1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Upgrading amps of a circuit to 12A

Discussion in 'General Electronics Chat' started by RafBR, Jun 23, 2012.

  1. RafBR

    RafBR New Member

    Joined:
    Jun 23, 2012
    Messages:
    6
    Likes:
    0
    Hi,
    I did motorize my kid's electric car with a 12v wiper motor that burns out any fuse lower than 12A because of it's high current at start. I think it's running amperage is about 6A.

    I found this great circuit that fits almost exactly in what I want, except that it have a bit weak output amperage.
    here is the circuit:
    http://www.soloelectronica.net/dcdc_12v_a_18v.htm

    I think this is also great because of the potentiometer for the output current that will be very useful.
    If anyone with such knowledge in electronics could help me to replace a few components that help rising the output power would be perfect!!!
    I also know that for this high current I should enlarge the pcb traces and place loads of solder on it.

    best regards!
     
  2. Sceadwian

    Sceadwian Banned

    Joined:
    Oct 27, 2006
    Messages:
    14,047
    Likes:
    141
    Location:
    Rochester, US
    You can't just replace a few components, you're more than doubling the running current and you're not even sure of the peak current, you can't 'modify' that pcb you'd have to redesign the whole thing, the components could be the same only higher power but you'd never fit them on the board (mainly the heatsink)

    Have you tried a different fuse type? You want a very slowblow fuse. standard or fastblow fuses will causes problems like that.
     
  3. tcmtech

    tcmtech Well-Known Member Most Helpful Member

    Joined:
    Feb 22, 2009
    Messages:
    6,699
    Likes:
    432
    Location:
    Sawyer, North Dakota, USA
    If it was me I would just go and use the speed controller out of a old cordless drill that in the same voltage range and refit that in as the speed control system.

    Even thehe cheap ones can easily take 20 - 30 amp peak loads and are generally not the least bit fussy about voltage variations as the battery runs down.

    Ask around and you probably get an old drill with a bad battery set for free!
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. Jaguarjoe

    Jaguarjoe Member

    Joined:
    Sep 24, 2010
    Messages:
    481
    Likes:
    4
    Location:
    Grosse Ile, MI

    Inrush current is about is maybe 3-4 times running current. Using ohm's law the inrush is the running voltage/armature resistance when the motor is at rest. To accommodate that, you need about 18amps. This is extreme because you only need that for a fraction of a second.

    As Sceadwian said, use slo-blo fuses, or a circuit breaker. JY's are full of either, cheap too.
     
  6. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

    Joined:
    Jun 21, 2006
    Messages:
    6,061
    Likes:
    520
    Location:
    Cleveland, OH, USA
    It is not clear to me what you want to do:

    1) Do you just want recommendations for the ampere rating for the fuse at 12V? If so, that has been give in posts 3&4.

    2) The schematic you show, however, is a boost converter. Do you want to increase the power and speed? If you boost the voltage to 18 volts, the motor will consume considerably more current -- perhaps beyond the motor's safe operating power. The circuit you show will need to be modified; although, the modifications needed may not be that great. In all likelihood, you will probably need a different inductor for the higher current. The mosfet shown is rated at 50A and 60V, so it may be able to handle that power.

    This datasheet for the LM3478 used as a boost converter is offered as an example and describes the calculations needed:

    http://www.electro-tech-online.com/custompdfs/2012/06/lm3478.pdf

    A more general discussion is here: http://www.electro-tech-online.com/custompdfs/2012/06/snva035a.pdf

    Designing a boost converter to go from 12V to 18V at that higher, as yet unknown current will take some time. TI ( National) does offer several online design tools to help. Is that a project you want to launch?

    John
     
  7. tcmtech

    tcmtech Well-Known Member Most Helpful Member

    Joined:
    Feb 22, 2009
    Messages:
    6,699
    Likes:
    432
    Location:
    Sawyer, North Dakota, USA
    Personaly if it was me and I ws going for a 18 volt conversion of a 12 volt toy I would just add a 6 volt battery of equal Ah rating as to what the 12 volt unit is.

    Simpler, more usable energy stored, a lot more reliable, and garanteed to work at what ever amp load needed.
     
  8. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

    Joined:
    Jun 21, 2006
    Messages:
    6,061
    Likes:
    520
    Location:
    Cleveland, OH, USA
    • Like Like x 1
  9. RafBR

    RafBR New Member

    Joined:
    Jun 23, 2012
    Messages:
    6
    Likes:
    0
    Hi John!
    These motors usually dont burn 12A fuses even in stalled conditions. So its safe to say 12A is enough.
    Here is the link to the car how it is today :D
    http://www.youtube.com/watch?v=0uDJWBNg9lI&list=UU0moHebOrEjWKqYmOKjRL8g&index=1&feature=plcp
    And an old current test with these wiper motors:
    http://www.youtube.com/watch?v=nzuCmBgE660&list=UU0moHebOrEjWKqYmOKjRL8g&index=3&feature=plcp

    And the progress so far with the board upgrade:
    View attachment 65186
    View attachment 65187
     
  10. RafBR

    RafBR New Member

    Joined:
    Jun 23, 2012
    Messages:
    6
    Likes:
    0
  11. Sceadwian

    Sceadwian Banned

    Joined:
    Oct 27, 2006
    Messages:
    14,047
    Likes:
    141
    Location:
    Rochester, US
    RafBR, the entire circuit needs to be redesigned, including the PCB schematic, what you're asking is not a trivial thing, it's not just a 'tweak here a tweak there' new components have to chosen along with a new layout, this is not something someone can just toss together in a few minutes, it would takes hours of work and research, and probably at least a little bit of a testing.

    This is like asking someone on an automotive forum to redesign and provided detailed instructions on how to rebuild an entire engine for twice it's rated power for free, using only a couple dozen words...

    Help is one thing, but no one here should go to this degree of effort on such a very simple problem, which is to purchase a board that handles the higher current.

    Hot wiring a battery to a wiper motor is one thing, doing it right is much much harder.
     
  12. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

    Joined:
    Jun 21, 2006
    Messages:
    6,061
    Likes:
    520
    Location:
    Cleveland, OH, USA
    When you say "upgrade" the board, it is still not clear to me what you want to do. Are you trying to keep the max amps <12A to avoid blowing fuses?

    Please tell us what exactly you are trying to do?

    Regards, John
     
  13. RafBR

    RafBR New Member

    Joined:
    Jun 23, 2012
    Messages:
    6
    Likes:
    0
    No, 12A is just the max current the board is meant to be able. 12A fuse > max current the motor draws.
    So if the board is able to give 12A it is more than good. Maybe 12A peak current or so. So it is not THAT big tweak I think.
    The schemes I posted today (previous page) are what I am planning to do based on a few friends tips.
    In the begining of the thread you can find a link to the original circuit.

    best regards,
    Rafael.
     
  14. ronv

    ronv Well-Known Member Most Helpful Member

    Joined:
    May 30, 2010
    Messages:
    4,725
    Likes:
    488
    Location:
    Tucson, AZ. USA
    Speed Control

    If what you want to do is control the speed of the motor try this simple circuit.
     
  15. RafBR

    RafBR New Member

    Joined:
    Jun 23, 2012
    Messages:
    6
    Likes:
    0
    Hi ronv, thanks for the interest!
    Yes I want to control speed as well but a little more volts are welcome too :D
    Do you know how many amps we get on the output of your schematic?
    regards!
     
  16. ronv

    ronv Well-Known Member Most Helpful Member

    Joined:
    May 30, 2010
    Messages:
    4,725
    Likes:
    488
    Location:
    Tucson, AZ. USA
    Getting speed control is easy, getting more voltage is hard. :(

    The circuit with the parts listed should do 20 Amps easy enough. You need a small heatsink on the diode across the motor.
     
  17. Sceadwian

    Sceadwian Banned

    Joined:
    Oct 27, 2006
    Messages:
    14,047
    Likes:
    141
    Location:
    Rochester, US
    The board you referenced is meant to handle 5 amps..... that's it, 5 amps. 10 peak for a few ms.. Not 12 amps for any length of time.

    You can test it if you want, simply replace it with a slow blow fuse or a 15amp fuse, and pray the power dissipation equalizes out to something that doesn't weld the PN junction of the FET.
     
  18. RafBR

    RafBR New Member

    Joined:
    Jun 23, 2012
    Messages:
    6
    Likes:
    0
    No, 5 amps is the original circuit. The circuit now being modified that is meant to handle 10A with peaks of 12A.
     

Share This Page