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Thread: Charge multiple power packs

  1. #1
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    Charge multiple power packs

    Hey Folks,

    I've been building a Robot based on the iRobot Create platform. My design calls for 4 14.4v 3800mAh battery packs (12 sub-C NiMH each) wired in parallel to power the Mini-ITX PC board, and everything else (the create will continue to use it's own battery pack). So, Here is my question: How can I charge 4 packs wired in parallel? Would a standard iRobot APC Faster charger be able to do it? (It's Rated at 22.5vdc 1.25Amps, I know that if it could, it would take over 4 times longer than the normal pack.. so, 12-14 hours on a standard charge)..

    I also have another option... I'm using a universal power adapter for notebooks during my development. It output's 15-24v at 8.0A I thought I perhaps could use that to power the Bot when he's docked and charge his battery packs. Also. I do have a voltage and current measuring circuitry on the bot now, so I can measure the voltage and current of the battery (and incoming charge). I'm using the phidgets 20Amp current Sensor and precision voltage sensor. So, from what I can tell.. I need some diodes to put inline, some sort of switching circuit that allows me to turn on/off the charge.. Maybe some sort of trickle charge circuit.. I do have a Phidgets 8/8/8 with 3 of the analog inputs are in use already (1 for the current sensor, 1 for the voltage sensor, and 1 for a pressure sensor that will be used on the gripper.) I could hook up the 4 temperature sensors from the battery packs independently as well, leaving me with just a single analog sensor for a sonar device. A digital output could be used to toggle the charging circuit on or off... or pulse it for a trickle charge?? I'm open to ideas, suggestions, schematics or whatever. BTW, I know I could use LiON's, however, I wanted the added weight of the NiMH packs to help offset the weight of the arm I'm planning to add (which is on the robot's right hand side, and will be able to pickup 6-8lbs) Oh Yea.. I'm also in need of a 7.2-7.4v high current voltage regulator for the arm.. 2 of the servo's I'm using are capable of 5.2A stalled, So, I need something for that.

    Thanks, Connor

  2. Re: Charge multiple power packs

    Your project sounds really cool. If you're planning to use a bunch of NiMH packs in parallel, you should read up on how they're charged, because there are some safety considerations. I recommend checking out this page at Powerstream:
    http://www.powerstream.com/NiMH.htm
    Powerstream is a good resource for all things battery-related. Their NiMH page goes into detail on how they're charged, what current you should use depending on the capacity, etc. Actually, they sell some battery monitoring boards that you may want to check out, as well.

    Also, here's an interesting paper to read:
    http://www.freescale.com/files/micro...ual/DRM051.pdf
    It's a reference design for a microcontroller-based battery charger, and it has schematics and voltage/current/temperature graphs that may help you out. It also describes how the firmware should respond to the sensor inputs.

    > I'm also in need of a 7.2-7.4v high current voltage regulator for the arm.. 2
    > of the servo's I'm using are capable of 5.2A stalled, So, I need something for that.

    I've been looking for somehting like that for ages, without success. I usually just use multiple 1A regulators in parallel.
    New to the TR Community? Feel free to introduce yourself and show off your projects!

  3. Re: Charge multiple power packs

    Quote Originally Posted by Connor View Post
    Yea.. I'm also in need of a 7.2-7.4v high current voltage regulator for the arm.. 2 of the servo's I'm using are capable of 5.2A stalled, So, I need something for that.

    Thanks, Connor
    Digikey lists one regulator that I can find with those specs:

    STMicroelectronics L4977A (Digikey part # 497-5336-5-ND)

    Its a 7 amp, 5.1 - 40 Volt switching regulator. They also have models available with 5 amp and 10 amp outputs.

    - Jon

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    Re: Charge multiple power packs

    We'll, Like I said, these packs are already made up.. They each have a Thermosister, and some sort of resister that gets really hot when the packs short out (to protect the cell's).. I've been looking a unit called the MAX712/MAX713 which looks very promising.

    I several options, 4 of these 3800mAh packs, or 12 D 10000mAh cells, or 12 F 14000mAh cells.. The 4 3800mAh packs give me more mAhs, and are cheaper.. but, is it going to causes issues charging them. in parallel.

    Thanks, Connor

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    Re: Charge multiple power packs

    Quote Originally Posted by JonHylands View Post
    Digikey lists one regulator that I can find with those specs:

    STMicroelectronics L4977A (Digikey part # 497-5336-5-ND)

    Its a 7 amp, 5.1 - 40 Volt switching regulator. They also have models available with 5 amp and 10 amp outputs.

    - Jon
    That's a pretty complicated looking regulator.. and the support circuits looked Huge! (The capacitors), I'm stating to think it might be easier to use a seperate battery pack for the Servo's.

    Thanks, Connor

  6. #6
    robot maker Guest

    Re: Charge multiple power packs

    i working on a design that will charge batteries upto 10 amps charging current and more at 24 volts using max712,prototype the circuit and works great,it has a automatic sensing resistor design i made for selecting current and when fully charged goes to trickle charge
    building the pcb board to be sent out to a pcb company to have it made
    also 10 amp charging current is for charging 35 AH BATTERY at 12 volts or 24 volts,can do LI-PIO AND NICADS

    Quote Originally Posted by Connor View Post
    We'll, Like I said, these packs are already made up.. They each have a Thermosister, and some sort of resister that gets really hot when the packs short out (to protect the cell's).. I've been looking a unit called the MAX712/MAX713 which looks very promising.

    I several options, 4 of these 3800mAh packs, or 12 D 10000mAh cells, or 12 F 14000mAh cells.. The 4 3800mAh packs give me more mAhs, and are cheaper.. but, is it going to causes issues charging them. in parallel.

    Thanks, Connor

  7. #7
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    Re: Charge multiple power packs

    How about some photos of the prototype and the ammeter showing current output?
    I Void Warranties´┐Ż

  8. #8
    robot maker Guest
    also on a high current regulator ,i also using 2 servos at near 5.2 amps and the one i found is LT1083cp low dropout regulator, with 1 volt dropout so 7.4 volt will work down to 6.4 volts
    digi-key does have them in stock,at work we make mostly handheld test equipment and we use mostly low dropout regulators because of the batteries and on the charging side i made a 50 nicad automatic battery charger for production ,since that is my job,it chargers 50 battery packs one at a time
    making one close for my robots for automatic home base charger ,one is IROBOT create robot and other designs i am working on that take different charging current and voltage
    design is kinda based on the beacon design that IROBOT it has on thier charging base but a better design without the dreaded robot dance as its called


    Quote Originally Posted by Connor View Post
    Hey Folks,

    I've been building a Robot based on the iRobot Create platform. My design calls for 4 14.4v 3800mAh battery packs (12 sub-C NiMH each) wired in parallel to power the Mini-ITX PC board, and everything else (the create will continue to use it's own battery pack). So, Here is my question: How can I charge 4 packs wired in parallel? Would a standard iRobot APC Faster charger be able to do it? (It's Rated at 22.5vdc 1.25Amps, I know that if it could, it would take over 4 times longer than the normal pack.. so, 12-14 hours on a standard charge)..

    I also have another option... I'm using a universal power adapter for notebooks during my development. It output's 15-24v at 8.0A I thought I perhaps could use that to power the Bot when he's docked and charge his battery packs. Also. I do have a voltage and current measuring circuitry on the bot now, so I can measure the voltage and current of the battery (and incoming charge). I'm using the phidgets 20Amp current Sensor and precision voltage sensor. So, from what I can tell.. I need some diodes to put inline, some sort of switching circuit that allows me to turn on/off the charge.. Maybe some sort of trickle charge circuit.. I do have a Phidgets 8/8/8 with 3 of the analog inputs are in use already (1 for the current sensor, 1 for the voltage sensor, and 1 for a pressure sensor that will be used on the gripper.) I could hook up the 4 temperature sensors from the battery packs independently as well, leaving me with just a single analog sensor for a sonar device. A digital output could be used to toggle the charging circuit on or off... or pulse it for a trickle charge?? I'm open to ideas, suggestions, schematics or whatever. BTW, I know I could use LiON's, however, I wanted the added weight of the NiMH packs to help offset the weight of the arm I'm planning to add (which is on the robot's right hand side, and will be able to pickup 6-8lbs) Oh Yea.. I'm also in need of a 7.2-7.4v high current voltage regulator for the arm.. 2 of the servo's I'm using are capable of 5.2A stalled, So, I need something for that.

    Thanks, Connor
    i can set it up and post them
    uses a few very high current mosfets and max712cpe ,mostly i build it on my lunch break at work and few other times in between,bring the circuit home this weekend and i ordered a 36 volt 15 amp power supply i found at mpja getting it thursday


    lucky the design is not one i made for work because i can not use any designs that i design for work

    Quote Originally Posted by Adrenalynn View Post
    How about some photos of the prototype and the ammeter showing current output?
    Last edited by Adrenalynn; 08-30-2008 at 12:13 AM.

  9. #9
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    Re: Charge multiple power packs

    Sounds very cool robot maker, Got any spare boards when they come back from being made? Do you have a schematice you can post? Here or pm?
    People yearn after this robotic dream, but you can't strip your life of all meaning, emotion and feeling and expect to function.


  10. #10
    robot maker Guest

    Re: Charge multiple power packs

    yes after a few more tests,took all the parts home to put on my breadboard,since i cant take the one from work home,mostly keeping me from working on johnny five and my other robots
    on spare boards it might be hard since,i get 3 for $61 inc shipping and i need atleast 2 maybe 3
    but can order more,mostly its for gel cells but can with a few parts and jumpers for setting of different charge rates ,and cell count and has 2 trim pots one for current select and one for charge voltage for other types of batteries
    max712 is a universal charging chip,need to buy only 8 soic surfboard,since i cant use the one from work for my breadboard ,it only has 1 smt chip,1 p-channel,1 n-channel 1 high current diode and 3 chips,on auto current side you can use a sense resistor .25/charging current or auto circuit


    update on my automatc charging design adding another circuit for having a different charging voltage and different trickle charging voltage
    like i a gell cell i am using is 12v 35ah i need 14.4v to 14.7v at 10 amps charging current and then switch to trickle for 13.8 volts like the manufactory recommends



    Quote Originally Posted by 4mem8 View Post
    Sounds very cool robot maker, Got any spare boards when they come back from being made? Do you have a schematice you can post? Here or pm?

    try LT1083 regulator 3 pin TO-220 package up to 7 amps and adjustable

    Quote:
    Originally Posted by Dave
    Your project sounds really cool. If you're planning to use a bunch of NiMH packs in parallel, you should read up on how they're charged, because there are some safety considerations. I recommend checking out this page at Powerstream:
    http://www.powerstream.com/NiMH.htm
    Powerstream is a good resource for all things battery-related. Their NiMH page goes into detail on how they're charged, what current you should use depending on the capacity, etc. Actually, they sell some battery monitoring boards that you may want to check out, as well.

    Also, here's an interesting paper to read:
    http://www.freescale.com/files/micro...ual/DRM051.pdf
    It's a reference design for a microcontroller-based battery charger, and it has schematics and voltage/current/temperature graphs that may help you out. It also describes how the firmware should respond to the sensor inputs.

    > I'm also in need of a 7.2-7.4v high current voltage regulator for the arm.. 2
    > of the servo's I'm using are capable of 5.2A stalled, So, I need something for that.

    I've been looking for somehting like that for ages, without success. I usually just use multiple 1A regulators in parallel
    Last edited by robot maker; 09-01-2008 at 12:55 PM. Reason: update

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