drive circuit for 1 hp 24V dc motor

Discussion in 'General Electronics Chat' started by shaqour, Oct 28, 2012.

  1. shaqour

    Thread Starter New Member

    Oct 24, 2012
    4
    0
    haay all

    I'm trying to design a drive circuit to control a 1 hp, 24 V DC motor using PWM.
    The rated current for this motor is 40 Amp.

    Unfortunately, I could not find any transistors that could handle this current in my local electronic store.

    I found the MJ15003 ( http://www.onsemi.com/pub_link/Collateral/MJ15003-D.PDF ) which can handle 20 Amp. So i tried to use 4 of them parallel (as in the image) ( http://imgur.com/AOugw ) . But the current passed through only one transistor and damaged it.

    Anyone can suggest anything to help me with my problem

    thanks :)
     
  2. panic mode

    Senior Member

    Oct 10, 2011
    1,321
    304
    obviously you could try larger transistor (usually power MOSFET) but if you cannot source them locally, alternative is to connect multiple transistors in parallel. the key is sharing load current evenly among transistors. transistors tolerances are poor even among samples from same batch so you need to linearise them. this is done by placing small resistor in emitter of each transistor. this resistor will provide negative feedback needed to stabilize circuit and ensure reasonable sharing of current.

    something like this:
    http://www.learnabout-electronics.org/Amplifiers/amplifiers51.php
     
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  3. ScottWang

    Moderator

    Aug 23, 2012
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    When you use the transistor in the high current circuit, you have to reduce the current flow through the transistor, you better never over 1/5 max rating, the 2N3055 has 15A max rating, but only used 2.5A each 2N3055 as the below linked page.

    I had a power supply provided 4A current, and I used two 2N3055, so only used 2A each 2N3055 in my circuit.

    Now, if you want to use MJ15003, it has 20A max rating, then you can calculate how many Mj15003 that you will need them.

    How to parallel the Power transistors.
    http://www.eleccircuit.com/regulator-0-30v-5a-by-ic-723-2n3055-2part/

    Another way is the Power MOSFET as panic mode just point out.

    Here are some kinds of High current MOSFETs, you can choose the kind you like and easy to buy it.

    RU3205 _Nch_60V 90A_7.5mΩ
    IRF3205s _Nch_55V 110A_8mΩ
    IRFS3004-7PPBF _Nch_40V 240A_Vgs-4-10V_1.25mΩ_D2PAK-7
    NXP-PSMN5R6-100BS _Nch_100V 100A_Vgs-3-10V_4.72mΩ
    IRF1010E _Nch_60V 84A 200W 12mΩ Vgs10V

    If you want to check the datasheet of MOSFET.
    http://www.datasheetcatalog.net/
     
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  4. shaqour

    Thread Starter New Member

    Oct 24, 2012
    4
    0
    "panic mode" and "ScottWang"

    thank you very much for the answer. I went to the local electronics store in my city. unfortunately, i could not find any of what u suggest. i found IRFP460 MOSFET with max. current of 20A.

    So, i used 3 parallel MOSFETS. as here ( http://imgur.com/X0aGZ ) when current passes through them (even for few seconds and no load on the motor) they heat up very much, although I put heat sinks.

    how much MOSFETs can i put on parallel ??
    is there any limitation for that???
     
  5. ScottWang

    Moderator

    Aug 23, 2012
    4,855
    767
    I pasted your circuit on.
    [​IMG]

    When you want to use the MOSFET to provide the high current to the load, the first thing that you should care about, that is you need to find a MOSFET have a low resistance between DS, you can see that what I showed you the MOSFETs, they are all have low resistance(Rds), the V = I x R, when the R is Low, then the V will getting low too, as the MOSFET that you bought, the Rds 0.22~0.27Ω is too high, so the V will getting High, and the P = V x I will getting high too, that is the problem that you got.

    The high current or high voltage of MOSFETs, that is not easy to buy them in the local store, it's same with me, you may buy them from the online stores.

    In your project that you maybe need to add sink and fan to take the heat away.

    For the Vg voltage level, so you can adjust the 10K to 100Ω, and add 10K from Vg to ground, it will turn the Vg down to ground when the Power SW is OFF, just don't put the Vg in a floating situation, it will make something go wrong.
     
    Last edited: Oct 29, 2012
  6. ifixit

    Distinguished Member

    Nov 20, 2008
    639
    108
    Also... put the motor on the drain side, not the source side.
     
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  7. ScottWang

    Moderator

    Aug 23, 2012
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    The circuit was modified as you can see, many MOSFET Vgs(sat) ≧10V, so that is also very important when you choose a MOSFET, so I changed the valtage of battery, if you can't find a high current MOSFET with a low Vgs that you can use 9V battery, then you must be use the battery>10V for Vgs.

    [​IMG]
     
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  8. shaqour

    Thread Starter New Member

    Oct 24, 2012
    4
    0
    "ScottWang"
    I really appreciate your help. it is very helpful for me.
    but one last question. pleaze pear with me!!!!

    If I put the cooling system (which is used for the CPU) on the MOSFETs.
    Is it going to solve the heating problem???
     
  9. ScottWang

    Moderator

    Aug 23, 2012
    4,855
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    About the heat of MOSFET:

    1. Low Rds(sat), it better less than 10mΩ.
    2. heat sink.
    3. Fan.
    4. The holes on the Box for cool air in and hot air out, there are two ways.

    a) Two holes, if you put the PCB and parts in the Box, then you have to do this, one hole for the hot air out from fan, and one hole for the cool air in, we do this way for our products of power supply.

    b) One Big hole from fan for the hot air out, and many small holes for the cool air in, this way is just like the Power of PC, so you can see the way of power of PC.

    >If I put the cooling system (which is used for the CPU) on the MOSFETs.
    >Is it going to solve the heating problem???

    I think it is depends on how low the Rds(sat) of MOSFET that you can buy, you can calculate:
    V = I x R, P = V x I, I is the current flow through the DS of MOSFET, V is the I x Rds(sat), So P = V x I, You also can measure the temperature of MOSFET using your finger(be careful) and temperature meter, to see how high of the temperature, the continuing temperature better not to over 65℃, the testing time at least over one hour.

    The below list of high curent MOSFETs is that I collected, but I only got the IRF1010E in my hand, some are two new, maybe the price is too high, or some is not easy to buy.

    IRF1010E, Nch, 60V, 84A, 200W, 12mΩ, Vgs10V
    IRF3205, Nch, 55V, 110A, 8mΩ
    IRF3205s, Nch, 55V, 110A, 8mΩ
    IRF3710, Nch, 100V, 57A, 23mΩ
    IRF3710s, Nch, 100V, 57A, 23mOhm
    IRFS3004-7PPBF, Nch, 40V, 240A, Vgs-4-10V, 1.25mΩ
    IRFZ44N, Nch, 55V, 49A, 17.5mΩ, Vth(2~4V)
    IRFZ44N, Nch, 55V, 49A, 22mΩ
    IRLB3036GPbF, Nch, 60V, 195A, 2.4mΩ, Vgs4.5V
    NXP-PSMN5R6-100BS, Nch, 100V, 100A, Vgs-3-10V, 4.72mΩ
    RU3205, Nch, 60V, 90A, 7.5mΩ

    You also can search the MOSFET to suit your need, here and here.
     
    Last edited: Oct 30, 2012
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  10. shaqour

    Thread Starter New Member

    Oct 24, 2012
    4
    0
    Finally, I found the IRFZ44 (BV_DSS = 60 V, R_DS(on) = 0.024 W, I_D = 50 A) in on of the near stores :D :D :D
    I will by two and but them on parallel in the same circuit you have suggested. I think it will do the work I need.

    thank you very much ;)
     
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