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Anyone know exactly how a "smart" batt charger works? — Parallax Forums

Anyone know exactly how a "smart" batt charger works?

terahertzterahertz Posts: 55
edited 2006-11-09 15:43 in General Discussion
I'm to the point where I need to·buy a power source for my project. I had originally planned to use a deep cycle marine battery but it needs to be in a sealed container and I don't want to deal with potentially explosive outgassing issues.

After some research I ordered some of the new generation high power·NiMh rechargeable batteries. I ordered 10 cells at 12,000mAh each·at 1.2 V, for a total of 120Ah, 12V when wired in series. With 120Ah of reserve power that is way more than I could get from a lead acid deep cycle marine battery.

So far so good, but I ordered the batteries before I looked into chargers.· It turns out·a charger capable of a 120Ah-12V charge is EXTREMLY expensive, or·I can charge the cells one at a time, which will take literally days.

My question to ya'll: I would like to be able to use my bench-top power supply to charge·these batteries all together in series, but·I obviously don't want to damage them. I'm willing to build whatever circuit I need to accomplish this. I assume a "smart charger" is just some sort of voltage comparator and current limiter???

Does anyone know for sure, or have any ideas?

Comments

  • Evil AxisEvil Axis Posts: 9
    edited 2006-11-07 02:02
    google groups know

    read this thread:
    http://groups.google.com/group/rec.bicycles.tech/browse_thread/thread/150f4cf2e4c44cf3/995cd9818a8cf133#995cd9818a8cf133

    scroll down until you see the post by Giles Morris it gets good starting there.
  • BeanBean Posts: 8,129
    edited 2006-11-07 02:46
    Ahhh,
    A quantity of (10) 1.2 Volt 12 Amp-hours cells put in series gives you 12 Volts at 12 Amp-hours NOT 120 Amp-hours.

    Bean.

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  • terahertzterahertz Posts: 55
    edited 2006-11-07 03:27
    OOPS blush.gif

    You are correct Bean cool.gif . I guess I should have put a little more thought into my "calculations".


    Why buy when you can build?·I suppose I could use a BS2 as some sort of current controller. If I can figure out what makes a smart charger smart.confused.gif
  • BeanBean Posts: 8,129
    edited 2006-11-07 03:42
    You just need to buy 90 more batteries [noparse];)[/noparse]

    Bean.

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    Cheap used 4-digit LED display with driver IC·www.hc4led.com

    Low power SD Data Logger www.sddatalogger.com
    SX-Video Display Modules www.sxvm.com

    "People who are willing to trade their freedom for·security deserve neither and will lose both." Benjamin Franklin
    ·
  • terahertzterahertz Posts: 55
    edited 2006-11-07 04:39
    You just need to buy 90 more batteries [noparse];)[/noparse]
    Naah, ·I've· got a Mr. Fusion I can use, but I was trying to save it·for a different project.tongue.gif

    After some poking around, it seems like NiMh cells exhibit a brief 20mV drop when they are fully charged,·"smart" chargers then go into a trickle charge mode when this drop is detected. I've already got 2 ADC's mounted on my BOE. I just need to find that·AC relay board I have somewhere and I have my own BS2 "smart" charger.···· Hey, a mini-project!·smilewinkgrin.gif
  • GadgetmanGadgetman Posts: 2,436
    edited 2006-11-07 08:05
    You may also want to watch the temperature of the cells...

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  • cocokiwicocokiwi Posts: 75
    edited 2006-11-07 11:50
    ·I found this Charger for $49.95·· and is it SMART,do everything except make coffee!

    ·Computer driven,no BIG transformer,very light,will do:

    ·Lead Acid Std kind···· Desulfate··· Alternator check!

    2 / 10 /25 /75 Auto

    ·WET/GEL/AGM··· mode



    ·got it from SAMs club!· Made by POWER on BOARD·· Smart battery charger #VEC 1095 APOB····· DSC microprocessor Digital smart control!

    Vector manufacturing,ltd

    ·FT,lauderdale,FL,33312



    ·Nice unit, something to play with!

    There are plenty of NI-Cad charging stuff around,the only difference is this kind of battery don,t have the memory problems ni-cads do!

    ·do a search on google for smart Ni-cad charger!

    Cheers Dennis

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  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-11-07 16:19
    Here is some food for thought.

    You can easily by Lead Gelcels that don't have the gasing problem and they both retain a charge for longer periods than NiCad or NiMh and they survive better on a long-term trickle charge. That outgasing is a large part of why they went to the gel.

    A smart charger is usually a 3 mode charging device. Though it would be wonderful if it also included a thermal shut down as overheating during charging is likely to be the biggest wasteful destroyer of battery life.

    The modes are usually an intial charge mode, a fast charge mode, and a trickle charge mode. The idea here is to not damage the battery by immediately putting it unnecessisarily into a fast charge. If it is not deeply depleted, the intial charge rate may be enough to top off the battery. Fast charge is for batteries that are more depleted. The trickle charge is obvious.

    As you can see, the smart charger is all about rate. Still, the darn things are not smart enough to have one size fits all batteries. Chargers need to be matched to what they are charging as charge rates are determined in ratios to the amp/hours of the battery.

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  • sam_sam_samsam_sam_sam Posts: 2,286
    edited 2006-11-07 19:00
    terahertz

    I do not know if this will help you

    This is·the battery charger that i have used in the past

    This comes as a kit that you built your self a very easy kit to put together

    At this web page

    With this charger you charge one battery to 12 battery with a·dip switch and you select charing rate from 250 milamps·,500· 750 ,to one amp

    That you hard wire select

    http://www.gibsonteched.com/R-DN1.html



    Sam
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-11-07 23:45
    terahertz said...(trimmed)
    After some poking around, it seems like NiMh cells exhibit a brief 20mV drop when they are fully charged,·"smart" chargers then go into a trickle charge mode when this drop is detected.
    Are you sure about the trickle-charging part?· I know Ni-Cad chargers do that, but all the NiMH battery chargers I have seen shut off after the charge, not go into trickle charge.· In fact, I didn’t think you could do that on NiMH batteries.

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    Chris Savage
    Parallax Tech Support
  • LSBLSB Posts: 175
    edited 2006-11-08 04:26
    Chris,
    As an R/C flyer I use NiMH packs and my charger advertises that it fast charges to 95% capacity the does two hours of trickle charge to top off. How much is hype? I can't tell the difference in flying time.
  • GadgetmanGadgetman Posts: 2,436
    edited 2006-11-08 11:03
    My AA-sice Ni-Cad/Ni-mh charger only allows Ni-mh cells to be tricke-charged.
    And it does so until I remove the batteries.
    (Yes, I have had them in the charger for a week with no noticeable effect.)
    They call it 'top-up charging' but that's just what Trickle-charging is supposed to do, anyway...

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  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-11-08 15:36
    Interesting, I guess I will have to do a little more research.· The subject of a BASIC Stamp powered battery charger came up once before and I did some digging into how the batteries were charged, including a few trips to www.howstuffworks.com and what I came up with seemed to match what my own chargers did, which was on the NiMH batteries it simply shut off at the end.· This applies to both my HP Camera Dock as well as the Ray-O-Vac (I think that is the brand) 4AA charger that plugs into the wall.· When the charger detects the voltage drop the LED goes out on that cell and it never comes back on.· My assumption was that it was done, not trickle-charging, bug again, I will do more research into it.· Take care.

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    Chris Savage
    Parallax Tech Support
  • terahertzterahertz Posts: 55
    edited 2006-11-08 18:25
    I ordered a charger from eBay yesterday. Thanks Bean for not letting me waste time/money (12Ah vs. 120Ah).

    When I get it and test it, I'll post on this thread·how it works.

    The confusion probably comes from the fact that most chargers are not specific to the battery type, yet the batteries themselves have different charging characteristics (NiMh,NiCD,LioN).
    Chris Savage said...
    The subject of a BASIC Stamp powered battery charger came up once before
    Do you know if anyone actually built one? It seems like it would be a fairly·easy and usefull thing to make. Maybe I'll put that on my list, I have 5 projects due to myself/others/school by the end of the month.shocked.gif
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-11-08 18:58
    I believe someone just asked if it could be done, and I started researching it since I was interested in the idea…Of course, so many ideas, so little time.· But it is worth pursuing.

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    Parallax Tech Support
  • steve_bsteve_b Posts: 1,563
    edited 2006-11-08 19:00
    I had thought one was built using the CDS photocell and lamp to determine charge level....

    Something to keep in mind....many types of batteries, none of them charge the same (duration and intensity)....
    It's hard to do immediate damage to a battery by charging it wrong (within reason) but prolonged and repeated 'wrong-doing' will kill it.

    We have a lot of remote stations that use solar/RV batteries to keep them going. A lot of the guys will try to 'equalize' the battery because they were told it will extend the life!
    More often than not, the batteries died because of this. Either because the batteries were equalized too long (and the electrolyte evaporated or the casing cracked) or it was done too hard (too high current) and the plates warped and killed a cell.

    Anyhow, IMHO the most 'cheaper' chargers really only trickle charge a battery. You have to pay for the benefits of 'smart' chargers....but what the 'more' that they do isn't all that fancy, but how they do it is (microprocessor controlled PWM chargers..etc..).

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    ·

    Steve

    "Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
  • terahertzterahertz Posts: 55
    edited 2006-11-08 19:38
    Steve said...
    You have to pay for the benefits of 'smart' chargers....but what the 'more' that they do isn't all that fancy, but how they do it is (microprocessor controlled PWM chargers..etc..).
    I noticed some of the·expensive chargers used PWM at a few KHz, the question is why? The only reason I can think of is maybe they use the off time of the cycle to sample the voltage, looking for that ~20mV drop.

    Chris Savage said...
    …Of course, so many ideas, so little time
    · ^ what he said lol.gif
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-11-09 15:43
    The PWM is a new science and actually has the potential to speed charging while saving money.
    The idea is the a steady flow of electricity does not allow the physical chemistry of the battery to properly organize and restructure the molecules on the plates. It may be that it also eliminates accumulation of heat created by internal resistances during the charge

    By pulsing it, you charge a little and wait a little -- but in the end you come up to charge sooner and have more battery life.

    Of course the theory of battery charging has to be compared with the harsh reality of users just pluging and unpluging whenever. Also, user leave batteries on the dashboard of their car [noparse][[/noparse]too hot an environment for storage] and run them down to near zero [noparse][[/noparse]for recharge they should be used to about 50% onlly].

    So.... what good is a smart charger with a dumb user? {forgive me, but it was just too easy to make that statement}

    BTW, I see lots of advertizers tht tout 'smart chargers', but none will actually explain the superiority of their inteligences. I have my doubts that you are getting your money's worth. Most of this feels like the marketing department created a perception of additional value. Look at where Sony is today with Lithium batteries -- a $94,000,000 loss.

    I have gone back to lead gel cells as they are well documented for surviving use and abuse while holding a charge in storage the longest. Seems at least a path to buying less heavy metal devices over the long haul.

    The Art of Electronics has a good introduction to comparing the different kinds of batteries.· But for me, it is far easier to manange only one kind than to deal with all the information.· It becomes like keeping a wine cellar.· You have to enjoy watching your inventory.· If I have a special need [noparse][[/noparse]like my PDA], it is mated with a special charger.

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    Post Edited (Kramer) : 11/9/2006 3:52:35 PM GMT
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