DC to DC converter. Increase current.

Discussion in 'The Projects Forum' started by mohitjindal, Jan 15, 2013.

  1. mohitjindal

    Thread Starter Active Member

    May 25, 2009
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    Hi,
    I want to make a dc to dc converter. I want to increase current from 1amp to 5amp with constant 12volts. Any ideas ?:eek:
     
  2. wayneh

    Expert

    Sep 9, 2010
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    I don't understand. What are you starting with, and what do you want as output?
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    You can do this if you want an output voltage of around 1.5V

    If you want to magically create an extra 4 amps at the output at 12V, you need a battery in between, at which point, it will only run until the battery dies.

    Energy cannot be created. 12V@1A input = 12W. If you wanted 12V@5A output, you are trying to convert 12W into 60W. Without a source for the other 48 Watts, this cannot be done.

    Stepping 12V at medium high current to 1.2V At VERY high current is common in PC Motherboards for CPUs built today. There are 2 12V lines delivering about 150 W of power to the area of the CPU. At that point, a bank of Switching Power supplies changes those 12V@10A lines into 1.25V @ 100 Amps+ to meet the power needs of the CPU. Hence the need for active cooling on today's processors, many dissipate over 100 W at low voltages.

    Add in the fact that supplies tend to only be 85-95% efficient at design load, and you will NEVER get more power out than you have power in.
     
  4. mohitjindal

    Thread Starter Active Member

    May 25, 2009
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    Ok i can place a 4000mah battery to get 4amp but how ? I think that will burn the dc motor controller board. How will i connect battery so that it give power to motor only, not to circuit board ? Please help.
     
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    I think you are looking at a solution to a problem you may not have.

    Start from the top with your project, what you intend to do, and members here can walk you through it so you don't burn things up.

    Do you have a schematic diagram you are working from? If so, post it as a .PNG attachment.

    Otherwise, describe ENTIRELY what you are trying to do with enough detail for people to get an idea for suggestions and what to look for, and what to avoid before spending a lot of money on stuff that you won't be able to use.
     
  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    You can't get out 5X as much power as goes in.

    Explain design objectives clearly and we can suggest a design.
     
  7. mohitjindal

    Thread Starter Active Member

    May 25, 2009
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    Ok I attached the Circuit PDF file. I want to attach a battery(to give extra current) to JP1 and JP2 of motor.Without burning the circuit board. I was thinking of parallel combination but it can burn the circuit.Currently the board is giving 1amp to the motor but I want to fix big motor and give 5amp.
     
  8. wayneh

    Expert

    Sep 9, 2010
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    The MOSFETs on the board may be your limiting factor. The rest of the board will be fine as long as the voltage is the same. The supply could be infinite.

    But the current of the larger motor may exceed the safe limits for those MOSFETs. Can you read the identification numbers on them? Are they on heat sinks? You might be able to replace them with better ones that can handle the higher current.
     
  9. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    An often used trick to beef up a circuit board trace is to get some 14ga wire (yanked out of a piece of romex house wiring, solid core), and simply solder it on the track that needs to carry the current.

    For lower demands, putting a few layers of solder on the track to pad the thickness works as well.

    Just remember to use terminals and wire to the motor rated for the current as well. I typically go 150% to 200% over, so if stall current is 15A, I use wire capable of 25-30A.
     
  10. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    +1 Their current rating and heat dissipation will be what determines if they can handle it. Raising the current by 5X will almost surely kill them. Manufacturers do not generally design in 500% headroom because it costs too much.
     
  11. mohitjindal

    Thread Starter Active Member

    May 25, 2009
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    The MOSFET are SUF2001. I attached the datasheet.
    If I attach a battery in parallel to JP1 and JP2 then it will burn the circuit.Somehow I have to tell the battery "Give your current to motor only":D I cannot remove MOSFETs from circuit because its a SMD board.Any other idea to give extra current to motor ?:rolleyes:
     
  12. wayneh

    Expert

    Sep 9, 2010
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    All you have to do is add capacity to Vdd, not to JP1 and JP2. As I said before, the capacity of the power supply does not affect your circuit. It does affect the current available to your motor, as controlled by the MOSFETs.

    But, that MOSFET is too small for a 5A motor. Two or 3A, maybe. Use the datasheet information to calculate the heat dissipation, which must be held below 2W. And don't forget that the PEAK current needed by a motor (to start it or when it stalls) can be a lot higher than the normal running current.
     
  13. mohitjindal

    Thread Starter Active Member

    May 25, 2009
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    Ok can I buy a 5000mah battery and connect +(of battery) to VDD in yellow ? And ground to the negative of motor ? I attached the Atmega chip pdf which controls this motor. Please check.
     
  14. wayneh

    Expert

    Sep 9, 2010
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    Now I'm confused. How does this relate to the first schematic you posted?

    The bottom line is that the circuit doesn't care about the capacity of the power supply, only the supplied voltage. As long as the voltage is right, all is well.

    The circuit DOES care about the load - your motor. If the load is too great, some parts of the circuit may experience an overload. An unlimited power supply can exacerbate the overload by not "sagging". The weak link will be exposed.
     
  15. mohitjindal

    Thread Starter Active Member

    May 25, 2009
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    The circuit board can hold 12 volts. I want 12volts. But i want to give more current so that the circuit can run big motor. Can i just add 12volt 5000mah battery to same board ?
    And tiny heat sinks on 2 mosfets and atmega 8a ic ?
     
  16. vortmax

    Member

    Oct 10, 2012
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    No you cannot. The h-bridge is not able to switch that much current. You might be able to replace the mosfets, or rig it up so that the h-bridge drives another set of larger mosfets that can handle the power, but for all that effort, you can buy a new controller that is properly designed to handle the loads you need for ~$15.
     
  17. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    If your motor is 5 Amp continual, peak will likely be over 10A.

    You will need a Different Motor Driver, Like this one. That driver is rated for continual duty over 5 Amps, and could be used with a high output battery.

    If you tried to load down your existing motor driver with a high current motor, it would shutdown from thermal load if it is a good one, or just die if it is a low cost one.

    There isn't a modification you can easily make to the controller board you have to work with a 500% continual overload.
     
  18. mohitjindal

    Thread Starter Active Member

    May 25, 2009
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    Can I connect a Battery of 5000mah through Gauge Wire ? Where in the circuit I have to attach it ?
     
  19. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    To connect a battery of higher voltage than rated (which would give a higher current than rated), you could only connect the motor directly to the battery, assuming it is a brushed DC Motor (not a stepper motor or a brushless DC motor, both of which require controllers).

    If the voltage is what the circuit is rated for, you can simply connect it, assuming the motor is also within the ratings of the circuit. If the motor draws more current than the driver is capable of delivering, you'll need a new motor driver.

    If going through the motor driver, there should be a jumper to use different battery than logic supply that you either place or remove, and on the motor driver board itself, it should have inputs for logic in, logic power ground, and motor power in/motor power ground. If your board doesn't have those separate connections, you cannot use a different battery to run the motor.
     
  20. mohitjindal

    Thread Starter Active Member

    May 25, 2009
    49
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    I am planning to buy a new DC motor driver board which can run 5amp motor but I don't know how to connect it with Atmega 8A chip. Please see the proccesor.pdf I attached on this page earlier for Atmega 8A.

    Here are the 7 pins on DC motor controller\driver board:-

    Pin No. Pin Functionality
    1 GND Ground
    2 IN-1 Logic input for the motor direction.
    3 Diagnostic 1
    (DG-1) Output pin with logic 1 output in normal operation. Represents side of the internal
    H bridge corresponding to IN-1. Pin is pulled to logic low by the motor driver in
    case of over temperature or overload due to short circuit.
    4 PWM Used to apply Pulse Width Modulation to control motor velocity
    5 Diagnostic 2
    (DG-2) Output pin with logic 1 output in normal operation. Represents side of the internal
    H bridge corresponding to IN-2. Pin is pulled to logic low by the motor driver in
    case of over temperature or overload due to short circuit.
    6 IN-2 Logic input for the motor direction.
    7 CS* Current Sense output to measure the current flowing through the driver:confused:
     
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