ICs that they have "preconditioning" for recharging "severely depleted" cells but that confuses me a bit - is it safe to do that, because I've read that lion cells should not be discharged below ~2.75V, but apparently these chargers claim to be able to charge them properly with a very low current precharge?Regarding powering a laptop from its DC input, all the ones I've seen have a buck converter to generate the system 12/5/3.3/2.5/1.8V rails (actually a lot of the more recent ones don't have a 12V rail) from the adapter or battery, and it usually accepts a rather wide range (e.g. 3-28V for a TPS51124), so anything >12V is usually OK - just make sure to take into account any fuses in the path and the higher current that may be drawn with a lower input voltage. For example my laptop has a 19V adapter and that's the voltage the MAX1977 buck converter gets when it's plugged in, but on battery the same rail only measures ~11V.

author: nukie
author_rank: Frequent Contributor
timestamp: March 12, 2012, 01:27:23 pm
content: What is NiCd designed for? A lot of current. Some cells can dump 40A at a time. What's a 40A fuse going to look like? You can look it up in your car. I've never heard of a NiCd with a fuse. Some people actually short the terminals to vaporize those dendrites/whiskers. If there's fuse it would be on the device.

author: bfritz
author_rank: Regular Contributor
timestamp: March 13, 2012, 08:47:49 pm
content: Quote from: amyk on March 12, 2012, 11:42:03 amThe preconditioning is safe. Here is the way it works. Most packs have a protection circuit that disables discharge at some undervoltage threshold, usually when any cell reaches 3V. The electronics in the pack consume a very small current, usually in the 5-10 uA range. This small current, along with the small self discharge present in Li chemistries could lead to a pack going to a fairly low voltage if allowed to sit uncharged for an extended time. As long as the cell doesn't go below a safety threshold, usually around 2.5V, then charging to recover the cell is allowed, but typically must be done at a C/10 rate or less. These preconditioning charge circuits apply this lower rate charge, and check that the cells comes above the approximately 3V undervoltage threshold within a reasonable time. If it doesn't achieve the undervoltage threshold in a reasonable time, the circutit will typically blow a fuse that disables the pack for safety reasons.QuoteIn general I see one of two pack topologies for most laptops. The most common involves series connections of 3 Li cells, for a maximum pack voltage of 12.6V. The other involves series connection of 4 Li cells, for a maximum pack voltage of 16.8V.Most systems identify the AC adapter by using a comparator in either a charge IC, or other circuitry, that looks for an input on the adapter input that is above the battery voltage. If you have a 4 cell battery and plug in a 15V adapter (This is common for a 3 series config) if the battery is fully discharged, it may start charge as the pack is only at 12V (3V/cell * 4 cells). As the pack starts charging it will run out of headroom for the internal charger as a 4 cell charges to 16.8, but the adapter only is supplying 15V. This will cause charge to terminate early. This can lead to problems in the fuel gauging circuitry in the laptop pack, as it may decide charge was terminated at full, and update the fuel gauge info incorrectly. It learns a new capacity, but the charge termination was incorrect.So, just choose an input voltage which is about a volt or higher than your highest battery pack voltage, and all will likely work well.

author: I Shout Loud
author_rank: Newbie
timestamp: October 25, 2012, 09:41:28 pm
content: hi Simon, Did you succeed with Eneloop? I am also interested in this topic. I came across this crude method of replacing batteries at youtube. But, tryhttp://www.duracelldirect.com. They have batteries for all equipments and it is from the manufacturer directly. All the best.

author: Thor-Arne
author_rank: Unknown
timestamp: October 25, 2012, 09:59:24 pm
content: Just have to show you guys this in case you missed it:http://www.gooddealchina.com/Batteries/50000mAh-Portable-Power-Station-External-Laptop-Lithium-Battery-c22224.htmlA proper test of this one would be nice.