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Thread: Pick me a Mosfet for a RC Boat

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    Quote Originally Posted by Skepticist View Post
    The lower the resistance, the lower the heat losses for a given current and there are high current mosfets available with Rds less than 0.001 ohm (at a cost of course) so you can get away without using a heatsink apart from the copper on the PCB. A good example is the PWM ESC modules available for RC applications.

    This surface mounted one is 500 microOhms and rated for 30V, 300A
    You'd need about 35 IRFZ44N's in parallel to get the total Rds that low!
    Had a look at RS components for the IPT004N03LATMA1 N-Channel MOSFET, 300 A, 30 V OptiMOS, 8+Tab-Pin HSOF Infineon so HELP!!!! how do you connect that 8 pin monster to suit my simple diagram.



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    have a looky here theres only three connections needed

    just gate, drain ,source , same as before ?????

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    You'll need a PCB for it - needs a good size area of copper for the drain (like 5cm^2 or so) to sink the heat if you want to push it at all.
    The chip itself is 10mm x 10mm and 2mm thick so only a monster in terms of performance.

    If the drain connection copper pad is 2cm x 3cm that's 6cm^2 so overall size so can still be quite small and should fit just about anywhere.
    Will post an example PCB if I ever work out how to insert a pic from my PC.

    Can be as simple as this and could be made by filing or dremeling a piece of blank PCB - this one is 38mm x 20mm



    If it just has to be non-smd I'd try this TO220 0.0013 ohm option
    Last edited by Skepticist; 03-02-19 at 07:37 PM.

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    Quote Originally Posted by hinekadon View Post
    have a looky here theres only three connections needed

    just gate, drain ,source , same as before ?????
    Gate Pin 1, Source Pin 2, Drain Tab.
    Ok
    I prefer to use the Usual type of Mosfets for ease of connections. I tried the 49 Amp single IRFZ44N and it died immediately not unless I did something wrong.

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    Quote Originally Posted by Skepticist View Post

    If it just has to be non-smd I'd try this TO220 0.0013 ohm option
    I prefer to use a mosfet like the above, It simple and easy and should get away with a single. You think that 195A should be ok for the surge current just in case if I update the Motor to have more torque.

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    Last edited by Mr 672A; 04-02-19 at 11:01 AM.

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    I'd still use a heatsink on it as just as little as a few cm^2 will make a big difference and it gives you more mounting options as well.

    Is the motor you're using brushless or a simple commutator type?

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    Quote Originally Posted by Skepticist View Post
    I'd still use a heatsink on it as just as little as a few cm^2 will make a big difference and it gives you more mounting options as well.

    Is the motor you're using brushless or a simple commutator type?
    Yes I try to use a Heat sink. Because they are really cheap I will buy few and test them.
    For unknown reason they ALWAYS use simple commutator type. Funny thing is on my Jets that I use to fly before I had a Stroke (they are parked on the ceiling now) they use outrunners 3 phase motors. Yes Very expensive as I purchase a pair of matched ones (one spin clockwise and the other Counter Clockwise) Dr Mad Motors for my SU 35 Rissian Jet.


    Yes the Motors used for my latest use are the brush types and even the most expensive ones cost about $70 thats nothing like the Ducked Fan ones

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    Quote Originally Posted by Mr 672A View Post
    Gate Pin 1, Source Pin 2, Drain Tab.
    Ok
    I prefer to use the Usual type of Mosfets for ease of connections. I tried the 49 Amp single IRFZ44N and it died immediately not unless I did something wrong.
    That looks like a typo there IE Gate Pin 1, Source Pin 2, Drain Tab
    Should be 1 - gate, 2 - drain, 3 - source, tab - internally connected to drain

    The SMD 'monster' is 1 - gate, 2345678 - source, tab - drain

    About the motor: I only asked because a standard brush type motor at standstill is a short-circuit during the nanoseconds/microseconds between applying power and it actually beginning to rotate whereas a brushless motor's controller is smarter and reduces that startup peak current by doing a 'soft' start.

    The 'locked rotor current' is limited only by the DC resistance of the wiring and motor winding, brushes/commutator plus the internal resistance of the power source. That current can be extremely high under the right circumstances for long enough (microseconds) to destroy a semiconductor device and you'd need an oscilloscope to catch what the peak current actually is.
    Last edited by Skepticist; 05-02-19 at 11:10 AM.

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    Quote Originally Posted by Skepticist View Post

    About the motor: I only asked because a standard brush type motor at standstill is a short-circuit during the nanoseconds/microseconds between applying power and it actually beginning to rotate whereas a brushless motor's controller is smarter and reduces that startup peak current by doing a 'soft' start.

    The 'locked rotor current' is limited only by the DC resistance of the wiring and motor winding, brushes/commutator plus the internal resistance of the power source. That current can be extremely high under the right circumstances for long enough (microseconds) to destroy a semiconductor device and you'd need an oscilloscope to catch what the peak current actually is.
    Arghh!!!The ABOVE this the reason why the Mosfet Dies because of this issue of "standard brush type motor at standstill" "motor at standstill is a short-circuit during the nanoseconds/microseconds between applying power and it actually beginning to rotate"
    I have a Good oscilloscope at home but I forgotten how to use it. One of the Many thing I knew with my eyes shut one second before the Stroke but after the Stroke I have completely 100% forgotten how to use it but I understand the above and this is the reason why the Mosfet dies and this is these reason it better to over rate but not underate. You would think that 195A should be ok? Thats a lot of DC amps but I can tell you this that the Mosfet IRFZ44N (49 Amps)is not enough but the second one I used lasted two starts before it died.

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    You may find that a high current diode in series with the mosfet will reduce the inrush current to make it more usable also a low resistance (0.5ohms ) with the gate will also soften it as well . In my opinion the smd is the best to use ! whats the running current of the motor ??? regards don

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    Not surprising that the microswitches didn't last long under those conditions.
    The way to catch those starting spikes is to put a known very low value resistance in circuit and monitor the voltage drop across it on the CRO. Something like a high current ammeter shunt should do nicely for that if you can get one.

    Question tho: why is it your motor has only 2 speeds IE 0 and flat out?
    If it's just because of the existing (ON/OFF) mechanical switch, once you have a reliable MOSFET acting as the switch you could drive it with a simple PWM circuit which would give you infinite speed variation with solid torque across the range. Just a thought

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    Quote Originally Posted by hinekadon View Post
    You may find that a high current diode in series with the mosfet will reduce the inrush current to make it more usable also a low resistance (0.5ohms ) with the gate will also soften it as well . In my opinion the smd is the best to use ! whats the running current of the motor ??? regards don
    Sorry I dont know what the Running Current is. I was worried that I might stuff up my multi meter because of the High current on start or even run as my Multimeter in series only can do a MAX of 20A . So you think that I should run that 8 legged SMD?
    Last edited by Mr 672A; 06-02-19 at 10:05 AM.

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    Quote Originally Posted by Skepticist View Post
    Question tho: why is it your motor has only 2 speeds IE 0 and flat out?
    If it's just because of the existing (ON/OFF) mechanical switch, once you have a reliable MOSFET acting as the switch you could drive it with a simple PWM circuit which would give you infinite speed variation with solid torque across the range. Just a thought
    Yes like a switch as its on and off and its simple. If a Mosfet can do the same It would be good. I had to google what PWM is and as I stand Its to complicated for me ATM.
    Yes its a drag racing boat.

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    Yes its a drag racing boat aha!
    my advise is to use pwm on the mosfet as the boat will get to max speed quicker if you set a time for it to get there as now ( off on off) will make cavitation a major issue and i doubt you will achieve full drive therefore never reaching full speed . Dont be afraid of the pwm mode as once you get familiar with it ,it gets easier to work with and is quite simple really and great controll of your project without the bangs cheers don

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    Quote Originally Posted by hinekadon View Post
    Yes its a drag racing boat aha!
    my advise is to use pwm on the mosfet as the boat will get to max speed quicker if you set a time for it to get there as now ( off on off) will make cavitation a major issue
    Come to think of it you are right. Cavitation is a big issue that I forgot.

    A guy just emailed me and told me he is using a 150N03 without no issues but googling 150N03 come in many formats and they are no good for me. What I need is to measure the Current on a Average motor and by this I can get a mosfet that has a larger capacity and use it but at the same time I have to think about the spike current and see if a Mosfet (suggested) that has a constant 195A rating will do. Will find out soon after I buy 6 off them and it they hang in there I will convert to variable speed pwm.

    type Designator: BSC150N03LDG
    Type of Transistor: MOSFET
    Type of Control Channel: N -Channel
    Maximum Power Dissipation (Pd): 26 W
    Maximum Drain-Source Voltage |Vds|: 30 V
    Maximum Drain Current |Id|: 20 A
    Maximum Drain-Source On-State Resistance (Rds): 0.015 Ohm
    Package: SuperSO8
    .................................................. .............................

    Type Designator: BSO150N03

    Type of Transistor: MOSFET
    Type of Control Channel: N -Channel
    Maximum Power Dissipation (Pd): 1.4 W
    Maximum Drain-Source Voltage |Vds|: 30 V
    Maximum Drain Current |Id|: 7.6 A
    Maximum Drain-Source On-State Resistance (Rds): 0.015 Ohm
    Package: SO8
    .................................................. .........................
    Type Designator: BSO150N03MDG
    Type of Transistor: MOSFET
    Type of Control Channel: N -Channel
    Maximum Power Dissipation (Pd): 2 W
    Maximum Drain-Source Voltage |Vds|: 30 V
    Maximum Drain Current |Id|: 9.3 A
    Maximum Drain-Source On-State Resistance (Rds): 0.015 Ohm
    Package: SO8
    .................................................. ...........................

    Type Designator: CS150N03_A8

    Type of Transistor: MOSFET
    Type of Control Channel: N -Channel
    Maximum Power Dissipation (Pd): 100 W
    Maximum Drain-Source Voltage |Vds|: 30 V
    Maximum Gate-Source Voltage |Vgs|: 20 V
    Maximum Drain Current |Id|: 150 A
    Maximum Junction Temperature (Tj): 175 °C
    Rise Time (tr): 20 nS
    Drain-Source Capacitance (Cd): 940 pF
    Maximum Drain-Source On-State Resistance (Rds): 0.0035 Ohm
    Package: TO220AB
    .................................................. .................................

    Type Designator: RMW150N03

    Type of Transistor: MOSFET
    Type of Control Channel: N -Channel
    Maximum Power Dissipation (Pd): 3 W
    Maximum Drain-Source Voltage |Vds|: 30 V
    Maximum Gate-Source Voltage |Vgs|: 20 V
    Maximum Drain Current |Id|: 15 A
    Maximum Junction Temperature (Tj): 150 °C
    Rise Time (tr): 38 nS
    Drain-Source Capacitance (Cd): 337 pF
    Maximum Drain-Source On-State Resistance (Rds): 0.0065 Ohm
    Package: PSOP8
    .................................................. .................

    Type Designator: UTT150N03

    Type of Transistor: MOSFET

    Type of Control Channel: N -Channel

    Maximum Power Dissipation (Pd): 160 W

    Maximum Drain-Source Voltage |Vds|: 30 V
    Maximum Gate-Source Voltage |Vgs|: 20 V
    Maximum Drain Current |Id|: 150 A
    Maximum Junction Temperature (Tj): 150 °C
    Rise Time (tr): 105 nS
    Drain-Source Capacitance (Cd): 970 pF
    Maximum Drain-Source On-State Resistance (Rds): 0.0034 Ohm
    Package: TO-220
    .................................................. ....................

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    Definitely don't go using your multimeter to measure this current or you'll likely be in the market for a new meter as well.
    These are the sort of shunts I meant (the 100A one particularly)

    It's just a power resistor, in the case of the 100A one - 0.00075ohm 7.5W and should be made of 'eureka' alloy for a stable temperature coefficient but they don't expressly say that and it's from China after all but still would give you the best idea with a CRO. 100A through that shunt will produce a voltage of 75mV across the terminals.

    Only the 3rd last and last of the FETs listed (CS150N03_A8, UTT150N03) are 150A and both have Rds about .0035ohm so they'd be worth a try if they're cheaper & easier to obtain than the other good options (150A or higher).

    And when I said use a heatsink earlier - doesn't have to be a fancy finned aluminium type as just a flat piece of copper sheet will work really well. (Cu is a better heat conductor too)
    Last edited by Skepticist; 06-02-19 at 04:41 PM. Reason: fixed URL

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    had a looky last fet seem to be best for you but you will have to step it two or three times to get up to speed with a bit of copper bar you should be right as a heatsink can you step something to stop the fet from going from off to flatout from your remote control, Ive found the forward resistance of diodes good as current limiters just stack them up in series and then switch across them Skepticist; is correct about the shunt dont use your meter unless you dont like it any more lol ... if you want some mental exercise and have a hand full of resisters you can make a shunt say ten x 5 ohm in parallel and you end up with about 0.5 ohms , the rest is just maths to work out the total current. cheers don

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    Quote Originally Posted by Skepticist View Post
    Definitely don't go using your multimeter to measure this current or you'll likely be in the market for a new meter as well.
    These are the sort of shunts I meant (the 100A one particularly)

    It's just a power resistor, in the case of the 100A one - 0.00075ohm 7.5W and should be made of 'eureka' alloy for a stable temperature coefficient but they don't expressly say that and it's from China after all but still would give you the best idea with a CRO. 100A through that shunt will produce a voltage of 75mV across the terminals.

    Only the 3rd last and last of the FETs listed (CS150N03_A8, UTT150N03) are 150A and both have Rds about .0035ohm so they'd be worth a try if they're cheaper & easier to obtain than the other good options (150A or higher).

    And when I said use a heatsink earlier - doesn't have to be a fancy finned aluminium type as just a flat piece of copper sheet will work really well. (Cu is a better heat conductor too)
    You can see how many people have purchased that ebay shunts, I wonder if they have made a mistake like I was before I said to myself, Hang on this meter does only 20Am in series.

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    100Amp one is cheap and I will get it. Who knows I might be able to use it with other stuff I play with. Chinese New Years ATM it talk 3 months t0 get it. Well I'm no in a hurry

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    It's one of those things that spend most of their time at the back of the parts drawer but when you need it, you'll have it. Use it with your CRO & calculator and you can observe those very short spikes that will be shown as 0.75mV/amp.

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