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Homemade battery packs 48volts

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  1. Apr 22, 2015 #1
    is it safe to wire like 4 turnigy 11volt 2200mah 25c lithium polymer batteries in series and 4 in parrell using dean connectors? The reason I am asking is becuase I see some battery packs online that are expensive for the power they output. If lithium polymer is unsafe is it safe to use smaller lithium ion cells to make like a 48v 8800mah volt battery pack? I can get lithium ion cells pretty easily from laptop batteries.
     
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  3. Apr 22, 2015 #2

    berkeman

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    First of all, don't be wiring batteries in parallel unless you know a *lot* more about batteries.

    Second, why do you want to use Lithium? Can you just use lead-acid batteries like car batteries to make the 4x12V=48V? Or even gel cell 12V batteries... What are you wanting to power? How are you going to recharge them?
     
  4. Apr 23, 2015 #3
    There are many applications to having like 422,400 watts of power friend. I like to do experiments and engineering projects that require a lot of power, for example maybe I want to power a turnigy 80cc motor.

    Lead Acid batteries are bulky and heavy, I want a battery pack that weighs more around 10 pounds or less. I have not used gel cell before so I am looking into it.

    Recharging the battery pack should not be too much of a problem, I can use a lab power supply like this http://www.ebay.com/itm/30V-5A-Dual...980?pt=LH_DefaultDomain_0&hash=item541c51d57c
    although the thing about recharging batteries is that the charger should have about the same voltage as the battery but the amp/hour from the power supply only affects the time it will take for the battery to reach the power supply voltage with that being said you do not want a charger that has more amp/hour than the battery.

    What would you do if you wanted to make like a 30-48 volt battery friend?
     
  5. Apr 23, 2015 #4

    berkeman

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    I'm going to assume that you are using the European convention for the decimal point, and your power is 422W. 422W at 48V and 2.2Ahr give about 15 minutes of battery life. Not so great...

    I would use four 12V gel cell batteries to make the 48V. Choose a type that is small enough that it comes close to your weight goal (are you wanting it to be portable?), and has an Amp-Hour rating that gives you better battery life. I would go for the "deep cycle" type if you can. :smile:
     
  6. Apr 23, 2015 #5
    Thank you for the correction friend, I was doing quick calculations in my head should have done all the unit conversion on paper.

    Gel cell batteries are expensive but they are nice. I would want around 4 of them costing something like 4*150=$600 gee wiz! Do you know if they are rechargeable and how much does a typical unit weigh?

    I am planning on making the project portable. I caddy during the summer so I can afford $600 on a battery pack that has so much power:nb) but I was looking to spend more around $150-200. Do you have any other cheap alternatives batteries if the weight limit is about 20 pounds?
     
  7. Apr 23, 2015 #6

    berkeman

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    Another alternative (probably better) is to use a single 12V battery and a "Boost" circuit to make the 48V for you. Boosting 12V to 48V is pretty common, so you should be able to find an off-the-shelf unit. That way you can use a single 12V gell cell battery. Can you say what the application is, and what kind of current you will need for how long from the 48V source?
     
  8. Apr 23, 2015 #7
    The machine should not draw more than 100 amps; I know I will need a high rated pulse modulating speed controller for that much amperage. I would expect the machine to last around a 15 minutes so I would need a battery that has around 25amp/hour. I could use the battery in my lab when I need it. No further information will be revealed about my summer engineerng project/science fair project, maybe I will say what it is later.

    I never heard of boost circuits untill now, I am going to dedicate some research to them when I can.
    Thank you for the possible battery sources friend.
     
  9. Apr 23, 2015 #8

    berkeman

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    100 Amps! Holy cow. That's a lot of power. 100A * 48V = 4.8kW. I hope you have a *big* circuit breaker in series with that power supply output.

    BTW, battery energy capacity in Amp * Hours is generally rated at a set output current. For example, if you have a 10Ahr battery, that 10Ahr capacity is usually when you are drawing 10A for 1 hour. If you draw 20A, it will last for less than 30 minutes. There are discharge curves in most battery datasheets. Also, if you draw a high current from a battery, it can overheat and potentially burst. That's a bad thing, as you can imagine...
     
  10. Apr 23, 2015 #9
    thank you for the discharge burst tip, I have never seen a battery burst surpisingly but what factor of the battery amp/hour does the load have to draw to cause a general battery to burst? *

    I see that you are a ham, I will have to contact you sometime during the summer ok? Do you make your own antennas? I am getting my license this summer but I recently finished reading the AARL licencse manual and am currently reading AARL understanding basic electronics, 2 great books.
     
  11. Apr 23, 2015 #10

    berkeman

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    Good for you getting your license! I mostly use the 2meter and 70cm bands for local disaster preparation type communication. And I help out at large public events (like bike rides and long runs) with communication using HAM radios. I've made some simple antennas, but mostly I buy mine. I have some friends who love making all kinds of unusual antennas to use with their equipment. :smile:
     
  12. Apr 23, 2015 #11
    Must be a fun hobby to help the community using sciene. Thank you for doing emergency services volunteer work. Some day I will do the same.

    There are some very attractive antennas like the dish antennas, too bad a technical licence cannot operate on Ghz freqencies:sorry: or can they?
     
  13. Apr 23, 2015 #12

    berkeman

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  14. Apr 25, 2015 #13

    rbelli1

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    Another reason for a circuit breaker is that in a fault mode any battery that can put out 100A for 15 minutes will probably put out several thousand for long enough to vaporize all of the conductors in your setup. Along with any body parts that may be in proximity.

    Be sure that your circuit breaker or fuse is DC rated and capable of opening under any possible faults you can even remotely think of.

    Be safe

    BoB
     
  15. Apr 26, 2015 #14

    jim hardy

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    might four of these do ?

    http://[URL='http://www.mkbattery.com/images/ES2_9-12.pdf']www.mkbattery.com/images/ES2_9-12.pdf[/URL] [Broken]


    cheap enough to try, weigh ~3 pounds apiece, they'll do 100 amps for 5 sec 58 amps for 30 sec and only cost around fifteen bucks,.
     
    Last edited by a moderator: May 7, 2017
  16. Apr 26, 2015 #15
    Thank you for letting me know about those batteries, do you know how many ma/h each battery is? I know that maximum dishcarge from a battery=c*amp/hours=>amp/hours=maximum discharge continuously/C rating, do we have enough information to calculate the mah of battery?
     
    Last edited by a moderator: May 7, 2017
  17. Apr 26, 2015 #16

    jim hardy

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    nominal 2900,

    that link is the spec sheet. did you take a look ?

     
  18. Apr 26, 2015 #17
    Yes, I took a look at the page earlier. Do you know the difference between 20hour rate at 2.9Ah vs 10 hour rate 2.755Ah> Take it look at this sexy battery http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=26787 [Broken] it can output 260amps constantly and 540 amps in bursts! I could absorb all of its Electrical potential energy :bow:
     
    Last edited by a moderator: May 7, 2017
  19. Apr 26, 2015 #18

    jim hardy

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    You might spend some time here
    http://batteryuniversity.com/
    to get some vocabulary.

    The faster you discharge a battery the less of its capacity you'll be able to use.
    Basically there's ion migration happening in the electrolyte and that takes some time.

    That battery you referenced is made for high discharge rates, gel cells are not.

    Wow - 44 volts? Couple hundred amps? That thing's dangerous !

    be careful. Look up "lithium battery fires" .

    old jim
     
  20. Apr 26, 2015 #19
    Thank you for the link Mr.Hardy. Gee wiz there is a lot of content to be covered at that website, have you read every single article there?
     
  21. Apr 26, 2015 #20

    jim hardy

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    not by a long shot.

    But it's good to learn as much as you can absorb about every hobby you undertake....

    i've not played with these modern high energy density batteries.
    Once i put an A size lithium cell in my pocket. I'd found it in a dead piece of electrical equipment after a hurricane. It got across my car keys and darn near set my pants afire - I decided to leave those things alone until i had a need for them.

    So be careful. That battery could make a flash like an arc welder that'd last several seconds and hurt you.
    I dont know if it's the type prone to burn. Look at youtubes of lithium battery fires.

    They've brought down airplanes so the danger is real.

    https://gigaom.com/2011/04/04/lithium-ion-batteries-faulted-for-jet-crash/
    ups-dubai-accidentsite.jpg
    One hopes anything sold to the public would be pretty safe, but any concentrated energy source demands respect.

    so be aware of what you have there. Read up on lithium battery safety
    http://www.nrel.gov/education/pdfs/lithium-ion_battery_safety_hazards.pdf

    and battery university
    http://batteryuniversity.com/learn/article/lithium_ion_safety_concerns
    partone-5b-3.jpg

    Have fun , just be aware of "energy density" .
     
    Last edited by a moderator: May 7, 2017
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