9v to 12v Boost Converter (30A)

Discussion in 'The Projects Forum' started by benchaz, Dec 31, 2011.

  1. benchaz

    Thread Starter Member

    Feb 2, 2009
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    Hi guys,

    I'm hoping I could get some advice on my project.

    I need to supply 12v DC over a pair of 15 meter 10AWG cable with a maximum load of 30A. The problem is, however, that at max. load there is the total voltage drop of 3v across the cables (1.5v in each direction) resulting in 9.5v at the terminal. I need to boost the voltage back to 12v.

    Due to other limitations, I'm not allowed to start out with a higher voltage and I cannot use thicker cables.

    How do you guys suggest I could tackle this problem? Is a boost converter the best solution? If so, could someone point me in the right direction and provide a starting point?

    Thanks! Any help is much appreciated!
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    You will only melt the insulation on your cables if you use the same voltage.

    Boost the voltage to 100VDC and reduce it back down to 12VDC after 50 feet and the current would only be 6A, which is workable, provided the insulation on the cable can withstand 100V

    What is the exact project you are working on? There may be a better solution to your problem than a solution for your solution.
     
  3. benchaz

    Thread Starter Member

    Feb 2, 2009
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    I forgot to mention - 30A is only the maximum burst current. On average it runs about 10A.

    The specs of the project does not allow me to use any voltages higher than 12v, actually... So boosting it to a higher voltage is not an option either. What a pain!!
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Solution: cool the wires to absolute zero, then they will become superconductors and will have no voltage drop. Problem solved!

    Now if you could only figure out a way to cool 15 meters of wire to absolute zero... or even a single millimeter...
     
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  5. SgtWookie

    Expert

    Jul 17, 2007
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    From your PM:
    You've basically eliminated the most practical solutions.

    If you could move the power source to the other end of the 15 meters of wire, and use the wire as signal-level control lines only, that would be a good solution.

    But as it is, about your only option left would be to put the booster at the far end of the 15 meters of wire. This will increase the current requirement through the wire, which will increase the losses.

    If you're sourcing 30A @ 12v, and getting 9v on the load side, you'll have to draw another 10A or so if you were using an ideal boost circuit to raise the voltage back up. However, a real circuit will have losses. If you did a good job of designing/building a boost circuit, you might have ~80% efficiency. So, you're going to need ~50A current through the AWG 10 wiring, which will give you a total of 5v drop instead of 3v drop - which means you'll have to draw even more current.

    It's quite late here, and I'm too tired to figure it out.
     
  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    A boost with remote sense to hold the voltage at 12V at the load. If not, the voltage will rise and fall with load current.
     
  7. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Who in the right mind would even think about this......!!!?

    It's not practical.

    {ed}
    Ooooooh!! A revelation...

    Use a 12V SLA. Simple :D
     
  8. benchaz

    Thread Starter Member

    Feb 2, 2009
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    Thanks for all the replies!

    This is for an underwater ROV that I'm making for the MATE competition this year. The rules of the competition do not allow voltages higher than 12v, (for safety in the water). We are given a 12v car battery on the surface for power. All the power must go through tether - no onboard batteries (for safety, again, in case of leakages). The tether is 15 meters long. And finally, the tether cannot be too thick and heavy or else it'll lose flexibility and thus mobility.

    I am using 12v underwater brushed thrusters on the robot and controlling them with a MOSFET pwm motor controller. Turn them all full on and the voltage drops to 8/9v... which isn't ideal for the performance of the ROV. I was hoping to improve it this year by boosting the voltage back to 12v so the thrusters can run on full power, without making the tether heavier and thicker and less flexible.

    Guess I'll just make my tether thicker and heavier to compensate...
     
  9. DigitalReaper

    Member

    Aug 7, 2010
    70
    2
    Here's a few ideas/thoughts in no particular order:

    Remove the insulation on one of the tether wires (probably ground) to lighen it up a bit and make it more flexible. If the insulation on the other wire becomes badly damaged then it may cause a direct short though. If this isn't for use in salt water then both conductors touching the water only won't cause too much extra current to flow.

    If the entire cable is in the water then you don't have to worry about heat so much letting you pump more current down the cable. If you can't have the whole cable in to begin with then you could put in as much as you can using lighter wire and have the rest in heavier wire suitable for use in air. Make sure the join is waterproof though if you're running this in salt water.

    Add floats to the cable to make it neutrally buoyant. Doesn't help with flexibility though.

    Some types of insulation on cables are more flexible than others.

    Large capacitors (or banks of capacitors) might help with surge currents, reducing the peak current in the tether and dropping less voltage. Won't help with the continuous draw though.

    Switching to 9v motors and using a current limiting driver would eliminate the need to boost the voltage back up to 12v without having to worry about overvoltage at light loads. This may be difficult and/or expensive to do since you already have a 12v setup installed.
     
  10. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Use smaller/more efficient motors. Maxon is well known for powerful efficient motor design.

    Use less aggressive props in the drive.

    Put the H-Bridge driver and batteries on the ROV itself, and use the tether for control signals only. Water is an AWESOME heat sink, so anything you put in contact with the outer shell will be kept at a steady temperature.

    Look at your power budget, write one down if you don't have one already, find places to cut. Use high power LEDs instead of Halogen bulbs, good motors instead of cheap motors, etc.
     
  11. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    U cannot do it without boosting the Voltage more than 12 or using low loss copper which makes it thicker.

    Only option is like one guy said to use low voltage high performance motors.

    Or use gold cables.
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Gold is not only more expensive than copper, it has a much higher resistance.

    Silver is a better conductor than copper; however a 15 meter long AWG-10 silver cable would be rather pricey.
     
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  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Gold is higher ?? Funny, and I always thought they were lower since IC packages uses gold wire for interconnect..

    Hmm....Guess I had that way wrong...
    But I remember reading something about gold vs copper. Gold being better.
     
  14. Sparky49

    Active Member

    Jul 16, 2011
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    I think it's because gold doesn't oxidise as easily as copper (at all?) - also gold can be made much thinner - useful for using in ICs.

    Some contacts are actually gold plated copper.
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Gold is used because it is so stable; it corrodes so slowly that you would not live long enough to notice it.

    Here are some metals and their resistivity as compared to copper (copper=1):

    Code ( (Unknown Language)):
    1.         Relative
    2.           to   
    3. Metal       Copper  ρ (nΩ m)
    4. silver       0.930    15.9
    5. copper       1.000    17.1
    6. gold         1.292    22.1
    7. aluminum     1.550    26.5
    8. tungsten     3.088    52.8
    9. zinc         3.450    59
    10. brass        3.743    64
    11. nickel       4.053    69.3
    12. lithium      5.427    92.8
    13. iron         5.620    96.1
    14. platinum     6.140   105
    15. palladium    6.164   105.4
    16. tin (0 ℃)  6.725   115
    17. chromium     7.368   126
    18. tantalum     7.661   131
    19. solder       8.772   150
    20. steel, plain    10.526   180
    21. lead        12.164   208
    22. uranium (0 ℃) 16.374   280
    23. titanium (0 ℃)    22.807   390
    24. steel,stainless 42.105   720
    25. mercury (0 ℃) 55.029   941
    26. plutonium   82.690  1414
    27. manganese   84.211  1440
    28. nichrome    87.719  1500
    29.  
    Note that tin/lead solder has almost 9x the resistance of copper.
     
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  16. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    If you simply add remote sensing (add two tiny thin sense wires at the load) you can have the source voltage booster compensate for the volatge drop along the cable.
     
  17. Adjuster

    Well-Known Member

    Dec 26, 2010
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    Apparently not, as the safety rules of the competition the OP is entering have a rigid 12V input limit.

     
  18. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    You could build a converter that could take the 12V input and boost it up however much is required to force the voltage out at the robot to be 12V, but you need two thin sense lines run back from the load to the controller of the boost converter.

    It would only need to boost a few volts maximum, it would pose no risk and they would not know since it still runs off 12V and supplies 12V to the unit being powered.
     
  19. SgtWookie

    Expert

    Jul 17, 2007
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    I believe that if they get caught with greater than 12v in any part of the system, they will not be allowed to enter the competition - or will be disqualified at the end of it.
     
  20. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    http://www.materover.org/rov_competition_files/2012/2012_Specs_Rules_FINAL.pdf

    Selected relevant entries:
    So basically, you get 12V, 25A, and that's it - except for your on-board batteries. Better make the most of it.
     
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